Methods of forming metallic glass multilayers
10166740 ยท 2019-01-01
Assignee
Inventors
- William L. Johnson (San Marino, CA)
- Marios D. Demetriou (West Hollywood, CA)
- Joseph P. Schramm (Sierra Madre, CA, US)
Cpc classification
B33Y10/00
PERFORMING OPERATIONS; TRANSPORTING
B33Y70/00
PERFORMING OPERATIONS; TRANSPORTING
B32B15/015
PERFORMING OPERATIONS; TRANSPORTING
B32B15/01
PERFORMING OPERATIONS; TRANSPORTING
B32B15/018
PERFORMING OPERATIONS; TRANSPORTING
C22C45/04
CHEMISTRY; METALLURGY
B22D23/003
PERFORMING OPERATIONS; TRANSPORTING
C22C45/10
CHEMISTRY; METALLURGY
B22D27/20
PERFORMING OPERATIONS; TRANSPORTING
B33Y80/00
PERFORMING OPERATIONS; TRANSPORTING
C22C45/003
CHEMISTRY; METALLURGY
International classification
B32B15/01
PERFORMING OPERATIONS; TRANSPORTING
C22C45/04
CHEMISTRY; METALLURGY
C22C45/10
CHEMISTRY; METALLURGY
B32B7/02
PERFORMING OPERATIONS; TRANSPORTING
C22F1/18
CHEMISTRY; METALLURGY
B22D27/20
PERFORMING OPERATIONS; TRANSPORTING
Abstract
The disclosure is directed to methods of forming metallic glass multilayers by depositing a liquid layer of a metallic glass forming alloy over a metallic glass layer, and to multilayered metallic glass articles produced using such methods.
Claims
1. A method of forming a multilayer of metallic glass, the method comprising providing a base layer of the metallic glass formed of an alloy having thickness d.sub.o, and initial temperature T.sub.o, wherein the alloy has a critical cooling rate R.sub.c and a time to crystallize at different temperatures upon heating the metallic glass formed of the alloy t.sub.h(T); selecting a thickness d.sub.i and initial temperature T.sub.i for a molten layer of the alloy such that: (i) an interface temperature T.sub.s determined by the Half-Enthalpy criterion is at least as high as the glass transition temperature T.sub.g of the metallic glass formed of the alloy, (ii) a characteristic cooling rate of the molten layer given by .sub.l.sup.2(T.sub.iT.sub.s)/4d.sub.i.sup.2, where (.sub.l=310.sup.6 m.sup.2/s, is greater than Rc, and (iii) a characteristic time scale of the base layer given by 4d.sub.o.sup.2/.sub.o.sup.2, where .sub.o=310.sup.6 m.sup.2/s, is shorter than t.sub.h(T) at the interface temperature T.sub.s, depositing the molten layer with the thickness d.sub.i and initial temperature T.sub.i over the base layer forming a multilayer.
2. The method of claim 1, where the interface temperature T.sub.s is at least 25 C. higher than T.sub.g.
3. The method of claim 1, where a characteristic time scale of the molten layer is given by [(T.sub.LT.sub.n)/(T.sub.iT.sub.s)][4d.sub.i.sup.2/.sub.l.sup.2], where T.sub.n is the crystallization nose temperature of the alloy, and where the characteristic time scale is shorter than the crystallization nose time of the alloy.
4. The method of claim 1, where d.sub.i is less than the thickness given by (/2)[.sub.lt.sub.cn(T.sub.iT.sub.s)/0.2T.sub.L], where T.sub.L is the liquidus temperature and t.sub.cn the crystallization nose time of the alloy.
5. The method of claim 1, where d.sub.i is less than the critical casting thickness of the alloy.
6. The method of claim 1, where d.sub.o is less than the thickness given by (/2)[.sub.ot.sub.h(T.sub.s)], where t.sub.h(T.sub.s) is the time to crystallize upon heating the metallic glass formed from the alloy at the interface temperature T.sub.s.
7. The method of claim 1, where the metallic glass formed from the alloy has T.sub.x of at least 50 K.
8. The method of claim 1, where the metallic glass formed from the alloy has T.sub.x/T.sub.L of at least 0.1.
9. A multilayer produced according to the method of claim 1.
10. The multilayer of claim 9, where the multilayer is substantially amorphous.
11. The multilayer of claim 10, where the bending stress of the multilayer substantially matches that of a monolithic metallic glass sample having substantially the same geometry.
12. The multilayer of claim 10, where the bending strain of the multilayer substantially matches that of a monolithic metallic glass sample having substantially the same geometry.
13. A method of forming a composite metallic glass multilayer comprising depositing a molten layer of a metallic-glass forming alloy of a first alloy composition over a metallic glass layer of a second alloy composition, where the first alloy composition and the second alloy composition are different, where the thickness d.sub.i and initial temperature T.sub.i of the molten layer and the thickness d.sub.oand initial temperature T.sub.o of the metallic glass layer produce an instantaneous interface temperature T.sub.s that is at least as high as the effective glass transition temperature T.sub.g*, where the characteristic cooling rate in the molten layer given by .sub.l.sup.2(T.sub.iT.sub.s)4d.sub.i.sup.2, where .sub.l=310.sup.6 m.sup.2/s, is greater than the critical cooling rate of the metallic glass forming alloy, where the characteristic time scale in the metallic glass layer following the deposition process given by 4d.sub.o.sup.2/.sub.o.sup.2, where .sub.o=310.sup.6 m.sup.2/s, is shorter than the time for the metallic glass to crystallize at the interface temperature T.sub.s, and where the effective glass transition temperature is given by T.sub.g*=0.5(T.sub.g1 +T.sub.g2), where T.sub.g1 and T.sub.g2 are the glass transition temperatures of the first alloy composition and the second alloy composition, respectively.
14. The method of claim 13, where the difference between T.sub.g1 and T.sub.g2 is less than 50 C.
15. The method of claim 13, where the difference between T.sub.L1 and T.sub.L2 is less than 150 C., where T.sub.L1 and T.sub.L2 are the liquidus temperatures of the first alloy composition and the second alloy composition, respectively.
16. The method of claim 13, the difference between T.sub.x1 and T.sub.x2 is less than 50 C., where T.sub.x1 and T.sub.x2 are the crystallization temperatures of the first alloy composition and the second alloy composition, respectively.
17. A metallic glass multilayer composite comprising at least two bonded metallic glass layers, where at least two layers comprise different metallic glass alloy compositions, where the relative difference between the shear moduli of the metallic glass alloy compositions is at least 2%, and where the thickness of each layer does not exceed the plastic zone radius of the metallic glass alloy composition of the layer.
18. The metallic glass multilayer composite of claim 17, where the yield strength of the metallic glass multilayer composite is within 20% of the volumetric average between the yield strengths of the different metallic glass compositions.
19. The metallic glass multilayer composite of claim 18, where the fracture toughness of the metallic glass multilayer composite is higher than the fracture toughness of the metallic glass alloy composition having the lowest fracture toughness.
20. The metallic glass multilayer composite of claim 18, where the tensile ductility of the metallic glass multilayer composite is higher than the tensile ductility values of the metallic glass compositions.
21. The method of claim 1, wherein no crystallization occurs in the molten and base layers of the multilayer.
22. The method of claim 1, wherein the multilayer has a bending strength within 40% of the bending strength of a monolithic metallic glass formed of the alloy having substantially the same geometry.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) The description will be more fully understood with reference to the following figures and data graphs, which are presented as various embodiments of the disclosure and should not be construed as a complete recitation of the scope of the disclosure.
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DETAILED DESCRIPTION
(15) The disclosure is directed to methods for producing metallic glass multilayers by layer-by-layer deposition, where the multilayered metallic glass exhibits substantial interlayer adhesion and mechanical integrity. In the context of this disclosure, a multilayer refers to an object that comprises at least two layers. Under suitable processing conditions, the multilayer will exhibit a substantially amorphous structure (substantially free of crystallinity in all layers), a substantially homogeneous structure (substantially free of pores), and mechanical properties such as strength, hardness, fracture toughness, etc., that substantially match those of a monolithic metallic glass.
(16) In some embodiments of the disclosure, an object being substantially amorphous (or substantially free of crystallinity) means that the volume fraction of crystals is less than 1%. In other embodiments it means that the volume fraction of crystals in the object is less than 2.5%, while in yet other embodiments it means that the volume fraction of crystals is less than 5%. In other embodiments of the disclosure, an object being substantially amorphous (or substantially free of crystallinity) means that the volume fraction of crystals in the object is less than the volume fraction detectable by x-ray diffraction. In other embodiments of the disclosure, an object being substantially amorphous (or substantially free of crystallinity) means that the volume fraction of crystals in the object is less than the volume fraction detectable by differential scanning calorimetry.
(17) In some embodiments of the disclosure, an object being substantially homogeneous (or substantially free of pores) means that the volume fraction of pores in the object is less than 0.1%. In other embodiments it means that the volume fraction of pores in the object is less than 0.25%, in yet other embodiments it means that the volume fraction of pores in the object is less than 0.5%, while in yet other embodiments it means that the volume fraction of pores in the object is less than 1%.
(18) In some embodiments of the disclosure, two objects being of substantially the same composition means that the atomic concentration of each of the elements forming the compositions of the objects varies by less than 1% between the objects. In one embodiment, two objects being of substantially the same composition means that the atomic concentration of each of the elements forming the compositions of the objects varies by less than 0.5% between the objects. In another embodiment, two objects being of substantially the same composition means that the atomic concentration of each of the elements forming the compositions of the objects varies by less than 0.25% between the objects.
(19) In some aspects of the disclosure, the layers in the multilayer are substantially bonded such that the bending stress and/or bending strain of the multilayer substantially matches those of a monolithic metallic glass sample having substantially the same geometry (i.e. is within 5% in all dimensions). The bending strength and strain are respectively defined as the maximum stress and strain attained before failure when the sample is subjected to a 3-point bend test. In some embodiments, the bending strength of the multilayer is within 5% of the corresponding property of a monolithic metallic glass. In other embodiments, the bending strength of the multilayer is within 10% of the corresponding property of the monolithic metallic glass. In yet other embodiments, the bending strength of the multilayer is within 20% of the corresponding property of the monolithic metallic glass. In yet other embodiments, the bending strength of the multilayer is within 40% of the corresponding property of the monolithic metallic glass. In some embodiments, the bending strain of the multilayer is within 5% of the corresponding property of a monolithic metallic glass. In other embodiments, the bending strain of the multilayer is within 10% of the corresponding property of the monolithic metallic glass. In yet other embodiments, the bending strain of the multilayer is within 20% of the corresponding property of the monolithic metallic glass. In yet other embodiments, the bending strain of the multilayer is within 40% of the corresponding property of the monolithic metallic glass.
(20) The disclosed method includes forming a metallic glass multilayer by depositing a second layer of hot molten liquid over a previously deposited and quenched first layer of metallic glass without inducing substantial crystallization in either layer while enabling substantial interlayer wetting. In the context of the current disclosure, molten liquid layer refers to a layer of liquid deposited by any means, including without limitation, a continuous liquid or melt stream (e.g. a homogeneous liquid or melt), or a stream of discrete liquid droplets or molten powder particulates (e.g. a spray).
(21) The previously deposited metallic glass layer(s) will heretofore be referred to as the base layer, and the terms base layer and metallic glass layer can be used interchangeably to refer to the previously deposited metallic glass layer(s). The newly deposited molten layer will be referred to as the added layer, and the terms added layer and molten layer can be used interchangeably to refer to the newly deposited molten layer. A couple formed by an added layer deposited over a base layer will be referred to as the multilayer. As previously noted, a multilayer refers to an object that comprises at least two layers.
(22) Crystallization may be expected if the added layer or any portion thereof is not cooled sufficiently fast to bypass crystallization and form the metallic glass phase. But crystallization may also be expected if the base layer or any portion of it is reheated above its glass transition during the transient deposition period during which the two layers thermally equilibrate. Whether crystallization of the base and added layers occurs during deposition depends on the detailed temperature history of the two layers as the added layer cools and the base layer heats and eventually thermally equilibrate with each other. Without wishing to be limited to a specific mechanism or mode of action, thermal quenching of the added layer to form metallic glass can require that an intimate thermal contact is established with the base layer in order to achieve cooling of the added layer that is sufficiently rapid to prevent crystallization. To ultimately produce multilayered metallic glass articles with substantially amorphous structure and mechanical integrity also requires that the added layer is bonded with the first layer by an intimate metallurgical interface that is free of gaps or areas of poor interlayer adhesion. These interfacial requirements may be satisfied when the molten layer wets the initial layer during the transient thermal equilibration time.
(23) The added layer can wet the base layer during deposition to produce a well bonded interface with good thermal contact between the base and added layers. Following its deposition, the added layer is subsequently cooled by heat conduction to the previously deposited base layer(s) by quenching the added layer at a sufficient cooling rate to produce a solidified added layer of metallic glass. During deposition of the added layer, the base layer(s) will undergo a transient heating and cooling cycle upon thermal contact with the hotter added layer. To prevent inducing crystallization of the base layer during this transient heating and cooling cycle, the temperature history of the base layer during deposition of the added layer can be controlled. Accordingly, the initial deposition temperature of the added layer can be below a critical value. A substantially amorphous and coherently bonded metallic glass multilayer can be fabricated when the above conditions of wetting between the layers, sufficient quenching of the added layer, and controlled heating of the base layer are met. By continuing a layer-by-layer sequential deposition while meeting the above conditions, a three dimensional metallic glass articles of desired shape and architecture with substantially amorphous structure and mechanical integrity can be built up. Accordingly, the disclosure in some embodiments provides a method for additive manufacturing of high precision, net shape, three-dimensional metallic glass articles.
(24) In various embodiments of the disclosure, the base and added layers may be of different composition and have different thicknesses. Such embodiments having layers of different composition and/or thickness may be advantageous if one desires a composite multilayered metallic glass utilizing more two or more metallic glass compositions having different properties that are utilized over different thicknesses. In other embodiments of the present invention, the base and added layers are of the same composition and have the same thickness.
(25) Regardless of any variation in the composition or thickness between the multilayer layers, It has now been discovered that to produce an added layer of metallic glass by deposition onto a previously deposited metallic glass base layer(s) without inducing detectable crystallization in either the base or added layer, the temperature history of the layers as the added layer cools and the base layer(s) heat and eventually thermally equilibrate with each other during the deposition process may be controlled in accordance with several criteria, which are presented below in accordance with certain embodiments.
(26) An added layer of thickness d and temperature T.sub.i brought into contact with a base layer at temperature T.sub.o of the same thickness d will thermally equilibrate with time. The process is illustrated in
(27) To overcome this problem in accordance with embodiments, the multilayer may be exposed to an environment temperature T.sub.e<T.sub.s in order to allow for the multilayer to cool before it crystallizes. In such embodiments, if the environment has a much higher thermal mass than the multilayer, the final multilayer temperature can approximately evolve to the environment temperature, i.e. T.sub.fT.sub.e. This condition can be achieved, for example, by having the multilayer laid on a substrate 240 having temperature T.sub.e<T.sub.s, as shown in
(28) In the above embodiments an assumption has been made that the heat capacities of the materials are independent of temperature, however, this is not necessarily the case for a metallic glass and its corresponding liquid (i.e., the metallic glass when heated above its glass transition temperature, T.sub.g). The heat capacities of the glass and liquid are generally both temperature dependent and different. For the glass (for T<T.sub.g), the specific heat capacity is nearly temperature independent and roughly equal to 3R25 J/mol-K (where R=8.314 J/mol-K is the gas constant). Above T.sub.g, the alloy is liquid and the specific heat capacity jumps (typically by 20 J/mol-K at the glass transition) and then becomes strongly temperature dependent.
(29) The complexity of the temperature dependence of the heat capacity in the different states of a metallic glass-forming alloy adds to the complexity of working with these materials in a layer-by-layer deposition process. It has now been determined that a relationship between the initial added and base layer temperatures T.sub.i and T.sub.o and the initial interface temperature T.sub.s can be established from an enthalpy balance. As discussed above, if the multilayer is thermally insulated from the environment, i.e. the process of thermal equilibration between the layers is adiabatic, the final equilibrium multilayer temperature T.sub.f can evolve to be equal to the initially established interface temperature T.sub.s. For a given T.sub.i and T.sub.o, T.sub.f and T.sub.s, which are equal to each other under such adiabatic conditions, can be determined from an enthalpy balance. But in a non-adiabatic heat exchange process, where heat exchange between the multilayer and the environment at temperature T.sub.e is allowed (e.g. the multilayer may exchange heat with a cold substrate), T.sub.f is no longer equal to T.sub.s and no longer determined by T.sub.i and T.sub.o, as its evolution is determined by T.sub.e. The interface temperature T.sub.s however, which is the initial temperature established spontaneously at the interface, is determined solely by T.sub.i and T.sub.o and is independent of whether the process is adiabatic or not. That is, for a given set of T.sub.i and T.sub.o, T.sub.s can be the same whether the process is adiabatic or not. As described above, the initial interface temperature in some embodiments can be established within 100 milliseconds of thermal contact, in other embodiments, within 10 millisecond of thermal contact, while in other embodiments, within 1 millisecond of thermal contact spontaneously at the interface between the layers immediately following thermal contact.
(30) It has now been determined that for a metallic glass layer-by-layer deposition process as disclosed in the present embodiments, being able to determine T.sub.s for a given T.sub.i and T.sub.o is of importance, as it represents the highest temperature that the base layer can reach independent of whether the process is adiabatic or non-adiabatic. In the context of this disclosure, embodiments of an enthalpy balance approach are disclosed that enables the determination of T.sub.s for a given T.sub.i and T.sub.o. The disclosed enthalpy balance approach assumes an adiabatic heat exchange process among the layers, however, the determined T.sub.s value for the given T.sub.i and T.sub.o values can also represent the T.sub.s value for the same T.sub.i and T.sub.o values if the process were non-adiabatic.
(31) In some embodiments of the enthalpy balance approach, any heat exchange with the environment is disregarded (i.e. an adiabatic heat exchange process among the layers is assumed). In such embodiments, the interface temperature of a multilayer consisting of a base and an added layer having equal thickness depends on the enthalpy of the two layers being equal in equilibrium. The excess enthalpy of the added layer at T.sub.i compared with the enthalpy of the base layer at T.sub.o will be divided equally between the two layers following equilibration. In such embodiments of the enthalpy balance, for layers of substantially equal thickness, T.sub.s is simply the temperature for which the enthalpy of the added layer H.sub.L at T.sub.s becomes half its initial value at T.sub.i In the context of this disclosure, this condition is termed the Half Enthalpy criterion.
(32) Embodiments that allow for the determination of the enthalpy as a function of temperature for a metallic glass in the both glass and liquid phases may therefore be used in determining T.sub.s. Such enthalpy functions of temperature may be determined for a specific metallic glass alloy composition using calorimetry. Such data is available in the literature for certain metallic glass alloys. However, for metallic glass alloys of interest that such data is not available, calorimetric measurements may be performed to determine the temperature dependent enthalpy functions. Here embodiments of methods are provided that allow for approximate but fairly accurate determination of the enthalpies of metallic glass alloys without the need to perform calorimetric measurements. The methods according to these embodiments are based on dimensionless functions that can approximately estimate the enthalpies of any specific metallic glass alloy.
(33) The universal enthalpy functions disclosed herein arise from recognizing that metallic glass forming alloys demonstrate an enthalpy of melting (i.e. latent heat of melting) that is approximately equal to RT.sub.L (where T.sub.L is in units of Kelvin), and that metallic glass forming alloys demonstrate linear temperature dependence of enthalpy below T.sub.g (i.e. in the glass phase) and a 1/T temperature dependence above T.sub.g (i.e. in the liquid phase). The embodiments also identify that at T.sub.L, the difference between the enthalpy of the liquid and the hypothetical (extrapolated) enthalpy of the glass is approximately between 0.7 RT.sub.L and 0.8RT.sub.L, depending on the fragility of the glass former. Specifically, the higher the fragility of the glass former, the higher the fraction of RT.sub.L. In some embodiments, glass formers with fragilities between 40 and 50 may be assumed to have a difference between the enthalpy of the liquid and the hypothetical (extrapolated) enthalpy of the glass of approximately between 0.7 RT.sub.L and 0.75RT.sub.L, while in glass formers with fragilities between 50 and 60, the difference between the enthalpy of the liquid and the hypothetical (extrapolated) enthalpy of the glass is approximately between 0.75RT.sub.L and 0.8RT.sub.L. Accordingly, in embodiments of the method of determining the enthalpy relation of a metallic glass with temperature, the difference between the enthalpy of the liquid and the hypothetical (extrapolated) enthalpy of the glass is approximately 0.75RT.sub.L.
(34) In accordance with embodiments, by normalizing the temperature T with the liquidus temperature T.sub.L (in units of Kelvin) and the enthalpy H with RT.sub.L, a dimensionless universal enthalpy relation with temperature can be given by the following function between the normalized enthalpy and normalized temperature:
H/RT.sub.L=3(T/T.sub.LT.sub.r/T.sub.L) for T/T.sub.L<T.sub.g/T.sub.LEq. (1)
H/RT.sub.L=3(T/T.sub.LT.sub.r/T.sub.L)+c[(T.sub.g/T.sub.L).sup.1(T/T.sub.L).sup.1] for T/T.sub.L>T.sub.g/T.sub.LEq. (2)
where c is a constant given by c=3T.sub.g/4(T.sub.LT.sub.g) (i.e. satisfying the requirement that H/RT.sub.L3(1T.sub.r/T.sub.L)= at T/T.sub.L=1), and T.sub.r is the reference temperature where the normalized enthalpy is taken to be zero. The reference temperature T.sub.r is arbitrary, and can be taken to be the base layer temperature T.sub.o.
(35) Therefore, in accordance with embodiments, an enthalpy function for any given metallic glass may be determined by Eqs. (1) and (2) above, provided one knows T.sub.g and T.sub.L for the specific metallic glass alloy along with T.sub.o. Accordingly, in such embodiments, enthalpy functions of temperature for the metallic glass and undercooled liquid phases may be constructed. For illustrative purposes, T.sub.o is assumed to be at 300 K (i.e. at about room temperature) in the below examples. In one example, the enthalpy function for a metallic glass having T.sub.g=650 K and T.sub.L=1100 K, which yields a constant c of 1.08, is presented in
(36) Using embodiments of the enthalpy vs. temperature curve as shown in
(37) Therefore, according to embodiments of the disclosure, one may construct a plot of an Half-Enthalpy criterion for a given metallic glass alloy, like those in
(38) Criterion for Achieving Wetting at the Interface
(39) The wetting of a copper surface by a glass-forming metallic liquid was studied by Suh et. al. (J.-Y. Suh, B. Lohwongwatana, C. M. Garland, R. D. Conner, W. L. Johnson, and D. Suh, Novel Thermoplastic Bonding Using a Metallic Glass Solder, Scripta Materialia 59, 905-908 (2008), the reference of which is incorporated herein in its entirety). Specifically, they studied the wetting of a copper substrate by a bulk metallic glass alloy above its T.sub.g and below its crystallization temperature T.sub.x under an applied normal load. It was found that for temperatures of about 60-70 C. above T.sub.g, wetting occurred within a time scale of about 1 minute when an applied pressure of about 1 MPa is used to achieve contact. More generally, it is known that metallic glass surfaces favor wettability by other liquid alloys (e.g. solders). Wetting of two layers of the same metallic glass above T.sub.g under a normal load has also been demonstrated (J. G. Wang, J. C. Fan, Y. F. Zhang, G. Wang, W. H. Wang, and K. C. Chan, Diffusion Bonding of a Zr-based Metallic Glass in its Supercooled Liquid Region, Intermetallics 46, 236-242 (2014)).
(40) Despite this general knowledge about how metallic glasses may wet substrates of disparate metals or other liquid alloys, less is known about how to achieve consistent wetting between a metallic glass base layer and an added layer of a metallic glass forming liquid. It has now been determined that the contact between a metallic glass and a metallic glass forming liquid can result in rapid wetting (i.e. in a time scale of about 1 s or less) when the liquid/glass interfacial temperature T.sub.s exceeds T.sub.g by an amount sufficient to enable local atomic rearrangement at the interface. Therefore, in embodiments the criterion to achieve intimate contact and wetting may be governed by the following condition:
T.sub.s>T.sub.gEq. (3)
(41) In short, rapid wetting can occur at a wetting temperature T.sub.w that is about 50-100 C. above T.sub.g. At higher temperatures, wetting may be essentially spontaneous (i.e. occur over a fraction of a second, and in some embodiments, under 100 millisecond) upon establishing surface contact, occurring over durations of under 1 s, and in some embodiments under 0.1 s. In embodiments, wetting may require some minimum applied pressure P.sub.min (typically 0.1 MPa or more) required to ensure contact at the interface. In other embodiments both the wetting temperature T.sub.w and minimum required pressure P.sub.min may be determined experimentally for a given metallic glass forming alloy.
(42) In particular, the interface temperature T.sub.s is experimentally accessible. In some embodiments, T.sub.s can be measured by placing a thermocouple at the interface between the added and base layers, and record the temperature following the deposition process.
(43) In the disclosure, wetting may be considered a sufficient criterion for establishing intimate thermal contact of the base and added layers. Upon adding a liquid layer at temperature T.sub.i to a base layer at temperature T.sub.o, one can determine the interface temperature upon wetting, T.sub.s by using the plot in
(44) Criteria for Avoiding Crystallization of the Layers
(45) In accordance with embodiments, conditions for avoiding crystallization in the base layer during addition of an added layer may be formulated for any combination of metallic glasses. Upon adding a liquid layer at temperature T.sub.i to a base layer at temperature T.sub.o, it is possible, according to embodiments, to determine the interface temperature upon wetting, T.sub.s by using the methods described above, an exemplary embodiment of which is provided in the plot in
(46) Added Layer: The TTT diagram of a metallic glass forming alloy during cooling from an equilibrium liquid state (i.e. at or above T.sub.L), representing the crystallization time t.sub.c as a function of temperature, t.sub.c(T), is known to exhibit a C-shape curve, characterized by the nose time t.sub.cn, which is the minimum time for crystallization, and the nose temperature T.sub.n associated with t.sub.cn. Generally, for metallic glass-forming alloys the longer t.sub.cn is the better the glass former.
(47) According to embodiments, to avoid crystallizing the added layer, the thickness of the added layer d and its initial temperature T.sub.i are selected such that the cooling rate of the added layer during the enthalpy exchange process is higher than the critical cooling rate required to bypass t.sub.cn. Specifically, the cooling rate R during cooling of an added layer of thickness d.sub.i from its initial temperature T.sub.i to the nose temperature T.sub.n is approximately given by the leading term of the solution to the Fourier heat flow equation:
R=.sub.i.sup.2(T.sub.iT.sub.s)/4d.sub.i.sup.2Eq. (4)
Where .sub.i is the thermal diffusivity of the metallic glass forming liquid, and T.sub.s is the interface temperature of the multilayer, which in this analysis is assumed to be lower than T.sub.n. On the other hand, the critical cooling rate R.sub.c to bypass t.sub.cn is given by:
R.sub.c=(T.sub.LT.sub.n)/t.sub.cnEq. (5)
(48) Therefore, the criterion for bypassing crystallization, according to embodiments is governed by the following condition:
[(T.sub.LT.sub.n)/(T.sub.iT.sub.s)][4d.sub.i.sup.2/.sub.i.sup.2]<t.sub.cnEq. (6)
(49) Typically, the nose temperature T.sub.n of most metallic glass-forming alloys is approximately 0.8 T.sub.L (where T.sub.L is in units of Kelvin). Since t.sub.cn is unique for a given metallic glass alloy and .sub.i is a measurable property that is either known for the specific metallic glass forming liquid or can be determined experimentally, the above criterion can be met by determining the maximum thickness for which Eq. (6) is satisfied. According to embodiments, substituting T.sub.n=0.8T.sub.L into Eq. (6) and solving for d.sub.i one can determine the maximum added layer thickness to avoid crystallization in the added layer, as follows:
d.sub.i<(/2)[.sub.it.sub.cn(T.sub.iT.sub.s)/0.2T.sub.L]d.sub.cEq. (7)
(50) This maximum thickness will be denoted as d.sub.c.
(51) In accordance with still other embodiments, Eq. (7) can be used to estimate the maximum thickness d.sub.c for an added layer for a given T.sub.i and T.sub.s in order to avoid crystallization. Specifically, variables .sub.i and t.sub.cn(T) are experimentally accessible properties of the metallic glass forming liquid, while variable T.sub.s may be determined for a given T.sub.i by using the Half Enthalpy criterion as in the plots of
(52) This maximum thickness d.sub.c could also related to the critical casting thickness, which is a measure of the largest lateral dimension that can be formed with the amorphous phase by quenching the alloy from the equilibrium liquid state (i.e. at or above T.sub.L), and quantifies the glass forming ability of a given alloy. Specifically, for a given alloy, d.sub.c may be approximately of the critical casting thickness. The critical casting thickness for a given alloy is typically evaluated by quenching experiments, and is independent of the evaluation of the TTT diagram, which is typically performed by calorimetry. Therefore, for alloys where the TTT diagram on cooling has not been evaluated and t.sub.cn is not known but the critical casting thickness is known, d.sub.c can be taken as of the critical casting thickness.
(53) The TTT diagram, for example, for metallic glass forming alloy Au.sub.49Ag.sub.5.5Pd.sub.2.3Cu.sub.26.9Si.sub.16.3 during cooling from the equilibrium liquid state (i.e. at or above T.sub.L) is presented in
(54) In embodiments of the disclosure, the cooling rate in the added layer, given by Eq. (4), is higher than the critical cooling rate of the metallic glass forming alloy. In one embodiment, the cooling rate in the added layer, given by Eq. (4), is at least twice as high as the critical cooling rate of the metallic glass forming alloy. In another embodiment, the cooling rate in the added layer, given by Eq. (4), is at least three times as high as the critical cooling rate of the metallic glass forming alloy. In another embodiment, the cooling rate in the added layer, given by Eq. (4), is at least four times as high as the critical cooling rate of the metallic glass forming alloy. In another embodiment, the cooling rate in the added layer, given by Eq. (4), is at least five times as high as the critical cooling rate of the metallic glass forming alloy.
(55) In other embodiments of the disclosure, the time scale [(T.sub.LT.sub.n)/(T.sub.iT.sub.s)][4d.sub.i.sup.2/.sub.i.sup.2] given by the expression of Eq. (6) is shorter than the crystallization nose time of the metallic glass forming alloy, t.sub.cn. In another embodiment, the time scale [(T.sub.LT.sub.n)/(T.sub.iT.sub.s)][4d.sub.i.sup.2/.sub.i.sup.2] given by the expression of Eq. (6) is less than the crystallization nose time of the metallic glass forming alloy, t.sub.cn. In another embodiment, the time scale [(T.sub.LT.sub.n)/(T.sub.iT.sub.s)][4d.sub.i.sup.2/.sub.i.sup.2] given by the expression of Eq. (6) is less than the crystallization nose time of the metallic glass forming alloy, t.sub.cn. In another embodiment, the time scale [(T.sub.LT.sub.n)/(T.sub.iT.sub.s)][4d.sub.i.sup.2/.sub.i.sup.2] given by the expression of Eq. (6) is less than the crystallization nose time of the metallic glass forming alloy, t.sub.cn. In another embodiment, the time scale [(T.sub.LT.sub.n)/(T.sub.iT.sub.s)][4d.sub.i.sup.2/.sub.i.sup.2] given by the expression of Eq. (6) is less than the crystallization nose time of the metallic glass forming alloy, t.sub.cn.
(56) In other embodiments of the disclosure, the added layer thickness d.sub.i is less than the maximum thickness d.sub.c=(/2)[.sub.it.sub.cn(T.sub.iT.sub.s)/0.2T.sub.L] given by the expression of Eq. (7). In one embodiment, the added layer thickness d.sub.i is less than of the maximum thickness d.sub.c=(/2)[.sub.it.sub.cn(T.sub.iT.sub.s)/0.2T.sub.L] given by the expression of Eq. (7). In another embodiment, the added layer thickness d.sub.i is less than of the maximum thickness d.sub.c=(/2)[.sub.it.sub.cn(T.sub.iT.sub.s)/0.2T.sub.L] given by the expression of Eq. (7). In another embodiment, the added layer thickness d.sub.i is less than of the maximum thickness d.sub.c=(/2)[.sub.it.sub.cn(T.sub.iT.sub.s)/0.2T.sub.L] given by the expression of Eq. (7). In another embodiment, the added layer thickness d.sub.i is less than of the maximum thickness d.sub.c=(/2)[.sub.it.sub.cn(T.sub.iT.sub.s)/0.2T.sub.L] given by the expression of Eq. (7).
(57) In other embodiments of the disclosure, the added layer thickness d.sub.i is less than the critical casting thickness of the metallic glass forming alloy. In one embodiment, the added layer thickness d.sub.i is less than the critical casting thickness of the metallic glass forming alloy. In another embodiment, the added layer thickness d.sub.i is less than the critical casting thickness of the metallic glass forming alloy. In another embodiment, the added layer thickness d.sub.i is less than the critical casting thickness of the metallic glass forming alloy.
(58) As discussed above, the thermal diffusivity of the molten metallic glass forming alloy, .sub.i, is an experimentally accessible property of the material and is known for certain alloys, while it can be measured for other alloys of choice using established measurement methods and standards. The thermal diffusivity is not expected to vary much with temperature in the undercooled molten region, i.e. between T.sub.g and T.sub.L. Therefore, in one embodiment of the disclosure, .sub.l is the thermal diffusivity of the molten metallic glass forming alloy measured experimentally at any temperature between T.sub.i and T.sub.g. In another embodiment, .sub.l is the thermal diffusivity of the molten metallic glass forming alloy measured experimentally at any temperature between T.sub.L and T.sub.g. In another embodiment, .sub.i is the thermal diffusivity of the molten metallic glass forming alloy measured experimentally at a temperature halfway between T.sub.i and T.sub.g. In another embodiment, .sub.l is the thermal diffusivity of the molten metallic glass forming alloy measured experimentally at a temperature halfway between T.sub.L and T.sub.g. The thermal diffusivity in the molten state .sub.i also does not vary much between metallic glass forming alloys. Generally for most metallic glass forming alloys, .sub.i is in the range of 110.sup.6 m.sup.2/s to 510.sup.6 m.sup.2/s, and more specifically in the range of 210.sup.6 m.sup.2/s to 410.sup.6 m.sup.2/s. Therefore, in some embodiments of the disclosure it can be assumed that .sub.l=310.sup.6 m.sup.2/s.
(59) Base Layer: In still other embodiments, to prevent crystallization in the base layer, the time-temperature history of the base layer near the interface can be prevented from crossing the TTT-diagram during heating of the base layer as well as during eventual cooling to T.sub.f. Unlike the TTT on cooling of a metallic glass-forming liquid, which exhibits a clear C shape, the TTT diagram on heating of a metallic glass is nearly monotonic. That is, the nose of the TTT diagram on heating typically appears at temperatures much higher that are near T.sub.L, and as such, the time for crystallization appears to decrease monotonically with increasing temperature above T.sub.g. Therefore, unlike the case of cooling of a metallic glass-forming liquid, a unique critical time for crystallization may not exist in the case of heating a metallic glass, as the crystallization time decreases approximately monotonically with increasing temperature.
(60) In the context of the disclosure, it will be assumed that the crystallization time t.sub.h is a monotonically decreasing function of temperature T, i.e. t.sub.h(T), and can be determined from the TTT-diagram associated with heating of the metallic glass from low temperature into the undercooled liquid above T.sub.g. Because t.sub.h decreases monotonically with temperature and because the highest base layer temperature should be T.sub.s, the t.sub.h value of interest is that at T.sub.s, i.e. t.sub.h(T.sub.s). Specifically, the heating rate R.sub.h during heating of a base layer of initial temperature T.sub.o and thickness d.sub.o, after depositing an added layer of higher initial temperature onto it is approximately given by the leading term of the solution to the Fourier heat flow equation:
R=.sub.o.sup.2(T.sub.sT.sub.o)/4d.sub.o.sup.2Eq. (8)
Where .sub.i is the thermal diffusivity of the metallic glass, and T.sub.s is the interface temperature of the multilayer. On the other hand, the critical heating rate R.sub.h to bypass t.sub.h(T.sub.s) is given by:
R.sub.h=(T.sub.sT.sub.o)/t.sub.h(T.sub.s)Eq. (9)
(61) Therefore, in accordance with embodiments the criterion for bypassing crystallization is governed by the following condition:
4d.sub.o.sup.2/.sub.o.sup.2<t.sub.h(T.sub.s)Eq. (10)
(62) In accordance with other embodiments, the maximum base layer thickness d.sub.o to avoid crystallization in the base layer can then be determined as follows:
d.sub.o<(/2)[.sub.ot.sub.h(T.sub.s)]d.sub.hEq. (11)
(63) This maximum thickness will be denoted as d.sub.h.
(64) Accordingly, in embodiments, Eq. (11) can be used to estimate the maximum thickness d.sub.h for an added layer for a given T.sub.i and T.sub.s in order to avoid crystallization. Specifically, variables .sub.o and t.sub.h(T) are experimentally accessible properties of the metallic glass forming liquid, while variable T.sub.s may be determined for a given T.sub.i by using the Half Enthalpy criterion described in embodiments and as exemplified in the plots of
(65) The TTT diagram, for example, for metallic glass forming alloy Au.sub.49Ag.sub.5.5Pd.sub.2.3Cu.sub.26.9Si.sub.16.3 during heating from the glass state into the supercooled liquid state (i.e. between T.sub.g and T.sub.L) is presented in
(66) In embodiments of the disclosure, the time scale 4d.sub.o.sup.2/.sub.o.sup.2 in the base layer given by Eq. (10) is shorter than the time for the metallic glass to crystallize when heated at the interface temperature T.sub.s. In one embodiment, the time scale 4d.sub.o.sup.2/.sub.o.sup.2 in the base layer given by Eq. (10) is less than than the time for the metallic glass to crystallize when heated at the interface temperature T.sub.s. In another embodiment, the time scale 4d.sub.o.sup.2/.sub.o.sup.2 in the base layer given by Eq. (10) is less than than the time for the metallic glass to crystallize when heated at the interface temperature T.sub.s. In another embodiment, the time scale 4d.sub.o.sup.2/.sub.o.sup.2 in the base layer given by Eq. (10) is less than than the time for the metallic glass to crystallize when heated at the interface temperature T.sub.s.
(67) In other embodiments of the disclosure, the base layer thickness d is less than the thickness d.sub.h=(/2)[.sub.ot.sub.h(T.sub.s)] given by the expression of Eq. (11). In one embodiment, the base layer thickness d is less than the thickness d.sub.h=(/2)[.sub.ot.sub.h(T.sub.s)] given by the expression of Eq. (11). In another embodiment, the base layer thickness d is less than the thickness d.sub.h=(/2)[.sub.ot.sub.h(T.sub.s)] given by the expression of Eq. (11). In another embodiment, the base layer thickness d is less than the thickness d.sub.h=(/2)[.sub.ot.sub.h(T.sub.s)] given by the expression of Eq. (11).
(68) In general, for a given metallic glass alloy at any temperature Tin the supercooled/undercooled liquid state (i.e. between T.sub.g and T.sub.i), the crystallization time upon cooling from the equilibrium liquid state t.sub.c(T) is equal to or greater than the crystallization time upon heating from the glass state t.sub.h(T). This can be observed by comparing the TTT diagrams, for example for metallic glass forming alloy Au.sub.49Ag.sub.5.5Pd.sub.2.3Cu.sub.26.9Si.sub.16.3 for cooling and heating, presented in
(69) Accordingly, in embodiments, if T.sub.s is a relatively high temperature in the undercooled region (i.e. is closer to T.sub.L than T.sub.g), the criterion given by Eq. (9) for bypassing crystallization in the base layer may be more stringent than that of Eq. (6) for bypassing crystallization in the added layer. Hence, if T.sub.s is a relatively high temperature in the undercooled region, the criterion of Eq. (11) may be the limiting criterion. In such cases, the layer more susceptible to crystallization during layer-by-layer deposition of metallic glasses may be the base layer (provided that the layers are of the same composition and have the same thickness).
(70) On the other hand, if T.sub.s is a relatively low temperature in the undercooled region (i.e. is closer to T.sub.g than T.sub.i), the criterion given by Eq. (7) for bypassing crystallization in the added layer may be more stringent than that of Eq. (11) for bypassing crystallization in the base layer. Hence, if T.sub.s is a relatively low temperature in the undercooled region, the criterion of Eq. (7) may be the limiting criterion. In such cases, the layer more susceptible to crystallization during layer-by-layer deposition of metallic glasses may be the added layer (provided that the layers are of the same composition and have the same thickness).
(71) As discussed above, the thermal diffusivity of the metallic glass, .sub.o, is an experimentally accessible property of the material and is known for certain alloys, while it can be measured for other alloys of choice using established measurement methods and standards. The thermal diffusivity is not expected to vary much with temperature in the glass phase region, i.e. between room temperature and T.sub.g. Therefore, in one embodiment of the disclosure, .sub.o is the thermal diffusivity of the metallic glass measured experimentally at any temperature between T.sub.o and T.sub.g. In another embodiment, .sub.o is the thermal diffusivity of the metallic glass measured experimentally at any temperature between room temperature and T.sub.g. In another embodiment, .sub.o is the thermal diffusivity of the molten metallic glass forming alloy measured experimentally at a temperature halfway between T.sub.o and T.sub.g. In another embodiment, .sub.o is the thermal diffusivity of the molten metallic glass forming alloy measured experimentally at a temperature halfway between room temperature and T.sub.g. The thermal diffusivity in the metallic glass phase .sub.o also does not vary much between metallic glass alloys. Generally for most metallic glass alloys, .sub.o is in the range of 110.sup.6 m.sup.2/s to 510.sup.6 m.sup.2/s, and more specifically in the range of 210.sup.6 m.sup.2/s to 410.sup.6 m.sup.2/s. Therefore, in some embodiments of the disclosure it can be assumed that a, =310.sup.6 m.sup.2/s.
(72) Exemplary Alloy Systems: The ability of five different metallic glass alloys to be processed into multilayers by successive layer deposition without crystallizing according to embodiments of the current disclosure is investigated. Exemplary embodiments of the deposition of an added liquid layer at temperature T.sub.i, over a metallic glass base layer at room temperature of the same composition and same thickness are provided. In this case study, the layers are assumed to have the same composition and thickness. It is also assumed that the critical condition to avoid crystallization of the multilayer during the deposition process is to avoid crystallization of the base layer, as given by Eq. (10).
(73) Firstly, the lower limit in the added layer temperature T.sub.i for each metallic glass alloy such that crystallization in the base layer is avoided for a fixed layer thickness is determined. A thickness of 1 mm is considered for both layers (i.e. d.sub.i=d.sub.o=1 mm), and the base layer temperature is taken to be T.sub.o=300 K, i.e. approximately room temperature. The thermal diffusivity of all metallic glass alloys considered here both in the molten state as well as in the glass phase (i.e. .sub.i and .sub.o) is assumed to be 310.sup.6 m.sup.2/s. According to Eq. (10), in order to avoid crystallizing a base layer of 1 mm thickness, the heated metallic glass should be capable of resisting crystallization for at least 0.135 s, i.e. t.sub.h>0.135 s.
(74) Ni-based Metallic Glasses: The TTT-diagrams on heating two Ni-based metallic glasses having compositions Ni.sub.68.17Cr.sub.8.65Nb.sub.2.98P.sub.16.92B.sub.3.28 and Ni.sub.71.4Cr.sub.5.52Nb.sub.3.38P.sub.16.67B.sub.3.03 are presented in
(75) Zr-based and Cu-based Metallic Glasses: The TTT-diagrams on heating a Zr-based and a Cu-based a metallic glass having compositions Zr.sub.41.2Ti.sub.13.8Cu.sub.12.5Ni.sub.10Be.sub.22.5 and Cu.sub.47Ti.sub.33Zr.sub.11Ni.sub.8Si.sub.1 are presented in
(76) Au-based Metallic Glass: The TTT-diagram on heating an Au-based metallic glass having composition Au.sub.49Ag.sub.5.5Pd.sub.23Cu.sub.26.9Si.sub.16.3 is presented in
(77) TABLE-US-00001 TABLE 1 Glass transition temperature, liquidus temperature, ratio of glass- transition to liquidus temperature, and upper limits in the interface and added layer temperatures for the layer deposition process of five example metallic glass alloys, where the base layer is held at room temperature and the thickness of all layers is 1 mm. T.sub.g T.sub.L T.sub.s [K] T.sub.i [K] Composition [K] [K] (upper limit) (upper limit) Ni.sub.68.17Cr.sub.8.65Nb.sub.2.98P.sub.16.92B.sub.3.28 676 1152 920 1486 Ni.sub.71.4Cr.sub.5.52Nb.sub.3.38P.sub.16.67B.sub.3.03 666 1139 753 1002 Zr.sub.41.2Ti.sub.13.8Cu.sub.12.5Ni.sub.10Be.sub.22.5 623 993 >T.sub.L >>T.sub.L Cu.sub.47Ti.sub.33Zr.sub.11Ni.sub.8Si.sub.1 683 1165 803 1165 Au.sub.49Ag.sub.5.5Pd.sub.2.3Cu.sub.26.9Si.sub.16.3 401 644 577 882
(78) A high T.sub.i value generally indicates suitability of the metallic glass for processing amorphous multilayers by layer-by-layer deposition. That is, the higher the estimated T the more stable the metallic glass can be for layer-by-layer deposition. Therefore, in embodiments the estimated T.sub.i, may be used as a measure of the suitability of the metallic glass for layer-by-layer deposition at a given thickness. In general, if the estimated T.sub.i is at least as high as the liquidus temperature T.sub.L, the overall process becomes more manageable as the liquid may be held at T.sub.i in some reservoir prior to deposition for extended periods without crystallizing. However, if the estimated T.sub.i is below the liquidus temperature T.sub.L, the overall process becomes somewhat more complicated as the liquid is already unstable against crystallization. In accordance with embodiments, solutions may be devised for cases where T.sub.i<T.sub.L, where the liquid is held in a reservoir at a temperature above T.sub.L and is actively cooled to T.sub.i prior to being deposited. Nevertheless, metallic glasses having an estimated T.sub.i for additive manufacturing at a specific thickness that is at least as high as the liquidus temperature T.sub.L, the metallic glass may be considered suitable for such process.
(79) In other embodiments, it is possible to carry out the inverse analysis, where the maximum layer thickness d.sub.h for which T.sub.i is equal to or greater than T.sub.L is estimated for a given alloy. The thickness d.sub.h is assumed to be the maximum base layer thickness for a given alloy where the multilayer processing by layer-by-layer deposition process is performed with the melt in the equilibrium liquid state (i.e. at or above T.sub.L). In such embodiments, T.sub.s/T.sub.L associated with T.sub.i/T.sub.L=1 can be determined from the Half Enthalpy criterion as in the plots of
(80) Ni-based Metallic Glasses: Because the two Ni-based metallic glass alloys have T.sub.g of about 650 K and T.sub.L of about 1100 K, and since T.sub.o is at 300 K, the enthalpy function of
(81) Zr-based and Cu-based Metallic Glasses: Because the Zr-based and the Cu-based metallic glass alloys have T.sub.g of about 650 K, and T.sub.L of about 1100 K and since T.sub.o is at 300 K, the enthalpy function of
(82) Au-based Metallic Glass: Because the Au-based metallic glass alloy Au.sub.49Ag.sub.5.5Pd.sub.2.3Cu.sub.26.9Si.sub.16.3 has T.sub.g of about 400 K and T.sub.L of about 650 K and since T.sub.o is at 300 K, the enthalpy function of
(83) TABLE-US-00002 TABLE 2 Interface temperature, crystallization time, and maximum layer thickness for five example metallic glass alloys associated with the condition of the added layer temperature being equal to the liquidus temperature. Composition T.sub.s [K] t.sub.h(T.sub.s) [s] d.sub.h [mm] Ni.sub.68.17Cr.sub.8.65Nb.sub.2.98P.sub.16.92B.sub.3.28 794 0.74 2.3 Ni.sub.71.4Cr.sub.5.52Nb.sub.3.38P.sub.16.67B.sub.3.03 785 0.082 0.78 Zr.sub.41.2Ti.sub.13.8Cu.sub.12.5Ni.sub.10Be.sub.22.5 684 360 52 Cu.sub.47Ti.sub.33Zr.sub.11Ni.sub.8Si.sub.1 803 0.135 1.0 Au.sub.49Ag.sub.5.5Pd.sub.2.3Cu.sub.26.9Si.sub.16.3 477 7.0 7.2
(84) The variation in the maximum added layer thickness to avoid crystallization in the added layer, d.sub.h, between the alloys is related to the differences in the TTT-diagrams upon heating (
(85) On the other hand, Zr.sub.41.2Ti.sub.13.8Cu.sub.12.5Ni.sub.10Be.sub.22.5 is known to have a t.sub.cn of 70 s (Y. J. Kim, R. Busch, W. L. Johnson, A. J. Rulison, and W. K. Rhim, Experimental determination of the time-temperature-transformation diagram of the undercooled liquid Zr.sub.41.2Ti.sub.13.8Cu.sub.12.5Ni.sub.10Be.sub.22.5 alloy using containerless electrostatic levitation processing, Appl. Phys. Lett., 68, 1057-1059 (1996)), and Au.sub.49Ag.sub.5.5Pd.sub.2.3Cu.sub.26.9Si.sub.16.3 has a t of 0.23 s (
(86) Lastly, the critical casting thickness of Cu.sub.47Ti.sub.33Zr.sub.11Ni.sub.8Si.sub.1.5 is known to be 3-4 mm, which suggests a d.sub.c of 1-2 mm. The estimated d.sub.h is 1 mm (Table 2), i.e. of the same order as d.sub.c. The reason d.sub.c and d.sub.h are nearly equal for Cu.sub.47Ti.sub.33Zr.sub.11Ni.sub.8Si.sub.1.5 is because T.sub.s for this alloy is near the middle of the undercooled liquid region (i.e. not closer to either T.sub.g or T.sub.L).
(87) Since the metallic glass dimension of every metallic glass forming alloy is inherently limited by the critical casting thickness d.sub.c, metallic glasses with d.sub.h>d.sub.c may be more suitable for layer-by-layer deposition compared to those with d.sub.h<d.sub.c, as their layer thickness is not limited by the critical casting thickness.
(88) In embodiments, the estimated d.sub.h for a given a metallic glass alloy may be correlated to the parameter T.sub.x, defined as the difference between the crystallization temperature T.sub.x measured at constant heating rate of 20 K/min and T.sub.g, i.e. T.sub.x=T.sub.xT.sub.g. The T values for the example alloys are presented in Table 3. As seen in Table 3, T correlates well with d.sub.h, and adequately predicts the suitability of a metallic glass alloy for multilayer processing by layer-by-layer deposition. Specifically, alloys with T.sub.x greater than 50 K are those that have been determined to be generally stable against crystallization for multilayer processing by layer-by-layer deposition, while alloys with T.sub.x less than 50 K are those determined not to be quite as stable. Therefore, in some embodiments of the disclosure, metallic glasses that demonstrate T.sub.xof at least 50 K are considered suitable for multilayer processing by layer-by-layer deposition. In other embodiments of the disclosure, metallic glasses that demonstrate T.sub.x of at least 60 K are considered suitable for multilayer processing by layer-by-layer deposition. In yet other embodiments of the disclosure, metallic glasses that demonstrate T.sub.x of at least 70 K are considered suitable for multilayer processing by layer-by-layer deposition.
(89) TABLE-US-00003 TABLE 3 T.sub.x, T.sub.L, d.sub.h and d.sub.c data for five example metallic glass alloys associated with the condition of the added layer temperature being equal to the liquidus temperature. Composition T.sub.x [K] T.sub.L [K] T.sub.x/T.sub.L d.sub.h [mm] d.sub.c [mm] d.sub.h/d.sub.c Ni.sub.68.17Cr.sub.8.65Nb.sub.2.98P.sub.16.42B.sub.3.28 58 476 0.122 2.3 3.5 0.657 Ni.sub.71.4Cr.sub.5.52Nb.sub.3.38P.sub.16.67B.sub.3.03 42 473 0.089 0.78 5.5 0.142 Zr.sub.41.2Ti.sub.13.8Cu.sub.12.5Ni.sub.10Be.sub.22.5 89 370 0.241 52 20 2.600 Cu.sub.47Ti.sub.33Zr.sub.11Ni.sub.8Si.sub.1 43 482 0.089 1.0 1.5 0.667 Au.sub.49Ag.sub.5.5Pd.sub.2.3Cu.sub.26.9Si.sub.16.3 58 243 0.239 7.2 2.5 2.813
(90) In other embodiments correlating d.sub.h/d.sub.c and quantifying the suitability of a metallic glass alloy for multilayer processing by layer-by-layer deposition may be accomplished through the ratio T.sub.x/T.sub.L, where T.sub.L is defined as the difference between T.sub.L and T.sub.g and is a measure of the undercooled liquid region. The parameter T.sub.x/T.sub.L quantifies the stability of the metallic glass against crystallization, i.e. T.sub.x=T.sub.xT.sub.g, in relation to its undercooled liquid region, i.e. T.sub.L=T.sub.LT.sub.g. As seen in Table 3 and
d.sub.h/d.sub.c=15.59T.sub.x/T.sub.L1.056(12)
(91) Embodiments of the correlation function given by Eq. (12) may provide an approximate estimate of d.sub.h provided that d.sub.c, T.sub.x and T.sub.L are known for a given metallic glass forming alloy, as d.sub.h=d.sub.c(15.59T.sub.x/T.sub.L1.056). According to Eq. (12), d.sub.h/d.sub.c>1 when T.sub.x/T.sub.L>0.132. Therefore, in embodiments using alloys with T.sub.x/T.sub.L greater than about 0.1 may be considered generally stable against crystallization for multilayer processing by layer-by-layer deposition, while alloys with T.sub.x/T.sub.L less than about 0.1 may be considered not quite as stable. Therefore, in some embodiments of the disclosure, metallic glasses that demonstrate T.sub.x/T.sub.L of at least 0.1 are considered suitable for multilayer processing by layer-by-layer deposition. In other embodiments of the disclosure, metallic glasses that demonstrate T.sub.x/T.sub.L of at least 0.132 are considered suitable for multilayer processing by layer-by-layer deposition. In other embodiments of the disclosure, metallic glasses that demonstrate T.sub.x/T.sub.L of at least 0.15 are considered suitable for multilayer processing by layer-by-layer deposition. In yet other embodiments of the disclosure, metallic glasses that demonstrate T.sub.x/T.sub.L of at least 0.2 are considered suitable for multilayer processing by layer-by-layer deposition.
(92) Example Layer Deposition Methods: The disclosure is generally directed to methods of forming a metallic glass multilayer by depositing a layer of metallic glass-forming liquid over a layer of metallic glass. In certain embodiments, the disclosure is directed to any methods capable of depositing a metallic glass-forming liquid over a layer of metallic glass.
(93) In one embodiment, the layer deposition method is melt spinning (see, for example, R. Pond and R. Maddin, Transactions of the Metallurgical Society of AIME, Volume: 245, Issue: 11, Page: 2475, 1976, the reference of which is incorporated herein in its entirety), in which a base metallic glass layer may be formed by injecting a continuous melt stream on a thermally conducting wheel rotating at high speed. Subsequently, an added layer may be deposited by injecting a continuous melt stream at temperature T.sub.i on a rotating roll or mandrel of the base metallic glass layer at temperature T.sub.o to form a metallic glass multilayer.
(94) In another embodiment, the layer deposition method is planar flow casting (as described, for example, in U.S. Pat. No. 4,290,476, the reference of which is incorporated herein in its entirety), in which a base metallic glass layer may be formed by injecting a continuous melt stream on a thermally conducting movable chill surface. Subsequently, an added layer may be deposited by injecting a continuous melt stream at temperature T.sub.i on a movable base metallic glass layer at temperature T.sub.o to form a metallic glass multilayer.
(95) In yet another embodiment, the layer deposition method is by a spray deposition method (as described, for example, in United States Patent Applications No 20130306198 and 20140202595, the references of which are incorporated herein in their entirety), in which a base metallic glass layer may be formed by injecting a stream of discontinuous droplets on a moving substrate. Subsequently, an added layer may be deposited by injecting a stream of discontinuous droplets at temperature T.sub.i on a movable base metallic glass layer at temperature T.sub.o to form a metallic glass multilayer.
(96) In yet another embodiment, the disclosure is directed to the shearless melt deposition method, as disclosed in Provisional Patent Application No. 61/884,653, titled Production of Metallic Glass Sheet by Melt Deposition, filed on Sep. 30, 2013, the reference of which is incorporated herein in its entirety. That method includes forming of a metallic glass layer by a melt deposition process, where a molten alloy is deposited inside a channel formed by two substrate plates, and shaped and quenched by conduction to the substrates in a manner that enables the melt to deposit and vitrify, i.e. to transform to the metallic glass phase, without undergoing substantial shear flow. The melt is held in a reservoir at a controlled temperature and is injected at a controlled deposition rate Q. In some embodiments, the temperature of the melt is more precisely controlled as the melt exits a nozzle. The two substrate plates include (1) a chill plate, which may be moving at a controlled speed V and (2) a guide plate, which may be attached to the nozzle, may be thermally insulated from the nozzle, may be at a temperature below T.sub.cn, and may be stationary. Once a metallic glass base layer is formed, the chill plate may be transporting the base layer held at temperature T.sub.o while melt may be deposited over the metallic glass base layer at temperature T.sub.o to form a metallic glass multilayer. This embodiment is illustrated schematically in
(97) In some embodiments, as shown schematically in
(98) Composite Multilayers
(99) The disclosure in embodiments is directed to methods of forming metallic glass multilayer composites by layer-by-layer deposition of liquid layers of metallic glass-forming alloys, where each layer has a different metallic glass-forming alloy composition.
(100) Having multilayers of different composition and/or thickness may be advantageous if one desires a composite multilayered metallic glass utilizing more two or more metallic glass compositions having different properties that can be utilized over different thicknesses. Specifically, a composite multilayer may offer a combination of properties that is not available in one of the component metallic glasses. One such combination of properties may be strength and toughness. It is generally known that strength and toughness in metallic glasses is usually mutually exclusive. For example, metallic glasses that exhibit a high to very high fracture toughness, K.sub.c, generally exhibit a modest to low yield strength, .sub.y, while metallic glasses that exhibit a high to very high yield strength generally exhibit a modest to low fracture toughness (see for example, M. D. Demetriou et al., Nature Materials, Vol. 10, pp. 123-128, 2011, the disclosure of which is incorporated herein by reference).
(101) In some embodiments, the compressive yield strength can be used to represent the material yield strength, .sub.y. The compressive yield strength is the stress at which the material yields plastically when loaded in compression. Specifically, the compressive yield strength is the measure of the material's ability to resist non-elastic yielding under compression.
(102) In some embodiments, the notch toughness can be used to represent the material fracture toughness, K.sub.c. Notch toughness is the measure of the material's ability to dissipate mechanical energy without propagation of a pre-existing crack. Specifically, notch toughness is a measure of the resistance to propagate a crack originating from a pre-existing notch. In the context of the disclosure, the notch toughness is defined as the stress intensity factor at crack initiation when measured on a 3 mm diameter rod containing a notch with length ranging from 1 to 2 mm and a notch root radius ranging from 0.1 to 0.15 mm.
(103) In the context of the disclosure, the plastic zone radius r.sub.p, defined as the length scale over which plastic deformation is accommodated in the absence of fracture, is a unique property for each metallic glass composition and is given by r.sub.p=K.sub.c/.sub.y.sup.2.
(104) In the context of the disclosure, tensile ductility is defined as the amount of plastic strain attained by the material following yielding under tensile loading.
(105) In the context of the disclosure, certain criteria have been established by which a metallic glass multilayer composite that comprises at least two bonded metallic glass layers, where at least two layers comprise different metallic glass alloy compositions, may exhibit improved yield strength and fracture toughness over the constituent metallic glass compositions.
(106) Specifically, the yield strength is a global property, and consequently the yield strength of the composite may approximately follow the rules of mixtures such that it may have a value that is near the volumetric average between the yield strengths of the constituent metallic glass compositions. In some embodiments, the yield strength of the composite may approximately lie between the upper and lower bound of the rules of mixtures as defined by the Voigt and Reuss models, respectively. In embodiments where the layers have equal thickness, the yield strength of the composite may have a value that is near the arithmetic average between the yield strengths of the constituent metallic glass compositions.
(107) Fracture toughness on the other hand is a local property, and consequently the fracture toughness of the composite may be closer to the fracture toughness of one of the constituent metallic glass compositions rather than the average. The fracture toughness of metallic glasses is related to the total sliding distance in a shear band prior to crack opening (see for example, M. D. Demetriou et al., Nature Materials, Vol. 10, pp. 123-128, 2011, the disclosure of which is incorporated herein by reference). This limiting sliding distance can be related to plastic zone radius of the metallic glass, r.sub.p. Shear bands initiated in the softer metallic glass layer (i.e. in the layer with the lowest shear modulus G) may be arrested by the stiffer metallic glass layer (i.e. by the layer with the highest shear modulus G) provided that they don't extend beyond the limiting sliding distance at which crack opening occurs. Therefore, if a significant shear modulus mismatch between the layers exists, and the layer thicknesses are confined within their respective plastic zone radii, the fracture toughness of the composite may be closer to the fracture toughness of the constituent metallic glass composition having the higher fracture toughness. Accordingly, in some embodiments, the fracture toughness of the composite may match or exceed the fracture toughness of the constituent metallic glass composition having the higher fracture toughness.
(108) For a metallic glass, tensile ductility is also a local property like fracture toughness. This is because metallic glasses fail catastrophically almost immediately after yielding under tensile loading, because a propagating shear band under tension is unstable and evolves nearly spontaneously into a crack prior to networking with other shear bands, thus failing to produce any substantial global ductility. According to the mechanism introduced above, where shear bands initiated in the softer metallic glass layer (i.e. in the layer with the lowest shear modulus G) may be arrested by the stiffer metallic glass layer (i.e. by the layer with the highest shear modulus G) provided that they don't extend beyond the limiting sliding distance at which crack opening occurs, may enable the metallic glass multilayer composite to exhibit tensile ductility. Therefore, if a significant shear modulus mismatch between the layers exists, and the layer thicknesses are confined within their respective plastic zone radii, the tensile ductility of the composite may exceed those of the constituent metallic glass compositions.
(109) Mechanistically, the concept of strengthening or toughening of composite materials has been widely utilized in composites with different morphologies that may include particles, fibers, or laminates (i.e. multilayers). However, for the same volume fraction of reinforcing phase, the laminate morphology has the maximum toughening efficiency, followed (in order of potency) by fiber and particulate morphologies. To design stronger and tougher composite materials, the material properties and microstructural components at multiple length scales can be controlled in order to promote toughening of the composite by optimizing the contributions from each layer phase without compromising the strength of the composite.
(110) Lamellar (i.e. multilayered) composites are highly anisotropic materials such that the mechanical response, i.e., global strength and toughness, of the composite is dependent on the loading orientation. For example, the strength and toughness of a lamellar composite will differ whether the composite is loaded longitudinally or transversally to the layers. Assuming that the orientation of the crack-growth direction is perpendicular to the layers, lamellar metallic glass composites may derive most of their resistance to fracture during crack growth rather than during crack initiation. Extrinsic crack-tip shielding mechanisms, which may include crack bridging via the softer metallic glass layer (i.e. the layer with the lowest shear modulus G), may primarily act behind the crack tip and locally screen the crack from the applied (far-field) stress. Such extrinsic shielding mechanisms may generate a fracture toughness of the metallic glass multilayer composite that is higher than either of the fracture toughness values of the component metallic glasses while also retaining a strength near the volumetric average of the component metallic glass strengths. Such extrinsic shielding mechanisms may also generate a tensile ductility of the metallic glass multilayer composite that is higher than either of the tensile ductility values of the component metallic glasses while also retaining a strength near the volumetric average of the component metallic glass strengths.
(111) Hence, the following criteria are established in accordance with the disclosure:
(112) The relative difference between the shear moduli of the metallic glass alloy compositions is at least 2%.
(113) The thickness of each layer does not exceed the plastic zone radius of the metallic glass alloy composition comprising the layer.
(114) In the context of the disclosure, the relative difference between two values means the difference between two values divided by the larger of the two values.
(115) In some embodiments, the yield strength of the metallic glass multilayer composite is measured on a multilayer that is loaded in a direction parallel to the layers. In some embodiments, the yield strength of the metallic glass multilayer composite is higher than the yield strength of the constituent metallic glass composition having the lowest yield strength. In one embodiment, the yield strength of the metallic glass multilayer composite is within 20% of the volumetric average between the yield strengths of the constituent metallic glass compositions. In another embodiment, the yield strength of the metallic glass multilayer composite is within 10% of the volumetric average between the yield strengths of the constituent metallic glass compositions. In yet another embodiment, the yield strength of the metallic glass multilayer composite is within 5% of the volumetric average between the yield strengths of the constituent metallic glass compositions.
(116) In some embodiments, the fracture toughness of the metallic glass multilayer composite is measured on a multilayer that contains a notch and/or a pre-crack oriented normal to the layers. In some embodiments, the fracture toughness of the metallic glass multilayer composite is higher than the fracture toughness of the metallic glass composition having the lowest fracture toughness. In one embodiment, the fracture toughness of the metallic glass multilayer composite is higher than the arithmetic average of the fracture toughness values of the constituent metallic glass compositions. In another embodiment, the fracture toughness of the metallic glass multilayer composite is higher than the fracture toughness of the metallic glass composition having the highest fracture.
(117) In some embodiments, the tensile ductility of the metallic glass multilayer composite is multilayer is measured on a multilayer that is loaded in a direction parallel to the layers. In some embodiments, the tensile ductility of the metallic glass multilayer composite is higher than the tensile ductility values of the constituent metallic glass compositions. In one embodiment, the tensile ductility of the metallic glass multilayer composite is at least 0.1%. In another embodiment, the tensile ductility of the metallic glass multilayer composite is at least 0.25%. In yet another embodiment, the tensile ductility of the metallic glass multilayer composite is at least 0.5%. In yet another embodiment, the tensile ductility of the metallic glass multilayer composite is at least 1%. In yet another embodiment, the tensile ductility of the metallic glass multilayer composite is at least 2%.
(118) In some embodiments, the relative difference between the shear moduli of the metallic glass alloy compositions is at least 5%. In other embodiments, the relative difference between the shear moduli of the metallic glass alloy compositions is at least 10%. In other embodiments, the relative difference between the shear moduli of the metallic glass alloy compositions is at least 20%. In some embodiments, the difference between the shear moduli of the metallic glass alloy compositions is at least 1 GPa. In other embodiments, the difference between the shear moduli of the metallic glass alloy compositions is at least 2 GPa. In other embodiments, the difference between the shear moduli of the metallic glass alloy compositions is at least 5 GPa.
(119) In some embodiments the layers have an equal thickness, wherein the thickness does not exceed the plastic zone radius of the metallic glass alloy composition having the smallest plastic zone radius.
(120) The disclosure is also directed to methods of forming metallic glass multilayers composite by sequential layer-by-layer deposition. In the context of the disclosure, certain criteria have been established by which deposition of an added metallic glass layer over a base metallic glass layer of different alloy composition will promote wetting between the layers and avoid crystallization of either layer. These criteria are as follows:
(121) The difference in the glass transition temperatures of the metallic glass compositions, T.sub.g, is less than 50 C.
(122) The difference in the liquidus temperatures of the metallic glass-forming alloy compositions, T.sub.L, are less than 150 C.
(123) Meeting these criteria enables the use of methods to fabricate metallic glass multilayers according to methods disclosed in the disclosure by assuming an effective T.sub.g* and T.sub.L* that are averages between the compositions. Specifically, T.sub.g*=0.5(T.sub.g1+T.sub.g2) and T.sub.L*=0.5(T.sub.L1+T.sub.L2), where T.sub.g1 and T.sub.g2 are the glass transition temperatures of the two metallic glass alloy compositions, and T.sub.L1 and T.sub.L2 are the liquidus temperatures of the two metallic glass forming alloy compositions. Hence, embodiments of methods in accordance with this disclosure for the formation of metallic glass multilayers may apply for the formation of metallic glass composite by substituting T.sub.g by T.sub.g* and T.sub.L by T.sub.L*.
(124) In the context of this disclosure, different compositions means that compositions vary by at least 1 percent in the atomic concentration of at least one element. In other embodiments, different compositions means that compositions vary by at least 2 percent in the atomic concentration of at least one element. In yet other embodiments, different compositions means that compositions vary by at least 5 percent in the atomic concentration of at least one element.
(125) In some embodiments, the difference in the glass transition temperatures of the metallic glass compositions, T.sub.g, is less than 30 C. In other embodiments, the difference in the glass transition temperatures of the metallic glass compositions, T.sub.g, is less than 20 C. In yet other embodiments, the difference in the glass transition temperatures of the metallic glass compositions, T.sub.g, is less than 10 C.
(126) In some embodiments, the difference in the liquidus temperatures of the metallic glass-forming alloy compositions, T.sub.L, is less than 80 C. In some embodiments, the difference in the liquidus temperatures of the metallic glass-forming alloy compositions, T.sub.L, is less than 80 C. In other embodiments, the difference in the liquidus temperatures of the metallic glass-forming alloy compositions, T.sub.L, is less than 60 C. In yet other embodiments, the difference in the liquidus temperatures of the metallic glass-forming alloy compositions, T.sub.L, is less than 40 C.
(127) In other embodiments, a criterion about the crystallization temperatures, T.sub.x, similar to the criterion about the glass transition temperatures, T.sub.g, may be met. Specifically, the difference in the crystallization temperatures of the metallic glass compositions, T.sub.x, is less than 50 C. Meeting this criterion will enable the use of methods to fabricate metallic glass multilayers according to embodiments of the disclosure by assuming an effective T.sub.x* that is an average between the compositions. Specifically, T.sub.x*=0.5(T.sub.x1+T.sub.x2), where T.sub.x1 and T.sub.x2 are the crystallization temperatures of the two metallic glass compositions. Hence, embodiments disclosed above for the formation of metallic glass multilayers may apply for the formation of composite metallic glass by substituting T.sub.x by T.sub.x*.
(128) In some embodiments, the difference in the crystallization temperatures of the metallic glass compositions, T.sub.x, is less than 30 C. In other embodiments, the difference in the crystallization temperatures of the metallic glass compositions, T.sub.x, is less than 20 C. In yet other embodiments, the difference in the crystallization temperatures of the metallic glass compositions, T.sub.x, is less than 10 C.
(129) Example Alloy Pairs for Multilayer Composites
(130) Several example alloy pairs are presented that satisfy the criteria introduced above for the formation of a multilayer composite.
EXAMPLE 1
Ni68.17Cr8.65Nb2.98P16.42B3.28Si0.5 and Zr52.5Ti5Cu17.9Ni14.6Al10
(131) Table 4 lists the shear modulus G, compressive yield strength .sub.y, notch toughness K.sub.c, plastic zone radius r.sub.p, glass-transition temperature T.sub.g, crystallization temperature T.sub.x, and liquidus temperature T.sub.L for exemplary alloy pair Ni.sub.68.17Cr.sub.8.65Nb.sub.2.98P.sub.16.42B.sub.3.28Si.sub.0.5 and Zr.sub.52.5Ti.sub.5Cu.sub.17.9Ni.sub.14.6Al.sub.1. The difference between the shear moduli of the metallic glass alloy compositions is about 8 GPa, while the relative difference is about 16%. The difference in the glass transition temperatures of the metallic glass compositions is 2 C., and T.sub.g* is 399 C. The difference in the crystallization temperatures of the metallic glass compositions is 13 C., and T.sub.x* is 468.5 C. The difference in the liquidus temperatures of the metallic glass-forming alloy compositions is 14 C., and T.sub.i,* is 877 C. In embodiments of composite metallic glass multilayers according to the disclosure, the layer thickness of Ni.sub.68.17Cr.sub.8.65Nb.sub.2.98P.sub.16.42B.sub.3.28Si.sub.0.5 should not exceed 0.3 mm, while the layer thickness of Zr.sub.52.5Ti.sub.5Cu.sub.17.9Ni.sub.14.6Al.sub.10 should not exceed 1 mm. In embodiments of metallic glass multilayer composites having layers with equal thickness according to the disclosure, the layer thickness should not exceed 0.3 mm.
(132) TABLE-US-00004 TABLE 4 Shear modulus G, compressive yield strength .sub.y notch toughness K.sub.c, plastic zone radius r.sub.p, glass-transition temperature T.sub.g, crystal- lization temperature T.sub.x, and liquidus temperature T.sub.L for example alloy pair Ni.sub.68.17Cr.sub.8.65Nb.sub.2.98P.sub.16.42B.sub.3.28Si.sub.0.5 and Zr.sub.52.5Ti.sub.5Cu.sub.17.9Ni.sub.14.6Al.sub.10 G .sub.y K.sub.c r.sub.p T.sub.g T.sub.x T.sub.L Composition (GPa) (MPa) (MPa m.sup.1/2) (mm) ( C.) ( C.) ( C.) Ni.sub.68.17Cr.sub.8.65Nb.sub.2.98P.sub.16.42B.sub.3.28Si.sub.0.5 50.0 2418 77 0.3 400 462 884 Zr.sub.52.5Ti.sub.5Cu.sub.17.9Ni.sub.14.6Al.sub.10 31.8 1700 95 1.0 398 455 870
EXAMPLE 2
Ni71.4Cr5.52Nb3.38P16.67B3.03 and Fe67Mo6Ni3.5Cr3.5P12C5.5B2.5
(133) Table 5 lists the shear modulus G, compressive yield strength .sub.y, notch toughness K.sub.c, plastic zone radius r.sub.p, glass-transition temperature T.sub.g, crystallization temperature T.sub.x, and liquidus temperature T.sub.L for exemplary alloy pair Ni.sub.71.4Cr.sub.5.52Nb.sub.3.38P.sub.16.67B.sub.3.03 and Fe.sub.67Mo.sub.6Ni.sub.3.5Cr.sub.3.5P.sub.12C.sub.5.5B.sub.2.5. The difference between the shear moduli of the metallic glass alloy compositions is 9.5 GPa, while the relative difference is about 16%. The difference in the glass transition temperatures of the metallic glass compositions is 49 C., and T.sub.g* is 417.5 C. The difference in the crystallization temperatures of the metallic glass compositions is 44 C., and T.sub.x, is 457 C. The difference in the liquidus temperatures of the metallic glass-forming alloy compositions is 138 C., and T.sub.L* is 959 C. In embodiments of metallic glass multilayer composites according to the disclosure, the layer thickness of Ni.sub.71.4Cr.sub.5.52Nb.sub.3.38P.sub.16.67B.sub.3.03 should not exceed 0.5 mm, while the layer thickness of Fe.sub.67Mo.sub.6Ni.sub.3.5Cr.sub.3.5P.sub.12C.sub.5.5B.sub.2.5 should not exceed 0.07 mm. In embodiments of metallic glass multilayer composites having layers with equal thickness according to the disclosure, the layer thickness should not exceed 0.07 mm.
(134) TABLE-US-00005 TABLE 5 Shear modulus G, compressive yield strength .sub.y, notch toughness K.sub.c, plastic zone radius r.sub.p, glass-transition temperature T.sub.g, crystal- lization temperature T.sub.x, and liquidus temperature T.sub.L for example alloy pair Ni.sub.71.4Cr.sub.5.52Nb.sub.3.38P.sub.16.67B.sub.3.03 and Fe.sub.67Mo.sub.6Ni.sub.3.5Cr.sub.3.5P.sub.12C.sub.5.5B.sub.2.5 G .sub.y K.sub.c r.sub.p T.sub.g T.sub.x T.sub.L Composition (GPa) (MPa) (MPa m.sup.1/2) (mm) ( C.) ( C.) ( C.) Ni.sub.71.4Cr.sub.5.52Nb.sub.3.38P.sub.16.67B.sub.3.03 48.9 2375 94 0.5 393 435 890 Fe.sub.67Mo.sub.6Ni.sub.3.5Cr.sub.3.5P.sub.12C.sub.5.5B.sub.2.5 59.4 3145 48 0.07 442 479 1028
EXAMPLE 3
Ni71.4Cr5.52Nb3.38P16.67B3.03 and Ni67.5Cr10Nb3P16.5B3
(135) Table 6 lists the shear modulus G, compressive yield strength .sub.y, notch toughness K.sub.c, plastic zone radius r.sub.p, glass-transition temperature T.sub.g, crystallization temperature T.sub.x, and liquidus temperature T.sub.L for exemplary alloy pair Ni.sub.71.4Cr.sub.5.52Nb.sub.3.38P.sub.16.67B.sub.3.03 and Ni.sub.67.5Cr.sub.10Nb.sub.3P.sub.16.5B.sub.3. The difference between the shear moduli of the metallic glass alloy compositions is 3.3 GPa, while the relative difference is about 6%. The difference in the glass transition temperatures of the metallic glass compositions is 2 C., and T.sub.g* is 394 C. The difference in the crystallization temperatures of the metallic glass compositions is about 4 C., and T.sub.x, is about 439 C. The difference in the liquidus temperatures of the metallic glass-forming alloy compositions is 17 C., and T.sub.L* is 898.5 C. In embodiments of metallic glass multilayer composites according to the disclosure, the layer thickness of Ni.sub.7.4Cr.sub.5.52Nb.sub.3.38P.sub.16.67B.sub.3.03 should not exceed 0.5 mm, while the layer thickness of Ni.sub.675Cr.sub.10Nb.sub.3P.sub.16.5B.sub.3 should not exceed 0.08 mm. In embodiments of metallic glass multilayer composites having layers with equal thickness according to the disclosure, the layer thickness should not exceed 0.08 mm.
(136) TABLE-US-00006 TABLE 6 Shear modulus G, compressive yield strength .sub.y, notch toughness K.sub.c, plastic zone radius r.sub.p, glass-transition temperature T.sub.g, crystal- lization temperature T.sub.x, and liquidus temperature T.sub.L for example alloy pair Ni.sub.71.4Cr.sub.5.52Nb.sub.3.38P.sub.16.67B.sub.3.03 and Ni.sub.67.5Cr.sub.10Nb.sub.3P.sub.16.5B.sub.3 G .sub.y K.sub.c r.sub.p T.sub.g T.sub.x T.sub.L Composition (GPa) (MPa) (MPa m.sup.1/2) (mm) ( C.) ( C.) ( C.) Ni.sub.71.4Cr.sub.5.52Nb.sub.3.38P.sub.16.67B.sub.3.03 48.9 2375 94 0.5 393 435 890 Ni.sub.67.5Cr.sub.10Nb.sub.3P.sub.16.5B.sub.3 52.2 2446 38 0.08 395 443.5 907
(137) Having described several embodiments, it will be recognized by those skilled in the art that various modifications, alternative constructions, and equivalents may be used without departing from the spirit of the disclosure. Additionally, a number of well-known processes and elements have not been described in order to avoid unnecessarily obscuring the disclosure. Accordingly, the above description should not be taken as limiting the scope of the disclosure.
(138) Those skilled in the art will appreciate that the presently disclosed embodiments teach by way of example and not by limitation. Therefore, the matter contained in the above description or shown in the accompanying drawings should be interpreted as illustrative and not in a limiting sense. The following claims are intended to cover all generic and specific features described herein, as well as all statements of the scope of the present method and system, which, as a matter of language, might be said to fall therebetween.