Nickel-aluminium-zirconium alloys

Abstract

The present subject matter describes Ni—Al—Zr alloys, which include Ni as the major component, with the additions of 9-20% Al and 4-14% Zr by atomic percentage. In one embodiment, the present subject matter describes a group of alloy compositions in a Nickel-Aluminum-Zirconium (Ni—Al—Zr) system corresponding to a concentration range of about 9-20% Al and about 4-14% Zr by atomic percentages, and the balance being Ni. In other embodiment, the present subject matter includes at least one eutectic constituent including at least two of the intermetallic compounds or phases Ni.sub.3Al, NiAl, Ni.sub.5Zr, Ni.sub.7Zr.sub.2 and derivatives that are realized within the aforementioned composition group.

Claims

1. A Nickel-Aluminum-Zirconium alloy comprising a plurality of intermetallic phases, wherein a composition of Aluminum (Al) and Zirconium (Zr) within the Nickel-Aluminum-Zirconium alloy is in a range of about 13.5 to about 19, about 4 to about 14 by atomic percentages, respectively, with the balance being Nickel; wherein the plurality of intermetallic phases is selected from the group consisting of at least two of Ni.sub.3Al, NiAl, Ni.sub.5Zr, Ni.sub.7Zr.sub.2 and a combination of structural derivatives of the corresponding intermetallic phases; wherein the Nickel-Aluminum-Zirconium alloy includes at least one eutectic composition comprising eutectic constituents Ni.sub.3Al+Ni.sub.5Zr, Ni.sub.3Al+Ni.sub.7Zr.sub.2, NiAl+Ni.sub.7Zr.sub.2, or combinations thereof.

2. The Nickel-Aluminum-Zirconium alloy as claimed in claim 1 wherein the Nickel-Aluminum-Zirconium alloy is characterized by a yield strength of at least 0.8 Giga Pascal (GPa) at room temperature and a yield strength of at least 0.8 GPa at 700° C.

3. The Nickel-Aluminum-Zirconium alloy as claimed in claim 1, further comprising at least one primary solidification phase, wherein the at least one primary solidification phase is one of Ni.sub.3Al, Ni.sub.5Zr, Ni Zr.sub.2 and NiAl.

4. The Nickel-Aluminum-Zirconium alloy as claimed in claim 3, further comprising at least one additive, wherein at least one additive is one of an alloying additive and a trace additive.

5. The Nickel-Aluminum-Zirconium alloy as claimed in claim 3 wherein the Nickel-Aluminum-Zirconium alloy is characterized by a yield strength of at least 0.8 Giga Pascal (GPa) at room temperature and a yield strength of at least 0.8 GPa at 700° C.

6. The Nickel-Aluminum-Zirconium alloy as claimed in claim 1, further comprising at least one additive, wherein at least one additive is one of an alloying additive and a trace additive.

7. The Nickel-Aluminum-Zirconium alloy as claimed in claim 6 wherein the Nickel-Aluminum-Zirconium alloy is characterized by a yield strength of at least 0.8 Giga Pascal (GPa) at room temperature and a yield strength of at least 0.8 GPa at 700° C.

8. The Nickel-Aluminum-Zirconium alloy as claimed in claim 6, wherein the at least one additive is selected from the group consisting of Hafnium (Hi), Scandium (Sc), Cobalt (Co), Platinum (Pb), Palladium (Pd), Chromium (Cr), Ruthenium (Ru), Rhenium (Re), Tantalum (Ta), Titanium (Ti), Niobium (Nb), Molybdenum (Mo), and Tungsten (W).

9. The Nickel-Aluminum-Zirconium alloy as claimed in claim 8 wherein the Nickel-Aluminum-Zirconium alloy is characterized by a yield strength of at least 0.8 Giga Pascal (GPa) at room temperature and a yield strength of at least 0.8 GPa at 700° C.

10. The Nickel-Aluminum-Zirconium alloy as claimed in claim 8, wherein the at least one additive retains eutectic constituents within the Nickel-Aluminum-Zirconium alloy.

11. The Nickel-Aluminum-Zirconium alloy as claimed in claim 10 wherein the Nickel-Aluminum-Zirconium alloy is characterized by a yield strength of at least 0.8 Giga Pascal (GPa) at room temperature and a yield strength of at least 0.8 GPa at 700° C.

12. The Nickel-Aluminum-Zirconium alloy as claimed in claim 10 wherein the Nickel-Aluminum-Zirconium alloy is characterized by a yield strength of at least 0.8 Giga Pascal (GPa) at room temperature and a yield strength of at least 0.8 GPa at 700° C.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) The detailed description is provided with reference to the accompanying figures. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the drawings to reference like features and components.

(2) FIG. 1 illustrates a ternary section of a Ni—Al—Zr system showing a concentration range of elements therein, according to an embodiment of the present subject matter.

(3) FIG. 2a, 2b, 2c depict microstructures of various Ni—Al—Zr based alloys, according to an embodiment of the present subject matter.

(4) FIGS. 3a, 3b, and 3c depict microstructures of certain other alloys, denoted by alloys D till L, according to an embodiment of the present subject matter.

(5) FIG. 4a illustrates stress-strain curves of alloys A till L in compression, measured at room temperature, according to an embodiment of this present subject matter.

(6) FIG. 4b illustrates the values of compressive yield strength at room temperature of the alloys A till L shown in FIG. 4a, according to an embodiment of the present subject matter.

(7) FIG. 5 illustrates values of the compressive yield strength of the alloys from A till L at 700° C., according to an embodiment of the present subject matter.

(8) FIG. 6 depicts the compressive yield strength of alloys X, Y and Z at room temperature.

(9) FIG. 7 illustrates a plot depicting comparison of compressive yield strength at different temperatures between Ni—Al—Zr alloys of the present subject matter and conventional Ni based alloys, according to an embodiment of the present subject matter.

(10) FIG. 8 illustrates a micrograph of indents performed using a Vickers indentor for alloys A to I.

(11) FIG. 9 illustrates a tensile stress strain curve for alloy B at room temperature, according to an embodiment of the present subject matter.

(12) FIG. 10 illustrates micrographs depicting the stability of the microstructures of alloy B at different temperatures, according to an embodiment of the present subject matter.

(13) FIG. 11a illustrates a graph depicting comparison of percentage mass gain suffered by alloy B after exposure at different temperatures, according to an embodiment of the present subject matter.

(14) FIG. 11b illustrates a graph depicting comparison of percentage mass changes suffered by alloy B after exposure at 900° C. and 1100° C., according to an embodiment of the present subject matter.

(15) FIG. 12a illustrates a graph depicting comparison of weight changes suffered by alloy B in comparison with conventional alloys within the same range of temperatures, when subjected to a static oxidation, according to an embodiment of the present subject matter

(16) FIG. 12b illustrates a graph depicting comparison of weight changes suffered by alloy B in comparison with conventional alloys within the same range of temperatures, when subjected to a cyclic oxidation, according to an embodiment of the present subject matter.

DETAILED DESCRIPTION

(17) The present subject matter utilizes an interaction between eutectic and peritectic reactions that form intermetallic compounds, including γ′ in certain binary systems with Ni as the base, to form fine scale structures constituted of different combinations of intermetallic compounds in ternary and further complex systems. The alloys described herein exhibit superior strength over conventional Ni base superalloys at temperatures up to 700° C. Such alloys also have high oxidation resistance and micro-structural stability at elevated temperatures up to about 1100° C. Further, the alloys possess reasonable tensile ductility at ambient temperature In addition, the alloys exhibit a comparatively low density ranging from 7.3-7.9 gm/cm.sup.3. Furthermore, the aforementioned properties of the alloys have been realized with alloying additions to Ni, such as Al and Zr that have a relatively low cost.

(18) In one embodiment, the alloys in accordance with present subject matter have varying compositions of Nickel (Ni), Aluminum (Al), and Zirconium (Zr), primarily based on Ni. Such varying compositions of the alloys include Al and Zr, which are present in a concentration range of about 9 to 20%, and about 4 to 14%, respectively, the balance being Ni. The aforementioned composition range is described in FIG. 1 within a parallelogram 102 within a ternary section 100 of a Ni—Al—Zr system. These compositions are designated A to L and are shown in Table 1 along with their measured density. The Ni-rich side of a Ni—Zr based binary phase diagram shows a eutectic between Ni-based solid solution (γ) and a Ni.sub.5Zr phase, together with an intermediate phase Ni.sub.7Zr.sub.2. The Ni5Zr phase forms from a peritectic reaction L+Ni.sub.7Zr.sub.2.fwdarw.Ni.sub.5Zr. The Ni-rich side of a Ni—Al based binary phase diagram shows that a Ni.sub.3Al (γ′) phase forms from a peritectic reaction between a NiAl (β) and the γ′ phase in one form of the binary phase diagram. In addition, a eutectic reaction exists between L and the γ′ phase and β phase in another form. The NiAl (β) phase forms as an intermediate intermetallic phase. These intermetallics in the binary system may serve as the basis for the formation of fine-scale eutectic structures in the ternary system in the aforementioned concentration range through their interaction with each other.

(19) TABLE-US-00001 TABLE 1 at % Wt % Density Alloy Al Zr Ni Al Zr Ni (gm/cm.sup.3)±0.001 Alloy A 12 11 77 5.5 17.2 77.3 7.946 Alloy B 15 11 74 7.0 17.5 75.5 7.798 Alloy C 18 11 71 8.6 17.7 73.7 7.614 Alloy D 9 11 80 4.1 16.9 79.0 8.043 Alloy E 15 8 77 7.2 12.9 79.9 7.842 Alloy F 18 8 74 8.7 13.2 78.1 7.643 Alloy G 20 11 69 9.7 17.9 72.4 7.209 Alloy H 15 14 71 6.9 21.9 71.2 7.709 Alloy I 12 14 74 5.5 21.5 73.0 7.878 Alloy J 14 6 80 6.73 9.746 83.53 7.798 Alloy K 15 4 81 7.33 6.61 86.06 7.743 Alloy L 20 6 74 9.95 10.09 79.97 7.354

(20) Further to the preparation, the alloys were melted in a laboratory scale non-consumable are melting unit and remelted several times to ensure homogeneity. A portion of the alloys was re-melted and suction cast into a cylindrical water-cooled copper (Cu) crucible. A combination of X-ray diffraction, electron probe microanalysis, and scanning electron microscopy in the back-scattered mode were used to analyze compositions and structures of various microstructural constituents. It is, however, understood that such alloys and their products may be manufactured by alternative methods known to those skilled in the art, such as wrought forms, or from consolidation of powder, or in equiaxed, directionally solidified or single crystal cast forms.

(21) In another embodiment of the present subject matter, the alloy compositions include a combination of eutectic constituents further including the intermetallic phases Ni.sub.3Al denoted by γ′, Ni.sub.5Zr, Ni.sub.7Zr.sub.2 and NiAl denoted by β, in various proportions. FIG. 2 illustrates the different eutectic constituents of various alloys by way of microstructures 200 of various Ni—Al—Zr based alloys, according to an embodiment of the present subject matter. Alloy A, as depicted in FIG. 2a includes a eutectic constituent including the γ′ and Ni.sub.5Zr phases. Alloy B, as depicted in FIG. 2b, includes a mixture of two eutectic constituents comprising respectively [γ′+Ni.sub.7Zr.sub.2] eutectic and a [β+Ni.sub.7Zr.sub.2] eutectic. The [γ′+Ni.sub.7Zr.sub.2] eutectic has a coarser structure, while the [β+Ni.sub.7Zr.sub.2] eutectic is extremely fine. Alloy C, as depicted in FIG. 2c, includes the same combination of eutectic structures, but with a larger volume fraction of the [β+Ni.sub.7Zr.sub.2] eutectic.

(22) In another embodiment, FIG. 3 shows the microstructures 300 of a set of compositions that contains primary solidification phases in addition to the aforementioned eutectics. FIG. 3(a-c) depicts the microstructures 300 of Alloys D till L. The primary solidification phase is the first phase to form during solidification. Accordingly, as depicted in the FIG. 3a, Alloy D includes the primary solidification phase Ni.sub.5Zr, in addition to the eutectic [Ni.sub.5Zr+γ′]. Alloy E includes γ′ as the primary solidification phase which is surrounded by small amounts of Ni.sub.5Zr together with the [Ni.sub.5Zr+γ′] eutectic. In Alloy F, Ni.sub.3Al (γ′) is the primary solidification phase, together with Ni.sub.7Zr.sub.2 and the [β+Ni.sub.7Zr.sub.2] eutectic. As depicted in the FIG. 3b, Alloys H and I include Ni.sub.7Zr.sub.2 as the primary solidification phase in addition to the eutectics [Ni.sub.5Zr+γ′] and [Ni.sub.7Zr.sub.2+γ′]. Alloy G has β and γ′ as the primary solidification phases with the [β+Ni.sub.7Zr.sub.2] eutectic. FIG. 3c depicts the microstructures 300 of Alloys J till L. Like Alloy E, alloys J and K also show γ′ as the primary solidification phase, surrounded by small amounts of Ni.sub.5Zr together with the [Ni.sub.5Zr+γ′] eutectic. The eutectic volume fraction decreases from Alloy E to Alloy K. In Alloy L, β acts the primary solidification phase and is surrounded by γ′ together with Ni.sub.7Zr.sub.2 and the [β+Ni.sub.7Zr.sub.2] eutectic.

(23) Further, in another embodiment, alloys including the eutectic structures as well as the alloys including primary solidification phases in addition to the eutectic structures have been tested in compression, at room temperature and at 700° C. Samples for compression testing were derived from the suction cast samples following American Society for testing and materials (ASTM) standards. FIG. 4a shows stress-strain curves in compression for Alloys A to L. The measured values of yield strength at room temperature derived from these curves for Alloys A to L are shown in FIG. 4b. In addition, these values have been depicted therein in accordance with the alloy compositions shown in the ternary Ni—Al—Zr section 100. Alloys A, B, and C, which are solely composed of the eutectic constituents, show the highest yield strength. These alloys respectively show yield strengths of 2.2, 1.94, and 1.75 GPa. Alloys D, E, F, G, H, I, J, K and L respectively show the yield strength of 1.8, 1.76, 1.6, 0.85, 1.41, 1.55, 1.4, 1.1, and 1.45 GPa. It may be understood that the presence of the primary phase in Alloys D-L results in a decrease of the yield strength.

(24) FIG. 5 illustrates the measured values of the yield strength of the alloys from A till L tested at about 700° C., depicted according to the alloy compositions shown in the ternary section 100 of the Ni—Al—Zr section. As depicted in the FIG. 5, the alloys from A till L, respectively, show the yield strength of 1.9, 1.8, 1.5, 1.6, 1.5, 1.4, 1.2, 1.31, 1.4, 1.1, 0.8, and 1.4 GPa at 700° C. It may be understood that the presence of the primary phase in Alloys D-L results in a decrease of the yield strength at 700° C. It may also be understood from the tests conducted for Alloy B at 800° C. and 900° C., as an example, that the alloys of the present subject matter retain their strength till about 700° C.

(25) In order to illustrate relevant compositions from which substantially high strengths that can realized, FIG. 6 comparatively depicts the yield strength in GPa at room temperature of Alloys X, Y and Z, corresponding to the compositions marked as X, Y and Z, as well as the yield strength of Alloys A to L. Alloy X contains includes Ni-based solid solution, along with a [Ni+Ni.sub.5Zr] eutectic structure. The yield strength of Alloy X is high at room temperature but has very low yield strength of 0.3 GPa at 700° C. Alloy Y shows a large amount of a primary phase Ni.sub.7Zr.sub.2 and has low yield strength at room temperature and a yield strength of 0.75 GPa at 700° C. Alloy Z includes a substantially large amount of the primary phase β (NiAl) and also shows comparatively lower yield strength at room temperature and at 700° C. (0.54 GPa).

(26) FIG. 7 illustrates a plot 700 depicting comparison of the yield strength of the alloys of the present subject matter with the conventional Ni based alloys known in the art. It is observed that the alloys of the present subject matter provide a range of substantially high yield strengths, thereby being improved in comparison to the conventional alloys. It may also be understood from the tests conducted for Alloy B at 800° C. and 900° C., that the alloys of the present subject matter retain their strength to 700° C.

(27) Further, the resistance to fracture, of various primary solidification phases and eutectic constituents as present within Alloys A to I, is probed by examining the corners of hardness indents made at various regions of the microstructure of Alloys A to I with a Vickers indent at a load of 200 gm. FIG. 8 illustrates a micrograph 800 of such indents. As can be observed from the microstructures in FIG. 8, the primary solidification phase Ni.sub.7Zr.sub.2 as present in Alloys D to I develops cracks at the corners of the hardness indents. However, the eutectic structures as present within Alloys A and B, both of which include the Ni.sub.7Zr.sub.2 phase do not undergo cracking. It may be gathered that the presence of the aforementioned intermetallics in a fine scale in the eutectic constituents provides additional plasticity to these high strength alloys.

(28) As known in the art, heavy duty applications of structural materials require a reasonable tensile ductility present within the structural materials. FIG. 9 illustrates tensile stress strain curves 900 for Alloy B room temperature as an example. In case of Alloy B, a tensile ductility of 3-4% has been achieved.

(29) As a part of another embodiment of the present subject matter, a number of experiments have been conducted upon Alloy B to determine various properties thereof in order to investigate the high temperature stability of the alloys of the present subject matter. However, the present subject matter is not restricted by the results of the below-mentioned experiments, which may be extended to cover experiments conducted over Alloys A, C, D, E, F, G, H, I, J, K, and L. The high temperature stability of the alloys has been investigated by exposure of Alloy B to high temperature for varying amounts of time followed by an examination of the microstructure.

(30) FIG. 10 illustrates micrographs 1000 depicting the stability of the microstructures of Alloy B at different temperatures for 2 hours and for different time durations at 900° C. It can be gathered from the micrographs that very high temperature exposure, of Alloy B, for extended lengths of time has no effect on the micro structural condition. Further, it can be observed from the micrographs 1000 that Alloy B shows stable microstructure upto 1100° C. with no change in length scale.

(31) Also as a part of the high temperature stability, weight gain of Alloy B was determined after exposure to air at different temperature both under static and cyclic oxidation conditions. Such studies were carried out in a thermo gravimetric analyzer. Samples were heated at rate of 20° C./min and held for different times and temperatures for the static study. In the case of cyclic tests samples, each cycle consisted of heating to a particular temperature at a rate of 20° C./min and cooling at same rate down to 300° C.

(32) FIG. 11 illustrates graphs 1100 and 1110 depicting comparison of percentage mass gain and percentage mass change suffered by Alloy B at various temperatures for different durations, respectively. FIG. 11a shows a comparison of percentage mass gain suffered by Alloy B due to oxidation after exposure at various temperatures for 2 hours. FIG. 11b shows a comparison of the percentage mass change suffered by Alloy B after exposure for long durations at 900° C. and 1100° C., for 2, 4, 16, and 256 hours. As understood from FIG. 11a and FIG. 11b, the mass gain and mass change suffered by Alloy B is substantially less. Further, FIG. 12a and FIG. 12b illustrate graphs 1200 and 1210 depicting comparison of weight change suffered by Alloy B and weight change suffered by conventional alloys (as depicted by Reference 1 and Reference 2 in US Patent 2010/0143182A1 and US Patent 2008/0008618A1) and within the same range of temperatures, in both static and cyclic oxidation tests, respectively. As understood from the FIG. 12a and FIG. 12b, the weight change suffered by Alloy B is substantially less as compared to the conventional alloys, when subjected to static and cyclic oxidation.

(33) In yet another embodiment of the present subject matter, the alloys listed in Table 1 may include limited alloying additives or trace additives. These additives also retain the eutectic constituents within the alloys of the present subject matter. The effect of limited alloying additions or the presence of trace additions in improving the properties of the alloys listed in Table 1 is considered by way of examples. The addition of such additives does not substantively affect the nature of the intermetallic phases, their derivatives, their combinations and their distribution as illustrated in FIGS. 2 and 3. Such alloying additions may replace Zr, Ni, or Al in the compositions of the Table 1. For example, additions which may be expected to replace Zr without affecting the formation of the Ni.sub.5Zr and Ni.sub.7Zr.sub.2 phase are Hafnium (Hf) and Scandium (Sc). Additions which may substitute for Ni are Cobalt (Co), Platinum (Pt), Palladium (Pd), Chromium (Cr), Ruthenium (Ru), and Rhenium (Re). Additions, such as Tantalum (Ta) and Titanium (Ti) may be expected to substitute for Al in the γ′ or β phase.

(34) Similarly, additions of Niobium (Nb), Molybdenum (Mo), and Tungsten (W) may be used to suitably alter the properties of the aforementioned intermetallic compounds. Further, Boron (B) may be added to affect grain boundary strength in materials of this class.

(35) Table 2 illustrates the additional alloying elements that may be added to alter properties of described Ni-based alloys.

(36) TABLE-US-00002 TABLE 2 Alloy Mo, W, Nb Ti, Ta Hf, Sc Co, Pt, Pd Cr, Re, Ru B A-L 0.0-5 0.0-5 0.0-5 0.0-5 0.0-5 0.0-0.1 at % at % at % at % at % wt %

(37) Table 3 illustrates the compressive yield strength properties of some alloys with such additional alloying elements, as an example. Such alloying additions are to be understood as examples with respect to the microstructure and various intermetallic phases and their

(38) TABLE-US-00003 TABLE 3 Compressive Yield Compressive Yield Strength (GPa) at Strength (GPa) at Alloy (at %) Room Temperature 700° C. Ni—5Co—15Al—10.9Zr 2.1 2 Ni—5Ti—15Al—5.9Zr 1.85 1.8 Ni—5Cr—15Al—10.9Zr 2.0 1.9
derivatives that correspond to embodiments of this present subject matter.