Platinum based alloys

Abstract

An article made of an alloy of the general formula Pt.sub.1-a-bM.sub.a(B.sub.1-xMd.sub.x).sub.b in which i) M stands for one or a mixture of metallic element(s) of the group Zr, Ti, Fe, Ni, Co, Cu, Pd, Ag, Al; ii) Md stands for one or a mixture of several metalloids of the group Si, P, C, S, As, Ge; iii) a is smaller than 0.2; iv) b is comprised between 0.2 and 0.5; v) x is comprised between 0 and 0.8; vi) the overall P content, if present, is less than 10 atomic percent the proportions of the elements forming the alloy having been selected to confer a hardness of at least 400 HV, a melting point below 1000 C. and improved processibility to the alloy.

Claims

1. A metallic glass made of an alloy of the formula Pt.sub.1-a-b-c M.sub.aA.sub.c (B.sub.1-xMd.sub.x).sub.bwherein M stands for one or a mixture of metallic elements of the group Cu and Ni, A stands for one or a mixture of alloying metallic elements Al, Ti, Zr, and Ag, Md stands for one or a mixture of metalloids of the group Si, P, C, S, As, Ge, and wherein Md includes Si, a is greater than 0 and smaller than 0.2, b is between 0.2 and 0.55, c is smaller than 0.03, x is between 0.1 and 0.8, the overall P content, if present, is less than 10 atomic percent, and wherein the alloy has a hardness of at least 700 HV when in a crystalline state, a melting point below 1000 C., and is capable of being shaped in a super cooled liquid region (SCLR).

2. The metallic glass according to claim 1 wherein Md stands for one or a mixture of several metalloids of the group Si, C, S, As, Ge, and Md includes Si.

3. The metallic glass according to claim 1 wherein the alloy has the composition Pt.sub.0.48Ni.sub.0.16(B.sub.0.75Si.sub.0.25).sub.0.36.

4. The metallic glass according to claim 1 wherein the alloy has the composition Pt.sub.0.695Ni.sub.0.035(B.sub.0.55Si.sub.0.44).sub.0.27.

5. The metallic glass according to claim 1 having an overall Pt-content of at least 850/1000 by weight.

6. The metallic glass according to claim 5 having an overall Pt-content of at least 900/1000 by weight.

7. The metallic glass according to claim 6 having an overall Pt-content of at least 950/1000 by weight.

8. A metallic glass made of an alloy of the formula Pt.sub.1-a-bNi.sub.a(B.sub.1-xSi.sub.x).sub.b wherein a is greater than 0 and smaller than 0.2, b is between 0.2 and 0.55, and x is greater than 0 and less than 0.8, wherein the alloy has a hardness of at least 700 HV when in a crystalline state, and is capable of being shaped in a super cooled liquid region (SCLR).

9. The metallic glass according to claim 8 having an overall Pt-content of at least 850/1000 by weight.

10. The metallic glass according to claim 8 having an overall Pt-content of at least 900/1000 by weight.

11. The metallic glass according to claim 8 having an overall Pt-content of at least 950/1000 by weight.

12. A jewelry or watch article including a part made of a metallic glass according to claim 1.

13. A jewelry or watch article including a part made of a metallic glass according to claim 8.

14. A metallic glass made of an alloy of the formula Pt.sub.1-a-b-c Cu.sub.aA.sub.c(B.sub.1-xMd.sub.x ).sub.bwherein A stands for one or a mixture of alloying metallic elements Al, Ti, Zr, and Ag, Md stands for one or a mixture of metalloids of the group Si, P, C, S, As, Ge, and wherein Md includes Si, a is greater than 0 and smaller than 0.2, b is between 0.2 and 0.55, c is smaller than 0.03, x is between 0.1 and 0.8, the overall P content, if present, is less than 10 atomic percent, and wherein the alloy has a hardness of at least 700 HV when in a crystalline state, a melting point below 1000 C., and is capable of being shaped in a super cooled liquid region (SCLR).

15. The metallic glass according to claim 14, wherein Md stands for the one or a mixture of several metalloids of the group Si, C, S, As, Ge, and Md includes Si.

16. A jewelry or watch article including a part made of a metallic glass according to claim 14.

17. A metallic glass made of an alloy of the formula Pt.sub.1-a-b-c M.sub.aA.sub.c (B.sub.1-xMd.sub.x).sub.bwherein M stands for one or a mixture of metallic elements of the group Cu, Fe, Co and Ni, A stands for one or a mixture of alloying metallic elements Al, Ti, Zr, and Ag, Md stands for one or a mixture of metalloids of the group Si, P, C, S, As, Ge, and wherein Md includes Si, a is greater than 0 and smaller than 0.2, b is between 0.2 and 0.55, c is smaller than 0.03, x is between 0.1 and 0.8, the overall P content, if present, is less than 10 atomic percent, and wherein the alloy has a hardness of at least 700 HV when in a crystalline state, a melting point below 1000 C., and is capable of being shaped in a super cooled liquid region (SCLR).

Description

BRIEF DESCRIPTION OF THE FIGURE

(1) FIG. 1 represents a ternary eutectic trough in the PtBSi system. Indicated are also the hardness values for the binary eutectic compositions (in HV) and the compositions corresponding to the Pt950 and the Pt900 standard, respectively.

DETAILED DESCRIPTION OF THE INVENTION

(2) The present invention will be better understood below by way of non-limiting examples relating to Platinum base alloys exhibiting a high hardness, i.e. in excess of at least 450 HV.

(3) These alloys are based on the binary PtB system with at least one more metallic alloying element or on the PtBSi ternary system. While alloys solely based on the PtBSi ternary may suffice to obtain hardness in excess of 650 HV one or several additional alloying elements may be introduced to further increase hardness or improve processibility.

(4) The alloys disclosed in this invention may be described by the general formula (subscripts refer to atomic fractions)
Pt.sub.1-a-bM.sub.a(B.sub.1-xMd.sub.x).sub.b
in which i) M stands for one or a mixture of metallic element(s) of the group Al, Ti, Fe, Ni, Co, Cu, Zr, Pd, Ag ii) Md stands for a metalloid of the group Si, P, C, S, As, Ge iii) a is smaller than 0.2 iv) b is comprised between 0.2 and 0.55 v) x is comprised between 0 and 0.8 vi) the overall P content, if present, is less than 10 atomic percent

(5) The specific composition is chosen in the limits of the parameters given above to obtain an alloy with a minimum Pt content of 850/1000 by weight, preferably 900/1000 by weight or even more preferably 950/1000 by weight.

(6) Alloys according to this definition exhibit a low melting point, i.e. below 1000 C., preferably below 800 C. and even more preferably below 700 C.

(7) Alloys of particular interest in the context of this invention are those located close to the regions of lowest melting point indicated as a light grey area in FIG. 1. While for ternary systems intersections of liquidus surfaces associated with stable solids are given by well defined lines, additional alloying elements may shift these lines both in the composition range in the ternary alloy as well as in terms of the temperature, justifying the indication of a low melting point area in FIG. 1 rather than neat lines.

(8) Nevertheless, if high hardness is of prime importance, alloys outside this ternary eutectic trough, yet in accordance with the general formula given above may be chosen, cf. Example 9 below.

(9) The preparation of the alloy is preferably achieved by melting under protective atmosphere by arc melting or melting in a quartz crucible by induction heating, resistance heating or heating by a torch flame.

(10) For alloys that are cast into parts and are obtained in crystallized form, vacuum melting and casting in a copper mould is the preferred processing route. Alternatively, melting can be done under protective atmosphere and casting in investment moulds.

(11) Alloy compositions leading to a melting point below 800 C. preferably below 750 C. may be particularly desirable. The low melting point confers to the alloy two desirable properties: On the one hand some of the difficulties associated with casting of platinum alloys, e.g. the high heat input in the refractory mould material and shrinkage upon cooling down, can be considerably reduced as the alloys concerned by this disclosure have melting characteristics comparable to gold alloys that are known to be much better castable. On the other hand, due to the low melting point and the rather complex unit cells in the boron and silicon containing phases forming in thermodynamic equilibrium as well as the alloying elements employed for rendering crystallization more difficult, the alloys described above may be obtained in an amorphous state depending on the cooling conditions after melting. Processes to obtain this amorphous state include, yet are not limited to, splat quenching, melt spinning, melt atomization, and copper mould quenching. The amorphous state may also be obtained by re-melting and solidifying when submerged in de-hydrated B.sub.2O.sub.3 flux. This step may be crucial for cases where the preliminary melting procedure did not effectively eliminate or prevent the creation of heterogeneous nucleation sites for crystallization.

(12) Semi finished products or feedstock in wire or powder form may be easily deformable in their super-cooled liquid region (SCLR), i.e. a temperature range between their glass transition temperature and their crystallization temperature. Thus, even complex shaped items may be formed from amorphous feedstock. Given the high hardness of the boron and or silicon containing phases in the PtSiB system, a heat treatment subsequent to the viscous shaping process may substantially increase their hardness at the price of reduced fracture toughness and ductility.

(13) As an example (example A) of a way to produce an amorphous Pt-based alloy, an alloy with the composition Pt.sub.0.48Ni.sub.0.16(B.sub.0.75Si.sub.0.25).sub.0.36 was melted under purged argon atmosphere in a quartz tube heated by a torch flame. As such the present alloy contained more than 850/1000 by weight of platinum. After solidification the ingot was transferred in another quartz tube with an orifice of 0.8 mm inserted in a melt spinner. After heating under vacuum by induction a helium pressure of 100 mbars was applied over the melt projecting the melt onto a rotating copper wheel, a process known as melt spinning The obtained ribbon was 2 to 3 mm wide and approximately 25 m thick and had an even and shiny surface. A DSC run under high purity argon at a heating rate of 10 K/min revealed in the first heating cycle an slightly endothermic bump with onset at roughly 550 K followed by an exothermic peak at roughly 590 K. Another endothermic peak was observed at roughly 970 K. Subsequent cooling from 1200 K exhibited an exothermic peak at 945 K. No further peak was observed below this temperature. The onset of the first bump is interpreted as the glass transition temperature while the second peak is considered to be due to crystallization.

(14) An XRD scan of the ribbon yielded a single broad peak characteristic for an amorphous state. Microhardness on the ribbon was measured with a load of 10 g due to the limited width of the ribbon yielding values around 500 HV. In its crystallized state after DSC the alloy had coagulated to a sphere and exhibited a hardness in excess of 700 HV.

(15) As second example (example B) of a way to produce an amorphous Pt-based alloy, an alloy with the composition Pt.sub.0.695Ni.sub.0.035(B.sub.0.55Si.sub.0.44).sub.0.27 was melted under purged argon atmosphere in a quartz tube heated by a torch flame. As such the present alloy contained more than 950/1000 by weight of platinum. After solidification the ingot was transferred in another quartz tube with an orifice of 0.8 mm inserted in a melt spinner. After heating under vacuum by induction a helium pressure of 100 mbars was applied over the melt projecting the melt onto a rotating copper wheel, a process known as melt spinning The obtained ribbon was 2 to 3 mm wide and approximately 20-40 m thick and exhibited a shiny yet slightly uneven surface. A DSC run under high purity argon at a heating rate of 10 K/min revealed in the first heating cycle a slightly endothermic bump with onset at roughly 520 K followed by an exothermic peak at roughly 550 K. Another endothermic peak was observed at roughly 950 K. Subsequent cooling from 1200 K exhibited an exothermic peak at 945 K. No further peak was observed below this temperature. The onset of the first bump is interpreted as the glass transition temperature while the second peak is considered to be due to crystallization.

(16) Based on the values of glass transition, crystallization, and melting temperature the parameters of glass forming ability (GFA) of these alloys can be evaluated. A number of currently used GFA parameters are given in Table 1 together with their range characteristic for good bulk metallic glass formability.

(17) TABLE-US-00001 TABLE 1 Various parameters characterizing the GFA and the glass stability of BMGs and their appropriate ranges compared to the values of examples A and B. Good Exam- Exam- GFA High glass Parameter Definition ple A ple B range stability T.sub.rg T.sub.rg = T.sub.g/T.sub.1 0.58 0.55 T.sub.rg 0.6 = T.sub.x/ 0.38 0.37 0.4 (T.sub.g + T.sub.1) T T = T.sub.x T.sub.g 40 30 T 50K

(18) As can be seen, the current parameters are all gathered at the lower end of good GFA and glass stability and will thus confer a relatively low critical casting thickness (<2 mm) to the alloy in the example given. This however does not mean that this is a limitation applying to all the alloys described in this disclosure.

(19) Influence of Alloying Elements

(20) Several alloying elements may be added to the base alloys near the eutectic trough. Ni, Co, Cu, and Fe are essentially interchangeable and are used to substitute a small fraction of Pt. They act in essence to i) reduce the melting temperature of the ternary PtBSi alloy ii) increase the hardness of the resulting alloy

(21) These alloys may furthermore have a weak influence on the glass transition temperature and the crystallization temperature.

(22) Alloying elements of the group Al, Ti, Zr, and Ag are in small quantities, i.e. below 3 at.-pct, helpful for rendering the crystallisation of the thermodynamically stable phases more difficult and thus may contribute to a increased ease of obtaining the amorphous state. At higher concentrations an increasing tendency to form stable silicides and borides particularly of Zr and Ti may hamper the formation of the amorphous state.

(23) Pd may be used as a substitute for Pt with the effect of essentially increasing the disorder in the alloy according to the confusion principle often employed in making of amorphous metals.

(24) Alloying elements of the group C, P, Ge, S, and As may be used as partial substitutes of the main metalloid components B and Si. Ge has been found to increase the hardness of the resulting alloys. Small amounts of P will essentially reduce the melting temperature and the glass transition temperature and may slightly reduce the hardness both of the glassy state and the crystallized state.

EXAMPLES

Example 1

(25) An alloy of 4.756 g of Pt, 0.123 g of Si and 0.121 g of boron is melted in an electric arc under Ar protective atmosphere. The overall Pt content is higher than 950/1000. The resulting metallic droplet has a metallic luster and is hot-mounted and then cut by a diamond wheel. The polished surface exhibits a very fine two-phase structure appearing homogeneous under low magnification. The microhardness is measured with a Gnehm Microhardness tester at a load of 1 kg. The indicated hardness is 670 HV.

Example 2

(26) An alloy of 3.918 g of Pt, 0.117 g of Si and 0.079 g of boron is melted in an electric arc under Ar protective atmosphere. The overall Pt content is higher than 950/1000. The resulting metallic droplet has a metallic luster and is hot-mounted and then cut by a diamond wheel. The polished surface exhibits a very fine two-phase structure with a very small amount of slight grey primary phase. The microhardness of the matrix is measured with a Gnehm Microhardness tester at a load of 1 kg. The indicated hardness is 630 HV on average.

Example 3

(27) An alloy of 19.009 g of Pt, 0.654 g of Si and 0.337 g of boron is melted in an electric arc under Ar protective atmosphere. The overall Pt content is higher than 950/1000. The resulting metallic droplet has a metallic luster and is hot-mounted and then cut by a diamond wheel. The polished surface exhibits a very fine two-phase structure appearing homogeneous under low magnification. The microhardness is measured with a Gnehm Microhardness tester at a load of 1 kg. The indicated hardness is 660 HV on average.

Example 4

(28) An alloy of 5.515 g of Pt, 0.114 g of boron, and 0.164 g of Cu is melted in an electric arc under Ar protective atmosphere. The overall Pt content is higher than 950/1000. The resulting metallic droplet has a metallic luster and is hot-mounted and then cut by a diamond wheel. The polished surface exhibits a very fine two-phase structure appearing homogeneous under low magnification. The microhardness is measured with a Gnehm Microhardness tester at a load of 1 kg. The indicated hardness is 680 HV on average.

Example 5

(29) An alloy of 4.507 g of Pt, 0.344 g of Si and 0.149 g of boron is melted in an electric arc under Ar protective atmosphere. The overall Pt content is higher than 900/1000. The resulting metallic droplet has a metallic luster and is hot-mounted and then cut by a diamond wheel. The polished surface exhibits a very fine two-phase structure with roughly 20 vol % of a dark gray primary phase of a few tens of m in size. The microhardness of the matrix is measured with a Gnehm Microhardness tester at a load of 1 kg. The indicated hardness is 690 HV on average. The microhardness of the dark gray primary phase is in excess of 3000 HV. Macrohardness of the two-phase structure is measured on a Gnehm Hardness tester with a load of 62.5 kg. The hardness deduced from the indentation is 720 HV.

Example 6

(30) An alloy of 4.518 g of Pt, 0.265 g of Si, and 0.216 g of boron, is melted in an electric arc under Ar protective atmosphere. The overall Pt content is higher than 900/1000. The resulting metallic droplet has a metallic luster and is hot-mounted and then cut by a diamond wheel. The polished surface exhibits a very fine multiphase structure in the matrix with roughly 30 vol % of a facetted dark gray primary phase of a few tens of m in size. The microhardness of the matrix is measured with a Gnehm Microhardness tester at a load of 1 kg. The indicated hardness is around in the range between 650 and 780 HV with a value of 725 HV on average.

Example 7

(31) An alloy of 4.605 g of Pt, 0.162 g of Si, 0.112 g of boron, and 0.120 g of Ge is melted in an electric arc under Ar protective atmosphere. The overall Pt content is higher than 900/1000. The resulting metallic droplet has a metallic luster and is hot-mounted and then cut by a diamond wheel. The polished surface exhibits a very fine two-phase structure in the matrix with roughly 30 vol % of a dark gray primary phase of a few tens of m in size. The microhardness of the matrix is measured with a Gnehm Microhardness tester at a load of 1 kg. The indicated hardness is around 700 HV on average. The microhardness of the dark gray primary phase is in excess of 3000 HV.

Example 8

(32) An alloy of 2.742 g of Pt, 0.187 g of Si, 0.026 g of boron, and 0.045 g of Cu is melted in a fused silica tube under Ar protective atmosphere by a torch flame. The overall Pt content is higher than 900/1000. The resulting metallic droplet has a metallic luster and is hot-mounted and then cut by a diamond wheel. The polished surface exhibits a very fine three-phase structure appearing homogeneous under low magnification. The microhardness of the alloy is measured with a Gnehm Microhardness tester at a load of 1 kg. The indicated hardness ranges between 720 and 800 HV.

Example 9

(33) An alloy of 4.516 g of Pt, 0.280 g of Si, 0.045 g of boron, 0.084 g of Ge and 0.075 g of Cu is melted in a fused silica tube under Ar protective atmosphere by a torch flame. The overall Pt content is higher than 900/1000. The resulting metallic droplet has a metallic luster and is hot-mounted and then cut by a diamond wheel. The polished surface exhibits a very fine three-phase structure appearing homogeneous under low magnification. The microhardness of the alloy is measured with a Gnehm Microhardness tester at a load of 1 kg. The indicated hardness ranges between 650 and 890 HV.

Example 10

(34) An alloy of 2.710 g of Pt, 0.167 g of Si, 0.027 g of boron, 0.026 g of Ge, 0.045 g of Cu, and 0.025 g Ag is melted in a fused silica tube under Ar protective atmosphere by a torch flame. The overall Pt content is higher than 900/1000. The resulting metallic droplet has a metallic luster and is hot-mounted and then cut by a diamond wheel. The polished surface exhibits a very fine three-phase structure appearing homogeneous under low magnification. The microhardness of the alloy is measured with a Gnehm Microhardness tester at a load of 1 kg. The indicated hardness ranges between 680 and 720 HV.

(35) The invention is of course not limited to the alloys disclosed in the examples discussed above.

REFERENCES

(36) 1. Biggs, T., S. S. Taylor, and E. van der Lingen, The hardening of platinum alloys for potential jewellery application. Platinum Metals Review, 2005. 49(1): p. 2-15.

(37) 2. Ainsley, G., A. A. Bourne, and R. W. E. Rushforth, Platinum investment casting alloys. Platinum Metals Review, 1978. 22(3): p. 78-87.

(38) 3. Schroers, J. and W. L. Johnson, Pt-base bulk solidifying amorphous alloys. 2006: US patent application 2006/0124209, pp. 18.

(39) 4. Schroers, J., et al., Precious bulk metallic glasses for jewelry applications.

(40) Materials Science and Engineering A-Structural Materials Properties Microstructure and Processing, 2007. 449: p. 235-238.

(41) 5. Johnson, W. and J. Schroers, Bulk-solidifting amorphous alloy for jewelry applications, comprises at least four elemental components having specified Poisson's ratio, elastic strain limit, ductility, bend ductility and fracture toughness. 2006, PCT patent application WO 2006/066215, pp. 49.

(42) 6. Demetriou, M. D., et al., Liquid-like platinum-rich glasses. Scripta Materialia, 2011. 65(9): p. 799-802.

(43) 7. Yuichiro, Y., Hard platinum alloy for ornamentation. 1987: Japanese patent application JP 1985/0268628 pp. 3.

(44) 8. Kretchmer, S., Heat treated platinum alloy for jewellery makingcontains platinum, gallium and palladium. WO 00/32829, pp. 21.

(45) 9. Weber, W., K. Zimmermann, and H. Beyer, Objects made of platinum and palladiumcomprise hard scratch-resistant surface layer contg. boron in the metal lattice. European patent application EP 1993/0120771 pp. 4.