Metal alloys

Abstract

Metal alloys including platinum are disclosed. The alloys have a similar variety of applications to platinum-based alloys. The alloy with a solid solution matrix consisting of: Platinum (Pt) 20 to 70 at. %; Palladium (Pd)>0 to 70 at. %; Cobalt (Co)>0 to 50 at. % and at least one of: Nickel (Ni) up to 50 at. %; Chromium (Cr) up to 50 at. % and Iron up to 50 at. %.

Claims

1. An alloy, with a solid solution matrix consisting of: A) TABLE-US-00033 Platinum (Pt) 20 to 70 at. %, Palladium (Pd) >0 to 70 at. %, and Cobalt (Co) >0 to 50 at. %; and B) at least one of: TABLE-US-00034 Nickel (Ni) up to 50 at. %, Chromium (Cr) up to 50 at. %, and Iron up to 50 at. %; wherein the alloy has a microsegregation of less than 3%.

2. The alloy of claim 1, with a solid solution matrix consisting of: A) TABLE-US-00035 Platinum (Pt) 20 to 70 at. %, Palladium (Pd) 0 to 70 at. %, and Cobalt (Co) 0 to 50 at. %; and B) at least one of: TABLE-US-00036 Ni up to 50 at. %, and Cr up to 50 at. %.

3. The alloy of claim 2, with a solid solution matrix consisting of: A) TABLE-US-00037 Pt 20 to 60 at. %, Pd 10 to 70 at. %, and Co 10 to 50 at. %; and B) at least one of: TABLE-US-00038 Ni up to 40 at. %, and Cr up to 40 at. %.

4. The alloy of claim 3, with a solid solution matrix consisting of: A) TABLE-US-00039 Pt 20 to 50 at. %, Pd 10 to 40 at. %, and Co 10 to 40 at. %; and B) at least one of: TABLE-US-00040 Ni 10 to 40 at. %, and Cr 10 to 40 at. %.

5. The alloy of claim 4, with a solid solution matrix consisting of: A) TABLE-US-00041 Pt 20 to 50 at. %, Pd 10 to 25 at. %, and Co 20 to 40 at. %; and B) at least one of: TABLE-US-00042 Ni 20 to 25 at. %, and Cr 10 to 25 at. %.

6. The alloy of claim 1, wherein Ni is present in an amount of 20 to 25 at. %.

7. The alloy of claim 1, wherein Pt is present in an amount of 35 to 55 at. %, Pd is present in an amount of 5 to 25 at. %, and Co is present in an amount of 35 to 45 at. %.

8. The alloy of claim 1, wherein the alloy consists of Pt 35 to 45 at. %, Pd 15 to 25 at. %, Co 15 to 35 at. % and Cr 5 to 25 at. %.

9. The alloy of claim 1, wherein the alloy consists of Pt 25 to <35 at. %, Pd 15 to 25 at. %, Co 35 to 45 at. % and Cr 15 to 25 at. %.

10. The alloy of claim 1, wherein the solid solution matrix has a heat-treated hardness (H.sub.v) in the range of 163 to 243.

11. The alloy of claim 1, wherein the alloy is a heat-treated alloy.

12. The alloy of claim 11, wherein the heat-treatment comprises heating the alloy above 900° C. in an inert atmosphere.

13. The alloy of claim 12, wherein the heating is for a time in the range of 24 to 140 hours.

14. The alloy of claim 13, wherein the time is in the range of 45 to 100 hours.

15. The alloy of claim 11, wherein the heat-treatment comprises heating the alloy to 1,100° C.

16. An alloy, selected from Pt.sub.25Pd.sub.25Co.sub.25Cr.sub.25, Pt.sub.40Pd.sub.20Co.sub.40, Pt.sub.50Pd.sub.10Co.sub.40, Pt.sub.40Pd.sub.20Co.sub.20Cr.sub.20, Pt.sub.40Pd.sub.20Co.sub.30Cr.sub.10, or Pt.sub.30Pd.sub.20Co.sub.30Cr.sub.20.

17. An alloy, selected from Pt.sub.25Pd.sub.25Co.sub.25Ni.sub.25 or Pt.sub.20Pd.sub.20Co.sub.20Cr.sub.20Ni.sub.20.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 depicts volume magnetization as a function of external magnetic field for selected alloys.

DESCRIPTION OF EMBODIMENTS

(2) Test work carried out by the applicants has identified HEPAs as having desirable properties in comparison to the properties of typical platinum-based alloys. In particular, the HEPAs are based on the realisation by the applicants that the desirable properties are obtained by replacing a significant portion of platinum in typical platinum-based alloys with palladium and cobalt and with at least one of nickel, iron and chromium to produce alloys with considerably higher entropy of mixing compared with the entropy of mixing for typical platinum-based alloys.

(3) Examples of alloys identified by the applicant were prepared and tested to determine their properties. The examples are outlined below in Table 1. All examples were prepared by the following method.

(4) Pure elements Pt, Pd, Co, Cr, Ni were alloyed using a Buhler MAM1 mini arc melter in a Ti-gettered argon atmosphere to produce the nominal alloy compositions shown in Table 1. During the arc melting process, the samples were flipped and melted eight times to ensure homogeneity. Samples were heat treated in an elevator furnace at 1100° C. for 48 h and slowly cooled in a circulating argon atmosphere, with the exception of Pt.sub.30Pd.sub.20Co.sub.30Cr.sub.20 which was heat treated at 1100° C. for 96 h.

(5) TABLE-US-00031 TABLE 1 Selected alloy compositions Alloy Hardness (HV.sub.1kg) No. Composition E (GPa) σ.sub.y0.2% (MPa) UTS (MPa) ε.sub.f As-Cast Annealed 1 Pt.sub.25Pd.sub.25Co.sub.25Cr.sub.25 64.407 392 514 0.039  216 ± 15 200 ± 5 2 Pt.sub.25Pd.sub.25Co.sub.25Ni.sub.25 40.241 284 668 0.404  196 ± 19 181 ± 7 3 Pt.sub.20Pd.sub.20Co.sub.20Cr.sub.20Ni.sub.20 55.819 354 734 0.435 200 ± 4 191 ± 6 4 Pt.sub.40Pd.sub.20Co.sub.40 173 ± 5 171 ± 8 5 Pt.sub.50Pd.sub.10Co.sub.40 185 ± 8 183 ± 8 6 Pt.sub.40Pd.sub.20Co.sub.20Cr.sub.20  246 ± 12 236 ± 7 7 Pt.sub.40Pd.sub.20Co.sub.30Cr.sub.10 204 ± 9 200 ± 6 8 Pt.sub.30Pd.sub.20Co.sub.30Cr.sub.20 220 ± 9  210 ± 11

(6) Compositional characterization of the samples/phases was performed via scanning electron microscopy using a Hitachi S3400 with backscatter detection and energy dispersive X-ray spectroscopy (EDS). The compositions of as-cast alloys were analyzed over large areas and found to be within ±2.2% of nominal compositions. The overall compositions of the alloys were determined via line scans and point sampling.

(7) Powder X-ray diffraction (XRD) was used to characterise the crystal structure, [degree of ordering, and specific lattice parameters] of the equiatomic alloys (alloys using a PanAnalytical Xpert Multipurpose X-ray Diffraction System and a Cu K.sub.α radiation source. The samples were powdered with a carbon steel file to avoid intensity bias in diffraction peaks due to texture.

(8) Tensile testing was conducting on samples using an Instron 5982 screw mechanical testing unit with a 10 kN load cell. The samples were strained at 0.5 mm/min=8.33*10-3 mm/s until failure. The elongation and force were recorded by the Instron and converted to engineering stress and strain. The nominal sample geometry was; gauge length of 10 mm, gauge width of 3 mm, gauge thickness of 1 mm, overall length of 25 mm.

(9) Vickers microhardness measurements were conducted on the samples using a Struers Duramin-A300 with a 1 kg load held for 10 seconds. Samples were polished to a 0.1 micron finish before testing and 10 measurements were made on each sample. The loadings were spaced at least five indent widths away from one another.

(10) A common 1.1 T Fe—Nd—B permanent magnet was used to test whether magnetic attraction was present in the as-cast and heat treated samples and whether any observed magnetic behaviour was permanent/residual (hard magnetic materials) or non-permanent (soft magnetic).

(11) The magnetic properties of representative alloys were tested. The samples were ground to powder and aligned magnetically to obtain the majority easy axis of the grains. The magnetic moment was measured as a function of external field at room temperature in a field range of −80 kOe<H<80 kOe (see Table 2). FIG. 1 shows the magnetic moment of the representative alloys as a function of external magnetic field. PtPdCoNi exhibits a high saturation magnetic moment of 565 emu/cm.sup.3 (corresponding to a magnetization of 0.73 T).

(12) TABLE-US-00032 TABLE 2 Volume magnetic moment and average magnetic moment per atom at H = 80 kOe and T = 300 K. Sample M.sub.vol at 80 kOe (emu/cm.sup.3) PtPdCo 580 PtPdCoNi 565 PtPdCoCr 137 PtPdCoCrNi 69 PtPdNi 27

(13) All 8 of the as-cast alloys exhibited dendritic structure and microsegregation. The microsegregation was due to the difference in melting points of Pt (1769° C.) and Pd (1555° C.). Upon heat treatment, the alloys became predominantly single phase, with less than 4 at % variation between the microsegregated regions. The microstructure of the as-cast equiatomic Pt—Pd—Co—Cr can be observed by the light and dark regions in FIG. 1.

(14) In the process of preparing the alloy no. 8, it was removed from Bakelite mounting in a vice and subject to an unquantified compression. This resulted in twinning behaviour.

(15) There was little variation in the hardness of the as-cast and heat treated samples, as observed in Table 1. The hardness of the heat treated samples were slightly lower than the as-cast samples, likely due to structural homogenisation and removal residual stresses as a result of casting.

(16) By way of summary, the test work revealed the following properties.

(17) Mechanical Properties: The HEPAs are harder and stronger than pure platinum and typical platinum-based alloys and the HEPAs maintain high ductility/formability.

(18) Production & Casting: The HEPAs may be prepared in a similar manner to typical platinum-based alloys, they maintain high castability/fluidity and have lower melting points than typical platinum-based alloys.

(19) Oxidation/Tarnishing: Although platinum and palladium are essentially noble and do not corrode/oxidise, the other constituents of the HEPAs (cobalt, chromium and nickel) do. However, these oxides are very stable and are essentially self-healing and incredibly thin (not observable to the human eye); similar to that found with pure chrome or stainless steels. In other words, the HEPAs form a hard and passive oxide film which significantly reduces tarnishing and scratching.
Biocompatibility: Platinum and to an extent palladium are considered as bio-inert metals and do not interact with bodily function. Currently, Co—Ni—Cr alloys are used as acceptable orthopaedic implant materials due to the highly passive/inert oxide layer developed by such materials. However, Ni is now being critically analysed as it alone can be an irritant and toxic to cells. It is anticipated that a similar passive effect will exist with the HEPAs.
Alloy Variants by Application

(20) The HEPA examples in Table 1 are a subset of the full range of potential HEPAs that can be usefully applied by adjusting the alloy composition to produce desired properties. Examples of the potential applications for HEPAs are set out below.

(21) Pt-based Jewellery: Despite having large concentrations of other elements such as palladium, cobalt and chromium, in terms of their weight percentage, these alloys are predominantly platinum and would attract hallmark grades between Pt500 and Pt850 (Pt850 is quite popular in the current jewellery market). There is also room for commemorative or specialised currency/coinage applications.

(22) Magnetic Pt-based Jewellery: Given the unique composition ranges and constituents of the HEPAs, some exhibit strong permanent magnetic properties. This fact gives rise to a range of unique and diverse potential applications in jewellery including; rings/components that attract one another magnetically, levitating jewellery, rotating/spinning jewellery components (like an electric motor).

(23) Bio-alloys and components: The HEPAs are presumed to be bio-compatible and bio-inert. Similar to current Co—Ni—Cr bio-alloys, these alloys form a completely safe and passive Co—Cr oxide layer compatible with the human body, suitable for permanent orthopaedic or dental implants. These alloys however are much more malleable/formable than Co—Ni—Cr, making them better suited to permanent implants that need to be formed in-situ e.g. stents. Further, their magnetic properties open up an entirely new application as bio-inert implantable devices, e.g. micro bio-engines for inside the human body that are powered by the electrolysis of body fluids and bio-inert magnets, (magnetic fields have been shown to stimulate cell growth).

(24) Catalytic Converters: Currently catalytic converters in cars contain platinum and palladium as the oxidation activation components of the system, The HEPAs could effectively be a lower-cost or high efficiency replacement for this platinum-palladium component.

(25) Photocatalysts, Batteries and Fuel Cells: Platinum is currently used as an effective catalyst in the photocatalysis of water (splitting water into hydrogen and oxygen for fuel) and as catalysts in electrochemical batteries and fuel cells. The HEPAs may provide a high-yield, low-cost alternative to pure platinum in some of these applications.

(26) Magneto-Optical Devices and Magnetic Data Storage: Similar to the technology used in re-writable DVDs and hard drives etc., Pt-based magneto-optical materials may offer long-life data storage options due to their environmentally inert properties.

(27) Special Application Electric motors: Given their magnetic properties and biocompatibility, the HEPAs may be used in particular biological, cell-based or in vitro applications, e.g. biomotors (some bacteria use magnetic particles to move) and nanobots.

(28) Magnetic Transistors/Spintronic Devices: Essentially the next generation in device switching and data storage—the potential end result is devices that can store more data in less space and consume less power—given their stable magnetic properties and environmentally inert nature, HEPAs have high potential in specific applications of this technology.

(29) In the claims which follow, and in the preceding description, except where the context requires otherwise due to express language or necessary implication, the word “comprise” and variations such as “comprises” or “comprising” are used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the apparatus and method as disclosed herein.