Metal alloys including copper

Abstract

The present invention relates to matter alloys including copper.

Claims

1. An alloy consisting of: TABLE-US-00015 Copper 17 to 50 at. % Nickel 17 to 50 at. % Manganese 17 to 50 at. % Zinc 20 to 35 at. % Chromium  0 to 2 at. % Iron  0 to 2 at. % Cobalt  0 to 2 at. % Lead  0 to 2 at. % and wherein the alloy has entropy of mixing (ΔS.sub.mix) of at least 1.1 R when calculated according to: $\begin{array}{cc}{\Delta S}_{\mathrm{mix}}=-R\underset{i=1}{\overset{n}{.Math.}}\left(c_i\mathrm{in}{c}_i\right)& \left(\mathrm{Equation}1\right)\end{array}$ where c is the molar percentage of the ith component and R is the gas constant, and wherein the copper, nickel and manganese are present in substantially equal atomic percentages.

2. The alloy defined in claim 1, wherein the alloy has entropy in the range of 1.1 R to 2.5 R.

3. The alloy defined in claim 1, wherein the alloy has entropy in the range of 1.3 R to 2.OR.

4. The alloy defined in claim 1, wherein the alloy consists of Cu, Mn, Ni and Zn and has an as-cast hardness (H.sub.v) in the range of 102 to 253.

5. The alloy defined in claim 1, wherein the alloy has compressive yield strength in the range of 140 to 760 M Pa.

6. The alloy defined in claim 1, wherein the alloy has strain at compressive failure of 2% to 80%.

Description

DESCRIPTION OF EMBODIMENTS

(1) Test work carried out by the applicants has identified HEBs as having desirable properties in comparison to the properties of typical brasses and bronzes. In particular, the HEBs are based on the realisation by the applicants that the desirable properties are obtained by replacing a significant portion of copper in typical brasses and bronzes with manganese and nickel to produce alloys with considerably higher entropy of mixing (ΔS.sub.mix according to Equation 1 above) compared with the entropy of mixing for typical brasses and bronzes.

(2) A range of typical brass compositions and their associated mechanical properties are listed in Table 1. Amongst them, the copper-content ranges from 61 at. % to 85 at. % and the tensile yield strength ranges from 186 MPa to 315 MPa. It will be appreciated, however, that tensile yield strength does not vary linearly with copper-content. These alloys all have entropy of mixing that is no greater than approximately 0.82 R when calculated according to Equation 1.

(3) TABLE-US-00009 Alloy Crystal Hardness Yield Elongation Composition at. % Structure (Vickers) σ.sub.T (MPa) (Tensile Strain) Cu.sub.76Zn.sub.19.5Al.sub.4.5 fcc  95 186 55% (Al-Brass) Cu.sub.61Zn.sub.38.5Sn.sub.0.5 fcc + bcc 146 315 27% (Naval Brass) Cu.sub.70Zn.sub.30 fcc 100 275 43% (C26000) Cu.sub.85Zn.sub.15 fcc 100 270 25% (C23000) Cu.sub.65Zn.sub.32.5Pb.sub.2.5 fcc 138 310 25% (C35300) $\hspace{1em}\begin{array}{c}\Delta S_{\mathrm{mix}}=-R\underset{i=1}{\overset{n}{.Math.}}\left(c_i\ln c_i\right)\\ \left(\mathrm{Equation}1\right)\end{array}$

(4) The applicants have found that alloys with comparable or improved mechanical, chemical and physical properties can be obtained by replacing a significant amount of copper in typical brasses and bronzes with manganese and nickel and other alloying elements to produce alloys that have entropy of mixing according to Equation 1 that is at least 1.1 R.

(5) The alloys may have Cu 10 to 50 at. %, Ni 5 to 50 at. % and Mn 5 to 50 at. %. The alloys optionally include varying amounts of Zn (0 to 50 at. %), Sn (0 to 40 at. %), Fe (0 to 2 at. %), Cr (0 to 2 at. %), Pb (0 to 2 at. %), Co (0 to 2 at. %) and Si (0 to 25 at. %) depending on the desired properties of the alloy. It will be appreciated, however, that the alloys may include other alloying elements in amounts alongside Cu, Mn and Ni so that the alloy has entropy of mixing according to Equation 1 that is at least 1.1 R.

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

(7) A ternary master alloy of substantially equi-atomic Cu, Mn and Ni was prepared from high purity elements Cu (99.95 wt. %), Ni (99.95 wt. %) and Mn (99.8 wt. %) using a Buhler MAM1 arc melter in a Ti-gettered argon (99.999 vol. %) atmosphere. Ingots of the master alloy were turned and melted five times to ensure a homogeneous master alloy was achieved. Care was also taken to ensure a sufficiently low melt superheat as to avoid the evaporation of Mn.

(8) Quaternary and quinary alloy ingots containing Zn were alloyed using an induction furnace by combining the master alloy with pure Zn (99.99 wt. %) in a boron nitride-coated graphite crucible. These alloys were heated in a step-wise fashion with sufficient holding times at 700° C., 900° C. and 1050° C. to enable the dissolving of the master alloy in Zn in order to minimise Zn evaporation, yet produce a homogeneous alloy melt. Once a steady Zn evaporation rate was determined for this alloying process, excess Zn was added to these alloys to compensate for this loss. Although the Zn loss through evaporation was less than 20%, it is expected that industrial-scale production according to current production processes for alloys including Zn would result in around 20% loss of Zn during manufacturing.

(9) Quaternary alloys containing Al or Sn were produced by adding the balance of Al (99.99 wt. %) or Sn (99.95 wt. %) to the master alloy, arc melting and vacuum casting into a copper mould to produce 3 mm diameter rods.

(10) Once solidified, alloy samples were removed from the mould and allowed to cool to room temperature. They were then were heat treated in an elevator furnace at 850° C. for 18 hours under a circulating argon atmosphere and then quenched in water.

[Cu, Ni, Mn].SUB.100-x.Al.SUB.x .Alloy System

(11) Table 2 below lists six samples of Cu, Ni, Mn, Al alloys and some key properties.

(12) TABLE-US-00010 TABLE 2 Crystal Hardness Structure (Vickers) Yield Alloy As- Heat As- Heat σC Comp Mag- Composition Cast treated Cast Treated (MPa) Strain netic [CuNiMn].sub.95Al.sub.5 fcc fcc.sub.1 + 166 ± 173 ± 290 60% No fcc.sub.2 12    2.5 [CuNiMn].sub.90Al.sub.10 fcc.sub.1 + fcc.sub.1 + 241 ± 220 ± 480 40% No fcc.sub.2 fcc.sub.2  2.5  4.3 [CuNiMn].sub.80Al.sub.20 fcc.sub.2 + fcc.sub.2 346 ± 355 ± — <5% No bcc.sub.2  8.2  9.1 [CuNiMn].sub.75Al.sub.25 fcc.sub.2 + bcc.sub.2 377 ± 373 ± — <2% Yes bcc.sub.2  2.1  4.9 [CuNiMn].sub.70Al.sub.30 fcc.sub.2 + bcc.sub.2 355 ± 359 ± — <2% Yes bcc.sub.2 10.3  9.5 [CuNiMn].sub.60Al.sub.40 bcc.sub.2 + bcc.sub.3 395 ± 398 ± — <2% Yes bcc.sub.3  2.7 16.8

(13) The samples exhibit increasing hardness with increasing aluminium content. However, even the alloy with the lowest aluminium content at 5 at. % exhibited higher hardness than any of the typical brasses listed in Table 1. Furthermore, strength is comparable with the naval brass and C26000, C23000 and C35300 alloys, but ductility is considerably higher for the same comparable strength.

(14) Above 20 at. % aluminium the samples had considerably higher hardness than the brasses in Table 1, but considerably less compressive strain. Samples at and above 25 at. % aluminium exhibited magnetic properties.

(15) Samples with 10 at. % and 20 at. % aluminium have entropy according to Equation 1 of 1.314 R and 1.379 R respectively.

[Cu, Ni, Mn].SUB.100-x.Si.SUB.x .Alloy System

(16) Table 3 below lists four samples of Cu, Ni, Mn, Si alloys and some key properties.

(17) TABLE-US-00011 TABLE 3 Crystal Structure Hardness (Vickers) Alloy Heat Heat Mag- Composition As-Cast treated As-Cast Treated netic [CuNiMn].sub.97.5Si.sub.2.5 fcc.sub.1 + bcc.sub.2 fcc.sub.1 + bcc.sub.2 193 ± 6.1  183 ± 6.5  Faint [CuNiMn].sub.95Si.sub.5 fcc.sub.1 + bcc.sub.2 fcc.sub.1 + bcc.sub.2 293 ± 12.7 250 ± 7.1  Yes [CuNiMn].sub.90Si.sub.10 fcc.sub.1 + bcc.sub.2 fcc.sub.1 + bcc.sub.2 330 ± 7.8  334 ± 14.4 Yes [CuNiMn].sub.85Si.sub.15 fcc.sub.1 + bcc.sub.2 fcc.sub.1 + bcc.sub.2 — 376 ± 10.4 Yes

(18) As with the quaternary system including aluminium, the quaternary system including silicon has higher hardness than the typical brasses listed in Table 1. However, faint magnetism exists with even small amounts of silicon.

[Cu, Ni, Mn].SUB.100-x.Sn.SUB.x .Alloy System

(19) Table 4 below lists four samples of Cu, Ni, Mn, Sn alloys and some key properties.

(20) TABLE-US-00012 TABLE 4 Crystal Hardness Structure (Vickers) Yield Alloy As- Heat As- Heat σC Comp Mag- Composition Cast treated Cast Treated (MPa) Strain netic [CuNiMn].sub.95Sn.sub.5 fcc.sub.1 + fcc.sub.1 + 205 ± 178 ± 420 60% Faint bcc.sub.2 bcc.sub.2  7.6  5.8 [CuNiMn].sub.90Sn.sub.10 fcc.sub.1 + fcc.sub.1 + 318 ± 255 ± 760 20% Yes bcc.sub.2 bcc.sub.2  4.2 16.4 [CuNiMn].sub.80Sn.sub.20 fcc + fcc.sub.1 + 402 ± 533 ± brittle Yes bcc.sub.2 bcc.sub.2  1.9 15.4 [CuNiMn].sub.75Sn.sub.25 bcc.sub.1 + bcc.sub.2 467 ± 507 ± brittle Yes bcc.sub.2 19.7 37.0

(21) Results for the quaternary alloy system including tin exhibits considerably higher hardness and strength compared to the typical brass alloys listed in Table 1. Relatively small amounts of tin cause the quaternary alloy system to exhibit magnetism.

(22) The samples including at least 20 at. % tin had hardness in excess of 400 Hv in the as-cast from and, even then, responded well to the heat treatment with the result that hardness for both samples increased to well above 500 Hv.

[Cu, Ni, Mn].SUB.100-x.Zn.SUB.x .Alloy System

(23) Table 5 below lists four samples of Cu, Ni, Mn, Zn alloys and some key properties.

(24) TABLE-US-00013 TABLE 5 Crystal Hardness Structure (Vickers) Yield Alloy As- Heat As- Heat σC Comp Mag- Composition Cast treated Cast Treated (MPa) Strain netic [CuNiMn].sub.80Zn.sub.20 fcc.sub.1 fcc.sub.1 109 ± 113 ± 140 80% No 7.1 2.8 [CuNiMn].sub.75Zn.sub.25 fcc.sub.1 fcc.sub.1 147 ± 108 ± 225 55% No 5.9 9.7 [CuNiMn].sub.70Zn.sub.30 fcc.sub.1 fcc.sub.1 118 ± 122 ± — No 7.4 4.4 [CuNiMn].sub.65Zn.sub.35 fcc.sub.1 + fcc.sub.1 + 246 ± 248 ± — No bcc.sub.2 bcc.sub.2 7.1 20  

(25) The zinc-based quaternary alloys did not exhibit magnetic properties and, below 35 at. % zinc, the alloys exhibited relatively low hardness compared to other quaternary alloy samples. However, the samples with relatively low zinc (i.e. 20 at. % and 25 at. % zinc) exhibited relatively high ductility.

[Cu, Ni, Mn].SUB.100-x.[Al, Sn, Zn].SUB.x .Alloy System

(26) Table 6 below lists five samples, one of which consists of Cu, Ni, Mn, Al, Sn and the remainder consisting of Cu, Ni, Mn, Al, Zn.

(27) TABLE-US-00014 TABLE 6 Crystal Structure Hardness (Vickers) Heat Heat Mag- Alloy Composition As-Cast treated As-Cast Treated netic [CuNiMn].sub.90Al.sub.5Sn.sub.5 fcc.sub.1 + bcc.sub.2 fcc.sub.1 + bcc.sub.2 297 ± 4.4  303 ± 9.4 Yes [CuNiMn].sub.75Al.sub.5Zn.sub.20 fcc.sub.1 + fcc.sub.2 fcc.sub.1 + fcc.sub.2 250 ± 10.8 271 ± 8.8 No [CuNiMn].sub.60Al.sub.5Zn.sub.35 fcc.sub.1 + bcc.sub.1 fcc.sub.1 + bcc.sub.1 295 ± 8.5  — No [CuNiMn].sub.80Al.sub.10Zn.sub.10 fcc.sub.1 + bcc.sub.1 fcc.sub.1 ± fcc.sub.2 256 ± 12.8 — No [CuNiMn].sub.70Al.sub.10Zn.sub.20 fcc.sub.1 + bcc.sub.2 fcc.sub.1 + bcc.sub.2 214 ± 14.4 — No

(28) The hardness for all quinary samples is considerably greater than the hardness of the typical brasses listed in Table 1. As with both the tin- and zinc-based quaternary alloys disclosed in Tables 4 and 5, the quinary alloy sample including tin exhibits magnetic properties, but the quinary alloys including zinc do not. Although aluminium can cause magnetic properties in the alloys, there is insufficient aluminium in the quinary alloys to cause magnetic properties.

(29) To give these alloys context in terms of entropy, the sample consisting of [CuNiMn].sub.80Al.sub.10Zn.sub.10 has entropy of 1.518 R when calculated according to Equation 1.

(30) Although the alloys disclosed in Tables 2 to 6 are based on a master alloy comprising Cu, Ni and Mn in substantially equi-atomic amounts, the invention is not limited to equi-atomic amounts of Cu, Mn and Ni. It is contemplated that the relative amounts of Cu, Ni and Mn in a given alloy will be selected depending on the properties required for the designated application of that alloy. The following description addresses some applications and how the alloy composition might be adjusted to produce the desired properties for that application.

Alloy Variants by Application

(31) The above examples are a subset of the full range of potential HEBs that can be usefully applied by adjusting the alloy composition to produce desired properties. Examples of the different application and how the composition would be adjusted are outlined below.

Reduced Cost Alloys

(32) Based on 5-year market prices, nickel is more expensive than copper (around 1½ times the price) and manganese is essentially ⅓ the price of copper on a per kilogram basis. Given that the HEBs involve replacing a significant quantity of copper in brasses and bronzes with nickel and manganese, savings in terms of raw materials cost are expected to be 5 to 10% and higher if less nickel is used in the alloy. For example, an alloy with a lower Ni and higher Mn content would be considerably cheaper to produce and display similar strengths to the equal ratio alloy (i.e. Cu, Ni and Mn in equal atomic amounts), but may work harden faster and will likely be less corrosion resistant.

Corrosion Resistant

(33) On the other hand, an alloy with a higher Ni content would exhibit superior corrosion resistance. Alloys that contained Al were found to be particularly corrosion resistant. These would be suited to conditions where high corrosion resistance is imperative (although the typical brasses already exhibit good corrosion resistance, it is anticipated that the higher nickel content will result in HEBs have even better corrosion resistance)—say for marine applications.

Anti-Bacterial

(34) It is anticipated that these alloys would have similar ‘anti-microbial’ properties to conventional brasses. Copper is known to be highly antimicrobial in a range of environments—this is why door knobs and marine components are typically brasses—microbes/barnacles simply don't grow on them. Nickel is also known to be anti-microbial, but is slightly more toxic than copper. Essentially, higher copper and nickel content is preferred for these anti-microbial/anti fouling type alloys.

High Formability Applications

(35) Similar to regular brasses, with small additions of Al, Sn and Zn these alloys only contain the soft and ductile ‘alpha’ phase in the annealed state. As more Al, Sn or Zn are added these alloys begin to precipitate the much harder and less ductile ‘beta’ phase. When Al<4 at. % or Sn<4 at. % or Zn<30 at. % there is no beta phase present and these alloys are lower strength, but highly ductile. These alloys would be best suited to forming applications, similar to say munitions brasses (spinning/forming of bullet cartridges) or musical instruments or tubing where the metal is drawn and formed extensively.

High Wear Resistance and Low Friction Applications

(36) When 5<Al<20 or 4<Sn<10 or 30<Zn<40 (at. %), these alloys exhibit a duplex microstructure, which is considerably stronger and harder than alpha phase only alloys, but still quite tough. These alloys would be best suited to the high wear/low friction applications such as keys, hinges, gears/cogs, zippers, door latches. With higher Zn and Al additions, these alloys are also slightly lighter (lower density) and considerably cheaper to produce than regular brasses.

Light Weight

(37) The HEB alloys would not necessarily be considered as ‘light weight’ when compared with titanium or aluminium alloys for weight savings alone. However, they are always ‘lighter’ than typical brasses (which are quite heavy) simply due to the presence of Mn and Ni (which is still an advantage). The densities of HEB are still generally comparable to steel.

(38) However, for items that require specific strengths to function with dimensions that can be altered based on this requirement, further materials savings can be made. Specifically, the HEBs exhibit strengths 10-30% higher than that of brasses or bronzes with similar copper-to-zinc or copper-to-aluminium contents and, therefore, less material is required to give the same product strength. It follows that total materials cost savings from 19 to 47% are realistic for a given application.

Low Temperature Fracture Toughness

(39) Traditional steel bolts are bcc and bcc microstructures exhibit a temperature dependent ductile to brittle transition. It is for this reason that cooling steel/bcc metals to a low temperature can result in them shattering or cracking easily under load. With Al<4at % or Sn<4at % or Zn<30at. % these alloys are fcc, hence do not display this ductile to brittle behaviour at low temperatures. Even with a small amount of the bcc phase, these alloys are expected to be ductile at low temperatures.

Non-Sparking

(40) Steel, stainless steel, titanium and magnesium all give off sparks when ground with abrasives. This is not suitable for some environments, particularly where volatiles/flammables are present. Similar to regular brasses and bronzes, the HEB alloys do not spark when ground.

Non-Marking/Staining (Fingerprints)

(41) When polished, the HEB alloys seem to not stain or fingerprint in the same way stainless steel does (for example, brushed metal finish fridges and household appliances are quite prone to permanent staining due to reactions with iron). This is likely due to the oxidising potential of copper (metallic copper is more stable). An HEB with higher Cu, Ni content and containing Al (e.g. [Cu,Mn,Ni].sub.85-99Al.sub.1-15) is less susceptible to marking in the same ways as stainless steel.

Magnetism

(42) Some of these alloys exhibit strong ferromagnetic properties. This is due to the presence of Mn in combination with Al, Sn or Si in a magnetically ordered bcc phase. As Al, Sn and Si content increases the volume fraction of the magnetic phase increases, and so does the magnetic strength of the alloys. The composition range is quite specific. For quaternary alloys, the ranges are: [Cu,Mn,Ni].sub.70-80Al.sub.20-30, [Cu,Mn,Ni].sub.70-95Sn.sub.5-30, [Cu,Mn,Ni].sub.70-97.55Si.sub.2.5-30. Based on this ordered bcc phase, the optimum quantity of Mn and (Al or Sn) is 25 at. %, e.g. [Cu,Ni].sub.50Mn.sub.25[Al or Sn].sub.25. The optimum range for Si is 15-25 at. %, e.g. [Cu,Ni].sub.50-60Mn.sub.25Si.sub.15-25. These alloys are quite brittle and conventional powder consolidation methods would be required to create permanent magnets.

(43) Tin containing alloys show the highest magnetic response. Zinc quaternary alloys are non-magnetic. Also, quinary alloys show magnetism. Any combination of Sn and Al within this composition range, e.g. [Cu,Mn,Ni].sub.70-95[Al,Sn].sub.5-30, will be magnetic. Quinary alloys of Cu, Ni and Mn and including Zn and Al show faint magnetism. However, quinary alloys of Cu, Ni and Mn and including Zn and Sn exhibit moderate magnetism. This is due to Sn causing strongly magnetic behaviour in alloys with relatively small amounts of Sn, e.g. more than 5 at. %. For the same reason, it is expected that alloys of Cu, Mn, Ni, Al, Zn and Sn will be magnetic due to the presence of an ordered bcc phase.

Processing and Machinability

(44) The HEB alloys may be processed in the same way as current brasses with no modification to existing processing technology, with similar melting and casting properties to conventional brasses and similar post production working/machining properties.

(45) Specifically, the addition of small amounts of Pb will improve machinability. It is understood that Pb is immiscible with regular brass and, therefore, forms a fine dispersion within the brass which improves machinability of the bulk brass. It is expected that similar additions of Pb in the HEBs will have a similar effect.

(46) This includes processes for application of coatings. To be more specific, many brass-based products are plated with harder, more corrosion resistant or more aesthetically pleasing coatings such as chrome, nickel, silver or even gold. The electrochemical properties allowing easy plating for these new high entropy brasses remains unchanged compared to traditional brasses, hence these commercial treatments are still completely compatible.

Recyclability

(47) There already exists a world-wide brass recycling industry and due to the corrosion resistance and relatively lower melting point of brass—this is more economically viable and efficient than recycling steels. These HEB alloys are no exception, and in-fact could be reliably manufactured in-part by recycled traditional brasses, reducing cost further per recycling iteration.

(48) 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.