EP1797211A1 - Hardening of metal alloys - Google Patents

Hardening of metal alloys

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Publication number
EP1797211A1
EP1797211A1 EP05782474A EP05782474A EP1797211A1 EP 1797211 A1 EP1797211 A1 EP 1797211A1 EP 05782474 A EP05782474 A EP 05782474A EP 05782474 A EP05782474 A EP 05782474A EP 1797211 A1 EP1797211 A1 EP 1797211A1
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EP
European Patent Office
Prior art keywords
alloy
parent metal
item
platinum
solute
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Application number
EP05782474A
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German (de)
French (fr)
Inventor
Silethelwe Nxumalo
Candace Irene Lang
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
University of Cape Town
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University of Cape Town
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Filing date
Publication date
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Publication of EP1797211A1 publication Critical patent/EP1797211A1/en
Withdrawn legal-status Critical Current

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
    • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
    • C22F1/16—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of other metals or alloys based thereon
    • C22F1/18—High-melting or refractory metals or alloys based thereon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C5/00—Alloys based on noble metals
    • C22C5/04—Alloys based on a platinum group metal
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
    • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
    • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
    • C22F1/14—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of noble metals or alloys based thereon

Definitions

  • This invention relates to alloy metals.
  • this invention relates to a method of rendering an alloy metal with increased hardness.
  • the invention has particular relevance to platinum alloys and hardening of low-solute platinum alloys by heat treatment.
  • T n * is material dependent but is usually approximately 1000 degrees Centigrade (deg C) for common platinum jewellery alloys, although this figure can vary by several hundred degrees depending on the material.
  • cold working is inherent in hand-working jewellery manufacturing processes. As such, cold working includes rolling, drawing, etc of the alloy material.
  • cold worked platinum 5 wt.% tungsten can have a HV of
  • age-hardening or precipitation hardening which increases hardness by solid-state precipitation of a second phase. This process involves:
  • a method of rendering an alloy with increased hardness including the steps of heat treating the alloy until the formation of at least one ordered region in the alloy, wherein the alloy is not a PtCr alloy.
  • increased hardness refers to the comparison of the alloy including ordered regions and that alloy not including ordered regions.
  • 'increased hardness' is intended to encompass rendering an alloy with a hardness not predictable or obtainable using conventional hardening mechanisms.
  • the term 'ordered region' is intended to mean the existence of a super-lattice structure, in which the location of different atomic species is periodic and predictable.
  • the ordered region is an X 8 Y ordered region within the alloy wherein X is a parent metal and Y is the solute atom type.
  • the parent metal is preferably platinum (Pt).
  • Pt platinum
  • other metals such as palladium (Pd) and nickel (Ni) are also considered to fall within the ambit of the present invention.
  • Pd alloys like Pt alloys, find particular application in jewellery applications and Ni has application in high temperature and other applications.
  • the solute atom is a transition metal element.
  • the solute atom may be selected from Ti, V, Zr, Cr (where the parent metal is not Pt), Nb, Mo, Hf, Ta and W.
  • the metal alloy may be a binary alloy, i.e. comprising the parent metal and one other solute atom, or it may be a ternary alloy, i.e. comprising the parent metal and two solute atoms. It will be appreciated that quaternary and other alloys are also contemplated to lie within the ambit of the present invention.
  • the alloy preferably includes at least 85wt.% parent metal, more preferably at least 90wt.%, more preferably at least 95wt.% parent metal.
  • the solute atoms may be present in not more than 15wt.% more preferably not more than 10wt.%, more preferably not more than 5wt.%
  • the alloy comprises 95wt.% of the parent metal, 0.01 to 4.99wt.% of a first solute atom, the balance of the alloy comprising at least one further solute atom selected to enhance predetermined criteria of the alloy.
  • the parent metal is Pt and the solute atom is V.
  • the alloy preferably contains more than 94 wt.% Pt, more preferably more than 95 wt.% Pt, preferably more than 96 wt.% Pt, most preferably more than 96.5wt.% Pt.
  • the alloy may contain less than 99.99wt.% Pt, preferably less than 98wt.% Pt, preferably less than 97wt.% Pt, more preferably less than 96wt.% Pt.
  • the alloy preferably contains less than 6wt.% V, more preferably less than 5wt.% V, more preferably less than 4wt.% V, most preferably less than 3.5wt.% V.
  • the alloy may contain more than 0.01wt.% V, more preferably more than 1wt.% V, more preferably more than 2wt.% V, more preferably more than 3wt.% V.
  • the alloy comprises 95wt.% Pt, 3.2wt.% V, the balance being selected from the group of transition metals set out above.
  • the alloy is heated to below its recrystallisation temperature (T 1x ).
  • the alloy is preferably cooled to ambient temperature following heating.
  • the alloy is preferably heated to below the order/disorder temperature (T c )of the alloy to induce ordering. It will be appreciated that a given alloy may present one of two scenarios according to the present invention:
  • T c is below the recrystallisation temperature T 1x - in which case heating below T 0 means heating below T 1 *.
  • T 0 is above J n - in which case it may be required to heat above J n to induce ordering.
  • heating above J n may negate the effect of any prior cold work with the result that there may be a reduced nett hardening effect.
  • T c is above J n the alloy is heated below J n (which is below T c ).
  • the method may include the step of initially cold working the alloy to a predetermined degree of deformation/strain. In this manner it is possible to achieve a particular hardness prior to heating the alloy as hereinbefore described. This may be achieved by cold working the alloy for a pre-determined period of time at a pre-determined strain rate.
  • the subsequent heat treatment is preferably effected in a furnace.
  • an alloy comprising a parent metal selected from Pt, Pd and Ni and a solute atom wherein the alloy has a Vickers Hardness Value of more than 370, preferably more than 400, more preferably more than 420, more preferably more than 440, more preferably more than 450, more preferably more than 470, more preferably more than 490, most preferably more than 500.
  • an item fashioned or including an alloy as hereinbefore described and/or prepared as hereinbefore described.
  • an alloy including an ordered region and/or as hereinbefore described in the preparation of an item.
  • the item may be an item of jewellery, cutlery or other valuable.
  • the hard alloys according to the present invention are achieved by the formation of ordered regions within the metal alloy, Ordered regions' meaning the existence of a super-lattice structure, in which the location of different atomic species is periodic and predictable, rather than simply being a random solid solution of different atomic types.
  • the preferred type of ordered region has the stoichiometry X 8 Y, where X is the parent metal and Y is the solute atom type.
  • a preferred alloy is a platinum alloy and Pt 8 X is believed to exist in the following alloys set out below.
  • Other preferred alloys include palladium and nickel alloys and the same stoichiometry also exists in these alloys. This has been predicted from first thermodynamic principles known in the art [AJ. Ardell, Metallic alloys: Experimental and theoretical perspectives, 93-102 (1994). Z.W. Lu and B.M. Klein, Phys. Rev. B 50, 5962-5970 (1994)].
  • PtTi the Pt 8 Ti structure has been predicted, observed, and reported in the open literature.
  • PtV the Pt 8 V structure has been predicted, observed and reported in the open literature D. Schryvers, J. Van Landuyt and S. Amelinckx, Mat. Res. Bull, 18, 1369 (1983).
  • PtZr the Pt 8 Zr structure has been predicted, observed and reported in the open literature.
  • PtCr The Pt 8 Cr structure has been predicted and was observed by the applicant.
  • PtNb the Pt 8 Nb structure has been predicted, but not yet observed.
  • PtMo the Pt 8 Mo structure has been predicted, but not yet observed.
  • PtHf, PtTa, PtW the Pt 8 Hf , Pt 8 Ta and Pt 8 W structures have been predicted, but not yet observed.
  • the formation of the Pt 8 X structure confers an impressive increase in hardness to an alloy - something that has not previously been observed.
  • a HV of over 500 is achieved. This is a significant value compared to the HV of cold-worked stainless steel at 400.
  • the above HV of over 500 is particularly surprising considering the HV of the annealed 3.2%.wt PtV alloy is approximately 210 and the HV of the cold worked alloy is approximately 360. (Annealing is heat treatment designed to negate the effect of cold working.)
  • the alloys according to the present invention must be heat treated to produce the Pt 8 X structure. There are several important practical considerations here:
  • the method comprises only a single heat treatment, of as short a duration as 15 minutes. No further change in hardness is observed following heat treatments of up to 2500 hours.
  • precipitation hardening which produces the next highest hardening in jewellery alloys, requires two heat treatments, possibly lengthy.
  • Figure 1 is a graph of hardness vs. heat treatment temperature for platinum 3.2 wt.% vanadium alloy heat treated for three hours.
  • Figure 2 is a graph of hardness vs. time for platinum 3.2 wt.% vanadium alloy heat treated at 400 deg C.
  • Figure 3 is a graph of hardness vs. heat treatment temperature for platinum 2.9 wt.% chromium alloy heat treated for three hours.
  • Figure 4 is a graph of hardness vs. time for platinum 2.9 wt.% chromium heat treated at 300 deg C.
  • Figure 5 is a graph of hardness vs. heat treatment temperature for platinum 5.2 wt.% molybdenum heat treated for three hours.
  • the platinum alloy is cast and homogenised to provide an alloy having a uniform structure.
  • the term 'uniform structure' refers to compositional homogeneity and an equiaxed grain structure.
  • the platinum alloy is then cold worked to produce the jewellery item by a process of rolling, drawing or any other suitable means of working, resulting in a HV of approximately HVi OOg 366.
  • the jewellery item is then heat treated in a furnace at a temperature below 600 0 C for three hours, followed by cooling to room temperature.
  • the jewellery item After the heat treatment the jewellery item has an enhanced HV of approximately 500 which is higher than the HV that can be attained by cold working, i.e. approximately 360.
  • the platinum/chromium alloy is cast and homogenised to provide an alloy having a uniform structure.
  • the platinum alloy is then cold worked to produce the jewellery item by a process of rolling, drawing or any other suitable means of working, resulting in a HV of approximately HV 1OOg 295.
  • the jewellery item is then heat treated in a furnace at a temperature below 600°C for three hours, followed by cooling to room temperature.
  • the jewellery item After the heat treatment the jewellery item has an enhanced HV of approximately 330 which is higher than the HV that can be attained by cold working, i.e. approximately 295.
  • the platinum/molybdenum alloy is cast and homogenised to provide an alloy having a uniform structure.
  • the platinum alloy is then cold worked to produce the jewellery item by a process of rolling, drawing or any other suitable means of working, resulting in a HV of approximately HVi 0 o g 360.
  • the jewellery item is then heat treated in a furnace at a temperature below 600 0 C for three hours, followed by cooling to room temperature.
  • the jewellery item After the heat treatment the jewellery item has an enhanced HV of over 400 which is higher than the HV that can be attained by cold working, i.e. approximately 360.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
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Abstract

A method of rendering an alloy with increased hardness is provided, the method including the steps of heat treating the alloy until the formation of at least one ordered region in the alloy. An alloy prepared according to this method and an item of jewellery fashioned from or including such an alloy are also provided.

Description

HARDENING OF METAL ALLOYS
BACKGROUND OF THE INVENTION
This invention relates to alloy metals. In particular, this invention relates to a method of rendering an alloy metal with increased hardness. The invention has particular relevance to platinum alloys and hardening of low-solute platinum alloys by heat treatment.
Pure platinum is too soft (Vickers Hardness Value (HV) of around 45) to survive wear and tear as a jewellery item. For this reason all platinum jewellery is made from platinum alloyed with other elements, because the addition of the other elements results in an alloy of increased HV. There is a limit to alloying additions, however, the limits being imposed by hallmarking requirements.
Internationally, jewellery can only be hallmarked as "platinum" if it contains a minimum platinum value, for example, 85%, 90% or 95% platinum by weight (wt.%). Different countries have different requirements. In South Africa, for example, platinum jewellery must contain 95% by weight platinum in order to secure the platinum hallmark. The addition of up to 5 wt.% of other elements to platinum can improve its HV (e.g. platinum 5 wt.% tungsten has a HV of 135) but the hardness nevertheless remains low relative to other metals (e.g. mild steel has a HV of 140 and stainless steel a HV of 250+). In this specification 'low-solute' alloys are intended to encompass those alloys having 15wt.% or less solute.
The hardness of an alloy can be further improved by cold work defined as plastic deformation below the recrystallisation temperature T1*. Tn* is material dependent but is usually approximately 1000 degrees Centigrade (deg C) for common platinum jewellery alloys, although this figure can vary by several hundred degrees depending on the material. It will be appreciated that cold working is inherent in hand-working jewellery manufacturing processes. As such, cold working includes rolling, drawing, etc of the alloy material. For example, cold worked platinum 5 wt.% tungsten can have a HV of Another method of hardening alloys known in the art is age-hardening or precipitation hardening, which increases hardness by solid-state precipitation of a second phase. This process involves:
1 ) an initial high-temperature heat treatment (the temperature depends on the particular alloy),
2) a quench (to room temperature or below), and
3) a second heat treatment, at lower temperature than (1 ), (again, this temperature depending on the particular alloy).
This process can only be carried out for specific alloys but it can result in HV of up to 350 in commercial, precipitation hardening platinum alloys (known as "heat treatable" platinum alloys).
In 2002, Nzula et al. (Nzula, MP. and Lang, C.I. Ordering in platinum-chromium alloys, Proc.
ICEM: International Congress on Electron Microscopy, Durban, South Africa (2002)) reported that a cold worked Pt 10 atomic weight (at.)%Cr alloy had an increased hardness (approximately HV of 370) which conventional hardening mechanisms could not account for when heat treated at 300 deg C. It was further reported that an electron diffraction pattern of the alloy was consistent with the diffraction patterns observed in the Pt8Ti type structure. However, the equilibrium phase diagram for the PtCr system did not show an ordered phase at this composition.
Although the crystallography and thermodynamics of an X8Y (where X is a parent metal and Y is a solute atom) ordered structure have been the subject of considerable interest, to date little attention has been paid to the effect of the formation of the X8Y ordered structure on the properties of these alloys and the effect of the formation of Pt8Y on the mechanical properties of platinum alloys has not previously been thoroughly investigated.
It therefore remains a goal to produce alloys having increased hardness, over and above that taught by heat treatment. The reason for these efforts to increase hardness of an alloy, whilst still retaining its hallmark, is that high hardness confers high scratch-resistance and wear resistance, which are desirable characteristics in jewellery items such as rings. Jewellery items such as rings bearing a hallmark will obviously be of higher value commercially.
A need exists to provide a method for rendering an alloy with increased hardness.
SUMMARY OF THE INVENTION
According to a first aspect to the present invention there is provided a method of rendering an alloy with increased hardness, the method including the steps of heat treating the alloy until the formation of at least one ordered region in the alloy, wherein the alloy is not a PtCr alloy.
The term increased hardness refers to the comparison of the alloy including ordered regions and that alloy not including ordered regions. Thus the term 'increased hardness' is intended to encompass rendering an alloy with a hardness not predictable or obtainable using conventional hardening mechanisms.
The term 'ordered region' is intended to mean the existence of a super-lattice structure, in which the location of different atomic species is periodic and predictable.
Preferably the ordered region is an X8Y ordered region within the alloy wherein X is a parent metal and Y is the solute atom type.
The parent metal is preferably platinum (Pt). However, other metals such as palladium (Pd) and nickel (Ni) are also considered to fall within the ambit of the present invention. Pd alloys, like Pt alloys, find particular application in jewellery applications and Ni has application in high temperature and other applications.
Preferably the solute atom is a transition metal element. As such the solute atom may be selected from Ti, V, Zr, Cr (where the parent metal is not Pt), Nb, Mo, Hf, Ta and W. The metal alloy may be a binary alloy, i.e. comprising the parent metal and one other solute atom, or it may be a ternary alloy, i.e. comprising the parent metal and two solute atoms. It will be appreciated that quaternary and other alloys are also contemplated to lie within the ambit of the present invention.
The alloy preferably includes at least 85wt.% parent metal, more preferably at least 90wt.%, more preferably at least 95wt.% parent metal.
The solute atoms may be present in not more than 15wt.% more preferably not more than 10wt.%, more preferably not more than 5wt.%
In a preferred embodiment of the present invention, the alloy comprises 95wt.% of the parent metal, 0.01 to 4.99wt.% of a first solute atom, the balance of the alloy comprising at least one further solute atom selected to enhance predetermined criteria of the alloy.
In a preferred embodiment of the present invention, the parent metal is Pt and the solute atom is V. The alloy preferably contains more than 94 wt.% Pt, more preferably more than 95 wt.% Pt, preferably more than 96 wt.% Pt, most preferably more than 96.5wt.% Pt. The alloy may contain less than 99.99wt.% Pt, preferably less than 98wt.% Pt, preferably less than 97wt.% Pt, more preferably less than 96wt.% Pt. The alloy preferably contains less than 6wt.% V, more preferably less than 5wt.% V, more preferably less than 4wt.% V, most preferably less than 3.5wt.% V. The alloy may contain more than 0.01wt.% V, more preferably more than 1wt.% V, more preferably more than 2wt.% V, more preferably more than 3wt.% V. In a most preferred embodiment of the present invention, the alloy comprises 95wt.% Pt, 3.2wt.% V, the balance being selected from the group of transition metals set out above.
Preferably the alloy is heated to below its recrystallisation temperature (T1x). The alloy is preferably cooled to ambient temperature following heating. The alloy is preferably heated to below the order/disorder temperature (Tc)of the alloy to induce ordering. It will be appreciated that a given alloy may present one of two scenarios according to the present invention:
(1) Tc is below the recrystallisation temperature T1x - in which case heating below T0 means heating below T1*. (2) T0 is above Jn - in which case it may be required to heat above Jn to induce ordering. However, heating above Jn may negate the effect of any prior cold work with the result that there may be a reduced nett hardening effect. In accordance with the present invention, if Tc is above Jn the alloy is heated below Jn (which is below Tc).
The method may include the step of initially cold working the alloy to a predetermined degree of deformation/strain. In this manner it is possible to achieve a particular hardness prior to heating the alloy as hereinbefore described. This may be achieved by cold working the alloy for a pre-determined period of time at a pre-determined strain rate. The subsequent heat treatment is preferably effected in a furnace.
According to a second aspect to the present invention there is provided an alloy prepared according to the method of the first aspect to the invention.
According to a third aspect to the present invention there is provided an alloy comprising a parent metal selected from Pt, Pd and Ni and a solute atom wherein the alloy has a Vickers Hardness Value of more than 370, preferably more than 400, more preferably more than 420, more preferably more than 440, more preferably more than 450, more preferably more than 470, more preferably more than 490, most preferably more than 500.
According to a fourth aspect to the present invention there is provided an item fashioned or including an alloy as hereinbefore described and/or prepared as hereinbefore described.
According to a fifth aspect to the present invention there is provided the use of an alloy including an ordered region and/or as hereinbefore described in the preparation of an item. The item may be an item of jewellery, cutlery or other valuable.
DESCRIPTION OF EMBODIMENTS
The hard alloys according to the present invention are achieved by the formation of ordered regions within the metal alloy, Ordered regions' meaning the existence of a super-lattice structure, in which the location of different atomic species is periodic and predictable, rather than simply being a random solid solution of different atomic types.
The preferred type of ordered region has the stoichiometry X8Y, where X is the parent metal and Y is the solute atom type. A preferred alloy is a platinum alloy and Pt8X is believed to exist in the following alloys set out below. Other preferred alloys include palladium and nickel alloys and the same stoichiometry also exists in these alloys. This has been predicted from first thermodynamic principles known in the art [AJ. Ardell, Metallic alloys: Experimental and theoretical perspectives, 93-102 (1994). Z.W. Lu and B.M. Klein, Phys. Rev. B 50, 5962-5970 (1994)].
PtTi: the Pt8Ti structure has been predicted, observed, and reported in the open literature.
P. Pietrowski, Nature, 206, 291 (1965).
PtV : the Pt8V structure has been predicted, observed and reported in the open literature D. Schryvers, J. Van Landuyt and S. Amelinckx, Mat. Res. Bull, 18, 1369 (1983).
PtZr: the Pt8Zr structure has been predicted, observed and reported in the open literature.
P. Krautwasser, S. Bhan and K. Schubert, Z. Metallkd. 59, 724 (1968)
PtCr: The Pt8Cr structure has been predicted and was observed by the applicant.
PtNb: the Pt8Nb structure has been predicted, but not yet observed.
PtMo: the Pt8Mo structure has been predicted, but not yet observed.
PtHf, PtTa, PtW: the Pt8Hf , Pt8Ta and Pt8W structures have been predicted, but not yet observed.
(It will be appreciated that these latter systems are less urgent because the Pt8X occurs at above 10 wt.% solute and such an alloy therefore does not meet South African hallmarking requirements.) Without wishing to be bound by theory, it is believed that the reason that the X8Y structures have been observed so rarely in the art is because the kinetics of the ordering transformation are very slow. The applicants have found that the kinetics can be accelerated by appropriate cold work. It must be appreciated that the acceleration of the kinetics is not essential according to the present invention. If the kinetics for a particular alloy are slow, the kinetics can be accelerated by quenching from high temperatures and/or the kinetics can be accelerated by irradiating the metal alloy.
The applicants have found that the formation of the Pt8X structure confers an impressive increase in hardness to an alloy - something that has not previously been observed. For example, when the Pt8V structure forms in the 3.2%.wt PtV alloy, a HV of over 500 is achieved. This is a significant value compared to the HV of cold-worked stainless steel at 400. The above HV of over 500 is particularly surprising considering the HV of the annealed 3.2%.wt PtV alloy is approximately 210 and the HV of the cold worked alloy is approximately 360. (Annealing is heat treatment designed to negate the effect of cold working.)
To achieve this elevated hardness (higher than any other platinum jewellery alloy), the alloys according to the present invention must be heat treated to produce the Pt8X structure. There are several important practical considerations here:
- the method comprises only a single heat treatment, of as short a duration as 15 minutes. No further change in hardness is observed following heat treatments of up to 2500 hours. By comparison, precipitation hardening, which produces the next highest hardening in jewellery alloys, requires two heat treatments, possibly lengthy.
- the heat treatment temperatures (which differ from alloy to alloy) are between 300-1000 deg C, - the slow kinetics of the Pt8X transformation are greatly accelerated by cold work prior to heat treatment. Since most jewellery processes involve cold work anyway, this would not have to be an additional step.
In other words, once a jewellery item has been made by (cold) hand-working of an alloy, it can simply be placed into a furnace for approximately15 minutes at a temperature below the T^ for that alloy to induce the formation of X8Y stoichiometry. This will confer a greater HV to the alloy than heretoknown before and may even confer the alloy with a HV higher than stainless steel. Further features of a method of hardening low-solute platinum alloys, in accordance with the invention, are described hereinafter by way of the following non-limiting examples and figures.
Figure 1 is a graph of hardness vs. heat treatment temperature for platinum 3.2 wt.% vanadium alloy heat treated for three hours.
Figure 2 is a graph of hardness vs. time for platinum 3.2 wt.% vanadium alloy heat treated at 400 deg C.
Figure 3 is a graph of hardness vs. heat treatment temperature for platinum 2.9 wt.% chromium alloy heat treated for three hours.
Figure 4 is a graph of hardness vs. time for platinum 2.9 wt.% chromium heat treated at 300 deg C.
Figure 5 is a graph of hardness vs. heat treatment temperature for platinum 5.2 wt.% molybdenum heat treated for three hours.
In Figures 1 , 3 and 5, the hardness of the cold worked alloy is shown at heat temperature treatment 0.
Example 1
With reference to Figures 1 and 2, a method of manufacturing an item of jewellery from a platinum alloy containing 3.2 wt.% vanadium in accordance with the invention is described hereinafter.
The platinum alloy is cast and homogenised to provide an alloy having a uniform structure. The term 'uniform structure' refers to compositional homogeneity and an equiaxed grain structure. The platinum alloy is then cold worked to produce the jewellery item by a process of rolling, drawing or any other suitable means of working, resulting in a HV of approximately HViOOg 366. The jewellery item is then heat treated in a furnace at a temperature below 6000C for three hours, followed by cooling to room temperature.
After the heat treatment the jewellery item has an enhanced HV of approximately 500 which is higher than the HV that can be attained by cold working, i.e. approximately 360.
Example 2
With reference to Figures 3 and 4 the platinum/chromium alloy is cast and homogenised to provide an alloy having a uniform structure. The platinum alloy is then cold worked to produce the jewellery item by a process of rolling, drawing or any other suitable means of working, resulting in a HV of approximately HV1OOg 295. The jewellery item is then heat treated in a furnace at a temperature below 600°C for three hours, followed by cooling to room temperature.
After the heat treatment the jewellery item has an enhanced HV of approximately 330 which is higher than the HV that can be attained by cold working, i.e. approximately 295.
Example 3
With reference to Figure 5 the platinum/molybdenum alloy is cast and homogenised to provide an alloy having a uniform structure. The platinum alloy is then cold worked to produce the jewellery item by a process of rolling, drawing or any other suitable means of working, resulting in a HV of approximately HVi0og 360. The jewellery item is then heat treated in a furnace at a temperature below 6000C for three hours, followed by cooling to room temperature.
After the heat treatment the jewellery item has an enhanced HV of over 400 which is higher than the HV that can be attained by cold working, i.e. approximately 360.

Claims

1. A method of rendering an alloy with increased hardness, the method including the steps of heat treating the alloy until the formation of at least one X8Y ordered region within the alloy wherein X is a parent metal and Y is the solute atom type and wherein the alloy is not a platinum/chromium (PtCr) alloy.
2. A method according to claim 1 wherein the parent metal is selected from platinum (Pt), palladium (Pd) and nickel (Ni).
3. A method according to claim 1 or 2 wherein the solute atom is a transition metal element.
4. A method according to claim 3 wherein the solute atom is selected from Ti, V, Zr, Cr (where the parent metal is not Pt), Nb, Mo, Hf, Ta and W.
5. A method according to any one of claims 1 to 4 wherein the alloy is a binary alloy.
6. A method according to any one of claims 1 to 4 wherein the alloy is a ternary or quaternary alloy.
7. A method according to any one of claims 1 to 6 wherein the alloy includes at least 85wt.% parent metal.
8. A metal according to any one of claims 1 to 7 wherein the solute atoms are present in not more than 15wt.%.
9. A method according to any one of claims 1 to 8 wherein the alloy comprises 95wt.% of the parent metal, 0.01 to 4.99wt.% of a first solute atom, the balance of the alloy comprising at least one further solute atom selected to enhance predetermined criteria of the alloy.
10. A method as claimed in claim 9 wherein the alloy comprises 95wt.% Pt, 3.2wt.% V, the balance being selected from the group of transition metals.
11. A method according to any one of the preceding claims wherein the alloy is heated to below its recrystallisation temperature (Tn).
12. A method as claimed in claim 11 wherein the alloy is cooled to ambient temperature following heating.
13. A method as claimed in claim 12 wherein the alloy is heated to below an order/disorder temperature (Tc) of the alloy to induce ordering.
14. A method according any one of the preceding claims including the step of initially cold working the alloy to a predetermined degree of deformation/strain.
15. An alloy prepared according to the method of any one of claims 1 to 14.
16. An alloy comprising a parent metal selected from Pt, Pd and Ni and a solute atom wherein the alloy has a Vickers Hardness Value of more than 370.
17. An item fashioned from or including an alloy according to claim 15 and/or 16.
18. Use of an alloy including an X8Y ordered region wherein X is a parent metal and Y is the solute atom type in the preparation of an item.
19. Use as claimed in claim 18 wherein X is selected from Pt, Pd and Ni.
20. An item as claimed in claim 17 wherein the item is an item of jewellery, cutlery or other valuable.
EP05782474A 2004-09-02 2005-09-01 Hardening of metal alloys Withdrawn EP1797211A1 (en)

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PCT/IB2005/002580 WO2006024928A1 (en) 2004-09-02 2005-09-01 Hardening of metal alloys

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EP3020835B1 (en) * 2014-11-17 2021-04-21 Omega SA Piece of watchmaking, bijouterie or jewelry comprising a component made of a palladium-based alloy
EP3121297B1 (en) * 2015-07-23 2020-12-16 Cartier International AG Method for obtaining a trim component in platinum alloy

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US20080245449A1 (en) 2008-10-09

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