Advanced Search
RSS LinkedIn Twitter

Journal Archive

Platinum Metals Rev., 2013, 57, (3), 202

doi:10.1595/147106713x668596

PGM Highlights: Platinum Alloys: A Selective Review of the Available Literature

SHARE THIS PAGE:

Introduction

More than half of the platinum that is produced around the world each year currently finds use in automotive and other areas of industry as a catalyst and as a major constituent in various engineering alloys (Figure 1) (1). Platinum also has a place in jewellery manufacturing. The objective of this article is to review the existing phase diagrams and known properties of some platinum alloys that are used in industrial and jewellery applications, and also to present published data on some less used platinum alloys which nevertheless have interesting properties. The alloys covered are of platinum with palladium, iridium, rhodium, ruthenium, gold and nickel.

Fig. 1.

Platinum demand by application. Industrial applications include chemical, electrical, glass, petroleum and other (1)

Platinum demand by application. Industrial applications include chemical, electrical, glass, petroleum and other (1)     

 

The data on mechanical properties of the platinum alloys presented in Tables IVII are obtained from the monograph by R. F. Vines (2) published in 1941, still the most comprehensive source, from The PGM Database (3) hosted by Johnson Matthey, and from the internal database and website of Sigmund Cohn Corporation (4), a US pgm alloy fabricator. To keep the uniformity of units of measure all tensile strength (TS) data is presented in psi, and all the hardness data is presented in Vickers hardness (HV) (some of these values are converted from MPa and Brinell respectively). All alloy compositions are given in weight per cent (wt%) unless otherwise specified.

Table I

Colour of White Jewellery Alloys

MaterialBrightness, L*Green-red, a*Yellow-blue, b*
Platinum and pgm alloys 85 0 4.5
Fine silver 95 −0.5 4.2
18 carat white gold 84 0 9.5
14 carat white gold 84 −0.5 9.0
Table II

Mechanical Properties of Platinum, Palladium and Their Alloys in the Annealeda and Cold Workedb Conditions

Metal or alloyVickers hardness, HVannTensile strength, TSann, psiPercentage elongation, %EannVickers hardness, HVcwTensile strength, TScw, psi
Pt 40 18,100 40 90 49,300
Pd 40 27,500 40 100 47,000
Pt-10% Pd 80 21,300 25 140 49,700
Pt-40% Pd 100 50,000 180
Pt-10% Pd-6% Ru 200 75,000 25 320 90,900

[i] a ann = annealed

[ii] b cw = cold worked

Table III

Mechanical Properties of Platinum, Iridium and Their Alloys in the Annealeda and Cold Workedb Conditions

Metal or alloyVickers hardness, HVannTensile strength, TSann, psiPercentage elongation, %EannVickers hardness, HVcwTensile strength, TScw, psi
Pt 40 18,100 40 90 49,000
Ir 210 18,000 21
Pt-5% Ir 85 36,500 35 145 65,000
Pt-10% Ir 110 51,000 30 185 70,000
Pt-20% Ir 190 100,000 20 240 188,500
Pt-30% Ir 280 159,500 20 315 269,500
Pt-20% Ir-10% Rh 120,000 20 200,000

[i] a ann = annealed

[ii] b cw = cold worked

Table IV

Mechanical Properties of Platinum, Rhodium and Their Alloys in the Annealeda and Cold Workedb Conditions

Metal or alloyVickers hardness, HVannTensile strength, TSann, psiPercentage elongation, %EannVickers hardness, HVcwTensile strength, TScw, psi
Pt 40 18,100 40 90 49,000
Rh 100 81,000–125,000 9–33 215,000
Pt-10% Rh 90 45,000 35 150 90,000
Pt-20% Rh 115 68,000 33 200 133,500
Pt-30% Rh 130 71,000 30 235 152,000
Pt-40% Rh 145 83,500 30 290 178,000
Pt-15% Rh-5% Ru 95,000 18 200,000

[i] a ann = annealed

[ii] b cw = cold worked

Table V

Mechanical Properties of Platinum, Ruthenium and Their Alloys in the Annealeda and Cold Workedb Conditions

Metal or alloyVickers hardness, HVannTensile strength, TSann, psiPercentage elongation, %EannVickers hardness, HVcwTensile strength, TScw, psi
Pt 40 18,100 40 90 49,000
Ru 250 65,200 3
Pt-5% Ru 130 65,000 30 200 115,000
Pt-10% Ru 185 123,000 30 220 150,000

[i] a ann = annealed

[ii] b cw = cold worked

Table VI

Mechanical Properties of Platinum, Gold and Their Alloys in the Annealeda and Cold Workedb Conditions

Metal or alloyVickers hardness, HVannTensile strength, TSann, psiPercentage elongation, %EannVickers hardness, HVcwTensile strength, TScw, psi
Pt 40 18,100 40 90 49,000
Au 20 15,500 40 60 31,000
Pt-2.5% Au 70 31,000 26 138 49,000
Pt-5% Au 85 45,000 20 155 63,500
Pt-10% Au 130 77,500 12 91,500
Pt-3.5% Au-1% Rh 90 36,000 30

[i] a ann = annealed

[ii] b cw = cold worked

Table VII

Mechanical Properties of Platinum, Nickel and Their Alloys in the Annealeda and Cold Workedb Conditions and After Heat Treatmentc

Metal or alloyVickers hardness, HVannTensile strength, TSann, psiPercentage elongation, %EannVickers hardness, HVcwTensile strength, TScw, psiTensile strength, TSht, psi
Pt 40 18,100 40 90 49,000
Ni 85 45,000 45 220 90,000
Pt-5% Ni 130 66,500 26 100,000
Pt-10% Ni 220 118,000 28 380 230,000 300,000
Pt-20% Ni 280 132,000 250,000

[i] a ann = annealed

[ii] b cw = cold worked

[iii] c ht = heat treated

Platinum Alloys for Jewellery

Platinum alloys containing other platinum group metals (pgms), gold and some base metals present a variety of workable materials that demonstrate high strength, increased hardness and springiness. Many of these alloys are used for making jewellery (5), as they exhibit platinum's desirable white colour, and can be cast (6), extruded (7), rolled, drawn and formed (8).

A moderate brightness in combination with low red and yellow colour components make the colour of platinum a unique and attractive jewellery material that effectively accents the reflectivity of precious stones. Table I compares the colour of platinum with that of fine silver and typical 18 carat and 14 carat white golds using CIELAB colour coordinates, as measured by the author using a Macbeth Color-Eye® spectrophotometer model M2020PL. Platinum and its alloys show brightness L* about 85, neutral a* and fairly low b* components. Silver shows a* and b* values similar to those of platinum but a much higher brightness L*, about 95. The L* and a* values of white golds are similar to those of platinum, however such alloys exhibit much higher yellow components b* of at least 9.0 and most of them require rhodium plating.

The Santa Fe Symposium presentation by Jurgen Maerz in 1999 provides a comprehensive review of common platinum jewellery alloys (5). The legal requirements of minimum platinum content narrow the alloy range and prohibit the utilisation of the enhanced mechanical properties of many alloys outside this range.

PGM Alloy Properties

One of the key factors affecting the properties of an alloy is the crystalline structure of the pure metals of which it is composed. The crystalline structures of the pgms are shown in Figure 2. Four elements, Pt, Pd, Ir and Rh, have a face-centred cubic (fcc) structure, where the atoms are positioned at each corner and in the centre of each face of the cube. In general, the fcc metals are soft in the annealed condition and are quite workable, similarly to gold, silver and copper. The structure of the other two pgms, Ru and Os, is the more complex hexagonal close-packed (hcp) structure, similar to that of zinc. Such a major difference in crystalline structure suggests the significant hardening effect of Ru and Os when alloyed with Pt. In fact, additions of Os to Pt make the resultant alloys extremely hard and practically unworkable.

Fig. 2.

Crystalline structures of the platinum group metals

Crystalline structures of the platinum group metals

 

It is not surprising that binary phase diagrams (9) of Pt-Pd, Pt-Ir and Pt-Rh (Figures 3, 4 and 5 respectively) show similarity, whereas the Pt-Ru (Figure 6) phase diagram has a different and more complex form. Pd, Ir and Rh show solubility in Pt for the entire compositional range at high temperatures and miscibility gaps are seen at lower temperatures. In contrast, Pt-Ru is a peritectic system. Ru has solubility in Pt within certain compositional ranges (10). The miscibility gap feature is a potential mechanism for age hardening of Pt-Pd-Ir-Rh alloys, although little published data is available, probably because of fairly slow ageing kinetics (11).

Fig. 3.

Platinum-palladium phase diagram (9)

Platinum-palladium phase diagram (9)

 

Fig. 4.

Platinum-iridium phase diagram (9)

Platinum-iridium phase diagram (9)

 

Fig. 5.

Platinum-rhodium phase diagram (9)

Platinum-rhodium phase diagram (9)

 

Fig. 6.

Platinum-ruthenium phase diagram (9)

Platinum-ruthenium phase diagram (9)

 

Platinum-Palladium Alloys

Pt-Pd alloys are soft and workable. Figure 7 shows that the hardness and tensile strength of Pt-Pd alloys reach their maximum values at about 40% Pd. The mechanical properties of pure Pt, Pd and some of their alloys are compared in Table II. Pt and Pd are very similar: both have low hardness and tensile strength in annealed and cold worked conditions. The additions of 10% and even 40% Pd to Pt increase the hardness and strength somewhat; however these values still remain fairly low. The use of Pt-Pd alloys is therefore quite limited. It is remarkable that when 6% Ru is alloyed with Pt in addition to 10% Pd, the resultant all pgm alloy shows significantly increased hardness and strength, and retains good ductility (25% elongation) and excellent resistance to corrosion.

Fig. 7.

Tensile strength and hardness of platinum-palladium alloys (2)

 

 Tensile strength and hardness of platinum-palladium alloys (2)

Platinum-Iridium Alloys

Pt-Ir alloys are noticeably harder and stronger than Pt-Pd. Pure Ir is fairly hard. Additions of Ir to Pt result in a rapid rise in alloy hardness and strength as shown in Figure 8. Pt-Ir alloys with about 30% Ir and higher become extremely springy and practically unworkable – probably that is why the data in Figure 8 is limited to 30% Ir.

Fig. 8.

Tensile strength and hardness of platinum-iridium alloys (2)

Tensile strength and hardness of platinum-iridium alloys (2)

 

The mechanical properties of pure Pt and Ir and some of their alloys are listed in Table III. Even though the hardness of the annealed Ir is about four or five times higher than that of Pt, Ir shows a tensile strength similar to that of Pt and a fairly good percentage elongation of 21%. Pt-5% Ir and Pt-10% Ir are common jewellery alloys. Pt-20% Ir alloy is much harder, stronger, and still maintains good ductility (20% annealed elongation). In the sheet form it can be rolled down to 0.0005″ (0.0127 mm) thickness. In the wire form it can be drawn to 0.001″ (0.0254 mm) diameter. This pgm alloy is used for precision machining of parts for implantable medical devices.

Pt-30% Ir alloy shows extreme hardness and strength. This alloy is not easily workable. Its main application is found in medical devices as a spring wire. The mechanical properties of Pt-20% Ir alloy can be enhanced by adding 10% Rh. The Pt-20% Ir-10% Rh alloy is less springy than Pt-30% Ir, shows good workability, and retains good ductility (20% annealed elongation).

Platinum-Rhodium Alloys

Pt-Rh alloys are primarily used in thermocouples for operation at high temperatures (up to 1700ºC) in an oxidising or inert environment. Type S consists of Pt versus Pt-10% Rh, type R of Pt versus Pt-13% Rh and type B of Pt-6% Rh versus Pt-30% Rh. The standard wire sizes that are used to manufacture these thermocouples range between 0.001″ (0.0254 mm) and 0.032″ (0.813 mm). Table IV lists the mechanical properties of Pt, Rh and some of their alloys. Rh is very difficult to work and anneal. As a result, the published tensile properties of annealed Rh are inconsistent; its strength is reported between 81,000 psi and 125,000 psi, and the elongation between 9% and 33% (3). Pt-Rh alloys, however, are quite ductile, and show consistent and moderate rise in hardness and strength as the Rh content increases. The elongation stays practically constant at between 30% and 35% with Rh content up to at least 40 wt%. Pt-20% Rh alloy shows good hardness and strength, and excellent machining properties. It is used for precision part fabrication for the aerospace industry. Replacing some Rh with Ru, such as in Pt-15% Rh-5% Ru alloy, enhances the strength, but also results in the loss of some ductility from 33% to 18% elongation.

Platinum-Ruthenium Alloys

The hardening effect of Ru additions to Pt was first recognised by Adolph Cohn almost a century ago (12). Since then Ru-containing Pt alloys have become widely used in a variety of applications especially jewellery. Table V lists hardness, tensile strength and percentage elongation values for Pt, Ru, and two Pt alloys containing 5% and 10% Ru respectively. This data shows that alloying Ru with Pt yields much harder and stronger alloys without compromise in ductility.

Platinum-Gold Alloys

The addition of Au for hardening Pt was first suggested by Adolph Cohn in 1919 (13). The Pt-Au phase diagram in Figure 9 shows a fairly broad liquidus–solidus melting range and a miscibility gap with the peak close to the solidus. A wide range of Pt-Au alloys undergo spinodal decomposition within the miscibility gap as shown in Figure 10. The tensile properties as a function of Au content are shown in Figure 11. Although both Pt and Au are very soft, Au acts as an extremely effective hardener for Pt (14). Table VI lists the mechanical properties of Pt, Au and Pt alloys with low Au content. The hardness and strength rise with the Au content; however the percentage elongation dramatically decreases. This limits the practical use of such alloys. The deterioration of elongation is attributed mainly to grain growth during solution annealing (15).

It is found that small Rh additions broaden the miscibility gap and displace it up towards the solidus line forming a peritectic-type system (15). Small Rh additions to Pt-Au alloys not only enhance the hardness and strength but also improve ductility by increasing the elongation as illustrated by the Pt-3.5% Au-1% Rh alloy. A similar effect of Rh additions is also observed at higher Au concentrations. Pt-Au alloys with small additions of Rh are hardenable (1416).

Fig. 9.

Platinum-gold phase diagram (9)

 

 Platinum-gold phase diagram (9)

Fig. 10.

Platinum-gold phase diagram (9) – spinodal curve

Platinum-gold phase diagram (9) – spinodal curve

 

Fig. 11.

Tensile properties of solution treated platinum-gold alloys (14)

Tensile properties of solution treated platinum-gold alloys (14)

 

Platinum-Base Metal Alloys

A fairly detailed review of Pt-base metal alloys was compiled by R. F. Vines (2). Pt-tungsten and Pt-cobalt alloys have been most studied; and these alloys are commonly used for industrial applications (16, 17). A variety of Pt-base metal alloys such as those containing copper, cobalt, nickel and gallium effectively respond to age hardening (18, 19). Ni, however, finds limited use as an alloying element with Pt even though it belongs to the same group in the Periodic Table. The Pt-Ni phase diagram in Figure 12 shows the solubility of Ni in Pt for the entire compositional range.

Table VII lists the mechanical properties of pure Pt, Ni and their alloys. It is evident that the hardening effect of Ni on Pt is more pronounced than that of Ir: compare with Table III. The phase diagram also shows that alloys containing as little as 10% Ni undergo order-disorder transformation, a typical mechanism for age hardening. For example, an ageing heat treatment increases the tensile strength of Pt-10% Ni alloy from 230,000 psi up to 300,000 psi (TSht in Table VII). The magnetic transformation curve in Figure 12 indicates that Pt-Ni alloys with Ni content below 40% are practically non-magnetic. This is in contrast with Pt-Co alloys which show magnetism even at 5% Co.

Fig. 12.

Platinum-nickel phase diagram (9)

 

 Platinum-nickel phase diagram (9)

Conclusions

Platinum alloys play a significant role in industry and in jewellery manufacture. It is apparent that there is a wealth of information available from a range of sources and suppliers, and some of it is more readily available than others. The present paper is an attempt to bring together, in convenient form, the basic data that exists in the literature for some of these alloys and to emphasise their interesting properties for industrial and jewellery applications.

BACK TO TOP

References

  1.  J. Butler, “Platinum 2012 Interim Review”, Johnson Matthey Plc, Royston, UK, 2012 LINK http://www.platinum.matthey.com/publications/pgm-market-reviews/market-review-archive/platinum-2012-interim-review
  2.  R. F. Vines, “The Platinum Metals and Their Alloys”, ed. E. M. Wise, The International Nickel Company, Inc, New York, USA, 1941
  3.  The PGM Database: http://www.pgmdatabase.com/ (Accessed on 29th April 2013)
  4.  Sigmund Cohn: http://www.sigmundcohn.com/ (Accessed on 29th April 2013)
  5.  J. J. Maerz, ‘Platinum Alloy Applications for Jewelry’, in “The Santa Fe Symposium on Jewelry Manufacturing Technology 1999”, Proceedings of the 13th Santa Fe Symposium in Albuquerque, New Mexico, USA, ed. D. Schneller, Met-Chem Research, Albuquerque, New Mexico, USA, 1999, pp. 55–71
  6.  T. Fryé, ‘Platinum Alloys in the 21st Century: A Comparative Study’, in “The Santa Fe Symposium on Jewelry Manufacturing Technology 2011”, Proceedings of the 25th Santa Fe Symposium in Albuquerque, New Mexico, USA, ed. E. Bell, Met-Chem Research, Albuquerque, New Mexico, USA, 2011, pp. 201–229
  7.  P. W. Nordt III, ‘Modern Manufacture of Seamless, Wrought Wedding Bands – an Engineering Approach’, in “The Santa Fe Symposium on Jewelry Manufacturing Technology 2011”, Proceedings of the 25th Santa Fe Symposium in Albuquerque, New Mexico, USA, ed. E. Bell, Met-Chem Research, Albuquerque, New Mexico, USA, 2011, pp. 411–441
  8.  G. Normandeau, ‘Platinum Fabrication Processes’, Platinum Guild International, 1996: http://www.platinumguild.com/files/pdf/V2N4W_platinum_fabrication.pdf (Accessed on 29th April 2013)
  9.  ASM Alloy Phase Diagram Database: http://www.asminternational.org/portal/site/www/info/apdc/ (Accessed on 15th May 2013)
  10.  J. M. Hutchinson, Platinum Metals Rev., 1972, 16, (3), 88 LINK https://www.technology.matthey.com/article/16/3/88-90/
  11.  A. S. Darling, Platinum Metals Rev., 1960, 4, (1), 18 LINK https://www.technology.matthey.com/article/4/1/18-26/
  12.  A. Cohn, ‘Alloy’, US Patent 1,545,234; 1925
  13.  A. Cohn, ‘Alloy’, US Patent 1,323,834; 1919
  14.  A. S. Darling, Platinum Metals Rev., 1962, 6, (2), 60 LINK https://www.technology.matthey.com/article/6/2/60-67/
  15.  A. S. Darling, Platinum Metals Rev., 1962, 6, (3), 106 LINK https://www.technology.matthey.com/article/6/3/106-111/
  16.  A. G. Knapton, Platinum Metals Rev., 1980, 24, (2), 64 LINK https://www.technology.matthey.com/article/24/2/64-69/
  17.  A. S. Darling, Platinum Metals Rev., 1963, 7, (3), 96 LINK https://www.technology.matthey.com/article/7/3/96-104/
  18.  R. S. Irani and R. W. Cahn, Platinum Metals Rev., 1972, 16, (2), 48 LINK https://www.technology.matthey.com/article/16/2/48-49/
  19.  G. Normandeau and D. Ueno, ‘Understanding Heat Treatable Platinum Alloys’, in “The Santa Fe Symposium on Jewelry Manufacturing Technology 1999”, Proceedings of the 13th Santa Fe Symposium in Albuquerque, New Mexico, USA, ed. D. Schneller, Met-Chem Research, Albuquerque, New Mexico, USA, 1999, pp. 73–103
  20.  T. Biggs, S. S. Taylor and E. van der Lingen, Platinum Metals Rev., 2005, 49, (1), 2 LINK https://www.technology.matthey.com/article/49/1/2-15/

Supplementary Information

A datasheet (PDF) containing all phase diagrams featured in this article can be downloaded for quick reference: Raykhtsaum_Suppl.

The following sources may contain additional data and phase diagrams for a range of platinum and pgm alloys:

The PGM Database: a collection of published data and internal Johnson Matthey data defining the physical properties and characteristics of platinum group metals and their alloys. Access is FREE: http://www.pgmdatabase.com/

“Precious Materials Handbook”, Edited by U. Sehrt (PR Beratung Sehrt, Germany) and M. Grehl (Umicore AG & Co KG, Germany), Umicore AG & Co KG, Hanau-Wolfgang, Germany, 2012, 576 pages, ISBN: 978-3-8343-3259-2

http://www.vogel-buchverlag.de/product_info.php/info/p487_Precious-Materials-Handbook.html

The book can be purchased from the publisher:

http://bookview.libreka.de/retailer/urlResolver.do?id=9783834332592&retid=100008

Journal of Phase Equilibria and Diffusion, Editor: J. F. Smith, ISSN: 1547-7037 (print version), Journal no. 11669

The journal is available to subscribers only:

http://www.springer.com/materials/journal/11669

ASM Alloy Phase Diagram Database: a fully-searchable database containing over 35,000 binary and ternary alloy phase diagrams, from over 6,200 systems.

The database is available to subscribers only:

http://www.asminternational.org/portal/site/www/info/apdc/

The Author

Grigory Rakhtsaum is Director of Metallurgy at LeachGarner in Attleboro, Massachusetts, USA. He holds an MS degree in Physics from the Polytechnic Institute in St. Petersburg, Russia. He also studied Materials Science at Northwestern University in Evanston, Illinois, USA. He has worked in the precious metals industry since 1984, focusing on gold and pgm alloy and process development, quality assurance and failure analysis. This paper was written while with Sigmund Cohn Corp in Mount Vernon, New York, USA. He has coauthored 12 patents and about 40 publications, as well as giving numerous presentations at venues including the Santa Fe Symposium on Jewelry Manufacturing Technology, the International Precious Metals Institute and Manufacturing Jewelers and Suppliers of America.

Read more from this issue »

BACK TO TOP

SHARE THIS PAGE: