Palladium is not widely recognised as a preciousmetal in jewellery and watchmaking. Yet, with theprice evolution of precious metals over the lastfew years, use of palladium in these markets hasseen renewed interest (1–3). For illustration, goldwas roughly double the price of palladium in 2006and about four times the price of palladium at theend of 2008 (4). In addition, palladium alloys forjewellery, which usually contain 95 wt.% Pd (950Pd), have a lower density (around 12 g cm–3) than18 carat white gold (close to 15 g cm–3) and 950platinum (about 21 g cm–3). Hence, an item of vol-ume 1 cm3 in 950 Pd contains 11.4 g Pd. Bycomparison, the same item made in 18 carat whitegold (750 Au) or 950 Pt will contain, respectively,11.3 g Au or 20 g Pt.

Furthermore, the 950 Pd alloys approach the‘ideal’ white colour of platinum without requiringrhodium plating like most white gold alloys. Unlikefor gold alloys, the white sheen will therefore notwear off, eliminating the bother and expense of re-plating. 950 Pd alloys also satisfy the generalrequirements for jewellery and watch alloys: they

are nickel-free, malleable, easy to polish, and havedesirable setting and forming characteristics. Theirhigh Pd content also confers good corrosion andtarnishing resistance, a crucial aspect in jewelleryand watchmaking.

The inherently low hardness of Pd alloys is,however, an important technical limitation fortheir use in jewellery and particularly in watchmak-ing. The hardness of existing 950 Pd alloys, withalloying metals such as ruthenium (PdRu), gallium(PdGa) or copper (PdCu), falls between 70 HV(PdCu) and 120 HV (PdGa) in the annealed state,and between 145 HV (PdCu) and 200 HV (PdGa)after 75% strain hardening. These values are sub-stantially lower than those typical of platinum orwhite gold alloys (≥ 130 HV annealed, ≥ 250 HVwork hardened).

In an attempt to develop a 950 Pd single-phasealloy with substantially higher hardness, compara-ble with platinum and white gold, whilemaintaining the favourable colour and workabilityof conventional Pd alloys, we investigated PdAl-based compositions, in particular the PdAlRu

189Platinum Metals Rev., 2009, 53, (4), 189–197

Precious Palladium-Aluminium-BasedAlloys with High Hardness and Workability PROMISING POTENTIAL FOR APPLICATION IN JEWELLERY AND WATCHMAKING

By Julien Brelle and Andreas Blatter*PX Holding SA, R&D, Boulevard des Eplatures 42, CH-2300 La Chaux-de-Fonds, Switzerland;

*E-mail: andreas.blatter@pxgroup.com

and René ZiegenhagenCartier Horlogerie, Branch of Richemont International SA, 10 Chemin des Aliziers, CH-2300 La Chaux-de-Fonds, Switzerland

New palladium-aluminium-based alloys with promising potential for application in the areasof jewellery and watchmaking are presented. A particular emphasis is placed on the mechanicalbehaviour of ternary palladium-aluminium-ruthenium (PdAlRu) alloys with 95 wt.% Pd.The new alloys combine high plasticity with high hardness relative to common Pd alloys.The low work-hardening rate enables cold working in excess of 95% reduction withoutintermediate annealing. The hardness (Vickers pyramid indentation) ranges from 100 HV to300 HV in the annealed condition, depending on the Al:Ru ratio. Their whiteness in terms ofcolour coordinates is compared with platinum and white gold. The feasibility of porcelainfusion to PdAlRu for decorative purposes is also demonstrated.

DOI: 10.1595/147106709X472192

system. This paper describes the background tothe alloy development, presents the main charac-teristics of 950 PdAlRu alloys in terms ofmechanical properties and workability, andaddresses the possibility of fusing coloured ceram-ic material to the alloy for decorative purposes.

Background to the Development ofthe PdAlRu Alloys

While precipitation hardening may also be ofinterest to further increase the rigidity and wearresistance of finished components, solid solutionstrengthening is the mechanism that must providethe base hardness of the alloy in the annealed state.

Solid solution strengthening is the result ofstrain produced in the crystal lattice, mainly by thesize misfit between matrix and solute atoms. Sincesize misfit also limits the terminal solid solubility,as described by the Hume-Rothery rules (5), itmust be kept within certain limits to ensure a solu-bility of at least 5 wt.%, which is necessary for a950 Pd single-phase alloy. For a given solute, thestrength increases with its atomic fraction (at.%).Higher atomic fractions are achieved when alloy-ing with light elements. In 950 Pd, for illustration,5 wt.% aluminium corresponds to 17.2 at.%. A 950Pd alloy may include several alloy additions, whichmust be fully soluble and must add up to a total of5 wt.%.

The effects of a great number of solute ele-ments on the hardness of palladium have beencompiled previously (6, 7). Germanium, silicon andboron have a strong hardening effect. However, Bis difficult to alloy and Ge and Si both exhibit near-ly zero solubility. As a result, when added insufficient concentrations to give a hardness above150 HV, these elements tend to precipitate at thegrain boundaries and thereby render the alloy toobrittle for practical use. For those elements whichare more practical in terms of alloying, such asother precious metals or 3d transition metals, thehardness values attained at concentrations of 5wt.% barely exceed 100 HV. Ru is one of the ele-ments showing the most pronounced effect on thehardness of Pd alloys. Hardness values in the range150 HV to 200 HV can be achieved with rare earthmetals such as cerium (8).

With respect to the light elements, 5 wt.% tita-nium raises the hardness to 150 HV (9), while Alboosts the value to 320 HV (440 HV after 80%cold work), according to our own experiments.While a hardness of 150 HV is at the lower edgeof the target range, a value of 320 HV may beinconveniently high for many conventional jew-ellery manufacturing operations such as stampingor setting.

The present study therefore focused on PdAl-based alloys, incorporating ternary additions of Ru,Ti and magnesium in order to moderate the hard-ness. Ru was chosen because it is a noble metal, agood solution hardener, and commonly used in 950Pd alloys. Ti and Mg were chosen because they arelightweight, good solution hardeners, and may pos-sibly provide a mechanism of precipitationhardening by the formation of tiny AlTi or AlMgcompounds upon ageing – in similarity with super-alloys. Table I shows the hardness values obtainedfor various ternary alloys in the annealed and 80%work hardened conditions, respectively. This showsthat the hardness values in the annealed state lie inthe target range and that cold work generates sub-stantial hardening. The values displayed are thosefor ‘low’ and ‘high’ concentrations of the ternaryadditions; intermediate concentrations gave inter-mediate values for hardness. All alloys were singlephase and sufficiently malleable for a rolling reduc-tion of 80% without cracking. It is interesting tonote that there have been two independent patentapplications for 950 PdAl-based alloys (10, 11).

Platinum Metals Rev., 2009, 53, (4) 190

Table I

Vickers Hardness Values of Various PdAl-(Ti, Mg,Ru) Alloys in the Annealed and 80% ReductionWork-Hardened States*

Alloy Hardness, HV

Annealed Work-hardened

Pd95.5Al1.3Ti3.2 154 366Pd95.5Al0.4Ti4.1 128 338Pd95.5Al3.8Mg0.7 242 400Pd95.5Al1.9Mg2.6 170 340Pd95.5Al2.8Ru1.7 224 343Pd95.5Al0.9Ru3.6 158 247

* The standard deviations associated with the displayed meanvalues are below ± 7 HV

The advantage of Ru as the ternary element isthat unlike Mg or Ti, it does not cause a violentreaction with Al upon alloying. In this paper, wefocus on our development work on the 950PdAlRu system.

PropertiesTwo alloys of nominal composition (in wt.%)

Pd95.5Al0.9Ru3.6 and Pd95.5Al2.8Ru1.7 were prepared ina vacuum induction melting unit. The unit cham-ber was evacuated and purged with argon severaltimes before backfilling with argon to 600 mbar.The elemental metals were melted in a zirconiacrucible. The Al flakes were wrapped in Pd sheetsto avoid any reaction with the crucible and also toalloy the Al with the higher melting point Pdwithout significant expulsion of Al. Plate-likeingots of 5 kg each were cast into an oxidised copper mould to constitute the feedstock for thevarious tests. After a first flat rolling, rods werecut off the plate and further rolled to adequatesize for tensile testing while the rest of the platewas used for workability tests and microstructuralinvestigations.

The X-ray diffraction pattern in Figure 1reveals that the ternary alloys are essentially singlephase, face centred cubic (f.c.c.) solid solutions. InRu-rich alloys, a new diffraction peak appears, andits intensity increases with increasing Ru content.Additional peaks, too weak to be seen in Figure 1,become visible when zooming into the data. Thesepeaks, located at scattering angles, 2θ, of 44.0º,

58.3º, 78.2º, 84.8º, and 104.8º, respectively, areclose to those of pure Ru and enable the secondphase to be assigned to a Ru-rich PdRu hexagonalclose packed (h.c.p.) solid solution.

The measured lattice constants, a, of theternary f.c.c. matrix are accurately reproduced witha hard sphere approximation by the linear combi-nation of the atomic sizes, Sj, defined as theminimum interatomic distance in the unit cell ofelement j (Equation (i)):

(i)

where the coefficients cj correspond to the atomicfraction of element j.

The atomic sizes for Pd, Al and Ru are, respec-tively, 2.750 nm, 2.863 nm and 2.650 nm (12).Since Al has a greater atomic size than Pd by4.1%, whereas Ru is smaller by 2.6%, the apparentshift in a is marginal among different ternaryalloys. In other words, strengthening due to latticedistortion is not apparent through a significantshift of the diffraction peaks. In particular, thereexists a ternary composition for which the latticeconstant almost matches that of elemental Pd.The lattice constant derived from the diffractionpattern of Pd95.5Al0.9Ru3.6 is 3.888 nm, compared to3.886 nm for Pd.

Hardness The hardness of the PdAlRu alloys in the

annealed state (1000ºC for one hour), measuredusing a Vickers hardness tester with a 1 kg load

Platinum Metals Rev., 2009, 53, (4) 191

∑⋅=j

jjSca 2

Pd95.5Al0.9Ru3.6

Scattering angle, 2θ

0 20 40 60 80 100 120

Inte

nsity, a.u

.

Fig. 1 X-Ray diffraction patterns ofannealed Pd95.5Al0.9Ru3.6. A θ–2θconfiguration and Cu Kα1 radiation(α = 0.15408 nm) were employed.The sample is predominantly f.c.c.single phase. An additional peak at2θ ≈ 42 indicates the presence of asecond phase

×

(HV1), approximates to a linear function of the Alcontent, as shown in Figure 2. Therefore, thehardness can be tuned to any value from about100 HV (PdRu) to 320 HV (PdAl). The hardnessvalues in the work-hardened condition range from165 HV (PdRu) to 440 HV (PdAl). Correspondingvalues for two ternary compositions are given inTable I. Upon ageing of annealed samples at700ºC for twenty minutes, the hardness of thosealloys with higher Ru content increases slightly,indicating a mechanism of precipitation harden-ing. The intensity of age hardening remainsmodest, however: it approaches but does notexceed the increase of 25 HV observed at thehighest Ru content, i.e. for the binary 950 PdRualloy. This strengthening is also evident in an

increase in yield strength of 50 MPa forPd95.5Al0.9Ru3.6 (Figure 3).

Age hardening is accompanied by a substantialincrease in electrical resistivity, ρel, as measured bymeans of the four-point probe technique on discsof thickness 2 mm and diameter 27 mm (13). ForPd95.5Al0.9Ru3.6, ρel reversibly switches from25.5 μΩ cm in the annealed state to 91 μΩ cm inthe age hardened state. By comparison, the valuesfor Pd95.5Al2.8Ru1.7, which does not exhibit agehardening, are 32.1 μΩ cm and 35.6 μΩ cm,respectively. Since an increase in electrical resistiv-ity is caused by additional scattering of electrons atcrystal imperfections, such as a lattice distortion orthe presence of precipitates, and since age harden-ing occurs with the appearance of a PdRu phase as

Platinum Metals Rev., 2009, 53, (4) 192

R2

= 0.9911

Aluminium, wt.%

01 2 3 4 5 6

50

100

150

200

250

300

350V

ickers

hard

ness, H

V1

y = 42.523x + 109

Fig. 2 Variation of Vickers hardnessvalues, HV1, with Al content x (wt.%)of annealed Pd95AlxRu(5 – x) alloys. Thelinear approximation is shown

Pd95.5Al2.8Ru1.7

Pd95.5Al0.9Ru3.6

Engineering strain, %

Engin

eering s

tress, M

Pa

5 10 15 20 25 30 350

200

400

600

800

1000

1200

CW

AH

AH

AN

AN

Fig. 3 Typicalengineering stress-strain curves recordedfor Pd95.5Al2.8Ru1.7 andPd95.5Al0.9Ru3.6 in theannealed (AN), age-hardened (AH) and85% cold-worked(CW) states

discussed above, it is tempting to correlate agehardening with PdRu precipitates. However, themain diffraction peak of the PdRu phase persistsupon annealing, suggesting that the precipitatesare not fully solubilised.

Figure 4 shows the variation of conventionalyield strength, Rp0.2, ultimate tensile strength, Rm,and fracture strain, A50, with cold work. The alloysundergo significant strain hardening only upon initial cold working. Beyond about 30% of coldwork, yield strengths (Figure 4) and hardness values (Figure 5) remain essentially constant. It isworth mentioning that the tensile properties of theRu-rich alloy after standard annealing (1000ºC for1 hour) depend on its thermomechanical history.

This is no longer the case after cold working. Weattribute this memory behaviour to a variable evo-lution and dissolution of the PdRu precipitates.

The work hardening exponent, n, can be rough-ly estimated from a fit of the Hollomon equation(Equation (ii)) to the true stress-true strain curve(14):

σt = Kεtn (ii)

Here, K, the strength index, is a constant and thetrue stress-true strain data (σt, εt) is obtained fromthe engineering data (σ, ε) by Equations (iii) and (iv):

σt = σ(1 + ε) (iii)

εt = ln(1 + ε) (iv)

Platinum Metals Rev., 2009, 53, (4) 193

Cold work, %

Rm

/Rp

0.2, M

pa

20 40 60 80 1000

200

400

600

800

1000

1200

7

14

21

28

35

42

A50 , %

Pd95.5Al0.9Ru3.6

Pd95.5Al2.8Ru1.7

A50

Rm

Rm

Rp0.2

Rp0.2

0

Pd95.5Al2.8Ru1.7

Pd95.5Al0.9Ru3.6

Cold work, %

Vic

kers

hard

ness, H

V1

350

300

250

200

150

100

50

0 20 40 60 80 100

Fig. 5 Variation of Vickers hardness,HV1, with cold work. Each data pointis the average of five tests (standarddeviation < 5%)

Fig. 4 Yieldstrengths, Rp0.2,ultimate tensilestrengths, Rm, andfracture strains, A50,as derived fromstandard tensiletesting (EN 10002-1:1990) of two PdAlRualloys at variousdegrees of cold work.Each data point is theaverage of five tests(standard deviation < 3% except for A50).Connecting linesserve as a guide tothe eye

where σt is the true stress, σ is the engineeringstress, εt is the true strain and ε is the engineeringstrain.

When applied to the stress-strain curves ofannealed samples in the plastic domain (Figure 3),this approximation returns n = 0.29 forPd95.5Al2.8Ru1.7 and n = 0.25 for Pd95.5Al0.9Ru3.6, val-ues that are typical of low stacking-fault energyalloys such as Al alloys.

Figure 6 depicts the mechanical properties ofPdAlRu alloys in comparison with those of com-mon Pd, Pt or Au alloys. The ternary 950 PdAlRualloys exhibit higher strength and hardness thanconventional 950 PdRu, but lower fracture strains.Tensile strengths and hardness values are similar tothose of Pt or Au alloys. Fracture strains are com-parable or somewhat lower in the annealed state,whereas they are higher after 75% cold work. Yieldstrengths may be somewhat lower or higher in theannealed condition, depending on the Al content.

After cold working, however, the yield strengths ofthe PdAlRu alloys remain largely below those ofthe Pt or Au alloys – another clear manifestation ofthe low work-hardening rate, i.e. the high plasticity,of these ternary alloys.

Young’s modulus, E, and Poisson’s ratio, ν, arelisted in Table II. These elastic properties werededuced from measurements of the longitudinaland transverse sound velocities (15). The pulse-echo measurements were performed on plates2 mm to 3 mm thick, using appropriate transduc-ers to excite either the longitudinal (at 10 MHz) orthe transverse (2.5 MHz) acoustic mode. ThePoisson’s ratio of 0.37 is typical for precious met-als. The Young’s modulus of 139 GPa to 145 GPais comparable to that of the conventional PdRualloy (148 GPa). It lies between those of 18 caratAu alloys (90 GPa to 110 GPa) and 950 Pt alloys(approximately 170 GPa to 210 GPa). Regardingspecific stiffness, E/ρ, the PdAlRu alloys with

Platinum Metals Rev., 2009, 53, (4) 194

CW CW

CW CW

An AH An AH

An AH An AH

Rp

0.2, M

Pa

Rm

, M

Pa

A50, %

Vic

kers

harn

ess, H

V

1000

800

600

400

200

0

0

10

20

30

40

50

0

200

400

600

800

1000

1200

0

50

100

150

200

250

300

350

PtRuGa

5N red gold

PdRu

PdAl2.8Ru1.7 PdAl0.9Ru3.6

AuPdCu 3N yellow gold

Fig. 6 Comparison of mechanical properties of two PdAlRu alloys with commonly used precious metal alloys: a 950 Pt alloy (PtRuGa); a 950 Pd alloy (PdRu); a 13 wt.% Pd-containing 18 carat white gold (AuPdCu); 3N yellowgold; and 5N red gold. The comparison is made for 75% cold-worked (CW), annealed (AN), and age-hardened (AH)materials. Rm = tensile strength; Rp0.2 = conventional yield strength; A50 = fracture strain; HV = Vickers hardness

densities, ρ, in the range 10.5 g cm–3 to 11.6 g cm–3

slightly exceed Pt alloys (ρ ≥ 20 g cm–3) and clearlyoutperform Au alloys (ρ ≥ 15 g cm–3).

Colour The CIELab colorimetric indices L* (lightness),

a* (red-green chromaticity index) and b* (yellow-blue chromaticity index) of polished samples weredetermined using a spectrophotometric colorimeter(Konica Minolta CM-3610d spectrophotometer)(16). The measurement was carried out in a stan-dard configuration with D65 illumination, a 10ºobserver, and in specular component included(SCI) mode. The ideal white would return(L*/a*/b*) indices of (100/0/0). The measuredvalues are (84/1/4.5) for Pd95.5Al2.8Ru1.7 and(86/0.9/4.1) for Pd95.5Al0.9Ru3.6. These values arecomparable to those of standard 950 PdRu, andcloser to the colour of the platinum alloy 950 PtRu(87.7/0.7/3.4) than to ‘premium’ 18 carat whitegold (82/> 1.5/> 6). However, the colour indicesof the two PdAlRu alloys suggest that the effect ofaluminium is to add a slight yellowish tinge and tosomewhat diminish the brightness.

For the classification of white gold alloys, asimple colour grading system based on the ASTMD1925 (1988) yellowness index (YI) has recentlybeen proposed (17). Within this system, the lowerthe YI the whiter the alloy. The whitest metals andalloys such as silver or 950 PtRu have values ofYI ≈ 8. The PdAlRu alloys attain YI ≈ 10, which iscomparable to pure Pd or Pt. White gold alloys, incontrast, have substantially higher indices, atYI ≥ 15.

WorkabilityFigure 4 shows another characteristic feature of

the two PdAlRu alloys: their yield strengths do not

steadily approach their tensile strengths withincreasing cold work. Rather, the gap between thetwo parameters remains relatively large, thus facil-itating the forming of complex and asymmetricshapes.

The good workability of the two alloys wasconfirmed by the fabrication of watch cases, backsand bezels by employing rolling, stamping andannealing operations. Plate ingots with surfacesmachined to eliminate possible microcracks andflaws were used as a starting material. The plateswere easily rolled to over 90% reduction withoutintermediate annealing. In accordance with thedata in Figure 5, the hardness rose by only about40 HV upon increasing the cold work from 23%to 95% reduction. Blanks were then roughlypunched out from bands of thickness 8.8 mm,followed by fine punching for improved surfacefinish and dimensional tolerances. The final shap-ing of larger series of components by progressivedie stamping is in progress.

The most intriguing observation during theseoperations was the pronounced tendency of bothalloys to heat up considerably during plastic work.While heating to a certain extent is usual forrolling processes, the heating up of a disc duringpunching to temperatures so high that it cannotbe touched by hand is extraordinary. This signifi-cant temperature rise during plastic deformationmight be related to the low work hardening bypromoting dynamic recovery.

Use of the Ceramic FusionTechnique with PdAlRu Alloys

Inspired by the dental technique of ceramicveneering of precious metals, the feasibility of fus-ing coloured ceramic overlays on PdAlRu alloysfor decorative purposes was investigated. In the

Platinum Metals Rev., 2009, 53, (4) 195

Table II

Density, Young’s Modulus and Poisson’s Ratio of PdAlRu Alloys

Alloy State Density, Young’s modulus, Poisson’s ratio,

ρ, g cm–3 E, GPa ν

Pd95.5Al2.8Ru1.7 Annealed 10.8 139 0.37

Pd95.5Al0.9Ru3.6 Annealed 11.4 145 0.37

dental technique, Pd-containing alloys are in factpreferred. Pd oxidises more readily than Au or Pt,which guarantees a better bonding to the ceramic.The presence of Al in the PdAlRu alloys is certain-ly favourable in this respect. The dental sectorcommercialises a broad range of ceramic materialswith coefficients of thermal expansion (CTE) inthe range 8 × 10–6 K–1 to 14 × 10–6 K–1 (18, 19). TheCTE of Pd is 12 × 10–6 K–1, and alloying with atotal of 5 wt.% Al and Ru is not expected tochange this value significantly. A close match ofthe ceramic CTE to the metal CTE is important toavoid cracking, notably during cooling after thefiring process.

Two types of commercial dental ceramics weretested: VITA VM®13 veneering material for inten-sive or translucent colours, and the VITA Akzent®

stain powder for pitch black dyeing (19). Theceramics were either applied as overlays or filled into trench patterns machined into the PdAlRudiscs.

The ceramic-to-metal fusion was performedfollowing the directions of the ceramic supplier(19). In short, it consists of preparing the metalsurface by sandblasting and controlled thermaloxidation. Different ceramic layers are thenapplied and fired one after the other at 890ºC forone to two minutes: a first layer to promote cohe-sion, a second opaque layer, and a finalglass-ceramic coloured layer. Additional layersmay be necessary in order to fill in possible gapsproduced upon firing.

Figure 7 exemplifies PdAlRu discs preparedand polished by the methods described above,with differently coloured ceramic inlays. Thecolours are uniform and no pores or cracks areapparent.

ConclusionsIn search of 950 Pd alloys with improved

mechanical properties, PdAlRu alloys proved partic-ularly promising. The PdAlRu alloys presented inthis paper possess beneficial characteristics forapplications in jewellery, and in particular in watch-making. The palladium content of 95 wt.% iscommon to most countries. The PdAlRu alloys arewhiter than most 18 carat white gold alloys.Furthermore, they are compatible with the dentalveneering technique, which opens up the potentialfor decorating articles with ceramic ornaments inappealing colours. The PdAlRu alloys exhibit excel-lent workability and forming characteristics, similarto those of commonly used 950 Pd alloys. At thesame time, they exhibit much higher strength andhardness, more comparable to those of gold or plat-inum alloys. Moreover, the mechanical propertiescan be tuned in an extended range by varying theAl:Ru ratio. Upon cold working, for a given strain,the yield stress increases much less than it does inother precious metals, while the tensile strengthincreases in broadly similar fashion. This character-istic imparts to the alloys enhanced plasticity andexcellent workability.

Platinum Metals Rev., 2009, 53, (4) 196

Fig. 7 PdAlRu alloy discs with ceramic inlays

1 S. A. Forrest and B. Clarke, ‘End-Users, Recyclers andProducers: Shaping Tomorrow’s PGM Market andMetal Prices’, in “International Platinum Conference‘Platinum Surges Ahead’”, Sun City, South Africa,8th–12th October, 2006, Symposium Series S45, TheSouthern African Institute of Mining and Metallurgy,Johannesburg, South Africa, 2006, p. 307

2 B. Libby, ‘Palladium Premieres’, MJSA Journal, March2006, p. 35

3 “The Santa Fe Symposium on Jewelry ManufacturingTechnology 2008”, ed. E. Bell, Proceedings of the22nd Symposium in Albuquerque, New Mexico,U.S.A., 18th–21st May, 2008, Met-Chem ResearchInc, Albuquerque, New Mexico, U.S.A., 2008

4 Kitco, Inc, Past Historical London Fix: http://www.kitco.com/gold.londonfix.html (Accessed on3rd July 2009)

5 W. Hume-Rothery, R. E. Smallman and C. W. Haworth,

References

“The Structure of Metals and Alloys”, 5th Edn., TheMetals and Metallurgy Trust, London, U.K., 1969,407 pp

6 G. Beck, in “Edelmetall-Taschenbuch”, 2nd Edn., ed.A. G. Degussa, Hüthig-Verlag, Heidelberg, Germany,1995, p. 217

7 The PGM Database:http://www.platinummetalsreview.com/jmpgm/index.jsp (Accessed on 3rd July 2009)

8 J. R. Hirst, M. L. H. Wise, D. Fort, J. P. G. Farr andI. R. Harris, J. Less-Common Met., 1976, 49, 193

9 J. Evans, I. R. Harris and L. S. Guzei, J. Less-CommonMet., 1979, 64, (2), P39

10 A. Blatter, J. Brelle and R. Ziegenhagen, PX HoldingSA, ‘Alliage à Base de Palladium’, Swiss Appl.CH00032/08; 2008

11 P. Battaini, 8853 SpA, ‘High-Hardness Palladium Alloyfor Use in Goldsmith and Jeweller’s Art andManufacturing Process Thereof’, Italian Appl.TO2006/0086; U.S. Appl. 2008/0,063,556

12 H. W. King, Bull. Alloy Phase Diagrams, 1982, 2, (4),527

13 F. M. Smits, Bell Syst. Tech. J., 1958, 37, 711

14 R. Hill, “The Mathematical Theory of Plasticity”,Oxford Classic Texts in the Physical Sciences, OxfordUniversity Press Inc, New York, U.S.A., 1998, 366 pp

15 “Nondestructive Testing Handbook”, Volume 7,“Ultrasonic Testing”, eds. A. S. Birks, R. E. Green,Jr. and P. McIntire, American Society forNondestructive Testing, Columbus, Ohio, U.S.A.,2007, 600 pp

16 “Precise Color Communication: Color Control fromPerception to Instrumentation”, Product Applications,Konica Minolta Sensing Inc, Japan, 1998: http://www.konicaminolta.com/instruments/knowledge/color/pdf/color_communication.pdf (Accessed on3rd July 2009)

17 S. Henderson and D. Manchanda, Gold Bull., 2005,38, (2), 55

18 Wieland Dental online: Products: Veneering Ceramic:http://www.wieland-dental.de/produkte/verblendkeramik/page.html?L=1 (Accessed on 3rdJuly 2009)

19 VITA Zahnfabrik website: http://www.vita-zahnfabrik.com/ (Accessed on 3rd July 2009)

Platinum Metals Rev., 2009, 53, (4) 197

The Authors

Julien Brelle graduated in MaterialsScience and Engineering from theÉcole Polytechnique Fédérale inLausanne, Switzerland (2005), with aspecialisation in metal matrixcomposites. He is now working as aResearch Engineer at PX Group, aproducer of metal products for thewatch, jewellery and medical sectors.He is mainly involved in the

development of speciality alloys and related processing.

After his Ph.D. in Physics (1986),Andreas Blatter led a research group atthe Institute of Applied Physics in Berne,Switzerland, and spent a year at the IBMAlmaden Research Center, U.S.A, as aVisiting Scientist. His research wasfocused on non-equilibrium laserprocessing, thin films and metallicglasses. Since 1996, he has been theR&D Director of PX Group. His main

research topics include precious metals and speciality alloysand their related technologies, as well as corrosion andbiocompatibility studies.

René Ziegenhagen received his degree inMaterials Science and Engineering fromthe École Polytechnique Fédérale inLausanne, Switzerland (1986). He wasthen involved in the research of preciousmetals and the development of newindustrial processes, such as metalinjection moulding and forging, beforejoining Cartier in the Richemont Group asa Senior Project Manager. At Cartier, his

main concerns include the quest for new materials and newproduction technologies to meet requirements and regulationson biocompatibility and ecotoxicity.