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Phase Diagram Evaluations: Section II

Al-Pt-Ti (Aluminum-Platinum-Titanium) V. Raghavan

An update of this ternary system by [2005Rag] briefly reviewed the experimental isothermal sections of [2001Hil] at 1350 °C and of [2000Din] at 950 °C. Recently, [2009Yan] clarified the phase relationships at 950 °C in the region around the Ti(Pt, Al)2. Pe rc e nt Tit an ium

inu

Ato mi c

t Pla nt rce Pe m

In the partial phase relationships determined by [2009Yan], the only binary phases that appear are: Ti3Al (D019, Ni3Sn-type hexagonal, denoted a2), and TiAl (L10, AuCu-type tetragonal, denoted c). For a summary of the other binary phases, see [2005Rag].

c mi Ato

Binary Systems

Ternary Compounds [2000Din] reported three ternary compounds in this system: s1 (fcc) around the composition Ti26Pt7Al67, s2 (filled Mn23Th6-type cubic) around the composition TiPtAl2 and s3 (MgZn2-type hexagonal) around the composition Ti44Pt14Al42. Extension of the work of [2000Din] by [2009Yan] showed that s3 in annealed samples is a superstructure based the MgZn2-type Laves phase, with pffiffiffi a ¼ 3
aMgZn2 and c ¼ cMgZn2 , space group P63/mcm, Nb(Ir,Al)2-type. The MgZn2-type phase was found only in as-cast samples. It disappeared on annealing. A fourth ternary phase s4 (TiPtAl) with the ordered Ni2In-type (ZrBeSi-type) structure was found by [2009Yan], with lattice parameters of a = 0.43925 nm and c = 0.54844 nm. The site occupancies and interatomic distances were determined by [2009Yan] for both s3 and s4 phases.

Partial Isothermal Section at 950 °C With starting metals of 99.9+% purity, [2009Yan] arcmelted under Ar atm 12 ternary alloys around the s3 composition. The alloys were annealed at 950 °C for 10 days and quenched in water. The phase equilibria were studied with optical microscopy, electron probe microanalysis, x-ray powder diffraction, and x-ray single-crystal diffraction. The partial isothermal section at 950 °C

Atomic Percent Aluminum

Fig. 1 Al-Pt-Ti partial isothermal section at 950 °C [2009Yan]

constructed by [2009Yan] is shown in Fig. 1. The s3 phase is present with a small homogeneity range around 25 at.% Pt, with a Ti-range of 33.5-36 at.%. It forms tie-lines with s2 and s4 phases. The composition of s1 phase falls outside the range investigated by [2009Yan].

References 2000Din: J.J. Ding, P. Rogl, B. Chevalier, and J. Etourneau, Structural Chemistry and Phase Relations in Intermetallic Systems Ti-(Pd,Pt)-Al, Intermetallics, 2000, 8, p 1377-1384 2001Hil: P.J. Hill, L.A. Cornish, P. Ellis, and M.J. Witcomb, The Effects of Ti and Cr Additions on the Phase Equilibria and Properties of (Pt)/Pt3Al Alloys, J. Alloys Compd., 2001, 322, p 166-175 2005Rag: V. Raghavan, Al-Pt-Ti (Aluminum-Platinum-Titanium), J. Phase Equilib. Diffus., 2005, 26(2), p 188-189 2009Yan: X. Yan, A. Grytsiv, P. Rogl, H. Schmidt, G. Giester, A. Saccone, and X.Q. Chen, Laves Phases in the Ternary Systems Ti-{Pd,Pt}-Al, Intermetallics, 2009, 17, p 336-342

Journal of Phase Equilibria and Diffusion Vol. 31 No. 1 2010

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