Finding new phases for precipitate-hardening in platinum and palladium alloys

Precipitate hardening (via ordered phases rather than phase separation) of platinum and palladium can be effective even with a small volume-fraction of the ordered phase [M. Carelse, C.I. Lang, Scripta Materialia 54 (7) (2006) 1311]. The approach is particularly well suited to jewelry alloys which must be 95 wt.% pure and where ordered phases of 7:1 or 8:1 stoichiometries can be formed. We examined eight systems where this approach may lead to new applications: Pt–Al, Pd–Al, Pd–Cu, Pd–Mg, Pd–Nb, Pt–Mo, Pt–V, and Pd–V. In each system, using first-principles-based cluster expansion modeling, we have identified high stoichiometric-ratio phases that are stable. Furthermore, using Monte Carlo simulations, we have estimated the order–disorder transition temperatures to identify experimentally feasible phases. In three cases, the computational results are verified by experiment, suggesting that the remaining predictions are likely to be useful as well.

► We have identified additions to Pt- and Pd-based alloys may increase performance.
► But hallmarking standards require no more than 5 wt.% additions.
► We found new stable phases that to form precipitates even in small additions.
► We modeled the new phases thermodynamically to identify potentially useful cases.