The effects of Ta additions on the phase compositions and high temperature properties of Pt base alloys

Pt–Al alloys attain high creep strength by precipitation hardening of the face-centred cubic matrix phase by the L12 ordered intermetallic γ′ phase Pt3Al (analogous to Ni base superalloys). Along with superior environmental resistance these alloys have a potential as high-temperature materials. In this investigation the effect of Ta on strength, phase composition, lattice misfit and γ′ volume fraction are assessed. Starting from the composition with 12 at.% Al, 5 at.% Cr and Pt balance, precipitation hardened Pt–Al–Cr–Ta alloys were analysed. Ta contents higher than 9 at.% lead to a decrease of γ′ volume fraction. Ta increases the lattice parameters of both phases, but decreases the lattice misfit. By substitution of Al by Ta more Al partitions to the γ′ phase, while Ta shows an inverse tendency.