Microstructure, oxidation resistance and high-temperature strength of γ′ hardened Pt-base alloys

Starting from the base composition with 12 at.% Al, 6 at.% Cr, 5 at.% Ni and Pt balance, precipitation hardened Pt–Al–Cr–Ni alloys with additions of 2 at.% Mo, Re, Ru and W, respectively, were investigated. After homogenization heat treatment and air cooling, all five-component alloys show a bimodal distribution of γ′ precipitates. Along with a fraction of fine γ′ precipitates embedded in a Pt-rich matrix, some coarse primary γ′ particles are observed. Mo, Re and W additions increase strength above 1000 °C, whereas Ru has no beneficial effect on strength. W increases the γ′ volume fraction most effectively, however, the oxidation resistance is worsened dramatically by W additions. The Re-containing alloy shows the best resistance against γ′ growth and coarsening during long-term ageing.