High-order additions to platinum-based alloys for high-temperature applications

Abstract

Platinum-based alloys are being developed with microstructures similar to nickel-based superalloys for potential high-temperature applications in aggressive environments. Since the chemistries of nickel and platinum are similar, Pt-based alloys can be made with gamma prime ~Pt 3 Al precipitates in a gamma (Pt) matrix. Currently, the Pt-Al-Cr-Ru system is one of the bases for developing Pt-based alloys, where Al allows the formation of the Pt 3 Al precipitate and also gives protection from the alumina scale formed, Cr provides oxidation resistance and stabilization for the L1 2 ~Pt 3 Al phase, and Ru provides solid solution strengthening in the (Pt) matrix.Four Pt-Al-Cr-Ru-V and two Pt-Al-Cr-Ru-V-Nb alloys were made, with compositions based on a quaternary alloy, ~Pt 82 :Al 12 :Cr 4 :Ru 2 , which had previously been identified as having optimum properties. Four of the ascast alloys had the targeted two-phase structure of ~Pt 3 Al and (Pt), and two were single-phase ~Pt 3 Al. Vanadium partitioned more to (Pt) than to ~Pt 3 Al. There was an improvement in hardness compared to the quaternary alloys. The best addition of V was ~15 at.%; higher additions resulted in brittle intermetallic phases of the Pt-V system. The effect of Nb could not be ascertained because of its high losses.