Complex Intermetallics in the Al-Rich Part of Al-Pd-Cr System

Abstract

The Al-Pd-Cr alloy system was investigated at 680 to 990°C in the compositional range above 60 at.% Al. The binary Al-Cr , μ and phases dissolves up to 1 at.% of Al, the η-phase extends up to 2 at.% of Pd and the 2-phase extends up to 3 at.% of Pd, respectively. The binary Al-Pd -phases dissolves up to 3 at.% of Cr and -phase up to 4 at.% Cr. Close to the high-Pd limit of the -range a ternary phase is formed between about Al78Pd4Cr18, Al77Pd10Cr13 and Al74Pd7Cr19. Its structure is orthorhombic with lattice parameters: a = 1.47, b = 1.24 and c = 1.25 nm, resembling the lattice parameters of the high-temperature Al3Mn phase. A hexagonal structure with a = 1.77 and c = 1.25 nm resembling Al-Ni(Cu)-Cr ζ-phase [1-3] was revealed around Al81.5Pd1.5Cr27 and another hexagonal structure with very close lattice parameters around Al73Pd11Cr16. Another ternary phase was found in 970°C around the Al77.5Pd1.5Cr21 composition. It has orthorhombic structure with a = 1.24, b = 3.46 and c = 2.04 nm resembling the ternary -phase in Al-Ni-Cr. An additional orthorhombic phase with a = 2.48, b= 3.87 and c = 2.04 nm was found to be formed between about Al82Pd4Cr14, Al79Pd4Cr17 and Al79Pd9Cr12.