A refinement of the Al–Ni–Pt phase diagram

Abstract

Phase equilibria in the Al–Ni–Pt alloy system were specified. The total compositional region of the ternary phase diagram can coarsely be divided into three peculiar subregions. Above ∼70at.% Al this alloy system is characterized by the formation of complex binary and ternary phases. Between ∼40 and 70at.% Al the structures based on the CsCl-type configuration dominate, while below ∼40at.% Al the structures are based on the FCC (Ni, Pt) solid solution. The high-Al subregion was completed with the recently revealed binary high-temperature “Al3Pt” ξ-phase (Bmmb (No. 63), a=1.9718, b=1.6228, c=1.4266nm), which was found to extend up to 1.6at.% Ni. In the medium-Al subregion the ternary extension of the Al2Pt phase (β*) separates the compositional regions extending from Al3Ni2 and Al3Pt2. At 900–1100°C no complete separation was revealed between the compositional fields of the β-phase and β*. With decreasing temperature the total β+β* field shrinks around the compositional lines Al2Pt–Al2NiPt and AlNi–Al2NiPt. In the low-Al subregion the low-Ni limit of the γ♦-phase region, probably extending at low temperatures from Al3Ni5, was found to be below 4at.%.