The Constitution of Alloys and Phase Diagram of the Ternary Al–Cr–Pt System at 50–100 at.% Pt. I. Solidus Surface and Isothermal Section in the Al–Cr–Pt System at 1350 C in the Range 50–100 at.% Pt

The results of high-temperature diffraction, metallography, X-ray diffraction, electron microprobe analysis, and differential thermal analysis are used to specify the constitution of the Al–Pt system in the near-equiatomic range. The solidus surface is constructed for the first time on the composition triangle, and the constitution of the isothermal section at 1350°C in the range 50–100 at.% Pt of the Al–Cr–Pt ternary system is specified. The solidus surface consists of six single-phase surfaces corresponding to the ternary τ1 phase (unknown structure), solid solutions based on platinum, and four binary phases existing in the Al–Pt system; nine ruled surfaces bounding two-phase volumes; and four isothermal planes forming invariant four-phase equilibria with participation of a liquid phase. When temperature decreases from subsolidus to 1350°C, stability of the phase based on the <(Al, Cr)Pt2> compound (low-temperature modification) increases substantially. This phase takes part in equilibria with other intermediate phases and with the Pt-based solid solution.