A study of the Al–Co–Pt alloy system

Abstract

Phase equilibria in the Al-rich part of Al–Co–Pt are studied at 1100 °C below 35 at% Pt, at 850 °C below 25 at% Pt and at 700 °C above 75 at% Al. The maximal ternary extensions of Al9Co2 and m-Al13Co4 were found to have achieved ∼4 and ∼2 at% Pt, respectively, those of Al4Pt and ξPt ∼8 and 3.5 at% Co, respectively. The ternary extension of Al2Pt was found to propagate up to at least Al57Co16Pt27. The formation of four ternary phases, designated χ, ε, D and æ, was revealed. The χ-phase (P31c, a = 1.21617 nm, c = 2.7115 nm) was revealed between ∼Al76.5Co11Pt12.5 and Al75Co4Pt21. The ε-phase (ε6-type, Pnma, a = 2.3116 nm, b = 1.6363 nm, c = 1.2150 nm) was revealed between ∼Al75Co17Pt8 and Al72Co7Pt21. The D-phase of the D2-type (∼0.8 nm periodicity in the specific direction perpendicular to quasiperiodic planes) is formed at elevated temperatures in a small compositional region around Al73.4Co23.3Pt3.3. The structure of an æ-phase forming around ∼Al71Co20Pt9 and exhibiting a complex powder XRD pattern was not specified.