A study of phase equilibria in the Al–Pt–Rh alloy system

• The Al–Pt–Rh phase diagram was studied at 810–1100 °C.
• The majority of binaries widely extend along about constant Al.
• The Al2Pt phase extends toward about the Al2PtRh composition.
• The ternary χ-phase is formed between Al75Pt21.5Rh3.5 and Al76Pt6.5Rh17.5.
• The ternary C2-phase is formed around Al69Pt9Rh22.

Phase equilibria in Al–Pt–Rh were studied in the whole compositional range at 1100 °C and above 50 and 70 at.% Al at 900 and 810 °C, respectively. The continuous region of the fcc γ solid solutions extends from the Pt–Rh terminal up to 15 at.% Al. At elevated temperatures the isostructural AlRh and high-temperature AlPt β-phases probably form a continuous compositional region. Wide ternary extensions of the phases Al4Pt, Al21Pt8, low-temperature AlPt (μ), Al3Pt5, AlPt2 and AlPt3 were revealed along approximately constant Al concentrations. In contrast, the dissolution of Rh in the Al2Pt phase (β∗) results in a visible decrease of its Al concentration. The Al–Rh C-phase and ε-phase dissolve up to 15 and 18 at.%. Pt, respectively. Only the ε6 structural variant was observed at ternary compositions. The formation of the ternary χ-phase (P31c, a = 1.2201, c = 2.7243 nm for Al75.5Pt16.9Rh7.6) was revealed in a compositional region between ∼Al75Pt21.5Rh3.5 and ∼Al76Pt6.5Rh17.5. The other ternary C2-phase (Fm  3¯, a = 1.5419 nm) was revealed around Al69Pt9Rh22.