A study of the Al-Co-Cr alloy system

The Al-Co-Cr alloy system was studied by scanning and transmission electron microscopy, powder X-ray diffraction and differential thermal analysis. Partial isothermal sections of Al-Co-Cr were determined at 1150, 1100, 1000, 900, 800 and 700 °C. The region of the βCo-phase extends towards γCr up to ∼18.5 at.% Cr and ∼57 at.% Al. The solubility of Cr in HCo, MCo and Al9Co2 reaches ∼11.0, 6.0 and 1.5 at.%, respectively, while θCr-phase, μCr and γCr dissolve up to ∼3.0, 1.0 and 6.0 at.% Co, respectively. The ηCr phase extends up to ∼ Al74.5Co4Cr21.5. No ternary phases were revealed in Al-Co-Cr at 1100-1150 °C. Five ternary phases designated ζ1, O1, ν, ϕ and π were revealed. The ϕ-phase (P21 or P21/m, a ≈ 1.35, b ≈ 1.27, c ≈ 1.45 nm, β ≈ 100°) is formed between ∼ Al70.5Co8.0Cr21.5 and Al77.0Co7.5Cr15.5. The π-phase (C-center monocl., a ≈ 3.28, b ≈ 1.24, c ≈ 2.43 nm, β ≈ 108°) is formed between ∼ Al75.0Co11.5Cr13.5 and Al79.0Co11.5Cr9.5. The O1-phase (B-center orth., a ≈ 3.318, b ≈ 1.255, c ≈ 2.412 nm) is formed in a small region around ∼ Al72.5Co5.0Cr22.5. The ν-phase (P63/m, a = 4.0630, c = 1.2496 nm) is formed between ∼ Al75.5Co5.5Cr19 and Al81Co5.0Cr14. The ζ1-phase (R3¯or R3, a ≈ 1.75, c ≈ 8.0 nm) is formed in a small region around ∼ Al80.5Co3.5Cr16.0.