High-temperature γ (FCC)/γ′ (L12) Co-Al-W based superalloys

Interim results from the development of a polycrystalline Co-Al-W based superalloy are presented. Cr has been added to provide oxidation resistance and Ni has then been added to widen and stabilise the γ ′ phase field. The alloy presented has a solvus of 1010 °C and a density of 8.7 g cm −3 . The room temperature flow stress is over 1000 MPa and this reduces dramatically above 800 °C. The flow stress anomaly is observed. A microstructure with both ∼ 50 nm γ ′ produced on cooling and larger 100–200 nm γ ′ can be obtained. Isothermal oxidation at 800 °C in air for 200 h gave a mass gain of 0.96 mg cm −2 . After hot deformation in the 650–850 °C temperature range, both anti phase boundaries (APBs) and stacking faults could be observed. An APB energy of 71 mJ m −2 was measured, which is comparable to that found in commercial nickel superalloys.

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