Alloying effects in polycrystalline γ′ strengthened Co-Al-W base alloys

A polycrystalline hot working ingot metallurgy processing route for γ/γ′ Co-Al-W superalloys has been developed. Based on Co-7Al-7W (at%), substitutions of Mo, V, Ti, Ta, Ni, Si, Fe and Cr were examined. The γ′ solvus was found to follow the same trends as those exhibited by alloys with higher γ′ fractions considered by other investigators. Excessive Cr additions were found to lead to discontinuous coarsening and eventually, the loss of the γ′ phase from the microstructures observed. Ni additions were examined, with some success, and found to restore the γ′ phase and raise the solvus temperature. It was found that the addition of 13 at.% Cr improved the oxidation resistance at 800 °C by over 40 times.