New Co-based γ-γ′ high-temperature alloys

New cobalt-based alloys containing ordered L12 precipitates have been investigated. With additions of Cr, Mo, Ni, Re, Ta, and V to the ternary Co-Al-W system, two phase γ-γ′ microstructures have been established. Solidus and liquidus temperatures are 100°C–150°C higher than advanced nickel-based single-crystal alloys strengthened with the L12 phase. An anomalous rise in flow stress with temperature is observed. Single crystals have been solidified and partitioning during solidification is limited in the ternary system, suggesting a high resistance to convective instabilities. Oxidation at 900°C results in the formation of cobalt oxide. Following oxidation, an inner layer of Al2O3 is observed in uncoated Cr-containing alloys and Cr2O3 is observed in alloys subjected to chromization.