New Co-based gamma-gamma ' High-temperature Alloys

New, cobalt-based alloys Containing ordered L1(2) precipitates have been investigated. With additions of Cr, Mo, Ni, Re, Ta, and V to the ternary Co-Al-W system, two phase gamma-gamma' microstructures have been established. Solidus and liquidus temperatures are 100 degrees C-150 degrees C higher than advanced nickel-based single-crystal alloys strengthened with the L1(2) 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 degrees 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.