Microstructure and oxidation behavior of Co–Cr–Ta ternary alloys

Abstract

The improvement of oxidation resistance of alloys is one of the key points to develop components for ultra-high temperature applications. The formation of a CrTaO4 oxide layer has attracted attention because of its thermal stability and good protection against oxidation above 1000 °C where more commonly used protective oxide layers such as Cr2O3 show their limits. This study investigates the microstructure evolution and oxidation resistance of the Co-Cr-Ta ternary alloys in comparison to the Calphad predictions. The Co-Cr-Ta samples tested here are composed of an FCC Co-rich phase and a C15 laves phase, and an increase of Cr content was linked to the formation and growth of an additional σ phase. Thermogravimetric analysis, together with the isothermal oxidation tests in air at 1200 °C proved that alloys exhibited good oxidation resistance formed a continuous CrTaO4 layer. Also, optimization of Co-Cr-Ta composition with improved oxidation resistance was attempted using data-driven strategy and the results demonstrated the potential of such approach for the future of alloy design.