Characterisation of the oxidation and creep behaviour of novel Mo-Si-Ti alloys

Abstract

The oxidation and creep behaviour of novel eutectic-eutectoid Mo-Si-Ti alloys were studied and compared to previously investigated entirely eutectic Mo-20Si-52.8Ti (at%) and eutectoid Mo-21Si-34Ti reference alloys [Schliephake et al. in Intermetallics 104 (2019) 133–142]. While the latter reference alloys showed either outstanding oxidation behaviour in the temperature range of 800 to 1200 °C (eutectic alloy) or reasonable creep resistance (eutectoid alloy), a combination of both was successfully achieved in a Ti-rich alloy variant (Mo-21Si-43.4Ti). The ubiquitous catastrophic oxidation (“pesting”) of Mo-based alloys at 800 °C is suppressed in this alloy and reasonable oxidation resistance at higher temperatures is observed. For the first time, the unexpected oxidation resistance of the alloys exhibiting eutectic volume fractions of more than 50 vol% is rationalised by a systematic deconvolution of mass gain by scale formation and mass loss by evaporation of volatile species. Furthermore, creep is revealed to be based on similar creep mechanisms throughout the alloy series. Therefore, the observed improvement in creep resistance of the pesting-resistant Ti-rich alloy variant over the eutectic alloy is attributed to the decreasing homologous temperature when testing both at 1200 °C.