III - Stabilité mécanique des couches d’oxydes formées lors de l’oxydation de superalliages monocristallins

Mechanical stability of oxide layers resulting from single-crystal superalloys oxidation

Abstract

Mechanical stability of oxide layers resulting from several commercial single-crystal superalloys (AM3, CMSX4 and MC2 modified by Si and Hf addition) oxidation in oxygen at 1100°C was investigated.

These layers are usually under compressive stresses as a result of differences in thermal expansion coefficients between oxide and metal. Thus, oxide spallation occurs regardless of cooling rate. The critical temperature drop to initiate spallation (ΔT) depends on the oxide layer thickness (ξ) and the interfacial rupture energy (γ_F). In fact, for a given oxide/metal couple, [math] is constant (EVANS and LOBB model). AM3 and CMSX4 alloys follow this model while MC2 modified alloy has a diffe rent behavior. Addition of Si and Hf improves scale adherence according to a mechanism not yet investigated.