Investigation on non-uniform oxidation behaviour in dendritic and interdendritic regions in a single-crystal Ni-based superalloy

Oxidation behaviour of a third-generation Ni-based single-crystal superalloy was investigated at 900 and 1050°C by scanning electron microscopy, X-ray diffraction and electron probe microanalysis. The alloy showed non-uniform oxidation behaviour in dendritic and interdendritic regions. Re and W were enriched in the dendritic region, leading to the formation of Re₂O₇ and WO₃, which were easy to volatile. As a result, the film in the dendritic region was loose and contained number of pores, providing an easy path for the outward diffusion of cations and inward diffusion of O²⁻. Moreover, the high Pilling–Bedworth ratio of Ta₂O₅ accumulated in the dendrite region, resulting in the occurrence of cracking and cyclic oxidation behaviour. Eventually, the synergistic effect between the loose oxide film and cyclic oxidation leads to more severe oxidation behaviour in dendritic regions of the alloy compared to interdendritic regions.