Multidimensional microscopic investigation of oxidation-induced hollow cavities in a Co–Al–W–Ti–Ta alloy nanotip by electron tomography

Abstract Spallation of thermal oxidation-induced cavities is the main failure mode in CoAl-based alloys, and the γ/γ′ phase structure in Co–Al–W–Ti–Ta alloys has a propensity to form oxide cavities. Multidimensional investigations were carried out herein on irregular oxide cavities by analytical microscopy, including electron tomography and energy dispersive X-ray spectroscopy techniques, to disclose the time-resolved three-dimensional morphological structure and elemental distributions. The alloy nanotip was exposed isothermally in air at 350 °C, and its oxidation evolution was characterized and analysed. The size and quantities of cavities in the γ phase were larger than those in the γ′ phase, which was attributed to the higher content of cobalt in the γ phase than in the γ′ phase. Different migration rates between cobalt outward and aluminium inward prompted the formation of cavities between the outer and inner layers.