Local and global fracture toughness of a flame sprayed molybdenum coating

This study deals with the failure of a flame sprayed molybdenum coating and its fracture mechanical characterization. The microstructure of the coating was examined by scanning electron microscopy. Local hardness and Young’s modulus values were measured by nanoindentation methods. X-ray measurements were used to estimate the grain size within the molybdenum splats. Special fracture mechanical tests were made to study the fracture mechanical behavior of cracks parallel and perpendicular to the coating-substrate interface. Indentation fracture toughness tests were made to examine the local fracture behavior of the material. Using these local toughness values and taking into account the microstructure, crack path, and mismatch effects it was possible to explain the global fracture toughness values.