Instrumented spherical micro-indentation of plasma-sprayed coatings

The mechanical response of plasma-sprayed coatings is studied by recourse to instrumented spherical micro-indentation. It is shown that the elastic moduli of the coatings can be determined in a more reliable and reproducible manner with instrumented spherical indentation than prior (Knoop) indentation methods, while at the same time minimizing damage to the coating during indentation. The results show that the values of the elastic moduli, E, of air plasma-sprayed (APS) materials are much lower than those of vacuum plasma-sprayed (VPS) materials. The VPS deposits are more homogeneous at a microstructural level as splat formation, microcracking and the development of oxide scales are suppressed. Such homogenization increases the value of E to the point where it becomes similar to that of fully dense materials. Larger amounts of inelastic flow occur in APS deposits as compared with VPS deposits. This flow is associated with fracture and sliding of splats.