Estimation of plastic anisotropy in Ni-5% Al coatings via spherical indentation

Computational models were performed to simulate spherical indentation on the free edge of a material exhibiting anisotropy in plastic behavior. Anisotropy was correlated with out of plane sub-surface deformation fields that persisted after unloading. It was further shown that some aspects of the fields were sensitive only to this anisotropy, and insensitive to yield strain, hardening behavior, elastic anisotropy, or in-plane residual stresses, suggesting an indentation-based method of property measurement. Results from the simulations were compared with Brinell indents on bonded interface specimens of Ni-5% Al coatings deposited by various spray techniques. The coatings applied via air plasma spray, high velocity oxy-fuel and cold spray were found to have normal to in-plane yield ratios of 1.15, 1.30 and 0.60, respectively. Micromechanical arguments are provided for the differences in anisotropy.