Evaluation of the mechanical properties of plasma sprayed hydroxyapatite coatings

The mechanical behaviour of plasma sprayed hydroxyapatite coatings was evaluated using Vickers hardness measurements on the cross-section as well as on the top surface of coatings. The effects of applied load, measurement direction and indent location on the microhardness were investigated. Indentation was performed on dense and porous areas of the coatings. After Vickers indentation on the polished cross-section, the surface roughness on the indenter horizontal impression was measured to establish any influence on local surface tropology. The data was statistically analysed using the Weibull distribution to examine their variability and distribution within the coatings. It was found that the effect of lower applied loads (50 and 100 gf) and higher applied loads (300 and 500 gf) showed two distinct trends concerning the microhardness, indent roughness, and Weibull modulus of microhardness throughout the coating thicknesses in the dense area. Top surface microhardness was higher compared to the cross-section microhardness for 100, 300 and 500 gf whereas equal for 50 gf. The statistical analyses showed that the Weibull modulus of microhardness was related to the applied load and indent position. The Weibull moduli of microhardness were high on the dense areas of the coatings.