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Abstract
Abstract
In the present paper, the authors report the observation of pronounced nanohardness anisotropy in a phase pure, 230 μm thick microplasma sprayed bioactive hydroxyapatite coating on a surgical grade SS316L substrate. The coating had a very heterogeneous microstructure with a large number of macrocracks, microcracks, inter- and intrasplat cracks, intra- and interlamellar macro- and micropores, etc. The nanohardness values measured by the nanoindentation technique at various loads in the range 10-1000 mN on cross-section was usually higher than those measured on plan-section of the coating. This anisotropy of nanohardness could be attributed to the larger volume per cent porosity as well as higher spatial density of planar defects, pores and cracks on plan-section over those in the cross-section. In addition, the dependence of hardness on porosity of hydroxyapatite was studied in detail.