Nanoindentation study of microplasma sprayed hydroxyapatite coating

The microplasma sprayed (MPS) hydroxyapatite (HAP) coating on surgical grade SS316L, is an emerging material for bio-ceramic based implant application involving higher reliability. For this purpose, a 200 μm thick MPS-HAP coating was developed on SS316L substrate and characterized by XRD, SEM and FE-SEM techniques. The local mechanical properties of the coating, e.g. nano-hardness and Youngʹs modulus were evaluated by nanoindentation technique carried out with a Berkovich indenter at various depths in the range of about 170–3000 nm on a polished top surface. The characteristic values of nano-hardness (1.5–5 GPa) and Youngʹs modulus (∼60–100 GPa) obtained through the application of Weibull statistics to the experimentally measured data revealed a strong indentation size effect (ISE). Attempts were made to explain the genesis of ISE on the basis of some existing and some new concepts.