Evaluation of residual stress in microplasma sprayed hydroxyapatite coating by nanoindentation

The evaluation of residual stress in bioactive hydroxyapatite (HAP) ceramic coating by nanoindentation technique has been attempted successfully for the very first time ever in the present work. The HAP coatings were deposited on surgical grade 316 L austenitic stainless steel and Ti–6Al–4V substrates by microplasma spraying (MIPS) process. The coatings had Ca/P ratio of 1.67 and were ∼80–90% crystalline. The results showed a residual compressive stress of ∼22 MPa for the MIPS-HAP coatings on the SS316L substrates. For the coatings deposited on the Ti–6Al–4V substrates, however, a residual tensile stress of ∼11 MPa was estimated. These data matched well with those obtained by XRD based technique. Thus, favorable data comparison provides further support to the efficacy of the nanoindentation based technique utilized in the present work for residual stress estimations.