Physical-metallurgy properties of hydroxyapatite plasma coating on TiNi shape memory alloy

Microstructure of plasma sprayed ceramic coatings on a TiNi shape memory al loy substrate was investigated. Hydroxyapatite (HAP) or so called "duplex" TiNi/TiO2/TiO2 + HAP/HAP coatings were applied. From the adherence point of view, the interface TiNi/HAP possesses higher strength than 30 MPa. In the case of duplex coating, the mixed TiO2 + HAP region was found as critical and the failure was detected at strength lower than 30 MPa in this region. Hence, the hydroxyapatite coating with higher strength reliability and rela tively simple process technology was preferred. The observed favourable strength of metal/ceramic interfase was attributed to the energy dissipation due to stress induced martensite formation (SIM) and/or martensite reorientation (RE) before and during a failure. Grain siz e of the deposited HAP particles influences porosity and precipitation proc esses in ceramics.