Abstract
Microstructure of plasma sprayed ceramic coatings on a TiNi shape memory alloy 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 relatively simple process technology was preferred. The observed favourable strength of metal/ceramic interface was attributed to the energy dissipation due to stress induced martensite formation (SIM) and/or martensite reorientation (RE) before and during a failure. Grain size of the deposited HAP particles influences porosity and precipitation processes in ceramics.

Key words
ceramic plasma coating, interface metal/ceramic properties, duplex coating, shape memory alloy, adhesion strength

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