Physics of hydroxyapatite plasma coatings on TiNi shape memory materials

The microstructure of hydroxyapatite (HAP) ceramics coatings on TiNi shape memory alloy substrates was investigated. From the point of view of adherence, these coatings posses higher strength than approx. 30 MPa. The three levels of power input parameters were applied during the spraying process (55, 50 and 45 V). At lower voltage, the prepared HAP coatings contained pure Ca10(PO4)6(OH)2 with a Ca/P ratio of 1.65. At the highest voltage (55 V), the transition phase Ca10(PO4)6(OH)0.5O0.75 was detected. The observed good metal/ceramic interface strength is given by the formation of chemical bonding and by the energy dissipation due to stress induced martensite formation (SIM) and/or martensite reorientation (RE) during stressing the investigated composite.