Yttria stabilized zirconia reinforced hydroxyapatite coatings

The low bonding strength between the coating layer and the substrate of pla sma sprayed hydroxyapatite (HA) coatings is the weakness in its application as a bio-medical prosthesis. In this study, 30 wt.% of yttria (8 wt.%) sta bilized zirconia (YSZ) has been used to reinforce the hvdroxyapatite coatin gs and to improve the bond strength of the HA coatings. Fine YSZ coated HA powders, which can minimize the effects of amorphorization and dissociation of HA by use of the much more thermal resilient YSZ particles to protect H A particles from the high plasma temperature, were prepared by using a cera mic slurry method. These powders are plasma sprayed to obtain the YSZ reinf orced hydroxyapatite coatings. The influences of plasma spraying energy on the phase composition, the HA relative phase ratio, microstructure and mech anical properties (bond strength, micro-hardness and fracture toughness) ha ve been studied. The results show that CaO, tri-calcium phosphate (TCP) and tetra-calcium phosphate (TTCP) are reduced significantly and more crystall ine HA transforms to amorphous calcium phosphate during plasma spraying wit h the addition of YSZ. The mechanical properties of the YSZ reinforced KA c oatings have thus been improved significantly. The bond strength, micro-har dness and the fracture toughness of the YSZ reinforced HA coatings increase with increasing plasma energy, associated with a greater content of CaO. T he results of heat-treated YSZ reinforced HA coatings show that the amorpho us calcium phosphate, TCP and TTCP in the as-sprayed coatings transform to the crystalline HA after heating at 800 degrees C for 2 h. (C) 2000 Elsevie r Science S.A. All rights reserved.