PREFERRED ORIENTATION OF PLASMA-SPRAYED HYDROXYAPATITE COATINGS

The long-term stability of hydroxyapatite (HA) coatings has been under investigation for a long time. The evaluation of crystallinity is imp ortant since a relationship exists between the degree of crystallinity and the degradation by in vitro cellular reaction. However, the choic e of a representative peak to calculate the crystallinity is the subje ct of some controversy with the (211) peak and the (002) peak being th e most commonly analysed peaks. Thus the determination of the degree o f crystallinity may be biased due to preferred orientation (texture) i n the coatings. Therefore, the dependence of texture on thickness duri ng plasma spraying was investigated by the calculation of a texture co efficient (TC). Experiment results showed that the TC value of the (00 2) and (004) peaks increased with thickness and that the TC value in t he (211) peak decreased. This was caused by a high temperature gradien t during spraying and also the growth direction for a hexagonal system . It was observed that appropriately controlled temperature increases during annealing did not bring about notable texture to the recrystall ized crystallites. However, if the temperature gradient was high durin g annealing, notable (002) texture can exist. The effect of particle s ize on the texture was also investigated.