Gas tunnel type plasma spraying of hydroxyapatite coatings

A crystalline hydroxyapatite (HA) coating was deposited using gas tunnel type plasma spraying at different spraying distances. In this study, the microstructure, adhesion and microhardness of the resulting coatings were investigated to clarify the effect of the spraying distance on the features of sprayed coatings. The results showed that the spraying distance greatly affects the microhardness, adhesion, and crystallinity of the sprayed HA coatings. Microhardness value was increased as the spraying distance was decreased, mainly due to the formation of dense coating with lower porosity. Adhesion was increased, as the spraying distance was decreased due to a good mechanical bonding between the first apatite layer and the substrate. X-ray diffraction patterns of HA coatings showed the formation of high crystalline apatite coating at short spraying distance