Effect of saturated steam treatment on the crystallinity of plasma-sprayed hydroxyapatite coatings

•The crystallinity of HA coatings can be increased greatly at a low temperature with the existence of water.•Treatment temperature has a more pronounced effect on the crystallinity than the holding period.•Nanocrystallites of HA can form in the coatings when processed with suitable saturated steam treatment technology.

Hydroxyapatite (HA) coatings were treated with saturated steam at various temperatures and holding periods. The results show that during plasma spraying a large amount of HA decomposes or transforms to amorphous calcium phosphate (ACP), which results in low crystalline HA coatings. After treated with saturated steam the crystallinity of the HA coatings increases significantly. The relative index of crystallinity indicates that the process temperature together with the corresponding steam pressure has a more pronounced effect on HA crystallinity than the holding period. In addition, HA nanocrystallites form as a result of this process.