Effect of post-deposition heating temperature and the presence of water vapor during heat treatment on crystallinity of calcium phosphate coatings

In this study, radiofrequency sputtered calcium phosphate (CaP) coatings were evaluated after 1h post-deposition heat treatment at either 350°C, 400°C, 450°C, 500°C or 600°C in the presence or absence of water vapor. X-ray diffraction analyses indicated the as-sputtered coatings to be amorphous. With different post-deposition heat treatments used, in this study, crystallinity of CaP coatings was observed to be in the range of 0-68%. The 400°C and 450°C heat-treated CaP coatings in the absence of water vapor were poorly crystalline, exhibiting a crystallinity of 2±1%. In comparison to heat treatments at 450°C in the absence of water vapor, the presence of water vapor at 450°C heat treatment resulted in a significant increase in coating crystallinity. However, this effect was not observed at higher temperatures. A coating crystallinity of 60-68% was observed for coatings heat treated at 450°C in the presence of water vapor, and at 500°C and 600°C in the presence or absence of water vapor. In addition, increases in the degree of coating crystallinity were observed to be consistent with the increasing number of PO₄ peaks observed as a result of different post-deposition heat treatments. It was concluded that the presence of water vapor at 450°C post-deposition heat treatment significantly affect the crystallinity of CaP coatings, whereas an increase to temperature higher than 450°C and in the presence of water vapor has no significant effect on crystallinity.