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 1 h 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.