Effect of post vacuum heating on the microstructural feature and bonding strength of plasma-sprayed hydroxyapatite coatings

Plasma-sprayed HA coatings (HACs) on Ti−6Al−4V substrate with post vacuum heating treatment were employed to improve the properties of HACs. The heating temperatures are 400, 500, 600, 700 and 800 °C. According to the experimental results, post vacuum heating treatment could improve the average bonding strength and the minimum strength of HACs by using Weibullʹs reliability analysis. The HACs with 600 °C vacuum heating shows the highest strength value of all. On the other hand, the index of crystallinity (IOC) of heat-treated HACs increases and impurity phase content decreases with increasing heating temperature. The crystallization during vacuum heating also leads the variation in thermal expansion coefficient and the volume contraction of heat-treated HACs, especially at higher than that of 600 °C vacuum heating. Therefore, the volume contraction induces apparent and concentrated large cracks and reduces the bonding strength of heat-treated HACs.