Effects of processing parameters and heat treatment on phase structure of the hydroxyapatite coating on pure Ti surface by laser cladding in-situ synthesis

Hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂, HA) coatings were prepared on pure Ti substrates by laser cladding (LC) in situ synthesis using mixed powders of CaCO₃ and CaHPO₄. In order to increase the amount of HA in the coatings, the effects of processing parameters including laser power and scanning velocity and heat treatment on the phase structure of the coatings were investigated. The results show that the coatings consist of large amount of tetracalcium phosphate (Ca₄(PO₄)₂O, TTCP) as well as a little HA, α-tricalcium phosphate (α-Ca₃(PO₄)₂, α-TCP), calcium oxide(CaO) and CaTiO₃ when the laser power is low. As the laser power increases, the amount of TTCP, HA and CaO in the coatings decreases gradually, and finally only α-TCP and CaTiO₃ remain. Compared with the laser power, the effect of scanning velocity on the phase structure of the coatings is much weaker. At the laser power of 400 W, there is no obvious difference for the phase structures at different scanning velocities and the main phase is always TTCP. It is found that the amount of HA can be increased greatly by heat treatment at 800°C for 5 h followed by furnace cooling, due to the total transformation from TTCP and α-TCP to HA.