Effects of Processing Parameters and Heat Treatment on Phase Structure of the Hydroxyapatite Coating on Pure Ti Surface by Laser Cladding in-situ Synthesis

Abstract:

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 oC for 5 h followed by furnace cooling, due to the total transformation from TTCP and α-TCP to HA.

Key words:processing parameters; heat treatment; laser cladding; hydroxyapatite; tetracalcium phosphate