Design And Optimization Of Plasma Sprayed Graded Hydroxyapatite Coating

The plasma sprayed hydroxyapatite coating on the titanium alloy surface faced contradictory problems between the mechanical properties and the biological performance requirements in practical application.The gradient coating structure can effectively solve the problem.In this paper,firstly by controlling the melting state of the particles and adjusting the temperature of the substrate,a gradient coating consisted of upper loose layer and a dense lower layer.Gradient coatings with different thickness ratios were designed and prepared.The microstructure and mechanical properties of the layer were studied.And the HA gradient coating fatigue performance and its influencing factors were preliminarily studied.Firstly,operational window was found for controlling the melting state of HA pacticle.Several typical particle melting states were used,and coating with loose structure and dense structure were prepared by adjusting melting state.The crystallinity and bonding strength of the coating were improved by means of substrate heating,wherein the porosity of the porous structure coating reached 8.8%,which also contained a certain amorphous phase as the upper coating.The bonding strength of the dense structure coating reaches 30.62 MPa,the crystallinity reaches 71.43%,the microhardness reaches 320.79 Hv,it has good comprehensive performance.The gradient coating with different thickness ratios was prepared using the above two kinds of coatings,and their microstructure and mechanical properties were tested.It was found that no CaO phase was detected on coating surface.The strength of the gradient coating decreases as the proportion of the loose structure coating increases.To test the HA coating fatigue performance,a fatigue test platform for was set-up.The result showed that the microstructure and thickness of the coating have an important influence on the fatigue performance of the coating.The fatigue performance increased with the decrease of the fraction of loose structural coatings.In the gradient coating with a thickness of 200?m,the bonding strength of the hydroxyapatite gradient coating with porosity ratio of 1:3 is 36.23 MPa,and the crack density only increases by 2.81% after test,showing a good comprehensive performance.