Surface Texturing And Plasma Nitriding Treatment Of Titanium Alloy And Study Of Its Bio-tribological Properties

Titanium and its alloys are widely usually used as metallic bio-material for their excellent biocompatibility and corrosion-resistance.However,they were limited by their poor wear-resistance.Two approaches are usually used to reduce wear,one is to improve their mechanical properties such as hardness,the other is to improve their lubrication condition. The Surface hardness of titanium alloys can be enhanced by plasma nitriding while the lubrication condition can be improved by surface texturing in the form of changing the thickness of lubricating film.Several kinds of nitrding layers were prepared by plasma nitriding in various temperatures and keeping time.Surface phases of nitriding layer were analyzed by XRD and the microstructure and the thickness of nitride layers were observed by optical microscope. The hardness and modulus were obtained by nano-indentation tester and micro-hardness tester. The bonding strength between TiN compound layer and matrix was measured by the scratch tester.A set of optimal parameters of nitriding was obtained.Surface texturing with different dimple densities was achieved by pulse laser.The effect of dimple density on friction properties was investigated.At last,plasma nitriding was performed on the textured Ti6Al4V samples with optimal nitriding parameters and the tribological properties of texturing/nitriding samples were tested.The analysis results of nitriding layer show that the nitride layer with finer microstructure and high thickness value was obtained under the condition of 700℃,6h and its brittle compound layer is the thinnest.The critical scratch load of compound layer has reached 40N and its hardness,elastic modulus are all improved.After bio-tribological and wear property testing,the result shows the friction coefficient and wear rates of Ti6A14V was reduced by plasma nitriding in the counter pair of nitride Ti6Al4V/Al₂O₃,while the wear rate of UHMWPE pin and the friction coefficient in the wear couple of Ti6Al4V/UHMWPE was reduced by laser texturing.Furthermore,the optimal dimple density is 6.4%,where the wear rate of UHMWPE and the friction coefficient is reduced to the lowest.In the case of textured/nitride Ti6Al4V,all the friction coefficients and wear rates are lower in both counter pairs,which suggest that texturing/nitriding treatment can improve the tribological and wear properties in different counter pairs.