Laser Nitriding Of Titanium Alloy And Hydroxyapatite Layer Deposition On The Surface

Laser gas nitrided (LGN) layer was fabricated on the surface of the Ti6A14V alloy after irradiated by a continuous wave Nd-YAG laser in N₂ environment to improve the abrasion resistance, corrosion resistance, biocompatibility and bioactivity of the material. Chemical method was used for the deposition of apatite layer. SEM, XRD, EDAX, electrochemical and micro sclerometer were carried out to study the microstructure, phase, composition, corrosion properties and microhardness. The ability of deposition of bone-like apatite and biological activity including hemolysis and cytotoxicity were also investigated before and after laser surface modification.Dense TiN strengthedned metal base composite layer was obtained on the surface of titanium with proper laser irradiation parameters. The average thickness of the layer is 400μm, distributing by graduation. The outmost surface is ceramic TiN with thickness 2～3μm. Hardness curves indicated that the microhardness of Ti6A14V alloy was increased from HV350 to HV1000. The hardness of the surface was highest and hardness changed with the modified layer thickness. Test results indicated that there was a good metallurgical bonding between the modification layer and the Ti6A14V alloy substrate. The composition of the interface is homogeneous and free of cracks. The electrochemical test in the simulated body fluid (Hank's solution) at 37¨showed that the corrosion reaction can be inhibited effectively by means of laser gas nitriding. The corrosion potential was increased from -0.23V to -0.17V. Thus the release of poisonous elements of Al and V were inhibited.Compared with substrate, the hemolytic rate of LGN Ti6A14V alloy was decreased from 3.9% to 1.14%, which is less than 5%, meeting the requirement of biomedical materials. The cytotoxicity level was increased from 1 to 0.Apatite layer, which has the Ca/P atomic ratio of 1.53, was obtained on the surface of the samples after biomineralization. Laser gas nitriding improved the bioactivity of Ti6A14V used as biomedical material. The ability of deposition of hydroxyapatite is enhanced.