In-situ formation of textured TiN coatings on biomedical titanium alloy by laser irradiation.

The Ti-35Nb-7Zr-5Ta (TNZT) alloy has received much research attention among the biomedical titanium alloys for its low Young's modulus and outstanding biocompatibility. This paper provided an innovative technique for improving the wear and corrosion resistance of the TNZT alloy, by developing in-situ formed TiN coatings on the surface of the TNZT alloy through laser irradiation. The new technique combines the advantages of laser surface texturing and laser gas alloying. The experimental results showed that the phase compositions of the textured TNZT samples were β-Ti, martensitic α'' phase and TiN after laser texturing in N2. The diameter of the surface dimples increased, when the width of laser pulse increased from 0.3ms to 0.7ms, and the depth decreased accordingly. In comparison to the samples without treatment, both the wear rate and the frictional coefficient of the TNZT samples with textured TiN coatings decreased significantly. The surface dimples served as micro-hydrodynamic bearing, which were able to keep liquid inside. As a result, the sample with a width of pulse of 0.3ms treated in N2 exhibited the lowest wear rate of 0.025 × 10-2m3/Nm, while the value of the sample without treatment was 0.351 × 10-2m3/Nm. The TiN contained surface coatings also exhibited higher electrochemical impedance, higher corrosion potential and lower corrosion current density.