Microstructure evolution and vacuum tribological properties of surface nitriding layer on a TiZrAlV alloy fabricated by laser nitriding

The evolution mechanisms of phase, microstructure and vacuum tribological properties for Ti–20Zr-6.5Al–4V under different laser beam diameters have been investigated by using laser surface nitriding (LSN). Results indicate that all the LSN samples are mainly composed of α phase and Ti(Zr)N phase, besides, Ti(Zr)N0.3 phase can also be obtained, which is based on a change in the ratio of liquefied nTi(Zr)/nN. With the laser beam diameter decreasing from 3 to 1 mm, the thickness and density of nitride layer increase significantly, which contribute to the increased energy input density. EPMA results indicate that the nitrides mainly exist in the form of Ti(Zr)xNy, and the distribution transformation of Al and V elements has also been analyzed. As the laser beam diameter decreases, the coefficient of friction decreases, and the sample with 1 mm laser beam diameter display the lowest coefficient of friction (∼0.333). Also, the wear volume and wear rate of the LSN sample with 1 mm laser beam diameter are the smallest, which are both reduced by about 40% compared with the original sample. After analysis, the wear pattern of the LSN samples can be confirmed as the composite of adhesive wear and abrasive wear. Nitride dendrites can form a support skeleton between the wear surface and friction pair, which can significantly reduce the wear of LSN sample surface. The results of this work prove the feasibility of improving the surface wear resistance of Ti–20Zr-6.5Al–4V by LSN.