Preparation of TiN compound layer by intermittent vacuum diffusion nitriding on Ti6Al4V titanium alloy

An intermittent vacuum diffusion nitriding (IVDN) treatment was used for the preparation of a TiN compound layer on the surface of the Ti6Al4V titanium alloy. The underlying microstructure evolution and the properties were thoroughly investigated. The IVDN process was performed alternately by using intermittent nitriding and vacuum diffusion. The TiN compound layer was formed on the surface discontinuously, layer by layer. As a result, the TiN compound layer was formed easily on the surface of titanium alloy compared to the vacuum nitriding. Dislocations were also generated in the adjacent α-Ti grains of the TiN compound layer. Interestingly, the induced dislocation defects possessed high free energy and contributed to the generation of the TiN grain nucleus, which facilitated the diffusion of the N atoms towards the inner substrate. The acquired results disclosed the intrinsic reason for the diffusion behaviour of N atoms. The Ti6Al4V titanium alloy was nitrided by using IVDN treatment at the temperature of 700 °C for 10 h. The surface microhardness reached 900–950 HV and presented continuous gradient change. In addition, the IVDN sample exhibited enhanced wear resistance properties than the un-nitrided sample. •TiN compound layer was prepared by intermittent vacuum diffusion nitriding.•The IVDN process can facilitate the N atoms diffusion and significantly improve the surface properties.•The fundamental reason for the diffusion behaviour of N atoms was identified by the relevant dislocation theory.