Surface nitrocarburizing of Ti-6Al-4Â V alloy by YAG laser irradiation

The surface nitrocarburizing of a Ti-6Al-4 V alloy was performed by YAG laser irradiation in a nitrogen and argon mixed gas flow. The optimal condition was investigated by varying the volume ratio of nitrogen in the mixed gas. The microstructure, chemical composition, hardness and wear behavior of the nitrocarburized Ti-6Al-4 V alloy were analyzed. The results indicated that after surface nitrocarburizing, a double-layer composite film, for which the up layer was a Ti(C, N) layer and the down layer was a TiN0.3 layer, formed on the surface of the Ti-6Al-4 V alloy. The observed cross sectional microstructure can be clearly divided into three parts: film, heat affected zone (HAZ) and unaffected substrate. When treated in a mixed gas flow of 70 vol% N2 and 30 vol% Ar, the optimal conditions were obtained with an average nano-indentation hardness of 41.6 GPa and a wear volume loss of approximately 22 times less than that of the non-treated substrate.