Effect of pre-treatment with fine particle peening on surface properties and wear resistance of gas blow induction heating nitrided titanium alloy

In order to develop a rapid nitriding process for titanium alloy at a low temperature, fine particle peening (FPP) was performed prior to gas blow induction heating (GBIH) nitriding. The surface microstructures of a Ti-6Al-4V alloy treated by FPP and GBIH nitriding were characterized using X-ray diffraction, optical microscopy, scanning electron microscopy, laser microscopy and micro-Vickers hardness testing. The results indicate that nitrogen diffusion into titanium during GBIH nitriding was accelerated by the pre-treatment with FPP, and a nitrided layer was formed on the surface of the Ti-6Al-4V alloy at a relatively low temperature (923 K), which grain coarsening and phase transformation did not occur and a nitrided layer was not formed only by GBIH nitriding. This is because a fine-grained surface layer was generated by the pre-treatment with FPP. Reciprocating ball-on-disk wear tests were carried out to examine the wear resistance of the prepared specimens. GBIH nitriding at a low temperature improved the wear resistance of the Ti-6Al-4V alloy following the pre-treatment with FPP, due to the formation of a hard nitrogen compound layer at the surface. The results show that the proposed surface treatment process was effective at modifying the surface properties of a titanium alloy at a low temperature and within a short span of time while avoiding grain coarsening and phase transformation.