Effects of gas blow velocity on the surface properties of Ti-6Al-4V alloy treated by gas blow IH nitriding

In this study, the effects of gas blow velocity on the surface properties of a Ti-6Al-4V alloy treated by a gas blow induction heating (IH) nitriding system were investigated. The surface microstructure of the treated specimens was characterized using scanning electron microscope and X-ray diffraction. In addition, micro-Vickers hardness and nanohardness were measured and reciprocating wear tests were conducted to evaluate the modified surface layers. The results showed that the nitriding of a specimen was facilitated by using a smaller gas blow nozzle. Incorporating the smaller nozzle resulted in an increase in gas blow velocity, which in turn increased the IH power and the temperature inside a specimen, thus accelerating the nitrogen diffusion. Moreover, nitriding at a lower treatment temperature (973 K) was achieved by increasing gas blow velocity. The specimen nitrided at a lower temperature with a high gas blow velocity exhibited better wear resistance than the untreated specimen. This process also inhibited transformation to an acicular α phase, which involves apparent grain coarsening.