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

In the present study, gas blow IH (Induction Heating) nitrided specimens were produced under variable nitrogen gas blowing velocities. This was done to investigate the effects of nitrogen gas velocity on the surface properties of Ti-6Al-4V alloy. The surface properties of the specimens were characterized using X-ray diffraction, scanning electron microscopy, a micro-Vickers hardness tester and nano-indentation tester. The results showed that the surface hardness and thickness of the hardened layer increased with increasing gas blowing velocity. This occurred because of the elevated temperatures in the interior of the alloy relative to the surface temperatures at a higher gas blowing velocity. Furthermore, increasing the magnetic field strength around the IH coil and the eddy current density around the circumference of the specimen also accelerated the formation of a hardened layer on the surface of the titanium alloy. Consequently, a high-hardness layer can be formed by applying a treatment temperature less than the β transus of the Ti-6Al-4V alloy, while increasing the gas blowing velocity. This layer improves the wear resistance of the alloy by suppressing both grain coarsening and the formation of an acicular α phase.