Atmospheric-pressure-plasma nitriding of titanium alloy Ti-6Al-4V has been achieved by using a pulsed-arc plasma jet with a N 2 /H 2 gas mixture, where the plasma jet plume is sprayed onto the titanium surface under atmospheric pressure. We successfully formed a titanium nitride layer on the sample surface. Moreover, the diffusion layer was also formed, the hardness of which was increased from that of as-received titanium. The nitride layer growth was found to be diffusion-controlled, as in other conventional nitriding methods.

Irradiating the plume of atmospheric-pressure pulsed-arc plasma jet with nitrogen/hydrogen mixture gas enables to harden steel surface by nitrogen diffusion into steel. An important parameter is the hydrogen mixture ratio. Images of plasma-jet plume and formed hard layer for several hydrogen mixture ratios are presented.Index Terms-Nitriding, pulsed-arc plasma jet, surface hardening.