Feasibility study of active screen plasma nitriding of titanium alloy

A feasibility study of active screen plasma nitriding (ASPN) of Ti6Al4V titanium alloy was conducted using a CP-Ti cage as the active screen under various process conditions. The process variables included active screen setup parameters (two different potentials of 0%-bias and 100%-bias), treatment temperature (750 and 850 degrees C), gas mixture (10/90, 25/75, 50/50 and 100/0 of N-2/H-2) and treatment time (10 h) under 1.5 mbar pressure. The samples were characterised by X-ray diffraction, optical microscopy, scanning electron microscopy, micro-hardness and surface roughness tests. The experimental results have demonstrated that Ti-6Al-4V alloy can be treated by ASPN using a Ti screen. A Ti nitride compound layer consisting of TiN followed by Ti2N was formed on top of the surface and an Al rich layer was formed between the Ti nitride layer and the alpha-Ti case. The surface hardness of the samples nitrided at 750 and 850 degrees C was 800 and 1400 HV respectively.