Feasibility study of active screen plasma nitriding of titanium alloy

Abstract

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°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, microhardness 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 Ti 2 N was formed on top of the surface and an Al rich layer was formed between the Ti nitride layer and the α-Ti case. The surface hardness of the samples nitrided at 750 and 850°C was 800 and 1400 HV respectively.