Oxinitriding of Ti-6Al-4V by Glow-Discharge Process

Titanium and its alloys are known to be characterised by high strength to weight ratio and excellent corrosion resistance. Owing to their low surface hardness and poor wear resistance, many thermochemical treatments have been developed to improve these properties. In this paper we report the preliminary results of a study carried out with the aim of evaluating the effect of the contemporary glow-discharge oxidising and nitriding treatments on Ti-6Al-4V alloy. For this purpose, samples have been treated in an atmosphere with variable contents of nitrogen and oxygen at 1173 K. The modified surface layers properties depend on the working conditions. The outstanding feature is a markedly increased hardness and a higher thickness of the diffusion layer, in comparison with the equivalent values presented by titanium alloys components submitted to nitriding treatment: samples treated for 8 hours show a maximum diffusion layer thickness of similar to 120 mm with a maximum hardness of similar to 12.7 GPa, that gradually decreases to the matrix value.