Plasma Nitriding with Nitrogen, Hydrogen, and Argon Gas Mixtures: Structure and Composition of Coatings on Titanium

Abstract

The glow discharge plasma nitriding of titanium, like that of steels, is usually carried out in cracked ammonia or in a nitrogen-hydrogen gas mixture or, alternatively, in pure nitrogen. The nature of the nitride layers produced is dependent on the gas composition. A study has therefore been made of the effects of using a wide range of nitrogen, nitrogen-hydrogen, and nitrogen-argon mixtures on the structure and composition of the surface layers produced. The problems associated with light element analysis of the resulting titanium nitride coatings were overcome by the use of Rutherford backscattering spectrometry and nuclear reaction analysis (NRA), and nitrogen concentration depth profiles (4-5 üm depth) were obtained. The extent of oxygen contamination was measured using NRA and electron probe microanalysis. X-ray diffraction was used to investigate the degree of preferred orientation in the coatings and also provided information on the amount of various nitride phases present in the coatings (TiN, Ti 2 N, (α- Ti). Evidence is presented which indicates that the outermost surface layer can consist of a hypernitride of composition TiN x’ where x is ∼ 1·5.