CHARACTERIZATION OF SURFACE-LAYERS IN ION-NITRIDED TITANIUM AND TITANIUM-ALLOYS

Surface layers having elevated hardness were produced by ion nitriding of titanium and α-β alloys of Ti-6wt.percent Al-4wt.percent V, Ti-4wt.percent Al-2wt.percent Sn-4wt.percent Mo and Ti-4wt.percent Al-2wt.percent Mn. The treatment was conducted at temperatures between 1073 and 1273 K for times of 4-32 h, using gaseous mixtures of nitrogen and hydrogen containing 20-80 vol. percent nitrogen. X-ray diffraction, optical microscopy and microhardness were used to characterize the hardened surfaces. In most of the samples, this surface was composed of the phases δ (TiN type), Ε (Ti2N type) and α (solid solution of nitrogen in titanium); in other cases only the δ and α phases were present. The operating parameters which influence the composition of the layer were identified and the particular crystalline texture of the Ε phase is discussed.