Production of Ti-TiN short fibres with a structurally gradient cross-section by a reaction between nitrogen plasma and rotating molten titanium metal

Abstract

Ti-TiN short fibres in which the outer surface was composed of a TiN phase were formed through a reaction between nitrogen plasma and rotating molten titanium metal in a rotating electrode process. The cross-section of the fibres was an ellipsoidal shape. The mean diameter and average length were about 0.15 mm and 2.9 mm, respectively, and the thickness of the TiN surface layer was in the range 2–6 μm. The cross-sectional structure of the fibre changed gradually from the TiN surface layer to titanium phase in the central region through the coexistent Ti + TiN phases. Vickers hardness also changed gradually from 1860 in the surface region to 300 in the central region. The nitrogen content was evaluated to be 4.6 at% for the titanium phase and 30 at% for the TiN phase from the lattice parameters. In addition, the weight ratio of the fibres to the consumed titanium electrode reached as high as 80% under conditions where the mixing ratio of N₂ to (Ar + N₂) was 0.2 and the rotation speed of the titanium rod was 10000 r.p.m. It is therefore concluded that the present technique is useful for the production of the structurally gradient short-fibres consisting of titanium and TiN phases.