Studies on the Nitriding of Titanium and Vanadium Metals

Abstract

Nitriding of Ti powder, Ti and V plates with N₂ (1 atm) has been carried out at 900-1440 ° C, to obtain fundamental information for the nitriding of Ti-V alloys. The process of nitriding was Investigated by gravimetric method, X-ray diffractometry, X-ray microprobe analysis and microscopic observation. Two stages were observed in the nitriding of Ti; (1) the solution of nitrogen in α -Ti, (2) formation and increase of TiN layer on the surface of α -Ti phase, after the disappearance of the concentration gradient of nitrogen in α -Ti phase. In the nitriding of V, VN and V₃N were observed on the surface of metal and V₃N developed in the inner part of metal saturated with nitrogen. The solution of nitrogen in the V metal proceeded so rapidly that the nitrogen concentration gradient was not observed. The initial rate of nitriding followed the parabolic law, and the diffusion of nitrogen in metal phases was rate-determining. The rate constants of this reaction were as follows for Ti and V, respectively.
The apparent diffusion coefficients of nitrogen in α -Ti and TiN were calculated by using-the nitrogen concentration in each phase boundaries obtained from Ti-N equilibrium phase diagram.