Formation of titanium nitride by mechanical milling and isothermal annealing of titanium and boron nitride

The formation of titanium nitride with rock salt structure (δ-TiNx) was studied by mechanical milling of a mixture of Ti and hexagonal boron nitride (h-BN) powders and isothermal annealing of the mixture after milling for 70 h under argon atmosphere. The mole ratio of Ti to h-BN is 22:78. In the milling process, an amorphous Ti-N alloy was formed firstly by a diffusion reaction between Ti and BN, and then the amorphous Ti-N alloy transformed into δ-TiNx driven by mechanical milling. However, in the annealing process, a Ti(N) solid solution was formed firstly by incorporation of N into Ti, and the N content in the Ti(N) increased with increasing annealing temperature. When the N content exceeded the solubility limit of the Ti(N) at some annealing temperature, the Ti(N) decomposed into δ-TiNx and Ti(N) with the solubility limit. No self-sustaining reaction occurs in the present work. No TiB2 is observed to form in the two processes. The thermodynamic and kinetic mechanisms of formation of the δ-TiNx are discussed.