Rapid synthesis of titanium nitride powder by electrical discharge assisted mechanical milling

The aim of this work was to investigate nitrogen uptake and nitridation characteristics of titanium metal powder during processing by electrical discharge assisted mechanical milling under flowing nitrogen. Samples were prepared using an in-house reactor with an AC high voltage transformer, generating impulses within kV/mA range. The structures of reaction products were characterized by X-ray diffractometry, nitrogen contents by CHN combustion analysis and powder morphologies by SEM. An extremely rapid nitridation reaction was found to take place during milling under an electrical discharge and within 3–5 min titanium nitride (TiN) particles were directly synthesized from titanium powder. In contrast, under the same milling conditions without a discharge no TiN was detected after 30 min milling. The nitrogen uptake rate was extremely fast for milling under both low and high energy electrical discharges, however, the total nitrogen content of the product was higher in samples milled under a high energy discharge. The formation of TiN during milling was believed to occur via a complex process, involving rapid particle fracturing due to the combined effects of milling and an electrical discharge, interaction of the fine particles with hot nitrogen gas and free radicals generated by the electrical discharges, and thermally activated local diffusion of the nitrogen into the powder particles.