Instant formation of titanium nitride by reactive milling of titanium in nitrogen

Mechanical milling of Ti powder in a controlled quantity of nitrogen gas by a high energy ball mill was performed. In the initial stage, the nitrogen pressure was gradually reduced. Nitrogen was dissolved in Ti to form a solid solution. Under suitable conditions, when a critical solubility limit had been reached, the nitrogen pressure drastically dropped to a much lower value and instant formation of titanium nitride took place. Continuation of the milling led to increased content of nitrogen in the nonstoichiometric compound titanium nitride. The particle size also continued to decrease. The phases before and after the rapid reaction to form titanium were carefully studied by x-ray diffraction. The morphological change of the particles during the milling was examined by scanning electron microscopy. The titanium nitride compound was formed by means of self-propagating combustion which was triggered by the large clean surface area and the high strain energy of the Ti powder induced by the milling.