Microstructural observation of titanium wires heated by combustion nitridation in liquid nitrogen

Microstructures of titanium wires heated in liquid nitrogen have been made clear by scanning and transmission electron microscopy to investigate the effects of the combustion nitridation of Ti with liquid N2. High density N2 generated from liquid N2 strongly reacts with Ti wire during heating. Microstructural observations revealed the precipitation of TiN at the surface and the several α phases at the inside of the wire. The heated Ti wire was aligned in order of the TiN thin film, the primary-α phase and the α-acicular phase from the wire surface. The region of the primary-α phase which indicates high solubility of N2 into Ti was increased by the nitridation with liquid N2. An increase in the primary-α phase leads to the accelerated nitridation.