Gradient microstructure of titanium nitride fabricated by combustion synthesis with liquid nitrogen

Titanium nitride has been fabricated by combustion synthesis from a titanium powder compact and liquid nitrogen in a closed vessel. This method drastically increases the pressure around the sample, resulting in combustion propagation. The products obtained in this system are non-homogeneous in morphology and composition along the propagation direction. The nitridation and densification of the products have improved with the increase of the maximum pressure or pressure gradient. With a pressure gradient of 9.5 MPa s⁻¹, the first combustion part of the product is almost unreacted titanium, but the main product at the last combustion part is titanium nitride (TiN_0.75) with a dense body. The Vickers micro-hardness of the product (at 0.98 N force) along the propagation direction is gradually increased from 9.7 to 17.3 GPa.