Hot pressed titanium nitride obtained from SHS starting powders: Influence of a pre-sintering heat-treatment of the starting powders on the densification process

Synthesis of titanium nitride (TiN) powders by the self propagating high temperature synthesis (SHS) process is economically appealing. This chemical reaction allows producing fine grains powders with a high specific surface area (12 m2/g). After a thermal treatment above 1000 °C under argon atmosphere, the physical and microstructural characteristics of the powders are drastically modified: density increases and specific surface decreases. Powders morphology and heat treatment influence are investigated by transmission electron microscopy. Observations reveal a regular nanocrystalline layer, surrounding the particles. After heat treatment, this layer disappears from grains surface and powders undergo important morphological changes. The behavior of these special ceramic powders during the sintering stage by the hot press process is investigated. Bulk specimens obtained are characterized from a physical, microstructural and mechanical point of view and the beneficial effect of the heat treatment on starting powder is explained. Bulk specimens processed in the optimum conditions reach a relative density superior to 98%, a microhardness of 1790 Hv and a Young modulus of 430 MPa.