Superplastic behavior of composites prepared from mechanically alloyed Ti-Si3N4 powders

In situ synthesis of fine grain composites of TiN and Ti5Si3 has been conducted by the reaction milling of Ti and Si3N4 powder mixtures followed by hot-consolidation. Formation of TiSi2 could be suppressed by increasing the Ti content in the starting powder mixtures to more than 75 wt.%. Full densification was attained at sintering temperature of 1300°C using Hot-Isostatic-Pressing. The mean grain size in the compacts was hundreds nm when HIP treated at 1300°C. Tensile strength at high temperatures was improved by the elimination of TiSi2. Even in this case, substantial plastic deformation appeared at testing temperatures over 1300°C, and the elongation at 1500°C exceeded 100%. The strain rate exponent of the flow stress at 1400°C and at strain of 0.1 was 0.47. It indicates intrinsic superplasticity in this type of ceramics composites.