Size effect of B4C powders on metallurgical reaction and resulting tensile properties of Ti matrix composites by in-situ reaction from Ti–B4C system under a relatively low temperature

Ti matrix composites (TMCs) were prepared by using spark plasma sintering (SPS) and hot extrusion from Ti–B4C powder system with different sizes of B4C addition. Tensile properties, O/N contents, grain sizes, microstructures, phase compositions and fractured surfaces were investigated systematically. Then, the effect of B4C particle size on the strength and ductility of TMCs were discussed based on the experimental results and strengthening theory. Results showed that coarse B4C powders led to incomplete reaction and decrease of the amount of both TiCp and TiBw in the Ti matrix, thus resulting in the significant decrease of strength but increase of elongation. The strength improvement of TMCs could be mainly attributed to the strengthening effect of in-situ formed TiCp and TiBw, especially the load-bearing transformation of TiBw. However, the limitation of the TiBw on the deformation of Ti matrix decreased the ductility of the TMCs dramatically.