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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 TiC_p and TiB_w 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 TiC_p and TiB_w, especially the load-bearing transformation of TiB_w. However, the limitation of the TiB_w on the deformation of Ti matrix decreased …