Microstructure and mechanical properties of in situ synthesized (TiB plus TiC)-reinforced Ti6Al4V composites produced by directed energy deposition of Ti and B4C powders

In situ synthesized titanium boride (TiB) and titanium carbide (TiC)-reinforced Ti6Al4V composites were pro-duced by directed energy deposition from a ball-milled mixture of Ti6Al4V and B4C powders. The effect of adding B4C on the microstructure, texture and mechanical properties was systematically investigated. The results showed that whisker TiB and equiaxed TiC were homogeneously distributed in the matrix. Also, the B4C/Ti composites are mainly composed of alpha-Ti, ll-Ti, TiB, and TiC. The grain size of the as-deposited alloy decreased drastically from 550 to 120 mu m due to the in situ-synthesized TiB and TiC. The formation of TiB and TiC pro-moted the precipitation of alpha-Ti with a non-Burgess orientation relationship, increasing the varieties of alpha variants and weakening the texture intensity of alpha-Ti. The tensile strength improved significantly because of the in situ -synthesized TiB and TiC. The ultimate tensile strength was 1126.1 MPa at room temperature, exhibiting a 15% maximum increase over the Ti6Al4V alloy, whereas the fracture elongation was reduced by 48.8%. Finally, the microstructure refinement mechanism was discussed in detail.