Microstructure and Mechanical Properties of in Situ Synthesized (Tib+Tic) Reinforced Ti6al4v Composites Produced by Directed Energy Deposition of Ti and B4c Powders

Abstract

In situ synthesized titanium boride (TiB) and titanium carbide (TiC) reinforced Ti6Al4V composites were produced by directed energy deposition from a ball-milled mixture of Ti6Al4V and B4C powders. The effect of B4C addition on microstructure, texture and mechanical properties were systematically investigated. The results showed that whisker TiB and equiaxed TiC are uniformly distributed in the matrix and the B4C/Ti composites are mainly composed of α-Ti, β-Ti, TiB and TiC. The grain size of the as-deposited alloy drastically decreased from 550μm to 120 µm due to the in situ synthesized TiB and TiC. The formation of TiB and TiC promoted the precipitation of α-Ti with non-Burgess orientation relationship, which increased the variety of α variants and weakened the texture of α-Ti. The tensile strength was significantly improved due to the in situ synthesized TiB and TiC, and the ultimate tensile strength was 1126.1MPa at room temperature, which exhibited a maximum increase of 15% over the Ti6Al4V alloy. Finally, the microstructure refinement mechanism and strengthening mechanism was discussed in detail.

Keywords: Ti6Al4V alloy, Directed energy deposition, TiB+TiC, Microstructure, Mechanical properties