Research of Electron Beam Remelting on Microstructure and Properties of TiBw/TC4 Composite

Abstract

Electron beam remelting of TiB / TC4 composites can effectively improve can improve the strength and hardness of the material surface. Nano TiB grains were obtained after remelting. Microstructure and properties of remelted layer with different heat input was investigated and analyzed in details. The thickness of the reaction layer was obviously increased with increasing heat input. TiB grains changes from fine equiaxed crystal with low heat input to coarse dendrite with high heat input. In the whole remelting process, the preferentially precipitated TiB will become a heterogeneous nucleation point, TC4 will adhere to the precipitated TiB nucleation and grow, and push TiB out to the grain boundary. TEM results showed that there were two crystal structures: B₂₇ and B_f in the remelted nanoscale TiB. There are also lots of stacking fault in the TiB whisker, but as the interface between the reinforcing phase and the matrix is clean, no interface products appear. When the line energy is 48 J/mm (2mA), 96 J/mm (4mA) and 128J/mm (6mA), the average hardness values of the cross section of the remelting zone are 531HV, 564HV, and 510HV, respectively. Due to 4mA TiB reinforcement presents a smaller network structure than the parent material, and the thickness of the remelting layer is moderate without coarse dendrites, the surface hardness increases by nearly 40%.

Keywords: Titanium matrix composites, Electron beam remelting, Microstructure evolution