Refinement behaviour of microstructure in in-situ synthesised (TiB+TiC)/Ti6Al4V composites by laser melting deposition

Laser melting deposition (LMD) was used to stimulate the columnar to equiaxed transition (CET) of Ti6Al4V grains by adding a few of nano-B4C particles. The results showed that the grains were gradually refined with the increase of B4C content. When the B4C content is 3 wt-%, the titanium matrix composite material of B4C and Ti6Al4V reached CET. Ti6Al4V and B4C happened in-situ reaction to form TiB and TiC reinforcements at high temperature, which not only precipitate at grain boundaries to limit grain growth but also act as nucleation to accelerate the non-spontaneous nucleation of β grains to achieve fine grain strengthening. It reveals the epitaxial growth mechanism of β grains at the deposition bottom, the transition pattern and CET mechanism of the interface structure in successive deposition layers.