Microstructure evolution of Ti64-TiBw composites via electron beam powder bed fusion using as-prepared composite powder as feedstock

A self-designed spherical Ti64 powder containing nanosized TiB whisker(TiBw) was developed by electrode induction melting gas atomization (EIGA), which was used as feedstock to prepare Ti64-TiBw composites by electron beam melting (EBM). Nano-scaled TiBw distributed along the grain boundaries, forming a discontinuous network structure in EBM-Ti64-TiBw composites. In order to elucidate the effect of nano-sized TiBw on microstructure and properties of EBM-Ti64-TiBw composites, heat treatment of as-fabricated EBM-Ti64-TiBw is performed from 800 to 1200 degrees C with interval of 100 degrees C, to regulate the size characteristics (diameter, aspect ratio) of TiBw, the revolution of microstructure and interface were studied in detail. The results indicate that Ti64/TiBw interface structure transforms from a semi-coherent interface to a coherent interface with increasing heat treatment temperature (HTT). Furthermore, TiBw begin to coarsen after the heat treatment above the beta-transus temperature, leading to a weakening of its pinning effect on Ti64 matrix, and the discontinuous network structure disappears at 1000 degrees C. The growth and coarsening of TiBw are closely related to the diffusion rate of B atom in alpha-Ti and beta-Ti phases. This work provides a theoretical foundation for size control of TiBw reinforcement and the elucidation of its evolution effect on microstructure in EBM-Ti64-TiBw composites.

Automated summary

This study developed a self-designed spherical Ti64 powder containing nanosized TiB whisker (TiBw) and used it as feedstock to prepare Ti64-TiBw composites by electron beam melting (EBM). The size characteristics and heat treatment temperature have significant effects on the interface structure and microstructure evolution of the composites.