Boron-induced microstructural manipulation of titanium and titanium alloys in additive manufacturing

While the role of boron (B) has been thoroughly clarified in titanium (Ti) castings, the microstructural changes triggered in additive manufacturing (AM) are still the subject of debate in the literature. Many contributions have confirmed the B-induced microstructural refinement in Ti-based AM parts. The formation of TiB in titanium matrix composites (TMCs) may increase strength. In some cases, B may also promote the columnar-to-equiaxed transition, thus mitigating the anisotropic effects associated with the strong epitaxial growth of unidirectional columnar grains typical of AM. However, as critically discussed in this review, some pitfalls remain. Due to fast cooling, the microstructural evolution in AM may deviate from equilibrium, leading to a shift of the Ti-B eutectic point and to the formation of out-of-equilibrium phases. Additionally, the growth of TiB may undermine the ductility and the crack propagation resistance of AM parts, which calls for appropriate remediation strategies.

Automated summary

This review examines the impact of boron on the microstructure of titanium during additive manufacturing. It discusses the refining effect of boron on the microstructure and its role in regulating columnar grain growth. However, it also highlights the potential issues that can arise during fast cooling, such as eutectic point shift and formation of out-of-equilibrium phases, as well as the impact of TiB growth on ductility and crack propagation resistance in additive manufacturing parts.