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

The role of boron (B) in microstructural changes in titanium (Ti) castings has been clarified, but its effects in additive manufacturing (AM) are still debated. Many studies have found that B can refine the microstructure in Ti-based AM parts and increase their strength. However, there are still issues such as deviation from equilibrium due to fast cooling in AM, which can lead to the formation of out-of-equilibrium phases, and the growth of TiB may negatively impact the ductility and crack propagation resistance of AM parts, requiring appropriate remediation strategies.