Microstructure and mechanical properties of B modified Ti–Fe alloy manufactured by casting, forging and laser melting deposition

Titanium alloys manufactured via additive manufacturing are suffering from coarse columnar grains due to the insufficient spontaneous nucleation rate during solidification. In this study, a newly designed Ti–2Fe-0.1B alloy with higher nucleating agent were introduced and manufactured by laser melting deposition method. The manufactured part is presenting a fully equiaxed grain morphology with 779 MPa on ultimate tensile strength. In order to reveal the mechanism of equiaxed grain formation and its influence on mechanical properties, a comprehensive study of microstructure evolution was carried out on Ti–2Fe-0.1B alloy manufactured via casting, forging and laser melting deposition. The results indicate that cooling speed are playing an important role on TiB morphology and Ti–2Fe-0.1B grain size simultaneously. The TiB formed from fast cooling speed are presenting a 3D quasi-network structure and improves the ultimate tensile strength of laser melting deposited part by 1.7 and 1.5 times when compared with casting and forging parts correspondingly. The study reveals that B addition is a sufficient method to control equiaxed grain formation in additive manufacturing of Ti–Fe alloy and promotes B addition as grain morphology controlling method in other additive manufactured titanium alloys in future.