Enhanced strength and ductility of nano-TiBw-reinforced titanium matrix composites fabricated by electron beam powder bed fusion using Ti6Al4V–TiBw composite powder

Abstract

TiB whisker (TiBw)-reinforced Ti6Al4V (Ti64) based composite powder (as an alternative to premixed Ti64 +TiB 2 powders) was designed and produced via electrode induction melting gas atomization as the feedstock for electron beam powder bed fusion (EB-PBF), to synthesize nanosized TiBw reinforced Ti64 based composites with a quasi-continuous network microstructure and well-matched strength and ductility. To understand the interactions among the TiBw morphology, microstructures and mechanical properties, the phase composition, microstructural orientation, interface relationships, tensile properties, and fracture mechanism were investigated systematically. The formation of a quasi-continuous network in the microstructure, with nanosized TiBw distributed along the grain boundary, is primarily attributed to the high cooling rates and low solid solubility of boron in the Ti matrix. In addition, the (102) plane of α-Ti and the cylindrical plane of the nanosized TiBw had a semi-coherent interface, whereas the transverse face of the TiBw had an incoherent interface with the Ti matrix in the EB-PBF-fabricated Ti64–TiBw composites. The ultimate tensile strength of EB-PBF-fabricated Ti64–TiBw composites reached 1121 MPa, which is 27% higher than that of the EB-PBF-fabricated Ti64 alloy, and the elongation after fracture remains at 8.9%, which is 82% remarkable higher than that of forged composites with the same TiBw volume content. This study provides a novel strategy for producing Ti matrix composites with matched high strength–ductility by additive manufacturing employing Ti-based composite powder as the feedstock.