Enhancing the strength and plasticity of laser powder bed fused NbMoTaW refractory high-entropy alloy via Ti alloying

NbMoTaW refractory high-entropy alloy (RHEA) exhibits excellent high-temperature performance, making it suitable for extreme service conditions. However, its brittleness and low ductility at room temperature caused by the enrichment of oxygen at the grain boundaries have hindered its industrial applications. In this work, in-situ alloyed NbMoTaWTix (x=0, 0.125, 0.25, 0.5, 0.75) RHEAs were additively manufactured using the laser powder bed fusion (LPBF) process. The results show that the investigated NbMoTaWTix RHEAs retain a single-phase microstructure with BCC crystal structure. With the addition of Ti, nanoscale TiO2 particles appear at the cell boundaries and grain boundaries. The yield strength, compressive strength, and strain to failure at room temperature and at 1000 °C, of the NbMoTaWTi0.75 RHEA were found to be superior to those of NbMoTaW. The addition of Ti reduced the oxygen content at the cell boundaries and grain boundaries to form nanoscale TiO2 particles, which mitigated the oxygen induced embrittlement and improved the plastic strain to fracture. The dispersion strengthening of TiO2 and solid solution strengthening of Ti also improved the strength. This work illustrates a possible pathway to fabricate near-net shaped RHEAs parts with an excellent combination of strength and ductility.