Enhanced Mechanical Properties Via Boron‐Induced Multi‐Mechanism Strengthening in (NbTaTi _1.5 V) _100‐x B _x Refractory High Entropy Alloys

ABSTRACT In this study, a trace amount of boron was added to the NbTaTi _1.5 V RHEA to enhance its strength. Specifically, (NbTaTi _1.5 V) _100‐x B _x alloys with varying boron contents were fabricated by ball milling and spark plasma sintering (SPS). With the addition of 1 at.% boron, the compressive fracture strength of the alloy increased by 21.3% relative to the B0 alloy, rising from 2975 to 3610 MPa. A compressive fracture strain of 14.8% was maintained. The microhardness increased from 881 ± 67 HV to 1060 ± 60 HV, corresponding to an improvement of 20.4%. The microstructure analysis indicated that the (NbTaTi _1.5 V) _100‐x B _x alloys were composed of three fine‐grained phases, namely BCC phase, TiO phase and TiB phase. The addition of trace amounts of boron led to significant grain refinement, resulting in a uniform and refined microstructure in the sintered alloys. The average grain size of B1 alloy was only 0.91 µm, representing a 67% reduction compared with that of the B0 alloy (2.82 µm). This provided a favorable microstructural foundation for the synergistic strengthening of the alloys. The boron element contributed 48.2% of the yield strength enhancement in B1 alloy by grain boundary strengthening through grain refinement, which was the dominant strengthening mechanism. TiB and TiO particles promoted dislocation proliferation, resulting in an additional strengthening contribution of approximately 28.7%. Furthermore, the TiB phase enhanced resistance to plastic deformation by impeding dislocation slip through crack deflection. This synergistic multi‐mechanism strengthening strategy offers an effective approach for improving the mechanical properties of (NbTaTi _1.5 V) _100‐x B _x alloys.