Achieving high-performance in TiB_w/TC4 composites via introducing two types of boron sources-BNNSs and LaB₆

Room-temperature brittleness was still an open issue in powder metallurgy discontinuously reinforced titanium matrix composites (DRTiMCs) which was mainly attributed to the addition of brittle ceramic reinforcements and excessive oxygen (O) content to the titanium matrix. Boron nitride nanosheets (BNNSs) is an idea reinforcement in DRTiMCs due to its two-dimensional structure and excellent mechanical property. The present study employed the LaB₆ and 2D-structured BNNSs as hybrid boron sources to address the strength-ductility trade-off in TiB_w/TC4 (Ti6Al4V) composites. Field-Assisted sintering technique (FAST) in conjunction with hot rolling (HR) was applied to consolidate the composite. The results showed that TC4-based composite exhibited the yield strength of 1339 MPa with fracture elongation of 17.9 % when adding merely 0.1 wt% BNNSs + 0.1 wt% LaB₆ reinforcements, achieving simultaneously enhanced strength (+20 %) and ductility (+38 %) compared with TC4 matrix. In particular, the partial reacted BNNSs provided an obviously crack resistance and damage tolerance capability in composite, while the LaB₆ effectively reduced the concentration of O impurity via in-situ formed La₂O₃ nano-particles. By employing the in-situ SEM experiment, we solve an existing debate, uncovering the synergistic toughening effect from BNNSs and heterogeneous interface which effectively inhibited the micro-cracks propagation. Together they made positive function that account for the high-performance in DRTiMCs. This study paved a pragmatic approach and valuable insights for addressing the strength-ductility synergy in DRTiMCs.