Tailoring strength-ductility of Ti-based composites by manipulating interfacial and intragranular TiB_w in Ti-BNNSs system

In the present work, the boron nitride (BN) was employed to fabricate Ti-based composite via powder metallurgy (P/M) and hot rolling (HR). Two types of ball milling methods we called as high-energy built-in grooves ball milling (HE-BGBM) and low-energy solution ball milling (LE-SBM) were used to disperse 0.1 – 0.5 wt% boron nitride nanosheets (BNNSs) with pure Ti powder via mechanical exfoliation mechanism. It revealed that the size, distribution behavior, morphologies and defects evolution of the BNNSs in powder mixtures were largely dependent on the ball milling strategy, thus further influenced the microstructure and mechanical properties of the composites. HE-BGBM uniformly dispersed the small-sized BNNSs (Ss-BNNSs) on Ti powder surface via ‘micro-rolling’ process and effectively boosted the Ti-B chemical activity, resulting in intragranular distributed nano-TiB_w in matrix. Whereas the LE-SBM route led to the partially reacted large-sized BNNSs (Ls-BNNSs) and formation of interfacial nano-TiB_w. The Ss-BNNSs/Ti composite exhibited the uniform dispersion of TiB_w, smaller grain size and higher GND density, which collectively contributed to its superior mechanical properties. The ultimate tensile strength of the Ss-BNNSs/Ti composite enhanced from 536.8 MPa to 966.7 MPa (compared with pure Ti) with high fracture elongation of ∼ 20.3 %. Quantitative analysis of strengthening mechanisms and investigation of failure behavior revealed that intragranular nano-sized TiB_w reinforcements induced prominent Orowan strengthening and substructure hardening. Additionally, these reinforcements promoted a more uniform stress–strain distribution within the matrix. This study paved a new way to obtain the well-balanced properties in Ti-BNNSs system, and underscored the importance of reinforcement design in metal matrix composites.