Microstructure evolution and mechanical properties of selective laser melted bulk-form titanium matrix nanocomposites with minor B4C additions

Crack-free and almost fully dense (≥99%) bulk-form titanium matrix nanocomposites in-situ synthesized from a ball-milled mixture of Ti-6Al-4V and B4C powders were achieved through an optimized selective laser melting (SLM) process. The effects of minor B4C addition on microstructure evolution, hardness, compressive properties and fracture mechanisms of the composites were systematically investigated. The in-situ synthesized nanoscale TiBw or TiCp ceramic reinforcements, exhibiting a quasi-continuous (TMC1) or full-continuous structure (TMC2), could play a prominent role in determining the microstructure refinement and mechanical properties of the composites. Results indicate that the SLM-processed nanocomposites exhibit a maximum increase of 45% of Vickers microhardness and 26% of ultimate compressive strength over the Ti-64 alloy. The enhancement of mechanical properties is mainly attributed to the second-phase strengthening, grain refinement strengthening as well as solid solution strengthening induced by the interstitial carbon in Ti matrix. This study provides a novel solution for microstructure tailoring with minor B4C addition and producing high-performance titanium matrix composites via SLM additive manufacturing. [Display omitted] •Crack-free bulk-form titanium matrix nanocomposites with relative density ≥99% were fabricated by selective laser melting.•In-situ synthesized nanoscale TiB whiskers or TiC particles distributed in the titanium matrix were achieved.•The composites evolve from quasi-continuous to full-continuous wall-like or network structure with increasing B4C content.•The composites show a maximum increase of 45% of Vickers microhardness and 26% of compressive strength over the Ti-64.