Unique opportunities for microstructure engineering via trace B4C addition to Ti-6Al-4V through laser powder bed fusion process: As-built and heat-treated scenarios

This research study examines the role of minor B4C addition (0.2 wt%) in improving the mechanical properties of the laser powder bed fusion (L-PBF) fabricated Ti-6Al-4V (Ti64) alloy in the as-built and heat-treated conditions. The fabricated titanium matrix composites (TMCs) were subjected to two different heat treatment scenarios, i.e., subtransus and supertransus, and were compared to the Ti64 counterparts exposed to the same thermal cycles. Both as-built and heat-treated Ti64 and TMC samples were characterized in terms of the grain structure, microstructure within the grains, and the size, morphology, volume fraction, and crystallographic orientation of the phases. The knowledge gained from microstructural investigations was correlated to the mechanical behavior of components, including compressive strength and ductility, microhardness, and scratch resistance. The governing strengthening mechanisms were identified, and the contribution of each mechanism in the overall yield strength was explored. Results revealed that TMCs possessed higher yield and ultimate compressive strengths than their Ti64 counterparts owing to the hard TiB needles homogeneously dispersed in the microstructure. However, except for the supertransus heat-treated condition, the TMCs showed slightly lower fracture strain than the Ti64 samples. The elimination of GB-α in the supertransus heat-treated TMC sample caused by the TiB needles led to a higher fracture strain than the corresponding Ti64 case. While the implemented heat treatment strategies could tailor the mechanical properties, the optimum thermal cycles for Ti64 were not necessarily applicable to TMC components.