Microstructural characterization and mechanical properties of nano-scale/sub-micron TiB-reinforced titanium matrix composites fabricated by laser powder bed fusion

Abstract

A B4C/Ti-6Al-4V(Ti64) composite powder containing a minor B4C content (0.2 wt%) was developed by a novel technique and was subjected to the laser powder bed fusion (L-PBF) process within a wide range of laser powers and scanning speeds to fabricate titanium matrix composite (TMC) parts. The relative density measurement results revealed the achievement of almost fully dense TMC parts. Compared to the Ti64 case, slightly higher Ev values were required in the TMC system to obtain the highest relative density. Microstructural characterization of the TMC parts revealed the formation of large columnar prior β grains containing in-situ formed nano-scale/sub-micron TiB needles homogeneously dispersed in a martensitic matrix. While having almost the same ductility, the fabricated TMC parts showed 25% and 8% higher nanohardness, compressive yield strength, respectively, and 12% lower wear rate than the Ti64 sample. The improved mechanical properties of the TMC were due to the contribution of several factors, including the incorporation of nano-scale/sub-micron TiB reinforcement, the refinement of the martensite α՛ laths, and the solid solution strengthening effects of carbon atoms. The contribution of TiB presence and solid solution strengthening was ~60% and ~40% in the overall yield strength enhancement of the TMC parts, respectively.