Laser powder bed fusion additive manufacturing, microstructure evolution, and mechanical performance of carbon nanotube-decorated titanium alloy powders

Novel TiC-reinforced titanium matrix composites (TMCs) were in situ synthesized by laser powder bed fusion (L-PBF) of unique carbon nanotube (CNT)-decorated Ti-6Al-4V powders. Acid-treated CNTs were coated on the surface of Ti-6Al-4V particles by electrostatic self-assembly without varying the powder sphericity, leading to improved printability, as proved by laser-absorption and single-track experiments. During L-PBF, the CNTs were completely transformed into monocrystalline TiC dispersed in the α’-Ti matrix via a dissolution/precipitation mechanism. As illustrated by high-resolution transmission electron microscopy, the in situ-synthesized TiC crystals were closely bonded to the matrix, exhibiting typical TiC [001]//Ti [00−1] and TiC (220)//Ti (−100) orientation relationships. Significantly, the morphology of TiC underwent an interesting evolution from nanorods to micro-spheres, and to dendrites with an increase in the CNT content, causing a gradual increase in hardness of TMCs. This study may provide insights into the design of high-performance TMCs with unique microstructures, excellent properties, and tailored architectures.