Process induced multi-layered Titanium – Boron carbide composites via additive manufacturing

Abstract

Laser engineered net shaping (LENS) processing of an in-situ Ti-B 4 C composite, results in the natural formation of a novel periodically layered structure, when a mixture of Ti powders and B 4 C powders are used as a feedstock. One of the layers predominantly consisted of TiB 2 and inter-dendritic TiC phases, while the other alternating layer exhibited a rather complex microstructure, comprising of TiB, TiC, partially melted-B 4 C and α-Ti phases. Increasing the laser power (300–700 W) results in an increase in the height/thickness of these layers, as well as the number density of in-situ formed ceramic precipitates (TiB, TiC) in the TiB + TiC + α-Ti layer. Additionally, the Heipel-Roper theory of weld pool dynamics was employed to rationalize the unconventional microstructural evolution in these multi-layered LENS processed Ti-B 4 C composites. Microhardness and wear properties revealed that among the three powers, the 700 W condition exhibited the best combined wear and hardness which can be attributed to reduced porosity, and an increase in hardness of both layered regions due to an increase in number density of precipitates in the TiB + TiC + α-Ti layer. Such AM process induced naturally layered composites open up a new avenue for design and development of hybrid materials for future engineering applications. • First report on non-equilibrium multilayered microstructures in additively manufactured TMCs. • Ti-B 4 C TMCs were successfully fabricated using LENS, a laser directed energy deposition process. • A combined occurrence of the reactions, 3 Ti + B 4 C → 2 Ti B 2 + TiC and 5 Ti + B 4 C → 4 TiB + TiC is observed. • The alternatively repeating layers exhibited TiB 2, TiB, TiC, retained-B 4 C and α-Ti phases. • Schematics based on Heipel-Roper theory were presented to discuss the evolution of the layered microstructures.