In-situ TiC particle reinforced Ti-Al matrix composites: Powder preparation by mechanical alloying and Selective Laser Melting behavior

Mechanical alloying of Ti-Al-graphite elemental powder mixture was performed to synthesize nanocomposite powder with Ti(Al) solid solution matrix reinforced by in-situ formed TiC particles. The evolutions in phases, microstructures, and compositions of milled powders with the applied milling times were investigated. It showed that with increasing the milling time, the starting irregularly shaped powder underwent a successive change in its morphology from a flattened shape (10 h) to a highly coarsened spherical one (15 h) and, eventually, to a fine, equiaxed and uniform one (above 25 h). The prepared TiC/Ti(Al) composite powder was nanocrystalline, with the estimated average crystallite size of similar to 12 nm and of similar to 7 nm for Ti(Al) and TiC, respectively. Formation mechanisms behind the microstructural development of powders were elucidated. The Ti(Al) solid solution is formed through a gradual and progressive solution of Al into Ti lattice. The formation of TiC is through an abrupt, exothermic, and self-sustaining reaction between Ti and C elements. Selective Laser Melting (SLM) of as-prepared TiC/Ti(Al) composite powder was performed. The TiC particle reinforced TiAl(3) (a major phase) and Ti(3)AlC(2) (a minor phase) matrix composite part was obtained after SLM. Although a slight grain growth occurred as relative to as-milled powder, the SLM processed composites still exhibited a refined microstructure. (C) 2009 Elsevier B. V. All rights reserved.