In situ synthesized TiC/Ti5Si3 nanocomposites by high-energy mechanical alloying: Microstructural development and its mechanism

In situ synthesis of TiC/Ti5Si3 nanocomposites powder was performed by high-energy ball milling of a Ti-SiC powder mixture having an 8:3 molar ratio. The 25 h milled final product was featured by the nanocrystalline Ti5Si3 matrix reinforced with the uniformly dispersed TiC nanoparticles. The crystalline size of the in situ formed Ti5Si3 and TiC constituents was similar to 14 and similar to 8 nm, respectively. The evolutions of constitution phases and particle structures of the milled powders were studied and the predominant mechanisms behind the microstructural developments were elucidated. It showed that the disappearance of X-ray diffraction peaks of SiC in the milling system was significantly behind the disappearance of Ti peaks. The SiC constituent decomposed gradually within 25 h of milling, while the Ti constituent reacted speedily after a relatively short time of 10 h. The structures of the milled TiC/Ti5Si3 nanocomposites powders experienced a successive change: pre-refining - coarsening - re-refining on increasing the applied milling time, due to the competitive action between the mechanisms of cold-welding and fracturing. The plastic deformation and cold-welding occurred at the initial milling stage where the ductile Ti element existed. Only fracturing of the particles was operative in a long-term milling system (>= 15 h), due to the formation of brittle intermetallic compound Ti5Si3 and ceramic compound TiC. The refinement of the milled powder particles was based on a layered fracturing mechanism. (C) 2010 Elsevier B.V. All rights reserved.