Abstract
In the present work, in situ TiN/Ti5Si3 nanocomposite powder was prepared by high-energy mechanical alloying of a Ti and Si3N4 powder mixture via the following route: 9Ti+Si3N4 - Ti5Si3+4TiN. Constitution phases and microstructural features of the milled powders at different milling times were studied by XRD, SEM, and TEM. The operative formation mechanisms behind the microstructural developments were disclosed. It showed that the original Si3N4 and Ti constituents demonstrated two different reaction mechanisms during milling, i.e., a progressive mechanism of Si3N4 (<= 20 h) and a speedy mechanism of Ti (<= 10 h). The morphologies of the milled composite powders experienced a successive change: pre-refining - coarsening - re-refining on increasing the applied milling time. The variation of the operative mechanisms was ascribed to the existence/exhaustion of the ductile Ti constituent in the milling system due to the nonoccurrence/initiation of the in situ reaction. The 20 h milled powder was the typical nanocomposites featured by the nanocrystalline Ti5Si3 matrix reinforced with in situ TiN nanoparticles. The grain sizes of the in situ formed Ti5Si3 and TiN phases were generally <= 15 nm, exhibiting coherent interfacial structure between reinforcement and matrix.