Synthesis of nanocrystalline TiC reinforced W nanocomposites by high-energy mechanical alloying: Microstructural evolution and its mechanism

Abstract

High-energy mechanical alloying (MA) of a micrometer-scaled W and TiC powder mixture was performed to prepare TiC/W nanocomposites. X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), transmission electron microscope (TEM), and laser particle size analysis were used to study the morphological change and microstructural evolution occurred during MA process. It showed that the powder particles experienced a continuous refinement during 0–35h milling; on increasing the applied milling time up to 45h, the particles had a tendency to coarsen. The 35h milled powder had a considerably refined particle morphology, showing a narrow size distribution (D25=0.47μm, D50=0.61μm, D75=0.74μm, and D90=0.86μm) and a significantly elevated specific surface area of 4154.86 m2/kg. The TEM results revealed that the particles of 35h milled product consisted of a large number of ultrafine crystallites of W and TiC with sizes less than 20nm and the nanometer-sized TiC particulates were dispersed uniformly throughout the W matrix. The analysis of XRD spectra by Scherrer equation indicated that the average crystallite sizes of the W and TiC constituents in the 35h milled powder were 8.5nm and 13.6nm, respectively, showing a good agreement with the experimental results. On further increasing the milling time up to 45h, the partial amorphization of W constituent occurred in the milled powder. Formation mechanisms and theoretical basis for microstructural development and phase change in the milled powders were elucidated.