Diffraction Crystallite Size Effects on Mechanical Properties of Nanocrystalline (Ti0.8W0.2)C

The aim of this work is the study of the mechanical properties of nanostructured (Ti0.8 W0.2)C carbide synthesized by mechanical alloying process. The structural characterization was studied using X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Microstrain and grain size of the milled (Ti0.8W0.2)C powders were computed using Rietveld refinement method. Mechanical properties including microhardness (HV) and flow stress (σf) of the (Ti0.8W0.2)C powders were calculated. It has been found that morphology and particle size varied with milling time. When the milling time increases up to 20 h, we note a homogeneous and uniform dispersion of fine particles smaller than 1 μm in size. During the milling process, the formation of the substitutional solid solution (Ti0.8W0.2)C is favoured by the diffusion of W in the Ti crystalline sites of the Ti-C matrix. Thus, the lattice parameter decreases to reach the value of 4.2936 Ǻ after 20 h of MA duration due to the continual substitution of Ti by W. With a reduction of diffraction crystallite size (DCS), the (Ti0.8W0.2)C alloys were found to be noticeably hardened. The (DCS) dependence of (HV) was not following the simple Hall–Petch relationship over (DCS) whole range, showing distinct three stages matching three different Hall–Petch slopes. The slope of the H-P relationship becomes negative (k3 = − 16.157 GPa nm1/2) in the (DCS) range of 13–7 nm. Considering the calculated results, the optimum milling time which corresponds to the highest value of hardness (20.01 GPa) and flow stress (6.67 GPa), was determined as 4 h.