Evolution of Phase, Microstructure and ZrC Lattice Parameter in Solid-solution-treated W-ZrC Composite

Abstract

Zirconium carbide (ZrC) reinforced tungsten (W) composite was hot-pressed at 2200 °C for 1 h in vacuum, which was subsequently heat treated in the temperature range of 2200 to 2500 °C for 1.5 or 2 h. The relative ratios of ZrC phase were 21.0, 23.3 and 25.9 mol.% for the mixture of starting powders, composites sintered for 1 h and solid-solution treated at 2500 °C for 1.5 h, respectively. The solid solubility of W in ZrC increased with the increment in heat-treating temperature and time to a maximum value of 18.9 mol.% at 2500 °C for 1.5 h. The lattice parameter of cubic ZrC phase diminished from 0.4682 nm in the starting powder to 0.4642 nm in the solid-solution composite treated at 2500 °C for 1.5 h. This work demonstrated that the relationship between the solid solubility of W in ZrC and the lattice parameter of ZrC is linear, with a slope of −1.93 × 10−4 nm/at.%. Overall, more W atoms diffused into ZrC lattice after heat treatment, meanwhile, the previous precipitated nano-sized W dissolved in the supersaturated (Zr,W)C solid-solution, as detected by SEM and TEM.

Strong ZrC ceramics at high temperatures with the addition of W

“…It can be seen that the position of the (420) diffraction peak gradually shifted to higher 2 θ angles with increasing of temperature, which indicated that the lattice parameter of ZrC decreased concomitantly. The formation of carbon defects in ZrC 1‐x and the solution of W in ZrC lattice could cause the decrease of the ZrC lattice, since the covalent radius of W (1.38 Å) is smaller than that of Zr (1.57 Å) . Meanwhile, the solution of oxygen in ZrC lattice could also decrease the lattice of ZrC .…”

An investigation of the long-range and local structure of sub-stoichiometric zirconium carbide sintered at different temperatures

“…A single crystal silicon zero-background sample holder was used and the X-ray diffractogram was collected from 20° to 105° 2θ at room temperature with the -step interval being 0.015°. XRD was used to confirm the rock-salt structure 1,2,17,27 of ZrC 1−x , to determine if any other phases were present in the sample 15,28,29 and, using Rietveld refinement in the TOPAZ academic software suite, to determine the lattice parameter and the associated error.…”