Synthesis and Characterization of Nanostructured Tungsten-30 Atomic % Chromium Produced by Mechanical Attrition and Hydrogen Sintering

Abstract

Nanostructured W70Cr30 powders were produced by mechanical alloying (MA) of elemental tungsten (W), Chromium (Cr) powders in a high energy planetary ball-mill using tungsten carbide as grinding media and toluene as a process control agent. The crystallite size and lattice strain of the nanostructured powders at different milling time (0 h to 10 h) was calculated from X-ray diffraction patterns (XRD). The crystallite size of W in W70Cr30 powder reduced from 100 μm at 0 h to 32.8 nm at 10 h of milling with increase in lattice strain of 0.43% at 10 h of milling. The lattice parameter of tungsten shows initial expansion of lattice upto 0.56% at 5 h of milling and contraction of lattice upto 0.93% at 10 h of milling. The scanning electron microscopy (SEM) micrograph also revealed mixed morphology of elemental W and Cr powders consist of spherical and elongated particles during mechanical alloying (0 h to 10 h). The dark-field transmission electron microscopy (TEM) observations indicated that the crystallite size (~30 nm) of W in W-Cr alloy in the as-milled powder is in good agreement with calculated crystallite size from XRD. Maximum solid solubility of 4.4 at.% Cr in W was found at 10 h of milling. The dislocation density increases from 6.75 (1016/m2) to 17.56 (1016/m2) with increase in the milling time from 0 h to 20 h. No cracks in the sintered pellets were visible under scanning electron microscope (SEM). Hardness and Elastic Modulus of sintered W70Cr30 alloy determined by nanoindentation test are less compared to pure W.