Studies on the synthesis of a Mo–30 wt% W alloy by non-conventional approaches

In the present study, alternate routes for the synthesis of a single phase Mo–30 wt% W alloy were pursued to surmount the limitations experienced in conventional technique. The process essentially consists of preparation of active Mo and W powders by H2 reduction of the respective oxide intermediates through multiple processing steps and then converting those pure powders into Mo–30 wt% W alloy by mechanical alloying technique (MA) at RT under Ar atmosphere in a high-energy planetary ball mill. The structural evolution of the alloy from the milled powders at different interval of time was studied by X-ray diffraction (XRD) and phase corresponding to Mo–30W alloy was confirmed. The broadening of peaks in XRD pattern was due to crystallite refinement during milling towards the formation of the designated alloy. A high rate of densification for MA powder was achieved during sintering between 900 °C and 1200 °C and density close to theoretical density was attained. The microstructure of sintered alloy exhibited uniform, polyhedral grains with average grain size of about 3 μm. The morphological evolution of as-milled powder was studied by Scanning electron microscopy (SEM) which revealed the formation of nano sized crystallites with polyhedral shapes. The crystallites were initially arranged in clusters which later on got distributed uniformly with the progress in milling time. The average crystallite size of MA powder was found to be 7.3 nm after 25 h of milling.