Characterization of Ni-W solid solution alloy powders and sintered compacts synthesized via mechanically activated hydrogen reduction of NiO-WO3 mixtures

Abstract

Blended nickel oxide - tungsten oxide powders corresponding to the compositions of 70 wt% nickel - 30 wt% tungsten were mechanically alloyed (MA'd) for different durations such as 0 h, 6 h, 12 h and 24 h and reduced/alloyed at 550 C for 1 h followed by 600 C for 0.5 h under hydrogen (H2) atmosphere. H2 reduction of the MA'd fine oxide powders resulted in the fabrication of nanocrystalline Ni(W) solid solution alloy powders, whereas a mixture of Ni and WO2 powders were obtained via hydrogen reduction of asblended oxide mixtures, which revealed the activation of the reduction process by MA. Obtained powders were sintered at 1300 C for 1 h under H 2 and Ar gas flowing conditions. X-ray diffraction patterns taken from the sintered samples revealed the presence of the Ni(W) solid solution phase for all samples, whereas the presence of elemental W phase was observed in the sintered as-blended and reduced powders. The lowest relative density value of 92.04% and microhardness value of 1.27 GPa were measured for the sintered as-blended and reduced powders, which increased to between 97.62% and 98.72% and 2.19 GPa and 2.23 GPa, respectively, with the applied MA.