Characterization of Ni-W Solid Solution Alloy Powders and Sintered Compacts Synthesized via Mechanically Activated Hydrogen Reduction of NiO-WO_3 Mixtures

摘要

Blended nickel oxide - tungsten oxide powders corresponding to the compositions of 70 wr% nickel - 30 wr% 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 (H_2) atmosphere. H_2 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 WO_2 powders were obtained via hydrogen reduction of as-blended 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.