Pressureless Sintering of WNi Nanoparticles Prepared by Ultrasonic Spray Pyrolysis and Hydrogen Reduction

The synthesis of homogenous powder mixtures and the characteristic of the sintered W-0.4 wt% Ni compacts were investigated. Ultrasonic spray pyrolysis and polymeric additive solution route for developing the initial powder mixtures were compared based on the resulting microstructure and mechanical property of sintered WNi. The powder mixture synthesized by the ultrasonic spray pyrolysis and hydrogen reduction showed marked refinement of W particle size and homogeneous dispersion of the Ni activator in the form of nickel hydroxide. The WNi powder from ultrasonic spray pyrolysis, pressureless-sintered at 1400 °C, exhibited the increased relative density of 97.6% and hardness of 4.02 GPa compared with the powder from polymeric additive solution. XPS analysis revealed that Ni, existed as nickel hydroxide state in the powder mixture, was partially dissolved in W during sintering to form an alloy. The increase in relative density was explained by the uniform WNi nanocomposite powder synthesized by ultrasonic spray pyrolysis. The high hardness was mainly due to the refinement of W grains.