Double-stage sintering behavior of a nickel nanoparticle dispersed micro powder

Abstract

Powder metallurgy (PM) has undergone innovations through powder advances and novel process development. Another option for advancement of PM technology is exploitation of the extreme bimodality of nano/micro powder mixtures. The present study describes bimodal powder preparation involving dispersion of nickel nanoparticles onto the surface of a micro powder to facilitate the compaction ability and sinterability of the Ni micro powder. The bimodal powder is designed by synthesizing Ni nanoparticles by reactive RF thermal plasma from a Ni(OH)(2) micro powder, selecting a spikyshaped Ni micro powder as the supporting powder, and then filling the pockets on the surface of the micro powder with the nanoparticles. Simple 3-D turbulent mixing successfully produces spheroidized and smoothened micro-granules consisting of well-dispersed nanoparticles on the surface of the micro powder. Nanoparticle compaction is usually difficult, but the compaction behavior of the micro-granules is similar to that of the micro powder. The effect of nanoparticle addition on sinterability, investigated by dilatometry, includes double-stage sintering behavior of the micro-granule powder, whereas the spikyshaped micro powder shows a typical monotonous sintering behavior. Consequently, the first shrinkage at low temperature arises from the enhanced sinterability of the nanoparticles, while the second shrinkage shows similar behavior to the micro powder. Within the scope of this study, the microgranules show a higher relative density than the micro powder.