Preparation Of Ni Nano-powder By Dc Arc Plasma And Study Of SPS Sintering And High Pressure Torsion

Pure Ni nanopowders were prepared by the direct current arc plasma evaporationmethod in this experiment. The influence of different process parameters on the rate ofproduction and particle size of the nanopowders were discussed. The results suggested thatthe three factors, current, ratio of hydrogen to argon and total pressure were interactingeach other. The current and ratio of hydrogen to argon were the main factors whichinfluenced the rate of production and particle size of the Ni nanopowders. The optimalprocess conditions were determined to be a current of300A,1:1ratio of hydrogen toargon, and total gas pressure of0.07MPa.The morphologies of the prepared Ni nanopowders were observed. X-ray diffraction(XRD) showed that the prepared powders were high pure and with no unpurified phase,which belonged to the face centered cubic (FCC) structure; scanning electron microscope（SEM） and transmission electron microscope (TEM) results showed that most of thenanopowders were spherical particle, and the shapes were uniform with tiny aggregatesgenerated. The mean grain size of the most nanopowders was41nm.The Ni nanopowders were sintered by spark plasma sintering (SPS) equipment, andhow the different sintering temperatures and soaking times influenced the phase,morphology, density, hardness of the sintering bulks were also discussed. XRD showedthat the sintering bulk contained tiny NiO phase and belonged to FCC structure. Thesintered bulks in different sintering temperatures had different degrees of combination.The grain size, density, hardness increased first, and then dropped with temperatureincreased. They reached a maximum value of62.6nm,8.49g/cm3,406HV at600℃,respectively. Sintered in600℃with different soaking time, the highest density was at5minutes and the highest hardness was at4minutes. In a word, soaking time had littleeffect on the density and hardness.Using high pressure torsion (HPT) to dispose the sintered bulks and discussed theinfluence on grain size, density, hardness, internal organization. The results showed thatafter HPT, the grain size decreased obviously. The grain tended to rotate from (111) to (200). The density and hardness of the400℃sintered bulks were increased obviously,and the density increased by12%, the hardness increased by2.92times and the highestwas532.7HV. The fracture had layered structure happened, and combined denser thanbefore. Using steel ring to restrict the sintered bulks before HPT, the results showed thatthe hardness and deformation were lower than that without restriction, but the hardnessdistribution were better-distributed.