Effect of Preparation Parameters and Sintering Conditions on the Properties and Microstructure of Nickel Pellets Prepared by Conventional Powder Metallurgy

Abstract

Eleven types of nickel pellets were prepared from two types of nickel powders. The first type of Ni powder had filamentary particles in shape with particle size less than 63 µm, the second type of Ni powder possessed nearly spherical particles in shape with particle size less than 149 µm. One type of pellets was prepared from Ni(B) powder whose particle size was reduced to less than 70 µm. The pellets were fabricated by conventional powder metallurgy. Green pellets were initially formed by compaction under 420 MPa and then sintered at 1200 °C. The dependence of the characteristics and microstructure of sintered pellets on particle shape, size of particles, powder milling, binder addition, holding time at 1200 °C, and the rate of raising green pellets temperature at the early stage of heating was investigated. Weighing in air and in floating liquid (water), measuring the sintered pellets volume, X-ray diffractometry, optical microscopy, scanning electron microscopy, X-ray energy dispersion analysis, and Vickers microhardness measurements were used to determine the properties and microstructures of fabricated pellets. The apparent density and microhardness of pellets prepared from filamentary particles with the addition of wax as a binder were the highest, about 8.23 gm/cm3 and 158 VHN, respectively.