Search

Abstract: The sintering behavior of nanosized tungsten powder (25nm average size) synthesized by a thermal plasma process, in which ammonium paratungstate (APT) was reduced by hydrogen was investigated, compared with submicron W powder (0.5μm average size) and nanosized W powder (23nm average size) produced from the latter by high energy milling. The hardness of the compact of the plasma-synthesized powder (315 VHN) sintered at 1400°C was higher than that of submicron-sized powder (193 VHN) and was similar to that of the milled powder (309 VHN). The plasma-synthesized powder, however, yielded a compact with much lower tendency to form cracks than the milled powder. [Copyright &y& Elsevier]

Abstract: Nanosized tungsten powder was synthesized by a thermal plasma process using ammonium paratungstate (APT) as the precursor. The injected precursor was vaporized in the plasma flame and the subsequent reduction of the vaporized precursor produced nanosized tungsten powder. The effects of H2 concentration, plasma torch power, and the flow rate of plasma gas on the product properties were investigated and particle size was determined. From the results, nanosized tungsten powder of particle size less than 50nm was obtained by the thermal plasma process. [Copyright &y& Elsevier]

Abstract: Nanocrystalline WC–Co materials have been the subject of interests and focus of research programs around the world for the past two decades owing to the expectations that the mechanical behavior of the material may improve significantly when grain sizes reduce to nanometer scale. However, although numerous technologies are available for making nanosized tungsten carbide powders, obtaining true nanocrystalline WC–Co (average WC grain size <100nm) has been a great challenge due to the difficulties of controlling grain growth during sintering. Evaluation of the mechanical properties of nanocrystalline WC–Co materials is also difficult because there is little published data that are based on specimens with truly nanoscale grain sizes. In this review, the challenges and results of sintering nanocrystalline WC–Co powders will be examined as well as the various technologies for producing nanosized tungsten carbide powders. It will be discussed that the key challenge to the production of bulk nanocrystalline cemented tungsten carbide materials is to control the rapid grain growth during the early stage of sintering. The current understanding on the mechanical properties of cemented tungsten carbide made from nanoscaled WC–Co powders will also reviewed. [Copyright &y& Elsevier]