RESUMO
The synthesis and consolidation of nano-sized W powders are attempted with the combination process of hydrogen reduction of ball-milled WO3 powder and spark plasma sintering. The reduction behavior of WO3 is analyzed by temperature-programmed reduction. The reaction peaks for reduction of WO3 are observed in the temperature range of 590-782 °C. XRD and TEM analysis reveals that oxide powder is changed to metallic W with an average particle size of 100 nm by hydrogen reduction at 900 °C for 1 h. The densified specimen by spark plasma sintering at 1700 °C under an applied pressure of 50 MPa using nano-sized W powder shows increased relative density compared with that using micron-sized W powder. The results suggested that the W bulk with increased relative density fine microstructure can be fabricated by spark plasma sintering of hydrogen-reduced WO3 powder, more effectively.
RESUMO
Cu-70 vol% SIC composites with dense microstructure and sound interface between Cu and SIC grains were fabricated by solution chemistry route and spark plasma sintering. Two methods for developing powder mixtures of Cu and uncoated or pre-coated SIC were compared on the basis of the resulting microstructures. The pre-coating of Si(Al)OC onto SiC powders was prepared by curing and pyrolysis of Al-modified polycarbosilane. SiC/Cu composites were obtained by hydrogen reduction and densified using spark plasma sintering of pre-coated SIC and Cu-nitrate powder mixtures. The powder mixture showed a homogenous dispersion of nano-sized Cu particles on the surface of SIC powers. Microstructural observation revealed that the sintered composite using powder mixture with pre-coating of Al-PCS onto SiC powders showed dense microstructure and good contact between Cu and SIC grains due to the improved wettability by barrier coating. The results suggested that the SiC/Cu composite with required microstructural characteristics can be fabricated by using Al-PCS coated SIC powder mixture, more effectively.
