Synthesis Of Ultrafine WC And WC-Co Powders By Integrated Mechanical And Thermal Activation Process

Synthesis of ultrafine WC and WC-Co powders respectively using WO3-G and WO3-G-Co3O4 powder mixtures as starting materials by high energy ball milling followed by reduction and carburization has been comparatively investigated by XRD and SEM techniques. The energy transfer calculation during milling revealed that the mean velocity of milling ball increased linearly with the increase of milling speed Ω. The increase of the ball-to-powder weight ratio RBP resulted in significant increase of average impact frequency f, decrease of average free path S, and slight decline of milling ball velocity . During the milling of WO3-G and WO3-G-Co3O4 starting powders, the size of milled powders gradually decreased with the increase of the milling time, and the reduction reaction of WO3 to WO2 occured at different stages. With the higher milling speed Ω, the grain size would be finer. The ball-to-powder weight ratio RBP had a significant effect on solid-state reduction reaction between WO3 and graphite. The higher RBP, the shorter is the incubation period of the reduction reaction. Addition of Co3O4 is helpful to the improvement of the milling efficiency. The optimum milling process parameters were ball-to-powder weight ratio RBP of 40:1, milling speed Ω of 500r/min, miling time of 12h in WO3-G system, and RBP of 30:1, Ω of 500r/min, miling time of 9h in WO3-G-Co3O4 system. The grain size of final milled powders was in the range of 70-100nm.The WO3-G and WO3-G-Co3O4 powders milled by optimum milling process were respectively subjected to reduction reaction in a flowing gas mixture of H2 and Ar. With the increase of reduction temperature and time, the main reaction sequence appears as WO3→WO2.9→WO2→W in WO3-G system, and the main reaction sequence appears as WO3→WO2.9→WO2.72→WO2→W in WO3-G-Co3O4 system. The optimun reduction process parameters were reduction temperature of 700℃, redction time of 2h. The grain size of final reduced powders was in the range of 100-200nm.The powder reduced by optimum reduction process was carburized in a flowing Ar. In WO3-G system, with the carburation temperature and time increased, W2C formed at first, furthermore, it gradually converted to WC. With the increase of carburation temperature and time, the main carburization reaction sequence appears as W(Co3W)→Co6W6C→Co3W3C→W2C→WC in WO3-G-Co3O4 system. Co had catalysis on the reduction and carburization reaction. The optimun carburization process parameters were carburization temperature of 1000℃, carburization time of 2h. The grain size of final WC was in the range of 400-500nm. The optimum carburization process parameters were carburization temperature of 900℃, carburization time of 2h. The size of WC grain in the final WC-Co composite powders was in the range of 200-300nm.