The Chinese Journal of Nonferrous Metals
Synthesis of ultrafine WC-Co powders was investigated using WO_3, Co_3O_4 and graphite powders as starting materials by high energy ball milling followed by reduction and carburization. The results show that particle sizes of powder mixtures milled 30h are in the range of 70100nm. When the milled mixture is reduced in a flowing gas mixture of H_2 and Ar at different temperatures ranging from 450 to 700℃ for 2h, the reaction sequence of WO_3 to W appears as WO_3→WO_(2.9)→WO_(2.72)→WO_2→W with the increase of temperature, and WO_3 reduction completes at 700℃. Reduction reaction of Co_3O_4 to Co can be finished in 2h at 450℃ and the reduced Co keeps reacting with W to transform into Co_3W with the increase of reduction temperature and time. The final product of reduction reaction is composed of W, Co, Co_3W and graphite. The reduced mixture is carburized in a flowing Ar in temperature range of 7001000℃, carburization reaction takes place following the routine W(Co_3W)→Co_6W_6C→Co_3W_3C→W_2C→WC, and the carburization reaction completes at 900℃ in 2h. The size of the WC grain in the final WC-Co composite powders is in the range of 200300nm.