配碳量对原位碳热反应制备Co_(x)W_(y)C复合粉末微观结构的影响

Effects of Carbon Addition on Microstructure of Co_(x)W_(y)C Composite Powders Prepared by In-situ Carbothermal Reaction

采用Co_(3)O_(4)、WO_(3)和C为原料(配碳量即碳的质量分数分别为10.15%、11.47%、12.76%、14.01%),通过原位碳热反应工艺获得Co_(x)W_(y)C复合粉末,着重研究了配碳量对Co_(x)W_(y)C复合粉末微观结构的影响规律。结果表明,由于碳化反应在还原完成后进行,Co_(x)W_(y)C复合粉末的氧含量均低于0.1%。Co_(x)W_(y)C复合粉末的物相与配碳量密切相关:当配碳量为10.15%时,物相为W相和Co_(7)W_(6)相;增加配碳量至11.47%,物相转变为Co_(6)W_(6)C相;继续增加配碳量至12.76%,复合粉末中出现Co_(3)W_(3)C相和WC相;当配碳量为14.01%时,Co_(3)W_(3)C相和WC相的含量增加。原位碳热反应过程中钨和钴在高温下发生相互扩散而形成烧结颈,使Co_(x)W_(y)C复合粉末呈树枝状形貌。碳快速扩散形成密度较低的Co_(6)W_(6)C相,使复合晶粒的体积发生膨胀而裂开,提高了Co_(x)W_(y)C复合粉末粒度分布的均匀性。当配碳量增大至14.01%时,复合粉末树枝状颗粒表面原位析出细小的WC晶粒。

Co_(x)W_(y)C composite powders were synthesized by in-situ carbonthermal reaction using Co_(3)O_(4),WO_(3)and C as the raw powders with different carbon mass fraction(10.15%,11.47%,12.76%and 14.01%).And the influence law of carbon addition on the microstructure of Co_(x)W_(y)C composite powders was emphatically studied.The results show that the oxygen content of Co_(x)W_(y)C composite powders is less than 0.1%as the carbonization process is carried out after the completion of reduction.At the same time,the phase of Co_(x)W_(y)C composite powders is closely related to its carbon addition.When the carbon addition is 10.15%,the phase consists of W and Co_(7)W_(6).When the carbon addition increases to 11.47%,the phase changes to Co_(6)W_(6)C.And when the carbon addition increases to 12.76%,Co_(3)W_(3)C phase and WC phase appear in the composite powders.When the carbon addition reaches 14.01%,the content of Co_(3)W_(3)C phase and WC phase both increases.In addition,there is mutual diffusion between tungsten and cobalt at high temperature during the in-situ carbonthermal reaction to form sintering neck,resulting in the dendritic morphology of Co_(x)W_(y)C composite powders.And the rapid diffusion of carbon forms a Co_(6)W_(6)C phase with low density,which causes the composite grains to expand and crack,improving the homogeneity of the particle size distribution of Co_(x)W_(y)C composite powders.When the carbon addition increases to 14.01%,fine WC grains are in-situ precipitated on the surface of the dendritic particles of the composite powders.