球磨时间对超细WC-Co复合粉体粒度影响规律及其细化机制

Influence of Milling Time on Preparation of Ultrafine WC-Co Composite Powder and Its Refinement Mechanism

研究球磨时间对紫钨棒长径比及WC-Co复合粉粒度影响规律,通过对中间过程组织观察得WC-Co复合粉细化机制。采用扫描电子显微镜(SEM)、透射电子显微镜(TEM)、能谱(EDS)及X射线衍射(XRD)表征各阶段所获得的粉体的物相组成、微观形貌。试验表明,紫钨棒随着球磨时间延长平均直径减小,平均长度增长,当球磨时间为40 h时,紫钨棒平均直径为142 nm,平均长度可达6.95μm,经还原-碳化得到尺寸均匀,其平均颗粒尺寸为126 nm的超细WC-Co复合粉;所制备大长径比的紫钨棒之间相互交错形成连通的孔隙,使得紫钨颗粒具有良好的通透性,在还原过程中有利于还原性气体进入到紫钨内部,降低了原子扩散距离,大大缩短了还原时间,同时紫钨棒之间相互交错形成连通的孔隙有利于反应生成的水蒸汽溢出,有效抑制了WO2(OH)2生成,降低了颗粒长大趋势;WO2.72/CoWO4的还原-碳化过程中沿着棒的径向方向断裂,为固相局部化学反应机制占主导地位,紫钨棒的直径大小决定了WC-Co复合粉颗粒尺寸。

Influence of milling time on the aspect ratio of WO2.72 rods and the particle size of WC-Co composite powder was studied.The refinement mechanism of WC-Co particles was obtained by observing the microstructure of intermediate in the reduced carburization process.Phases and microstructures of powder obtained at each stage were characterized by scanning electron microscopy(SEM),transmission electron microscopy(TEM),energy dispersive spectroscopy(EDS) and X-ray diffraction(XRD).The results showed that the average diameter of WO2.72 rods decreased when the milling time increased,while the mean length of WO2.72 rods became longer with the increasing of milling time.When milling time was 40 h,the average diameter and the average length of WO2.72 rods were 142 nm and 6.95 μm,respectively.After reduced carburization,the as-synthesized ultrafine WC-Co composite powder had a homogeneous particle size distribution with the average size of about 126 nm.As-synthesized WO2.72 rods with large aspect ratio interlace each other to form interconnected pores,which made WO2.72 rods have good permeability.During reduction process,reductive gas could easily enter into WO2.72 rods inside,which could reduce atom diffusion distance and greatly shorten reduction reaction time.At the same time,the production of water vapor could overflow to outside and it inhibited growth trend of the particles.The reduced carburization process was controlled by solid-state local chemical reaction mechanism.Therefore,the particle size of WC-Co composite powders was determined by the diameter of WO2.72 rods.