Carbide Injection Molding Process

With the development of industry, the cemented carbide parts are developing to shape-complexity, high strength and hardness to satisfy the increasing demand for automobile and other industries fields. Powder injection molding (PIM) is a novel near-net-shape technology to fabricate complex-shape parts, which have the advantages, such as low cost, high dimensional precision, complex-shape. The development to superfine grain can make the cemented carbides obtain higher strength and hardness. According to the above aims, preparation processes of cemented carbides were studied deeply, which included PIM of fine particle cemented carbides, preparation of superfine WC-Co powder and PIM of superfine cemented carbides.First, the PIM of fine cemented carbides, including the design of binder, injection parameters, debinding process and the performance of sintered parts, were studied. That may provide a foundation to the PIM of superfine cemented carbides next study.Secondly, the effect of preparation of WC-8Co composite powder by high-energy milling, including liquid-to-solid, ball-to-powder, milling speed and milling time, were studied. Process parameters were optimized and good-dispersion powder with average grain size smaller than 0.3μm was fabricated.Finally, the PIM of WC-8Co powder fabricated by high-energy milling and WC-6Co powder by spray conversion process were studied. The results showed that the two PIM processes were uniform in substance, the PIM parts had higher performance by high-energy milling, which reached near-full-density, the transversal rupture strength and hardness reached 2500Mpa, 89HRA, respectively. The optical micrographs showed that the porosity was A02B00 , the two phases were homogeneous, and no graphite and η phase appeared. But the Co pool, WC grain conglomeration and growth appeared in the superfine YG6 sintered parts because of the uneven distribution of Co grain. C and O content of the superfine YG6 powder by spray conversion process can be controlledeasily, but it need later treatment.Compared with the PIM of fine grain cemented carbides, above two PIM process of superfine powder had lower powder loading and similar mixing, injection, debinding process, but the performance of sintered parts was lower. The main causes were that uneven distribution of Co grain in spray conversion powder and higher oxygen content in high-energy milling powder, which resulted in difficult control of carbon content in debinding and sintering process. On the other hand, the powder loading was lower, which induced distortion and inner defect.Thereby, the powder modification and design of binder need more improvement in the future, which is a main way to obtain high-performance PIM parts of superfine cemented carbides.