Study On Preparation Of Ultrafine Hardmetal Rods

With the great progress of electronics industries, there has been a strong tendency towards finer and finer microdrills for printed circuit boards (PCBs) and demand for them is growing. Over these years, although the research and exploitation of fine-grained WC-Co have dominated the application of WC-Co hardmetal rods, the development of industrialization of ultrafine-grained WC-Co hardmetal rods remains unfavorable. This study is in progress under these circumstances and reports the molding technique (die pressing, powder extrution molding) and sintering technique (vacuum sintering, sinter-HIP) of nanocomposite WC-Co powders, which is prepared in Wuhan University of Technology and in UM Company in USA.The process of die pressing and sintering is as follows: composite powders + binder + grain growth inhibitors - ball-milled - dried in vacuum -granulation process - die pressing - cold isostatic pressing (CIP) -vacuum sintered - sinter-HIP - rodsThe process of powder extrusion molding (PEM) is as follows: composite powders + binder + grain growth inhibitors - mixing --PEM - cold isostatic pressing (CIP) - debindering - vacuum sintered - sinter-HIP - rodsThe phases of composite powders, vacuum sintered samples and sinter-HIP samples were studied by XRD. Results showed that no phases and graphite phase appeared.The performance of die pressing rods and extrusion rods with CIPtreatment was studied by SEM. Results showed that CIP treatment affected the die pressing rods greatly, but affected hardly the extrusion rods.The microstructure of rods sintered in vacuum and by sinter-HIP was investigated by metallographic microscope, SEM and TEM. The metallographic figure showed that the WC grains were fine and uniform. The SEM micrographs showed that the grain size of WC sintered in vacuum or by sinter-SIP was 200-300 nm and 300-400 nm, respectively. The TEM micrographs showed that most WC particles exhibited polygonal forms and were surrounded by Co. The WC grain size was 300-400 nm, which was the same as the result of SEM.Transverse rupture strength, Rockwell A hardness, magnetic saturation induction and magnetic coercivity of samples sintered in vacuum or by sinter-HIP were measured. Results showed that sinter-HIP treatment can enhance the transverse rupture strength of WC-Co cemented carbides effectively. The magnetic saturation induction and magnetic coercivity can be the measurement of content of carbon and grain size of WC, respectively. The WC-Co cemented carbides rods with superior strength (3300 MPa) and high hardness (HRA = 93.2) were produced by sinter-HIP technology from nanocomposite WC-Co powder prepared in Wuhan University of Technology.