Study On Preparation And Characterization Of Ultrafine WC-Co And WC-Ni₃Al Cermets

Abstract:Cemented carbides are widely used as machining, drilling, cutting, forming and mining tools, as well as high-performance construction and wear resistant parts due to their high hardness and strength. Ultrafine grained cemented carbides have been used extensively in industrial areas owing to their enhanced hardness, wear resistance and toughness than traditonal coarse grained hard materials. However, abnormal grain growth during sintering substantially inhibits the wide application of ultrafine grained cemented carbides. WC-Co composites are the most important conventional and commercial grade WC cermets. However, due to some shortcomings of cobalt, such as poor resistance to corrosion and low strength at elevated temperatures, a significant research effort has been made to find a replacement for Co as the binding metal. Intermartallic aluminides have potential as an alternative binder in WC-Co composites. Aluminides are known to be extremely resistant to corrosion under sulfidizing and oxidizing atmospheres and in molten salts, as well as having high strength at elevated temperatures. Among the intermetallic aluminides, Ni3Al attracts greatest interest as a new binder due to the special properties.In this paper, the ultrafine grain WC-10Co and WC-Ni3Al cemented carbides were prepared through planetary ball milling method and low pressure sintering. The effects of LaB6addition on the microstructures and mechanical properties of WC-10Co alloys, and the effect of LaB6addition and content of Ni3Al on the microstructures, mechanical properties and corrosion resistances of WC-Ni3Al alloys were investigated by X-ray diffraction, scanning electron microscope, mechanical property testing and electrochemical experiments. The main conclusions are summarized as following:1. For the WC-10wt.%Co alloys, the addition of small amount of the LaB6(less than1wt.%) can inhibit the continuous and discontinuous growth of WC particles. The addition of LaB6can increase the relative densities, micro-hardness and fracture toughness of alloys. However, adding excess LaB6can lead to the decrease in micro-hardness and toughness of alloys. The LaB6addition decreases the formation of Co3W3C phase and promotes the formation of CoWB, W2Co21B6and LaBO3phases.2. For the WC-20vol.%Ni3Al alloys, the addition of small amount of the LaB6(0.0967wt.%) can inhibit the growth of WC particles. The addition of LaB6decreases the formation of Ni2W4C phases. However, adding excess LaB6can lead to the formation of Ni3W9C4phases in WC-20vol.%Ni3Al alloys. The addition of LaB6can increase hardness, fracture toughness and compressive strength, but reduce the corrosion resistances of WC-20vol.%Ni3Al alloys. With increasing the content of Ni3Al, the corrosion resistance of WC-Ni3Al alloys decreases. Compared to WC-Co composites, of WC-Ni3Al hard metal show better corrosion resistance in acid solution.