Comparative Study on Microstructure and Mechanical Properties of Coarse-grained WC-based Cemented Carbides Sintered with Ultrafine WC or (W+C) as Additives

The effects of ultrafine WC(WC_(UF),0.5μm) or W(1μm) and C(0.3μm)(W+C)_(UF) additives on the densification,microstructure and mechanical properties of coarse-grained cemented carbides were compared systematically.Overall,the cemented carbides with WC_(UF)/(W+C)_(UF) additives are almost fully densification to be higher than 99%,and the average grain size is kept above 2.8μm.The WC_(UF) additive assists grains to(truncated)trigonal prism shape by two dimensional(2D) growth,whereas the(W+C)_(UF) additive assists grains to rounded shape by three dimensional(3D) growth,lowers WC contiguity and increases face-centered-cubic Co.The hardness and bending strength of(75WC_(C)-15WC_(UF))-10Co are 86.6 HRA and 2 272 MPa,respectively,both higher than those of(75WC_(C)-15(W+C)_(UF))-10Co,which could be ascribed to the enhanced densification and unblemished grains.However,the fracture toughness of the(75WC_(C)-15(W+C)_(UF))-10Co is 23.5 MPa·m^(1/2),higher than that of the(75WC_(C)-15WC_(UF))-10Co due to the uniform WC-Co structure and flexible binder phase.

Surface Features and Friction Characteristics of Porous and Coarse-grain WC-3%Co

The main components of cemented carbides include tungsten carbide(WC) and cobalt(Co),of which their melting point and density vary widely.It is not suitable for preparing porous cemented carbides according to the preparation process of the ordinary porous metal.In the paper,the porous cemented carbide was prepared with coarse-grain and low-cobalt alloy by modifying its sintering process.The surface features were observed through the metallurgical microscope,scanning electron microscope and three-dimensional profile instrument.The friction characteristics of WC/GCr15 sliding couplings under the dry condition were evaluated with the adoption of a ball-on-disk tribometer.The experimental results show that the porosity of porous cemented carbides varies from 7.5%to 9.0%.Their density and hardness decrease slightly.The size and depth of pits on their surfaces of porous cemented carbides are not quite uniform,namely,the depth ranges from several microns to 32 urn,which can be used to store the particles.The friction coefficient of porous cemented carbides is lower than the dense ones,and the wear resistance accordingly increases.It can be indicated that porous structure may have exerted an important influence on the dry friction properties of cemented carbides.