Abstract

Cemented tungsten carbide (WC-Co) is an indispensable material used in many manufacturing sectors including metalworking, oil and gas drilling, geothermal energy exploration, mining, construction, high-wear components, and other applications. The wide range of applications of WC-Co is because of its superior combination of high modulus, high hardness, wear resistance, and moderate fracture toughness. However, the wear resistance and fracture toughness of WC-Co composites are inversely related to each other. Wear resistance is often improved at the expense of the fracture toughness, and vice versa. This, in turn, limits the potential use of the material in manufacturing operations.

One method for improving the fracture toughness without sacrificing wear resistance (or vice versa) of WC-Co materials is to use functionally graded WC-Co composites that have varying cobalt content from surfaces to the interior. With the cobalt gradient, the hardness and toughness of the material change correspondingly. The surface of the part with relatively low cobalt content has high wear resistance, while the interior of the part with relatively high cobalt content exhibits high toughness. The functionally graded structure with cobalt gradient thus offers advantages in terms of the combinations of fracture toughness and wear resistance in comparison to the conventional homogeneous WC-Co materials.

Manufacturing functionally graded WC-Co, however, presents a difficult problem. Cemented tungsten carbide is typically sintered via liquid phase sintering process in vacuum. When WC-Co with an initial cobalt gradient is subject to liquid phase sintering, the migration of liquid phase can easily occur and any gradient of cobalt content is easily eliminated. A solution to this problem is to employ pressure assisted sintering techniques such as Hot Isostatic Pressing (HIP) and spark plasma sintering to consolidate the graded WC-Co compact at solid state. However, these alternative processes have limited industrial applications because the high pressure processes are very costly.