Microstructure and fracture toughness of a WC-Fe cemented carbide layer produced by a diffusion-controlled reaction

To improve the mechanical properties of the surface of iron-based alloys, a tungsten carbide-iron (WC-Fe) cemented carbide layer is produced on an alloy by adopting an isothermal annealing process, which was performed at 1050 °C for 4 h. By deeply etching the obtained sample, the morphologies of the WC ceramic grains in the WC-Fe hardmetal layer are characterized via scanning electron microscopy. The present results reveal three distinct morphologies consisting of rectangular, triangular prism and multi-layered shapes. Furthermore, the mechanical properties and fracture toughness of the WC-Fe layer are investigated through combined nanoindentation and Vickers indentation techniques. Nanoindentation testing is performed in a load range of 100 to 450 mN. Based on the data collected from the nanoindentation results, the average values of the hardness, Young' modulus and deformation ratio are evaluated, and the fracture toughness is determined to have a value of 3.08 MPa·m½ at 450 mN. In the Vickers indentation technique, however, by identifying the crack type and choosing the appropriate model, the fracture toughness is calculated to be 1.85–3.44 MPa·m½ at applied loads ranging from 0.98 to 4.9 N. The obtained fracture toughness results exhibit good consistence between the nanoindentation and Vickers indentation methods.