Fracture toughness of WC-Fe cermet in W-WC-Fe composite by nanoindentation

Abstract To enhance the strength of iron-based alloys, tungsten carbide (WC)-reinforced iron (Fe) matrix composite with a double-scale structure is proposed and produced through a general heat-treatment process at 1150 °C for 40 min. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses reveal that the double-scale structure involves both reinforcement elements of WC particle and W-WC pillar, where the WC-Fe cermet enwraps the metal tungsten wire. The chemical composition of WC-Fe cermet is studied, and the contents of Fe and W elements present a gradient distribution. Moreover, the hardness, elastic modulus and fracture toughness of WC-Fe cermet are evaluated via nanoindentation. The evaluation of toughness is based on the indentation method and the appropriate selection of equation at the same load. The results obtained show that the fracture toughness value is within the range of 4.11 ± 0.91–7.89 ± 1.02 MPa m 1/2 , which is considerably dependent on the composition. The investigations of crack surface morphologies indicate that radial cracks at the corners of the indentation originate from the crossing of slip bands and that the toughening mechanism is mainly crack deflection, grain bridging and intergranular fracture in the Fe-rich zone.