Structure and mechanical properties of WC interlayers between iron substrate and thin tungsten plate

Abstract

To improve the mechanical properties of cast iron (Fe) surface, tungsten carbide (WC) interlayers were fabricated by the in-situ reaction at 1050 °C and 1100 °C for different heat-treatment times. The structure and phase composition of the layer were investigated via scanning electron microscopy, transmission electron microscopy and X-ray diffraction analyses. The effect of vacuum atmosphere temperature on the interfacial structure of sample was discussed. The results indicate that the thickness of the layer, consisting of a dominant WC phase, has a range of 11.12 ± 1.32 to 51.51 ± 1.36 μm obtained at 1050 °C. Based on growth kinetics, the diffusion coefficient of carbon in the WC layer is calculated to be 1.57×10−9 cm2/s. Furthermore, under the load of 100 mN, nanoindentation tests demonstrate that values of hardness and elastic modulus of the layer are approximately 25.09–39.74 GPa and 649.54–834.17 GPa, which are 2.4–3.8 times and 3.5–4.4 times larger than that of the substrate, respectively. By means of Vickers indentation mode using the available equation for Palmqvist crack system, the value of the calculated fracture toughness for the layer changes in a range from 2.55 ± 0.14 to 6.34 ± 0.54 MPa⋅m1/2, and the value decreases with the increasing load. This result may be caused by the reason that the fracture resistance also strongly depends on the applied load.