WC-Fe layer with high volume fraction and fracture toughness on cast iron fabricated by in situ solid-phase diffusion

A WC-Fe layer on cast iron was fabricated by in situ solid-phase diffusion method near the Fe-W-C ternary eutectic temperature. The phase composition and microstructure of the WC-Fe layer were studied by XRD, SEM, and EBSD. Meanwhile, the fracture toughness (K-IC) of the layer was tested and calculated by indentation method. The results showed that the main phases were WC and alpha-Fe on the surface WC-Fe layer after removing excess tungsten plate, while the volume fraction of WC reached up to 86%. WC/alpha-Fe/WC laminar structure was formed due to the Fe atoms continued the stacking sequence of WC when they diffuse into the growth front. The cross-section microstructure showed evident gradient distribution characteristics. With the increase in holding time from 5 min to 135 min, the amount of Fe6W6C decreased, and the particle size of WC increased from 1.9 mu m to 3.1 mu m in the average. The K-IC of the WC-Fe layer was 7.45 MPa m(0.5), while the average hardness of WC-Fe layer was 16.88 GPa. The excellent K-IC of the WC-Fe layer when the volume fraction of WC was extremely high due to WC-Fe-WC laminar structure, was formulated by the incorporation of WC-layered growth and Fe atom stacking mode.