Growth mechanism of in-situ WC grain in Fe-Ni-W-C alloys system

In-situ WC grains were synthesized by using in-situ metallurgical reaction in W-Fe-Ni-C alloys system. The growth mechanisms as well as the coarsening process of WC grains were analyzed by XRD, SEM and ab initio calculation. Results show that the morphology evolution of in-situ WC growth unit evolves from sphere-like→icosahedron→octahedron→truncated-octahedron→flat-tri-prism. The final flat-tri-prism is bound by two basal facets {001} and three prismatic facets {1¯10}. In short, the growth process of in-situ WC grain includes two independent stages, one is the formation of WC growth unit on basal facets {001}, and the other is the lateral stack of WC growth units in facets {001} as well as the vertical stack of WC growth units along 〈001〉 direction. Finally the in-situ WC grain grows into multi-layered triangular prism. The coarsening of in-situ WC grains, known as the Ostwald ripening, is partly due to the prior formed WC grains basal facets {1¯10} can act as the heterogeneous nucleus of other newly generated WC grains hence promoting the forming of in-situ WC nucleus. The excellent mechanical properties, such as high hardness and good toughness, of WC grain benefit from its growth characteristics.