Origin of the distinction in hardness of lower tungsten carbides: An experimental and ab initio theoretical study

Abstract

The so-called lower tungsten carbides W 2 C and Fe 3 W 3 C often appear in tungsten carbide-reinforced iron matrix (WC-Fe) composites. The effect of their presence on the mechanical properties of the material, such as hardness, is not well understood. In this study, we extensively measured the hardness distribution in the WC-Fe composites and also performed hundreds of microhardness measurements to determine the hardness values for the lower carbides. The hardness values calculated by ab initio were compared, where the theoretical values of Fe 3 W 3 C had little difference from the experimental values. However, the experimentally obtained hardness data for W 2 C were significantly smaller than the reported theoretical data. Moreover, the experimental hardness values for W 2 C reported in the literatures are very different. To understand the origin of the discrepancy, the focused-ion-beam-transmission-electron-microscopy technique was used to obtain the high-resolution images of W 2 C, which revealed a high density of planar defects. As a further comparison, ab initio molecular dynamics simulations illustrate that the complex interactions between different atomic pairs in Fe 3 W 3 C make it difficult for this type of crystal defect to occur. The lattice of W 2 C can adjust-resulting in shuffle defects and stacking faultsto a certain degree affecting its hardness, which was not revealed in previous studies.