Fig. 1. Sequential TEM images showing the in situ TEM mechanical bending experiment conducted on a FIB lamella. (a) The configuration before loading. The purple symbol denotes the indentation direction pushing downward along the beam direction, and a precut notch was indicated by a white arrow. (b) No crack was observed after 3 min of continual loading. The arrows indicate bending contours. A crack initiated at the notch (c) and propagated along with a WC-Co interface (d, e). (f) The crack deflected into an abutting WC grain. The red arrows in (d-f) indicate the fracture path.

Fig. 2. AC-STEM characterization of an interested WC-Co interface before fracture. (a, b) Kikuchi patterns of the Co binder and the WC grain, respectively. (c) High-resolution HAADF image of the interface. Inset: Low magnified BF image of the interface. EDS maps across the interface were given in (d-g). (h) Line profile of W (M edge), Co (K edge), and V (K edge) signals integrated across the interface. (i) Composition profile of W, Co, and V solutes for each interfacial layer. The shaded areas in (h, i) are used to denote the interfacial complexion.

Fig. 3. AC-STEM characterization of the as-fractured WC-Co interface. (a) The first frame of the HAADF image of the cleavage surface on the WC side, acquired under a low screen current (20 pA) without introducing discernable beam damage. Inset was a low magnified BF image of the interface. EDS maps (b-e), EDS intensity line profile (f), and composition profile (g) analysis were performed across the interface. The shaded areas in (f, g) are used to highlight the interfacial complexion.

Fig. 4. (a) DFT-optimized interfacial structure of a V-doped WC(B)-Co interface. The atomic configuration was constructed from the experimental interfacial structure in Fig. 2. The interfacial layers dominated by metallic and carbon atoms are labeled by subscript M and C, respectively. (b) Works of separation (Wsep) as a function of separation positions across the interface.