Fig. 1. Backscattered electron images of microstructures of as-sintered (a) WC-8Co and (b) WC-8Co-0.8TaC ultra-coarse cemented carbides, with rounded edges of WC grains marked by white arrows. Inset: the corresponding WC grain size distributions.

Fig. 2. Compressive strength of WC-8Co and WC-8Co-0.8TaC specimens at different temperatures. The insert shows the WC contiguity in the specimens at different compression temperatures.

Fig. 3. Statistical analysis of crack density at different temperatures for WC-8Co and WC-8Co-0.8TaC specimens.

Fig. 4. Stress distributions in the microstructures of WC-8Co (a) and WC-8Co-0.8TaC (b) specimens after compression at 800 ℃, and comparison of the stress distribution at representative locations at WC skeleton between WC-8Co (left panel) and WC-8Co-0.8TaC (right panel) specimens (c). The local regions in (c) are corresponding to those circled in (a) and (b), respectively.

Fig. 5. Average dislocation density in WC grains and the dislocation density at (0001) WC plane in WC-8Co and WC-8Co-0.8TaC specimens compressed at different temperatures.

Fig. 6. Dislocations in WC-8Co (a, b) and WC-8Co-0.8TaC (c, d) specimens after compression at 800 ℃, observed along [$\bar{1}$2$\bar{1}$0] and [0001] directions, respectively.

Fig. 7. Composition analysis in the vicinity of WC/Co phase boundary with round edge of WC grain in the WC-8Co-0.8TaC specimen: (a) HAADF image of a phase boundary; (b-e) Elemental distributions of Ta, C, Co, and W in the vicinity of phase boundary; (f) Composition distribution along the line marked in (a).

Fig. 8. 3DAP analysis on the position in WC grain (a), Co phase (b), and at WC/Co phase boundary (c) in the WC-8Co-0.8TaC specimen. The analyzed positions are marked by white circles in the SEM image.

Fig. 9. Microstructure evolution of the ultra-coarse grained cemented carbide with TaC addition during sintering, and schematic diagrams illustrating the processes of Ta dissolving into WC grains: (a1, a2) Mixing of powder particles; (b1, b2) Solid-state sintering stage, where rapid WC grain growth occurs; (c1, c2) Liquid-state sintering stage, where Ta diffuses into WC during the dissolution-precipitation processes; (d) Ta distribution in WC lattice by occupying W sites.

Fig. 10. Schematic diagrams for the formation of WC dislocation patterns: (a) Typical dislocations slip in WC crystal without any addition; (b) Dislocations slip in WC crystal containing substitutional Ta solute atoms; (c, d) Cross-slip of WC dislocations onto adjacent prismatic and basal planes, respectively, when hindered by Ta-rich clusters, leading to the formation of corrugated and short dislocation lines on the slip plane.