α-SiC-induced embrittlement in WC-(Co, Ni) hardmetals

Abstract

This study systematically investigates the effect of adding α-SiC (0, 0.7, 1.3, and 3.2 wt%) on the microstructure, residual stresses, and mechanical performance of WC-11(Co, Ni)-based hardmetal processed by liquid-phase sintering at 1400 °C. A slight increase in hardness was observed, rising from 12.64 to 13.24 GPa with the addition of 0.7 wt% α-SiC. However, the transverse rupture strength (TRS) dropped by approximately 71% (from 1219 ± 114 MPa to 355 ± 87 MPa) at 1.3 wt% α-SiC, far exceeding the 10–20% losses typically associated with conventional grain growth inhibitors. Fracture toughness (KIC) decreased by 57% (from 26.0 ± 5.6 to 11.2 ± 1.9 MPa m1/2), accompanied by a transition from the Palmqvist crack regime to the radial-median crack regime, indicating pronounced embrittlement. Densification was progressively impaired, with the apparent density falling by 3.4%. XRD and SEM analyses revealed the underlying degradation mechanism: partial dissolution of α-SiC t promotes the formation of brittle Co0.85Si0.15, Co₂Si and Ni₂Si silicides, which consume the ductile binder phase, promote abnormal WC grain growth, and intensify compressive residual stresses (from −150 to −1000 MPa). These combined effects result in a pronounced reduction in mechanical strength and toughness. These combined effects result in a marked loss of mechanical strength and toughness. Overall, the results demonstrate that α-SiC, under the evaluated conditions, does not function as an effective reinforcement or grain growth inhibitor, but rather promotes microstructural instability through binder modification, silicide formation, and increased residual stresses, underscoring the need for careful control of composition and processing parameters for industrial applications.