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The transition of material removal mode of polycrystalline 3C-SiC cutting with temperature, i.e., from brittle mode cutting that is dominated by inter-granular fracture and grain pulling-out at low temperature to ductile mode cutting that is governed by intra-granular cracking and dislocation slip. [Display omitted] • Temperature-dependent mechanical properties of both grains and GBs in polycrystalline 3C-SiC at elevated temperatures are derived. • Temperature-dependent properties of 3C-SiC GBs are bridged between MD simulation and FE simulation with cohesive zone model. • There is transition from brittle mode by inter-granular fracture toductile mode by intra-granular cracking with temperature. While the deformation behavior of grain boundaries has a strong impact on the mechanical response of polycrystalline materials, investigating the coupled thermal–mechanical properties of grain boundaries in their real formats is crucial for enhancing the ductile machinability of hard brittle polycrystalline ceramic materials. In the present work, we report the thermal softening-suppressed inter-granular fracture, accompanied with enhanced stacking fault formation, increased healing ability of grain boundaries and promoted ductile material removal, in diamond cutting of polycrystalline 3C-SiC at elevated temperatures by multi-scale simulations. Molecular dynamics simulations and experiments of high temperature nanoindentations are performed to derive the temperature-dependent mechanical properties of bulk polycrystalline 3C-SiC. Furthermore, molecular dynamics simulations of Mode I (tension) and Mode II (shearing) loading of a Σ9<1 1 0>{1 2 2} symmetric tilt grain boundary at elevated temperatures are performed to extract the temperature-dependent mechanical properties of grain boundaries in polycrystalline 3C-SiC. A novel finite element model of heat treatment-assisted diamond cutting of polycrystalline 3C-SiC with the comprehensive consideration of thermal properties of both grains and grain boundaries at elevated temperatures is established to reveal the transition of material removal mode, grain boundary failure behavior, cutting force characteristics and chip profile with temperature. [ABSTRACT FROM AUTHOR]