Understanding anisotropic brittle-plastic transition mechanism of 4H-SiC monocrystal in ultra-precision micro grinding

4H-SiC monocrystal demonstrates outstanding physical and chemical properties. In this study, the anisotropic material removal behavior of three representative crystalline planes was investigated by variable depth flute ultra-precision grinding experiments. Surface morphology analysis, in-situ monitoring of grinding force and acoustic emission (AE) signals were conducted to reveal the damage formation mechanisms associated with different crystallographic directions. Experimental results indicated that C plane exhibited pronounced brittle fracture when subjected to grinding along the < 2–1–10 > directions. M plane exhibited brittle removal characteristics when ground along the [2−1−10] and [0001] directions. A plane exhibited a significant tendency toward plastic deformation, which was attributed to its relatively sparse atomic arrangement that facilitates the activation of slip systems. The dynamic model of grinding force prediction combined with wheel geometry parameters was developed according to the interaction mechanism between diamond abrasive and the material surface to be processed. The model quantified anisotropic behavior by evaluating the proportion of brittle removal. Moreover, AE signal analysis revealed the positive correlation between time domain energy intensity and grinding depth. Frequency domain results showed that AE signals in the 15–100 kHz range were primarily associated with plastic deformation, whereas those in the 100–130 kHz range corresponded to brittle fracture. Microscopic characterization of the etched post-grinding surface revealed that cracks preferentially propagated along slip or twinning planes, which aligned with the atomic rearrangement direction following Si-C bond rupture. The crack propagation was inherently governed by crystallographic direction.