Effects of crystal anisotropy on nanoindentation deformation in single-crystal 4H-SiC

Single-crystal 4H-SiC is widely used in semiconductor devices and precision optical systems owing to its outstanding properties. However, its high hardness, brittleness, and strong covalent bonding pose challenges for low-damage machining. In this study, nanoindentation tests were carried out on C, M and A planes using a Berkovich diamond indenter. Load-displacement responses, hardness, apparent indentation modulus and indentation morphologies were analyzed under different loads. A stress field model was then used to resolve the indentation stress onto representative slip systems. Schmid factors for the three Berkovich contact faces were also calculated. The results show that the indentation response exhibits significant crystal orientation dependence. At room temperature, C plane exhibits the largest indentation depth and the greatest decrease in apparent indentation modulus as the load increases from 50 to 400 mN, whereas M and A planes show relatively higher indentation resistance. Cracks become more pronounced at higher loads, and their propagation paths depend on the crystallographic orientation. Under the present indentation geometry and loading conditions, the stress distribution and Schmid factor analyses indicate that basal <a> slip dominates plastic deformation on C plane, whereas prismatic <a> slip is more readily activated on M and A planes. These results clarify the coupling among indentation response, stress distribution and slip-system activity, and provide a theoretical basis for understanding crystallographic-orientation effects during the ultra-precision and low-damage machining of single-crystal 4H-SiC.