Molecular Dynamics Simulation and Experimental Study of Brittle-Plastic Transition Behavior of Monocrystalline Ge at Micro- and Nano-scale

Molecular dynamics (MD) was used to study the brittle–plastic transformation behavior of monocrystalline Ge during nano-cutting. The cutting force, chip morphology, and atomic microstructure of monocrystalline germanium at different material removal stages were studied by establishing a variable depth molecular dynamics nano-cutting model. In the elastic stage, the cutting force fluctuated around 5 nN. When entering the plastic cutting stage, phase changes occurred inside the material, forming two phase variant atomic structures of Ge, and the number of phase change atoms increased with the increase of cutting depth. When the cutting distance reached 15 nm, the cutting force fluctuated markedly and the material was transformed into brittle plastic. The calculated cutting depth was 5.46 nm and the critical load was 74.82 nN. In the subsequent cutting process, material removal was carried out in a brittle manner, a large number of phase change structures appeared inside the material, and the chips began to accumulate in the front end of the tool. The monocrystalline Ge variable depth nano-cutting experiment was used to verify the simulation indirectly, and the critical depth of brittle plastic transition was 610.75 nm and the critical load was 34.87 mN.