Fundamental study on material removal mechanism in single-crystal germanium

Abstract

In this study, vary-loads and const-load nano-scratching tests were performed to investigate the material removal mechanism in single-crystal germanium. Based on the indentation size effect, the cutting force in the ductile regime was modelled analytically considering the elastic recovery and sliding friction. Subsequently, a novel specific cutting energy (SCE) model was proposed to quantitatively determine the ductile to brittle transition (DBT) depth. The surface topography of the workpiece was observed and measured using a scanning electron microscope (SEM) and an atomic force microscope (AFM). The surface morphology revealed the existence of a ductile regime, DBT regime, and brittle regime in the nano-scratching process. The DBT depth was calculated analytically using the proposed SCE model, which had a prediction error of less than 4.02%. Thus, the model results were in good agreement with the experimental results. The phase transitions of different material removal modes were characterised using Raman spectroscopy, which revealed that the phase transition from the crystalline phase to the amorphous phase dominated the material removal process. In addition, the feasibility of high-efficiency machining by increasing the cutting speed was verified: the surface integrity improved and the subsurface damage reduced at high cutting speeds. These findings provide a fundamental understanding of the ductile regime machining process for single-crystal germanium.