Research On Brittle-ductile Transition Mechanism Of Single Crystal Germanium In Micro-nano Scale

With the continuous development of micro nano machining technology,single crystal germanium brittle materials are widely used in infrared optics,microelectromechanical systems and other high-tech fields,where the material surface processing precision has reached the nanometer level,which requires processing theory and method for ultra precision as support.In order to make single germanium and other brittle material are removed in the way of brittle cutting,which can obtain high quality optical surfaces,the key point is controlling the condition of brittle-ductile transition,it is often necessary to control the cutting depth at the nanometer level.Due to the single crystal germanium is hard brittle material and anisotropy,it is very important to determine the critical cutting thickness of brittle-ductile transition to achieve brittle ductile transition and produce a smooth surface.However,there has not been a unified theoretical understanding and processing method for the plastic domain cutting of brittle materials such as single crystal germanium.With the help of molecular dynamics simulation,nanoindentation and scratch test and theoretical analysis,the cutting mechanism of the plastic domain in the different crystal surface of the single crystal germanium are studied.Critical cutting depth of single crystal germanium brittle-ductile transition is achieved by studying critical cutting depth of single crystal germanium brittle ductile transition,which has great theoretical significance and practical value for the further understanding of the nanometric cutting mechanism of brittle materials such as single crystal germanium.First of all,single crystal germanium(100),(110)and(111)crystal surface was studied by simulation and experiment of nano-indention and the indentation simulation model is established.The microscopic deformation mechanism and mechanical properties of different crystal surface were deeply investigated.The results show that the single crystal germanium(111)has smaller elastic modulus and hardness value than that of other crystal surface,surface hardness and elastic modulus of single crystal germanium each crystal show size effect with the increase of indentation depth,and the occurrence of sudden and sudden retreat in the process of loading and unloading,different deformation stages are divided in single crystal germanium under the different loading depth..Secondly,the molecular dynamics simulation of variable cutting depth of single crystal germanium of different crystal face is conducted,a variable depth cutting model is established,through the analysis of the formation and change of cutting force in the cutting process simulation to achieve the chip has two different stages of germanium single crystal elastic deformation,and the plastic removal and the elastic-plastic transition the critical cutting thickness and cutting force,(100)crystal surface between the elastic deformation and the plastic cutting critical cutting thickness and cutting force are respectively 0.48nm and 42nN.Then the different cutting speed and cutting thickness,cutting surface and rake angle machining parameters of single crystal germanium elastic effect of plastic deformation and surface quality are studied from the analysis of removal way,atomic change,potential energy and the change of cutting force angle,the influence mechanism of different cutting parameters on the deformation,the internal structure of single crystal germanium the surface quality,and different crystal plane anisotropic difference.Finally,the critical cutting depth,range and variation of the brittle ductile transition of single crystal germanium were determined by single crystal germanium nano indentation experiment and the factors affecting during the cutting process are analyzed.At the same time,the experiments of different crystal surface were performed to characterize the anisotropy of single crystal germanium.The critical cutting depth of single crystal germanium brittle ductile transition is summarized.The results showed that:(100)crystal face,due to its minimal surface density,is the deepest depth in the brittle ductile transition,scratches occur during the brittle ductile transition of late,and with the increase of the scratch velocity,brittle ductile transition critical depth and the critical load is also increased.