Mechanical Properties Analysis Of Monocrystalline Germanium's Nano-indentation Simulation Through Molecular Dynamics Method

Monocrystalline germanium has excellent characteristics,such as low-temperature coefficient,high hardness,high infrared refractive index,and low dispersion rate,and is widely used in ultra-precision parts in the fields of infrared optics and semiconductors.The application scenarios of monocrystalline germanium often require high processing accuracy.However,as a material with nature of anisotropic hard and brittle,the monocrystalline germanium can easily crumble during machining.Therefore,it is necessary to further analyze mechanical properties of monocrystalline germanium.Nanoindentation technology can measure parameters,e.g.,material hardness,stiffness,elastic modulus,and is widely used in material mechanical performance testing.Considering that the sensor of nanoindenter is extremely sensitive and has high requirements on the experimental environment,the method of molecular dynamics is commonly used in the academic field.The molecular dynamics simulation method,through the computer simulation of various parameters such as the movement trajectory of the microscopic particles under fixed conditions,can effectively simulate the changes of the microstructure.Many scholars at home and abroad have used molecular dynamics to analyze the nano-indentation and micro-cutting process,making remarkable achievements.In order to study the mechanical properties of monocrystalline germanium under special environment and conditions,and to find out the influence of single factors,the thesis used the nanoindentation test of monocrystalline germanium to examine the influence of test scale on the experimental results of mechanical properties.The mechanical properties of germanium are researched by using molecular dynamics simulation methods to study the loading and unloading process of monocrystalline germanium nanoindentation.The mechanical properties of monocrystalline germanium and its microscopic factors are in-depth studied from the crystal grid structure,revealing the change law of the hardness of different loading surfaces,stiffness,and the shape of the deformed-layer.Based on the molecular dynamics method,a nano-indentation model with different typical loading surfaces is constructed.By setting the temperature of the ultra-conventional system as the simulation test environment,the disadvantage that nanoindentation can only be performed at room temperature is overcome,and as well,the changes in mechanical properties caused by temperature changes are tested.By the simulation of nanoindentation test to the monocrystalline germanium with preset vacancies,carbon impurities,dislocations,the thesis finds out the influence of vacancy concentration,carbon atom impurity concentration,and the modulus and direction of Burst vector dislocations.By controlling the cutting depth and cutting speed,the research process the surface of monocrystalline germanium from the optimal loading direction,and use nanoindentation test to analyze the changes in the mechanical properties of monocrystalline germanium during and after cutting.The study found that: under the condition of the same pressing depth,the experiment loading on(110)surface is with the most phase transition atoms,with the performance of the deepest deformation layer,the highest hardness,and the highest temperature rise.It is the most unsuitable loading surface for processing.The(111)surface has the smallest hardness and the lowest rigidity.It is the optimal processing surface for monocrystalline germanium which is used for follow-up research;the surface atomic are activated extremely at high temperature,the traces left by the probe become blurred under the high-temperature system,and the hardness decreases accordingly;crystal atom vacancies,as a kind of internal energy defects,will significantly increase the cutting heat during the loading process,weaken the rigidity of monocrystalline germanium,and increase the brittleness of the material;when there are carbon atoms impurity in monocrystalline germanium,it can be strengthened within a certain concentration,and the hardness of monocrystalline germanium exceeds this concentration,the hardness decreases,but the increase of the carbon atom concentration always reduces the brittleness of the material;the increase of the Burst vector modulus will weaken the hardness and rigidity of monocrystalline germanium,and the direction of the Burst vector is for monocrystalline germanium have little effect on the hardness and rigidity of germanium;the increase of the cutting depth makes the thickness of the deformed layer increase significantly and reduces the hardness of the machined surface.The increase of cutting speed will also increase the thickness of the deformed layer,but it will affect the thickness of the machined surface and have little effect on the hardness.The feed has a relatively optimal choice,and the cutting speed should be a larger value within the range that the tool can withstand.This paper uses molecular dynamics to simulate the nanoindentation test process of monocrystalline germanium,systematically studies the mechanical properties of monocrystalline germanium,and reveals the mechanical properties of monocrystalline germanium with different crystal orientation,defects,and residual stress conditions.The change mechanism provides theoretical support for the ultra-precision machining of monocrystalline germanium.