The Plastic Deformation And Phase Transformation Of Single Crystal Silicon Under Intense Dynamic Loading

Single crystal silicon is widely used in micro-electro-mechanical（MEMS）,photovoltaic cells and infrared telescopes due to its good physical properties.These fields require single crys-tal silicon to maintain its surface integrity through precision machining,but the high brittleness and low plasticity of single crystal silicon at room temperature restrict its machining process.In this paper,the plastic deformation and phase transformation mechanism of single crystal sili-con at high strain rates are discussed by molecular dynamics simulation.By studying the plastic deformation and phase transformation of single crystal silicon at high strain rate,it can pro-vide some reference for the processing technology of single crystal silicon material.The main research contents are as follows:（1）Molecular dynamics was used to simulate the dynamic response of single crystal silicon[001],[110]and[111]crystals under single crystal silicon loading at room temperature.The shock Hugoniot state of single crystal silicon was investigated by plate impact loading at ambient temperature of 300K,and the plastic deformation and phase transformation mechanism of single crystal silicon under high strain rate loading were revealed.It is found that under impact loading,elastic-plastic transformation and solid-liquid transformation occur in[001],[110]and[111]crystal directions,and the plastic deformation of[001],[110]and[111]crystal directions is anisotropic.（2）Molecular dynamics was used to simulate the dynamic response of[001],[110],[111]crystals under syncline wave quasi-isentropic loading.Aiming at the problems of short loading time and significant temperature rise under shock loading,a quasi-isentropic loading method of ramp wave was proposed,which can realize temperature decoupling to a certain extent.Based on the dynamic similarity,the strain rate of oblique wave loading can be changed by changing the rise time of ramp wave.It is found that single crystal silicon[001]still has an obvious solid-solid phase transition,but the phase transition process is more sufficient than that of shock wave load-ing.Single crystal silicon[110]has partial phase transformation,while the plastic deformation of single crystal silicon[111]is still mainly amorphous.In addition,the crystalline plastic waves of[001]and[110]have obvious strain rate dependence,while the crystalline plastic waves of[111]have low strain rate dependence.（3）The effect of strain rate on the plastic deformation and phase transformation of single crystal silicon was studied by molecular dynamics simulation.A waveless quasi-isentropic load-ing method equivalent to oblique wave loading was used to study the deformation responses of[001],[110]and[111]crystals to materials respectively,and the multispan strain rate range from10⁸-10¹¹s^-1was realized.The study revealed significant strain rate effects on the plasticity and phase transformation of single crystal silicon.Therefore,in this paper,shock compression and quasi-isentropic loading were used to sys-tematically study the plastic deformation and phase transformation of single crystal silicon in three crystal directions,and the plastic deformation and phase transformation mechanism of single crystal silicon under different loading modes and different strain rates were studied.By studying the plastic mechanism and phase transformation of high pressure and high strain rate of single crystal silicon,the influence law of dynamic loading stress amplitude and strain rate was clarified,which provided scientific basis for material deformation related to material process-ing technology of single crystal silicon,and also provided reference for phase diagram study of single crystal silicon under high pressure condition.