Phase Transformation Research Of Crystal Silicon Induced By Axial Compress And Nanoindentation

Single crystalline silicon often experiences external loading that lead to reversible/irreversible structural deformation or fracture failure during the application process. It is found that the mechanical mechanism that controls the fracture failure process is not only slippage and dislocation; structural phase transformation also plays an important role. To some extent, it determines the material hardness and strength. Therefore, research on structural phase transformation under different loading conditions can help people to understand the failure mechanical mechanism of material. In addition, through studying the structural phase transformation people can predict the structure evolution process.Molecular dynamics simulations is carried out to investigate the mechanical properties and structural phase transformation of monocrystal silicon under uniaxial compression and nanoindentation. Tersoff potential Morse potential are adopted to simulate the interaction between silicon-silicon atoms and silicon-carbon atoms, respectively. Moreover, the effects from model size and temperature are also considered. After determined the correctness of the simulation, through analysis the structural phase transformation during deformation, several conclusions are obtained as follows: 1) During the process of the uniaxial compression, single crystal phase Si-I transfer to Si-II first when the stress value reaches around 11GPa; structural phase transformation was first observed at the surrounding surfaces, and then diffuses to the center gradually. Several phases were found simultaneously when the material becomes yielding. 2) Compared to temperature, pressure is proved to be the main reason that leads to phase transformation. The elastic property is hardly affected by temperature. However, material strength and the number of phase transformation atoms increase with the raise of temperature when the material comes into plastic stage. 3) During the process of the nanoindentation, structural phase transformation is observed mainly beneath the indenter. Besides regular phases, accumulated amorphous phase is also observed, and the amorphous region expands with a shape of human lungs. The phase transformation is believed to be mainly induced by shearing stress; therefore, it spreads along the cleavage plane.