Influences of grain size, alloy composition, and temperature on mechanical characteristics of Si100-xGex alloys during indentation process

Abstract

We perform molecular dynamics simulations to explore the effects of grain size, alloy composition, and temperature on the mechanical characteristics of Si100-xGex alloys during the indentation process. The structural evolution, von Mises shear strain, von Mises stress, and dislocation in workpiece are evaluated to explain the transformation of the loading force. Moreover, hardness and Young's modulus are also computed to evaluate the mechanical characteristics of different specimens. The results present that the loading force, hardness, Young's modulus of single crystalline are higher than polycrystalline. Besides, the loading force and hardness reduce as the grain size reduces; this result reveals a reverse Hall-Petch relation. In the indentation process of small grain size workpiece, the dislocation freely migrates to the grain boundary and absorbed, leading the amount of dislocation movement significantly reduces, which will instead promote the migration and sliding at the grain boundaries. It is confirmed that the grain boundaries play an essential role in the deformation behavior of the material. For the purpose of study the effect of various alloy compositions on the mechanical characteristics of the Si100-xGex substrate, a series of various alloy compositions are conducted: Si20Ge80, Si40Ge60, Si50Ge50, Si60Ge40, and Si80Ge20. The results reveal that the hardness, and Young's modulus of specimens increase as the Si content increases. In addition, the influence of temperature is also investigated in this work. It is found that when the temperature increases, leading to the atomic displacement and shear strain increase, the total dislocation length and the number of defect atoms increase, which leads to the hardness and Young's modulus reduction.