α-Fe 单晶拉伸变形热-动力学的分子动力学模拟

The microstructure and deformation mechanisms determine the strength and plasticity of structural materials. Specifically, the nucleation and movement of dislocations play a crucial role in the plastic deformation processing of crystalline materials. Just like the phase transformation, the plastic deformation and evolution of dislocations can be described as a kinetic behavior resulting from a thermodynamic driving force. In recent years, this research group has introduced the concept of thermo-dynamic correlation,which reflects the correlation between thermodynamics and kinetics as a trade-off relationship between thermodynamic driving forces (ΔG) and kinetic energy barriers (Q). It was found that an increase in ΔG is always accompanied by a decrease in Q in the processes of phase transformations and plastic deformations, and vice versa. Based on the so-called synergy rule of thermodynamics and kinetics, a new idea for the design and optimization of mechanical properties of materials has been proposed, that is the generalized stability criteria for phase transformation and deformation. The ΔG and Q are correlated by the concept of generalized stability, and it was suggested by many cases of metallic materials design that high driving forces and high generalized stability correspond to high strength and high ductility. To understand the thermo-dynamic correlation in the material deformation process and apply the generalized stability criteria for materials design, it is essential to comprehend the law of dislocation movement and evolution, and quantitatively describe the relationship between the driving force and the energy barrier of dislocation movement. The molecular dynamics (MD) simulation method has become an important means of studying the deformation mechanism of materials, dispite some limitations such as high deformation rate and small size of the description object. In this work, the thermo-kinetic behaviors of α-Fe deformation along [010], [111], [11^-0], and [112^-] crystal directions under uniaxial tension were studied by using MD simulation. The dislocation generation and evolution of α-Fe during the tensile process were analyzed. The results indicate that the yield strength of the material varies along the grain direction, with the order from high to low being [111], [110], [112^-], and [010]. When stretching along different crystal directions, the trend of dislocation density, dislocation type, and dislocation initiation time differs. The earlier the dislocation initiation time, the lower the yield strength. Generally, the dislocation initiation time of single crystal iron advances with an increase in temperature and a decrease in elastic modulus and strength. The results of thermo-kinetic and generalized stability analysis of dislocation evolution show that the thermo-kinetic driving force is opposite to the kinetic energy barrier, and the generalized stability value depends on crystal orientation and temperature.