Molecular Dynamics Simulation of the Effects of Point Defect Type and Concentration on Plastic Deformation Behavior of α-Fe

In order to investigate the effects of vacancies, self-interstitial Fe atoms and Frenkel defects on the plastic deformation behavior of alpha-Fe under tensile load furtherly, the molecular dynamic models of the alpha-Fe samples with different types of the point defects were established and related simulations under uniaxial tension were carried out for a series of point defect atomic concentration of 0%, 0.125%, 0.250%, 0.500%, 0.750% and 1.000%. The stress-strain curves was obtained, the dislocation generation and the crystal structure evolution of each alpha-Fe sample were observed and analyzed by the dislocation extraction algorithm and the common neighbor analysis, and the following understandings were concluded. Different types of point defects can lead to different lattice distortion and related plastic deformation. Both the lattice distortion and related plastic deformation caused by self-interstitial Fe atoms are greater than those caused by vacancies at the same defect concentration. The changes of plastic deformation mechanisms induced by point defect types and concentrations make the characteristics of stress-strain curves change, i.e. the greater the concentration of self-interstitial Fe atom or Frenkel defect is, the less the distance between the upper and lower yield points on a stress-strain curve is, even vanishes, while the vacancy concentration has no such influence. Specifically, both the local amorphization and the related amorphization plastic deformation caused by self- interstitial Fe atoms are higher than those caused by vacancies. For the samples with low concentration of each of the three types point defects or for the samples with high concentration of vacancies, the plastic deformation is of a mixture of the tensile stress-induced phase transformation and the dislocation slip, while for the samples with higher concentration of self-interstitial Fe atoms (such as 0.500%, 0.750% and 1.000%) or with higher concentration of Frenkel defects (such as 0.750% and 1.000%), the plastic deformation is dominated by both the dislocation slip and the amorphization plastic deformation and accompanied by a little phase transition. The research deepens the understandings of the effects of point defect on the plastic deformation mechanism of metals and lay a useful foundation for the subsequent analysis of the physical and mechanical properties of polycrystalline alpha-Fe materials.