Theoretical strength of austenite in the presence of a pore or vacancies in the crystal: Molecular dynamics study

Abstract

The molecular dynamics method was used to study the influence of pores of different diameters, as well as the corresponding concentration of individual vacancies, on the theoretical strength of austenite at different temperatures. The deformation in the model was carried out by shear at a cons­tant rate of 20 m/s. We considered a shear along two directions: [ \(\bar 1\ \bar 1\) 2] and [111]. The computational austenite cell had the shape of a rectangular parallelepiped 14.0 nm long, 14.0 nm high, and 5.1 nm wide. To describe interatomic interactions, the Lau EAM potential was used, which reproduces well the structural, energy, and elastic characteristics of austenite. The stress-strain curves obtained for both considered shear directions had a similar form. In the absence of dislocation sources, plastic deformation was carried out by the formation of dislocation dipoles (dislocations with opposite Burgers vectors). The presence of a pore significantly reduced the yield strength of austenite. In this case, it was found that single vacancies randomly scattered over the volume of the computational cell also lead to a decrease in the yield strength, but, of course, not as much as the pore. The emission of dislocations during deformation occurred by the formation of dislocation loops, as a rule, in two slip planes at once. The effect of pores and vacancies on the yield strength was stronger at low temperatures. As the temperature increased, the effect of defects on the critical stress at which dislocations were formed decreased. With an increase in the pore size, as well as the concentration of vacancies, the yield strength decreased. In this case, the strongest dependence was observed for pores up to 1 nm in diameter. The influence of the concentration of vacancies in the considered range on the yield strength turned out to be comparatively smoother and almost linear.