Nucleation and propagation of dislocations near a precipitate using 3D discrete dislocation dynamics simulations

Abstract
A 3D dislocation dynamics code linked to the finite element procedures is used to simulate the case of a matrix containing a cubical precipitate. Since the matrix and the precipitate do not have the same elastic moduli and thermal expansion coefficients, a heterogeneous stress field is generated in the whole volume when the sample is submitted to a temperature change. In many cases this may nucleate dislocations in the matrix as experimentally observed. Here, the phenomenon of dislocations nucleation in the matrix is simulated using dislocation dynamics and the first results are presented. In a first time, a glissile loop has been put surrounding a precipitate. The equilibrium position of the glissile loop is investigated in terms of the image stress field and the line tension of the loop. In a second time, the dislocations are introduced as a prismatic loop admitting a Burgers vector perpendicular to the plane containing the loop. The prismatic loops are moving in the sample according to the heterogeneous stress field resulting from the summation of the internal stress field generated by the dislocations and the stress field enforcing the boundary conditions, which is computed by the finite element method. The latter takes into account the presence of the precipitate as well as the interactions between the precipitate and the dislocations. The equilibrium configuration of the rows of prismatic loops is analysed and the spacing of loops is compared to the analytic solution.