Critical percolation stresses of random frank-read sources in micrometer-sized crystals of superalloys

摘要

2D dislocation dynamics simulations were used to investigate the size effect observed experimentally in the yield behavior of micrometer-sized crystals of γ-γ superalloys. Random Frank-Read sources were introduced on a (111) glide plane for three simulation cell sizes. Critical stresses were determined for the percolation of dislocations evolving from the Frank-Read sources in such cells populated with a distribution of γ precipitates at 73.5% by volume, consistent with the experiment. An APB energy of 250mJm ~2 was used in the simulations. The study found that the simulation results of percolation stresses were consistent with experimental 0.2% yield stress values with respect to both the scatter at each sample size, as well as the weak variation in critical stress with size. The weak size effect and the large scatter were found to be related to two factors: (1) strength of single-arm sources, as well as (2) the variation in precipitate structure at the single-arm source positions.