Dislocation depinning from nano-sized irradiation defects in a bcc iron model

At the atomic level, irradiation hardening of a body-centered-cubic (bcc) crystal of iron is investigated through the study of a dislocation interaction with nano-sized obstacles of various types, i.e. nano-voids, dislocation loops with 〈1 0 0〉 and 1/2〈1 1 1〉 Burgers vectors, and C15 clusters. The dislocation pinning is common to every type of cluster excepted for loops with 1/2〈1 1 1〉 Burgers vector, the mobility of which allows them to glide along with dislocation, thence yielding a minor contribution to hardening. At bypassing of anchoring clusters, the dislocation is found to yield a pair of jogs throughout a process of local climb due to the absorption of vacancies or of self-interstitial atoms that form the clusters. In order to rationalize our simulation results, we have employed an analytical theory proposed by Bacon and Scattergood (1982) which is extended phenomenologically to treat all anchoring defects, including C15 clusters and 〈1 0 0〉 loops. For small clusters, below 17 elementary defects, the simulation results deviate from the analytical predictions, and the different types of cluster correspond to different pinning strengths amongst those of C15 clusters appear to be the largest, emphasizing a possible important contribution to irradiation hardening in iron based alloys.