Orowan strengthening at low temperatures in bcc materials studied by dislocation dynamics simulations

In this paper, the first investigation of the Orowan strengthening mechanism in the thermal plastic regime of body-centered cubic (bcc) materials is made with dislocation dynamics simulations. In bcc crystals, the mobility of dislocations strongly depends on temperature and dislocation line characters. Unlike the classical picture of the Orowan mechanism, simulations show that the difference in mobility between screw and non-screw characters is the key parameter. Simulations at different temperatures and with different precipitate microstructures illustrate the contribution of two mechanisms to Orowan strengthening: a thermally activated mechanism induced by the length dependency of the screw dislocation mobility and an athermal mechanism associated with dislocation line tension. The influence of the particle distribution is studied with a comparison between regular and random particle arrangements. In most cases, distribution effect can be accounted for by calculating effective particle spacing in the screw dislocation directions.