Influence of carbon and oxygen impurities on the migration rate of <110> tilt boundaries in austenite

Abstract

The effect of impurity carbon and oxygen atoms on the migration rate of the tilt boundaries with the misorientation axis <110> in γ-Fe with fcc crystal lattice was studied by the method of molecular dynamics. Dependences of energy of the considered boundaries and rate of their migration at a temperature of 1600 K on the misorientation angle were obtained. The migration rate of <110> tilt boundaries under the same conditions turned out an order of magnitude lower than the migration rate of <111> and <100> boundaries, which is primarily due to the relatively low energy of <110> boundaries. In addition, the low-angle <110> tilt boundaries are unique compared to other tilt boundaries – grain­boundary dislocations in them are ordinary perfect edge dislocations with even cores that do not contain jogs periodically located on them as in <111> and <100> boundaries. The introduction of impurity carbon and oxygen atoms led to a significant decrease in migration rate of the grain boundaries. The binding energies of impurity carbon and oxygen atoms with grain-boundary dislocations in the austenite were calculated. The obtained values correlate well with the dependences of migration rate of <110> boundaries on the impurities concentration. Effect of impurities on migration of the boundaries in austenite turned out to be stronger than in the previously studied nickel and even more so in silver, which can be explained by the relatively low value of the electronegativity of iron atoms in comparison with nickel and silver. A higher value of the binding energy with dislocations in austenite and, accordingly, a greater effect on the migration rate of grain boundaries were obtained for carbon atoms.