I. Toda-Caraballo and P. D. Bristowe

• Molecular dynamics of grain boundary free energies, migration mechanisms and mobilities
• Grain boundary stiffness as a function of orientation and inclination
• Dislocations, facets and steps in asymmetric tilt boundaries

Research Highlight

A molecular dynamics study of grain boundary free energies, migration mechanisms and mobilities in a bcc Fe-20Cr alloy

I. Toda-Caraballo, P.D. Bristowe and C. Capdevila, Acta Materialia, 60. pp. 1116-1128 (2012)

Curvature driven migration of a series of <110> tilt grain boundaries in a bcc Fe-20Cr alloy is simulated using molecular dynamics to investigate the relationship between atomic migration mechanism and mobility at medium to high temperatures. The boundaries studied include low-angle boundaries (LAGBs), high-angle boundaries (HAGBs) and singular boundaries such as the coherent twin. The steady state boundary shape and curvature are compared to a simple analytical model which incorporates the dependence of absolute mobility and free energy on boundary inclination. The comparison indicates that the 109.5° (112) Σ3 coherent twin boundary will have relatively low energy but high mobility. This result is attributed to a particularly effective repeated shuffle mechanism which occurs on the twinning plane. Two other migration mechanisms are observed, one involving the motion of <111> glissile dislocations in LAGBs and the other involving uncorrelated atomic shuffles in HAGBs sometimes associated with interfacial steps.

Snapshots of the 11.5°<110> (771) Σ99 tilt boundary and its complementary counterpart (168.5° <110> (1114) Σ99) as they migrate downwards and reduce the areas of the half-loops. Grain boundary dislocations are highlighted in red.