A computer simulation study of the structures of twin boundaries in body-centred cubic crystals

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Abstract
The structures of {112} twin boundaries in body-centred cubic crystals have been studied using computer simulation methods and interatomic potentials representing iron, molybdenum and tungsten. Two distinct structures were found to be stable or metastable in the models used. These were the conventional twìn boundary defined by a reflection orientation relation and a twin in which the boundary consisted of a layer of cells which project on the {110} plane as interlocking isosceles triangles. In the case of iron the two boundaries, when fully relaxed, are found to have almost identical energies but for molybdenum and tungsten the reflection boundary is preferred. The twin boundary energies for these two metals are three or four times as large as those for iron. Volume increases are predicted for the reflection twins in all throe metals but for molybdenum a surprising volume decrease arises for the isosceles twin. The results suggest that in some b.c.c. metals both types of boundary may arise in which case each twinning dislocation is likely to be dissociated into two partials, each with Burgers vector 1/12 〈111〉. The reliability of the computer simulation method for investigating the structure of crystal interfaces, such as twin boundaries, is discussed.

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