Interactions between point and extended defects in body centred cubic metals.

The interactions between point and extended defects in b.c.c. metals have been studied using real space computer simulation techniques. With such techniques a model crystal is set up into which the defects are introduced and the equilibrium atomic configurations and energies are found by minimizing the potential energy of the system. For the present purposes, the interatomic interactions were defined using five different empirical potentials matched to physical properties of alpha-iron, molybdenum and tungsten. Initially, various properties of vacancies and divacancies were studied under controlled conditions of uniaxial and hydrostatic stress, The properties were the energy associated with the formation of a single vacancy, the binding energies of the 1/2 , and 1/2 divacancies and the migration energies of these defects, The uniaxial stresses were directed along several distinct axes for each defect and in general the changes induced in the properties were anisotropic and larger than those produced by equivalent hydrostatic stresses, The interactions of vacancies and divacancies with the two possible types of {112} twin boundary were then considered. Interaction and migration energies were obtained as a function of defect separation and uniaxial stress applied perpendicular to the interfaces. For both single and divacancies, the maximum binding energies for the two boundaries occur when the vacancies lie adjacent to the interface. In addition, marked changes in vacancy migration energy result for specific jumps near the boundaries. Finally, the interactions of single vacancies with the 1/2 {110} edge dislocation were studied. The dominant interaction mechanism was shown to be of the inhomogeneity type, and for certain vacancy locations within the dislocation slip plane, the position of the centre of the core was seen to move. The vacancy sites for which this behaviour occurs are correlated with the locations of the 'fractional' components of the Burgers vector, into which the dislocation core is split