On the unfaulting of vacancy loops in BCC metals

A review of radiation damage experiments on the bcc metals shows that differences in the crystallography of dislocation loops exist between the metals, and these differences can be important for the evolution of damage structure. This paper considers vacancy loops, for which the preferred Burgers vectors are observed to be in molybdenum and 〈100〉 in iron. All loops probably form from a common origin. The methods of computer simulation of discrete atomic crystallites and anisotropic elasticity theory are used to examine the energy and structure changes for the two unfaulting shears that produce the observed Burgers vectors. In computer simulation, unfaulting to 〈100〉 is favoured in both metals, and the elasticity calculations give the same result for loops which are only partially unfaulted. The apparent inconsistency between theory and experiment is discussed