Thermally-activated motion of dislocations through random localized obstacles

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Abstract
The motion of dislocations through randomly positioned localized and thermally-penetrable obstacles interacting with dislocations only at contact is in the form of local penetration and short range sideways’ unzipping ‘. Under an applied stress, the spacings of obstacles along the dislocation line obey a nearly exponential-type distribution resulting in a similar distribution of cusp forces which the dislocation exerts on the obstacles along its length. When the obstacles are thermally penetrable, the dislocation moves forward by first being released from obstacles subjected to cusp forces larger than 1·23 times the average cusp force, and then followed by a sideways’ unzipping’ of two average segment lengths and resulting in a forward motion time considerably shorter than the activation time of the obstacle subjected to the average cusp force. With decreasing temperature the forward motion time becomes a smaller fraction of the time for activation of the average obstacle. This jerky motion of the dislocation results in a Poisson distribution of average displacements in short stress pulses, by means of which the mean obstacle spacing and the forward motion time can be obtained directly from external etch-pit measurements.