A method for finding critical stresses of dislocation movement

Abstract

A method is presented which makes possible the determination of the critical resolved shear stress, τc, for dislocation movement in a crystal. The method is based on the analysis of dislocation rosettes which are generated either by microindentation, or by precipitates of a second phase. The method does not require a knowledge of the indentation (or precipitate) stress field; it requires only information on the positions of a set of leading dislocation loops. At once one can also obtain the effective indentation stress field and, for the first time, the precipitate stress field. For illustration, the method is applied to the determination of τc in silicon, using both indentation and precipitate dislocation rosettes. The value of τc thus obtained varies from a low of 3×107 dyn/cm2 in oxygen-free samples to a high of 5.5×108 dyn/cm2 in a sample containing ∼2×1018 atoms/cm3 of oxygen with clustering. The SiO2 precipitate stress field in the present case was found to vary as x-1, suggesting that the precipitate is probably a thin plate.