The interaction of non-glissile superdislocations and a coherent twin boundary in ordered Cu₃Au

Abstract

The glide behaviour of superdislocations at a coherent twin boundary in ordered Cu₃Au was examined in a transmission electron microscope by dynamic and static experiments for the case when superdislocations are sessile in the boundary. Possible schemes for dissociation of a superdislocation in the boundary were analysed geometrically.

The interacting superdislocations were for a part of their length still present in the twin. The leading superpartial of each superdislocation dissociated into a superpartial in the matrix and a residual Shockley partial in the boundary of glissile type. The trailing superpartial remained undissociated in the boundary. The superpartial in the matrix glided on a cube plane, and a ribbon of antiphase boundary connected to the boundary was left in its trail. The cube slip occurs as a result of firstly a maximal resolved shear stress for the observed slip system and secondly the geometric criteria for slip applied to all possible slip systems in the matrix. The Schmid factors for the slip systems in the matrix could be calculated by assuming a uniform tensile axis in the foil. The tensile axis was deduced from the observed slip systems in the twin. This method could be applied to both dynamic and static experiments.

The observed cracking along coherent twin boundaries appears to be the result of a thin-foil effect and is not representative for mechanical properties of bulk crystals.