TEM investigation of dislocation dissociation in L12-type Co74Ni3Ti23 single crystals II. The influence of the deformation temperature

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Abstract
TEM investigations have been made on dislocation structures and dissociations in L12-type Co74Ni3Ti23 single crystals deformed at various temperatures. At temperatures below T b (the minimum temperature in the critical resolved shear stress (CRSS) against temperature curves), both screw and edge or mixed dislocations are present, but dislocations with near-screw orientation are more frequently observed. Also, there is a strong tendency for dipole formation at low temperatures. It is shown using [200] reflection that the superdislocations are dissociated into two partials bounding a superlattice intrinsic stacking fault. At 873 K where the positive temperature dependence of the CRSS appears, the dislocation structures consist of screw dislocations which are probably pinned by cross slip from the (111) plane to the (010) plane. The screw dislocations observed at 873 K are APB dissociated pairs and show zig-zag patterns when imaged in the (200) reflection. These zig-zag portions are not observable on the (111) plane. The observed dislocation structures and dissociations are quite consistent with the proposed deformation model described in a companion paper.

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