Transmission electron microscopy study of the stacking-fault energy and dislocation structure in CuMn alloys

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Abstract
Single crystals of copper-based manganese alloys (Cu−1.05, 1.3, 3.3, 5.05 and 11.6 at.%Mn) were grown and deformed in tension at room temperature. The weakbeam method of electron microscopy has been used to resolve the partial dislocations and to determine the stacking-fault energy γ. Contrary to most other Cu alloys, the value of γ does not decrease with increasing solute content. It stays the same for all the investigated CuMn alloys and corresponds to the value of pure Cu (γ = 41 mJm−2). It is difficult to include the results in a γ against e/a plot since the valency value of Mn in Cu cannot be specified. In Cu−11.6 at.%Mn a pronounced planar dislocation structure is observed and it is suggested that this is caused by the occurrence of short-range order. The large values of the critical resolved shear stress of the investigated CuMn alloys cannot arise from chemical locking (the Suzuki effect) since γ does not change with solute concentration.