Behavior of misfit dislocations during diffusion of gold into copper-gold alloys

Upon electrochemical thinning of thin foils of the ordered Cu3Au alloy prior to examination in the electron microscope, a thin layer of gold is redeposited epitaxially on both surfaces of the foil. In order to relieve the long range stresses due to the difference in cell size between the two crystals, an array of misfit dislocations is formed in the Cu3Au-Au interface. These dislocations are generally of pure edge type, i.e. the extra half plane lies perpendicular to the foil surface while the 1/2 a0 〈110〉 Burgers vector lies perpendicular to the extra half plane. When two 〈110〉 directions lie in or close to the plane of the foil a crossed grid of misfit dislocations is generated. If on the other hand a single 〈110〉 direction lies in or close to the plane of the foil only one parallel set of dislocations perpendicular to this direction is observed. These results are satisfactorily accounted for on the basis of the anisotropy of strain energy in the foil. During annealing of the foils in the electron microscope, so as to allow diffusion to occur, the misfit dislocations climb into the foil from both sides and eventually annihilate one another as the foil composition becomes homogeneous. If the foil is annealed below the critical ordering temperature antiphase boundaries are generated as a result of dislocation climb. Because of the relatively high energies possessed by these boundaries, they can modify the misfit dislocation configuration rather markedly.