Extensive disordering in long-range-ordered Cu3Au induced by severe plastic deformation studied by transmission electron microscopy

Bulk nanocrystalline materials can be made by severe plastic deformation. In L12 long-range-ordered alloys, this leads to extensive disordering which influences the highly improved properties of these nanocrystalline alloys. Transmission electron microscopy methods were applied to Cu3Au; both diffraction contrast images and diffraction patterns reveal that disordering takes place locally. It is concluded that in addition to disordering by the refinement of the grown-in antiphase boundary domains, the formation of antiphase boundary tubes is a prominent process of disordering. The latter is facilitated by the fact that, unlike dislocations, antiphase boundary tubes can be stored at a very high density without causing long-range stresses. The local disordering indicates that the nanocrystalline structure nucleates inhomogeneously in the highly strained disordered regions.