Superlocalization of plastic deformation in crystals at high temperatures

Abstract

Plastic strain distribution and dislocation structure in alkali halide (LiF, LiF:Mg, NaCl, KCl) and ferroelectric (NaNO 2) crystals under constant tensile or compressive stress at high temperatures ( T > 0.6 T m) have been studied. It was found that plastic deformation instabilities at instantaneous deformation occur, namely deformed samples exhibit microbands with very high local shear strain of about 10 3%. The local strain rate in microbands is much more than 5 s −1. These narrow microbands (between 2 and 10 urn in different crystals) are oriented in accordance with the slip systems in crystals. The average distance between microbands is usually from 20 to 100 μm. The surface steps corresponding to local high shear strains are observed in the form of wavy slip. Sometimes, a change in the relief (a depression or a bump) of the surface parallel to the Burgers vector is also observed inside the microbands. The increase of local strain during deformation occurs mainly due to the creation of new microbands rather than by shear in already existing ones. Possible mechanisms of plastic instability in highly strained microbands are discussed.