Study of plastic deformation heterogeneousity at the prefracture stage of copper-nickel alloy

The most important regularity of plastic deformation process is its tendency to localize at all stages. Localization accompanies plastic deformation from beginning to end (until failure), taking on various regularly changing forms along the way. Localization of plastic flow can cause destruction of materials during technological processes associated with large plastic deformations. In this regard, it is necessary to clarify the laws governing the localization of plastic deformation throughout the entire length of the strain — stress curve from the yield strength to the strength limit. Knowledge of the patterns of localization of plastic flow will allow us to formulate a criterion for predicting the plasticity reserve of materials. The use of the speckle photography method has proven promising in studying the characteristics of plastic deformation of metals. The spatial resolution of this method corresponds to the level of optical microscopy with a significant advantage in the size of the field of view. This method makes it possible to obtain the values of the components of the plastic distortion tensor of the working surface of the sample with an interval of 30 sec (the maximum displacement of surface points is 100 μm) and, ultimately, to analyze the evolution of localization patterns, as well as to determine the kinetic parameters of moving localization foci, which is its main advantage. In this work, the kinetics of development of localized plastic deformation sites in the polycrystalline copper-nickel alloy Cu-40%Ni-1.5%Mn was studied using speckle photography. It was possible to find out that the forms of localization are completely determined by the laws of strain hardening of the material operating at the corresponding stage of the process. The localization of plastic flow in a copper-nickel alloy has an autowave character. At the same time, at the yield site, stages of linear and parabolic strain hardening, as well as at the pre-fracture stage, the observed localization patterns are different types of autowave processes. Analysis of the characteristics of such processes made it possible to measure their propagation speed and wavelength. In conclusion, a method for identifying the source of destruction to predict the ductility reserve of metals is proposed.