Regularities of Crack Development in Substructures of Cu–Al Alloys Near the Cracking Stability Threshold.

Using the method of transmission electron microscopy (TEM) of thin foils, the nucleation and propagation of microcracks in various structures of the plastic zone in the polycrystalline low-stability copper–aluminum alloys are studied in the vicinity of their structural-phase transformation into a crack-bearing state. The evolution of misoriented dislocation substructures (DSSs), formed in the low-stability pre-transitional states in the vicinity of the cracking stability loss in the stage of developed plastic strain, is discussed. The relationship between the fine structure surrounding the microcracks and the dislocation substructure formed by the time of the material failure, i.e., the low-stability state of the material in the vicinity of its structural-phase transition into a into a crack-bearing state, is revealed. The principal factors, characterizing the dislocation density in these states of the material and the dislocation density in the substructures where microcracks nucleate, are identified. These factors are the misorientation boundaries of different origins and the long-range stress fields. The changes of the structure and the long-range stress fields are examined as a function of the distance from the microcracks and their tips. [ABSTRACT FROM AUTHOR]