Gradient dislocation substructures at fracture of polycrystalline Cu-Mn alloys

Abstract

The paper presents the results of transmission electron microscopic (TEM) studies on the defect substructure of alloys and its modification with an increasing distance from the fracture surface. Cu-Mn polycrystalline FCC solid solutions with Mn contents of 0.4 and 25 аt. % and the average grain size of 100 μm are studied. A test machine INSTRON is used to perform tensile deformation of Cu-Mn samples at room temperature and 2 • 10 −2 s −1 strain rate. The strain is measured, the types of the dislocation substructure (DSS) and their parameters are studied with the step of 2 • 10 −3 m in the local zones of fractured samples at different distances from the fracture surface. As a result of the experiments, the sequence of changes in the substructure with an increasing distance from the fracture surface are established. In Cu + 0.4 at. % Mn alloy the following substructural sequence is observed: micro-bands, misoriented cells, nonmisoriented cells, and dislocation tangles. Substructural change sequence in Cu + 25 at. % Mn alloy includes microbands, cell-networks with and without misorientations, dislocation pileups , and chaotic dislocation distributions. In both alloys terminated subboundaries have a high density near the fracture surface. It is observed that the substructures change gradually depending on the distance to the fracture surface. Substructures that cause the fracture of the alloys at a meso-scale level were also detected. Near the fracture surface, deformation boundaries are misoriented and characterized by a large amplitude of the lattice curvature-torsion. Misoriented cell and microband DSS are observed within the fracture area of Cu + 0.4 at. % Mn alloy. In Cu + 25 at. % Mn alloy the formation of misoriented cellnetwork DSS and microband DSS is observed. Microcracks appear both along the boundaries of misoriented substructures and grain boundaries.