Changes of orientations and development of cracks during plastic deformation of two-dimensional polycrystals of aluminium

The results of orientation-changes' study and their influence, on arise of the cracks in two-dimensional aluminium polycrystals strained under active tension conditions at a constant straining rate are presented. For the purpose of orientation-changes' ascertainment in situ during a deformation of samples, the technique based on a white-light diffraction on the quasi-periodic surface structure of previously pickled specimen is used. The character of such a structure is determined by crystallographic orientation-of the-sample-surface part, and it changes during a deformation. The colouring of sample-surface part observed using the WEB-camera and the computer in RGB colour space serves as a criterion for ascertainment of its orientation. The orientation of grains for some samples-at certain point of deformation is determined by means of independent radiographic examination. Three fundamentally different types of the orientation changes conditioned by the sliding and bring about formation of primary and secondary reorientation bands are revealed. As also revealed, the failure of investigated two-dimensional aluminium polycrystals is viscous, and the character of failure is trans-crystalline. Cracks arise in well-developed rotation structure or in grains with certain crystallographic orientation; tensile axis and free surface of grain are in close agreement with crystallographic direction [311] and [114], respecttively. Such grains initially have previously mentioned orientation, or get this orientation during a plastic deformation.