It was revealed that low-cycle fatigue caused changes in the dislocation structure and in the structure of grain boundaries. At first, a cellular structure with low misorientation angles formed. A fragmented structure with very thin and perfect high-angle boundaries then formed. Increasing the number of cycles up to 1000 resulted in the formation of a sub-structure. It was noted that the appearance of so-called knife-like boundaries led to the observation of typical features of brittle failure, and to the presence of cellular structures and sub-structures which provided a basis for ductile failure. It was established that, during the transformation of grain-boundary structures, the values of the impact strength and mechanical properties changed. In the presence of knife-like boundaries, the values of the impact strength sharply decreased while the values of the yield strength and ultimate strength increased. It was noted that low-cycle fatigue led to the initiation and growth of micro-pores.

N.K.Tsenev, I.R.Kuseev, V.A.Baryshev, A.M.Gallyamov, B.E.Selsky: Materials Science Forum, 1996, 207-209, 685-8