The effect of the deformation sub-structure upon the hardening and fatigue life of cyclically deformed polysynthetically twinned crystals was investigated. Fatigue tests were performed in cyclic tension/compression mode, at room temperature, using total-strain controlled amplitudes. The load was applied at angles (between the loading axis and lamellar planes) of 0 or 45. When the angle was equal to 45, ½<110]-type ordinary dislocations, <101]-type super-dislocations and twins (whose density depended upon the type of ordered domain in the  phase) were observed. The presence of ½<112]-type super-dislocations, which decomposed from <101]-type super-dislocations, was also observed. These dislocations were found to lie on (111) planes that were parallel to the lamellar planes. When a stress was applied parallel to the lamellar planes (0), six types of domain in the  phase were observed that could be classified into vein-type and twin-type domains on the basis of characteristic features of the deformation sub-structure. In the case of vein-type domains, ½<110]-type ordinary dislocations glided on {111} planes which crossed the lamellar boundaries, tangled with each other, and formed an inhomogeneous vein-like structure that comprised high- and low-density regions. On the other hand, deformation twins which were accompanied by dislocations were observed mainly in twin-type domains. The fatigue properties were found to be very sensitive to the number of vein-type domains. Pronounced surface steps were produced by twin propagation, accompanied by dislocation motion.

H.Y.Yasuda, T.Nakano, Y.Umakoshi: Philosophical Magazine A, 1996, 73[4], 1035-51