BAUSCHINGER EFFECT DURING CYCLIC STRAINING OF 2 DUCTILE PHASE ALLOYS

The Bauschinger effect has been examined for monotonie and cyclic straining conditions in a series of binary α, α + β and β Ti-Mn alloys, heat treated to produce constant composition of phases with different morphologies and sizes. For monotonic straining the average Bauschinger strain (ABS) was found to increase with strain over the range of plastic strains used, up to 2%, to be maximum at about 26 vol.% β and to be higher for equiaxed E(α) than for Widmanstätten plus grain boundary (W + GB)α structures. Over the range of particle sizes (either α or β) studied (1-12 μm), the ABS decreased with increasing particle size. After a number of constant strain cycles, the ABS increased and the reverse stress, at which flow began, decreased in the β alloy, when the cyclic flow stress was the same as the monotonic flow stress. In a number of instances permanent softening, as illustrated by parallelism of forward and reverse curves, was not observed. Plastic flow commences in the softer phase, α. The maximum ABS in 26 vol.% β was attributed to interface effects, which restrict flow in α, and to strain concentration in α, which occurs because the β generally begins to deform plastically at much higher stresses. The lower ABS in W + GBα structure was attributed to the greater ease of slip transfer from α to β because of the Burgers orientation relationship between the two phases [29]. The greater ABS in β and the decreased reverse flow stress under cyclic straining conditions is ascribed to an increase in mobile dislocation density or to decreased flow resistance because of possible metallurgical changes and to an increased back stress. The form of the reverse stress-strain curve and conditions for the absence of permanent softening are considered. © 1979.