| A new experimental technique has been presented to demonstrate the Bauschinger effect in materials under dynamic loading conditions. In this study, tensile specimens were softly recovered after having been subjected to a single tension pulse of known magnitude and duration. The uniformly deformed gauge section of the tension sample was then sectioned and reloaded in compression, using essentially the same strain rate as in the tensile loading. The Bauschinger effect is found to increase with increase in the rate or decrease in temperature of loading. At high strain rates, the Bauschinger effect is found to increase with an increase in prestrain in the forward direction. Both these superalloys show strain-rate and temperature sensitivity and hence, at high strain rates or at lower temperatures the stresses reached in the forward loading are high. Due to high work hardening rate in these alloys, the flow stress increases significantly with strain. This increase in flow strength increases the number of nucleation sites for dislocations and enhances the tendency towards planar slip. Also, at high strain rates or at lower temperatures, the thermally activated processes like cross slip are slowed and hence, the planar slip is enhanced. As such, narrower deformation band spacings is observed in the sample loaded to a large forward stress. This narrower band spacing results in higher stored elastic energy resulting in lowering of the flow stress upon stress-reversal, i.e. the Bauschinger effect.The work-hardening and Bauschinger effect are strongly influenced by the precipitate size and distribution. The flow stress reached during the forward loading of precipitation-strengthened 230 alloy are double that of solid-solution strengthened 230 alloy. This enhances the planarity of slip and hence, the precipitation-strengthened 230 alloy showed the Bauschinger effect at both strain rates, The superalloys were shock-loaded to a shock pressure of 49 GPa. Shock hardening manifests itself through microtwins, dislocation tangles, and some small amount of recrystallization.Reload-compression tests performed on the shock-loaded superalloys given an additional low-temperature... |
