The High-Temperature Bauschinger Effect in Alloy 718

The final heat treatment of large aerospace components of alloy 718 typically comprises solution treatment followed by oil quenching and aging. Such operations give rise to small, but non-uniform, plastic strains that can produce significant levels of residual stress. During oil quenching, in particular, material elements may undergo not only concurrent cooling and straining, but also reversed-plastic flow. Therefore, constitutive relations for the simulation of residual-stress evolution should include a description of such transient phenomena. To meet this need, a series of experiments involving reversed straining of short-gage-length samples of 718 was performed at temperatures between 427 and 871 °C and strain rates of 0.0001 or 0.003 s⁻¹. These experiments revealed a measurable Bauschinger Effect (BE) over a range of temperatures. The temperature at which the BE disappeared was a function of the applied strain rate. A similar BE was also observed in experiments involving both reversed straining and continuous cooling.