Evolution of microstructures and properties leading to layer instabilities during accumulative roll bonding of Fe[sbnd]Cu, Fe[sbnd]Ag, and Fe[sbnd]Al

Abstract

Bi-metallic laminates (bcc/fcc) containing Fe and either Cu, Ag, or Al were processed by cold accumulative roll bonding (ARB). The evolving microstructures and properties were measured using optical microcopy, electron backscatter diffraction (EBSD), and nano-indentation up to and beyond when layer instabilities are observed. The evolution of layer morphology, grain size, bulk texture, layer dependent texture, and layer dependent hardness is found to be both material dependent and layer location dependent. Ultimately, the evolving difference in layer hardness between Fe and the fcc metal resulting from the microstructure evolution causes the formation of layer instabilities with the FeAl exhibiting layer pinch-off at a total strain of 2.2, the FeAg developing shear band instabilities at a strain of 3.2, and the FeCu developing shear band instabilities at a strain of 4.5. These finding indicate that once the evolving strength ratio approaches two, processing changes, such as annealing or warm rolling, that improve the strength ratio or materials’ capacity for work hardening are necessary for further processing without layer instabilities.