Bauschinger effect in unpassivated freestanding nanoscale metal films

We show experimentally that unpassivated freestanding nanoscale metal films, subjected to uniaxial tension, show substantial Bauschinger effect (BE) during unloading, even at large overall tensile stresses. Aluminum films (thickness 200-400 nm, grain size approximate to 200 nm) show BE at stresses as high as 150 MPa and their plastic strain after unloading is often less than 50% of the expected value. In gold, BE is relatively smaller. Possible mechanisms for BE in unpassivated thin metal films are discussed. (C) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.