LUDERS BANDS FORMATION IN A RAPIDLY SOLIDIFIED NI3AL ALLOY RIBBON

The phenomenology of Luders bands formation in a rapidly solidified Ni -20Al-12Cr-1.8Mo intermetallic alloy ribbon in the temperature range o f 300-770 K is discussed. It was observed that strength and Luders ban ds aspect on the specimen were irrespective of temperature. The flow c haracteristics in the Luders region of the load-elongation curve were, however, very temperature sensitive. At low temperatures (<470 K), a flat plastic region with few instabilities was seen; but at higher tem peratures (>470 K), a clear serrated behavior was manifested and the a mplitude of serration increased with temperature. It is suggested that yielding occurs by dislocation generation at grain boundaries and tha t the stress required for dislocation generation (sigma(eff)) is ather mal. A temperature dependent stress originated by the dynamic pile-up of dislocations at grain boundaries (dynamic stress) is, however, intr oduced as rate controlling for Luders front motion and responsible for serration appearance.