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MM: Metall- und Materialphysik
MM 12: Symposium Severe Plastic Deformation III
MM 12.3: Fachvortrag
Tuesday, March 28, 2006, 11:45–12:15, IFW A
Fatigue Behaviour of Ultrafine Grained BCC and FCC Materials — •Hans J. Maier1 and Heinz Werner Höppel2 — 1Lehrstuhl für Werkstoffkunde, Universität Paderborn — 2Lehrstuhl Allgemeine Werkstoffeigenschaften, Universität Erlangen-Nürnberg
The present study reports on the fatigue behaviour of ultrafine grained materials with BCC (interstitial free (IF) steel) and FCC (copper and aluminium) structure. The ultrafine microstructures were obtained using equal channel angular extrusion (ECAE) at room temperature. Low-cycle fatigue tests were conducted in total strain-controlled fully reversed push-pull loading. Transmission electron microscopy was employed to characterize microstructural evolution. Cyclic stress-strain response was monitored both in constant amplitude tests and incremental step tests. Stable cyclic stress-strain response was observed for optimized ECAE routes. For ultrafine grained FCC materials, ECAE processing is commonly reported to result in an increase in cyclic strength but a decrease in fatigue life when compared with unprocessed material. By contrast, a more than two-fold increase in strength and number of cycles to failure was observed after optimum ECAE processing of the IF steel in the current study. In addition, in-situ fatigue tests were conducted in an environmental SEM to understand the substantially different fatigue behavior of the ECAE-processed materials. The implications of the damage mechanisms observed are discussed with respect to optimization of ultrafine microstructures.