HIGH-TEMPERATURE FATIGUE BEHAVIOUR AND DAMAGE MECHANISMS OF A SIC-REINFORCED AND DISPERSOID-STRENGTHENED ALUMINUM ALLOY

摘要

The present study focusses on the damage mechanisms relevant to a SiC-reinforced and disper-soid-strengthened aluminium alloy and the suitable lifetime prediction methods for isothermal and thermomechanical fatigue loading conditions. The SiC particles were found to affect both mechanism and rate of damage evolution. At low temperatures, debonding of the SiC particles was observed giving rise to fatigue crack initiation, and fatigue crack propagation is connected with particle cracking. At elevated temperatures voids are formed at the SiC particle/matrix interface, and may interfere with fatigue crack growth which mainly takes place in the matrix. Different models were used in order to predict cyclic lifetime. It was found that the models which are based on concepts of fracture mechanics and combine the cyclic stress-strain response determined under fully plastic deformation conditions with the results obtained in long fatigue crack propagation tests lead to excellent predictions. However, this holds true only, if the relevant damage mechanisms are taken into account. Deviations between experimentally observed and predicted lifetimes arise under conditions, where a strong coupling of different damage mechanisms exists. This is particularly the case under thermomechnical loading conditions so that an accurate prediction of TMF life from isothermal data is hardly possible.