INFLUENCE OF GRAIN SIZE AND PERCIPITATIONS ON THE FATIGUE LIVES AND DEFORMATION MECHANISMS IN THE VHCF-REGIME

摘要

Research in the field of very high cycle fatigue (VHCF) strongly increased during the last decade. It is meanwhile established that when investigating the deformation mechanisms in the VHCF-regime it has to be separated between inclusion free type I materials and materials with inclusions (type II). Despite all the attempts made so far, a basic understanding on the dominating deformation mechanisms in the VHCF-regime is still missing. Hence, in this study the deformation mechanisms of the aluminium alloy AA6082 ( type II material) were investigated. The material was investigated in the as-received condition and after different heat treatments. The heat treatment changes the deformation mechanism from internal crack initiation to initiation from the surface. In the as-received condition a non-defect crack initiation site was detected. By thorough investigations using EBSD, FIB-techniques and nanoindentation it is shown that featureless crack initiation is rather unlikely to be triggered by the supergrain-mechanism, as it was suggested in literature.