ROLE OF PRE-STRAIN EFFECTS ON THE FATIGUE BEHAVIOUR OF NICKEL-BASE ALLOYS IN THE VHCF RANGE

摘要

Most manufacturing processes of metallic components lead to plastic deformation in the material and hence cause pre-strain effects. The plastic pre-deformation strongly affects the initial micro-structure of the material considered. Polycrystalline nickel-base alloys such as Nimonic 75 and Nimonic 80A, which were applied in this study, exhibit planar or wavy dislocation arrangements depending on the dominant strengthening mechanism (solid-solution or precipitation hardening) but also on the pre-strain history. By varying the heat-treatment conditions of the precipitation-hardened alloy (e.g., establishing the peak-aged and the overaged condition) a systematic adjustment of different microstructures, which were characterized by transmission electron microscopy, was carried out. Furthermore, possible grain size effects as well as the influence of surface roughness (by comparing mechanically and electro-chemically polished samples) were analysed. The results are reported and discussed in terms of the various contributions to the damage evolution during fatigue loading at constant load amplitudes in the VHCF range.