Cyclic deformation and lifetime of Alloy 617B during isothermal low cycle fatigue

• Cyclic hardening of A 617B at 700 °C is related to precipitation of fine M23C6.
• Higher amount of M23C6 after fatigue loading compared with isothermal aging.
• Viscoplastic deformation depends on heat treatment and thus on the microstructure.
• The Chaboche model describes several aspects of viscoplastic material behavior.
• Proposed lifetime model is reasonable approach to model fatigue life of Alloy 617B.

Isothermal low cycle fatigue tests are carried out on the nickel-base Alloy 617B in the solution-annealed, stabilized and long-term aged conditions at temperatures between room temperature and 900 °C. In addition, fatigue microcrack growth is measured using the replica technique. Transmission electron microscopy studies suggest that the observed differences in cyclic hardening between the different heat treatments result from the precipitation of fine carbides. Scanning electron microscope observations indicate a change in fracture mode for the solution-annealed and long-term aged material with temperature. The Chaboche model is able to describe the time and temperature dependent cyclic plasticity of the three material conditions. The measured lifetimes and crack growth rates can be described using a fracture mechanics based lifetime model. However, the data for room temperature and for temperatures above 400 °C fall into two different scatter bands due to differences in crack growth rates.