Abstract
Isothermal low cycle fatigue and thermomechanical fatigue tests are performed on Alloy617B in the solution-annealed and stabilized condition at temperatures between room temperature and 900 °C. In addition, the replica technique is applied to study the growth of microcracks. The Chaboche model is found to describe the cyclic viscoplastic behavior of both heats, except the pronounced cyclic hardening in the low-temperature branches of the TMF tests. A lifetime model based on the cyclic crack-tip opening displacement and the cyclic J integral is used to describe the measured lifetimes and crack growth rates. However, the description is not fully consistent, since the data for room temperature and for temperatures above 400 °C fall into two separate scatter bands.
Highlights
The nickel-base Alloy617 is a candidate for application in new ultra super critical (USC) power plants with steam inlet temperatures of 700/720 °C and pressure of 350 bar with the aim to improve thermal efficiency of fossil fuel power plants and reduce CO2 emission
4.2 Crack growth behavior of Alloy617B In order to understand the difference between the room temperature (RT) and the high temperature lifetimes, the replica technique was used to measure the propagation of microcracks
Viscoplastic deformations measured in the performed thermomechanical and isothermal low cycle fatigue tests depend on the heat treatment and on the microstructure
Summary
The nickel-base Alloy617 is a candidate for application in new ultra super critical (USC) power plants with steam inlet temperatures of 700/720 °C and pressure of 350 bar with the aim to improve thermal efficiency of fossil fuel power plants and reduce CO2 emission. To reduce the susceptibility to relaxation cracking a stabilizing heat treatment was introduced, whereas the alloy is conventionally used in the solution-annealed condition [4]. It is the aim of this work to investigate the isothermal low cycle fatigue (LCF) and TMF properties of Alloy617B in the solution-annealed and stabilized material condition and to derive suitable material models for the description of time and temperature dependent cyclic plasticity and fatigue crack growth behavior of Alloy617B. The material was supplied by ThyssenKrupp VDM in the form of 30 mm thick hot rolled sheets in two different heat treatments, namely solution-annealed (LG, 1175 °C/1h/water) and stabilized (SGH, 1175 °C/1h/water + 980 °C/3h/air). The temperature dependent fatigue crack growth of individual cracks was measured at RT and 700 °C in the stabilized condition using the replica technique
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