Time and Temperature Dependent Cyclic Plasticity and Fatigue Crack Growth of the Nickel-Base Alloy617B – Experiments and Models

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.

Cyclic deformation and lifetime of Alloy 617B during thermo-mechanical fatigue

“…The pronounced cyclic hardening of the solution-annealed material compared to SGH and SGA material in TMF tests (Figures 6b and 7b) was already observed in CLCF tests at 700 °C [5,7]. It is assumed that the strengthening effect of the solution-annealed material at temperatures around 700 °C is due to fine scale precipitation of M 23 C 6 carbides in the size of < 50 nm.…”

“…Figure 4a). The phenomenon of dynamic strain ageing was observed also during isothermal loading [5,7]. From Figure 4a it can also be seen that σ max increases with increasing peak temperature while σ min remains almost constant.…”

“…This is in agreement with Tvergaard [14] who proposed a theoretical value of about b = 0.33 from FE simulations. In Figure 14 the results of crack growth measurements under non-isothermal loading are compared with isothermal crack growth measurements from [5,7]. During non-isothermal loading in the temperature range from 50-700 °C microcracks grow by about a factor 4 faster than under isothermal loading at room temperature and about a factor of 2 slower compared to the isothermal loading at 700 °C.…”

“…Figure 5 shows a representative example of the model adjustment to isothermal CLCF tests for (a) room temperature, e a,t = 0.5% and (b) 700 °C, e a,t = 0.4%. Further details on the parameter adjustment to CLCF tests can be found in [5,7]. In this work, the adjusted Chaboche model is used to predict stresses and strains under non-isothermal loading conditions with model parameters that are linearly interpolated between the temperatures of the CLCF tests.…”

Lifetime assessment of the process-dependent material properties of additive manufactured AlSi10Mg under low-cycle fatigue loading

“…1 mm long macroscopic crack. Especially in the LCF regime with high strain amplitudes, the crack initiation phase has no significant influence on the lifetime [37,[48][49][50]. The lifetime N A is integrated from equation 3by separation of variables from an initial crack length a 0 to a final crack length a f .…”