Abstract
A crystal plasticity model of the creep behavior of alloys with lamellar microstructures is presented. The model is based on the additive decomposition of the plastic strain into a part that describes the instantaneous (i.e., high strain rate) plastic response due to loading above the yield point, and a part that captures the viscoplastic deformation at elevated temperatures. In order to reproduce the transition from the primary to the secondary creep stage in a physically meaningful way, the competition between work hardening and recovery is modeled in terms of the evolving dislocation density. The evolution model for the dislocation density is designed to account for the significantly different free path lengths of slip systems in lamellar microstructures depending on their orientation with respect to the lamella interface. The established model is applied to reproduce and critically discuss experimental findings on the creep behavior of polysynthetically twinned TiAl crystals. Although the presented crystal plasticity model is designed with the creep behavior of fully lamellar TiAl in mind, it is by no means limited to these specific alloys. The constitutive model and many of the discussed assumptions also apply to the creep behavior of other crystalline materials with lamellar microstructures.
Highlights
In high-temperature applications, the resistance to creep and thermomechanical fatigue are the key criteria for the choice of structural materials
1.3.4 Conclusion In the context of the frequent absence of a secondary creep stage and the gradual change in the apparent stress exponent, classical creep models that are based on Eq 1 are not well suited to describe the creep behavior of fully lamellar titanium aluminide (TiAl)
While to a certain extent being successful in describing the stress dependence of the minimum creep rates by using different stress exponents for different stress regimes, these models miss some vital details of the creep behavior
Summary
In high-temperature applications, the resistance to creep and thermomechanical fatigue are the key criteria for the choice of structural materials. As the weight of components and the resulting mass forces are highly relevant in most high-temperature applications, there is, an ongoing search for lightweight alternatives to these commonly used alloys In this context, intermetallic titanium aluminide (TiAl) alloys have frequently been discussed as promising candidates to replace the much heavier conventional alloys (Appel et al, 2011). Intermetallic titanium aluminide (TiAl) alloys have frequently been discussed as promising candidates to replace the much heavier conventional alloys (Appel et al, 2011) Due to their beneficial combination of high specific strengths and good thermomechanical properties (Appel et al, 2011), TiAl alloys open up a significant weight-saving perspective, provided they are used to their full potential. This does, necessitate profound understanding of their high-temperature (creep) behavior ideally manifested in a comprehensive constitutive model
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