Physically based mean-field modelling of dislocation creep
Bernhard Sonderegger
Johannes Kepler University Linz
https://tugraz.webex.com/tugraz/j.php?MTID=m203053e70a41fd4e7f4898dd77d5bc0d
11:15 - 12:15 Wednesday 08 January 2025 On a macrosopic scale, the phenomenon of "creep" is the slow plastic deformation of a solid material at high temperatures and mechanical stress. In the natural environment, creep is the main mechanism of deformation in the earth's solid crust at a dept greater than 20 km. In technical application, creep is responsible for the limited lifetime of many high-temperature components such as filaments of lightbulbs, blades in the turbine of a caloric power plant, or high-pressure pipes as part of high-temperature hydrogen fuel cells. The deformation continues over many years and, once a critical threshold is reached, destroys the component.
On a microscopic scale, the deformation rate (aka creep rate) is mostly governed by dislocation motion, which is activated by both, mechanical stress and temperature. In this presentation we show how the creep rate can be modelled on a physical base. Target materials are creep resistant complex martensitic steels at an operating temperature of 600-650°C. In this environment, spatially resolved models (such as crystal plasticity) are not practical due to the complex microstructure, the very large representative volume elements, and generally too long calculation times. Instead, we chose to represent the microstructure in a statistical manner and include all significant interactions on a rate-basis.
The result of a typical simulation is, on the one hand, the time-dependend creep rate and thus a meaningful estimate of the lifetime of a material, and on the other hand the underlying microstructural evolution during the temperature- and stress exposure. Since our simulation is extremely fast (<1s calculation time per 1 year of real lifetime), we are able to carry out parameter variations of the starting condition (starting micostructure) as well as system parameters (temperature, stress) in order to estimate their impact on the lifetime.
In a nutshell, our model can be used as assisting tool for the optimization of new alloys in high-temperature applications.
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Institute of Solid State Physics
