Modeling and simulation of creep rupture in high-temperature alloys
It has been well established that one of the main causes of rupture in high-temperature alloys is intergranular cavitation: the nucleation, growth, and coalescence of voids along grain boundaries. It is also well known that intergranular voids grow under the influence of several physical processes, including matter diffusion along the void surface, matter diffusion along the grain boundary, and bulk creep of the surrounding grains. Creep rupture modeling efforts to date have considered at most two of these three void growth mechanisms at a time. Furthermore, when bulk creep is accounted for, primary creep effects are rarely, if ever, addressed. The purpose of this dissertation is to develop more accurate micromechanical models of creep rupture that can be used to gain further insight into the failure of high temperature alloys. We consider such model systems as a stationary crack tip in the absence of voids, a single intergranular void growing under the influence of surface diffusion, grain boundary diffusion, and bulk creep (including primary creep effects), and several intergranular voids growing ahead of a crack tip. We find that the interplay between the three aforementioned void growth mechanisms can lead to interesting and sometimes unexpected predicted rupture behavior. We also find that void growth can be significantly accelerated in the primary creep regime, compared to the secondary creep regime. Our results lead us to believe that these physical processes, when present, play an important role in the rupture of high temperature alloys, and should therefore be taken into account when designing high-temperature system components. Failure to do so might result in overestimates of component lifetimes, and consequently, unsafe operating conditions.
Creep, Rupture, High-temperature, Metals, Cavitation, Void, Damage
University of Illinois - Urbana-Champaign
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University of Illinois at Urbana-Champaign