[SY-I10] Reverse engineering the kinetics of grain growth
Invited
At first glance, the strategy for modeling grain growth seems obvious: simply combine an expression governing the physics of grain boundary (GB) migration with a treatment of the connectivity of the boundary network, such that shrinkage of one grain corresponds to growth of its neighbor. However, 70 years of analytic models and three decades’ worth of computer simulations have left us with seemingly intractable discrepancies between theory and experiment—concerning, for example, the shape of the self-similar grain size distribution; the occurrence of growth stagnation at long annealing times; and, most strikingly, the emergence of a bimodal size distribution during instances of so-called “abnormal” grain growth.
In the world of industry, when repeated attempts to solve a technological challenge end in failure, employees sometimes try to “reverse engineer” a competitor’s product, dissecting the interplay between the device’s internal parts to uncover its working principle. Afflicted with a similar sense of desperation, we applied this approach to the phenomenon of grain growth! Exploiting three-dimensional x-ray diffraction (3DXRD) microscopy, we investigated thermally induced coarsening in two different Al alloys. From microstructural snapshots interspersed between isothermal annealing steps, we were able to track the morphology, misorientation and migration of thousands of GBs over time, acquiring the basis for a robust statistical analysis of local growth kinetics. The results allow extracting dependencies of reduced mobility (the product of GB mobility and energy) on GB misorientation and inclination. In one specimen, the measured dependency is consistent with expectations for normal grain growth, but, in the other case, we find evidence for boundary kinetics that lie beyond the scope of standard models.
In the world of industry, when repeated attempts to solve a technological challenge end in failure, employees sometimes try to “reverse engineer” a competitor’s product, dissecting the interplay between the device’s internal parts to uncover its working principle. Afflicted with a similar sense of desperation, we applied this approach to the phenomenon of grain growth! Exploiting three-dimensional x-ray diffraction (3DXRD) microscopy, we investigated thermally induced coarsening in two different Al alloys. From microstructural snapshots interspersed between isothermal annealing steps, we were able to track the morphology, misorientation and migration of thousands of GBs over time, acquiring the basis for a robust statistical analysis of local growth kinetics. The results allow extracting dependencies of reduced mobility (the product of GB mobility and energy) on GB misorientation and inclination. In one specimen, the measured dependency is consistent with expectations for normal grain growth, but, in the other case, we find evidence for boundary kinetics that lie beyond the scope of standard models.