DMREF: Grain Growth Beyond Isotropic Models: Microstructure Evolution with Experimentally-Derived Interface Properties

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NON-TECHNICAL DESCRIPTION: Nearly all man-made solids are made up of many small crystals referred to as grains. The sizes of these grains and the way that they are attached - characteristics determined when the material is made - influence many of the solid's properties. Existing models for the evolution of the grains during processing fail to predict observed outcomes. Because of the complexity of the problem, it is not even obvious that it is possible to make accurate predictions of how grains evolve during processing. The research will test the hypothesis that it is possible to predict the evolution of the grains within a material if information about the properties of the interfaces between the grains is included. The research will couple simulations with newly developed experimental techniques to test the hypothesis. Methods will be employed to identify where current models are insufficient, how they can be improved, and the degree to which it will be possible to predict grain evolution. The broader impact of this research is that the ability to predict how grains change during processing will make it possible to avoid trial and error experimentation and develop improved materials more quickly and at a lower cost.TECHNICAL DESCRIPTION: Predicting exactly how microstructures evolve during thermal annealing is one of the longstanding problems in materials science. While it is known how the average grain size will change with annealing, very little is known about the evolution of the grain boundary character distribution, the texture, and the grain shape. The main assertion of this research is that with knowledge of the grain boundary properties and how the properties vary with the crystallography of the grain boundary, it will be possible to predict how the microstructure will change during grain growth. A continuous feedback cycle of observations, simulation, comparison, and correction will be employed with the objective of creating accurate, predictive models for grain growth. The research will focus on materials with a range of anisotropic grain boundary properties. Ferritic iron has the most isotropic properties. The grain boundary properties of strontium titanate vary mostly with respect to grain boundary plane orientation. The grain boundary properties of nickel are anisotropic with respect to both lattice misorientation and grain boundary plane orientation. The studies of three-dimensional microstructure evolution in this research will make it possible to test proposed mechanisms for the development of anisotropic grain boundary character distributions and grain growth stagnation.