Tomographic characterization of grain-size correlations in polycrystalline Al-Sn

摘要

The inadequacies of current analytical models for grain growth are thought to arise in pan from their mean-field nature: they ignore the presence of correlations in the sizes of neighboring grains induced by the process of grain growth itself. Although grain-size correlations have been identified in microstructures generated by computer simulations of grain growth, no comparable evidence has been obtained from real samples―primarily because of the experimental difficulties assoeiated with evaluating this inherently three-dimensional property. Using absorption-contrast x-ray microtomography. we have attempted to characterize the network of grain boundaries in polycrystalline samples of Al doped with up to 3 at.% Sn. In princi ple. since the tin atoms segregate to the grain boundaries, it should be possible to determine the size and relative position of each grain from a three-dimensional reconstruction of the Sn distribution, from which the desired correlation function could be calculated directly. However, the grain boundaries in Al-Sn are not uniformly decorated with tin, which presents a formidable challenge to quantifying the microstructural properties of such samples. Significant progress toward overcoming this problem has been achieved by applying a constrained phase-field grain-growth algorithm to an approximate micro structure gleaned from the tomographic contrast data.