Grain structure evolution during heat treatment of a semisolid Al-Cu alloy studied with lab-based diffraction contrast tomography

Abstract

3D experimental data of simultaneously high temporal and spatial resolution are key to validating computational models of materials phenomena. In this study, we exploit lab-based X-ray imaging, combining absorption and diffraction contrast tomography, to capture the evolution of grain structure over a series of interrupted heat treatments of a semisolid Al-Cu alloy. The time resolved response measured on the present Al-Cu model system provides insights into the rearrangement, densification and coarsening of powder compacts at late-stage sintering. The initial Al-Cu microstructure containing 1934 grains dropped to 934 grains after ten annealing steps, while the mean grain size increased from 194 µm to 247 µm. The grain maps of all eleven temporal states are made publicly available to the scientific community for further analysis via the Materials Data Facility. Preliminary statistical investigations of the growth of individual grains show a clear tendency for disappearing grains to be among the smaller grains at the beginning of the experiment. In addition, the rotations of individual grains are generally small fluctuations, but when an abruptly large rotation is observed, it is more likely to occur for a smaller grain at the last annealing step(s) before the grain vanishes. The nature of the data also enables interrogating a few grains that display rotation bursts within the context of their entire local environment to reveal the impact of crystallography and grain contacts upon the microstructural evolution.