Computer tomographic investigation of Ostwald ripening

Similar to grain growth, Ostwald ripening is a competitive coarsening phenomenon in which larger particles grow at the expense of smaller ones. Improved understanding of Ostwald ripening—in particular, at volume fractions of the coarsening phase above 90%—is crucial to several technological applications, such as aging of multiphase metallic materials and liquid-phase sintering. Although such high volume fractions lie well outside the scope of current analytic modelling, they are feasible to study with modern methods of computer simulation and micro-computed tomography (microCT). Indeed, the latter technique promises to deliver in situ, real-time images of Ostwald ripening when carried out with synchrotron radiation. Alternatively, the evolution of sample microstructure can be characterized stepwise by alternating scans in a laboratory microCT at room temperature with ex situ anneals to induce coarsening. We have followed such a procedure to obtain 3D datasets of Ostwald ripening as it occurs in semisolid AlCu binary alloys. Segmentation of the tomographic reconstructions yields time-dependent maps of particle shapes and sizes that can serve both as starting configurations and as experimental tests for computer simulations of the coarsening process.