In materials science X‐ray microtomography has evolved as an increasingly utilized technique for characterizing the 3D microstructure of materials. The fundamentals of X‐ray microtomography experimental methods and the reconstruction and data evaluation processes are briefly described. A review of in‐situ synchrotron X‐ray microtomography studies in literature is given. Examples of recent work include in‐situ microtomography investiagtions of metallic foams, in‐situ studies of the sintering of copper particles, and in‐situ investigations of creep damage evolution in composites. Future perspectives of in‐situ X‐ray microtomography studies in materials science are outlined.

The complex transport processes contributing to sintering are not yet fully understood, partially because in-situ observations of sintering in three dimensions (3D) are very difficult. Here we report a novel experiment in which monocrystalline copper spheres are first marked with microscopic boreholes drilled using a focused ion beam, after which high-resolution synchrotron X-ray tomography is carried out to measure translational, rolling and intrinsic rotation movements of some hundred spheres during sintering. unlike in 1D and 2D systems, we show that, in 3D, intrinsic rotations are more pronounced than angular rolling rearrangements of the particle centres and become the dominant mechanism of particle movement. We conclude that in addition to the well-known neck growth and centre approach mechanisms, grain boundary sliding caused by the different crystallographic orientations of the individual spheres occurs.

The mechanisms of densification in spark plasma sintering (SPS) were investigated both analytically and numerically for a model system of two spherical metallic powder particles. From the microscopic temperature distribution, the possibility of a micro-local overheating of the particleparticle contacts was analysed for different particle sizes, contact geometries, materials, and electrical loads. It is shown that, for particles below the size of one millimetre, local overheating is below one Kelvin. Subsequently, the material transport by thermomigration, electromigration, and diffusion driven by surface curvature and external pressure was derived from microscopic field distributions obtained from analytical calculations and finite-element simulations. The results show that, while the mechanical pressure accelerates material transport by orders of magnitude, the electrical current and the temperature gradients do not. It is also shown that pulsing the current has no significant influence on the densification rate.

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