The ability to watch the three-dimensional (3D) evolution of structural materials is a breakthrough in non-destructive characterization. In particular, X-ray tomographic imaging techniques have found success in revealing the underlying mechanisms of microstructural transformations in partially and fully solidified metals. Here we review the most important developments in four-dimensional X-ray microscopy, focusing on absorption- and diffraction-based techniques in the laboratory and the synchrotron. In light of recent progress in this area, we identify critical issues that point to directions for future research in imaging the evolution of heterogeneous microstructures at extreme space and time scales.

IMPACT STATEMENT

Four-dimensional X-ray tomography has opened a new paradigm in physical metallurgy, allowing us to characterize the various epochs of microstructural evolution in 3D and as a function of time.

观察结构材料的三维（3D）演变的能力是无损表征中的一项突破。特别是，X射线断层扫描成像技术已成功揭示了部分和完全凝固的金属的微观结构转变的潜在机制。在这里，我们回顾了二维X射线显微镜最重要的发展，重点是实验室和同步加速器中基于吸收和衍射的技术。根据这一领域的最新进展，我们确定了一些关键问题，这些问题为未来研究在极端空间和时间尺度上异质微观结构的成像提供了方向。

影响陈述

二维X射线断层扫描在物理冶金学领域开辟了新的范式，使我们能够表征3D微观结构演化的各种时期以及其随时间的变化。