This review has discussed the application of X-ray tomographic microscopy to materials science. An X-ray tomographic microscope has been described that provides three-dimensional images of a material's microstructure with a spatial resolution of a few micrometers. Though XTM is similar in many respects to industrial CT, the applications and resolving powers are different. Whereas industrial CT is used to certify finished components for the absence of macrostructural flaws, XTM is useful for three-dimensionally imaging the microstructure of materials with much higher resolution and sensitivity.

The three examples described in this review were chosen to illustrate how XTM can be applied to a variety of problems in materials science. The example of the ceramic matrix composite demonstrates how complex networks of porosity can be mapped out and visualized in three dimensions. The metal matrix composite study is illustrative of how the noninvasive nature of XTM can be used to study dynamic response in materials-the time sequence of fiber failure during tensile loading, for example. Finally, imaging the mineral density variations caused by a caries lesion in a human tooth illustrates how fragile, nonconductive samples can be imaged quantitatively with little or no preparation.

XTM technology is in its infancy. Even so, XTM can now be used in many applications. The resolution and s(:​llsitivity are sufficient to image many of the important microstructural features that control the properties of advanced composite materials. Coupkd with its demonstrated ability to image materials during testing, XTM promises to provide valuable information as to the response of materials to creep and fatigue.

XTM is not meant to replace quantitative metallography or electron microscopies;​ rather, we see the technique:​ as augmenting existing characterization methods. The ability to nondestructively and three-dimensionally image microstructures prior to sectioning and polishing will add to the effectiveness of traditional methods for analyzing materials by indicating where important features are located within the sample and may even eliminate the need for destructive analytical methods in many cases.