![]() Increasingly, X-ray tomography is being used to follow the evolution of a microstructure under controlled environmental conditions (load, temperature and corrosive environment) through the collection of time lapse sequences to create 3D movies, a technique sometimes called 4D (3D plus time) imaging. when considering the potential for fluid flow through porous solids). art treasures or archival materials), or where 2D analysis is inadequate, for example for the quantification of the connectivity and/or the tortuosity of the different phases in the material (e.g. Good examples where 3D images are invaluable include cases where the samples are too fragile to be sectioned (e.g. In such cases it is important to identify the added value of 3D images over conventional quantitative metallography based on 2D sections. The review then focuses on the static analysis of 3D volumes as a basis for the quantitative characterisation of many aspects of materials microstructure using illustrative examples from the literature. It is also possible to go beyond attenuation imaging, for example to reveal the crystallographic orientation in 3D, thanks to methods such as 3D X-ray diffraction microscopy (3DXRD) and diffraction contrast tomography (DCT), or to image spatial variations in chemistry by X-ray Absorption Near Edge Structure (XANES) imaging Citation6 or colour imaging. Further, one can obtain high resolution images from specific regions of interest (RoI), even from within large objects by local tomography. For example, it is now feasible to achieve spatial resolutions below 100 nm or, largely due to advances in synchrotron X-ray tomography, to acquire thousands of projections (radiographs) sufficiently quickly to obtain many 3D images per second. The first part of this review examines recent imaging advances that, we believe, have significantly increased the power of the method for quantifying the evolution of materials, many of which have not received much attention to date. This review will attempt to outline the major strands of quantitative analysis that are beginning to emerge for both these aspects. In other cases comparisons are made between successive 3D images in order to quantify structural evolution in materials science and to support micromechanics experiments and modelling. In some cases this is focussed on the quantitative characterisation of microstructure from a single 3D volume. This has radically improved the level of information that can be gleaned from 3D imaging. More recently, there has been an increasing move towards extracting key materials science parameters from these images, through quantitative analysis. Citation3– Citation5 Initially, it was used predominantly as a means of acquiring 3D images from which diagnoses could be made based on visual judgement. Indeed, two excellent reviews have been published in IMR on the topic Citation1, Citation2 together with a number of books. X-ray computer tomography (CT) has seen a period of rapid growth over the last 15 years with considerable improvements in spatial resolution and image reconstruction times such that it is now a commonly available tool within materials labs. Finally the use of CT images is considered as the starting point for numerical modelling based on realistic microstructures, for example to predict flow through porous materials, the crystalline deformation of polycrystalline aggregates or the mechanical properties of composite materials. Besides the repeated application of static 3D image quantification to track such changes, digital volume correlation (DVC) and particle tracking (PT) methods are enabling the mapping of deformation in 3D over time. This includes information needed to optimise manufacturing processes, for example sintering or solidification, or to highlight the proclivity of specific degradation processes under service conditions, such as intergranular corrosion or fatigue crack growth. As a non-destructive technique, CT is an ideal means of following structural development over time via time lapse sequences of 3D images (sometimes called 3D movies or 4D imaging). Methods and shortcomings of CT are examined for the quantification of 3D volumetric data to extract key topological parameters such as phase fractions, phase contiguity, and damage levels as well as density variations. fast and high resolution imaging, crystallite (grain) imaging) than conventional attenuation based tomography. Our review considers first the image acquisition process, including the use of iterative reconstruction strategies suited to specific segmentation tasks and emerging methods that provide more insight (e.g. Here the authors review the current state of the art as CT transforms from a qualitative diagnostic tool to a quantitative one. X-ray computer tomography (CT) is fast becoming an accepted tool within the materials science community for the acquisition of 3D images. ![]()
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