Microcomputed Tomography in AM – Review of Current Technology and Applications

X-ray microcomputed tomography (microCT) has become an established method of testing and analyzing additively manufactured (AM) parts in recent years, being especially useful and accurate for dimensional measurement and porosity analysis. While this nondestructive analysis method is gaining traction among AM researchers and engineers, the capabilities of the method are not yet fully appreciated and are still being developed. This review aims to summarize the many diverse ways this technique has been applied to AM, including new and specialized applications. Examples are shown of many of these newly developed methods, while also discussing the practicality and limitations of each. The review ends with perspectives on the most time- and cost-effective ways to make use of microCT for various AM applications from R&D up to industrial production, with suggestions for scan strategies for different types of analyses.

Additive manufacturing is a layer-by-layer manufacturing method that has grown considerably in recent years, especially for producing functional metal parts for critical applications in medical and aerospace industries. Powder bed fusion (PBF) is the term used to describe specifically metal AM using a laser (LPBF) or electron beam (EB-PBF) to melt tracks and layers for the manufacture of complex shaped parts.

Despite the huge progress in recent years in this technology, and its increasing adoption, there remain some production issues. These issues include unwanted porosity from incorrect processing parameters or build conditions, surface roughness or other surface imperfections, deformation caused by residual stresses, and mechanical properties that are anisotropic, for example. These imperfections can be exaggerated due to the complex nature of the designs possible by PBF. Due to these challenges, process qualification is required and manufactured parts require careful testing, especially for high value and critical parts such as those for aerospace or medical applications.

MicroCT) is becoming an established technique for nondestructive analysis in various fields of application. In materials sciences, its increasingly widespread use was reviewed in Maire and Withers, which makes it clear that the method has evolved from a qualitative imaging technique in the past to a mature and quantitative analytical technique in recent years. It finds particular use as a high-quality and nondestructive analysis tool in various industrial applications as reviewed in De Chiffre et al. In this review of industrial applications, a section was devoted to AM, demonstrating quality control of complex parts and latticed parts—stating that this is the only method suitable to nondestructively analyze AM parts with internal cavities and porosities.

Since PBF allows the manufacturing of objects with complex shapes and internal design, including lattice structures and foams, microCT is very useful to quantify the porosity, to study the cell morphology, and to evaluate internal and external surface roughness, overall structural integrity, and the extent and distribution of internal defects.

While the use of X-ray microCT is gaining acceptance in the AM community, it is used most often to measure porosity and confirm dimensional measurements, as discussed in Thompson et al. This review article on the use of X-ray computed tomography in AM documented the historical development of the two technologies and their combined use, while focusing mainly on porosity inspection and dimensional measurement for quality controls. It was concluded that the main drawbacks to the wider uptake of the technique are costs and lack of standards.

The scope of the present review article is to demonstrate and discuss all the varied ways microCT has been used in AM, in addition to the above mentioned porosity and dimensional measurements. The aim of this review is therefore to broaden the general understanding of how this technique can be used to complement and support AM, which is not generally known and which is still under continuous development. This includes various interesting applications and new developments applicable to AM at different levels, from powder characterization to surface roughness assessment and to image-based simulations.

This summary of the capabilities will hopefully provide insight into how best to make use of this powerful technique, allowing a proper selection of microCT testing strategy for a particular application. Based on the various applications demonstrated and discussed in the review, suggestions are made of microCT testing strategies for most cost-effective use of the technique. Considering the fast progress in both fields of X-ray microCT and in AM, regular reviews of the synergies between these two technologies will remain important in the next few years as advances are made in both. While the discussions are broadly applicable to all AM, the focus of the work is on the most critical applications for aerospace and medical applications, that is, metal PBF, in particular LPBF.

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