3D X-ray Microscopy imaging is a recent innovation which provides high resolution, three-dimensional images with quantitative analysis of the internal features of a sample without having to cut through it. Basically, it can provide you with the Superman-like superpower of X-ray vision to peer into objects. But even better than Superman, it allows you to reconstruct these objects into a 3D image.
The principle of this technique is based on advanced X-ray computed tomography (CT) scanning. You have probably learned of a CT scan for medical purposes (think CAT scan). A patient remains immobile, and it is the emitter-receptor apparatus that moves and revolves. With XRM, it is the sample that is moved and turned in an industrial or research CT scan. And as opposed to medical CT scans that must have lower intensity values because of the effects of high radiation values on human health, XRM can achieve much better resolution and sharpness.
The system (Figure 1) is comprised of a micro-focus X-ray source, a sample stage and a lens-coupled CCD or CMOS detector. A series of 2D projection images is used to reconstruct a 3D image. A sample is placed on a rotary sample stage and the detector collects a series of 2D images as the stage rotates. The series of projection images are then used to create the 3D construct which is combined by multiple slices. An imaging software package is then used to visualize the 3D image.
XRM provides high resolution 3D imaging information that cannot be obtained by any other non-destructive technology. It can be used to study the interior structure of materials without having to cut or disassemble samples, preserving it for future studies. Quantitative information from XRM scanning can be obtained from the collected 3D images. And 3D digital models are created from XRM virtual slices which allow scientists to measure any parameters for comparison in before-and-after studies.
These unique features of XRM scanning allow scientists to look at the morphology of a sample and study features such as: porosity, structure, volume fraction, defect analysis, density, particle size, voids, fiber orientation, and more. Researchers commonly use XRM to study composite materials, microelectronics, medical devices, batteries, and more.
There are several applications for materials analysis that can benefit from XRM technology. And conversely, there are applications where XRM is not a good fit. When it comes to the analysis of materials, there isn’t a single, all-powerful instrument that can give us all the answers we might need. That said, if we were to put together criteria about what makes a good non-destructive technology, it all comes back to the application and the information obtained from it.
Let us start with the pros of XRM technology. The insight gained from imaging an object’s internal structure can supply significant value. It can help avoid defects that may become costly or worse, tragic if that material has structural flaws that cause it to fail for its intended purpose.
Here is brief list of applications that are ideal for XRM:
XRM has become a particularly useful instrument for defect analysis because of its many capabilities, like defect volume analysis. An XRM instrument can scan manufactured parts to determine voids and porosity. It can analyze for flaws, cracks, and inclusions and measure their size, position, volume, and even morphology on the whole part (even within its own packaging). This information is useful for research and development standpoint as engineers assess varied materials types or formulations. XRM has proven useful to guide process control to improve quality in manufacturing.
Through fast, reliable high-definition 3D imaging, part manufacturers are able analyze materials from the inside out, looking for things that might contribute to degraded performance and structural failure. It can capture and calculate for properties like hardness, strength, elasticity, and resistance. XRM has become an efficient and effective quality assurance inspection tool to help prevent parts that may potentially from being shipped, thus avoiding product recalls and considerable financial loss.
XRM also can provide dimensional metrology of external and internal features. This analysis can provide on the fly “go” or “no-go” inspection and traceability with quantifiable measurements of manufactured products. With scans gathered by XRM and enhanced software features, manufacturers can quickly compare part-to-CAD or part-to-part deviation and address potential issues in shorter periods of time compared to other techniques. As a bonus, XRM enables reverse engineering by converting the 3D reconstructed model of a part to an STL model. This can then be used for rapid prototyping, 3D printing or additive manufacturing, and computer-aided manufacturing. (1)
Lastly, the nondestructive nature of micro-CT makes it suitable for temporal investigations (time-lapse imaging or 4D micro-CT). For example, the effects of corrosive environment or different weather conditions on structural materials can be investigated or changes during the lifetime of an electronic device can be monitored. (2)
Now what about the bad? As mentioned before, there is not a silver bullet for materials analysis and there are other analytical instruments that may be more suitable for a specific application.
If identification of a material’s composition is needed, XRM is not the right tool for this application. Other X-ray tools such as XRF, XPS or EDX will probably be more suitable. As to which one of those is more suitable is a topic, we can dive into in another article sometime. Remember, the name of the game for XRM is imaging and the insights gained by taking a high-resolution picture of a sample’s insides nondestructively.
Imaging of dense materials is also not a great application of XRM. The denser or heavier the material is, the more trouble it causes for a good XRM 3D image. I think back to the scene in the early Superman movies, when Lex Luther was hiding a chunk of Kryptonite in a box made of lead (Pb) knowing that Superman would not be able to use his powers of X-ray vision. The denser a material is, more power and time is needed to try and penetrate the material and capture a useful image. And for some systems, it may not be possible.
Okay, that wasn’t so bad. But for most people who are evaluating XRM for their application needs, there is only primary con: the upfront costs.
All instruments and techniques have their pros and cons, and excellent performance can often come at a premium. How much does an XRM instrument cost? They can range between $250K to over $1M+. The reason for the wide price range is that the price of an XRM depends on the types of samples you are scanning and the results you need from the system. The resolution needed, the X-ray source and the detector type are contributing factors. The type and quality of these components determine the ultimate results you can achieve and dictate the cost of the system.
The real question to ask yourself is, will the Good applications and advantages of XRM outweigh the costs? Think about the value of this analysis as it relates to your business needs. Or simply put, will this analysis help improve your products/throughput/process and do the benefits far exceed the costs?
No matter what you call it, XRM, micro-CT, CAT scan – this technology is on the rise. It is becoming more popular in material sciences and accelerating materials development. These instruments are getting smaller and can now fit in a lab as bench-top instrument rather than needing to take up most of the floor space in a room. User interfaces are becoming designed for everyday users with push-button efficiency, further aiding in near real-time quality assurance and control. Laboratories who adopt the technology for a specific application, often find themselves expanding into other applications.
Bruker’s portfolio of 3D X-ray microscopes (XRM) offers turnkey solutions for non-destructive 3D imaging of a wide variety of industrial and scientific applications. This includes defect detection in casting, machining and additive manufacturing, inspection of complex electro-mechanical assemblies, pharmaceutical packaging, advanced medical tools, porosity and grain size analysis in geological samples, and in-situ microscopy.
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