Precision ‘taste-test’ your additive manufacturing powders with XRF

It’s easy enough to tell when something’s gone very wrong when you’re cooking. You don’t need to be a Michelin-starred chef to recognize the taste of burnt. But if you were one of these chefs yourself, the margin of error would be much narrower: just a little too much cayenne pepper, and the food critic might turn up the heat.

Additive manufacturing (AM) has a similar issue. Contaminants in metallic powders can damage AM parts and harm output quality if their presence is even just a little too high. But to avoid wasting powders with non-damaging levels of contamination, AM manufacturers must draw a fine line between ‘acceptable’ and ‘too much’. In other words, they need to test their powders are of the right standard. Just like a top-quality chef might check their ingredients and culinary creations.

Contaminant detection: A non-negotiable throughout the AM process

Contaminants can get into your metal powders at many stages of the AM process: from the base metal itself, during the atomization process, or even when the powder is handled for re-use. So, whether it’s upon reception of a new batch of powder or during its production cycle, being able to screen for contaminants quickly and effectively is key to preventing damage to AM parts. For example, Tungsten inclusions in Ti-6Al-4V may cause cracking and a resultant reduction in yield strength and elongation of aerospace parts, while Nickel is not tolerated well by all patients with a medical implant.

Why XRF is a great investigative tool

XRF is a great investigative tool for identifying inorganic contaminants in metallic powder feedstocks, so long as  the contaminant is present in high-enough concentrations, and ideally has one or more “signature elements” that are specific to the contaminant.

A major advantage of XRF with regards to this application, and more generally, is the relatively short measurement time (usually less than 10 min). And for metallic powders in particular, the time required for making the specimen is also extremely short (less than 2 min). It’s also non-destructive so the powder can be recovered and either subjected to additional tests or reintroduced into production. And it can be used at-line, as it does not require the use of chemicals or elaborate sample preparation protocols.

When searching for contaminants one needs a good strategy!

It is a lot easier to detect a contaminant when it contains specific “signature elements” not present in the feedstock. But even then it can be difficult to establish with certainty that a powder specimen is contaminated wth foreign particles when the contaminant is present at very low concentrations. This is especially so for powder forms, compared with solids, due to the random particle arrangements inside the measuring cup.

Taking these considerations into account, it is prudent to spend time developing a measurement strategy for your particular sample based on an understanding of your process and the likely contaminants. Key considerations are:

• Ensuring that screening is performed on a statistically relevant number (or volume) of samples – this is especially important when contaminant levels are small.
• Identifying key signature elements or spectral peaks that are specific to the contaminant you are looking for.

This strategy goes ‘hand in hand’ with the spectrometers being used of course. And in the case of EDXRF spectrometers such as Epsilon 4, the excellent spectral resolution, coupled with exceptional sensitivity, makes the task much simpler. You can detect lower concentrations and better distinguish between different elements. Also once the method has been developed the whole exercise becomes almost a push-button operation.

The solution: A tailor-made screening strategy

In summary, the key to addressing these challenges is designing your tests around the specific needs and requirements of your manufacturing process and materials, coupled with the use of high-resolution and high-sensitivity instrumentation. But what does this look like in practice?

In a recent whitepaper, we described how we used the Epsilon 4 benchtop EDXRF spectrometer to create a fit-for-purpose powder testing process. The Epsilon 4 is ideal for addressing the needs and challenges of AM. For instance, in our tests, the ‘clumping’ effect was prevented by the Epsilon 4’s continuous rotation of the sample during measurements, which ensured consistent information on the sample composition.

To account for differences between batches in commercial AM powders, our screening strategy also involved the input of fixed sample excitation settings across every batch. Screening the differences between batches was then fast and straightforward – done simply by comparing the spectra measured with these parameters.

With this in place, the speed of XRF came to the fore: sample preparation could be done in 2 minutes, and each sample measurement took only 10 minutes on average – almost a push-button operation. With a tailored XRF screening process, that powder-bed Michelin star will be yours in no time…

To explore the different tests we conducted for XRF powder composition analysis in more detail, read our whitepaper – and follow our Advanced Materials LinkedIn page to stay updated on all our additive manufacturing solutions!