To the untrained eye, the following colourful images might look like art, but they’re actually something unexpected: science. These are maps of metals such as titanium, nickel, and steel created using an electron microscope.
Jake Benzing, a materials research engineer at the National Institute of Standards and Technology, uses a method called electron backscatter diffraction, or EBSD, to generate the colourful maps. The maps show you what the metals’ structure is actually like at a microscopic level, which is critical information because it allows scientists to determine if a metal component is reliable and make suggestions to improve it if it’s not.
Benzing uses the EBSD technique to analyse 3D-printed metals, which are created by relatively new technologies, as well as metals made by conventional manufacturing processes. And while the maps might just be something amazing to look it for most of us, they can have far-reaching implications that could affect transportation, biomedical devices, and safety.
How the Maps Are Made
Benzing, a part of NIST’s Fatigue and Fracture Group in Boulder, Colorado, works on developing and disseminating tools that help quantify the reliability of metallic components that are subjected to a range of forces and loading conditions. He carries out his work with a range of mechanical testing equipment and an electron microscope, his hardworking sidekick. Before we go any further, you should know that, like wood, metal has grains. In fact, the thickness of some of those grains can be smaller than the thickness of a human hair. Our eyes can’t see these grains, obviously, which is where the electron microscope and the EBSD technique come in.
When Benzing applies the EBSD technique to a certain metal, the microscope fires an electron beam into the surface of the sample, which diffracts and creates a pattern on the camera. An EBSD scan — which is a dense dataset of the material’s underlying crystalline structure — contains millions of these patterns and represents the size, shape, and orientation of the grains inside the sample.
Every pixel is assigned a particular colour based on the measured pattern, which represents a grain’s orientation and crystalline structure. A metal’s structure will depend on the type of manufacturing process employed, a factor that also plays a role in reliability. Maps can take anywhere from a couple of hours to a few days to produce.
It’s All About the Grains
When you talk to Benzing, he really stresses the importance of the orientation of a metal’s grains. Benzing told Gizmodo that if a final product is considered reliable, that means that the engineers and part designers are confident that it will behave as expected. In other words, a reliable product will produce the expected mechanical response when subjected to the forces and loading conditions for which that product is designed.
“If the metallic grains have a wide range of orientations that weren’t expected or the grains are all one orientation, but an unexpected orientation, the material will produce a mechanical response in the final product that the engineers don’t expect,” Benzing said.
He added that this will result in a metal that’s weaker than they anticipated, or which exhibits a behaviour that is very wild, variable, and unpredictable. Such a part wouldn’t be reliable.
Zooming In on 3D-Printed Metals
Benzing said he spends most of his time analysing metals created by additive manufacturing, also known as 3D printing, although he also studies metals used in processes like welding and hot rolling. He works on NIST’s Additive Manufacturing Fatigue and Fracture project, which aims to enable the use of 3D-printed metal in critical applications. Manufacturers are really scared to use 3D-printed metals in critical applications because they don’t have confidence in the reliability of those parts yet, he said. An example of a critical application would be a jet engine.
“If you have like a critical component in a jet engine and it breaks, the engine blows up and takes out the whole wing with it, the plane’s going down,” Benzing said. “So right now, aerospace companies are only using 3D-printed metals in like areas of the plane that aren’t going to be critical if that part were to break.”
Increasing the confidence that aerospace companies have in the use of 3D-printed metals for critical applications could change a lot of things, though. According to Benzing, aerospace companies would probably save a lot of money and fuel. This would also trickle down to all of us via lower costs and a greener environment.
Beefing Up New Manufacturing Techniques
Although Benzing is not the first person to generate EBSD maps — he said that it’s a well-established microscopy technique used at most universities and labs around the world — what’s unique about his research is how he’s using the data from the maps. Benzing generates maps at different length scales for a variety of parts produced with different manufacturing conditions and measures the mechanical properties of those parts with NIST’s unique set of mechanical testing equipment.
He said that the data he generates can be used to accelerate the timeline for qualification and certification of parts produced with new manufacturing processes that are still considered uncertain and unreliable. This, in turn, decreases the time it takes to ensure reliability in a new manufacturing process.
Take a Closer Look
Benzing said he got interested in the science of metals when he was in undergraduate and graduate school. During that time, he worked with mechanical engineers and materials specialists who liked “breaking stuff and slamming metal together.” They encouraged him to start working with an electron microscope to find out why metals were reacting in a certain way. Many summers, he also worked at a steel research centre in Germany, where he helped design a type of steel alloy that gets stronger the faster you deform it.
In a car built with that type of steel alloy, for example, which hit a wall going about 50 kph, the metal would be strong. If the car were going roughly 100 kph, the metal would be even stronger.
You can see what the map of this medium manganese steel looked like above. Benzing said the team achieved this result by tailoring the colours in the map and the chemistry, or the ingredients, of the material. You check out Benzing’s published research here and on NIST’s website.
A Perfect Match
As mentioned above, Benzing’s maps can be used in a variety of different ways. The metals he studies could be used for components in a jet engine, to create hip and jawbone replacements, to develop a tougher pipeline for hydrogen transport, and to create a stronger and more fuel-efficient car. In some of these cases, 3D printing offers manufacturers customisation options beyond what is possible with conventional manufacturing.
“[With traditional manufacturing], your cutting process is eventually going to be limited and you won’t be able to make really complex shapes, especially, like, internally to that part,” Benzing said. “But with 3D printing, you can take any shape now. You can take an X-ray of your face and perfectly match what would be your jawbone.”
Say you make a map of a 3D printed metal and see something that could be problematic. What do you do? In basic terms, you modify the manufacturing process and then make another map of the resulting metal to see if you’ve gotten rid of the problem.
Benzing used laser 3D printing, a process that uses a laser to intelligently melt metal powder in a layer-by-layer fashion, as an example. With laser 3D printing, you can change the power of the laser, the speed at which the laser is rastered across the metal powder, the depth of the melted area, the powder diameter, and even the scanning strategy.
“Those all locally will change the material and will change the colour of those maps,” he said.
Benzing said that with his work, he wants to make sure that manufacturers that using 3D printing to design steels or tailor metals to any application have all the information they need to make a more informed decision on how to better tailor their processes to produce a part that is going to be reliable.
As for the public, he wants people to know that there’s a lot of information available to us that could be doing a lot of good for the world.
“These maps have real consequences and can really better the world, whether it’s economy, safety or just general like overall a feeling of reliability,” he said.
In terms of next steps for his research, Benzing said he would like to analyse the files of real 3D printed parts, such as a hip implant used in an actual patient, from companies that would be willing to share that information with NIST. This would allow him to test it in a real condition, which the industry already does on its own, validate what manufacturers are doing, and help improve their understanding of the reliability of, say, that hip implant.
Benzing and his team are currently presenting their results at conferences and have been generating interest. At the moment, a lot of companies don’t really look at these maps, or aren’t aware of the value that the maps could provide in relation to reliability, he said.
“But through our research, we’re saying, ‘Hey, you should pay attention to some of the finer details,’” Benzing said. “And here’s how you can manipulate your machine.”