Peter Lee from the University of Manchester looks inside materials to make them stronger, lighter and more reliable. Using the incredibly bright Diamond Light Source, his team creates ‘4D’ scans of objects – 3D scans that change over time. Lee spoke to Joseph Flaig about how the scans reveal the inner secrets of materials, helping to create the turbine blades and car engines of tomorrow.
I lead a group performing ‘4D science’ using the UK’s synchrotron source, the Diamond Light Source (DLS). The DLS uses electrons, which it accelerates with a linear accelerator up to nearly the speed of light. They’re actually moving so close to the speed of light that they are ageing at only 80% of the speed that we are.
The electrons only want to do one thing: go straight. They are put into a storage ring over half a kilometre in circumference and at each of the 48 corners is an electromagnet, which bends them. When you bend them, they shed light, and the more you bend them the more intense that light is. So the light goes from near-infrared, which is about the energy at which atoms in a molecule are bonded… all the way up to hard X-rays which can be even higher in energy than medical X-rays.
As with Superman’s X-ray vision, we can see inside materials with these X-rays. The work I do at the DLS is to use these X-rays to see inside a range of materials in 4D, creating 3D images as the material changes over time. This is much like a medical CAT scan but Diamond’s light is 10 billion times brighter than the Sun, allowing CAT scans to be taken at higher resolutions, seeing features at the sub-micron scale while applying a dynamic process like deformation or heat.
A medical CAT scan takes minutes but with DLS’s bright light we can get a complete 3D scan in less than a second. The maximum is about 10 times a second, and we are working to make it 100 times. However, unlike a medical scan where the X-ray source rotates around you, at DLS you rotate the object. The rotation speed of the object can become the limit, since we want to look at the kinetics of processes inside objects, and by rotating at too high a speed you can change that.
Additive manufacturing offers unprecedented control in the design and manufacture of lattice structures (Credit: MAPP)
My group’s research is using these 4D images to see inside the materials as we make or use them, improving their properties. Taking the example of aeroengine turbine blades, traditionally to improve the performance you would have to make the component and then forensically characterise it to analyse its properties. That involves melting the superalloy, casting it, machining it, heat-treating it, and then taking a section, polishing it and finally doing electron microscopy to characterise the microstructure and properties. Using 4D imaging, we can look inside the superalloy as we’re casting, forging or forming it, and as we dynamically alter the process we can see if it has improved the evolving microstructure, eliminating costly trial and error. It also shows how the microstructure forms, giving us insight into the kinetics of the processes.
Say you see me at the top of Mount Kilimanjaro, but you have no idea how I got there. Our scanning shows us the kinetics of a process, showing that I really did climb to the top of that mountain, rather than being helicoptered or parachuted on to it. What we have been looking at previously was the forensic final image, which didn’t tell us the kinetics of how that actual microstructure, or internal structure, evolved. Our scanning lets us see the real impact of the engineering processes the material experiences.
For example, we are trying to understand the metallurgy in nickel superalloys, which was previously done by looking at them forensically after they have already been produced, or in their final state. Now we are using 4D imaging to let us look inside the alloy as it is solidified, heat treated, or when other thermomechanical processing is applied. The scanning not only shows us how a process has happened, it lets us alter it in real time and hence adjust the parameters to produce a better product.
Looking in
A second example is if we want to then look at the surface of that component and how perhaps it might fracture under very heavy loads, or how it might corrode. Let’s say we are making an engine that might fly through volcanic ash – we can see in real time how ash interacts on the surface of its blades. We can also immediately see how the new alloys and coatings we produce react, to make them stronger, lighter and have a longer operating life.
Now we can see the microstructure evolve and we can alter it. We then take that information and feed it into models of the kinetics. This ensures we have the right physics within the model because we have not just seen an end-picture, which has many different paths to get to, but we have the path the process follows with time. This not only provides data to inform predictive simulations, but also to validate them.
For more than 15 years I have worked with a major company to look inside aluminium alloys as they are being cast, heat treated and in operation, with end applications of engine and suspension components. By observing how the microstructure evolves, we developed models which Ford now uses to help design the shape and processes of its components to make them lighter and stronger. The company has published numbers showing that its programme that uses these models, Atoms to Engines, has allowed it to save $100 million in design costs, getting the product into development faster and increasing reliability.