Feb 20 2023

3D Printing Superalloys

This is a cool material science development that nicely illustrates recent technological advancements. Researchers at Sandia National Laboratories have created a superalloy using additive manufacturing (3D printing). That may not sound that impressive at first, but consider the potential here. We are seeing the confluence of multiple modern technologies. This creates a synergistic effect that allows for new possibilities and accelerated progress.

First let’s talk about alloys – which are metallic substances comprised of two or more elements. The most famous, and most useful, alloy is steel, which is an alloy of iron and carbon. Another ancient and important alloy is bronze, which is a combination of copper and tin. There are about 3,500 different alloys of steel used in industry today, each with slightly different properties. Many alloys are just iron and carbon with different percentages of carbon and different heat treatments, but there are also about 20 elements added to carbon steel to make different alloys. Alloys alter the hardness, strength, ductility, melting point, resistance to rust, and performance in different conditions.

After a couple thousand years of working with steel you may think that we have figured out most of the optimal alloys already, but 75% of modern alloys were developed in the last 20 years. Think about the number of different alloy combinations with 20 different elements, all of which can be added in different amounts. We’ve likely only scratched the surface with trial and error.

Superalloys are essentially high-performance alloys. Most current superalloys are nickel-cobalt based, and the primary property that defined nickel-based superalloys is their ability to maintain high strength close to their melting point. Regular alloys typically start to lose significant strength beyond half their melting point. Remember the controversy over “fire melting steel” with regard to the Twin Towers? The heat produced by the building fires would not have been hot enough to melt steel – but it was more than hot enough to weaken the steel to the point that they could no longer support the structure.

Metals that operate at high temperatures are needed for many industrial applications, including aerospace and energy production. The blades of turbines, for example, can only get so hot before they weaken, and some heat must be removed as waste in order to keep them at their operating temperature. This represents a huge inefficiency in generating electricity from steam (which is how all fossil fuel, geothermal, and nuclear power plants work). An allow that can operate at a higher temperature would increase the efficiency of a large portion of power production. Air and spacecraft also need to operate at high temperatures, as do many engine parts for most applications.

What the Sandia researchers did was make an alloy of 42% aluminum, 25% titanium, 13% niobium, 8% zirconium, 8% molybdenum and 4% tantalum. This is unusual for most alloys in that there are a large number of alloys and none of them are greater than 50%. Most steel alloys, for example, are mostly iron. This new alloy is called a “multi-principal element alloy” because it has at least two main elemental constituents. The result is a light and strong alloy that maintains its strength up to 800 C (1,472 F). A light and strong alloy with a high functional temperature is idea for aerospace and energy production.

Perhaps more interesting is how they produced this new alloy – they 3D printed it. They took powdered metals, flash melted them with a laser, then combined them together in precise ratios as they printed the desired object. This is important because of another aspect of alloys – internal structure. The properties of an alloy do not come solely from the mix of elements of which it is made, but also the structure of the atoms. Steel, for example, can be heat treated in different ways to affect the size of the crystal grains to make it either more strong or more hard. A hardened blade edge is flash cooled (quenched) after heating to a precise temperature in order to create small grain sizes for optimal hardness.┬áThe 3D printing process can be leveraged not only to precisely control the percentage of alloys, but to affect their internal structure, which is just as important to the properties of the resulting superalloy.

The usual caveats apply. This is a proof-of-concept study. Some of these elements are expensive and therefore unlikely to appear in consumer goods, although NASA and SpaceX are likely very interested. Also, the 3D printing process can result in microcracks, which are bad for material performance and longevity. So keep an eye on research to solve that problem. The good news is that 3D printing scales easily. That’s one of its advantages – just buy more 3D printers. It also “retools” very easily – just change the mix of powders in the feeds and the programming and you can very quick change over to producing something else. For this reason it’s also ideal for prototyping and experimentation.

But still, with so many potential alloy combinations we can only hope to test the tiniest fraction of them looking for ideal superalloys. This is where another recent technology comes in – artificial intelligence. Another benefit of this recent study is that it allows the researchers to study why the new superalloy has the properties it does. The goal is to be able to predict how different percentages of different alloys and the production process will affect the final material, and then plug that information into an AI simulation. Then let it run and test trillions of potential combinations looking for promising results to then test physically.

I have often argued that material science is highly underrated in the popular media, but it has an incredible effect on our technology. Developing a new material with new properties can change the game, making new technologies possible and radically changing the trade-offs available with existing materials. Also often underestimate is the synergistic effect of multiple technologies. Often the default is to consider a new technology in isolation, but we always have to look at it in context of other technologies (both competitors and enablers). Here we are seeing the potential of AI, additive manufacturing and superalloy material science. This really is changing the game.

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