“We Need to Develop Materials for All Processes”

Material development is becoming a strategic issue across all metalworking industries. Metal 3D printing is no longer just a playground for special applications. It is increasingly becoming an integral part of industrial manufacturing. New alloy systems, hard phase combinations and even raw material-saving substitutes are coming into focus.

In this interview, Dr Horst Hill explains why the availability of cobalt, nickel and tungsten is now just as important as temperature and wear resistance, and how powder mixtures and graded structures enable completely new properties.

For the wire, cable and tube industry, this raises the question: How will materials, coatings and production processes change when additive manufacturing, new alloys and raw material strategies interact more closely than before?

hp: Dr. Hill, where does metallic 3D printing currently stand, and which developments have been most striking to you in recent years?

Dr. Horst Hill: The most important insight is this: In recent years, metal AM has definitively advanced from a niche hype technology to a serious production option—especially in aerospace, medical technology, and high-end automotive. It can be said that additive manufacturing has left the hype behind, and realism has taken in. The major discussion today is no longer about whether 3D printing fundamentally works, but rather where it truly makes sense to consider it for series production and to scale it up. Today it’s about process stability, automation, cost reduction, and above all, qualification and standardization — both in the AM processes themselves as well as in powder specifications and design guidelines.

hp: You’ve shifted your focus from iron-based to cobalt-based alloys. What makes cobalt so interesting?

Dr. Hill: That’s related to my change of employer. At Deloro Wear Solutions, we want to be at the core of every critical process and cobalt-base materials are our focus. I continue to work with iron-based materials and some interesting things can be seen on the horizon, but in the area of cobalt-based alloys, we’re currently working on the next major and exciting development step.

hp: ...which would be?

Dr. Hill: It’s about achieving even higher temperature resistance and strength while simultaneously improving corrosion and oxidation resistance. Where the classic Stellites and Tribaloy-alloys reach their limits, we’re looking at how to take the next step. Previously, these cobalt alloys were mainly cast or produced as welding material for coating. The current stage of development considers now also directly additive manufacturing.

hp: Where are these cobalt-based materials typically used?

Dr. Hill: The applications are very diverse. One major area is dental technology, for example—where we have cobalt-chromium materials in various product forms, either as powder for 3D printing or as discs for CAD-CAM milling processes. Major application areas also include energy technology and power plant construction, where tribological systems—high temperatures, oxidation, and wear—come together. Our cobalt-based materials are also used in aerospace, the chemical industry, and even in the food industry—wherever extreme corrosion resistance is required.

hp: What does development work with tribological systems specifically entail?

Dr. Hill: Tribology describes the interaction of all stresses that a material or component faces. We have the temperature component—this can be room temperature, but also temperatures of 800 degrees celsius. Then the wear component: metal-on-metal friction, where adhesion dominates, or abrasion from particles. If, for example, you’re regulating a liquid or gas medium via valve control and you have particle loading, you quickly get erosion from high flow velocities. And then you have the corrosion or oxidation effect. When you consider these examplary points together—and ultimately you must—then you have the tribological system for which the material must be optimized.

hp: That sounds like an enormous challenge in materials development.

Dr. Hill: Absolutely. The major challenge is that you often don’t even know exactly what tribological systems exist. You have the customer application with certain framework conditions or your own idea, but ultimately you always have to look at: What does the customer / the application specifically need? If you’re lucky and can cover a lot with one material. But often that’s not the case at all. Then, for instance, we have to look at: What chromium content do I need at minimum for sufficient corrosion and oxidation resistance? What carbide content must I set for the necessary hardness and abrasion resistance? And if I simultaneously have impact stress, maybe I don’t need so much hardness at all, but rather toughness. That’s our playground.

hp: You work intensively with powder mixtures. What does this technique enable?

Dr. Hill: Powder metallurgy generally offers many possibilities, as we can adapt properties to the respective application through the combination of metal matrix and hard phases to produce a so called metal matrix composite. In the simplest 

case, I mix two metal powders—for example, a high-alloy and a low-alloy cobalt-based matrix. Or I take a cobalt powder and add carbide powder. For carbide powder, I can use carbides like titanium carbide, (fused) tungsten carbide, niobium carbide or vanadium carbide—these are the typical (mono)-carbides with high hardness and good abrasion and adhesion resistance. Usually they’re also chemically inert, meaning corrosion resistance doesn’t suffer.

hp: How does this work in practice?

Dr. Hill: In classic overlay welding, especially in plasma transferred arc welding (PTA), we’ve been offering powder mixtures for quite some time. Usually it’s fused tungsten carbide mixed with nickel powder. We produce the metal powder, the hard phases are specified and purchased, and we make the mixture as the customer needs it—in principle, anything from 0-99% is possible, at least from a mixing technology standpoint. We’re now transferring this experience to additive manufacturing because you can naturally use the same advantages there.

hp: Are there special challenges in transferring from welding to 3D printing?

Dr. Hill: Definitely. When I process something like this additively, I have a similar problem as with tool steel: rapid heating rate, rapid cooling rate, which creates thermal stresses. Although there is no martensitc transformation as it is typical for a lot of tool steels, leading to more stresses within the material, thermal stresses alone pose a major challenge. If a material cannot flow sufficiently, meaning it cannot relieve the stresses, cracking occurs when the strength is exceeded. The advantage of our current development is that we’re work

ing with low-carbon alloy systems because we’re addressing the highly corrosion-resistant and oxidation-resistant corner. This makes it possible for us to PTA weld it, laser weld it, and also process it additively. So to speak, a universal material for all manufacturing methods with tailored properties due to the specific hard phase content. That’s a topic we’re currently intensively engaged with.

hp: You’re also researching graded structures. What’s behind that?

Dr. Hill: With graded layers, we can, starting from the substrate outward, increase the hard phase content where we need the final properties. The advantage: on the outside it’s then hard and wear-resistant. Associated with this, I do have poorer toughness, but I really only have the poor toughness on the outside. The rest of the component is still tough, and if a crack forms, it can be compensated for and stopped. This way we can design the properties across the component height. What we can do macroscopically in the welding process, we’re now trying to build up additively as well—in smaller and more complex ways. It is a really interesting topic. 

hp: That sounds like enormous, and especially time-consuming, development effort. What role does digitalization play in getting to the goal faster in product development and optimization?

Dr. Hill: A very large one by now. People have been trying for quite some time to monitor the process very precisely. In the powder bed process, for example, the melt pool is monitored very specifically to determine: Am I deviating somehow, in temperature or other parameters, where a pore, defect, or crack could later develop? There’s increased focus on improving the prediction. The next step is then for the system to automatically adjust the parameters when it determines that you’re heading toward a limit violation. This is particularly interesting with complex components with large transitions or thin-walled areas. So said, a lot of research projects are being carried out for this purpose by research institutions and universities.

hp: Speaking of AI—how do you see its influence on additive manufacturing?

Dr. Hill: I’ve seen promising approaches that combine real-time monitoring like melt pool cameras with AI-supported evaluation. The system detects defects in real time, evaluates their influence on properties, and in a second step adjusts the printing parameters—possibly even only locally. This can be done wonderfully via an AI-controlled system. This is currently being researched. In general, there’s a strong focus on: What sensors are available, what feedback do they provide, and what can I derive from that for controlling and optimizing the process?

hp: Because sensors are usually not cheap, the other question at this point is always one of economic viability.

Dr. Hill: Completely correct. You can install a lot of sensors, but if a printer costs 50,000 euros for instance and I install 10,000 euros worth of sensors, it may no longer be so economical—even if it’s technically perhaps highly interesting. I always have to look through the application lens and ask: What is actually necessary? What do I need to measure to control my process well? In the end, an economical product must result. We see the same thing with powder specifications. People are now trying to very strongly limit secondary elements like oxygen or nitrogen. You can work with protective gas in the furnace, smelt under vacuum, switch from nitrogen to argon to achieve higher purity via atomization. But is that technically really sensible? Am I thereby producing a product that generates real added value, or am I just making it more expensive?

hp: Speaking of costs—what about series production?

Dr. Hill: The leap from prototype to series—the scaling—is always the big hurdle. Often people only think about the quantities or the manufacturing costs per part—all correct, but you mustn’t forget quality assurance. How is the quality of finished components checked? How is it ensured that the process runs stably? Is the material specification defined? Especially in aerospace and medical technology, the regulatory requirements are enormous. Very important on the topic of costs is also: The principle of Design for AM must be 

considered as best as possible, because this always results in significantly less rework, more efficient manufacturing, and optimized properties.

hp: An increasingly important topic is raw material availability. How much does this influence your work?

Dr. Hill: The influence is increasing more and more. Take fused tungsten carbide, for example: roughly 90% comes from China, and there are currently certain export restrictions. Tungsten has now risen to over 100 dollars per kilogram, simply because it’s currently not being exported in the necessary quantities. These are topics that now play a central role in materials development. You not only have to look at: What gives me the best properties? Equally important is also: Where do I have a certain security of supply? We just had a project discussion with a customer about the next generation of wear-resistant materials—with the clear requirement to find a raw material system with which we can first achieve a certain independence again.

hp: Which elements are particularly critical in terms of availability?

Dr. Hill: Cobalt and nickel are historically volatile elements that can quite easily double and halve in price. Molybdenum and tungsten are currently strongly influenced by how exports are limited. We’re trying to accompany this from a materials technology perspective—through projects and materials research on how to reduce certain elements while largely maintaining the previous properties. We currently have a BMBF research application running, where we’re involved as project partners and it’s about exactly that: How can critical elements be substituted or at least reduced?

hp: Has awareness of this arrived in the industry?

Dr. Hill: My personal impression is: Not yet completely. How critical it can become if certain things are no longer available is not yet fully clear to many. Cemented carbide is maximally tungsten carbide-dominated—a huge industry that uses thousands of tons. If that were suddenly no longer available from one day to the next, it would have a massive impact on the entire machining industry, because the drills, indexable inserts, and so on are largely WC-based.

hp: On the other hand, these raw materials are used precisely because their properties are so good.

Dr. Hill: That’s exactly the point. These materials provides the needed properties due to the alloy system with cobalt, molybdenum or tungsten, for instance. These are alloys that have been used for decades, work superbly, and that you can’t simply substitute. Larger research projects are necessary to find alternatives.

hp: If you look into the future: Where will metallic 3D printing be in five to ten years?

Dr. Hill: Automation and series production, considering binder jetting processes and the already existing sintering routes, will certainly have made a big leap. Real-time process monitoring with direct intervention by AI will probably be an integral part of manufacturing. In addition to process technology improvements, there will also be new materials that better meet the requirements of different applications. Beyond pure materials technology, graded components and targeted hard phase additions will contribute to the success of this technology. And last but not least: Sustainability and resource conservation will now play a more central role as innovation drivers—both in powder recovery and in the development of materials that reduce or completely avoid critical elements.

hp: Thank you very much, Dr. Hill.