Prof. Dr. Sanjay Sampath is Distinguished Professor and Director of the Center for Thermal Spray Research at Stony Brook University in New York. He studied metallurgy at an institute in his native India and a scholarship to complete his Ph.D. in the U.S. changed his career.
by Randy B. Hecht
Metallurgy typically involves making big things like castings and forgings. “At Stony Brook, they were taking metals and even ceramic and basically making raindrops – thermal spray – that impact the surface,” Sampath says. “When you do that, you operate at extreme conditions of metallurgy or materials. That captivated my attention.”
Prof. Sampath uses “pretty much all” of Oerlikon’s equipment, including plasma spray and supersonic combustion equipment, and more than a dozen of his former students have worked at Oerlikon Metco’s facility in Westbury, New York. Teaching remains important to him because “I start to realize how you should manipulate your own thinking,” he says. “Everyone should teach, because then they’ll know their subject better.”
How is thermal spray technology evolving?
Thermal spray was widely used by skilled practitioners, not necessarily scientists and engineers. That’s how the technology started. We made it into a rigorous scientific and technological capability. And that has paid dividends. We have effectively transformed the technology from an art form to a robust, scientifically strong engineering technology.
How does that translate to benefits to people, society and the planet?
When thermal spray started, only a few people could do it well. In manufacturing, you want the technology to be more scalable, reliable and reproducible. You want a rigorous manufacturing technology. And you can only achieve that if you understand the science and the technology behind the process.
The consequence of that is, we have a much larger market base, and the technology is used in more industries. Coatings were generally used as an afterthought to, maybe, improve functionality. Now, design engineers are taking advantage of coatings as an actual capability. That has allowed the industry to flourish. Aircraft engines and power generation are the areas where the impact is most significant, with a double digit increase in efficiency, a significant reduction in CO2 – those are where you actually see the tangible, measured benefits.
One area of your research is thermal spray processing of materials, synthesis and application of multilayered surfaces. Can you help us understand that?
Let’s focus on the word multilayer, which I think is the future. When the technology was not very strong or the understanding was not very good, people just sprayed the same coating layer. But with our knowledge and the capabilities of the technology, we are depositing coatings not as monolithic uniform material, but as something more like designer structures.
No one material can satisfy all your needs. By layering them in a clever, strategic way, you can do many things at the same time, which is what we call multifunctionality. You basically stack materials (or material attributes) in layers, very similar to how they build semiconductor chips. We’re trying to do something like that on a large scale.
Another area of your research is the evolution of microstructures associated with suboptimal conditions in terms of equilibrium. What should we know about that?
An important aspect of thermal spray that is not well appreciated is that we basically create these modern raindrops of very high-temperature materials. These things hit the surface and cool extremely fast – like a million degrees per second. When meteorites impact with the Earth, you have craters, right? We do something like that at a very small scale. Each one of these droplets is the diameter of your hair. We’re taking these things and projecting them at extremely high temperatures and velocities. They cool very fast and impact at high energies, and so we use the term that these are materials synthesized from extreme conditions. What we’re trying to do is essentially bring in new ways to integrate these non-equilibrium processes. The global thermal spray community had to basically rebuild the whole research enterprise to think in a very different way that is not following tradition or established engineering thinking.
You also have “pioneered the development of mesoscale direct writing technologies based on thermal spray for applications in prototyping and manufacturing of wide-ranging thick film sensor structures, thick film electronics, and mesoscale multifunctional systems.” Is there a way to understand that?
I’ll simplify that. Thermal spray is a paintbrush. It creates broad, sweeping paint swaths. For a U.S. government project, I was asked to make a thermal spray pen rather than a paintbrush. That’s what mesoscale direct writing means. We took a thermal spray paintbrush and made it into a thermal spray pen. That’s not easy to do. It took more than USD 10 million and a lot of labor to get there, because you can’t simply miniaturize thermal spray. It takes a tremendous amount of not only understanding, but also hardware to implement that. Because we can now write in addition to paint, now I can do interesting things with it. For example, I can write a circuit on top of a coating that will allow me to sense what the component operating temperature is or collect electromagnetic signals by printing antennas on structures.
This is a normal way to combine layering and printing and allows us to do direct writing. Imagine if I can pattern materials precisely the way I want in 3D. Not only do I need a pencil or a pen to be able to write, but I also need the robotics and machine tools that allow me to actually print a circuit on a 3D part. We can write an antenna on top of an existing part – for example, on a helmet or even an aircraft structure. In fact, that’s what we did.
There are two important innovations. One is that we created a high-definition thermal spray printing process – which was revolutionary, and the technology is now being used commercially. And second, now we can take thermal spray and write as well as paint. We can build electronic devices, which are basically lines and layers. To do that, you need tremendous understanding of how you not only miniaturize these things but also get the correct material attributes. That required knowledge of thermal spray at a level that was not easily available. And if you’re making things so small, can I still get the materials to work right? That was the second big challenge. These two had to come together for the technology to succeed. That was possible only because of all the foundational work we had done in thermal spray.
So you are pioneering new levels of precision. How much further can that precision be taken?
This was considered a disruptive technology, so it came in sideways. The problem is, you then have a capability that’s looking for an application. That’s always a difficult thing to address. We have done a lot of innovation, maybe even reached the limit of what we can do with today’s technology. The real future effort is taking advantage of this breakthrough to many applications. And that is going much more slowly than we thought. My guess is that in the next 10 years, people will start to see more and more concepts of these intelligent machines.
Which areas of industrial development of thermal spray technologies do you monitor, and how do they affect the direction of your research?
I tend to go outside the mainstream to seek ideas. If you talk among yourselves, you’re not going to make progress. So I continue to collaborate with my peers, but I go out of my comfort zone. You can convince yourself you know everything until you see someone who tells you something completely different. Constantly challenging one’s own view is in my mind very important.
Where do you see the best opportunities for academia and industry to work together toward further development of this technology and its practical applications?
I created the Consortium for Thermal Spray Technology, which involves 30 companies. The idea is linking research to practice. Oerlikon is a founding member and a big supporter of it. And Oerlikon is a supplier of thermal spray equipment and materials, but its customers are companies like General Electric, Rolls-Royce, Siemens and Caterpillar. Our Consortium has all these companies as members. It’s a unique business model because we have competitors and customers in the same room. And that has been a successful and rewarding journey. We’ve met every six months for 15 years, and generations of students have experienced this concept of consortium.
We’ve been able to convince the companies that our fundamental research can provide value to their products and manufacturing processes – essentially to their bottom line. You have to provide value to companies, give them something they can actually use, and at the same time, make them realize that your fundamental research has value for them. For that to happen, you must understand what their needs are so there’s a very good partnership. Ultimately, we have to make the pie larger so we all can have a bigger piece of it.