SCHOOL OF ENGINEERING, TOHOKU UNIVERSITY Driving Force THE POWER TO MAKE TOMORROW INTERVIIEW REPORT
SCHOOL OF ENGINEERING, TOHOKU UNIVERSITY Driving Force THE POWER TO MAKE TOMORROW INTERVIIEW REPORT

Fascinated by the beauty of the “phase transformation” of metals wherein atoms move in unison Fascinated by the beauty of
the “phase transformation” of
metals wherein atoms move in unison

Assistant Professor
Department of Metallurgy
Graduate School of Engineering,
Tohoku University
Xiao Xu REPORT #30

© School of Engineering, Tohoku University

Impressed by
Japanese students’
earnest and serious
approach to their studies

At 0℃, water (its liquid phase) turns to ice (its solid phase), and at 100℃, it turns to steam (its gas phase). Even though water’s phases may change, they are all H2O when expressed in terms of chemical composition. Such a change is called a “phase transformation,” wherein the chemical composition remains the same but the phases (physical properties and atomic arrangements) are different. There is also a phase transformation unique to solids (metals). “When magnified to a million times or even ten million times, we can see that the atoms in metals are very neatly aligned. In a metal’s phase transformation, those neatly aligned atoms move in unison. Being moved by the beauty of those movements was the catalyst for continuing my research in the world of metallic materials,” says Assistant Professor Xiao Xu, who researches and develops shape memory alloys and new metallic materials at the Graduate School of Engineering of Tohoku University.

Asst. Prof. Xu is from Beijing, China. After graduating from high school, he was admitted to Zhejiang University, but to a department specializing in metals and not polymer chemistry, which he wanted to study. He says, “At first, I was quite disappointed that I couldn’t be admitted to the department I wanted, but I studied hard because there was a system that allowed us to change our major if we got good grades. That was when I encountered phase transformation, and that encounter was a major turning point for me.”

In his junior year, he came to Japan for the first time as an exchange student at the University of Fukui. Impressed by Japanese students’ earnest and serious approach to their studies, he strongly felt that he wanted to continue his studies in such an environment. When he mentioned that he wanted to study shape memory alloys in the future, a professor at the University of Fukui advised him that Tohoku University would be the right place for him. That conversation brought Asst. Prof. Xu to Tohoku University.

A shape memory effect
through cooling
A world’s first discovery
becomes the starting
point of research

Back in China to complete his college degree, Asst. Prof. Xu began to look for a university for his master’s degree. His search keywords were “Japan,” “functional materials,” and “shape memory alloys.” One of the search results was Professor Ryosuke Kainuma who at the time was working at the Institute of Multidisciplinary Research for Advanced Materials (IMRAM) at Tohoku University. “I emailed Prof. Kainuma, and he graciously accepted my request to study under him. IMRAM at the Katahira Campus became my starting place as a graduate student,” says Asst. Prof. Xu.

Looking back to his graduate student days at IMRAM, he says, “We students spent a lot of time discussing things among ourselves, which was very stimulating. There were all kinds of people; some were studying more physics-related themes, and there were those who were researching more about structural materials. Talking with them broadened my interests.”

When he was in the first year of his master’s degree, he wanted to study functional materials and shape memory alloys, but he still has not decided on a specific theme. Prof. Kainuma gave him a piece of advice, saying, “A research theme is merely one study material. It doesn’t matter whether it goes well or not. Let’s come up with a phenomenon that the world hasn’t seen so far.” Asst. Prof. Xu used these words as his motivation for his research. He explains, “It’s okay even if I were to continue to fail, as long as I obtained some kind of data. Prof. Kainuma’s approach that what’s important was thinking about what I could do with the data I got resonated with me. His approach was precisely how I was able to deal with my research without always thinking negatively.”

In 2013, Asst. Prof. Xu and his colleagues announced the world’s first physical phenomenon from such research. It was the discovery of “anomalous martensitic transformations in cobalt-base alloys.” Ice-water-steam transformations are called diffusional transformations (wherein molecules move discretely), whereas in martensitic transformations (diffusionless phase transformations), atoms move hand in hand then return to their original state. Martensitic transformation is precisely the basic mechanism of a shape memory effect. After changing the shape of a sample, conventionally, heating was necessary to make it return to its original state, but Asst. Prof. Xu and his colleagues discovered a shape memory effect through cooling. Using this discovery as a starting point, Asst. Prof. Xu decided to further continue and develop his research in cobalt-based alloys.

School of Engineering, Tohoku University Driving Force, The Power to Make Tomorrow. INTERVIIEW REPORT

In a field of research
that no one else is
engaged in, giving his
all and putting his name
on the line

Asst. Prof. Xu says, “The shape memory effect through cooling is interesting as a physical phenomenon, but it took me several years thinking about what it could be used for.” He also says, “As long as we (researchers) are in the engineering world, we must find some application for our discoveries. Even if we couldn’t find it right away, we must work toward our discoveries’ usage possibilities. As a result of my efforts through the years, I’ve begun to see various possibilities.” One possibility is its usage in the coming hydrogen-based society. A hydrogen-based society requires hydrogen to be liquefied at extremely low temperatures. He explains, “Our discovery could be applied if some kind of actuator (a device that transforms energy and electrical signals into physical movement) is needed in a low temperature environment.”

Based on research on cobalt-based alloys, a new metallic material was developed and announced to the world in 2022. It is a cobalt chromium-based biomaterial that is both tough and flexible, with properties similar to human bones. Asst. Prof. Xu says, “In a phase transformation when the atoms are about to move, they are in a softened state even though the material is metal. This is the key point of this research. We have developed a metallic material with suppleness as its main feature, combined with corrosion and wear-resistant properties, and it does not contain elements that are harmful to the human body.” He explains future developments for the material this way. “Applications of this material in bone plates and artificial joints, dental implants, spinal fixtures, stents, and guide wires are promising. It could also contribute to solving the problem of bone atrophy caused by implants.”

“The interesting part about my research is that it’s in a field that no one else studies. At best, we can say I’m a leader in this field. At worst, we can say it’s a field that hardly anyone pays attention to,” he laughs. “I can continue with this research because it has the interesting aspect of basic research while also possibly leading to applications. For research that no one else will do unless I do it, no matter how much I may not want to do it, I will give it my all and put my name on the line. That’s my way. Mindset is what’s important,” he says. His approach toward his research has always been positive. Asst. Prof. Xu adds, “If you persist in any research, at some point, it will open up. If your mindset is that no good result will ever come out, you won’t be able to notice a good result even if it does come out. Conversely, if you think that something good will indeed come out, you will notice everything with a keen eye, and things will go well. I believe that’s what the world of research is all about.”

Strong ties among
faculty members and
young researchers play
active roles

When he’s not working, Asst. Prof. Xu enjoys playing the piano, photography, growing vegetables in his balcony garden and playing with his child. He is so good at playing the piano that if he had not pursued a career in research, he would have aimed to become a professional musician. He says, “When I’m resting, taking a shower, aimlessly watching TV, playing the piano without thinking about anything, or fiddling with my camera or lenses when taking photos, there are times when something about my research pops up in my mind. It’s obvious that time off from work is important for a researcher.”

He also talks about what he feels as an assistant professor when he interacts with students. “Students may be so immersed in their research that they can’t see how their research will relate to their own futures. It’s important to put much effort into research, but I want them to remember that there will be times when things won’t go well. I hope juniors and seniors who are in their early 20s would think about what kind of person they want to be in their 40s and 60s, and the path they ought to take.”

What does Asst. Prof. Xu think the strengths of the School of Engineering are after more than ten years at Tohoku University and as an international student from China? He says, “The first is the strong ties among faculty members. Many of them do not only have relationships as researchers, but they also have personal relationships. When students are stuck in their research, I can immediately think of which professor is the best one to consult. And all the professors who are being consulted deal with the students earnestly.” He also says that young researchers having active roles to play is another strength. He explains, “Tohoku University has ‘The Young Researchers Initiative,’ a substantial support system for young researchers. Young researchers are close in age to students, so it’s a great benefit for students to be able to tail energetic, young researchers in their experiments for an entire day, and to be able to have time to discuss things with them. If you are an international student or a student who wishes to pursue higher education at Tohoku University’s School of Engineering or the Graduate School of Engineering, please know that this is a place where young researchers play active roles.”