Training metals like muscles to make them stronger and longer-lasting: New method combines controlled loading with restorative polishing

Q1. What inspired you to become a researcher?

A1. A childhood fascination with superalloy robots

I've always been the kind of person who can't let a question go unanswered. Whenever I encountered something that I didn't understand, I felt compelled to find out why, and that curiosity gradually drew me toward science.

My interest in metals began with the anime Mazinger Z. I was fascinated by scenes where the robot's armor, made from a fictional "superalloy," could withstand attacks that would otherwise destroy it. As a child, I simply thought strong metals were incredibly cool. In high school, I joined the science club and wanted to try making an alloy of copper and lead. However, my teacher told me it would be too difficult for a high school student, so the project never got off the ground. Later, I entered Kyoto University's Department of Physical Engineering. When it came time to choose a field of study, I decided on materials science because it underpins virtually every form of manufacturing and technological development. Looking back, I think my unresolved ambition from high school also played a role in steering me toward the field.

Q2. What research are you currently working on?

A2. Improving the fatigue resistance of steel

I am conducting research into improving the fatigue resistance of steel. When metals are subjected to repeated stress, cracks can form and eventually lead to failure. Because metal fatigue can cause accidents in aircraft and other structures, improving resistance to fatigue is an important challenge. Traditionally, most research has focused on increasing the fatigue limit by preventing cracks from growing once they form. However, as materials become stronger, it becomes more difficult to stop crack propagation in this way.

I've continued strength training as a hobby since my days on the university rowing team, and one day I found myself wondering: Why do human muscles become stronger when repeatedly stressed, while metals become weaker? Just as people can be injured by excessive training and become exhausted without adequate recovery, metals also have their own form of "injury" in the form of cracks. That led me to wonder whether metals could be strengthened through repeated loading, provided the stress remained below the level that causes cracks and was combined with a process equivalent to recovery.

This idea became the basis for a method I call "pre-fatigue training." Repeated deformation creates microscopic surface irregularities in metals. Normally, these irregularities can serve as starting points for cracks. However, by repeatedly applying an appropriate level of stress that does not produce cracks, and then removing the irregularities through polishing, the affected areas become harder than before, suppressing crack initiation. In this process, polishing serves as the metal's form of recovery. Using this method, we succeeded in doubling the fatigue limit of ultra-high-strength steel.

We are now investigating how the technique can be applied in hydrogen environments. Because hydrogen, the smallest element, can penetrate metals and cause embrittlement, this is an important issue for the development of hydrogen infrastructure, including fuel-cell vehicles. Our goal is to enable the safe and widespread use of stronger, lighter steel materials in such applications.

Q3. What message would you give to aspiring researchers?

A3. Follow the path that excites you

One of the greatest appeals of research is that anyone can stand at the frontier of their chosen field. In sports, not everyone can break a world record. In research, however, the starting line itself is already at the forefront of human knowledge. What makes research so fascinating is the opportunity to push beyond that frontier and explore territory no one has reached before. With both the pride and responsibility that come from working at the leading edge of human knowledge, I intend to continue pursuing the development of the strongest possible materials, ones that resist failure by preventing crack initiation. My goal is to become a leading researcher in this field. To those who aspire to become researchers, never lose sight of your curiosity and sense of excitement. Follow the path you truly believe in and let that excitement guide you forward.

(Article: Yasuhiro Hatabe)