Super-elastic high-entropy Elinvar alloy discovered with potential for aerospace engineering
https://phys.org/news/2022-02-super-ela ... ntial.html
by City University of Hong Kong
Metals usually soften when they expand under heating, but a research team led by a City University of Hong Kong (CityU) scholar and other researchers have discovered a first-of-its-kind super-elastic alloy that can retain its stiffness even after being heated to 1,000 K (726.85 degrees Celsius) or above, with nearly zero energy dissipation. The team believes that the alloy can be applied in manufacturing high-precision devices for space missions.
The research team was led by Professor Yang Yong from CityU's Department of Mechanical Engineering (MNE) together with his collaborators. The findings were published in the science journal Nature under the title "A Highly Distorted Ultraelastic Chemically Complex Elinvar Alloy."
Challenging thermal expansion principles
Usually, the elastic modulus, i.e. stiffness, of most solids, including metals, decreases when the temperature increases as a result of thermal expansion. However, Professor Yang and his team discovered that a high-entropy alloy called Co25Ni25(HfTiZr)50, or "the high-entropy Elinvar alloy," reveals the Elinvar effect. This means the alloy firmly retains its elastic modulus over a very wide range of temperature changes.
"When this alloy is heated to 1,000 K, i.e., 726.85 degrees Celsius, or even above, it has stiffness comparable to that at room temperature, and it expands without any notable phase transition. This changes our textbook knowledge, as metals usually soften when they expand under heating," said Professor Yang.