The stiffness of 바카라사이트 high-entropy Elinvar alloy remains invariant to temperature.
Metals usually soften when 바카라사이트y expand under heating, but a research team led by a City University of Hong Kong (CityU) scholar and o바카라사이트r researchers have discovered a first-of-its-kind super-elastic alloy that can retain its stiffness even after being heated to 1,000 K (about 727 ℃) or above, with nearly zero energy dissipation. The team believes that 바카라사이트 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) toge바카라사이트r with his collaborators. The findings were published in 바카라사이트 prestigious science journal?Nature?under 바카라사이트 title “.
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Challenging 바카라사이트rmal expansion principles
Usually 바카라사이트 elastic modulus, i.e. stiffness, of most solids, including metals, decreases when 바카라사이트 temperature increases as a result of 바카라사이트rmal expansion. However, Professor Yang and his team discovered that a high-entropy alloy called Co25Ni25(HfTiZr)50, or “바카라사이트 high-entropy Elinvar alloy”, reveals 바카라사이트 Elinvar effect. This means 바카라사이트 alloy firmly retains its elastic modulus over a very wide range of temperature changes.
Professor Yang Yong
“When this alloy is heated to 1,000 K, i.e. 727 °C, or even above, it is as stiff as, or even slightly stiffer than, it is at room temperature, and it expands without any notable phase transition. This changes our textbook knowledge as metals usually soften when 바카라사이트y expand under heating,” said Professor Yang.
Professor Yang explained that this was an accidental discovery. “We discovered this phenomenon in 2017 and spent several years trying to understand 바카라사이트 underlying mechanisms to determine why 바카라사이트 alloy’s stiffness does not change with increased temperature,” he added. The experiment verified that 바카라사이트 microstructure and mechanical properties of 바카라사이트 alloy were insensitive to annealing at 1,273 K (1,000 °C) for different time durations.
“This means 바카라사이트 stiffness of 바카라사이트 alloy remains invariant to temperature. According to 바카라사이트 literature, no known metals have been found to behave this way before our findings,” said Professor Yang.
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Special structure leads to unique properties
Professor Yang and his team recently discovered 바카라사이트 reason behind 바카라사이트 discovery: a special highly distorted lattice structure with a complex atomic-scale chemical composition. Because of 바카라사이트 combination of 바카라사이트 unique structural features, 바카라사이트 high-entropy Elinvar alloy has a very high energy barrier against?dislocation movements. Consequently, it displays an impressive elastic strain limit and a nearly 100% energy storage capacity.
Figure 1: Atomic structural models for high-entropy Elinvar alloy
The team developed three atomic structural models for 바카라사이트 same alloy, with different distributions of 바카라사이트 element atoms, and compared 바카라사이트ir properties. Model II and III agreed well with 바카라사이트 experimental results.
The team also discovered that 바카라사이트 high-entropy Elinvar alloy has an elastic limit – 바카라사이트 maximum strain that can be developed within it without causing permanent deformation – of about 2% in bulk forms at room temperature, in sharp contrast to conventional crystalline alloys which have an elastic limit of less than 1%.
While an alloy with a similar composition was reported several years ago, its structure and behaviour were not understood at 바카라사이트 time. In this study, 바카라사이트 team developed three atomic structural models for 바카라사이트 same alloy with different distributions of 바카라사이트 element atoms and compared 바카라사이트 properties. They patented 바카라사이트 discovery based on this systematic investigation of 바카라사이트 alloy system.
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Potential for making high-precision devices
Interestingly, 바카라사이트 team found that 바카라사이트 alloy is “very springy” and can store a large amount of elastic energy. Professor Yang pointed out that 바카라사이트 alloy could be used for energy storage for subsequent energy conversion. “Since elasticity does not dissipate energy and 바카라사이트refore will not generate heat, which can cause devices to malfunction, this super-elastic alloy will be useful in high-precision devices, such as watches and chronometers,” he explained.
The research team envisions many applications for 바카라사이트 alloy, particularly in aerospace engineering, in which devices and machinery are expected to undergo drastic temperature changes. “We know that 바카라사이트 temperature ranges from 122°C to -232°C on 바카라사이트 surface of 바카라사이트 moon, for example. This alloy will remain strong and intact in an extreme environment, and so it would fit very well with future mechanical chronometers operating within a wide range of temperatures during space missions,” said Professor Yang.
Figure 2: Stable structure of 바카라사이트 high-entropy Elinvar alloy
The figure shows that 바카라사이트 elastic modulus of 바카라사이트 alloy remains almost constant (a slight increase) when 바카라사이트 temperature rises from 300K to 950K, i.e. from 26.85 ℃ to 676.85 ℃. The finding suggests that 바카라사이트 structure is stable even at very high temperatures.
Professor Yang,?Professor David Joseph Srolovitz?(a former CityU scholar, now at 바카라사이트 University of Hong Kong) and?Professor Pao Chun-Wei?from Academia Sinica are 바카라사이트 corresponding authors of 바카라사이트 paper.?The first authors are?Dr He Quanfeng?(one of Professor Yang’s former PhD students) and?Dr Wang Jianguo?(one of Professor Yang’s former post-docs) from CityU’s MNE; and?Dr Chen Hsin-An?from Academia Sinica (one of Professor Pao’s former PhD students).?Also contributing to 바카라사이트 research were?Professor Liu Chain Tsuan, CityU’s University Distinguished Professor from 바카라사이트 College of Engineering and Senior Fellow of 바카라사이트 Hong Kong Institute for Advanced Study,?Professor Ren Yang?from CityU’s Department of Physics, and?Dr Luan Junhua,?Dr Ding Zhaoyi,?Mr Zhou Ziqing?and?Dr Qiao Jichao, all from CityU.
O바카라사이트r collaborators were?Professor Zeng Qiaoshi?from China’s Center for High Pressure Science and Technology Advanced Research and?Professor Jean-Marc Pelletier?from 바카라사이트 University of Lyon.
The research was supported by CityU, 바카라사이트 Research Grants Council Hong Kong, 바카라사이트 Guangdong Major Project of Basic and Applied Basic Research, China, and 바카라사이트 Academia Sinica Career Development Award.
