CoCrFeNi increases strength at cryogenic temperatures
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CoCrFeNi increases strength at cryogenic temperatures
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times less. For the simple one-pot reaction, the researchers mixed organic starting materials into a suspension of the perovskite nanocrystals. Blue-light illumination triggers reactions that generate several products. By tweaking the reaction condition, the researchers can selectively catalyze other important chemical reactions, the researchers report in the Journal of the American Chemical Society (doi:10.1021/jacs.8b08720).
form these extremely a low temperature experiments,” says Peter Liaw of The University of Tennessee, Knoxville, who is a co4.2 K author on this publica77 K 200 K tion. When subjected to 293 K original tensile strength testing at extremely low temperatures, the CoCrFeNi alloy deformed in Engineering Strain ε a slip-stick manner, as b demonstrated by jagged Ulitmate tensile strength or serrated stress–strain Yield strength curves at 20 K and 4.2 K. Elongation Performing mechanical property measurements at “the liquidhelium temperature is really remarkable,” says Richard LeSar of Iowa State University, “It opens up a different Temperature (K) realm for thinking about behaviors in these sys- Tensile properties of the CoCrFeNi alloy at different temperatures. tems.” LeSar was not (a) Engineering stress–strain curves and photograph of the doginvolved with this study. bone-shaped samples, before and after tensile tests. The enlarged stress–strain curve at 4.2 K is displayed in the inset and the jagged To explain the ser- serrations are clearly observed. (b) Strength and elongation versus rated behavior of the temperature for the high-entropy alloy. The ductility reaches a maxistress–strain curves, im- mum at 77 K. Credit: Science China Materials. ages of the CoCrFeNi samples after strain relative to one another. In addition to the testing were taken using both a transmistwinning behavior, a new crystal phase of sion electron microscope and a high-resthe CoCrFeNi alloy was also observed. olution scanning transmission electron Theoretical analysis of the serratmicroscope. The images revealed many ed stress–strain curves revealed an small parallel hatched features consistent “unstable dynamic process, which was with the formation of deformation twins, consistent with the instability caused which correspond to boundaries where two by the phase transition and twinning,” different regions of the alloy have shifted
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Elongation
n international team of researchers has discovered that the strength of a CoCrFeNi high-entropy alloy increases at the liquid-helium temperature while the sample maintains excellent ductility. These mechanical properties could make this new alloy useful for cryogenic applications, according to the study published recently in Science C
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