Development of Hysteresis Free Super-Elastic High Entropy Alloys: From Fundamental Understanding to Alloy Design

Project: Research

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The development of high performance ultra-elastic metals with superb strength, a large elastic strain limit and temperature insensitive elastic modulus (Elinvar effect) is important to a variety of industrial applications. Plastic deformation through dislocations, twinning and/or grain boundary sliding commonly limit the elastic strain of bulk crystalline metals to ~0.2% at room temperature. Because bulk amorphous alloys lack crystal defects, they may achieve ~2% elastic strain at room temperature. However, the high cooling rate required to form most amorphous metallic alloys provides severe limits on the size that can be produced, thereby seriously hindering their industrial application. On the other hand, shape memory alloys and Gum metals may achieve elastic strain limit up to several percent. However, this high strain limit is associated with reversible martensitic transformations which are accompanied by large mechanical hysteresis and energy dissipation. Interestingly, we recently discovered a high entropy alloy, which possessed a severely distorted lattice and exhibited hysteresis free super-elasticity with an unusual Elinvar effect. These results are intriguing and promising, which indicates that the notion of high entropy alloy is also applicable to the design of super-elastic materials. However, a few fundamental issues remain yet to be addressed. For example, one may ask whether there is a general rule to guide the design of super-elastic high entropy alloys and, if there is, how one can optimize the compositions of the high entropy alloys to enhance their super-elastic properties. In this project, we aim to address these fundamental issues by forming a research team that has already developed its strengths via the research of decades in alloy design and development, theoretical modeling, nano- and micro-mechanical testing, in-situ high energy X-ray diffraction experiments coupled with mechanical testing and atomistic simulations. Once this project was funded, we would achieve the following goals through the combined efforts from experiments, theoretical modeling and atomistic simulations, which include (1) to understand the fundamental deformation mechanisms that give rise to the super-elasticity of the designed high entropy alloys, (2) to understand the composition-processing-property correlations for this special class of super-elastic high entropy alloys, and (3) to provide a protocol that can guide the design and development of super-elastic high entropy alloys. In the long run, because of the unusual super-elastic behavior of high entropy alloys, the outcome of the research may lead to a great expansion of their applications in actuators, medical devices, and high precision instruments. 


Project number9043132
Grant typeGRF
Effective start/end date1/01/22 → …