Title
Superelasticity and micaceous plasticity of the novel intermetallic compound CaFe2As2 at small length scales
Conference Dates
October 1-6, 2017
Abstract
Shape memory materials have the capability to recover their original shape after plastic deformation when they are subjected to certain stimulus. Shape recovery usually occurs through a reversible phase transformation and, in general, has limited performance with 10% maximum strain. Here, we report the first discovery of superelastic and shape memory behavior with 12% recoverable strain in a novel intermetallic compound CaFe2As2, and discuss its unique elastic and plastic deformation behaviors in terms of a collapsed tetragonal phase transition and anisotropic stacking fault energy, respectively, with solution growth of the single crystal, in-situ micropillar compression, and density functional theory (DFT) calculations. Single crystals of CaFe2As2 were grown out from Sn flux and contains mirror-like clean facets of {0 0 1} and {3 0 1} type planes. We fabricated micropillars on these two planes, and conducted in-situ micropillar compression testing in a scanning electron microscope. The [0 0 1] CaFe2As2 micropillar exhibits unprecedented superelasticity: over 12% recoverable strain without negligible residual fatigue damage under cyclic deformation. Due to its high yield strength (2.6 GPa) and large elastic strain, it is possible to absorb and release a large amount of elastic strain energy. Also, it has potential to show one-dimensional shape memory effects at low temperatures (near 0 K) by the reversible phase transformation between the tetragonal/orthorhombic to the collapsed tetragonal phase. Furthermore, this material exhibits strong anisotropy in plasticity. For the [3 0 -1] CaFe2As2 micropillar, we found easy, preferential slip in the [1 0 0]/(0 0 1) slip system which we termed micaceous plasticity. Superelasticity and micaceous plasticity was quantitatively investigated through measuring the uni-axial stress-strain data and comparing our results to DFT calculations. DFT calculations revealed that making and breaking As-As bonds is responsible for superelasticity. A composite model was developed to monitor the volume fraction evolution of the two different phases under compression testing and successfully reproduced the experimental stress-strain curve we measured. In addition, DFT results showed a significantly low energy barrier for the [1 0 0]/(0 0 1) slip between Ca and As layers, which agrees with our experimental observation. We believe that our efforts in both experimental and computational analysis allow us to gain a fundamental understanding of the unique deformation behavior of CaFe2As2
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Recommended Citation
John T. Sypek, Seok-Woo Lee, Christopher R. Weinberger, Paul C. Canfield, and Sergey L. Bud’ko, "Superelasticity and micaceous plasticity of the novel intermetallic compound CaFe2As2 at small length scales" in "Nanomechanical Testing in Materials Research and Development VI", Karsten Durst, Technical University of Darmstadt, Germany Eds, ECI Symposium Series, (2017). https://dc.engconfintl.org/nanomechtest_vi/46