Novel Functional Behaviors: Beyond Shape Memory Effect & Superelasticity: Session 3
Program Organizers: Ibrahim Karaman, Texas A&M University
Wednesday 10:20 AM
July 12, 2017
Location: Hyatt Regency Chicago
Session Chair: James Monroe, Thermal Expansion Solutions/Texas A&M
Calorimetric Measurements of the Elastocaloric Entropy Change in Shape Memory Alloys: Lluis Manosa1; Enric Stern-Taulats1; Adria Gracia-Condal1; Antoni Planes1; 1University of Barcelona
The elastocaloric effect refers to the reversible thermal response of a solid subjected to uniaxial stress. Among the materials exhibiting elastocaloric effects, shape memory alloys are the best candidates for solid-state cooling devices based on this effect . Typically, the elastocaloric effect is quantified by the temperature or entropy changes that take place when the stress is applied either adiabatically or isothermally. While direct measurements of adiabatic temperature changes are readily feasible and have been reported for a variety of alloys, determination of entropy changes has only been possible by means of indirect methods. We have developed a differential scanning calorimeter which operates under the application of uniaxial stress which enables a direct determination of entropy changes. We have used this purpose-built set-up to obtain the elastocaloric isothermal entropy changes in shape memory alloys.1.- L. Maņosa and A. Planes, Adv. Mater. In press.
Elastocaloric Cooling Capacity of Shape Memory Alloys – Role of Deformation Temperatures and Mechanical Cycling: Yan Wu1; Huseyin Sehitoglu1; Elif Ertekin1; 1University of Illinois at Urbana Champaign
The elastocaloric cooling (EC) capability of shape memory alloys (SMAs), originating from the entropy change upon endothermic reverse phase transformation, has the potential to reduce the dependence on conventional scheme for refrigeration. In this study, the EC properties were explored for SMAs starting with CuZnAl, NiTi, NiTiCu that are well known and then Ni2FeGa and NiTiHf13.3 that are relatively new. Their correlations with entropy changes, functional fatigue resistance, superelastic temperature windows were also investigated. Remarkably, we found a temperature decrease of 14.2˚C for CuZnAl, 18.2˚C for NiTi, 15.2˚C for NiTiCu, 13.5˚C for Ni2FeGa, and 6.95˚C for NiTiHf13.3 upon adiabatic stress relieving, which is also proportional to the entropy difference between phases except for NiTiHf where strain localization engendered early failure. NiTi and Ni2FeGa showed better stability in superelastic response, hence EC effect. The latter possesses an operational temperature window near 200˚C, which is the highest among the chosen SMAs.
Deformation Behavior of Nb Nanowires in TiNiCu Shape Memory Alloy Matrix: Daqiang Jiang1; Yinong Liu2; Yang Ren3; Lishan Cui1; 1China University of Petroleum, Beijing; 2The University of Western Australia; 3Argonne National Laboratory
An in-situ nanowire Nb/TiNiCu composite is fabricated based on the concept of strain under-matching between a phase transforming matrix and high strength nanomaterials. The deformation behavior of the Nb nanowire was investigated by means of in-situ synchrotron X-ray diffraction when the TiNiCu matrix underwent different deformation modes. The maximum lattice strain of the Nb nanowires was about 5% when the matrix deformed via martensitic transformation or 1% when deforming plastically by dislocation slip. The Nb nanowires showed a lattice strain of 3.5% when the matrix deformed in the mixed mode of plastic deformation and martensitic transformation, which means that the occurrence of plastic deformation does not impede load transfer from the matrix to the nanowires.
11:50 AM Break