Regensburg 2016 – scientific programme

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MM: Fachverband Metall- und Materialphysik

MM 10: SYCE: Caloric effects in ferroic materials

MM 10.5: Invited Talk

Monday, March 7, 2016, 17:15–17:45, H1

TiNiCu-based thin films for elastocaloric cooling — •Eckhard Quandt and Christoph Chluba — Chair of Inorganic Functional Materials, Institute for Materials Science, Faculty of Engineering, University of Kiel, Germany

The elastocaloric effect is a promising alternative for the replacement of conventional vapor compression cooling which suffers from a high environmental impact and limited efficiency improvement possibilities. Instead of a vapor-liquid transition in a conventional cooling, the elastocaloric effect is based on a stress induced structural phase transition usually from a high symmetry to a low symmetry phase. At adiabatic conditions this results in a temperature change of the material. For a continuous use of this effect in a cooling cycle, several requirements have to be fulfilled. Transformation temperatures, effect size and efficiency have to be suitable, but most importantly a high functional and structural fatigue resistance is necessary.

Highly fatigue resistant Ti-rich TiNiCu compositions prepared by thin film technology have been found that can withstand 10 million transformation cycles without functional degradation [1]. Within this talk the reasons for the fatigue resistance will be discussed. In situ synchrotron and TEM investigations have been conducted to investigate the underlying microstructural mechanisms that ensure the reversible transformation. Cobalt and iron addition is used to adjust the transformation temperature to a suitable range to enable the use of this compositions at room temperature. The compositional influence on the elastocaloric parameters is investigated by temperature dependent tensile tests, infrared (IR) thermography and differential scanning calorimetry. Due to the small hysteresis of TiNiCu-based compositions an improved elastocaloric cooling efficiency is found in comparison to binary NiTi thin films. Considering also the high fatigue resistance, this class of materials is promising for future elastocaloric cooling applications.

[1] Chluba, C.; Ge, W.; Lima de Miranda, R.; Strobel, J.; Kienle, L.; Quandt, E.; Wuttig, M.: Ultralow-fatigue shape memory alloy films, Science 348 (2015), 1004-1007.