Elastocaloric properties of the optimized Ni-Ti alloy


Durak Yüzüak G., Yüzüak E.

5th INTERNATIONAL ANATOLIAN ENERGY SYMPOSIUM, Trabzon, Turkey, 24 - 26 March 2021, pp.48

  • Publication Type: Conference Paper / Summary Text
  • City: Trabzon
  • Country: Turkey
  • Page Numbers: pp.48

Abstract

Cooling /heating technologies have great importance for sustaining and maintaining the comfort of life in modern

societies such as long-term food storage, home and office air conditioning [1]. The problems of global warming

caused by damages to nature of materials used in existing cooling technologies operating in traditional vapor

compression cycle increase the concerns about environmental issues in society. For this reason, worldwide vapor

compression technologies are being abandoned gradually according to developing technology. Systems based on

solid state-caloric effects which are an alternative to existing cooling technology have been attracting attention

with the studies carried out in recent years [2]. In solid-state cooling technologies of magnetocaloric and

electrocaloric requires a high driving external field to achieve very uniform thermal entropy changes. Among

these, elastocaloric can be defined as different from others because having a stress-induced phase transitions. This

mechanical stress field can be easily produced with the current technological possibilities and the relatively cheaper

than related to the initial investment, maintenance and repair costs [3].

In this study, direct temperature changes under stress based on the elastocaloric effect near room temperature of

systems obtained in NiTi alloy were investigated. NiTi alloy was obtained through an arc melting furnace under

vacuum with Ni and Ti elements and then heat-treated. Surface and composition measurements were performed

by electron microscopy and the crystal structures were determined before and after heat treatment by X-ray powder

diffraction technique. Alloy transforms from B2 (Pm3m) ordered cubic structure to a monoclinic B19 P2 (P2/m)

martensitic phase. The phase transition temperatures of the materials were measured by the temperature-dependent

resistivity measurement system. A home-made system that sensed the temperature change of the material under

mechanical stress fields from 300 to 400 K was used to examine the elastocaloric temperature changes of the

materials in different stress values.

Keywords: Elastocaloric, Ni-Ti, Phase transition