Mechanical properties and latent heats of low hysteresis NiTi shape memory alloy components for elastocaloric cooling applications

Since the invention of the refrigerator the fundamental cooling technology of cooling systems has been unchanged. In the last years elastocaloric cooling based on NiTi SMA has been intensively studied by different research groups so that nowadays these materials seem to be a sophisticated approach next generation cooling solutions. The reason for that is the high latent heat of the martensitic phase transformation in NiTi shape memory alloys which results in very high COP-values if these materials are successfully applied as elastocaloric solid-state cooling elements. The current work presents data of mechanical and thermal properties of high purity NiTi SMA wires conducted to cyclic testing conditions. Tensile experiments were carried out to determine the mechanical properties during the cyclic stress induced phase transformation such as evaluate plateau stresses, irreversible strains and mechanical hysteresis at constant testing temperature. The results show very low mechanical hysteresis which corresponds to a high functional stability of the material. Furthermore the degree of efficiency of NiTi based cooling systems is not only a matter of mechanical but also thermal properties which unfortunately cannot always be measured appropriately by DSC analysis. This is also the case for the materials presented in this contribution, so that their latent heat is evaluated by a novel measurement procedure which is able to compensate the disadvantages of DSC technique. The results underline the usability of these improved SMA materials for elastocaloric applications and provide a realistic perspective to establish NiTi SMA as a technology for thermal management systems in general.