Thermoelastic Properties and Elastocaloric Effect in Rapidly Quenched Ribbons of Ti2NiCu Alloy in the Amorphous and Crystalline State

Abstract

The thermoelastic properties and the elastocaloric effect (ECE) were studied in rapidly quenched ribbons of the Ti2NiCu alloy samples in amorphous and crystalline states under periodic mechanical tension with a frequency of up to 50 Hz. In the amorphous samples, elastic behavior is observed, described by Hooke’s law, with a high coefficient of thermal expansion α = 1.7 × 10−4 K−1. Polycrystalline ribbons of the Ti2NiCu alloy have the classical shape memory effect (SME), the temperatures of the forward and reverse thermoelastic martensitic transitions being Ms = 345 K, Mf = 325 K, As = 332 K, and Af = 347 K and the coefficient of the dependence of the transition temperature on mechanical stress being β = 0.12 K/MPa. The experimentally measured value of the adiabatic temperature change under the action of mechanical stress (ECE) in the amorphous state of the alloy at room temperature (Tr = 300 K) was ΔT = −2 K, with a relative elongation of ε = 1.5% and a mechanical stress of σ = 243 MPa. For crystalline samples of Ti2NiCu alloy ribbons, the ECE is maximum near the completion temperature of the reverse thermoelastic martensitic transformation Af, and its value was 21 K and 7 K under cyclic mechanical loads of 300 and 100 MPa, respectively. It is shown that the ECE value does not depend on the frequency of external action in the range from 0 to 50 Hz. The specific power of the rapidly quenched ribbon was evaluated as a converter of thermal energy at an external mechanical stress of 100 MPa; its value was 175 W/g at a frequency of 50 Hz. The thermodynamic model based on the Landau theory of phase transitions well explains the properties of both amorphous ribbons (reverse ECE) and alloy ribbons with EPF (direct ECE).

Thermomechanics and statistical mechanics of an adiabatically isolated body

“…The disparity in the considered approximation is equal to the energy of oscillator oscillations with an amplitude equal to the average value of thermal expansion q E . The disparity in (23) confirms the rightfulness of the first law of thermodynamics (5) in the thermomechanics of an adiabatically isolated body. Indeed, the work of an external force, let us say, under tension (F > 0) of an anharmonic oscillator increases its internal energy…”

“…Thus, it is of current interest to find a proper substitute of distribution (2) for an adiabatically isolated body. While noting the long-time history of the thermomechanics of an adiabatically isolated body [4], we would like to point out the non-decreasing interest in it and the new experimental results obtained recently [5,6]. The thermoelastic effect can also be a ground for advanced technologies of solid-state cooling in cooling units [7].…”

Термомеханика И Статистическая Механика Адиабатически Изолированного Тела

“…Таким образом, представляется актуальным поиск надлежащей замены распределения (2) для адиабатически изолированного тела. Отмечая давнюю историю термомеханики адиабатически изолированного тела [4], обратим внимание на неубывающий интерес к ней и новые экспериментальные результаты, полученные в последнее время [5,6]. Термоупругий эффект также может быть основой перспективных технологий твердотельного охлаждения в холодильных установках [7].…”