NÉEL INSTITUTE Grenoble
Topic for Master 2 internship – Academic year 2020-2021
Elastocaloric microwires General Scope:
Due to the priorities of energy savings and environmental protection, new refrigeration techniques based on the elastocaloric effect of solid state transformation induced by uniaxial stress have been proposed as a potential alternative to conventional cooling by vapor compression [1]. Most investigations in elastocaloric materials are focused on the shape memory alloys (SMAs) and ferromagnetic shape memory alloys (FSMAs) which exhibit ferroelastic and/or magnetostructural phase transition. Large elastocaloric effect in these SMAs mainly originates from the large entropy change during the transition.
In Ni-Mn-based FSMAs, large adiabatic temperature change can be achieved under relatively small stress and magnetic field, making it a multifunctional material of choice. However, the poor mechanical properties (low ductility and intergranular fracture) of Ni-Mn-based alloys restrict their use for applications where large deformation is required. Mechanical resistance, damage and fatigue endurance are thus the key elements for the application of these materials since anelastic hysteresis of deformations up to about 10% are expected for an optimal energy cycle.
A promising strategy to circumvent the intrinsic brittle nature of these intermetallics is to drastically reduce grain boundaries and increase free surface strain relaxation: this can be achieved by processing long wires (m) made of extended (fraction of mm) single crystalline wires using Taylor wire process (100’s µm fibre diameter) [2]. Moreover, the resulting wire can be directly integrated in test devices.
Left : micrograph of two-phase Ni-Mn-Co-In melt spun ribbons.
Right : Melt spinning technique avalaible at Neel Institute
Research topic and facilities available:
Following our past experience in melt spinning processing and composition optimizing, we propose to setup a Taylor wire process [2]. The student will participate in the assembly of the Taylor-Ulitovsky induction technique as well as in the first physical properties measurements on the microwires: cyclic loading with InfraRed Thermometric CCD, microstructural and magnetic characterisations of the transformation.
[1]S. Kirsch et al. Energy Technol. (2018), 6, 1567 – 1587 [2] Z.Chen et al. (2019). IUCrJ, 6, 843–853.
Possible collaboration and networking:
Close collaboration with partners from SIMaP (Science et Ingénierie des Matériaux et Procédés) Possible extension as a PhD: Yes
Required skills:
-Knowledge in material science and/or metallurgy is welcome
-Interest in experimental physics with a desire to broaden one's knowledge in basic science.
Starting date: any time Contact:
Name:Porcar Laureline laureline.porcar@neel.cnrs.fr 04 76 88 90 33 Name:Miraglia Salvatore salvatore.miragia@neel.cnrs.fr 04 76 88 79 42
