Scale-Up of Magnetocaloric NiCoMnIn Heuslers by Powder Metallurgy for Room Temperature Magnetic Refrigeration

Cecilia Bennati,Massimo Solzi,Francesco Cugini,Nicola Sarzi Amadè,Simone Fabbrici,Franca Albertini,Valerio Mussi,Francesco Puglielli

doi:10.3389/fenrg.2019.00150

Abstract

We present a new approach for a large-scale production of the rare-earth free NiCoMnIn Heusler alloy for room temperature magnetic refrigeration applications. This class of compounds has recently attracted attention thanks to the large reversible isothermal entropy change (ΔSiso) and adiabatic temperature change (ΔTad) associated to a first order magneto structural phase transition. A large-scale production method, however, has not yet been proposed. For giant magnetocaloric materials and especially for Heusler compounds, the synthesis has a predominant role in tailoring the physical-chemical properties, due to the high sensitivity of the first order transition characteristics on chemical composition and microstructure. Up to 250 grams of the nominal composition Ni45.7 Co4.2Mn36.6In13.3 alloy were prepared in a unique sample starting from industrial grade powdered elements. The phase transition temperatures and magnetocaloric properties were investigated by magnetic and direct adiabatic temperature measurements and were found to be homogeneous in the whole sample. The mechanical stability of the produced alloy and its workability were investigated. A low-temperature thermal treatment was identified and showed promising results by reducing hysteresis and transition width.

Highlights

The mass-market introduction of affordable refrigeration technology has shaped the development of society and improved everyday life over the last century
They are magnetic materials with magnetic phase transitions around room temperature; when exposed to a magnetic field change in a temperature range close to the transition temperature, they respond by heating and cooling by a few degrees
The temperature change at the magnetocaloric transition grows with the intensity of the magnetic field change; yet, to build energetically efficient devices for room temperature applications, the magnetic field is limited in magnitudes to the values achievable by permanent magnets, typically ranging around 1–1.5 T

Summary

INTRODUCTION

The mass-market introduction of affordable refrigeration technology has shaped the development of society and improved everyday life over the last century. Spark plasma sintering is a technique recently used to obtain bulky Heusler compounds, which consists in heating the sample with pulsed dc current maintaining the powder under pressure This technique can produce textured materials with good mechanical properties starting from powdered alloy (Ito et al, 2009) or different shapes. Microwaves-assisted sintering was recently proposed to prepare Heusler compounds starting form elemental powders (Trombi et al, 2020), but the use of this technique for the preparation of off-stoichiometric martensitic compositions has not yet been optimized Both brittleness, and small sample mass can be considered as major obstacles for further development of the materials, in terms of structural reliability and workability. Suitable thermal treatments to reduce the hysteretic behavior are proposed

MATERIALS AND METHODS

A50 B50 B250

RESULTS AND DISCUSSION

DATA AVAILABILITY STATEMENT