Development of a self-consistent thermodynamically optimized database along with phase transition experiments in Ni-Mn-Ga system for magnetocaloric applications

TL;DR

This paper develops a thermodynamic database for Ni-Mn-Ga Heusler alloys using CALPHAD, combined with phase transition experiments, to optimize materials for eco-friendly magnetocaloric refrigeration.

Contribution

It presents a self-consistent thermodynamic database for Ni-Mn-Ga based on CALPHAD and experimental validation, addressing previous discrepancies in the system.

Findings

Thermodynamic properties of Mn-Ga and Ni-Ga binaries were optimized.

A thermodynamic database for Ni-Mn-Ga was developed and validated.

Phase regions suitable for magnetocaloric applications were identified.

Abstract

Magnetocaloric materials have received significant attention of research community as they can minimize the use of harmful gases (CFCs, HFCs) and render eco-friendly refrigeration. Heusler alloys (Ni2MnGa) are known for their magnetocaloric effects, which make them useful as energy efficient and eco-friendly refrigerating materials. Magnetocaloric properties significantly depend on the composition of these alloys. Ni-Mn-Ga is one of the interesting Heusler systems, which exhibits magnetocaloric properties. In the present study, we performed the thermodynamic optimization of two sub binaries of the Ni-Mn-Ga system: Mn-Ga and Ni-Ga, using CALPHAD approach. A Modified Quasichemical Model (MQM) was used to describe the thermodynamic properties of the liquid solutions in both the binaries. Both the binaries were combined with Mn-Ni to develop a self-consistent thermodynamic database for Ni-Mn-Ga. In order to resolve the existing experimental discrepancies in the Mn-Ga and Ni-Ga system, few alloy compositions were prepared and analyzed using differential thermal analysis. Finally, the developed thermodynamic database was used to calculate the ternary isothermal section of the Ni-Mn-Ga (Heusler alloy) system at 1073 K with a proposed phase region for magnetocaloric applications.