Analysis of Two Heat-Treated Ni-Mn Melt-Spun Heusler Alloys for Magnetocaloric Applications

Date of Award

6-2024

Degree Name

Master of Science

Department

Mechanical and Aerospace Engineering

First Advisor

Pnina Ari-Gur, D.Sc.

Second Advisor

Matthew Cavalli, Ph.D.

Third Advisor

Jinseok Kim, Ph.D.

Fourth Advisor

Yang Ren, Ph.D.

Keywords

Curie temperature, giant magnetocaloric effect, Heusler alloys, magnetic refrigeration, magnetocaloric effect, x-ray diffraction

Access Setting

Masters Thesis-Abstract Only

Restricted to Campus until

6-1-2034

Abstract

Heusler alloys based on nickel-manganese are recognized for their magnetic shape memory and giant magnetocaloric effect (GMCE). The extent of these effects is influenced by the alloy’s phases, transitions between crystallographic and magnetic phases among other factors. These properties are influenced by the processing parameters. In this thesis, two Ni-Mn-Ga-Si Heusler alloys of the same composition (Ni55.4Mn18.9Ga24Si1.7), but different processing routes were studied. They were fabricated using a melt-spinning process under helium atmosphere, with two different sets of parameters. Then, the samples were heat-treated at 900°C for 18 and 72 hours, and 850°C for 48 hours. The effect of heat treatment on the samples with varying melt-spinning process parameters, on their crystallographic structure, transformation temperatures, were studied using X-ray diffraction and magnetization measurements, and magnetic entropy change was calculated to assess the magnetocaloric behavior. Rietveld refinement of the X-ray diffraction data revealed that at room temperature the samples have a mix of cubic L21 austenite (Space group Fm3̅m) and monoclinic martensite (Space group I2/m). The values of lattice parameters and modulation vectors varied for samples with different heat treatments and fabrication parameters. Crystallography data show that the heat treatments resulted in an increase of martensite phase transformation temperature, and magnetization testing shows that the sample melt-spun with lower cooling rate and heat-treated at 900°C for 18 hours, had the largest entropy change (26 J/kg-K) at room temperature.

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