Perrin_cmu_0041E_10444.pdf (12.37 MB)
Characterization of High Entropy Alloys for Magnetocaloric Applications
Magnetocaloric refrigeration offers more energy efficiency than conventional gas compression refrigeration by up to 20%, and has the additional advantage of being environmentally friendly as it does not require the use of ozone depleting gases. The primary challenge in developing magnetocaloric refrigerators for commercial use is in developing suitable materials with large room temperature magnetocaloric effects. Critical rare earths metals (REs)
and compounds have been studied because of their large magnetocaloric response and working temperatures close to room temperature. However, the scarcity, high price and corrosion of REs limit their commercial use, leading to the investigation of more sustainable transition metal-based alloys. I explore the possibility of developing high performance high entropy alloys for magnetocaloric applications, and my approach to this problem follows on the materials paradigm: 1) synthesis, 2) structure, 3) properties, and 4) performance. Synthesis requires determining the best conditions for producing the alloys in the proper form, and this is important both for the initial production of my bulk alloys through rapid solidi fication.
and compounds have been studied because of their large magnetocaloric response and working temperatures close to room temperature. However, the scarcity, high price and corrosion of REs limit their commercial use, leading to the investigation of more sustainable transition metal-based alloys. I explore the possibility of developing high performance high entropy alloys for magnetocaloric applications, and my approach to this problem follows on the materials paradigm: 1) synthesis, 2) structure, 3) properties, and 4) performance. Synthesis requires determining the best conditions for producing the alloys in the proper form, and this is important both for the initial production of my bulk alloys through rapid solidi fication.
The structure of high entropy alloys is necessarily a random distribution of atoms, and an investigation of the homogeneity of this condition through electron dispersive spectroscopy is vital for determining the stability of the alloy. I investigate the magnetic and thermal properties of these alloys both to assess their fitness for speci fic magnetocaloric applications, and also to better understand the relationship between their structure and properties.
Mossbauer spectroscopy experiments for magnetic data was performed in collaboration with Monica Sorescu at Duquesne University. I extend this exploration through high pressure and low temperature studies to to develop a fundamental understanding of the magnetic
interactions in these alloys, including a novel approach to visualizing exchange using the Bethe-Slater curve that explore the importance of considerations of the d-orbital extent on changes in exchange. High pressure magnetic measurements were performed in collaboration
with Scott McCall at Lawrence Livermore National Lab. I began this study with a focus on performance in commercial refrigeration applications, but the complex magnetic
and structural attributes of these materials require rigorous study for a better understanding of magnetic high entropy alloys, and this work contributes to this relatively unexplored
but growing field.
Mossbauer spectroscopy experiments for magnetic data was performed in collaboration with Monica Sorescu at Duquesne University. I extend this exploration through high pressure and low temperature studies to to develop a fundamental understanding of the magnetic
interactions in these alloys, including a novel approach to visualizing exchange using the Bethe-Slater curve that explore the importance of considerations of the d-orbital extent on changes in exchange. High pressure magnetic measurements were performed in collaboration
with Scott McCall at Lawrence Livermore National Lab. I began this study with a focus on performance in commercial refrigeration applications, but the complex magnetic
and structural attributes of these materials require rigorous study for a better understanding of magnetic high entropy alloys, and this work contributes to this relatively unexplored
but growing field.
History
Date
2019-09-01Degree Type
- Dissertation
Department
- Materials Science and Engineering
Degree Name
- Doctor of Philosophy (PhD)