TY - THES

T1 - Magnetostrictive behavior of severe plastically deformed, nanocrystalline materials

AU - Paulischin, Alexander Benedikt

N1 - embargoed until null

PY - 2021

Y1 - 2021

N2 - The change of a materials shape, which is caused by the application of an external magnetic field, is referred as magnetostriction. Materials exhibiting either a high or a very low magnetostrictive effect are desirable for certain applications. The focus of this thesis was the investigation of the magnetostrictive behavior of the two material systems Fe-Cu and Fe-Cr in dependence on their chemical composition. While for the Fe-Cu system a low magnetostrictive behavior was expected, a high magnetostriction was assumed in the case of Fe-Cr. Powder mixtures of Fe and Cu with a nominal Cu-content of 5 at. % to 30 at. % as well as mixtures of Fe- and Cr-flakes with a nominal Cr-content between 30 at.% and 70 at.% were consolidated into solid specimens and subsequently deformed using high pressure torsion (HPT). The HPT processing led to an exceptional grain refinement and the formation of a nanocrystalline microstructure. In addition, the formation of supersaturated solid solutions was achieved. The measurements of the magnetostrictive behavior were conducted using a newly built experimental set-up. To examine the accuracy of this set-up, the magnetostrictive behavior of specimens of pure ferromagnetic Co, Ni and Fe with different microstructural states were measured. The results of the magnetostriction measurements were compared with literature values and showed good agreement. In the case of the Fe-Cu system, a decrease of the absolute magnetostrictive constants was determined. Compared to pure Fe, the results of the magnetostriction measurements of the Fe-Cr system showed a significant increase. For the determination of the magnetostrictive behavior, two measurement concepts were used. In the first concept, the specimen was oriented either parallel, perpendicular or in an angle of 45° to the applied magnetic field. The magnetic field was varied between 0 T and 2.25 T during the measurement. In the second concept, a constant field of 2T was applied while the specimen orientation was varied between 0° and 180° in steps of 10°. Besides the determination of the magnetostrictive behavior, a microstructural investigation of all specimens was conducted. Scanning electron microscopy, X-ray diffraction techniques and the determination of the specimen hardness were conducted for the characterization of the microstructure.

AB - The change of a materials shape, which is caused by the application of an external magnetic field, is referred as magnetostriction. Materials exhibiting either a high or a very low magnetostrictive effect are desirable for certain applications. The focus of this thesis was the investigation of the magnetostrictive behavior of the two material systems Fe-Cu and Fe-Cr in dependence on their chemical composition. While for the Fe-Cu system a low magnetostrictive behavior was expected, a high magnetostriction was assumed in the case of Fe-Cr. Powder mixtures of Fe and Cu with a nominal Cu-content of 5 at. % to 30 at. % as well as mixtures of Fe- and Cr-flakes with a nominal Cr-content between 30 at.% and 70 at.% were consolidated into solid specimens and subsequently deformed using high pressure torsion (HPT). The HPT processing led to an exceptional grain refinement and the formation of a nanocrystalline microstructure. In addition, the formation of supersaturated solid solutions was achieved. The measurements of the magnetostrictive behavior were conducted using a newly built experimental set-up. To examine the accuracy of this set-up, the magnetostrictive behavior of specimens of pure ferromagnetic Co, Ni and Fe with different microstructural states were measured. The results of the magnetostriction measurements were compared with literature values and showed good agreement. In the case of the Fe-Cu system, a decrease of the absolute magnetostrictive constants was determined. Compared to pure Fe, the results of the magnetostriction measurements of the Fe-Cr system showed a significant increase. For the determination of the magnetostrictive behavior, two measurement concepts were used. In the first concept, the specimen was oriented either parallel, perpendicular or in an angle of 45° to the applied magnetic field. The magnetic field was varied between 0 T and 2.25 T during the measurement. In the second concept, a constant field of 2T was applied while the specimen orientation was varied between 0° and 180° in steps of 10°. Besides the determination of the magnetostrictive behavior, a microstructural investigation of all specimens was conducted. Scanning electron microscopy, X-ray diffraction techniques and the determination of the specimen hardness were conducted for the characterization of the microstructure.

KW - Magnetostriktion

KW - Severe plastic deformation

KW - Hochdruck-Torsionsverformung

KW - Nanokristalline Werkstoffe

KW - Magnetostriction

KW - Severe plastic deformation

KW - High pressure torsion

KW - Nanocrystalline materials

M3 - Master's Thesis

ER -