Structural, magnetic and microstructural studies of composition-modified Sm-Co ribbons

Authors

Xiujuan Jiang, University of Nebraska-LincolnFollow

Date of this Version

5-2014

Comments

A DISSERTATION Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Doctor of Philosophy, Major: Engineering (Materials Engineering), Under the Supervision of Professor Jeffrey E. Shield. Lincoln, Nebraska: May, 2014

Copyright (c) 2014 Xiujuan Jiang

Abstract

There is an increasing interest in developing desirable microstructures in hard magnetic materials. Sm-Co-based magnets, bearing superior intrinsic magnetic properties, are good candidates for further development. Two Sm-Co-based alloys, (Sm₁₂Co₈₈)_100-x-yCr_yC_x (taking SmCo₇ phase) and SmCo_4-xFe_xB (a derivative of SmCo₅ phase), were produced using melt-spinning technique. The magnetic properties are correlated to the structural and microstructural properties.

Within the SmCo₇ stoichiometry, cumulative effects of Cr and C additions on the structural and magnetic properties have been investigated. Experimental results have shown that these additions along with nanostructuring stabilized the 1:7 phase, refined the grain size and triggered promising modifications in the magnetic properties. Annealing was also performed to further optimize the magnetic properties. For both the as-spun and as-annealed samples, structural, magnetic and microstructural results will be shown and correlated among each other to explain observed behavior. Specifically, the maximum coercivity obtained was 10.1 kOe at 3 at.% C and 4.5 at.% Cr conditions annealed at 600 °C.

Within the SmCo₄B stoichiometry, efforts were made to explore the possibility of a potential exchange coupled nanocomposite based on Fe additions into 1:4:1 structure. As-spun Fe-containing samples were amorphous. For the crystallized samples, different Fe content brought in significant changes in the phase evolution and magnetic behavior. A secondary phase Sm₂(Co,Fe)₁₇B_y was also observed at higher Fe content. We find that Fe additions increase the coercivity for up to x = 1 (SmCo_4-xFe_xB) and increase magnetization for up to x = 2, the latter of which is highly desired for permanent magnet applications. In order to further optimize the magnetic properties of the composition with both high coercivity and magnetization (SmCo₂Fe₂B), secondary annealing at a lower temperature was performed. Pronounced enhancement in both magnetization and coercivity was observed. Microstructural analysis and microchemistry information obtained from TEM/HRTEM and 3D atom probe revealed the possible reasons behind the improvement.

Adviser: Jeffrey E. Shield