Microstructure Selection of Sm-Co-Al Alloys to Increase Magnetization

Authors

Brian Dick, University of Nebraska-LincolnFollow

Date of this Version

Spring 4-2012

Comments

A THESIS Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master Science, Major: Mechanical Engineering, Under the Supervision of Professor Jeffrey E. Shield. Lincoln, NE: May 2012

Copyright (c) 2012 Brian Jerome Dick

Abstract

An ever increasing demand for higher performing magnets drives the need for new and innovative methods to achieve this goal. Sm-Co rare earth permanent magnets have a unique eutectic microstructure that, through refinement, could become a two-phase magnet which would significantly increase their energy product. The eutectic structure of Sm₈Co₉₂ is comprised of αCo rods embedded within a Sm₂Co₁₇ matrix. If the rods are small enough to encourage exchange coupling and the matrix is smaller than the single domain limit, then an efficient two-phase magnet is created.

Refining the Co rods and matrix size were the goal of this research. The method used to accomplish this goal was through adding Aluminum. Al was added in increments from 1-5 atomic percent. The goal of adding Al was to increase the number of nucleation sites and so increase the number of rods and decreasing their size. The Al would also act as an obstacle that the forming phases would have to push out of the way, slowing their progress. The beneficial by-product of the refinement of the microstructure is an increase in coercivty.

With the addition of Al to the alloy the average αCo rod size was reduced from 300 nm to about 70 nm. This was accomplished at a melt spinning wheel speed of 10 m/s. Therefore at higher wheel speeds this would be reduced further. Also it was shown that the volume fraction of aCo remained relatively constant throughout.

Magnetic analysis was performed and the coercivity of Sm₈Co₉₂ with additional 3% Al was not higher than Sm-Co magnets. This could be due to several factors but not to a creation of different phases. It was shown through x-ray diffraction that no new phases were formed when higher melt spinning wheel speeds were used.

With the addition of Al, the microstructure is considerably refined with the addition of up to 5% Al.

Advisor: Jeffrey E. Shield