Eutectic Solidification Limits and Mechanical Properties of Sm-Co-Fe Alloys

Authors

Wendy Ann Wagner, University of Nebraska - LincolnFollow

Date of this Version

5-2010

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 2010

Copyright (c) 2010 Wendy Ann Wagner

Abstract

Creating a permanent magnet with a higher energy product than existing materials is attractive in order to optimize magnetic performance. The eutectic microstructure of Sm-Co alloys is attractive for magnets since primary rods of the Co-phase can act as a soft magnetic phase in the matrix of the Sm₂Co₁₇ hard magnetic phase, forming two-phase magnets. Fe replacement in Sm-Co alloys provides an opportunity to maintain the desirable eutectic microstructure of Co_1-xFe_x rods embedded in a Sm₂(Co_1-xFe_x)₁₇ matrix while improving the magnetization and lowering the cost. The purpose of this study is to determine the eutectic solidification limit of Sm₈(Co_1-xFe_x)₉₂ alloys and their corresponding mechanical properties.

Samples were made with x from 0 to 1, in increments of 0.05 by arc melting followed by melt spinning at 10 m/s. Microstructural analysis revealed that the eutectic structure can be maintained up to x = 0.30 before the development Co/Fe dendrites. Compositional analysis found that Fe partitions to the Co/Fe rod phase. Magnetic analysis confirmed the increase in magnetization with increasing Fe content.

Mechanical testing revealed the hardness and relative strain at fracture of the alloys. The hardness increases to a maximum at x = 0.30 coinciding with the eutectic limit, and decreasing for x > 0.35 due to the presence of dendrites in the microstructure. Relative strain at fracture was determined from bend testing to reveal the increasing brittleness of the samples for x < 0.35. For x > 0.40, the relative strain at fracture was found to increase, then decrease, due to dendrites and then Sm₂Co₇ phase along grain boundaries, respectively.

Advisor: Jeffrey E. Shield