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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 Co1-xFex rods embedded in a Sm2(Co1-xFex)17 matrix while improving the magnetization and lowering the cost. The purpose of this study is to determine the eutectic solidification limit of Sm8(Co1-xFex)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