Abstract: Giant magnetostrictive Tb-Dy-Fe alloys in the form of thin sheets or fine wires are required in precision micro-actuators and sensors. However, Tb-Dy-Fe alloys are too brittle to undergo machining and application. In the present work, we investigated the effects of diffusing the Dy₃₆Cu₆₄ alloy into the grain boundary phases of the <110>-oriented Tb_0.30Dy_0.70Fe_1.95 alloy to modify the microstructural, mechanical, and magnetostrictive properties. Microstructural analysis revealed the introduction of Cu into the grain boundary phase through the diffusion treatment, transforming the brittle rare earth (RE)-rich grain boundary phase into a ductile (Tb,Dy)Cu grain boundary phase and changing the non-coherent interface to a semi-coherent one between the (Tb,Dy)Fe₂ matrix phase and the grain boundary phase without affecting the microstructure of the matrix phase. The as-diffused Tb_0.30Dy_0.70Fe_1.95 alloy exhibited significantly improved mechanical properties, with its tensile strength, bending strength, and fracture toughness at room temperature increasing to 44.6 MPa, 106.8 MPa, and 2.36 MPa m^1/2, respectively, which were 2, 2.4, and 1.5 times those of the non-diffused sample. This was attributed to the formation of ductile (Tb,Dy)Cu grain boundary phase and semi-coherent interfaces. Furthermore, the magnetostrictive strain of the as-diffused Tb_0.30Dy_0.70Fe_1.95 alloy reached 1448 ppm, suggesting that there was minimal impact on the magnetostrictive properties, due to the small influence of grain boundary diffusion on the matrix phase.

Key words: Tb-Dy-Fe alloys, Magnetostriction, Mechanical performance, Grain boundary diffusion, Semi-coherent interface