Sintered Fe-Co-Si alloy with excellent magnetic and mechanical properties by coherent precipitation of submicrometer-sized carbide particles

A novel sintered Fe-Co-Si alloy with coherent precipitation of submicrometer-sized carbide particles of Ta ₃Co ₃ C containing iron and silicon is fabricated by a unique synthesis route through evaporation of an Fe-Co-Si matrix and diffusion of tantalum and carbon by sintering in high vacuum at a high temperature. The carbide particles precipitate homogeneously on the surface, in the grain boundaries, and inside the grains of the matrix. In particular, many particles precipitate homogeneously along the grain boundaries, which can contribute to improving mechanical strength by preventing intergranular fracture in spite of very small volume fraction (0.8 vol%) of the precipitated particles. The strength improvement can be explained by the particle shearing mechanism by the coherent precipitation of carbide particles. The orientation relationships between the carbide particles and Fe-Co-Si matrix are ( 4 ̅ 04 ) _particle// ( 2 ̅ 02 ) _matrix, ( 0 4 ̅ 0 ) _particle// ( 0 2 ̅ 0 ) _matrix, and ( 4 ̅ 00 ) _particle// ( 2 ̅ 00 ) _matrix with a very small lattice mismatch (<2%). As a result of the coherent precipitation, the magnetic properties such as low magnetic loss and high magnetic permeability does not deteriorate, and are rather improved mainly by a promoted densification with very few pores and grain growth by sintering in high vacuum at a high temperature. It is also demonstrated that the fabricated alloy has excellent magnetic and mechanical properties compared to conventional sintered or compressed powder materials.