THE INFLUENCE OF REFRACTORY ELEMENT ADDITIONS ON THE MAGNETIC-PROPERTIES AND ON THE CRYSTALLIZATION BEHAVIOR OF NANOCRYSTALLINE SOFT-MAGNETIC FE-B-SI-CU ALLOYS

The influence of additions of the refractory elements R = V, Mo, W, Ta, Nb on the magnetic properties and on the microstructure of annealed amorphous Fe-(76.5-x)Si(15.5)B(7)Cu(1)R(x) (x = 1-3) was investigated. Crystallization temperature, grain size, and coercivity of the formed Fe3Si phase are controlled by the amount and the type of refractory element. The onset of crystallization is shifted to higher annealing temperatures while the particle size is lowered by the same order. This effect is correlated with the atomic diameter in the following order V (0.264 nm); Mo (0.272 nm); W (0.274 nm); Ta (0.286 nm); Nb (0.286 nm). The differences in atomic diameter between iron and the refractory elements stabilize the amorphous phase and slow the kinetics down by limiting diffusion in the alloys. The behaviour of the coercivity is correlated to the grain size but can not be described generally by a simple power law. The saturation magnetostriction fits well with a linear dependence on the volume fraction of the formed Fe3Si phase but not with a linear mixture model.