Center Of Ribbon Research Articles

Stress dependence of magnetization processes: Reversals and relaxation inFexCo85−xB15amorphous ribbons

The effect of stress on the domain-wall dynamics for magnetization reversal and relaxation in ${\mathrm{Fe}}_{x}{\mathrm{Co}}_{85\ensuremath{-}x}{\mathrm{B}}_{15}$ amorphous ribbons was investigated by inductance voltage measurements in the absence of applied field after pulse saturating the sample. Optical Kerr-effect and three-dimensional neutron depolarization experiments have been exploited. Residual domains at pinning sites are the main sources of the domains of reversed magnetization. Such a reversal is driven by an internal field through the motion of more than two walls, nucleated at residual domains and/or ribbon edges, and propagating towards the ribbon center. The number of active walls depends on the regularity of the domain structure. An external tensile stress decreases the voltage induced by the change of the magnetization of the sample and delays the ``depinning time ${t}_{c}''$ of the reverse domain walls. A modified Landau-Lifshitz equation was used to interpret the stress dependence of the magnetization reversal and relaxation. We found that ${t}_{c}$ is proportional to the coercive field, confirming the validity of the proposed model.

Microstructure of a rapidly-solidified Ni-base eutectic superalloy

A γ- γ’ -MC eutectic nickel-base superalloy was rapidly solidified by melt-spinning. The resulting ribbon microstructure was studied using light microscopy and transmission electron microscopy. In the as-spun ribbon, a chill zone was found at the surface in contact with the wheel, consisting of grains 0.2 to 2.0 μm in diameter with Ta-rich MC carbides, 25 nm in diameter, decorating the grain boundaries. An intragranular cell structure was seen with 10 to 20 nm MC carbides at cell walls. A uniform dispersion of γ’ particles, 20 to 40 nm in diameter, was also present. In the ribbon center, a columnar dendritic structure was observed, with a slight increase in grain size. Carbides were found in this region at grain boundaries, along secondary dendrite arm boundaries, and in extended intercellular regions. A randomly-oriented dendritic structure was present at the ribbon top surface. The chill zone structure and the cellular-to-dendritic transition are described in terms of classical solidification models. Heat treatment of the as-spun ribbon for 2 hours at 1000 °C caused significant coarsening of the γ’ particles, but the grain size and carbide size and distribution were only slightly altered. An additional Re-rich sigma phase precipitated at grain boundaries during the heat treatment. After heat treatment for 2 hours at 1200 °C, some grain growth occurred, the MC and γ’ particles coarsened, and the Re-rich sigma phase was found.