Papers by Author: Fernando José Gomes Landgraf

Abstract: In this study, a steel for semiprocessed electrical purposes of non-oriented grain with approximately 0.05% carbon content and 0.02% silicon content was evaluated. Lamellas with kind of thicknesses 0.58 mm, 0,66 mm and 0.87 mm were processed on an industrial scale with a strain rate in the hardening lamination between 3 and 5%. The magnetic properties were evaluated after the wet heat treatment. The loss separation method was applied, estimating the hysteretic plot with hysteresis measure in the quasi static condition and the parasitic losses calculated according to Thomson's Equation. By increasing grain size, permeability increases and coercivity decreases. However, in the case of losses, there is an optimum grain size. After the procedure of separation of losses, it was observed that increase of thickness results in increase of the anomalous parcel of magnetic losses.

Abstract: Microstructural and magnetic properties of thermal aged NdFeB-based powders, recycled by means of the HDDR process, are studied. The time aging causes a reduction of the remanent magnetic moment per unit mass and intrinsic coercivity of the magnetic powders. On the other hand, it has been verified an increase of the magnetic polarization at µ₀H = 2 T after aging during 16 hours. The oxygen concentration is superior in the grain boundary region (Nd-rich) compared to that verified in the hard magnetic phase.

Abstract: The ideal sheet texture for electric motor steels, the λ fiber, with 〈001〉 normal to the rolling plane, that can be produced by directional solidification, is largely lost by the required heavy rolling reduction and recrystallization needed to produce thin motor laminations. However by two successive light rolling reductions, followed in each case by recrystallization, the desired texture was largely recovered. Taylor and finite element modeling supported the hypothesis for this successful processing: the low Taylor factor of the λ fiber grains. Although starting from similar grain sizes, the second light deformation produced a much larger recrystallized grain size than did the first light deformation. This result suggests that a lower average Taylor factor in the structure before deformation, resulting in lower stored energy, can increase the recrystallized grain size.

Abstract: SmCo5 magnets are usually produced by powder metallurgy route, including milling, compaction and orientation under magnetic field, sintering and heat treatment. The samples produced by powder metallurgy, with grain size around 10 μm, are ideal for determination of intrinsic parameters. The first step for determination of intrinsic magnetic parameters is obtaining images of domain structure in demagnetized samples. In the present study, the domain images were produced by means of Kerr effect, in a optical microscope. After the test of several etchings, Nital appears as the most appropriate for observation of magnetic domains by Kerr effect. Applying Stereology and Domain Theory, several intrinsic parameters of SmCo5 phase were determined: domain wall energy 120 erg/cm2, critical diameter for single domain particle size 2 μm and domain wall thickness 60 Å. In the case of SmCo5, and also other phases with high magnetocrystalline anisotropy, Domain Theory presents several advantages when compared with Micromagnetics.

Abstract: MnZn ferrites are conventionally produced by the ceramic method that involves the solid state reaction of metallic oxides or carbonates at high temperatures. The particles obtained by this method are rather large and non-uniform in size. In order to overcome the difficulties arising out of the ceramic process, the coprecipitation method has been used as an alternative route to produce chemically homogeneous powders with fine particle size. In this work MnZn ferrites powders were produced by the coprecipitation method. The calcination conditions, such as temperature (900oC to 1100oC) and atmosphere (air and nitrogen), were investigated. X ray diffractometry, scanning electron microscopy, thermomagnetic analysis and vibration sample magnetometry were used to characterize the obtained samples. The results indicated that when the samples were calcined in nitrogen atmosphere, the ferrite formation occurred at low calcination temperatures and presented better magnetic properties than those calcined in air.

Abstract: The non-oriented electrical steels, produced with different processing procedures, base their magnetic property improvement mainly on the increase of the Goss component. This paper relates the anisotropy of magnetic properties to texture, describes the texture evolution in both the Fully-processed and the Semi-processed classes of electrical steels.