Marcos Flavio de Campos

Separating Components of the Hysteresis Loss of Non-Oriented Electrical Steels

This paper shows that the separation of quasi-static hysteresis losses into two components, one related to Low Induction and other to High Induction levels. The separation line between those two regions has been arbitrarily chosen as the induction at maximum permeability. Results show that the grain size has stronger effect on the low induction component, while the high induction component is more sensitive to sample measuring direction. This may provide basis for better materialsproperties correlation modeling and product development.

Electron backscattered diffraction texture analysis of SmCo5 magnets

The remanence of sintered SmCo5 magnets is a direct function of their crystallographic texture. The Jr∕Js ratio was determined by electron backscattered diffraction (EBSD) for SmCo5 magnets which had been oriented in a pulsed field of 6T, compressed isostatically, and then sintered at 1150–1170°C for 1h. The experimentally determined EBSD distribution does not follow a Gaussian or a function of the form f(θ=cosnθ). EBSD measurements provided the same Jr∕Js value (0.91) as a microstructural model plus remanence measurements. X-ray diffraction Schulz pole figures resulted in a slightly higher Jr∕Js value (0.92), probably due to neglecting misaligned grains.

Quenching and partitioning heat treatment in ductile cast irons

A commercial ductile iron alloy was submitted to a quenching and partitioning heat treatment. Samples were austenitized at 900 oC for two hours, quenched at 160 oC and kept at this temperature for 2 minutes and finally were re-heated at temperatures between 300 and 450 oC during time intervals between 2 and 180 minutes. The microstructural evaluation was performed with SEM and X-ray diffraction and the mechanical properties were measured using tensile strength and Charpy tests. In general, the quenching and partitioning treatment is viable to achieving expressive fractions of retained austenite in ductile cast irons. Generally, higher partitioning temperatures produce a higher fraction of retained austenite after shorter times. This behavior can be explained by the increase on diffusion rate of carbon at higher temperatures. For all tested conditions it was possible to see a well-defined process window and the combination of mechanical properties is very similar to the austempered ductile irons.

Estimative of the Stacking Fault Energy for a FeNi(50/50) Alloy and a 316L Stainless Steel

The effect of high energy milling on powders of a FeNi (50/50) alloy and a 316L stainless steel has been evaluated by means of X-Ray Diffraction (XRD). The average microstrain as function of the milling time (1/2h, 1h and 8h) was determined from XRD data. The displacement and broadening of the (XRD) peaks were used for estimate the stacking fault energy (SFE), using the method of Reed and Schramm. It was estimated SFE=79 mJ/m2 for the FeNi (50/50) alloy and SFE=14 mJ/m2 for the 316L stainless steel. The better experimental conditions for determining the SFE by XRD are discussed.

Determination of Intrinsic Magnetic Parameters of SmCo5 Phase in Sintered Samples

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.

Modeling of Effect of Plastic Deformation on Barkhausen Noise and Magnetoacoustic Emission in Iron With 2% Silicon

Before one models the effect of plastic deformation on magnetoacoustic emission (MAE), one must first treat non-180 domain wall motion. In this paper, we take the Alessandro‐Beatrice‐Bertotti‐Montorsi (ABBM) model and modify it to treat non-180 wall motion. We then insert a modified stress-dependent Jiles‐Atherton model, which treats plastic deformation, into the modified ABBM model to treat MAE and magnetic Barkhausen noise (HBN). Infitting the dependence of these quantities on plastic deformation, we apply a model for when deformation gets into the stage where dislocation tangles are formed, noting two chief effects, one due to increased density of emission centers owing to increased dislocation density, and the other due to a more gentle increase in the residual stress in the vicinity of the dislocation tangles as deformation is increased. Index Terms—Iron-silicon steel, magnetic Barkhausen noise, magnetoacoustic emission, plastic deformation.

A Simple Algorithm for the Calculation of Hysteresis for Isotropic NdFeB Magnets

The calculation of hysteresis curves with the Stoner-Wohlfarth model is somewhat laborious. For the Nd2Fe14B phase, the second order magnetocrystalline anisotropy (K2) constant is relevant, and this case only has been discussed in some studies. In this article, a simple algorithm for the calculation of the Stoner-Wohlfarth model for isotropic NdFeB magnets is described. This algorithm makes easier the modeling of the hysteresis curves of bonded melt-spun NdFeB magnets.

Optimizing the Heat Treatment of Rare Earth-Transition Metal Sintered Magnets

Rare earth transition metals magnets, as for example SmCo5, NdFeB and Sm(CoCuFeZr)z magnets are, very often, submitted to a post-sintering heat treatment where the coercivity increases. In many cases, a slow cooling between the sintering and the annealing temperatures is applied. To optimize the time and cooling rate of heat treatment, it was developed a model using the finite volume method. This model takes into account the diffusivities of the different atom species and also the boundaries of phase diagrams.

Texture Optimization in Non-Oriented Electrical Steels: The Role of the Goss Texture Component

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.

Modeling the Heat Treatment of Dy-Diffused Nd2Fe14B Magnets: The Shell Model

In Nd2Fe14B sintered magnets there is increase of coercivity after Dy diffusion in the region near the surface of the grains. A kinetical model evaluating the Dy surface diffusion is presented. This model is based on a shell hypothesis: the most relevant place for the nucleation is a tiny shell near the grain boundaries. The kinetical analysis shows that a heat treatment during 1 hour at 850°C is able to produce a Dy-rich layer on the surface of the Nd2Fe14B grains.