In this chapter, we will restrict our attention to the ferrites and a few other closely related materials. The great interest in ferrites stems from their unique combination of a spontaneous magnetization and a high electrical resistivity. The observed magnetization results from the difference in the magnetizations of two non-equivalent sub-lattices of the magnetic ions in the crystal structure. Materials of this type should strictly be designated as “ferrimagnetic” and in some respects are more closely related to anti-ferromagnetic substances than they are to ferromagnetics in which the magnetization results from the parallel alignment of all the magnetic moments present. We shall not adhere to this special nomenclature except to emphasize effects, which are due to the existence of the sub-lattices.

Ferromagnetic materials

http://physics.gmu.edu/~ymishin/Ni3Al.pdf

Atomistic modeling of the γ and γ'-phases of the Ni-Al system

The phenomenon of rafting in superalloys is described, with particular reference to modern superalloys with a high volume fraction of the particulate γ’ phase. It is shown that in the elastic regime, the thermodynamic driving force for rafting is proportional to the applied stress, to the difference between the lattice parameters of the γ matrix and the γ’ particles, and to the difference of their elastic constants. A qualitative argument gives the sign of this driving force, which agrees with that determined by Pineau for a single isolated particle. Drawing on the work of Pollock and Argon and of Socrate and Parks, it is shown that after a plastic strain of the sample of order 2 × 10-4, the driving force is proportional to the product of the applied stress and the lattice misfit, in agreement with the results of the calculations of Socrate and Parks. The rate of rafting is controlled by the diffusion of alloying elements. Here, the tendency of large atoms to move from regions of high hydrostatic pressure to those of low may outweigh the influence of concentration gradients. The deformation of the sample directly produced by rafting is small, of order 4.5 × 10-4. The rafted structure is resistant to creep under low stresses at high temperatures. Under most experimental conditions at relatively high stresses, rafting accelerates creep; this effect may be less pronounced at the small strains acceptable under operational conditions.

Rafting in superalloys

Power saving has been a central driving force for the development of new materials. In this framework, soft magnetic composites appear as a feasible concept to be applied in strategic topics for modern society including sensing, energy generation, and conversion. With a unique freedom regarding material selection based on powder metallurgy techniques, this engineering magnetic material class allows novel designs able to drive operation conditions to new limits, unlocking the potential of novel applications. This document reviews soft magnetic composites by using a multidisciplinary approach addressing underlying physics responsible for their magnetic performance, limitations, and future trends.

Past, present, and future of soft magnetic composites

https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=1243&context=ameslab_manuscripts

Review of Fe-6.5 wt%Si high silicon steel—A promising soft magnetic material for sub-kHz application

http://www.pmt.usp.br/ACADEMIC/landgraf/nossos%20artigos%20em%20pdf/06campos%20jmmm%20optimum.pdf

The optimum grain size for minimizing energy losses in iron

The nondestructive Magnetic Barkhausen Noise (MBN) technique was applied for the evaluation of SAE 4140 and SAE 6150 steels after a Jominy end-quench test. Microstructures were also characterized by SEM (Scanning Electron Microscope) and hardness tests. MBN measurements were performed on the same sample regions at three excitation frequencies. Different parameters of the measured signals (signal peak position and height, and Root mean square) were calculated. A relationship between mechanical hardness and MBN parameters was found for both materials, with the best correlation coefficient being found in low excitation frequency range.

Relation Between Magnetic Barkhausen Noise and Hardness for Jominy Quench Tests in SAE 4140 and 6150 Steels

In 2.2% Si electrical steel, the magnetic hysteresis behavior is sharply sheared by a rather small plastic deformation (0.5%). A modification to the Jiles–Atherton hysteresis model makes it possible to model magnetic effects of plastic deformation. In this paper, with this model, it is shown how a narrow hysteresis with an almost steplike hysteresis curve for an undeformed specimen is sharply sheared by plastic deformation. Computed coercivity and hysteresis loss show a sharp step to higher values at small strain due to an n=1∕2 power law dependence on residual strain. The step is seen experimentally.

/pdf/modeling-of-sharp-change-in-magnetic-hysteresis-behavior-of-3pf7kruy5d.pdf

Modeling of sharp change in magnetic hysteresis behavior of electrical steel at small plastic deformation

The effect of grain size on iron losses were compared for two electrical steels with 0.5 and 1.5 wt% Si. The results confirm that the optimum grain size for minimizing the energy losses decreases when the electrical resistivity decreases or when the frequency increases. Experimental results are compared to a model which considers the influence of grain size. The recrystallization texture of the alloys varies little with grain size and consists mainly of the fibers {111}languvwrang and lang110rang//RD

/pdf/effect-of-frequency-on-the-iron-losses-of-0-5-and-1-5-si-348s3qosbo.pdf

M.F. de Campos

Papers

The optimum grain size for minimizing energy losses in iron

Relation Between Magnetic Barkhausen Noise and Hardness for Jominy Quench Tests in SAE 4140 and 6150 Steels

Modeling of sharp change in magnetic hysteresis behavior of electrical steel at small plastic deformation

Effect of Frequency on the Iron Losses of 0.5% and 1.5% Si Nonoriented Electrical Steels

On the Steinmetz hysteresis law