Presentation influence texture or crystallography orientations on magnetic properties

The Influence of Texture on the

Magnetic Properties

Behzad Sadeghi PhD Student in Nanotechnology Engineering

Introduction to Magnetic properties & Electrical Steel.

Texture evolution during cold work and recrystallization.

Effect of metallurgical factors on the magnetic

properties.

grain size

annealing temperature

chemical composition

Heating Rate

annealing time

frequency

Effect of Crystallographic Texture on Magnetic

Characteristics of Cobalt Nanowires.

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Soft magnetic materials are:energy losses must be low ; one familiar exampleconsists of transformer cores.

A soft magnetic material must have a high initial permeability and a low Hc.

One alloy commonly used for this application is the Fe–3%Si alloy( Electrical Steel)

Hard Magnetic Materials: High resistance to demagnetization

High Mr ,Hc, as well as a low initial permeability, and high hysteresis energy losses

Iron Alloy with Si(0-6.5%); BCC

Manufactured in the form of cold-rolled strips

Depending on the requirement of magnetic properties

Grain oriented electrical steel (GOES)

Non-grain oriented electrical steel (NOES)

Desirable Properties of ES:

• High magnetic induction (Magnetic flux Density) (Permeability)

• Low core energy loss

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Core loss (or iron loss/watt loss) is divided into two

components;

Hysteresis loss

Eddy current loss.

However, effect of metallurgical factors on these two

components does not always follow similar trends and very

often an optimum value of these metallurgical variables

(e.g. grain size) is required to achieve best magnetic

properties in Electrical Steel.

Texture effects on magnetic properties in high-alloys NOES, S. K. Chang, J. Metal Science and Heat Treatment,2007

http://en.wikipedia.org/wiki/Cold_rolling



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Easy axis of magnetization

In Si non-oriented steel, Core loss is found to be the lowest for (100)

planes and highest for (111) planes,

Thus,the (100)⟨uvw⟩ or cube fiber texture is the most suitable one and

(111) ⟨uvw⟩ or gamma fiber is one of the worst one for non-oriented

electrical steels.

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One of the most effective stages for modify of the texture:

Annealing

Nucleation {110} <001> (Goss) grains mainly within

shear bands

These bands were often found in the coarse grains

specimens

Annealing cause coarsening the microstructure

Chemistry

Grain size

Crystallographic Texture

Stress states

Magnetic Properties (Core loss and the Permeability)

Effect of initial grain size on texture evolution and magnetic properties in NOES,J.T Park et al, J.Magnetism and Magnetic Materials,2009

Magnetic Induction (B) increase with increasing R (Size grain) in

the irreversible magnetization range (H¼80–200 A/m), whereas it

decreases with increasing R in the rotation magnetization range (H

>300 A/m).

So, there is an optimal grain size

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The Goss and the Cube components that have favorable magnetic

properties.

The orientation of recrystallized grains at the early stage of

recrystallization is maintained up to the late stage of recrystallization

without any significant change

T=790 C T=950 C

Strength Decrease

Effect of initial grain size on texture evolution and magnetic properties in NOES,J.T Park et al, J.Magnetism and Magnetic Materials,2009

Partial α-fiber from {001} <110>

to {111} <110> +

Complete γ-fiber {111} <110>

and {111} <112>

Weaker {001} <110>,{111} <110>

+

Stronger {111} <112> component

and {111} <112>

8Texture effects on magnetic properties in high-alloys NOES, S. K. Chang, J. Metal Science and Heat Treatment,2007

The coarse-grained specimens have weaker <112> and <110> at the

same temperature than the fine-grained specimens.

Increasing grain size lowers the core loss in non oriented electrical steels because

it reduces the area of grain boundaries which restrain the movement and rotation

of magnetic domains during magnetization

Grain-size has an opposite effect on the hysteresis and eddy current

losses, thus there is an optimal grain size, which can help minimize

the sum of hysteresis and eddy current losses (core loss)

ON THE CONTRARY

Eddy current loss ά D 0.5

Magnetic domain size increases with increasing grain size(D).

Hysteresis loss ά the nucleation and annihilation of domains. hysteresis

loss ά 1/d

D = grain boundary = barrier to domain wall motion = Hysteresis

loss


Ingots were hot-rolled to a thickness of 2.6 mm, then cold-rolled to 0.35

mm, and annealed at 1000 C for 2 min in an oxidation-free atmosphere


Higher than in steels bearing Co and Mo

Lower than in steels bearing Co and Mo

The texture factor was introduced to estimate the effect of favorable and unfavorable texture

Co and Mo form carbides and thus presumably hinder the development of

cubic and Goss textures but Ni does not form carbides thus does not hinder

magnetization

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Magnetic induction and core loss are directly related to the texture factor

The introduction of Co, Mo, or Ni clearly decreases the relation of the

texture factor to magnetic properties.

Texture effects on magnetic properties in high-alloys NOES, S. K. Chang, J. Metal Science and Heat Treatment,2007

Larger grains provide larger misorientation angles

Ni-bearing steel has a low fraction of grains with small-angle

boundaries + higher fraction of grains with large-angle boundaries

12Rapid heating effects on grain-size, texture and magnetic properties of 3% Si NOES, J. Wang et al, J. Bull. Mater. Sci, 2011

Heating

RateRecovery

Stored Energy

Nucleation & Growth

Rate

Smaller Grain Size

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Recrystallized texture depends on the nucleation and growth rates of

different orientations

Recrystallization nuclei mainly concentrate on the regions with high stored

energy, generally, the {110} and {111} texture components.

The recrystallized texture components is γ-fiber and the preferred orientations

mostly concentrated along the {111} <110> and {111} <112 > directions.High heating rate = reduce stored elastic energy recovery = increase the

driving force nucleation & coarsening =promote high angle grain boundaries

migration = decreases the <111>//ND intensity and increases the intensity

of the {110}<001> Goss texture component.

Rapid heating effects on grain-size, texture and magnetic properties of 3% Si NOES, J. Wang et al, J. Bull. Mater. Sci, 2011

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There are No easy magnetic directions in the {111} planes, and the

{110}<001> (Goss) orientation has <100> easy magnetization direction

along the rolling direction

Texture optimization of nonoriented electrical steels mainly consists of

avoiding the occurrence of grains with <111>//ND fiber and generating

more grains with <001>//RD and <001>//ND fibers.

rapid annealing is favorable to reduce the γ-fiber intensity

and increase the Goss texture component

Thus

Rapid heating effects on grain-size, texture and magnetic properties of 3% Si NOES, J. Wang et al, J. Bull. Mater. Sci, 2011

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The intensity of all texture components changes slightly.

With a high heating rate, the annealing time could decrease the intensity of

the recrystallized texture, including both the favorable Goss component

{110}<001> and unfavorable {111}<112> and {111}<110> texture components.

The decrease in intensity of the Goss {110}<001> component is less than that

of the {111}<112> and {111}<110> components.

Rapid Annealing Effects on Microstructure, Texture, and Magnetic Properties of NOES, J. Wang et al, J. Met. Mater. Int,2011

(a) 3 s

(b) 6 s

(c) 9 s

(d) 30 s

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This is due to magnetic induction so the intensities of the {111}<112> and

{554}<225> texture components are similar for both 15- and 30-second holding times

,but the intensity of the Goss component is higher at 15 seconds than at 30 seconds.Core loss decreases with holding time due to the larger mean grain size, which

decreases magnetic hysteresis losses.

There are appropriate annealing time (6 to 9 seconds)

ranges at a high heating rate of 300 C/s, which

simultaneously can optimize the core loss and magnetic

induction.

Rapid Annealing Effects on Microstructure, Texture, and Magnetic Properties of NOES, J. Wang et al, J. Met. Mater. Int,2011

17Effect of metallurgical factors on the bulk magnetic properties on NOES, P. Ghosh et al, J. Magnetism and Magnetic Materials,2014


B1 and B3 steels in non-SRA condition

showed two weak fiber components, one

along gamma fiber and the other parallel to α-fiber (RD [110]).

SRA treatment not only improved the

overall ODF intensity in these cases but

also improved the cube fiber intensity

In case of C3, the overall intensity of

ODF increased almost by double (just like

B1 and B3) but for C4 no significance

enhancement of ODF intensity was

observed after SRA.

SRA resulted in an improvement in the

cube fiber intensity for C3 and gamma

fiber intensity did not get affected by SRA

for C3


Increasing Si content and decreasing

grain size help to reduce eddy current loss

and in turn decreases overall core loss at

high frequencies.

Higher the carbon content, larger is the

probability of formation of small Fe3C

particles which act as pinning sites and

obstruct domain wall motion during

magnetization process

20Effect of Crystallographic Texture on Magnetic Characteristics of Cobalt Nanowires, K. Maaz et al, J. Nanoscale Res Lett. 2010

XRD studies of the samples reveal

that 70-nm-diameter wires are

strongly [002] textured, however,

with increasing diameter, [100] and

[101] textures also become strong.TC values larger than 1 indicate a preferred orientation of the crystals/grains

in the samples.

The cobalt nanowires of 70 nm diameter are strongly [002] textured.

Distinguishing between Local PH and Solution PH.

This difference increases as the pore diameter decreases.

Pores with large diameters lead to high current density

during electrodeposition.

smaller ad-atom mobility and thus a less distinct wire texture

21Effect of Crystallographic Texture on Magnetic Characteristics of Cobalt Nanowires, K. Maaz et al, J. Nanoscale Res Lett. 2010

Coercivity of the nanowires along the

wire long axis decreases with increasing

diameter most probably due to the effect

of decreasing [002] textureThe coercivity increase with increasing

diameter due the increasing [100] and [101]

textures and then decreases for 120 nm wire

due the dominant role of domain

transformation (from single to multi

domain) in thicker wires.

Parallel directionPerpendicular direction

The specimens having different initial grain sizes have significantly different

textures in the cold-rolled state and the annealed state.

During the recrystallization stage, new grains formed in the coarse-grained

specimens have stronger Goss but weaker γ-fibre texture

The magnetic induction of the coarse-grained specimens is always higher at

the same temperature than that of the fine grained specimens

The core loss of the coarse-grained specimens is lower at the same

temperature than that of fine-grained specimens

Recrystallized grains could be refined due to the high recrystallization

nucleation rates caused by higher heating rates.

There are appropriate annealing temperatures and annealing time (6 to 9

seconds) ranges at a high heating rate, which simultaneously can optimize the

core loss and magnetic induction.

Increasing Si content of these steels has the similar consequence like

decreasing grain size at higher frequency.

It seems that the effect of metallurgical variables on core loss comparatively

straight forward than permeability in NOES

The recrystallization texture of non-oriented electrical steels could be greatly

optimized by increasing the heating rate, which reduces the fraction of

<111>//ND γ-fiber and increases the fraction of the {110}<100> Goss

component.

In case of parallel applied field, the coercivity has been found to be

decreasing with increasing diameter of the wires while in perpendicular

case; the coercivity observes lower values for larger diameter..

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Presentation influence texture or crystallography orientations on magnetic properties

Engineering

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