Magnet properties D. Chateigner CRISMAT-ENSICAEN, Caen, France M. - - PowerPoint PPT Presentation

Texture development in Nd-Fe-B and Nd-Fe-V alloys by hot forging in view of improving permanent Magnet properties

• D. Chateigner

CRISMAT-ENSICAEN, Caen, France

• M. Morales

SIFCOM-ENSICAEN, Caen, France

• S. Rivoirard, I.Popa, P. de Rango, D. Fruchart

CRETA and Cristallographie-CNRS, Grenoble, France

• B. Ouladdiaf

Institut Laue Langevin, Grenoble, France

c

2nd International Conference Texture and Anisotropy of Polycrystals, Metz, France, July 2004

• Some intrinsic magnetic and extrinsic

magnet properties

• QTA and anisotropic magnetisation

curves: ErMn4Fe8C case

• Nd-Fe-B-Cu, Nd-Fe-V alloys
• conclusions

Permanent magnet characteristics

Intrinsic properties Hard magnetic phase

• Saturation magnetisation, Ms
• Magnetocrystalline anisotropy
• Curie temperature
• Anisotropy field

Extrinsic properties

• Remanence, Mr
• Coercive field, Hc
• Maximum energy product,

BH max

Introduction

2nd International Conference Texture and Anisotropy of polycrystals, Metz, France, July 2004

j i j j j j j j j j j j j i i i i i i i i i i i 2a 2a 2a 2a 2a z=0 z=1/2 z=1/4 et 3/4 a b f f f f

ErMn4Fe8C Structural determination:

• M. Morales et al.: J. Magn.

And Magn. Mat. 196 (1999) 703

Easy-plane tetragonal phase magnetic moments in the (a,b) planes

N S

Htext

θ θ

S(Q)

Htext radial Sample B N S z

Htext

θ θ

S(Q)

Htext axial Sample A

Hmeas // z ⊥ (a,b) // (a,b)

Same demagnetising factor

28 29 30 31 32 33 34 35 36 37 38 20 40 60 80 100 120 140 160

220 + 211 411 420 400+321 002 202 301 Sample B Intensity (a.u.) 2 θ (°)

002 301 220 + 211

Intensity (a.u.) 2 θ (°) A B

max {001}: 3.9 mrd min: 0.5 mrd Quantitative Texture Analysis

• --- // (a,b)
• --- ⊥ “

RP0 = 1.2 % F2 = 1.3 mrd2 S = -0.13 {001} radial distribution: ρ0 (0.5 mrd) + PV (HWHM = 12°)

1 2 3 4 5 6 7 8 2 4 6 8 10

aimantation ( µ

B / fu )

H (T) ErMn

4Fe 8C

T= 300K

Μ

/ / /

Μ

⊥

M random

Anisotropic magnetisation curves HA

M(Hmeas) = MS cos(θg - θ) E(Hmeas) = K1 sin2θ −Η MS cos(θg - θ) d dE = θ

θ) (θ sin M θ cos θ sin K 2 H

g S 1 meas

− =

HA = 2K1/MS

) θ

• θ

( sin θ cos θ sin H H

g A meas =

Model for M⊥:

c

• M
• x

O ⊥ (a,b)

H meas

θg θ φ

anisotropy energy Zeeman energy

MS = 5.24 µB/fu

1 dφ dθ sinθ ) φ , F(θ

g g 2 π 2 g

g

=

∫ ∫

= θ π = ϕ

Normalised Probability function F, to find c-axes in dy: Fibre texture:

1 dθ sinθ ) G(θ 2

g g 2 π g

g

= π ∫

= θ

( )

random 2 π g g g g S

M θ d ) θ θ cos( θ sin ) θ PV( 1 2 M M ρ + − ρ − π =

∫

⊥

Finally:

( )

) ( PV 1 ) ( G

g g

θ ρ − = θ

Morales, Chateigner, Fruchart: J. Magn.

• Mag. Mat. 2003

1 2 3 4 0.25 0.30 0.35 0.40 0.45 0.50 0.55 0.60 0.65 0.70 0.75 0.80 0.85 0.90 0.95 1.00

1 2 3 0.00 0.02 0.04 0.06 0.08 0.10

(M? - M

calculated

) / M

S

H / H A

M// M⊥ M / MS H / HA

Nd2Fe14B

Crystallographic structure

• Uniaxial anisotropy →

c-axis = easy magnetisation axis

• Ha= 7T
• Ms= 1.61 T
• Tc= 315°C

Introduction: intrinsic properties

a a c

Fe Nd B

Intrinsic magnetic properties: hard magnetic phase P42/mnm

2nd International Conference Texture and Anisotropy of polycrystals, Metz, France, July 2004

NdFe12-XVXN compounds

N

• space group I4/mmm

N atoms in 2b sites

Introduction: intrinsic properties

Crystallographic structure Nitrogenation Intrinsic magnetic properties: hard magnetic phase

• c-axis = easy magnetisation axis
• Ha= 1.5T → 11 T
• Ms= 1.13 T → 1.37 T
• Tc= 340°C → 510°C

2nd International Conference Texture and Anisotropy of polycrystals, Metz, France, July 2004

ANISOTROPY

common orientation of the easy magnetisation

axes of the crystallites

Orientation

• f magnetic particles in a non magnetic matrix

⊥ r r

M M //

Permanent magnet extrinsic properties: anisotropy

c c c c c c c c

Introduction: extrinsic magnetic properties 2nd International Conference Texture and Anisotropy of polycrystals, Metz, France, July 2004

COERCIVITY Grain size control

• f the hard magnetic phase

Intergranular phase distribution → Magnetic decoupling Secondary phases

Permanent magnet extrinsic properties: coercivity

10 µm

Introduction: extrinsic magnetic properties

C

H

2nd International Conference Texture and Anisotropy of polycrystals, Metz, France, July 2004

Preparation route

Hot forging Induction Melting and Casting Powdering (HD Process)

Magnet Powder

Anisotropy + Coercivity

Experimental details

Nitrogenation (Nd-Fe-V)

2nd International Conference Texture and Anisotropy of polycrystals, Metz, France, July 2004

Bulk Magnet

comme phase verte

High-speed hot forging

Thermomechanical treatment

• f the as-cast alloy

to induce permanent magnet properties

EXPERIMENTAL DEVICE

Working chamber Hammer Tachymeter Vacuum elements

Heating coil Airtight passage and sliding of the inductive coil Piston Sample

• uverture vitrée

de l’enceinte Window

Argon entrance

Experimental details 2nd International Conference Texture and Anisotropy of polycrystals, Metz, France, July 2004

ε = 125 s-1

Microstructures

5 µm

NdFe10.5V1.5 NdFe14B as-cast alloy forged sample

10 µm

Results: microstructure

Black: iron White intergranular phase Grey: hard magnetic phase

2nd International Conference Texture and Anisotropy of polycrystals, Metz, France, July 2004

20 µm 10 µm 10 µm

• 15
• 10
• 5

5 10 15

• 80 -60 -40 -20

20 40 60 80 H

int

(kOe)

Parallel to the Forging direction perpendicular to the forging direction

Permanent magnet properties

Hc = 10 kOe (795 kA/m) Br = 10 kG (1 T) BHmax = 24 MGOe (191 kJ/m3)

Nd15,5Fe78B5Cu1,5 alloys NdFe10,5V1,5N+10% Nd alloys

Results: permanent magnet properties 2nd International Conference Texture and Anisotropy of polycrystals, Metz, France, July 2004

0.2 0.4 0.6 0.8 1.0 1.2 1.4 1 2 3 4 5 6 7 forging direction paralel to the magnetic field forging direction perpendicular to the magnetic field

M(T) H(T)

Isotropic magnet

Texture development in the Nd2Fe14B phase

ILL, D1B

Texture

Cristallographic texture ⇒ extrinsic anisotropy

⇒ Fibre texture of Nd2Fe14B ⇒ c-axes // forging direction Y

239 100 (1 mrd) 24 2nd International Conference Texture and Anisotropy of polycrystals, Metz, France, July 2004 {001} {100}

forging direction Y

¤ ¤

Texture investigation

• f the NdFe10,5V1,5 phase

ILL, D20 texture with <100> axes // forging direction Y 2 components, ≈ fibre

X Z forging direction Y

Texture 2nd International Conference Texture and Anisotropy of polycrystals, Metz, France, July 2004

Texture development

• f the NdFe10,5V1,5 phase

X c2 a1 c1 a2 Y Z 60° 60° 30° 30°

[010] // Y [001] in (X,Z) plane ⊥ forging direction Y no extrinsic magnetic anisotropy can be observed on forged bulks

Texture 2nd International Conference Texture and Anisotropy of polycrystals, Metz, France, July 2004

Influence of primary iron on the NdFe10,5V1,5 phase stabilisation and texturing

Contribution of minor phases to the texturing process of the main phase

NdFe10,5V1,5 phase stabilisation:

• ptimised microstructure for Nd=10%

20 40 60 80 100 5 10 15 20 25

• pen the file again. If the red x still appears, you may have to delete the image and

Free iron centre (%) 1:12 phase centre (%) Free iron periphery (%) 1:12 phase periphery (%) %Nd a

NdFeV alloys Nd-rich phase+ (Fe,V) →NdFe10,5V1,5

2nd International Conference Texture and Anisotropy of polycrystals, Metz, France, July 2004

Influence of primary iron

• n the Nd2Fe14B phase texturing

2 4 6 8 10 12 14 16 18 10 12 14 16 18 20 22 y (Nd-at %) Free Iron (volume %) 2 4 6 8 10 12 14 16 18 10 12 14 16 18 20 22 y (Nd- at %) BHmax (10*kJ/m3) Free iron (volume %)

Contribution of minor phases to the texturing process of the main phase

Optimised microstructure and magnetic properties for Nd=15,5%

NdFeBCu as cast alloys NdFeBCu forged alloys

2nd International Conference Texture and Anisotropy of polycrystals, Metz, France, July 2004

Influence of the intergranular volume fraction on texturing

5 10 15 20 25 30 35 10 12 14 16 18 20 22 y (% Nd) Intergranular phase (volume %)

as cast alloys forged alloys

4 8 12 16 5 10 15 20 25 forged alloy: centre forged alloy: periphery as cast alloy (theoretical) %Nd

NdFeBCu alloys NdFeV alloys

Contribution of minor phases to the texturing process of the main phase

volume of intergranular phase = volume of liquid at Tf

NdFeBCu alloys volume fraction ↑ with %Nd NdFeV alloys %Nd>10%: liquid phase segregation

2nd International Conference Texture and Anisotropy of polycrystals, Metz, France, July 2004

20 µm

NdFe10.5V1.5 + 10%Nd Nd15,5Fe78B5Cu1,5

Effect of iron

• n the hot deformation process

Contribution of minor phases to the texturing process of the main phase

Forging energy mainly used for the plastic deformation of iron

2nd International Conference Texture and Anisotropy of polycrystals, Metz, France, July 2004

10 µm

Effect of iron

• n the hot deformation process

10 µm

Contribution on minor phases on the texturing process

Large amount of iron or non homogeneous distribution detrimental to the alloy deformation process

0,5 1 1,5 2 2,5 90 110 130 150 170 190 chi (°) density (m.r.d.) centre periphery (with iron aggregates

in the as-cast alloy) (with iron but no aggregates)

Inhomogeneous microstructure with non deformed areas in the periphery of the Nd15,5Fe78B5Cu1,5 alloy

weaker Nd2Fe14B texture in the presence of iron aggregates

2nd International Conference Texture and Anisotropy of polycrystals, Metz, France, July 2004

On the texturing mechanism

• f the hard magnetic phase…

Texturing mechanism

Some similitudes of the Nd-Fe-V and Nd-Fe-B alloys :

• TM-RE alloys
• Similar microstructures: nature of phases, proportions, distribution…
• At Tf: solid main phase, liquid intergranular phase
• At Tf: solid main phase in the brittle state

Fibre texture in both cases Uniaxial hot forging

2nd International Conference Texture and Anisotropy of polycrystals, Metz, France, July 2004

On the texturing mechanism

• f the hard magnetic phase…

Texturing mechanism

… But different texturing mechanisms of the Nd-Fe-V and Nd-Fe-B alloys

• At Tf, deformation behaviour
• f an alloy in the semi-solid

state

• At Tf, low liquid volume fraction

→ liquid not responsible for the main deformation process NdFeBCu NdFeV

Fiber texture with <010> axis parallel to the forging direction Y + 2 three-dimensional components Fiber texture with <001> axis parallel to the forging direction

2nd International Conference Texture and Anisotropy of polycrystals, Metz, France, July 2004

On the texturing mechanism

• f the hard magnetic phase…

Texturing mechanism

… and different deformation behaviours NdFeBCu NdFeV

Homogeneous Flow + Rotation Grain Cracking Liquid segregation

NdFe10,5V1,5 crystallisation + crystallites

• rientation

complex mechanism…

2nd International Conference Texture and Anisotropy of polycrystals, Metz, France, July 2004

Conclusion

Conclusion 2nd International Conference Texture and Anisotropy of polycrystals, Metz, France, July 2004

• Tf= 930°C, Nd=15,5% (fl= 10%)

NdFeBCu NdFeV

Fiber texture with <010> axis parallel to the forging direction Y + 2 three-dimensional components Fiber texture with <001> axis parallel to the forging direction

ε = 125 s-1

• Coercive and anisotropic powder

(patented process)

BHmax = 24 MGOe (191 kJ/m3)

• Tf= 980°C, Nd-excess=10% (fl<5%)

ε = 125 s-1

• Magnetic properties

still under optimisation