Combustion Driven Compaction of Nanostructured SmCo/Fe

• Exchange spring magnetic materials can potentially increase the energy-products of permanent magnets

• Powder consolidation has the ability to form composite magnets with arbitrary 3D shapes and sizes, less $ for expensive hard phase, possibility of mechanical fiber reinforcements

Approach

• Obtain high coercivity by ball-milling hard phase

• Increase magnetization of the ball-milled hard phase by mixing with soft-phase

• Obtain exchange coupling between the hard and the soft phase by compaction

Hard

Soft

Hard/Soft

H

M

Challenges for compacted nanocomposites

• Preserve original phases during compaction

• Achieve strong coupling across interfaces

Here compare results for consolidation by three different methods: Hot Isostatic Pressing (HIP), Plasma Pressure Compaction (P2C), and Combustion Driven Compaction (CDC)

Powder Precursors

• Sm2Co17 (= Sm(Co0.67Fe0.234Cu0.07Zr0.024)7.5)* or SmCo5 for the hard phase [d ~ 1 m]

• High crystallinity acicular-Fe nanoparticles for soft phase [length ~ 200 nm, d ~ 20 nm]

• SmCo and Fe powder precursors were mixed together by gentle milling

[*Courtesy of C. Chen, Electron Energy Corporation]

[Courtesy of J. Nakano, Toda Corporation]

Acicular Fe Nanoparticles

• TEM of commercial acicular-Fe particles with an average length of 200 nm and average diameter of 20 nm

• Hydrogen reduction at 400 °C used to remove surface Fe3O4

Consolidation Methods

Plasma Pressure Compaction (P2C)

Compaction done at Materials Modification, Inc., 600°C, 45 MPa, 5 min

Hot Isostatic Pressing (HIP)

Compaction done at Wright-Patterson AFB 550°C, 21.6 MPa, 5 min

V

Pressure

Graphite Electrodes also form Mold

Sealed Powderr

Combustion Driven Compaction

Compaction done at Utron, Inc.

Die

Powder

Ram

Gas InletIgnitor

CombustibleGas Mixture

• Reach 2 GPa maximum pressure after 500 ms

• Fast and low temperature compaction

• 95% of theoretical density

• Plasma Pressure Compaction (P2C): 73 MPa; 5 mins; 600oC

• Hot Isostatic Pressing (HIP): 435 kPa; 5 mins; 550oC

• Combustion Driven Compaction (CDC): 2 GPa; 500 ms; “room temperature”

-80

-60

-40

-20

0

20

40

60

80

Magnetization (A-m

2/kg)

-4x106

-3 -2 -1 0 1 2 3 4

Field (A/m)

(SmCo5)0.85 Fe0.15 : PPC

(SmCo5)0.80 Fe0.20 : HIP (SmCo5)0.85 Fe0.15 : CDC

T = 300 K

CDC: Retains HC but here loses M because not aligned

Different Compaction Methods

X-ray Diffraction and CDC

• Average Grain size estimates based on Scherrer analysis

Powder : 190 nm Pellet : 138 nm

• No SmCo phase decomposition occurred during CDC (unlike with HIP and P2C)

• Reduced grain-size after compaction

245403530

Sm2

Co17

Pellet

Powder

(101)

(110)

(111)

(002)

Different Compaction Methods• Plasma Pressure Compaction (P2C): 73 MPa; 5 mins; 600oC

• Hot Isostatic Pressing (HIP): 435 kPa; 5 mins; 550oC

• Combustion Driven Compaction (CDC): 2 GPa; 500 ms; “room temperature”

-80

-60

-40

-20

0

20

40

60

80

Magnetization (A-m

2/kg)

-4x106

-3 -2 -1 0 1 2 3 4

Field (A/m)

(SmCo5)0.85 Fe0.15 : PPC

(SmCo5)0.80 Fe0.20 : HIP (SmCo5)0.85 Fe0.15 : CDC

T = 300 K

CDC: Retains HC but here loses M because not aligned

Pre-Alignment of Powder

• Powder aligned in pulsed field (3 one second pulses of 10 T)

H = 10 T

• Green-compact formed by Cold Isostatic Pressing (at 35 kpsi)*

• Further densification using Combustion Driven Compaction (CDC)

*Courtesy of S. Sankar, Advanced Materials Corporation

CDC and Alignment

CDC

c-axis

Compaction done at Utron, Inc.

Die

Powder

Ram

Gas InletIgnitor

CombustibleGas Mixture

Studied unaligned, and samples with 2 different alignment directions:

c-axis

CDC

Parallel Perpendicular

CDC: via green-compact

• Compacted parallel to c-axis (BH)max = 1.2 x 105 J/m3 (15.5 MGOe)

• Compacted perpendicular to c-axis (BH)max = 2.5 x 105 J/m3 (31.3 MGOe)

• Density ~ 95% in both cases

80

40

0

-40

-80 Magnetization (A-m

2/kg)

-3.0x106

-2.0 -1.0 0.0 1.0 2.0 3.0

Field (A/m)

T = 300 K

Sm2Co17:Fe (20% at.) compacted perpendicular to c-axis compacted parallel to c-axis

Estimating Alignment Retention

• Estimate alignment retained during compaction (CDC), using X-ray Pole Figure analysis

• For a particular Bragg angle, diffraction from corresponding plane is recorded

2

Inte

nsit

y (a

rb. u

nits

)

Sm2Co17

X-rays

Diffracted beam

Pole Figures

For sample compacted in perpendicular orientation

(002)sample

(110)

(110)

(002)

(110) planes are perpendicular to (002), and are ~randomly oriented

In (002) pole figure, I is largest near the edges, suggesting c-axis nearly parallel to the sample surface.

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