Combustion Driven Compaction of Nanostructured SmCo/Fe

1. 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

2. 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

3. 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)

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

5. 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

6. Consolidation Methods Hot Isostatic Pressing (HIP) Plasma Pressure Compaction (P2C) r Compaction done at Wright-Patterson AFB 550°C, 21.6 MPa, 5 min Compaction done at Materials Modification, Inc., 600°C, 45 MPa, 5 min

7. Combustion Driven Compaction • Reach 2 GPa maximum pressure after 500 ms • Fast and low temperature compaction • 95% of theoretical density Compaction done at Utron, Inc.

8. 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” CDC: Retains HC but here loses M because not aligned

9. X-ray Diffraction and CDC • Average Grain size estimates based on Scherrer analysis • Powder : 190 nmPellet : 138 nm 2 • No SmCo phase decomposition occurred during CDC (unlike with HIP and P2C) • Reduced grain-size after compaction

10. 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” CDC:Retains HC but here loses M because not aligned

11. Pre-Alignment of Powder • Powder aligned in pulsed field (3 one second pulses of 10 T) • Green-compact formed by Cold Isostatic Pressing (at 35 kpsi)* • Further densification using Combustion Driven Compaction (CDC) H = 10 T *Courtesy of S. Sankar, Advanced Materials Corporation

12. CDC CDC c-axis c-axis CDC and Alignment Studied unaligned, and samples with 2 different alignment directions: Parallel Perpendicular Compaction done at Utron, Inc.

13. 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

14. 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 Sm2Co17 Intensity (arb. units) 2q Diffracted beam f X-rays y

15. (110) (002) sample (002) (110) Pole Figures For sample compacted in perpendicular orientation In (002) pole figure, I is largest near the edges, suggesting c-axis nearly parallel to the sample surface. (110) planes are perpendicular to (002), and are ~randomly oriented

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