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 (P 2 C), and Combustion Driven Compaction (CDC)

4. Powder Precursors Sm 2 Co 17 (= Sm(Co 0.67 Fe 0.234 Cu 0.07 Zr 0.024 ) 7.5 )* or SmCo 5 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]

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 Fe 3 O 4

6. Consolidation Methods Plasma Pressure Compaction (P 2 C) 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 r

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

8. Plasma Pressure Compaction (P 2 C): 73 MPa; 5 mins; 600 o C Hot Isostatic Pressing (HIP): 435 kPa; 5 mins; 550 o C Combustion Driven Compaction (CDC): 2 GPa; 500 ms; “room temperature” CDC: Retains H C but here loses M because not aligned Different Compaction Methods

9. 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 P 2 C) Reduced grain-size after compaction 22

10. Different Compaction Methods Plasma Pressure Compaction (P 2 C): 73 MPa; 5 mins; 600 o C Hot Isostatic Pressing (HIP): 435 kPa; 5 mins; 550 o C Combustion Driven Compaction (CDC): 2 GPa; 500 ms; “room temperature” CDC: Retains H C but here loses M because not aligned

11. 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

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

13. CDC: via green-compact Compacted parallel to c-axis (BH) max = 1.2 x 10 5 J/m 3 (15.5 MGOe) Compacted perpendicular to c-axis (BH) max = 2.5 x 10 5 J/m 3 (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 2 2  Intensity (arb. units) Sm 2 Co 17 X-rays Diffracted beam  

15. Pole Figures For sample compacted in perpendicular orientation (002) sample (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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