TABLE E-1 Summary of Properties of Various Ceramics for Personnel Armor Application


Material

Designation

Density ρ (g/cc)

Grain Size (μ)

Young’s Modulus E (GPa)

Flex Strength Σ (MPa)

Fracture Toughness K (MPa-m1/2)

Fracture Mode

Hardness (HK-Knoop hardness, HV-Vickers hardness)

HK 2 kg (kg/mm2)

Areal Density


Al2O3

CAP-3

3.90

370

379

4-5

1,440 (HK 1 kg)

1,292

20.2

B4C

Ceralloy-546 4E

2.50

10-15

460

410

2.5

TG

3,200 (HV 0.3 kg)

2,066

13.0

Norbide

2.51

10-15

440

425

3.1

TG

2,800 (HK 0.1 kg)

1,997

13.0

SiC

SiC-N

3.22

2-5

453

486

4.0

IG, TG

1,905

16.7

Ceralloy 146-3E

3.20

450

634

4.3

2,300 (HV 0.3 kg)

16.6

Hexoloy

3.13

3-50

410

380

4.6

TG

2,800 (HK 0.1 kg)

1,924

16.2

Purebide 5000

3.10

3-50

420

455

TG

1,922

16.1

SC-DS

3.15

3-50

410

480

3-4

2,800 (HK 1 kg)

16.4

MCT SSS

3.12

3-50

424

351

4.0

TG

1,969

16.2

MCT LPS

3.24

1-3

425

372

5.7

IG

1,873

16.8

Ekasic-T

3.25

1-3

453

612

6.4

IG

1,928

16.8

SiC (RB)

SSC-702

3.02

45

359

260

4.0

TG

1,757 (HK 0.5 kg)

15.7

SSC-802

3.03

45

380

260

4.0

TG

1,332

15.7

SSC-902

3.12

45

407

260

4.0

TG

1,536

16.2

SiC/B4C (RB)

RBBC-751

2.56

45

390

271

5.0

TG+Ductile Si

1,626

13.3

TiB2

Ceralloy 225

4.5

540

265

5.5

1,849

23.4


NOTE: Areal density in pounds per square foot (PSF): weight of a 12 × 12 × 1 in. panel in pounds; TG, transgranular fracture; IG, intergranular fracture.
SOURCES: CAP-3, SC DS: CoorsTek; Ceralloy, Ekasic-T: Ceradyne; Norbide, Hexoloy:Saint-Gobain; Purbide: Morgan AM&T; SiCN: Cercom (BAE); SSC, RBBC, BSC, SSS and LPS: M Cubed Technologies (MCT). Properties for other manufacturers’ materials are from their respective Web sites except for 2 kg Knoop hardness, grain size, and fracture mode.

growth. Aluminum (Al)7 and alumina8 with carbon promote silicon carbide sintering by means of a solid state mechanism at a temperature over 2000°C, while alumina and yttria lead to a high-density sintered sample by means of a liquid-phase mechanism at temperatures below 2000°C.9

Boron carbide (B4C) is mainly produced by the HP method. The cost of a B4C tile is in the range of $75/lb to $85/lb. The pressureless sintering processes of B4C and densification of B4C by solid state sintering techniques10 are slow, and it is difficult to reach high density due to low self-diffusion. Sintering aids such as SiC, Si, Al2O3, Mg, and Fe have been used to increase the density by means of liquid-phase sintering;11 however, the mechanical performance of liquid-phase-sintered B4C is inferior. It has been established that the presence of B2O3 coatings on B4C particles inhibits densification and facilitates grain coarsening.12 The boria can be removed by heat treatment in a hydrogen environment, which then permits direct contact between B4C–B4C grains, facilitating densification. As a result, the B4C powders with a particle size of approximately 1 μ can then be sintered to 96 percent of theoretical density and with hardness values similar to hot-pressed samples. Methods used to produce pressureless sintered B4C have been developed at the Georgia Institute of Technology and commercialized at Verco Materials,13as well as by larger armor producers such as Saint-Gobain. Armor-grade material of B4C with a zero porosity state can be produced using pressureless sintering combined with hot isostatic pressing.

Both SiC and B4C are harder materials with lower densities than alumina, yet alumina has been widely used in personnel and vehicle armor systems because of its lower

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7Stutz, D., S. Prochazka, and J. Lorenz. 1985. Sintering and microstructure formation of b–silicon carbide. Journal of the American Ceramics Society 68(9): 479-482.

8Sakai, T., H. Watanabe, and T. Aikawa. 1987. Effects of carbon on phase transformation of b–SiC with Al2O3. Journal of Materials Science Letters 6(7): 865-866.

9Omori, M., and H. Takei. 1988. Preparation of pressureless-sintered SiC–Y2O3–Al2O3. Journal of Materials Science 23(10): 3744-3749.

10Thévenot, F. 1990. Boron carbide—A comprehensive review. Journal of the European Ceramic Society 6(4): 205-225.

11H. Kim, H-W., Y-H. Koh, and H-E. Kim. 2000. Densification and mechanical properties of B4C with Al2O3 as a sintering aid. Journal of the American Ceramic Society 83(11):2863-2865.

12Cho, N., Z. Bao, and R. Speyer. 2005. Density and hardness-optimised pressureless sintered and post-hot isostatic pressed B4C. Journal of Materials Research 20 (8):2110-2116.

13Campbell, J., M. Klusewitz, J. LaSalvia, E. Chin, R. Speyer, N. Cho, N. Vanier, H. Cheng-Hung, E. Abbott, P. Votruba-Drzal, W. Coblenz, and T. Marcheaux. 2008. Novel processing of boron carbide (B4C): Plasma synthesized nano powders and pressureless sintering forming of complex shapes. ADM002187. Proceedings of the Army Science Conference (26th). Accessed April 1, 2011.



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