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Development of Oriented β -Si 3 N 4 for Ballistic Protection Final Presentation. Lance Blakeman Advisor: Professor Trice. Ballistic Protection. Break projectile using a very hard surface Prevent projectile or fragments from penetrating Absorb the residual energy using soft backing.

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Development of oriented si 3 n 4 for ballistic protection final presentation
Development of Oriented β-Si3N4 for Ballistic ProtectionFinal Presentation

Lance Blakeman

Advisor: Professor Trice

Ballistic protection
Ballistic Protection

  • Break projectile using a very hard surface

  • Prevent projectile or fragments from penetrating

  • Absorb the residual energy using soft backing


Many ceramics are suitable for portable armor.

They have high: hardness, fracture toughness, flexural strength.

low: density

Marc André Meyers, Dynamic Behavior of Materials, John Wiley & Sons, Inc., New York, New York, 1994.

Hot pressed ballistic materials
Hot-Pressed Ballistic Materials

All data from

Microstructure of si 3 n 4

α Grains

Equiaxed – dimensions ≈ in all directions

99% of grains in typical powder sample following formation

β Grains

Hexagonal rods. Can grow, be elongated further

1% of grains in a typical sample of powder

Microstructure of Si3N4

Image Source: R.W. Trice and J.W. Halloran, “Mode I Fracture Toughness of a Small-Grained Silicon Nitride: Orientation, Temperature, and Crack Length Effects,” J. Am. Ceram. Soc., 82 [10] 2633-40 (1999).

Beta grain effects
Beta Grain Effects

  • In Si3N4, elongated β grains have been found to greatly increase fracture toughness

  • β grains tend to deflect cracks or display frictional bridging rather than being cut by cracks

  • Toughening mechanisms expend more energy

Micrograph Source: Rodney W. Trice and John W. Halloran, “Mode 1 Fracture of a Small-Grained Silicon Nitride,” J. Am. Ceram. Soc., 82 [10] 2633-40 (1999).

Project motivation goals
Project Motivation/Goals

  • Precisely aligned, layered β may provide better ballistic protection

    Project Goals

  • Develop and document practical methods to create aligned β-Si3N4 in lab

  • Create Samples of aligned β-Si3N4 in layers with 0°/90° (cross-ply) orientation

  • Examine samples using x-ray diffraction, scanning electron microscopy, and mechanical tests

Experimental procedure
Experimental Procedure

  • Use similar procedures developed for work with fibrous monolithic ceramics and alignment1

  • Start With Si3N4 Powder (contains α and β grains)

  • Si3N4 powder is combined with polymer binder in 50 vol% / 50 vol% mixture

  • Alumina and Yttria added as sintering aids

    • 92g Si3N4 : 6 g Y2O3 : 2 g Al2O3

1Desiderio Kovar, Bruce King, Rodney Trice, and John Halloran, “Fibrous Monolithic Ceramics,” J. Am. Ceram. Soc., 80 [10] 2471-87 (1997).

Making filament sheets
Making Filament Sheets

  • Filament Winding

  • Adhering Filaments Together

    • Hair spray used

    • Super glue used to repair breaks and make splices

  • Finished ribbon cut into circular plies that will fit within die

Warm pressing
Warm Pressing

  • Plies are stacked in 2½” diameter cylindrical die at desired angle.

  • Release agent – Polyethylene Glycol 6,000 applied to die

  • Die heated to 170°C

  • Sample is pressed with load frame

    • Causes filaments to adhere to one another

    • ≈2.5 MPa of pressure is applied via axial force using a load frame

Binder burnout
Binder Burnout

  • Polymer and other hydrocarbon contaminants (hairspray, release agent, etc.) are removed through combustion

  • Slow burn prevents distortion from CO2 which would disrupt alignment

Hot pressing
Hot Pressing

  • Specifics

    • Graphite dies used to apply heat and uniaxial load for 1-4 hours

    • Heated to 1750°C (600°C/hr)

    • Pressure of 25 MPa (1.75 hr)

    • Nitrogen Atmosphere

    • Part needs to be machined into desired shape afterwards

  • Purposes

    • Sintering

    • Grain Transformation α→β

    • β grain growth

Grain transformation
α→β Grain Transformation

  • Occurs under high temperature, high pressure, low oxygen conditions.

  • Sintering agents interact with silica to form a liquid

  • α has greater solubility, more unstable.

  • This drives it into solution to precipitate as more stable, less soluble β grains.

  • New β grains will align themselves with the preexisting aligned grains (Seeds)


  • Five Samples were completed up to the hot pressing step

  • Practice sample of 0°/90°Si3N4/BN (Fibrous Monolith)

  • Unaligned Si3N4 (control sample)

  • Unaligned Si3N4/ 0°/90°Fibrous Monolith

  • 2 Samples of 0°/90° Aligned Si3N4

Factors investigated
Factors Investigated

  • Filament winding techniques

  • Minimizing damage in cutting plies

  • Discovering adequate warm pressing pressures for various samples

  • Controlling warm pressing pressures

  • Determining adequate warm pressing temperatures

  • Minimizing damage in removing sample from die

  • Documentation of how to produce these samples successfully in the Purdue MSE labs was produced.

Current status
Current Status

  • Hot press thermocouple was replaced

  • Still is a problem in the Honeywell Digital Control Programmer (DCP-700) that controls temperature

  • Tried to swap some boards with the controller for pressure. Failed to locate problem. Slightly different models.

  • Sent in for repair on July 7, no parts available.

  • Currently exploring options to replace/repair controller

  • These samples must be hot pressed. Pressureless sintering will not work for these particular samples.

Future work
Future Work

  • Hot-pressing all samples

  • Machining Samples

  • X-Ray Diffraction

    • to verify α→β transformation

    • to look for contaminants like SiC

    • to verify a high degree of grain alignment of β-Si3N4 grains



Future work1
Future Work

  • SEM to observe grain alignment directly

  • Vickers Hardness Testing

    • ASTM Standard C 1327-99

    • Apply known load using diamond


    • Measure indentations

  • ASTM Standard C 1327-99

Future work2
Future Work

  • Fracture Toughness

    • ASTM C 1421-01b

    • precrack is introduced into specimen and is propagated by loading in three point fixture

  • Flexural Strength

    • ASTM C 1161-02c

    • specimen loaded to fracture in four point fixture

    • uses

  • ASTM Standard C 1421-01b

  • ASTM Standard C 1161-02c


  • Dr. Rodney Trice

  • Dave Roberts

  • Emily Pickens

  • Hyun Jun Kim

  • National Science Foundation for funding


Source: Rodney W. Trice, Ph.D. thesis. University of Michigan, 1998.

Fibrous monoliths
Fibrous Monoliths


  • BN coated Si3N4 filament

  • Creates a weak interface

  • Failure by delamination rather than brittle fracture