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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