Lance Blakeman

Milwaukee School of Engineering
Advisor: Professor Rodney Trice
Project: Development of Oriented b-Si3N4 for Ballistic Protection

Introduction

Materials that provide ballistic protection are intended to shatter an incoming projectile with a hard surface and then prevent the projectile and any fragments from penetrating. Ceramics have high fracture toughness, hardness and flexural strength making them suitable for armor. Currently b-Si3N4 can be used for armor in the low to intermediate projectile velocity range.

Previous studies have shown that the elongated b grains are associated with toughening mechanisms that increase the fracture toughness of b-Si3N4 over a -Si3N4. It is proposed that if b-Si3N4 grains could be fabricated with layered grain alignment, increased mechanical properties such as fracture toughness, flexural strength, and hardness could possibly be achieved. These improved properties could enhance ballistic protection.

Objectives

  • Prepare samples of oriented b-Si3N4 for testing
  • Document methods for producing these samples in the Purdue MSE laboratories
  • Characterize these samples.

Experimental Approach

  • Methods of production devised for fibrous monolithic ceramics are adapted.
  • Si3N4 powder consisting of 99% b grains,1% a grains, and sintering aids are mixed 50 vol% / 50 vol% with a polymer binder.
  • This mixture is heated and extruded through a spinneret to produce a filament.. The flow of liquid in this extrusion process aligns the long b grain seeds in the extrusion direction.
  • These filaments are wound into sheets, cut out, heated, and pressed in a die to stick them together.
  • The polymer is slowly burned out in a programmable furnace leaving just ceramic and sintering aids.
  • The resulting ceramic powder is hot pressed to sinter the ceramic and cause the a grains to transform into more stable and desirable b grains.
  • XRD is used to verify a to b transformation.
  • The resulting samples must be machined into the desired part or specimen.

Results

  • Two Si3N4 samples with 28 filament-sheet layers aligned at 0o/90o between layers (cross-ply).
  • One Si3N4 sample with unaligned grains for comparison.
  • One bilayer sample with a layer of unaligned b-Si3N4 and a cross-ply layer of fibrous monolithic ceramic for possible future testing.
  • Documentation on how to use equipment at Purdue to produce these samples was also produced.

Fig. 1a. Polymer/Silicon Nitride mixture being extruded into a filament.
Fig. 1b. Large view of extruded filament with inner material cut away and simulated grains remaining.
Fig. 2. Warm Pressed 0o/90o sample.		  

Final Presentation