DEVELOPMENT OF A PRESSURELESS SINTERED SILICON CARBIDE MONOLITH AND SPECIAL-SHAPED SILICON CARBIDE WHISKER REINFORCED SILICON CARBIDE MATRIX COMPOSITE FOR LIGHTWEIGHT ARMOR APPLICATION

摘要

Thick tiles were fabricated to address higher ballistic threats in a continuing effort to develop a pressureless sintered a-silicon carbide ceramic for lightweight armor applications. Tiles with a thickness of 1.9 cm and 2.8 cm were pressed and sintered from a spray-dried SiC powder and evaluated for density and mechanical properties. These thick tiles exhibited a gradient in density and mechanical properties at the center of the tile with larger gradients present in the 2.8 cm thick tile. The Modulus of Rupture ranged from a low of approximately 300 MPa to a maximum of 500 MPa. It is concluded that adjustments to green part fabrication methods and/or to the sintering schedule are required to eliminate gradients in density and mechanical properties. Additionally, composites utilizing shape-modified, silicon carbide ceramic whiskers are investigated with the goal of increasing the toughness of an otherwise brittle silicon carbide ceramic. The ceramic reinforcement whiskers are heat treated at high temperature in an inert atmosphere to produce rounded ends (bone-shaped whiskers) via atomic transport. The whisker-reinforced composite exhibited reduced sintered density and exaggerated grain growth. Physical/mechanical properties, photomicrographs and ballistic test results are reported and compared to commercial, armor-grade silicon carbide.