Ronald Leroy Stewart

The Brittle to Ductile Transition In MgAl2O4 Spinel

The brittle to ductile transition in ceramic materials is often referred to as the ductile to brittle transition in the metallurgical literature.1–4 It has been a topic of interest in crystalline ceramics for nearly half a century, since the early efforts to develop “ductile” ceramics in the 1950’s. Although there have been efforts to address the topic by examining various phenomena, including the indentation hardness and the creep deformation, this transition is best described in the traditional sense of the energy dissipation during crack extcnsion as a function of temperature.

Fracture of Sic Fiber/Glass-Ceramic Composites as a Function of Temperature

SiC fiber reinforced LAS and BMAS glass-ceramic matrix composites have been recently developed. They show a combination of high strength and exceptional toughness over a wide temperature range. However, they suffer from significant embrittlement over the temperature range of 800°-1100°C when tested in air. The objective of the work was to understand this embrittlement behavior.