Characterization and control of the fiber-matrix interface in ceramic ...

1. INTRODUCTION
During the last several years, tremendous emphasis has been placed
on developing high-performance materials for use in elevated-temperature
applications. Advanced designs for high-velocity aircraft, efficient
power-conversion systems, and aerospace vehicles call for limited or
extended service at high temperatures in a variety of environments.
Conventional metals and alloys do not possess the thermal stability or
elevated-temperature properties to meet the advanced material
requirements. Ceramic fiber-reinforced metal-matrix composites have been
developed as replacements for conventional metallic materials (2-4), but
most a:-e susceptible to property degradation, particularly under
conditions of thermal cycling in which fiber-matrix thermal expansion
differences lead to internal failure caused by fiber fragmentation.
Many ceramics and glass-ceramics exhibit relatively high strength
and stability at elevated temperatures. These materials have low
densities and are chemically inert. Unfortunately, many conventional
monolithic ceramic materials lack stress-relieving or energy-absorbing
mechanisms, and therefore, are inherently brittle and sensitive to
thermal shock. In an attempt to increase the strength of ceramic
materials and, more importantly, the work of fracture and toughness,
barriers to crack propagation have been incorporated into ceramic
matrices. Particles, platelets, whiskers, and fibers have been used as
reinforcement in ceramic matrices, the most potential being in the areas
of fiber and whisker reinforcement.
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