Ceramics made from clay have been used as construction materials for thousands of years and are renowned for their ability to resist damage from water, chemicals, oxidation and most importantly - heat. Ceramics can stand up to temperatures that would melt most metals. However, traditional ceramics also suffer from a serious deficit brittleness. Today's advanced ceramics for extreme structural applications are much stronger and tougher. They're reinforced with ceramic fibers to form composites that can be structured along the lines of natural materials such as bone and shells. Jet or turbine gas engines made from ceramic composites would weigh considerably less than today's engines and operate at much higher temperatures. This translates into far greater fuel efficiencies and reduced pollution.
Still, while ceramic composites are far less prone to fracture than their clay ancestors, tiny cracks can form and grow within their complex microstructures, creating potentially catastrophic problems.
"Like bone and shells, ceramic composites achieve robustness through complexity, with their hierarchical, hybrid microstructures impeding the growth of local damage and preventing the large fatal cracks that are characteristic of brittle materials," Ritchie says. "However, complexity in composition brings complexity in safe use. For ceramic composites in ultrahigh temperature applications, especially where corrosive species in the environment must be kept out of the material, relatively small cracks, on the order of a single micron, can be unacceptable."
Exactly how micro-cracks are restrained by the tailored microstructures of a ceramic composite is the central question for the m
|Contact: Lynn Yarris|
DOE/Lawrence Berkeley National Laboratory