The NSF Faculty Awards for Women Scientists and Engineers recognizes the high quality of the awardee's record in teaching and scholarship, as well as potential research, the academic profession, and the education of future scientists and engineers. Dr. Faber's research under this award is directed at understanding the mechanical behavior of brittle materials. A ubiquitous feature of multiphase ceramics and ceramic- metal systems is residual stress. Such stresses are present due to thermal expansion mismatch strains that cannot be accommodated by deformation during processing. Such stresses in the extreme may serve as a source of failure, or alternatively, may enhance the fracture resistance of the material depending on the sign, the locale, and the magnitude of the stress. Given the pivotal role of residual stresses, it is essential to know both the magnitude and the profile of these stresses to aid in our understanding of fracture and toughening in multiphase materials. It is the aim of this study to characterize residual stresses in two ceramic-based systems, in particular, systems where residual stresses are altered through the application of an external stress or a thermal treatment. Two systems are proposed: (1) a silicon carbide - titanium diboride composite in which stress-induced microcracking and stress-relief on microcracking has recently been observed; and (2) zirconia thermal barrier coatings on metallic substrates in which the residual stresses change after high temperature exposure. X-ray diffraction and, when necessary, neutron diffraction will be the primary tools used to measure residual stresses. The residual stress profile and its change after stressing or heat treatment will be correlated to measured mechanical properties.
