Creep and Superplasticity in Materials with Ultrafine Grain Sizes

University Of Southern California, Los Angeles CA

Investigators

Abstract

The grant investigates processing and characterization of aluminum and magnesium alloys via severe plastic deformation (SPD) using equal channel angular pressing (ECAP). Appropriate dispersion of second phase particles are expected to pin the grain boundaries thereby retaining ultra fine grain size in submicron range. The relatively large range of grain sizes, from micron to nanometers, will provide an opportunity to unambiguously determine the creep and superplastic properties when the grain sizes are extremely small and to obtain fundamental information that will be needed in the longer term for the successful utilization of these materials. A goal of the study is to utilize advanced techniques such as atomic force microscopy to systematically investigate cavitation and grain boundary sliding following ECAP as well as deformation of the processed materials. Along with superplasticity, the underlying mechanisms of diffusional creep will be investigated. From a scientific viewpoint, there are well-developed theories predicting the plastic flow (or creep) of metals when the grain sizes are small but these theories remain open to considerable speculation and there has been much discussion and disagreement concerning their general validity. The study is expected to fill in the gaps and provide scientific understanding of deformation mechanisms at varied grain sizes and in a range of applied stresses and strain-rates. In addition, the investigations will have technological applications for forming operations. The grant avails participation of graduate and post-graduate students along with undergraduate senior projects. The project is co-funded by metals program in the division of materials research and manufacturing in the division of manufacturing and industrial innovation.