KSEF R&D Excellence: Micromechanical Behavior of Nanophase Al-Mg Alloys

Nanostructured AI-Mg alloys have great potential for aerospace applications because of their low density and high stiffness. Owing to the nanoscale size, nanostructured AI-Mg alloys exhibit unique mechanical, electronic, chemical etc. properties, such as increased strength and improved ductility that result from reducing critical scale size from macroscopic and microscopic regime to nanoscale. Navy, Air Force and manufacturers of aircraft engines are very interested in taking advantage of the nanostructured materials to improve the performance of parts. To this end, nanomechanical and micromechanical testing techniques must be developed by which the fundamental mechanisms controlling the micromechanical deformation of the nanostructured materials can be understood from measurements. This proposed project comprises two parts. The main objective of the first part is: . To use both impression and nanoindentation techniques to measure the time-dependent plastic deformation of the nanostructured materials especially the nanostructured AI-Mg alloys as a function of equal channel angular pressing (ECAP) and the post-annealing process. . To establish the continuwn theory of plasticity for describing the cre€:p behavior of the nanostructured materials. In our efforts we will continue and extend the promising study by Yang and Li (University of Rochester) by using the impression test, where they successfully measured the creep and stress relaxation behavior of Pb-Sn eutectic alloy and other metallic materials. The second part of the proposal concerns the effect of grain size and post-heat treatment on the contact fatigue of the nanostructured materials formed by the ECAP process. Our objectives are as follows: . To study the effect of grain refinement on the indentation crack nucleation and propagation of the nanostructured AI-Mg alloys with a view to building up a model that quanti11es the contribution of grain boundary effect on the crack behavior. . To investigate the possible change in grain structure caused by the ECAP process as well as the effect of this change on the contact crack propagation. . To study how different stress profiles affect the contact fatigue properties of the AI-Mg alloys, and to determine the process condition for optimal fatigue performance. The research results and data will be used as preliminary results to help the researche:rs at the University of Kentucky to seek federal funding to organize a research team and to conduct investigation of nanostructured materials.