9803045 Lavernia This award provides support for the acquisition of a nanoindenter to serve the research needs of several ongoing, as well as future research programs dealing with the synthesis-structure-property studies of nanocrystalline materials at the University of California at Irvine. Nanocrystalline materials provide the material scientist/engineer with the unique opportunity to achieve combinations of properties that are otherwise unachievable with equilibrium materials. For example, nanophase ceramics are reported to exhibit unusually high ductilities, whereas nanophase metals are noted to exhibit ultra-high hardness values. To that effect, the objective of the research program proposed herein is to investigate the various aspects of mechanical properties of nanocrystalline materials, including powders, coatings and bulk samples produced at the University of California at Irvine. More specifically, the research program will investigate: 1) the evolution of microhardness of various metals, ceramics and cermets as a function of grain size during ball milling, 2) experimental study of the microhardness depth distribution in thermal sprayed nanocrystalline coatings as a function of grain size, porosity and second phase dispersoids (dependent on cooling rate and the coating thickness), 3) Young's modulus behavior (depending on grain size and porosity of various nanocrystalline materials), in particular those present in small dimensions, 4) wear resistance of nanocrystalline coatings with low porosity, 5) time dependent properties (strain rate sensitivity, creep and stress relaxation) of nanocrystalline coatings, and 6) yield strength of nanocrystalline coatings. To accomplish these objectives the following approach is proposed. First, mechanical alloying will be used to synthesize nanocrystalline powders of Al based alloys, Inconel 718, Ni and WC/Co, emphasizing the control of contamination, particle size distribution and particle morphology. Second , the mechanically alloyed nanocrystalline powders will be consolidated using two different approaches: hot pressing, hot isostatic pressing or hot extrusion and high velocity oxygen-fuel (HVOF) thermal spraying to prepare nanocrystalline bulk samples or coatings. Third, the physical and mechanical properties of the as-milled, consolidated and HVOF thermal sprayed nanocrystalline powders will be studied in detail, paying particular attention to various nanocrystalline coatings prepared by high velocity oxygen-fuel spraying. Moreover, Hall-Petch strengthening mechanisms in the consolidated nanocrystalline materials will be studied. %%% This instrument will be shared by students and faculty across the campus at the University of California at Irvine. It is hoped that this research will impact the growth of nanocrytalline materials to create bulk 3-D samples having grain sizes less than 100 nanometers, which would dramatically increase the performance of all materials that display this behavior. This would impact strength of materials, corrosion resistance, and improve mechanical performance. ***
