Polymer-Derived In-Situ Metal-Matrix Nanocomposites: A New Paradigm in Processing, Structure, and Properties of Dispersion Strengthened (copper) Alloys

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TECHNICAL SUMMARY: A nanoscale dispersion of stable, non-coarsening ceramic particles into a metal matrix is a precondition for metallic composites that resist creep at high homologous temperatures. The goal of this program is to develop the scientific underpinnings for a new method for dispersing fine particles of a ceramic phase into a metal, and understanding how they influence the mechanical properties. In this method the ceramic is introduced into the metal as a polymer, which is then pyrolyzed in-situ to create the nanodispersed ceramic phase. This research program will explore the basic mechanisms for the in-situ conversion of the polymer into the ceramic. Copper, dispersed with nanoparticles of a polymer-derived ceramic phase constituted from Si-C-N-O, will be employed as the "model" material system for this investigation. The microstructural stability and the creep and creep fracture behavior of the alloy at temperatures approaching 950 °C (about 0.9 of the melting temperature) will be investigated. Fundamental mechanisms that include how the size and spacing, and the structure and bonding at the particle-matrix interface control the climb of dislocations and the nucleation of voids under mechanical loading at high temperatures, will be studied. A key issue is to elucidate how the interfacial bonding influences the threshold stress, the ultimate goal being to achieve a threshold stress that approaches the Orowan upper bound for the escape of dislocations pinned by hard particles. Atomistic modeling isexpected to inform the experimental results.NON-TECHNICAL SUMMARY: New nanomaterials with unusual properties are often highly complex, both in the way they are made and how they perform. For them to be successfully implemented into next-generation systems, their performance must be underpinned by scientific understanding and models. This research program is dedicated to the science and development of novel high temperature metallic alloys that are potentially important for future engineering systems. Their novelty lies in a polymer route to the creation of a highly stable, nanoscale dispersion of ceramic particles in a metal matrix. The research plan includes intimate international collaborations in Austria and Germany that provide important expertise in atomic scale characterization and modeling. The program has an aggressive plan for dissemination of the scientific outcomes of this research, primarily through International Meetings that are held every two years in Boulder, Colorado.