Deformation and Failure of Nanocrystalline Metals

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9980213EbrahimiThe aims of this project are to evaluate experimentally the mechanical behavior of FCC and BCC nanocrystalline metals and to develop mechanistic deformation models for various grain size regimes. The deformation and failure mechanisms of pure Ni, Ni-Cu and Fe-Ni alloys are studied by characterizing yielding, strain hardening, plastic instability, and fracture as functions of temperature and strain rate. Analysis of such results in conjunction with detailed microstructural analyses should lead to a systematic understanding of the operating mechanisms. Some alloy variations are examined. When copper is added to nickel the stacking fault energy is reduced significantly, thereby affecting the generation and accumulation of dislocations. A small increase in the concentration of nickel in Fe-Ni alloys results in a change of crystal structure from BCC to FCC. In this way, the effect of crystal structure can be investigated at comparable compositions. %%%Despite an expansion of research in the past decade on nanostructured metallic alloys, there have been few experimental studies that investigate the mechanical properties of these materials. Metallic solids with crystallite sizes less than approximately 100nm are referred to as nanocrystalline metals. These materials have attractive properties, including very high strength levels. The outcome of this research will contribute to the development of metallic structures that are as strong as hardened steels (700 - 1800 MPa) but have better physical properties (e.g. magnetic properties) and superior corrosion resistance.***