Severe plastic deformation in highly immiscible copper alloys: self-organization
Severe plastic deformation (SPD) techniques such as equal channel angular pressing (ECAP), high pressure torsion (HPT), high energy ball milling (BM), accumulative roll bonding (ARB), are well known to refine the microstructures of metals and alloys into non-equilibrium states with nanometer-size grains, and they are gaining widespread interest for processing bulk nanostructured materials. Existing models like the “Driven System Model” and “Effective Temperature Model” can explain existing experimental results for alloys systems with low to moderate heat of mixing, such as Cu-Ag, under SPD. For systems with high heats of mixing, however, e.g. the Cu-Nb, and Ni-Ag system, the previous models cannot be applied, especially when SPD is performed at low temperatures (T<0.25 Tm). Several atomistic computer simulations have been performed but few, if any, experimental results are available to validate the simulation results. In this dissertation, several model experiments were designed specifically to formulate a model for shear mixing in alloy systems with high heats of mixing during low-temperature SPD. We experimentally confirmed by deforming Ag50Ni25Cu25 at liquid N2 temperatures using HPT that dislocation driven diffusion can be biased by thermochemical interactions,. In a related study, CuAg10Nb5-10 was deformed using room temperature HPT to further elucidate the role of chemical interactions during shearing. Nb precipitates were observed to self-organize into nano-precipitates with an average size of ~20nm, independent of the initial Nb precipitate size. . Similarly, a solid solution of CuNb8.8 synthesized by magnetron sputtering was observed also to form nano-precipitates approximately 15 nm in size, during HPT shearing at room temperature and lower.
Self-organization, Copper (Cu) alloy, Severe Plastic Deformation
University of Illinois - Urbana-Champaign
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University of Illinois at Urbana-Champaign