This project is a critical assessment of the mechanical properties and structure of metals subjected to severe plastic deformation (SPD) processing. The project focuses on equal channel angular forging and on copper as the model material. Numerous reports have been made that SPD methods are capable of producing metals and alloys with a sub-microcrystalline grain size which have desirable mechanical properties and an unusual grain boundary structure. Although other possibilities were kept in mind, the experiments were conducted with the expectation that traditional metallurgical principles would explain the results. This expectation has been fulfilled. Briefly, the elastic behavior of SPD Cu is modified by texture; the tensile behavior is characterized by saturation and early plastic instability; the fatigue performance is marked by cyclic softening; and the creep behavior is dictated by microstructural instability. The microstructure is indeed very fine, having a cell size of ≈0.25 μm with boundaries which are indistinguishable from the original grain boundaries at first glance. However, through careful TEM examination it was determined that there is a more significant population of low angle boundaries in the SPD material than in an annealed polycrystal. Along with diffusion data obtained from creep experiments, this difference provides an explanation for rapid “grain” growth in terms of existing models of subgrain growth and coalescence. Finally, by using polycrystal plasticity simulations to model the equal channel angular forging process, the condition of simple shear has been verified and an accurate prediction of texture has been achieved.
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