Creep of ultrafine-grained Al and Cu produced by severe plastic deformation

摘要

Existing results [1] on the creep resistance at elevated temperature of Al (homologous temperature T_(homol)= 0.51) after severe plastic deformation at room temperature on various routes of equal channel angular pressing (ECAP) are supplemented by creep tests at T_(homol) == 0.28 on Cu after severe plastic deformation at room temperature on route B_C of ECAP and multiple uniaxial compression in three orthogonal directions. After severe plastic predeformation by epsilon_(pre) > = 7 Al is fine grained and Cu is ultrafine-grained (UFG). Undeformed coarse-grained (CG) Al and Cu showed distinct work hardening in the primary stage of creep preceding steady state creep. In contrast, the severely preformed Al exhibited a relative maximum of deformation resistance in the form of a minimum creep rate epsilon_(min) followed by work softening leading towards the steady state of creep. epsilon_(min) increases significantly with increasing epsilon_(pre). In the steady state of creep CG Al is slightly more creep resistant than the fine-grained state counterpart. This softening effect is even more pronounced for Cu with epsilon_(pre) = 8 which creeps much faster than Cu with epsilon_(pre) = 1 for all strains epsilon. The softening due to severe plastic deformation is interpreted by increase of the fraction of high-angle grain boundaries in the subgrain structure produced by severe plastic deformation allowing the dislocations to escape through high-angle grain boundaries.