Microstructure development in cryogenically rolled oxide dispersion strengthened copper

Abstract

Recently, advanced oxide dispersion strengthened (ODS) copper alloys have been developed using mechanical alloying process as a fusion material. In this study, to develop a superior ODS copper alloy containing 0.5wt% Y2O3, the effect of cryogenic rolling on microstructure development and tensile properties was studied using high resolution EBSD, TEM and tensile tests. During cryogenic deformation of ODS copper, grain structure remains in submicron size scale as a combinatorial result of geometrically effects, nanotwin bundle deformation, interaction of dislocations with fine oxide particles and some diffusional processes including static recovery and recrystallization. Clear microstructural characterizations confirmed nucleation of fine new oriented recrystallized grains mainly on the HABs of 80%cryogenic rolled ODS copper. Quantitative analyses indicated grain boundary migration at room temperature following cryogenic deformation originated from high driving force induced by grain boundary bulging and high mobility induced by vacancies. The tensile properties of cryogenic deformed samples showed superior tensile strength than room temperature deformation leading to UTS: 624 MPa, elt: 5.5%, while saturation of strength between 60%-80% reduction, approved occurrence of softening by diffusional processes.