Miaoslructure and Mechanical Properties of the Ultrafine-Grained Copper Thbe Produced by Severe Plastic Defonnation

In this paper. cyclic flaring and sinking (CFS) as a new severe plastic deformation (SPD) method was employed toproduce the ultrajine grain (UFG) copper tubes. The extrafriction has eliminated in the CFS method that provided the possibility for production of longer UFG tubes compared to the other SPD methods. This process was done periodically to apply more strain and consequently finer grain size and better mechanical properties. The CFS was performed successfUlly on pure copper tubes up to eleven cycles. Mechanical properties of the initial and processed tubes were extracted from tensile tests in the different cycles. The remarkable increase in strength and decrease in ductility take placed in the CFS-ed tubes. The materialflow behavior during CFSprocessing was analyzed by optical microscopy (OM), and a model was presented for grain refinement mechanism of pure copper based on multiplication and migration of dislocations (MMD). This mechanism caused that the initial grains converts to elongated dislocation cells (subgrains) and then to equiaxed ultrafme grains in the higher cycles. The CFS method refined the microstrocture tofine grains with the mean grain size of 1200nmfrom initial coarse grain size of 40pm