Effect of cryogenic impact deformation and subsequent annealing on microstructure and microhardness of pure copper

This article presents an application of cryogenic impact deformation in effective grain refinement in coarse-grained copper. Ultrafine-grained microstructure was processed by means of cryogenic impact deformation using an air hammer with an initial impact velocity of 7.35 m s(-1). For strain epsilon=2.21, TEM observation showed that the initial equiaxed coarse grains (18 mu m) evolved into a lamellar structure of submicron size narrow domains delineated by low-angle grain boundaries. The microhardness of the deformed sample increased from 74.2 +/- 1.2 HV to 118.3 +/- 1.8 HV. Subsequently annealed at 190 degrees C for 60 min led to a significant reduction of dislocation density. Elongated ultrafine grains (with a mean width of 175 nm) embedded with remaining nanoscale deformation twins were observed in the annealed sample. This study highlights the potential of cryogenic impact deformation to produce bulk ultrafine-grained materials. (C) 2015 Elsevier B.V. All rights reserved.