SEM EBSD and TEM structure studies of α-brass after severe plastic deformation using equal channel rolling followed by groove pressing

摘要

Commercial brass Ms36, 2 mm thick was annealed and deformed in 6 passes in dual rolls equipment with attached equal channel equipment (DRECE). Then, material was deformed again using constrained groove pressing (CGP) by pressing of grooves 4.2 mm thick, and the groove angle of 45°. The experiment was performed 8 times (pressing out grooves and straightening at room temperature). Both methods allowed deformation without changing of the thickness of the sample, which was almost constant near 2 mm. The tensile experiment have shown the Yield Strength YS after 8x groove pressing of 210 MPa and Ultimate Tensile Strength UTS increased 27% up to 430 MPa. At the same time total elongation decreased from 34 to 15%. The structure of the material after DRECE 6 passes was investigated using conventional TEM and have shown only rather uniform distribution of dislocations. After additional 8 groove pressing experiment, frequent, narrow deformation twins were observed accompanied by the formation of subgrains. The orientation imaging microscopy have shown average grain size after DRECE process near 5μm, which decreased after 8 groove pressing passes down to 2.9μm. The fraction of low angle boundaries (below 5°) decreased after groove pressing down to 73% from 85% after DRECE process and annealing, while the fraction of high angle grain boundaries (＞15°) increased after groove pressing up to 24% from 14%, however the total length of high angle boundaries increased more than 2 times since grain size decreased. The structure studies have shown rather mild effect on the grain refinement of both methods and they have to be modified to obtain material approaching nanosize range.