A study on embrittlement and fatigue behavior of ultra-fine grain crystals under corrosive environment

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New dividable die for equal channel angular pressing (ECAP) which was gotten a patent was produced, and using this die ultra fine grain (UFG) copper was manufactured. Dislocation cell that has submicron size was nucleated in the course grain of polycrystalline copper materials by first pass of ECAP process. By each pass under the processes, grain size became small, and after 8 passes, UFG copper having about 200nm in average diameter was obtained.Low strain rate stress corrosion test (SSRT) was performed under 1 kmol/m^3 NaNO_2 aqueous solution. From the results, the SCC susceptibility of UFG copper was extremely lower than that of commercial polycrystalline copper. SCC was preferentially initiated at the grain boundary and proper gated along the grain boundary in UFG copper. On the other hand, the crack was nucleated at the interior of the ordinary grain size copper. At the crack tips initiated and propergated in UFG copper, grain growth, which grows to a certain direction, was observed.Tension-compression fatigue test with constant plastic strain amplitude was performed under the above aqueous solution. Corrosion fatigue life of UFG copper was superior than that of commercial polycrystalline copper, and no persistent slip bands that is usually observed in course grain copper was observed.Grain refining process during ECAP process was discussed, using single crystals having 7 kinds of axis orientation. By ECAP process, 3 kinds of shearing texture which was about 200nm in width and were {111}<112>, {001}<110> and {112}<110> orientation, were formed