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

研制了获得专利的新型等通道转角挤压可分体式模具，并利用该模具加工了超细晶铜。采用第一道次ECAP工艺在多晶铜材料的晶内形核出亚微米级的位错晶胞。在该工艺下的每一道次，晶粒度都变小，经过8道次，获得了平均直径约为200 nm的UFG铜。在1kmol/m3NaNO2水溶液中进行了低应变速率应力腐蚀试验。结果表明，超细晶铜的应力腐蚀敏感性远低于商品多晶铜。超细晶铜的应力腐蚀开裂主要发生在晶界，沿晶界有适当的门控。另一方面，裂纹在普通晶粒度的铜的内部形核。在UFG铜的裂纹萌生和扩展尖端，观察到晶粒向一定方向长大。在上述水溶液中进行了恒塑性应变幅值的拉伸-压缩疲劳试验。超细晶铜的腐蚀疲劳寿命优于商品多晶铜，且未观察到晶态铜中常见的持续滑移带。通过ECAP工艺，形成了宽度约200 nm的三种剪切织构：{111}&lt；112&gt；，{001}&lt；110&gt；和{112}&lt；110&gt；

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