Structural instabilities during cyclic loading of ultrafine-grained copper studied with micro bending experiments

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• 作者：M.W. Kapp^a ; ^{marlene.kapp@stud.unileoben.ac.at} ; T. Kremmer^a ; ^b ; C. Motz^a ; ^c ; B. Yang^a ; R. Pippan^a
• 关键词：Severe plastic deformation ; Low cycle fatigue ; Cyclic softening ; Grain growth ; Grain boundary migration
• 刊名：Acta Materialia
• 出版年：2017
• 出版时间：15 February 2017
• 年：2017
• 卷：125
• 期：Complete
• 页码：351-358
• 全文大小：2505 K
• 卷排序：125

文摘

The cyclic mechanical properties and microstructural stability of severe plastically deformed copper were investigated by means of micro bending experiments. The ultrafine-grained structure of OFHC copper was synthesized utilizing the high pressure torsion (HPT) technique. Micron sized cantilevers were focused-ion-beam milled and subsequently tested within a scanning electron microscope in the low cycle fatigue regime at strain amplitudes in the range of 1.1 − 3.2 ∗ 10−3. It was found that HPT processed ultra-fine grained copper is prone to cyclic softening, which is a consequence of grain coarsening in the absence of shear banding in the micro samples. Novel insights into the grain coarsening mechanism were revealed by quasi in-situ EBSD scans, showing i) continuous migration of high angle grain boundaries, ii) preferential growth of larger grains at the expense of adjacent smaller ones, iii) a reduction of misorientation gradients within larger grains if the grain structure in the neighborhood is altered and iv) no evidence that a favorable crystallographic orientation drives grain growth during homogeneous coarsening at moderate accumulated strains, tested here.