AFMによる銅の低サイクル疲労下における粒界段差成長挙動の観察

概要

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The smooth specimen was machined from 99% purity copper and heat-treated at 940℃ for 9 hours in a vacuum after straining of 3%. The resultant grain size was about 320 μm in average. The push-pull low cycle fatigue tests were performed and the height of step developed at grain boundary during cyclic loading was measured using Atomic Force Microscope (AFM) . According to the AFM observations, steps were generated at grain boundaries with the inclined angles ranged from 60゜ to 80゜ with respect to the loading axis at first tensile loading, and the step heights grew as cyclic straining process progresses. Its growth rate dH/dN reduced with increase in number of straining cycles. The variation in step height during one strain cycle increased with increase in number of loading cycles. The development of step height with progress in the cyclic loading process was plotted against cumulative effective plastic strain range ΣΔε_<pe>, which might dominate fatigue damage. It was found that the growth behavior of grain boundary-step was successfully assessed in terms of ΣΔε_<pe>. The step height at crack initiation H_c decreased with increase in stress level, showing that crack initiation seems to be caused by stress concentrated at the root of grain boundary step.
一般社団法人日本機械学会の論文
2001-06-25