耐熱超合金の高温低サイクル疲労き裂進展における平均応力と酸化支配型圧縮ひずみ保持効果

概要

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Crack growth mechanisms considering the oxidation and mean stress effect for nickel-and cobalt-based superalloys are investigated.Crack growth tests, which employ the strain waveform to take into account compressive strain hold, were carried out.Cracks propagated at the dendrite boundary in both superalloys and crack growths were accelerated by increasing the compression hold time.Oxidation around the crack tip was detected by EPMA analysis and accelerated the fatigue crack growth.In compressive strain hold test, the increment of non-dimensional crack growth rate by oxidation was proportional to about 1/3power of the compressive hold time.Furthermore, mean stresses were increased by compressive strain hold in the nickel-based superalloy, which has a high proof strength even at high temperature.This mean sress effect for crack growth was also discussed.A crack growth model that considers effects of both oxidation at crack tip and mean stress was derived.
2000-01-25