In order to investigate the growth mechanism of a fatigue crack of Ni-based super alloy at ultrasonic frequency, ultrasonic fatigue and rotting bending fatigue tests were carried out for Inconel 718 in ambient air and in N<SUB>2</SUB> gas using plain and notched specimens and the results in both tests were compared by focusing on the effects of strain rate and environment. In ambient air, fatigue strength was higher in ultrasonic fatigue than in rotating bending fatigue in plain specimen, while the results in notched specimen were the reverse. Many transgranular cracks and cleavage like cracks were observed on the fracture surface in ultrasonic fatigue in addition to striation and transgranular facets observed in rotating bending fatigue and there was no difference in the fracture mechanism between plain specimen and notched one. Moreover, these effects of frequency on the growth mechanism of a crack in ambient air were nearly the same in N<SUB>2</SUB> gas, though fatigue strength in N<SUB>2</SUB> gas was higher than that in air. The increase in fatigue strength in N<SUB>2</SUB> gas was mainly caused by the retardation of a crack initiation.
|Translated title of the contribution||Effect of Loading Frequency on Fatigue Strength of Ni-Based Super Alloy|
|Number of pages||8|
|Journal||Nihon Kikai Gakkai Ronbunshu, A Hen/Transactions of the Japan Society of Mechanical Engineers, Part A|
|Publication status||Published - Oct 25 2006|