Takeo Yokobori1 and Hashime Shimura2
1Faculty of Engineering, Tohoku University, Sendai
High temperature creep behavior of Nimonic 75 alloy was studied under the test condition of the cavitation fracture. At what stage of the creep curve the cavity would nucleate and how it grows was observed continuously on the specimen surface by using a high-temperature microscope. In order to examine the shape of the cavitation fracture surface, electron fractomicrographical observations were made. Mesurement of angular distributions for grain boundary cavities was also carried out.
From the studies the following conclusions are obtained:
(1) The cavities on the surface and the interior of the specimen are initiated during the stage of transient creep and will grow during the stage of steady creep.
(2) The grain boundary sliding appears to contribute to the initiation and the growth of the crack of cavity type.
(3) The most probable value of the direction of the grain boundary at which cavities initiate is in agreement with the direction of the maximum shear stress component of applied stress.
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