The influence of long-term thermal exposure on intermediate temperature brittleness behavior of a Nickel-base superalloy

Abstract

The morphology of gamma' precipitates and intermediate temperature brittleness behavior of samples aged at 700 degrees C and 800 degrees C for different aging times then tested at 700 degrees C and 800 degrees C, is investigated. The results show that the gamma' precipitates remain cuboidal in shape and regularly aligned in the matrix after long-term thermal exposure at 700 degrees C and 800 degrees C. The size of secondary gamma' precipitates increases greatly after long-term exposure at 800 degrees C. The growth of gamma' precipitates would enhance the possibility of dislocation-dislocation and dislocation-gamma' precipitate interactions, resulting in a high yield stress after long-term thermal exposure. For samples tested at 700 degrees C, the elongation of samples aged at 700 degrees C and 800 degrees C gradually decreases with increasing aging time. However, for samples tested at 800 degrees C the elongation of samples aged at 700 degrees C and 800 degrees C gradually increases, and the elongation is higher for than samples tested at 700 degrees C. In addition, the gamma' precipitates are sheared easily by dislocations after long-term thermal exposure. The intermediate temperature brittleness behavior is not eliminated during long-term thermal exposure at intermediate temperatures, while the intermediate temperature brittleness behavior takes place at the lower temperature. Additionally, gamma' precipitates sheared by dislocations is dominant deformation mechanism. (C) 2012 Elsevier Inc. All rights reserved.