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

The morphology of γ' precipitates and intermediate temperature brittleness behavior of samples aged at 700 °C and 800 °C for different aging times then tested at 700 °C and 800 °C, is investigated. The results show that the γ' precipitates remain cuboidal in shape and regularly aligned in the matrix after long-term thermal exposure at 700 °C and 800 °C. The size of secondary γ' precipitates increases greatly after long-term exposure at 800 °C. The growth of γ' precipitates would enhance the possibility of dislocation–dislocation and dislocation–γ' precipitate interactions, resulting in a high yield stress after long-term thermal exposure. For samples tested at 700 °C, the elongation of samples aged at 700 °C and 800 °C gradually decreases with increasing aging time. However, for samples tested at 800 °C the elongation of samples aged at 700 °C and 800 °C gradually increases, and the elongation is higher for than samples tested at 700 °C. In addition, the γ' 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, γ' precipitates sheared by dislocations is dominant deformation mechanism.

► The yield stress drops sharply at the early stage of aging. ► The elongation increases with the prolongation of aging time. ► The intermediate temperature brittleness takes place at the lower temperature.