Tensile properties and deformation mechanisms of a fourth-generation nickel-based single crystal superalloy at intermediate temperatures

This paper comprehensively explores the causes of intermediate-temperature brittleness of a fourth-generation Nickel-based single-crystal superalloy through a systematic study of tensile properties and deformation mechanisms at intermediate-temperatures. The research was performed at temperature of 700 °C, 800 °C, 850 °C and 900 °C. The experimental alloy demonstrated the highest yield strength of 914 MPa and worst plasticity at 800 °C. It was found that pure-shearing fracture occurred at 700 °C and 800 °C, while the fracture characteristics of shear fracture and ductile fracture were found at 850 °C and 900 °C. Then, the slip bands extended in the same direction at 700 °C and 800 °C. The phenomenon was different at 850 °C and 900 °C. These deformation traces extended in the different directions. At 700 °C and 800 °C, the partial dislocation with Burgers Vector of a/3 <112> shearing into the γ′ phases was the predominate deformation mechanism, while both the partial dislocation with Burgers Vector of a/3 <112> and the super-dislocation with Burgers Vector of a <110> and a <010> shearing into the γ′ phases were present at 850 °C and 900 °C. Nevertheless, the mechanism of the super-dislocation with Burgers Vector of a <110> and a <010> shearing γ′ phases pervaded in the alloy at 900 °C. In general, it was concluded that the alloy underwent intermediate-temperature brittleness at 800 °C in terms of the changes of fracture features, slip bands and dislocation configurations. The results of this study provided an experimental reference and guidance for improving the safe serviceability of the fourth-generation single crystal superalloy.