Fig. 1 Microstructures of as-cast K416B alloy: a dendritic and inter-dendritic structures, b carbide morphologies and EDS analysis, c γ/γ′ phase in dendrite and inter-dendrite regions

Fig. 2 XRD patterns of the K416B superalloy with thermal exposure for different hours

Fig. 3 DTA cooling curve of as-cast K416B alloy

Fig. 4 SEM images of γ′ precipitates in K416B alloy in inter-dendritic region after thermal exposure for different hours at 1000°C: a 100 h, b 500 h, c 1000 h, d 1500 h

Fig. 5 SEM images of microstructures in K416B superalloy after thermal exposure for different hours at 1000 °C: a, b 500 h, c, d 1500 h

Fig. 6 Variation of the area fractions of two kinds of carbides in K416B alloy after thermal exposure for different hours at 1000 °C

Fig. 7 Tensile properties of K416B alloy after thermal exposure for different hours at room temperature (σ0.2—yield strength, σb—tensile strength, δ—elongation)

Fig. 8 Morphologies of the regions near the fracture after the alloy thermal exposure for different hours at 1000 °C: a, b as-cast, c, d 500 h, e, f 1500 h

Fig. 9 SEM images of tensile fracture of K416B alloy at room temperature after thermal exposure for different hours at 1000 °C: a, b as-cast, c, d 500 h, e, f 1500 h

Fig. 10 SEM images of tensile fracture morphologies of K416B superalloy at room temperature after thermal exposure for different hours at 1000 °C: a, d, g the macroscopic morphologies of the as-cast alloy, the alloy was exposed for 500 h and 1000 h, respectively; b, e, h high magnified morphologies of different alloys; c, f, i back scattering images of b, e, h

Fig. 11 Schematic diagram of crack initiation and propagation near grain boundary at room temperature after thermal exposure for different hours at 1000 °C