A Study On The Fracture Of GH4169Superalloy During Plastic Deformation

Due to the excellent mechanical properties, good corrosion resistance and breaking tenacity, GH4169superalloy is the most widely used superalloy in the aerospace field. However, an accurate control of the complex microstructure and forming defects is a bottleneck problem in the hot working process of GH4169superalloy. Therefore, investigating the flow behavior, microstructure evolution and the damage and fracture during the hot forming have great theoretical significance and engineering application value. In this dissertation, the effects of deformation parameters and initial aging time on the flow behavior, microstructural evolution and fracture characteristics of GH6169superalloy are discussed in detail by experimental and theoretical analysis. The results and achievements of the dissertation are as follows:(1) The effects of deformation parameters and initial aging time on the flow behavior of the studied GH4169superalloy were studied by uniaxial tensile test under elevated temperature. Results show that, the content of δ phase increases with the increase of initial aging time. In the work hardening-dynamic recovery stage, the existence of δ phase increases the rate of work hardening, and thus the peak stress increases with the increase of initial againg time. In the dynamic softening stage,δ phase can induce the nucleation of dynamical recrystallization and inhibit the growth of grains. Therefore, the extent of flow softening increases with the increase of initial aging time.(2) The effects of deformation parameters on the dynamic recrystallization during the hot tensile deformation were discussed. Results show that the dynamic recrystallization occurs during the hot tensile deformation of the solution treated material. With the increase of deformation temperature and decrease of strain rate, the fraction of recrystallized grains increases.(3) The effects of deformation parameters and initial aging time on the fracture mechanism were studied by analyzing the fracture morphology characteristics. Results show that the combined effects of the localized necking and microvoid coalescence cause the final ductile fracture of specimens. For the solution treated material, microvoids mainly nucleate through the interfacial debonding of matrix/carbides and the breaking of carbides. However, for the aged material, the precipitation of8phase increases the density of nucleus for the formation of microvoids, and accelerates the growth and coalescence of microvoids.(4) A constitutive equation is established to predict the peak stress of the aged GH4169superalloy. The effects of initial aging time on the material parameters of the established constitutive equation were analyzed. Results show that the material parameters are sensitive to the initial againg time. The peak stresses predicted by the established constitutive equation well agree with the measured results.(5) Based on the GTN model, the development of localized necking during the hot tensile deformation was analyzed. The Z parameter-based mathematical expressions of the characteristic parameters in GTN model were obtained. The results show that GTN model can well describe the flow softening phenomenon caused by the development of localized necking of the hot tensile deformation.