Influence Of Surface Recrystallization On Tensile And Stress Rupture Properties Of DZ17G Superalloy

DZ17G is an important nickel-base superalloy. It is widely used in the field of aeronautics and astronautics. As the recrystallization woud be detrimental for mechanical properties of superalloy, it is necessary to study the influence of recrystallization on mechanical properties of DZ17G superalloy in order to guarantee the safe use. When indentated and shot-peened on the surface of DZ17G superalloy, recrystallization was initiated after standard heat treatment. Influence of recrystallization induced by surface indentation or shot peening on tensile and stress rupture properties of DZ17G superalloy has been studied in this article.Local recrystallization occurred in the plastic deformation zone under the indentation. The depthes of the recrystallization after standard heat trentment are 400μm and 700μm when the indentation loads are 750kg and 1500kg, respectively. Indentation recrystallization decreases the tensile properties of DZ17G superalloy at the 760℃while increases the tensile properties at the 650℃and 20℃. Observation of the sample tensiled at 760℃revealed that cracks initiated along the transverse recrystallization grain boundaries. The cracks can connect with each other when propagating though the original materials, which reduces the tensile properties. When tensiled at 650℃and 20℃, the dislocations are piled up at the transverse grain boundaries. This may strengthen the original materials and increase the tensile properties.Shot-peening induced a recrystallization layer on the surface of the specimens. The average depth of the recrystallization after standard heat trentment is 40μm when the shot-peening pressure is 0.35MPa. Shot-peening recrystallization decreases the tensile properties of DZ17G superalloy at the 900℃and 760℃, while increases the tensile properties at the 650℃and 20℃. When tensiled at 760℃and 900℃, the transverse recrystallization grain boundary is prone to cracking and promotes the crack propagation into the original materials. The tensile properties were therefore reduced. When tensiled at 650℃and 20℃, the strength of the recrystallization layer is higher than that of the matrix, the recrystallization layer can hinder the cracks and increase the tensile properties. When tested at 900℃/325MPa and 760℃/675MPa, indentation recrystallization decreases the stress rupture properties of DZ17G superalloy. The transverse recrystallization grain boundary was found to prone to cracking. The connecting of the cracks makes the recrystallization layer have little loading capacity. When tested at 760℃/675MPa, the cracks initiated and propagated at the early stage of the test. The stress rupture properties reduced remarkablely.When tested at 900℃/325MPa and 760℃/675MPa, shot-peening recrystallization decreases the stress rupture lives of DZ17G superalloy. However, the elongation of the specimens increased at 900℃/325MPa. When crept at 900℃/325MPa, the recrystallization grain boundaries parallel to the stress axis slide and migrate, which may result in the increase of elongation. The residual eutectics, brittle carbides as well as the recrystallization layer reduce the rupture life of the specimen. When tested at 760℃/675MPa, the cracks initiated at the transverse recrystallization grain boundaries are propagating into the original materials rapidly, which reduces the rupture life of the specimen. The ability of grain boundary sliding and migrating is poor at this temperature. Therefore, the elongation does not change.