Low-cycle fatigue crack initiation behavior of nickel-based single crystal superalloy at 530℃ was investigated.Results show that the behavior of crack initiation is closely related to the maximum strain.When the maxi...Low-cycle fatigue crack initiation behavior of nickel-based single crystal superalloy at 530℃ was investigated.Results show that the behavior of crack initiation is closely related to the maximum strain.When the maximum strain is 2.0%,the fatigue crack is originated at the position of persistent slip bands on the surface of specimen,which is located on the{111}slip plane.No defects are observed at the crack initiation position.When the maximum strain is lower than 1.6%,the cracks are initiated at the casting defects on sub-surface or at interior of the specimen.The casting defects are located on the{100}slip plane vertical to the axial force.The crack is initiated along the{100}slip plane and then expanded along different{111}slip planes after a short stage of expansion.As the maximum strain decreases,the position of crack initiation gradually changes from the surface to the interior.Moreover,the secondary cracks extending inward along the fracture surface appear in the crack initiation area,and there is obvious stress concentration near the secondary cracks.The dislocation density is high near the fracture surface in the crack initiation zone,where a lot of dislocations cutting into the γ'phase exist.An oxide layer of 50‒100 nm is presented on the fracture surface,and Ni,Al,Cr and Co elements are mainly segregated into the oxide layer of the surface.展开更多
The influence of applied temperatures on the creep rupture life of the third-generation low-cost single crystal(SX)superalloy with Pt-Al coating was evaluated.The creep damage was observed under the conditions of 1100...The influence of applied temperatures on the creep rupture life of the third-generation low-cost single crystal(SX)superalloy with Pt-Al coating was evaluated.The creep damage was observed under the conditions of 1100℃/137 MPa,1120℃/137 MPa,and 1140℃/137 MPa.Results show that the properties of bare superalloy outperform those of coated superalloy under all test conditions.The most significant reduction in creep life reaches 50%when the test condition is 1100℃/137 MPa.At higher temperatures(1120 and 1140℃),the crack propagation rate in Pt-Al coatings to SX superalloy substrate decreases,thereby reducing the degradation degree of mechanical properties.Instead of the penetration into SX substrate,tip oxidation and Al diffusion of the coating cracks cause the formation of oxides,therefore leading to the slow degradation in microstructures of the substrate beneath the coating.At 1100℃,however,the microstructure of coating/SX superalloy substrate degrades due to the Al internal diffusion.This diffusion mechanism promotes the formation of harmful topologically close packed phases around 1100℃.At 1120 and 1140℃,the dislocation of SX superalloy substrate beneath the coating is relatively unchanged,compared to that in the inner superalloy.In contrast,the dislocation network of the substrate beneath the coating becomes sparse,and the number of superdislocations cutting intoγ′phases increases at 1100℃.展开更多
基金National Science and Technology Major Project(J2019-VI-0022-0138)。
文摘Low-cycle fatigue crack initiation behavior of nickel-based single crystal superalloy at 530℃ was investigated.Results show that the behavior of crack initiation is closely related to the maximum strain.When the maximum strain is 2.0%,the fatigue crack is originated at the position of persistent slip bands on the surface of specimen,which is located on the{111}slip plane.No defects are observed at the crack initiation position.When the maximum strain is lower than 1.6%,the cracks are initiated at the casting defects on sub-surface or at interior of the specimen.The casting defects are located on the{100}slip plane vertical to the axial force.The crack is initiated along the{100}slip plane and then expanded along different{111}slip planes after a short stage of expansion.As the maximum strain decreases,the position of crack initiation gradually changes from the surface to the interior.Moreover,the secondary cracks extending inward along the fracture surface appear in the crack initiation area,and there is obvious stress concentration near the secondary cracks.The dislocation density is high near the fracture surface in the crack initiation zone,where a lot of dislocations cutting into the γ'phase exist.An oxide layer of 50‒100 nm is presented on the fracture surface,and Ni,Al,Cr and Co elements are mainly segregated into the oxide layer of the surface.
基金National Key Research and Development Program of China(2017YFA0700704)China Postdoctoral Science Foundation(2023M733570)+1 种基金Excellent Youth Foundation of Liaoning Province(2021-YQ-02)Science Center for Gas Turbine Project(P2021-A-Ⅳ-002-002)。
文摘The influence of applied temperatures on the creep rupture life of the third-generation low-cost single crystal(SX)superalloy with Pt-Al coating was evaluated.The creep damage was observed under the conditions of 1100℃/137 MPa,1120℃/137 MPa,and 1140℃/137 MPa.Results show that the properties of bare superalloy outperform those of coated superalloy under all test conditions.The most significant reduction in creep life reaches 50%when the test condition is 1100℃/137 MPa.At higher temperatures(1120 and 1140℃),the crack propagation rate in Pt-Al coatings to SX superalloy substrate decreases,thereby reducing the degradation degree of mechanical properties.Instead of the penetration into SX substrate,tip oxidation and Al diffusion of the coating cracks cause the formation of oxides,therefore leading to the slow degradation in microstructures of the substrate beneath the coating.At 1100℃,however,the microstructure of coating/SX superalloy substrate degrades due to the Al internal diffusion.This diffusion mechanism promotes the formation of harmful topologically close packed phases around 1100℃.At 1120 and 1140℃,the dislocation of SX superalloy substrate beneath the coating is relatively unchanged,compared to that in the inner superalloy.In contrast,the dislocation network of the substrate beneath the coating becomes sparse,and the number of superdislocations cutting intoγ′phases increases at 1100℃.
