The precipitating regulation and mechanism of TCP phase (μ phase and σ phase) are studied, using electron hole number (EHN) theory, phase analysis technology and TEM observation. The results indicate that the EHN i...The precipitating regulation and mechanism of TCP phase (μ phase and σ phase) are studied, using electron hole number (EHN) theory, phase analysis technology and TEM observation. The results indicate that the EHN in studied alloy is 2.311-2.348 which is higher than that of critical EHN of μ phase precipitate (2.30), so μ phase could precipitate if there is enough thermo-exposition. In contrast, the calculated EHN is less than that of critical EHN of σ phase precipitate (2.52). However the σ phase is also observed by TEM. Enrich of Cr and Mo around γ phase after γ′phase precipitated leads to σ phase precipitated.展开更多
The microstructure of nickel-based single-crystal(SC) superalloys has a pivotal influence on their creep properties. The addition of the Re element not only enhances the long-term creep properties of nickel-based SC s...The microstructure of nickel-based single-crystal(SC) superalloys has a pivotal influence on their creep properties. The addition of the Re element not only enhances the long-term creep properties of nickel-based SC superalloys, but also results in the formation of a topologically close-packed(TCP) phase which is a harmful and brittle hard phase. Here, high-temperature creep interruption tests of a nickel-based SC superalloy that contains4.8 wt% Re were performed under various temperatures and stress conditions, and the evolution of microstructure during creep was observed by scanning electron microscopy(SEM). The volume fraction of the TCP phase was also extracted to explore the mechanism that controls the impacts of the TCP phase on the creep properties.According to the microstructure evolution mechanism, the influence of the TCP phase was attributed to the initial damage and critical shear stress of the material. A creep performance prediction model for nickel-based SC superalloys considering the precipitation of the TCP phase that is based on the crystal plasticity theory and a modified creep damage model was established. The simulation curves fit well with the experimental results and the errors between prediction creep life with test results are within 5%.展开更多
The nucleation and transition sequences of topologically close-packed(TCP)phases in a Re-containing Ni-based single crystal superalloy were systematically investigated using in-situ transmission electron microscopy(TE...The nucleation and transition sequences of topologically close-packed(TCP)phases in a Re-containing Ni-based single crystal superalloy were systematically investigated using in-situ transmission electron microscopy(TEM)and three-dimensional atom probe technology(3D-APT).During the initial stage of heat-exposure at 1100℃,the TCP phase forming elements(Re,Co,Cr,etc.)segregated at theγ/γin-terface near theγmatrix side to provide the concentration undulations for the nucleation sites of TCP phases,following which theσand P phase coherently nucleated along the(111)γand(022)γplanes from theγ/γinterface near theγmatrix side,respectively.With prolonged heat-exposure time,transitions fromσphase to P phase,σphase toμphase,and P phase toμphase occurred.Besides,the orientation relationships of TCP phase intergrowth structures indicated that the P phase grew along the(¯101)σplane of theσphase by co-lattice precipitation,meanwhile,theμphase grew with smaller lattice misfits along the(0¯40)σplane of theσphase and the(400)P plane of the P phase.Additionally,the result by first-principles calculation evidenced that theμphase had the lowest system energy to make the transition ofσphase and P phase toμphases inevitable,therefore,the TCP phase ultimately existed as the most stableμphase.Finally,the transition sequences of TCP phase during heat-exposure could be summarized into three types:γmatrix→σ→μ,γmatrix→P→μ,andγmatrix→σ→P→μ.展开更多
The application and component designs of single crystal superalloys are restricted by the precipitation of topologically closed packed(TCP)phases,which can deteriorate the microstructural stability of the alloys sever...The application and component designs of single crystal superalloys are restricted by the precipitation of topologically closed packed(TCP)phases,which can deteriorate the microstructural stability of the alloys severely.Limited researches concerning the type and morphology evolution of TCP phases under elevated temperature conditions have been reported previously.In the present work,three Re-containing single crystal alloys were designed to investigate TCP phase evolution via long term isothermal exposure tests at 1120℃while the effects of Re on the microstructural characteristic and elements segregation were also clarified.The results showed that the addition of Re increased the instability of the alloys and the volume fraction of the TCP phases exceeded 5 vol%when the Re content reached 3 wt%.The increasing Re content had also raised the precipitation temperature of TCP phases but it did not change the type of them after long term aging;all the TCP particles were identified asμphase in this study.Moreover,the elements segregation became considerably serious as Re addition increased constantly,which brought about various morphologies of theμphase in the experimental alloys.In particular,the rod-like and needle-likeμphases demonstrated the typical orientation withinγmatrix while the blockyμphase was dispersedly distributed in the space.No specific orientation relationship could be observed in theμphase when the addition of Re exceeded certain threshold value.展开更多
The volume fraction and morphology of the TCP-phase formed in two kinds of Ni- Mo-Cr-Re superalloys under different heat treatment conditions were investigated in this paper. In Re-5% alloy, with increasing of the hea...The volume fraction and morphology of the TCP-phase formed in two kinds of Ni- Mo-Cr-Re superalloys under different heat treatment conditions were investigated in this paper. In Re-5% alloy, with increasing of the heat treatment temperature and prolonging the holding time, the volume fraction of TCP-phase decreased and the TCP-phase size increased. At relatively lower temperature, the TCP-phase prefers to present in the dendrite cores. In Re-10% alloy, the volume fraction and size have the same change tendency as that of in Re-5% alloy, but the morphology will change from needle-like and block-like to sphere when the temperature increases. The TCP-phases formed in these two Ni-Mo-Cr-Re alloys are σ and P phase.展开更多
The precipitation of topologically close-packed(TCP)phases is the result of microstructure instabilities of Ni-based superalloys.This review seeks to comprehensively collate all the available information on TCP phases...The precipitation of topologically close-packed(TCP)phases is the result of microstructure instabilities of Ni-based superalloys.This review seeks to comprehensively collate all the available information on TCP phases in SX superalloys based on the latest findings.First,the thermodynamics and kinetics of the TCP phase precipitation are introduced.Meanwhile,the morphology,composition and orientation of TCP phases and their sequential transformation are summarized in detail.Further,the factors affecting the precipitation of these phases are sorted out.Besides,the proposed damage mechanisms of TCP phases are listed.Finally,several control and prediction methods of the TCP phase precipitation are reviewed,so the alloy designer can better balance the relationship between microstructure stabilities and properties of the superalloy.展开更多
文摘The precipitating regulation and mechanism of TCP phase (μ phase and σ phase) are studied, using electron hole number (EHN) theory, phase analysis technology and TEM observation. The results indicate that the EHN in studied alloy is 2.311-2.348 which is higher than that of critical EHN of μ phase precipitate (2.30), so μ phase could precipitate if there is enough thermo-exposition. In contrast, the calculated EHN is less than that of critical EHN of σ phase precipitate (2.52). However the σ phase is also observed by TEM. Enrich of Cr and Mo around γ phase after γ′phase precipitated leads to σ phase precipitated.
基金financially supported by the National Natural Science Foundation of China(No.51875462)the Fundamental Research Funds for the Central Universities(No.3102019PY001)+1 种基金the Seed Foundation of Innovation and Creation for Graduate Students in Northwestern Polytechnical University(Nos.ZZ2019015 and ZZ2019017)the National Science and Technology Major Project(Nos.2017-IV-0003-0040 and 2017-V-00030052)。
文摘The microstructure of nickel-based single-crystal(SC) superalloys has a pivotal influence on their creep properties. The addition of the Re element not only enhances the long-term creep properties of nickel-based SC superalloys, but also results in the formation of a topologically close-packed(TCP) phase which is a harmful and brittle hard phase. Here, high-temperature creep interruption tests of a nickel-based SC superalloy that contains4.8 wt% Re were performed under various temperatures and stress conditions, and the evolution of microstructure during creep was observed by scanning electron microscopy(SEM). The volume fraction of the TCP phase was also extracted to explore the mechanism that controls the impacts of the TCP phase on the creep properties.According to the microstructure evolution mechanism, the influence of the TCP phase was attributed to the initial damage and critical shear stress of the material. A creep performance prediction model for nickel-based SC superalloys considering the precipitation of the TCP phase that is based on the crystal plasticity theory and a modified creep damage model was established. The simulation curves fit well with the experimental results and the errors between prediction creep life with test results are within 5%.
基金supported by the National Natural Science Foundation of China(Nos.51771148,52071263,52031012,and 52322410)the Science Center for Gas Turbine Project(No.P2021-A-IV-001-001)+3 种基金the Key Research and Development Program of Shaanxi Province(No.2023-YBGY-432)the Natural Science Ba-sic Research Plan in Shaanxi Province of China(No.2021JC-13)the Science and Technology Funding Key R&D Industry Foresight and Key Technologies of Jiangsu Province(No.BE2022124)the Re-search Fund of the State Key Laboratory of Solidification Processing(NPU),China(No.2021-QZ-03).
文摘The nucleation and transition sequences of topologically close-packed(TCP)phases in a Re-containing Ni-based single crystal superalloy were systematically investigated using in-situ transmission electron microscopy(TEM)and three-dimensional atom probe technology(3D-APT).During the initial stage of heat-exposure at 1100℃,the TCP phase forming elements(Re,Co,Cr,etc.)segregated at theγ/γin-terface near theγmatrix side to provide the concentration undulations for the nucleation sites of TCP phases,following which theσand P phase coherently nucleated along the(111)γand(022)γplanes from theγ/γinterface near theγmatrix side,respectively.With prolonged heat-exposure time,transitions fromσphase to P phase,σphase toμphase,and P phase toμphase occurred.Besides,the orientation relationships of TCP phase intergrowth structures indicated that the P phase grew along the(¯101)σplane of theσphase by co-lattice precipitation,meanwhile,theμphase grew with smaller lattice misfits along the(0¯40)σplane of theσphase and the(400)P plane of the P phase.Additionally,the result by first-principles calculation evidenced that theμphase had the lowest system energy to make the transition ofσphase and P phase toμphases inevitable,therefore,the TCP phase ultimately existed as the most stableμphase.Finally,the transition sequences of TCP phase during heat-exposure could be summarized into three types:γmatrix→σ→μ,γmatrix→P→μ,andγmatrix→σ→P→μ.
基金financially supported by the State Key Lab of Advanced Metals and Materials Open Fund under Grant No.2018-Z07the National Science and Technology Major Project under Grant No.2017-VI-0002-0072+2 种基金the National Key R&D Program of China under Grant No.2017YFA0700704the National Natural Science Foundation of China(NSFC)under Grant Nos.51601192,51671188the Youth Innovation Promotion Association,Chinese Academy of Sciences
文摘The application and component designs of single crystal superalloys are restricted by the precipitation of topologically closed packed(TCP)phases,which can deteriorate the microstructural stability of the alloys severely.Limited researches concerning the type and morphology evolution of TCP phases under elevated temperature conditions have been reported previously.In the present work,three Re-containing single crystal alloys were designed to investigate TCP phase evolution via long term isothermal exposure tests at 1120℃while the effects of Re on the microstructural characteristic and elements segregation were also clarified.The results showed that the addition of Re increased the instability of the alloys and the volume fraction of the TCP phases exceeded 5 vol%when the Re content reached 3 wt%.The increasing Re content had also raised the precipitation temperature of TCP phases but it did not change the type of them after long term aging;all the TCP particles were identified asμphase in this study.Moreover,the elements segregation became considerably serious as Re addition increased constantly,which brought about various morphologies of theμphase in the experimental alloys.In particular,the rod-like and needle-likeμphases demonstrated the typical orientation withinγmatrix while the blockyμphase was dispersedly distributed in the space.No specific orientation relationship could be observed in theμphase when the addition of Re exceeded certain threshold value.
基金the financial support from the National High Magnetic Field Laboratory under NSF DMR-0084173
文摘The volume fraction and morphology of the TCP-phase formed in two kinds of Ni- Mo-Cr-Re superalloys under different heat treatment conditions were investigated in this paper. In Re-5% alloy, with increasing of the heat treatment temperature and prolonging the holding time, the volume fraction of TCP-phase decreased and the TCP-phase size increased. At relatively lower temperature, the TCP-phase prefers to present in the dendrite cores. In Re-10% alloy, the volume fraction and size have the same change tendency as that of in Re-5% alloy, but the morphology will change from needle-like and block-like to sphere when the temperature increases. The TCP-phases formed in these two Ni-Mo-Cr-Re alloys are σ and P phase.
基金financially supported by the National Science and Technology Major Project(No.2019-VII-0019-0161)Science Center for Gas Turbine Project(No.P2021-A-Ⅳ-001-002)+1 种基金National Key Research and Development Program of China under Grant(No.2017YFA0700704)National Natural Science Foundation of China(No.51971214).
文摘The precipitation of topologically close-packed(TCP)phases is the result of microstructure instabilities of Ni-based superalloys.This review seeks to comprehensively collate all the available information on TCP phases in SX superalloys based on the latest findings.First,the thermodynamics and kinetics of the TCP phase precipitation are introduced.Meanwhile,the morphology,composition and orientation of TCP phases and their sequential transformation are summarized in detail.Further,the factors affecting the precipitation of these phases are sorted out.Besides,the proposed damage mechanisms of TCP phases are listed.Finally,several control and prediction methods of the TCP phase precipitation are reviewed,so the alloy designer can better balance the relationship between microstructure stabilities and properties of the superalloy.
