An anisotropic micromechanics model based on the equivalent inclusion method is developed to investigate the rafting direction of Ni-based single crystal superalloys. The micromechanical model considers actual cubic s...An anisotropic micromechanics model based on the equivalent inclusion method is developed to investigate the rafting direction of Ni-based single crystal superalloys. The micromechanical model considers actual cubic structure and orthogonal anisotropy properties. The von Mises stress, elastic strain energy density, and hydrostatic pressure in dif- ferent inclusions of micromechanical model are calculated when applying a tensile or compressive loading along the [001] direction. The calculated results can successfully pre- dict the rafting direction for alloys exhibiting a positive or a negative mismatch, which are in agreement with pervious experimental and theoretical studies. Moreover, the elastic constant differences and mismatch degree of the matrix and precipitate phases and their influences on the rafting direction are carefully discussed.展开更多
The oxidation behavior of a novel Ni-based single-crystal 4774DD1 superalloy for industrial gas turbine applications was investigated by the isothermal oxidation at 980℃ and discontinuous oxidation weight gain method...The oxidation behavior of a novel Ni-based single-crystal 4774DD1 superalloy for industrial gas turbine applications was investigated by the isothermal oxidation at 980℃ and discontinuous oxidation weight gain methods.The phase constitution and morphology of surface oxides and the characteristics of the crosssection oxide film were analyzed by XRD,SEM and EDS.Results show that the oxidation kinetics of the 4774DD1 superalloy follows the cubic law,indicating its weak oxidation resistance at this temperature.As the oxidation time increases,the composition of the oxide film evolves as following:One layer consisting of a bottom Al_(2)O_(3)sublayer and an upper(Al_(2)O_(3)+NiO)mixture sublayer after oxidized for 25 h.Then,two layers composed of an outermost small NiO discontinuous grain layer and an internal layer for 75 h.This internal layer is consisted of the bottom Al_(2)O_(3)sublayer,an intermediate narrow CrTaO_(4)sublayer,and an upper(Al_(2)O_(3)+NiO)mixture sublayer.Also two layers comprising an outermost relative continuous NiO layer with large grain size and an internal layer as the oxidation time increases to 125 h.This internal layer is composed of the upper(Al_(2)O_(3)+NiO)mixture sublayer,an intermediate continuous(CrTaO_(4)+NiWO_(4))mixture sublayer,and a bottom Al_(2)O_(3)sublayer.Finally,three layers consisting of an outermost(NiAl2O_(4)+NiCr2O_(4))mixture layer,an intermediate(CrTaO_(4)+NiWO_(4))mixture layer,and a bottom Al_(2)O_(3)layer for 200 h.展开更多
A new insight into the microstructural stability was proposed in Ni-based single crystal superalloys with Ru addition,and the element segregation behavior atγ/γ′interface was investigated by three-dimensional atom ...A new insight into the microstructural stability was proposed in Ni-based single crystal superalloys with Ru addition,and the element segregation behavior atγ/γ′interface was investigated by three-dimensional atom probe technology(3D-APT).After standard heat treatment,it was found that Ru addition barely altered the element partitioning coefficient betweenγmatrix andγ′phase,and no element-segregation layer was observed atγ/γ′interface.During the heat exposure at 1100°C,Ru addition obviously promoted the rafting of theγ′precipitates and inhibited the precipitation of topological close-packed(TCP)phases.It was more important that an element-segregation layer containing Re,Co,and Cr was formed in theγmatrix close to theγ/γ′interface due to an“uphill diffusion”effect,and its concentration was obviously reduced after Ru addition.Finally,the microstructural stability based on the element segregation behavior atγ/γ′interface was discussed.This element-segregation layer increased theγ/γ′interfacial energy by increasing the absolute value of the lattice misfit ofγ/γ′interface to promote the rafting of theγ′precipitates after Ru addition.On the other hand,the decrease of the segregation concentration of Re,Co,and Cr elements as TCP phase-forming elements near theγ/γ′interface due to a“reverse partitioning”effect inhibits the precipitation of TCP phases in Ni-based single crystal superalloys after Ru addition.展开更多
The interactions between the moving dislocation within matrix channel and the interfacial misfit dislocation networks on the two-phase interfaces in Ni-based single crystal superalloys are studied carefully via atomic...The interactions between the moving dislocation within matrix channel and the interfacial misfit dislocation networks on the two-phase interfaces in Ni-based single crystal superalloys are studied carefully via atomic modeling, with special focus on the factors influ- encing the critical bowing stress of moving dislocations in the matrix channel. The results show that the moving matrix dislocation type and its position with respect to the interfacial misfit dislocation segments have considerable influences on the interactions. If the moving matrix dislocation is pure screw, it reacts with the interracial misfit dislocation segments toward dislocation linear energy reduction, which decreases the critical bowing stress of screw dislocation due to dislocation linear energy release during the dislocation reactions. If the moving matrix dislocation is of 60^-mixed type, it is obstructed by the interaction between the mixed matrix dislocations and the misfit interfacial dislocation segments. As a result, the critical bowing stress increases significantly because extra interactive energy needs to be overcome. These two different effects on the critical bowing stress become in- creasingly significant when the moving matrix dislocation is very close to the interracial misfit dislocation segments. In addition, the matrix channel width also has a significant influence on the critical bowing stress, i.e. the narrower the matrix channel is, the higher the critical bowing stress is. The classical Orowan formula is modified to predict these effects on the critical bowing stress of moving matrix dislocation, which is in good agreement with the computational results.展开更多
Due to the outstanding creep performance, nickel-based single crystal superalloys(Ni-SXs) are extensively applied in modern aero-engine and industrial gas turbine. Apart from the special single crystal structure which...Due to the outstanding creep performance, nickel-based single crystal superalloys(Ni-SXs) are extensively applied in modern aero-engine and industrial gas turbine. Apart from the special single crystal structure which is disadvantageous to extension of creep cracks, Ni-SXs derive the creep strength from intrinsic two-phase microstructure(γ phase and γ’ phase). Main microstructural parameters including volume fraction of γ’ phase and the lattice misfit, and the formation and distribution of precipitated phase are determined by the compositions of alloys. Besides, the creep properties are greatly influenced by these microstructural parameters and precipitated phase. This review has summarized the relationships between different alloying elements and microstructures and indicated their influence on creep properties of Ni-SXs. In addition, with the improvements of experimental methods and characterization technique, some recent discoveries have provided additional evidence to support or challenge the pervious creep theories of superalloys. In view of these new discoveries, this review has provided some perspectives which can be referenced in future compositional design of Ni-SXs.展开更多
The development of Ni-based single crystal superalloys relies heavily on the composition design with the addition of critical alloying elements,e.g.,Re and Ru.Understanding the role of alloying effects require to know...The development of Ni-based single crystal superalloys relies heavily on the composition design with the addition of critical alloying elements,e.g.,Re and Ru.Understanding the role of alloying effects require to know the configurations of the alloying element distribution betweenγ-Ni andγ′-Ni3Al phases and among various non-equivalent sites.This work employed firstprinciples density functional theory calculations to study the preference of phase and site occupancy of 11 alloying elements including Al and transition metal elements:3d (Ti,Cr,Co,Ni),4d (Mo,Ru),and 5d (Hf,Ta,W,Re) in Ni and Ni3Al.We calculated the substitution energies of 1298 triple-site doping configurations including 286 Ni Ni Ni site doping of Ni,726 Al Ni Ni site doping,and 286 Ni Ni Ni site doping of Ni3Al with alloying elements Ni,Co,Ru,Cr,Re,Mo,W,Al,Ti,Ta,and Hf.In the dual-site and triple-site doping of Ni and Ni3Al,all studied alloying elements preferred to occupy Ni phase rather than Ni3Al phase.We found that the most stable defect complexes often contained the favorable substitutions of Al,Ti,Ta,and Hf for the Ni sites that stabilized the alloying elements doping at the other one or two nearest neighbor sites.The co-substitutions of various alloying elements at multiple sites are critical to understanding the strengthening mechanism of alloying elements in Ni-based single crystal superalloys.展开更多
An analytical method to investigate the morphological evolution of the cellular mi-crostructure is explored and proposed. The method is essentially based on the Es-helby 's micromechanics theory, and it is extende...An analytical method to investigate the morphological evolution of the cellular mi-crostructure is explored and proposed. The method is essentially based on the Es-helby 's micromechanics theory, and it is extended so as to be applied for a material system containing inclusions with high volume fraction, by employing the average stress field approximation by Mori and Tanaka. The proposed method enables us to discuss a stable shape of precipitate in the material system, which must be influenced by many factors: e.g., volume fraction of precipitate; Young's modulus ratio and lattice misfit between matrix and precipitate; external stress field in multiaxial state; and heterogeneity of plastic strain between matrix and precipitate. A series of numerical calculations were summarized on stable shape maps. The application of the method to predict the γ' rafting in superalloys during creep showed that the heterogeneity of plastic strain between matrix and precipitates may play a significant role in the shape stability of the precipitate. Furthermore, it was shown that the method was successfully applied to estimate the morphology of the cellular microstructure formed in CMSX-4 single crystal Ni-based superalloy.展开更多
An Ni-AI-Co system embedded-atom-method potential is constructed for the γ(Ni)/γ'(Ni3A1) superalloy based on experiments and first-principles calculations. The stacking fault energies (SFEs) of the Ni(Co, A1...An Ni-AI-Co system embedded-atom-method potential is constructed for the γ(Ni)/γ'(Ni3A1) superalloy based on experiments and first-principles calculations. The stacking fault energies (SFEs) of the Ni(Co, A1) random solid solutions are calculated as a function of the concentrations of Co and A1. The calculated SFEs decrease with increasing concentrations of Co and A1, which is consistent with the experimental results. The embedding energy term in the present potential has an important influence on the SFEs of the random solid solutions. The cross-slip processes of a screw dislocation in homogenous Ni(Co) solid solutions are simulated using the present potential and the nudged elastic band method. The cross-slip activation energies increase with increasing Co concentration, which implies that the creep resistance of γ(Ni) may be improved by the addition of Co.展开更多
A single crystal Ni-based superalloy AM3 was processed at withdraw rates of 3.5, 10, 50, 100, 200, and 500 μm·s-1, respectively.The as-cast microstructures and solidification segregation ratio were characterized...A single crystal Ni-based superalloy AM3 was processed at withdraw rates of 3.5, 10, 50, 100, 200, and 500 μm·s-1, respectively.The as-cast microstructures and solidification segregation ratio were characterized with various withdraw rates.The shape and size of carbide microstructures were determined.As expected, the primary and secondary dendrite arm spacings (PDAS and SDAS) decrease with the increase of withdraw rate.The highest volume fraction of eutectic γ/γ' is observed at the 100 μm·s-1 withdraw rate.The volume fraction of eutectic γ/γ' does not appear to be a strong function of the withdraw rate.With increasing withdraw rate, interface morphologies change in the sequence of planar, cellular, and dendrite.There is a general refinement of the microstructure as the withdraw rate increases.EPMA analysis showed that withdraw rate does not have obvious influence on the segregation of elements.展开更多
Interfacial dislocations found in single crystal superalloys after long term thermal aging have an important effect on mechanical properties. Long term thermal aging tests for DD5 single crystal superalloy were carrie...Interfacial dislocations found in single crystal superalloys after long term thermal aging have an important effect on mechanical properties. Long term thermal aging tests for DD5 single crystal superalloy were carried out at 1,100 ℃ for 20, 100, 200, 500 and 1000 h, and then cooled by air. The effect of long term thermal aging on the dislocation networks at the γ/γ' interfaces was investigated by FE-SEM. Results showed that during the long term thermal aging at 1,100 ℃, misfit dislocations formed firstly and then reorientation in the(001) interfacial planes occurred. Different types of square or rectangular dislocation network form by dislocation reaction. Square dislocation networks consisting of four groups of dislocations can transform into octagonal dislocation networks, and then form another square dislocation network by dislocation reaction. Rectangular dislocation networks can also transform into hexagonal dislocation networks. The interfacial dislocation networks promote the γ' phase rafting process. The dislocation networks spacings become smaller and smaller, leading to the effective lattice misfit increasing from-0.10% to-0.32%.展开更多
The microstructure of experimental nickel-base single crystal superalloys with different levels of carbon has been studied. The results indicated that with increasing carbon addition, the liquidus temperature decrease...The microstructure of experimental nickel-base single crystal superalloys with different levels of carbon has been studied. The results indicated that with increasing carbon addition, the liquidus temperature decreased obviously and the as-cast microstructures exhibited a decrease in the amount of γ/γ′ eutectic structure and an increase in the volume fraction of carbides. The carbides formed in these alloys were most script-type MC carbides which appeared continuous dendritic networks in the interdendritic region. The segregation behavior of element W was influenced by the carbon addition.展开更多
The mosaic structure in a Ni-based single-crystal superalloy is simulated by molecular dynamics using a potential employed in a modified analytic embedded atom method. From the calculated results we find that a closed...The mosaic structure in a Ni-based single-crystal superalloy is simulated by molecular dynamics using a potential employed in a modified analytic embedded atom method. From the calculated results we find that a closed threedimensional misfit dislocation network, with index of (011){100} and the side length of the mesh 89.6A, is formed around a cuboidal γ′ precipitate. Comparing the simulation results of the different mosaic models, we find that the side length of the mesh only depends on the lattice parameters of the γ and γ′ phases as well as the γ/γ′ interface direction, but is independent of the size and number of the cuboidal γ′ precipitate. The density of dislocations is inversely proportional to the size of the cuboidal γ′ precipitate, i.e. the amount of the dislocation is proportional to the total area of the γ/γ′ interface, which may be used to explain the relation between the amount of the fine γ′ particles and the creep rupture life of the superalloy. In addition, the closed three-dimensional networks assembled with the misfit dislocations can play a significant role in improving the mechanical properties of superalloys.展开更多
The mechanism of stray grain formation at the platform of turbine blade simulator and the effect of withdrawal rate(V) on the stray grain phenomenon have been investigated using a macro-scale Pro CAST coupled with a 3...The mechanism of stray grain formation at the platform of turbine blade simulator and the effect of withdrawal rate(V) on the stray grain phenomenon have been investigated using a macro-scale Pro CAST coupled with a 3D Cellular Automaton Finite Element(CAFE) model. The results indicate that the stray grains nucleate at the edges of platform at V =150 μm·s^(-1) and 200 μm·s^(-1). Using Pro CAST computer simulation software, it was proven that the stray grain formation is signifi cantly dependent on the undercooling and the temperature fi eld distribution in the platform. The macroscopic curvature of the liquidus isotherm becomes markedly concave with an increase in the withdrawal rate. The probability of stray grain formation at the edges of platform can be increased by increasing the withdrawal rate in the range of 70 μm·s^(-1) to 200 μm·s^(-1).展开更多
The effect of different initial microstructures deftned by γ' precipitate morphology has been investigated at the creep/fatigue conditions of 900℃ and 500 MPa. The wave form of stress as a function of time for c...The effect of different initial microstructures deftned by γ' precipitate morphology has been investigated at the creep/fatigue conditions of 900℃ and 500 MPa. The wave form of stress as a function of time for cyclic load was of trapezoidal shape with a hold time of 10s at the upper stress level. The TEM was employed to examine the deformation process in strengthened γ' matrix in dependence of γ' precipitate morphology. The fracture lifetime and cycle number up to fracture were the criteria to evaluate the additional cyclic component efFect on the course of deformation展开更多
The effect of cobalt on chemical segregation and solution process in three nickel base single crystal superalloys was investigated. Three alloys containing the mass fraction of cobalt of 12% (named Alloy 1), 3% (named...The effect of cobalt on chemical segregation and solution process in three nickel base single crystal superalloys was investigated. Three alloys containing the mass fraction of cobalt of 12% (named Alloy 1), 3% (named Alloy 2) and 0 (named Alloy 3), respectively were studied, in which the contents of other elements were same. The results show that the segregation extent of W, Re, Ta, Al between dendrite and interdendritic region rises with the increase of cobalt content. The incipient melting points decrease by 10℃and 20℃respectively when the content of cobalt increases from 0 through 3% to 12%. During solid solution at 1 340℃, the solid solution of large gamma prime in interdendritic region and the dissolution of eutectic in alloy 1 become easier than in other two alloys. After heat-treatment at 1 340℃for 8 h, the segregation extent of elements in alloy 1 decreases dramatically, while in alloy 2 and alloy 3, the segregation ratios decrease slowly. It suggests that the higher content of cobalt can accelerate the diffusion process at high temperature.展开更多
In order to study the effect of the withdrawing rate on carbide morphology,MC-type carbide in single crystal superalloy AM3 was systematically investigated with sample growth rates from 3.5 μm/s to 500 μm/s.The carb...In order to study the effect of the withdrawing rate on carbide morphology,MC-type carbide in single crystal superalloy AM3 was systematically investigated with sample growth rates from 3.5 μm/s to 500 μm/s.The carbide morphologies were investigated by scanning electron microscopy(SEM),and the electron probe microanalysis(EPMA) was used to characterize the carbide composition.The results indicate that the solidification rate is the important factor governing MC carbide growth morphology,size and distribution,composition and growth mechanism.With the increase of withdrawing rate,nodular,rod-like,Chinese script types of carbide morphology are observed.For the low withdrawing rate,with the increase of withdrawing rate,the carbide size becomes larger.For the case of dendritic interface,the carbide size becomes smaller with refinement of dendrites as withdrawing rate increases.The volume fraction of carbides increases with the withdrawing rate increasing.展开更多
By means of pre-compressive creep treatment, the cubic γ′ phase in a nickel base single crystal superalloy is transformed into the P-type rafted structure. And the influence of the pre-compressive creep on the inter...By means of pre-compressive creep treatment, the cubic γ′ phase in a nickel base single crystal superalloy is transformed into the P-type rafted structure. And the influence of the pre-compressive creep on the internal friction stress and creep lifetimes of the superalloy are investigated by means of the measurement of the creep curves and microstructure observation. Results show that, compared to the P-type structure alloy, the full heat treated state alloy displays a bigger internal friction stress value of dislocation motion during steady state creep and a longer creep lifetimes. The creep activation energies of the full heat treated and P-type structures alloys are measured to be 462 kJ/mol and 412 kJ/mol, respectively. Thereinto, the P-type rafted γ′ phase in the alloy is transformed into the N-type structure during tensile creep. And the N-type γ′ phase transformed from the P-type structure displays a shorter size in length, this is a main reason of the P-type structure alloy possessing a shorter creep lifetimes due to creep dislocation moving easily over the rafted γ′ phase.展开更多
The floating phenomenon of MC carbide(TiC)in a hot corrosion resistant single crystal Ni-base superalloy was observed during planar and cellular interface directional solidification.The explanation about the phenomeno...The floating phenomenon of MC carbide(TiC)in a hot corrosion resistant single crystal Ni-base superalloy was observed during planar and cellular interface directional solidification.The explanation about the phenomenon is presented.展开更多
基金supported by The National Natural Science Foundation of China (Grants 11102139 and 11472195)The Natural Science Foundation of Hubei Province of China (Grant 2014CFB713)
文摘An anisotropic micromechanics model based on the equivalent inclusion method is developed to investigate the rafting direction of Ni-based single crystal superalloys. The micromechanical model considers actual cubic structure and orthogonal anisotropy properties. The von Mises stress, elastic strain energy density, and hydrostatic pressure in dif- ferent inclusions of micromechanical model are calculated when applying a tensile or compressive loading along the [001] direction. The calculated results can successfully pre- dict the rafting direction for alloys exhibiting a positive or a negative mismatch, which are in agreement with pervious experimental and theoretical studies. Moreover, the elastic constant differences and mismatch degree of the matrix and precipitate phases and their influences on the rafting direction are carefully discussed.
基金supported by the fund of State Key Laboratory of Long-life High Temperature Materials(Grant No.DTCC28EE200787)the Natural Science Basic Research Plan in Shaanxi Province of China(Grant No.2022JQ-553)+3 种基金the China Postdoctoral Science Foundation(Grant No.2021M692555)the Excellent Youth Foundation of Shaanxi Province of China(Grant No.2021JC-08)the Beilin district of Xi’an Science and Technology Project(Grant No.GX2123)the support from the Youth Innovation Team of Shaanxi Universities。
文摘The oxidation behavior of a novel Ni-based single-crystal 4774DD1 superalloy for industrial gas turbine applications was investigated by the isothermal oxidation at 980℃ and discontinuous oxidation weight gain methods.The phase constitution and morphology of surface oxides and the characteristics of the crosssection oxide film were analyzed by XRD,SEM and EDS.Results show that the oxidation kinetics of the 4774DD1 superalloy follows the cubic law,indicating its weak oxidation resistance at this temperature.As the oxidation time increases,the composition of the oxide film evolves as following:One layer consisting of a bottom Al_(2)O_(3)sublayer and an upper(Al_(2)O_(3)+NiO)mixture sublayer after oxidized for 25 h.Then,two layers composed of an outermost small NiO discontinuous grain layer and an internal layer for 75 h.This internal layer is consisted of the bottom Al_(2)O_(3)sublayer,an intermediate narrow CrTaO_(4)sublayer,and an upper(Al_(2)O_(3)+NiO)mixture sublayer.Also two layers comprising an outermost relative continuous NiO layer with large grain size and an internal layer as the oxidation time increases to 125 h.This internal layer is composed of the upper(Al_(2)O_(3)+NiO)mixture sublayer,an intermediate continuous(CrTaO_(4)+NiWO_(4))mixture sublayer,and a bottom Al_(2)O_(3)sublayer.Finally,three layers consisting of an outermost(NiAl2O_(4)+NiCr2O_(4))mixture layer,an intermediate(CrTaO_(4)+NiWO_(4))mixture layer,and a bottom Al_(2)O_(3)layer for 200 h.
基金funded by the National Science and Technol-ogy Major Project(Nos.2017-VI-0002-0072,2019-VI-0020-0135)the National Natural Science Foundation of China(Nos.51771148,52071263,52031012)+2 种基金the Key Research and Development Program of Shaanxi Province(Nos.2020ZDLGY13-02,2023-YBGY-432)the Natural Science Basic Research Plan in Shaanxi Province of China(No.2021JC-13)the Research Fund of the State Key Labora-tory of Solidification Processing(NPU),China(No.2021-QZ-03).
文摘A new insight into the microstructural stability was proposed in Ni-based single crystal superalloys with Ru addition,and the element segregation behavior atγ/γ′interface was investigated by three-dimensional atom probe technology(3D-APT).After standard heat treatment,it was found that Ru addition barely altered the element partitioning coefficient betweenγmatrix andγ′phase,and no element-segregation layer was observed atγ/γ′interface.During the heat exposure at 1100°C,Ru addition obviously promoted the rafting of theγ′precipitates and inhibited the precipitation of topological close-packed(TCP)phases.It was more important that an element-segregation layer containing Re,Co,and Cr was formed in theγmatrix close to theγ/γ′interface due to an“uphill diffusion”effect,and its concentration was obviously reduced after Ru addition.Finally,the microstructural stability based on the element segregation behavior atγ/γ′interface was discussed.This element-segregation layer increased theγ/γ′interfacial energy by increasing the absolute value of the lattice misfit ofγ/γ′interface to promote the rafting of theγ′precipitates after Ru addition.On the other hand,the decrease of the segregation concentration of Re,Co,and Cr elements as TCP phase-forming elements near theγ/γ′interface due to a“reverse partitioning”effect inhibits the precipitation of TCP phases in Ni-based single crystal superalloys after Ru addition.
基金supported by the financial support from NSFC (Grant 11472113 and Grant 11272130)
文摘The interactions between the moving dislocation within matrix channel and the interfacial misfit dislocation networks on the two-phase interfaces in Ni-based single crystal superalloys are studied carefully via atomic modeling, with special focus on the factors influ- encing the critical bowing stress of moving dislocations in the matrix channel. The results show that the moving matrix dislocation type and its position with respect to the interfacial misfit dislocation segments have considerable influences on the interactions. If the moving matrix dislocation is pure screw, it reacts with the interracial misfit dislocation segments toward dislocation linear energy reduction, which decreases the critical bowing stress of screw dislocation due to dislocation linear energy release during the dislocation reactions. If the moving matrix dislocation is of 60^-mixed type, it is obstructed by the interaction between the mixed matrix dislocations and the misfit interfacial dislocation segments. As a result, the critical bowing stress increases significantly because extra interactive energy needs to be overcome. These two different effects on the critical bowing stress become in- creasingly significant when the moving matrix dislocation is very close to the interracial misfit dislocation segments. In addition, the matrix channel width also has a significant influence on the critical bowing stress, i.e. the narrower the matrix channel is, the higher the critical bowing stress is. The classical Orowan formula is modified to predict these effects on the critical bowing stress of moving matrix dislocation, which is in good agreement with the computational results.
基金supported by the National Natural Science Foundation of China(Grant Nos.11102139&11472195)Natural Science Foundation of Hubei Province of China(Grant No.2014CFB713)
文摘An anisotropic micromechanical model based on Mori-Tanaka method is developed to calculate the effective elastic moduli
基金This work was jointly supported by the Fundamental Research Funds for the Central Universities(No.2019QNA4012)the Innovation Fund of the Zhejiang Kechuang New Materials Research Institute(No.ZKN-18-Z01).
文摘Due to the outstanding creep performance, nickel-based single crystal superalloys(Ni-SXs) are extensively applied in modern aero-engine and industrial gas turbine. Apart from the special single crystal structure which is disadvantageous to extension of creep cracks, Ni-SXs derive the creep strength from intrinsic two-phase microstructure(γ phase and γ’ phase). Main microstructural parameters including volume fraction of γ’ phase and the lattice misfit, and the formation and distribution of precipitated phase are determined by the compositions of alloys. Besides, the creep properties are greatly influenced by these microstructural parameters and precipitated phase. This review has summarized the relationships between different alloying elements and microstructures and indicated their influence on creep properties of Ni-SXs. In addition, with the improvements of experimental methods and characterization technique, some recent discoveries have provided additional evidence to support or challenge the pervious creep theories of superalloys. In view of these new discoveries, this review has provided some perspectives which can be referenced in future compositional design of Ni-SXs.
基金the Independent Research and Development Project of State Key Laboratory of Advanced Special Steelthe Shanghai Key Laboratory of Advanced Ferrometallurgy+2 种基金Shanghai University(Grant No.SKLASS 2019-Z024)the Science and Technology Commission of Shanghai Municipality(Grant No.19DZ2270200)the National Key Research and Development Program of China(Grant Nos.2017YFB0701502 and 2017YFB0702901)。
文摘The development of Ni-based single crystal superalloys relies heavily on the composition design with the addition of critical alloying elements,e.g.,Re and Ru.Understanding the role of alloying effects require to know the configurations of the alloying element distribution betweenγ-Ni andγ′-Ni3Al phases and among various non-equivalent sites.This work employed firstprinciples density functional theory calculations to study the preference of phase and site occupancy of 11 alloying elements including Al and transition metal elements:3d (Ti,Cr,Co,Ni),4d (Mo,Ru),and 5d (Hf,Ta,W,Re) in Ni and Ni3Al.We calculated the substitution energies of 1298 triple-site doping configurations including 286 Ni Ni Ni site doping of Ni,726 Al Ni Ni site doping,and 286 Ni Ni Ni site doping of Ni3Al with alloying elements Ni,Co,Ru,Cr,Re,Mo,W,Al,Ti,Ta,and Hf.In the dual-site and triple-site doping of Ni and Ni3Al,all studied alloying elements preferred to occupy Ni phase rather than Ni3Al phase.We found that the most stable defect complexes often contained the favorable substitutions of Al,Ti,Ta,and Hf for the Ni sites that stabilized the alloying elements doping at the other one or two nearest neighbor sites.The co-substitutions of various alloying elements at multiple sites are critical to understanding the strengthening mechanism of alloying elements in Ni-based single crystal superalloys.
基金supported by the Ministry of Education,Japan,as Grant-in-Aid for Scientific Research(No.12650072 and 15360046)are greatly acknowledged
文摘An analytical method to investigate the morphological evolution of the cellular mi-crostructure is explored and proposed. The method is essentially based on the Es-helby 's micromechanics theory, and it is extended so as to be applied for a material system containing inclusions with high volume fraction, by employing the average stress field approximation by Mori and Tanaka. The proposed method enables us to discuss a stable shape of precipitate in the material system, which must be influenced by many factors: e.g., volume fraction of precipitate; Young's modulus ratio and lattice misfit between matrix and precipitate; external stress field in multiaxial state; and heterogeneity of plastic strain between matrix and precipitate. A series of numerical calculations were summarized on stable shape maps. The application of the method to predict the γ' rafting in superalloys during creep showed that the heterogeneity of plastic strain between matrix and precipitates may play a significant role in the shape stability of the precipitate. Furthermore, it was shown that the method was successfully applied to estimate the morphology of the cellular microstructure formed in CMSX-4 single crystal Ni-based superalloy.
基金Project supported by the National Basic Research Program of China(Grant No.2011CB606402)the National Natural Science Foundation of China(Grant No.51071091)
文摘An Ni-AI-Co system embedded-atom-method potential is constructed for the γ(Ni)/γ'(Ni3A1) superalloy based on experiments and first-principles calculations. The stacking fault energies (SFEs) of the Ni(Co, A1) random solid solutions are calculated as a function of the concentrations of Co and A1. The calculated SFEs decrease with increasing concentrations of Co and A1, which is consistent with the experimental results. The embedding energy term in the present potential has an important influence on the SFEs of the random solid solutions. The cross-slip processes of a screw dislocation in homogenous Ni(Co) solid solutions are simulated using the present potential and the nudged elastic band method. The cross-slip activation energies increase with increasing Co concentration, which implies that the creep resistance of γ(Ni) may be improved by the addition of Co.
基金supported by the National Natural Science Foundation of China (Grant No.50771081,50931004)the National Basic Research Program of China (2010CB631202)
文摘A single crystal Ni-based superalloy AM3 was processed at withdraw rates of 3.5, 10, 50, 100, 200, and 500 μm·s-1, respectively.The as-cast microstructures and solidification segregation ratio were characterized with various withdraw rates.The shape and size of carbide microstructures were determined.As expected, the primary and secondary dendrite arm spacings (PDAS and SDAS) decrease with the increase of withdraw rate.The highest volume fraction of eutectic γ/γ' is observed at the 100 μm·s-1 withdraw rate.The volume fraction of eutectic γ/γ' does not appear to be a strong function of the withdraw rate.With increasing withdraw rate, interface morphologies change in the sequence of planar, cellular, and dendrite.There is a general refinement of the microstructure as the withdraw rate increases.EPMA analysis showed that withdraw rate does not have obvious influence on the segregation of elements.
基金supported by the National Natural Science Foundation of China(Grant No.:50901046)
文摘Interfacial dislocations found in single crystal superalloys after long term thermal aging have an important effect on mechanical properties. Long term thermal aging tests for DD5 single crystal superalloy were carried out at 1,100 ℃ for 20, 100, 200, 500 and 1000 h, and then cooled by air. The effect of long term thermal aging on the dislocation networks at the γ/γ' interfaces was investigated by FE-SEM. Results showed that during the long term thermal aging at 1,100 ℃, misfit dislocations formed firstly and then reorientation in the(001) interfacial planes occurred. Different types of square or rectangular dislocation network form by dislocation reaction. Square dislocation networks consisting of four groups of dislocations can transform into octagonal dislocation networks, and then form another square dislocation network by dislocation reaction. Rectangular dislocation networks can also transform into hexagonal dislocation networks. The interfacial dislocation networks promote the γ' phase rafting process. The dislocation networks spacings become smaller and smaller, leading to the effective lattice misfit increasing from-0.10% to-0.32%.
基金supported financially by the National Natural Science Foundation of China (Grant No. 50771081,50931004)the National Basic Research Program of China (2010CB631202)
文摘The microstructure of experimental nickel-base single crystal superalloys with different levels of carbon has been studied. The results indicated that with increasing carbon addition, the liquidus temperature decreased obviously and the as-cast microstructures exhibited a decrease in the amount of γ/γ′ eutectic structure and an increase in the volume fraction of carbides. The carbides formed in these alloys were most script-type MC carbides which appeared continuous dendritic networks in the interdendritic region. The segregation behavior of element W was influenced by the carbon addition.
基金Project supported by the State Key Development Program for Basic Research of China (Grant No G2000067102) and the National Natural Science Foundation of China (Grant No 90101004).
文摘The mosaic structure in a Ni-based single-crystal superalloy is simulated by molecular dynamics using a potential employed in a modified analytic embedded atom method. From the calculated results we find that a closed threedimensional misfit dislocation network, with index of (011){100} and the side length of the mesh 89.6A, is formed around a cuboidal γ′ precipitate. Comparing the simulation results of the different mosaic models, we find that the side length of the mesh only depends on the lattice parameters of the γ and γ′ phases as well as the γ/γ′ interface direction, but is independent of the size and number of the cuboidal γ′ precipitate. The density of dislocations is inversely proportional to the size of the cuboidal γ′ precipitate, i.e. the amount of the dislocation is proportional to the total area of the γ/γ′ interface, which may be used to explain the relation between the amount of the fine γ′ particles and the creep rupture life of the superalloy. In addition, the closed three-dimensional networks assembled with the misfit dislocations can play a significant role in improving the mechanical properties of superalloys.
基金financially supported by the fund of the State Key Laboratory of Solidifi cation Processing at NWPU(No.SKLSP201407)
文摘The mechanism of stray grain formation at the platform of turbine blade simulator and the effect of withdrawal rate(V) on the stray grain phenomenon have been investigated using a macro-scale Pro CAST coupled with a 3D Cellular Automaton Finite Element(CAFE) model. The results indicate that the stray grains nucleate at the edges of platform at V =150 μm·s^(-1) and 200 μm·s^(-1). Using Pro CAST computer simulation software, it was proven that the stray grain formation is signifi cantly dependent on the undercooling and the temperature fi eld distribution in the platform. The macroscopic curvature of the liquidus isotherm becomes markedly concave with an increase in the withdrawal rate. The probability of stray grain formation at the edges of platform can be increased by increasing the withdrawal rate in the range of 70 μm·s^(-1) to 200 μm·s^(-1).
文摘The effect of different initial microstructures deftned by γ' precipitate morphology has been investigated at the creep/fatigue conditions of 900℃ and 500 MPa. The wave form of stress as a function of time for cyclic load was of trapezoidal shape with a hold time of 10s at the upper stress level. The TEM was employed to examine the deformation process in strengthened γ' matrix in dependence of γ' precipitate morphology. The fracture lifetime and cycle number up to fracture were the criteria to evaluate the additional cyclic component efFect on the course of deformation
文摘The effect of cobalt on chemical segregation and solution process in three nickel base single crystal superalloys was investigated. Three alloys containing the mass fraction of cobalt of 12% (named Alloy 1), 3% (named Alloy 2) and 0 (named Alloy 3), respectively were studied, in which the contents of other elements were same. The results show that the segregation extent of W, Re, Ta, Al between dendrite and interdendritic region rises with the increase of cobalt content. The incipient melting points decrease by 10℃and 20℃respectively when the content of cobalt increases from 0 through 3% to 12%. During solid solution at 1 340℃, the solid solution of large gamma prime in interdendritic region and the dissolution of eutectic in alloy 1 become easier than in other two alloys. After heat-treatment at 1 340℃for 8 h, the segregation extent of elements in alloy 1 decreases dramatically, while in alloy 2 and alloy 3, the segregation ratios decrease slowly. It suggests that the higher content of cobalt can accelerate the diffusion process at high temperature.
基金Projects(50771081, 50931004) supported by the National Natural Science Foundation of ChinaProject(2010CB631202) supported by the National Basic Research Program of China
文摘In order to study the effect of the withdrawing rate on carbide morphology,MC-type carbide in single crystal superalloy AM3 was systematically investigated with sample growth rates from 3.5 μm/s to 500 μm/s.The carbide morphologies were investigated by scanning electron microscopy(SEM),and the electron probe microanalysis(EPMA) was used to characterize the carbide composition.The results indicate that the solidification rate is the important factor governing MC carbide growth morphology,size and distribution,composition and growth mechanism.With the increase of withdrawing rate,nodular,rod-like,Chinese script types of carbide morphology are observed.For the low withdrawing rate,with the increase of withdrawing rate,the carbide size becomes larger.For the case of dendritic interface,the carbide size becomes smaller with refinement of dendrites as withdrawing rate increases.The volume fraction of carbides increases with the withdrawing rate increasing.
基金Supported by the National Natural Science Foundation of China (No 50571070)
文摘By means of pre-compressive creep treatment, the cubic γ′ phase in a nickel base single crystal superalloy is transformed into the P-type rafted structure. And the influence of the pre-compressive creep on the internal friction stress and creep lifetimes of the superalloy are investigated by means of the measurement of the creep curves and microstructure observation. Results show that, compared to the P-type structure alloy, the full heat treated state alloy displays a bigger internal friction stress value of dislocation motion during steady state creep and a longer creep lifetimes. The creep activation energies of the full heat treated and P-type structures alloys are measured to be 462 kJ/mol and 412 kJ/mol, respectively. Thereinto, the P-type rafted γ′ phase in the alloy is transformed into the N-type structure during tensile creep. And the N-type γ′ phase transformed from the P-type structure displays a shorter size in length, this is a main reason of the P-type structure alloy possessing a shorter creep lifetimes due to creep dislocation moving easily over the rafted γ′ phase.
文摘The floating phenomenon of MC carbide(TiC)in a hot corrosion resistant single crystal Ni-base superalloy was observed during planar and cellular interface directional solidification.The explanation about the phenomenon is presented.