The prevention of hot cracking formation is of utmost importance in the production of the new Ni-Co based superalloys through the utilization of the electron beam smelting layered solidification technique(EBSL),as it ...The prevention of hot cracking formation is of utmost importance in the production of the new Ni-Co based superalloys through the utilization of the electron beam smelting layered solidification technique(EBSL),as it ensures exceptional homogeneity and dependable consistency of the specimens.In contrast to previous studies that focused on minimizing the liquid film and solidification range,our methodology adopts a distinct approach.In this research,a novel methodology was employed to mitigate internal stresses through the implementation of equiaxed grain layers via an alternately reduced cooling method.This ultimately resulted in the elimination of hot cracking.To be more specific,the transition from a columnar to an equiaxed structure was observed during the layer-by-layer construction process in the fabrication of the new Ni-Co based superalloy in EBSL.The EBSL-Ni-Co superalloy,when subjected to the alternating reduction cooling method,exhibited an internal stress of 49 MPa.This value represents a significant reduction of 83.8%compared to the internal stress observed when employing the linear reduction cooling method.Additionally,the solvus temperature of theγ-γ’eutectic phases in EBSL-Ni-Co superalloys produced by the alternating reduction cooling method is significantly higher.Intriguingly,the Nth layer of the EBSL-Ni-Co based superalloys produced by EBSL simultaneously heats treated with the preceding layers.And the low melting point phase gradually dissolved back into the matrix.The implementation of an alternating reduced cooling method successfully mitigated the formation of the liquid film in theγ-γ’eutectic phase and the buildup of internal stresses in the EBSL-Ni-Co superalloy during its manufacturing process.These discoveries open up a novel preparation procedure pathway for the manufacture of crack-free superalloys with superior mechanical characteristics using EBSL.展开更多
The interface healing mechanism of fine-grained Ni-Co-based superalloy during hot-compression bonding(HCB)is investigated.During HCB,the incompatibility of deformation between theγand the primary γ′leads to a large...The interface healing mechanism of fine-grained Ni-Co-based superalloy during hot-compression bonding(HCB)is investigated.During HCB,the incompatibility of deformation between theγand the primary γ′leads to a large number of dislocation pairs(DP),stacking faults(SF),and micro-twins(MT)in the primary γ′.These defects act as fast channels for elemental diffusion,leading to supersaturation of the primary γ′and promoting the growth of the γ-shell.On the one hand,the primary γ′with a γ-shell moves towards the bonding interface due to anomalous yielding phenomena of the primary γ′and plastic flow during HCB process.The increase in the number of defects leads to the growth of γ-γ′heterogeneous epitaxial recrystallization(HERX)grain with coherent structure at the bonding interface,which promotes the bulge of the interface grain boundaries(IGBs).On the other hand,the nucleation and growth of a necklace-like distribution of discontinuous dynamic recrystallization(DDRX)grain at the interface lead to the healing of IGBs.With the synergistic action of DDRX and HERX,the mechanical properties of Ni-Co-based superalloy joints through HCB achieve the same level as the base material.This finding further enriches the theory of interface healing in HCB.展开更多
The hot deformation behavior of a newly developed Ni–W–Cr superalloy for use in 800℃molten salt reactors(MSRs)was looked into by isothermal compression tests in the temperature range of 1050–1200℃with a strain ra...The hot deformation behavior of a newly developed Ni–W–Cr superalloy for use in 800℃molten salt reactors(MSRs)was looked into by isothermal compression tests in the temperature range of 1050–1200℃with a strain rate of 0.001–1 s^(−1)under a true strain of 0.693.An Arrhenius-type model for the Ni–W–Cr superalloy was constructed by fitting the corrected flow stress data.In this model,the effect of dispersion of solid solution elements during thermal deformation on microstructure evolution was considered,as well as the effects of friction and adiabatic heating on the temperature and strain rate-dependent variation of flow stresses.The hot deformation activation energy of the Ni–W–Cr superalloy was 323 kJ/mol,which was less than that of the Hastelloy N alloy(currently used in MSRs).According to the rectified flow stress data,processing maps were created.In conjunction with the corresponding deformation microstructures,the flow instability domains of the Ni–W–Cr superalloy were determined to be 1050–1160℃/0.03–1 s^(−1)and 1170–1200℃/0.001–0.09 s^(−1).In these deformation conditions,a locally inhomogeneous microstructure was caused by flow-i.e.,incomplete dynamic recrystallization and hot working parameters should avoid sliding into these domains.The ideal processing hot deformation domain for the Ni–W–Cr superalloy was determined to be 1170–1200℃/0.6–1 s^(−1).展开更多
The mechanism behind void formation during superplasticity remains a subject of uncertainty.This study presented a novel insight into the void formation in a fine-grained Ni-Co-based superalloy during superplasticity....The mechanism behind void formation during superplasticity remains a subject of uncertainty.This study presented a novel insight into the void formation in a fine-grained Ni-Co-based superalloy during superplasticity.It was observed that the dissolution ofγ′-particles resulted in the creation of vacancies due to differences in atomic size between the matrix and the particles.These vacancies acted as inclusions,leading to the formation of micro-voids.Notably,excessive void formation correlated with higher particle dissolution was experimentally observed,highlighting a direct relationship between void formation and particle dissolution.展开更多
The Ni-based K417G superalloy is extensively applied as aeroengine components for its low cost and good mid-temperature （600-900 ~C） properties. Since used in as-cast state, the comprehensive under-standing on its m...The Ni-based K417G superalloy is extensively applied as aeroengine components for its low cost and good mid-temperature （600-900 ~C） properties. Since used in as-cast state, the comprehensive under-standing on its mechanical properties and microstructure evolution is necessary. In the present research, the tensile, creep behavior and microstructure evolution of the as-cast K417G superalloy under differ-ent conditions were investigated. The results exhibit that tensile cracks tend to initiate at MC carbide and γ＇/γ＇ eutectic structure and then propagate along grain boundary. As the temperature for tensile tests increases from 21 ℃ to 700 ℃, the yield strength and ultimate tensile strength of K417G superalloy decreases slightly, while the elongation to failure decreases greatly because of the intermediate tem- perature embrittlement. When the temperature rises to 900 ℃, the yield strength and ultimate tensile strength would decrease significantly. The creep deformation mechanism varies under different test-ing conditions. At 760 ℃/645 MPa, the creep cracks initiate at MC carbides and γ/γ＇ eutectic structures, and propagate transgranularly. While at 900℃/315 MPa and 950℃/235 MPa, the creep cracks initiate at grain boundary and propagate intergranularly. As the creep condition changes from 760 ℃/645 MPa to 900 ℃/315 MPa and 950 ℃/235 MPa, the γ＇ phase starts to raft, which reduces the creep deformation resistance and increases the steady-state deformation rate.展开更多
The Portevin-Le Chatelier(PLC) effects in a wrought Ni-base superalloy with different γ' precipitates contents have been investigated. Detailed analysis on the serration type of the tensile curves indicates that ...The Portevin-Le Chatelier(PLC) effects in a wrought Ni-base superalloy with different γ' precipitates contents have been investigated. Detailed analysis on the serration type of the tensile curves indicates that the γ' precipitates have a decisive influence on the transformation from normal to inverse PLC behavior, which is rarely proposed in other works. It is considered that the γ' precipitates play the same role in PLC effect as temperature and strain rate for the investigated wrought Ni-base superalloy.展开更多
The effect of thermal exposure on microstructure and creep properties of a fourth-generation nickelbased single crystal superalloy was investigated.The thermal exposure of samples after the full heat treatment was car...The effect of thermal exposure on microstructure and creep properties of a fourth-generation nickelbased single crystal superalloy was investigated.The thermal exposure of samples after the full heat treatment was carried out at 1000℃,1100℃ and 1140℃ for 100 h and 200 h.The γ’ coarsening,γ’ rafting and γ channel widening were observed in samples after thermal exposure.When the thermal exposure time was constant,the morphology of γ’ phase in the alloy evolved significantly with increasing aging temperature.The interracial dislocation networks in aged samples after creep ruptured gradually became irregular and sparse with the increase of exposure temperature.When the higher exposure temperature was used,enla rgement of the defect pores was observed in samples,the microcracks were more likely to initiate and propagate at the corner of these pores.After aging at 1000℃ for 100 h,the creep life at 1140℃/137 MPa was slightly longer than that of heat-treated sample,which could be attributed to the slightly coarsened γ’ phase,homogenization of refractor elements.In contrast,the creep life of sample exposed at 1140℃ for 100 h was greatly decreased.The decrease of creep life was dominated by the rafting of γ’phase,the irregular interfacial dislocation networks as well as the enlargement of homogenization pores.展开更多
To reduce microsegregation,a series of homogenization treatments were carried out on a Ni-Co based superalloy prepared through directional solidification(DS).The element segregation characteristics and microstructural...To reduce microsegregation,a series of homogenization treatments were carried out on a Ni-Co based superalloy prepared through directional solidification(DS).The element segregation characteristics and microstructural evolution were investigated by optical microscopy(OM),scanning electron microscopy(SEM),and electron probe microanalysis(EPMA).The results show that the elements are non-uniformly distributed in the solidified superalloy,in which W and Ti have the greatest tendency of microsegregation.Furthermore,severe microsegregation leads to complicated precipitations,includingη-Ni_(3) Ti and eutectic(γ+γ’).EPMA results show that Al and Mo are uniformly distributed between the eutectic(γ+γ’)andγmatrix,whereas Ti is segregated in the eutectic(γ+γ’)andηphases.The positive segregation element Ti,which is continuously rejected into the remaining liquid duringγmatrix solidification,promotes the formation of eutectic(γ+γ’)and the transformation of theηphase.According to the homogenization effect,the optimal single-stage homogenization process of this alloy is 1180℃for 2 h because of the sufficient diffusion segregation of the elements.In the present study,a kinetic diffusion model was built to reflect the degree of element segregation during homogenization,and the diffusion coefficients of W and Ti were estimated.展开更多
The effects of strain rate on the microstructural evolution and deformation mechanism of a Ni-Co based superalloy were investigated by isothermal compression tests performed atγ'sub-solvus(1090℃)andγ'super-...The effects of strain rate on the microstructural evolution and deformation mechanism of a Ni-Co based superalloy were investigated by isothermal compression tests performed atγ'sub-solvus(1090℃)andγ'super-solvus temperatures(1150℃)with a wide strain rate range from 0.001 to 10 s^(-1)under a true strain of 0.693.Electron backscatter diffraction(EBSD),electron channeling contrast imaging(ECCI)and transmission electron microscope(TEM)techniques were used to characterize the microstructures.The results revealed that the dynamic recrystallization(DRX)volume fraction increased and stored energy of theγ'matrix grains decreased with increasing the strain rate duringγ'sub-solvus temperature deformation,while the opposite phenomena were observed duringγ'super-solvus temperature deformation.The comprehensive effect of initial grain size,primaryγ'phase,twins and adiabatic temperature rise led to these results.The primaryγ'particles undergone the deformation behavior within itself and obviously accelerated the DRX of the matrix.The microstructural evolution proved that discontinuous dynamic recrystallization(DDRX)was the dominant mechanism during the hot deformation carried out at bothγ'sub-solvus andγ'super-solvus temperatures.Primaryγ'particles obviously accelerated the nucleation step and retarded the growth step of DDRX duringγ'sub-solvus temperature deformation.Besides,the acceleration effect of primaryγ'particles on DDRX increased with the increase of strain rate.Continuous dynamic recrystallization(CDRX)was confirmed to be an assistant mechanism duringγ'super-solvus temperature deformation and was promoted with the increase of strain rate.展开更多
The Portevin-Le Chatelier(PLC)effect is a plastic instability in alloys at certain strain rates and deformation temperatures.This plastic instability exhibits serrated yielding in the temporal domain and strain locali...The Portevin-Le Chatelier(PLC)effect is a plastic instability in alloys at certain strain rates and deformation temperatures.This plastic instability exhibits serrated yielding in the temporal domain and strain localization in the spatial domain.Wrought Ni-based superalloys often exhibit the PLC effect.To guarantee the safe and stable operation of equipment,it is important to study the PLC effect in wrought Ni-based superalloys.This paper provides a review of various experimental phenomena and micromechanisms related to the PLC effect in wrought Ni-based superalloys,which have been reported in various publications in recent years and include work from our own group.The influences of stacking fault energy andγ’precipitates on the PLC effect in wrought Ni-based superalloys are also discussed in detail.Additionally,several suggestions for the future study of the PLC effect in wrought Ni-based superalloys are provided.展开更多
The macroscopically localized deformation behaviors of Ni–Co-based superalloys with differentγ’precipitate content were investigated at 500?C and 1×10-4 s-1 via an in situ method namely,digital image correlati...The macroscopically localized deformation behaviors of Ni–Co-based superalloys with differentγ’precipitate content were investigated at 500?C and 1×10-4 s-1 via an in situ method namely,digital image correlation(DIC).The DIC results showed that the serrated flow of the stress–strain curves was accompanied by localized deformation of the specimens.The fracture morphology was characterized mainly by transgranular fracture with numerous dimples in the lowγ’content alloy,and intergranular fracture with large fracture section in the highγ’content alloy.The Portevin–Le Chatelier(PLC)effect occurred in the investigated Ni–Co-based superalloys.Furthermore,the localized deformation of the highγ’content alloy was more severe than that of the lowγ’content alloy,and the band width was slightly larger.Moreover,for the first-time ever,a special propagation feature,namely±60?zigzag bands characterized by head-to-tail connections,was observed in the highγ’content alloy.展开更多
The new Ni-Co-based superalloy featuring a"fusion structure"was produced utilizing electron beam smelting layered solidification technology(EBSL).Experimental examination of hot compression deformation with ...The new Ni-Co-based superalloy featuring a"fusion structure"was produced utilizing electron beam smelting layered solidification technology(EBSL).Experimental examination of hot compression deformation with varied settings for EBSL and conventional duplex process melting Ni-Co superalloys was performed.As per the study,EBSL-Ni-Co superalloys exhibited enhanced recrystallization susceptibility during hot deformation.Furthermore,elevating deformation temperature,lowering strain rate,and augmenting strain collectively contribute to enlarging the volume fraction of dynamically recrystallized grains.Aberrant growth of grains occurred when the deformation temperature equaledγ′sub-solvus temperature and the strain rate was slower.Moreover,exceeding theγ′solvus temperature during deformation significantly increases the particle size of dynamic recrystallization(DRX)grains.Theγ′phase can effectively modulate the DRX grain size through the pegging effect.Additionally,it was revealed that the presence of the fusion structure aids in the generation of continuous dynamic recrystallization,discontinuous dynamic recrystallization,and twinning-induced dynamic recrystallization while the alloy undergoes hot deformation.This mechanism promotes DRX granule formation and permits complete recrystallization.Ultimately,the fusion structure was identified as playing a catalytic role in the dynamic recrystallization process of the new Ni-Co superalloy.展开更多
The trade-off between strength and ductility has been an enormous difficulty in the field of materials for an extended time due to their inverse correlation. In this work, friction stir processing(FSP) was for the fir...The trade-off between strength and ductility has been an enormous difficulty in the field of materials for an extended time due to their inverse correlation. In this work, friction stir processing(FSP) was for the first time performed to high-strength and high-melting-point Ni-Co based superalloy(GH4068),and enhanced strength and ductility were achieved in FSP samples. At room temperature, the FSP sample demonstrated significantly higher yield strength and ultimate tensile strength(1290 and 1670 MPa)than that of the base material(BM, 758 and 904 MPa) and advanced wrought GH4068 alloy(982 and 1291 MPa), concurrent with high tensile ductility(~24%). Compared with the BM, 70% higher yield strength of the FSP sample results from the remarkable contribution of grain-boundary and nanotwin strengthening, which has been confirmed by the multimechanistic model studied in this work. More importantly, with increasing temperature, an excellent strength-ductility synergy was obtained at 400 ℃,i.e., the yield strength of the FSP sample was increased by more than 50% compared with the BM(from789 to 1219 MPa);more interestingly, the elongation was also significantly increased from 17.9% in the BM to 28.5% in the FSP sample. Meanwhile, the Portevin-Le Chatelier effect was observed in the engineering stress-strain curve. The occurrence of this effect may be attributed to the interaction between solutes and defects like twins and mobile dislocations. Moreover, the grain refinement mechanism of FSP samples was proved to be discontinuous dynamic recrystallization.展开更多
In the Original publication of the article,the Chinese title and author names appeared inadvertently in the Ref.[24].The corrected Ref.[24]is given below.
A turbine disk alloy was prepared by electron beam sheet lamination(EBSL),giving a refined microstruc-ture and high purity,and the microstructure-property relationship of this alloy has been developed.The alloy showed...A turbine disk alloy was prepared by electron beam sheet lamination(EBSL),giving a refined microstruc-ture and high purity,and the microstructure-property relationship of this alloy has been developed.The alloy showed an outstanding creep life of 1266.3 h at 953 K/500 MPa.Compared with the conventional vacuum induction melted and vacuum arc re-melted alloy,a smaller dendrite arm spacing of less than 23μm was obtained through the EBSL method,which restricted the formation of large inter-dendritic carbides.As a result,the typical intergranular failure mode was observed in the EBSL alloy,whereas the transgranular fracture mode was dominant in the conventional alloy.The inter-dendritic MC carbides formed from the reverse diffusion of Nb are believed to either impede grain boundary sliding or initi-ate cracks,depending on their size and morphology.The tiny grain boundary precipitates of theδphase in the EBSL alloy could reduce the critical stress for microvoid nucleation to 161.07 MPa by decoher-ing the particle/matrix interface,or allowing vacancy condensation near theδinterface,resulting in the formation of grain boundary microcracks.In the conventional alloy,however,the larger-sized MC car-bides which were formed during the solidification process(0.36 vol.%)nucleated the microcracks within the particles,leading to the transgranular fracture.Furthermore,the results indicated that the nanoscaleγ′andγ″precipitates contributed primarily to strengthening and coordinating intragranular deforma-tion during creep,in which the Orowan mechanism and shearing of a/6<211>partial dislocations and a/2<110>doublets were active forγ′andγ″precipitates,respectively.展开更多
Deformation twinning is an important deformation mechanism in nickel-based superalloys. For superalloys, deformation twins are generally observed at low or intermediate temperatures and high strain rates;however, the ...Deformation twinning is an important deformation mechanism in nickel-based superalloys. For superalloys, deformation twins are generally observed at low or intermediate temperatures and high strain rates;however, the appearance of microtwins(MTs) at high temperatures has rarely been reported. In this study, transmission electron microscopy(TEM) was used to study MT formation in Ni-Co-based superalloys following compression at 1120 °C/1 s. The deformation behavior was discussed in detail to reveal the mechanism of MT formation. The twinning mechanism at elevated temperatures was theoretically attributed to the low stacking fault energy(SFE) and poor dislocation-driven deformations caused by the high strain rate in specific directions.展开更多
The grain boundary microstructures of a heat-treated Ni-based cast superalloy IN792 were investigated. The results show that M5B3 boride precipitates at the grain boundary. A special orientation relationship between M...The grain boundary microstructures of a heat-treated Ni-based cast superalloy IN792 were investigated. The results show that M5B3 boride precipitates at the grain boundary. A special orientation relationship between M5B3 phase and the matrix at one side of the grain boundary is found. At the same time, two M5B3 borides with different orientations could co-exist in a single M5B3 particle as an intergrowth besides existing alone, thus forming orientation relationship between the two M5B3 phases and matrix. This phenomenon could be attributed to the special orientation relationship between M5B3 phase and the matrix.展开更多
Characteristics of dynamic strain aging （DSA） in a Ni-Co-base superalloy were studied by tensile tests at temperatures ranging from 250 ℃ to 550 ℃ and strain rates ranging from 3 x 10-5 to 8 x 10-4 s-1. Serrated f...Characteristics of dynamic strain aging （DSA） in a Ni-Co-base superalloy were studied by tensile tests at temperatures ranging from 250 ℃ to 550 ℃ and strain rates ranging from 3 x 10-5 to 8 x 10-4 s-1. Serrated flow in the tensile stress-strain curves was observed in the temperature range from 300 ℃ to 500 ℃. Normal DSA behavior was found at temperatures ranging from 300 ℃ to 350 ℃, while inverse DSA behavior was observed at temperatures ranging from 400 ℃ to 500 ℃. The yield strength, ultimate tensile strength, elongation, work hardening index, and fracture features were not affected by temperature and strain rates in DSA regime. Negative strain-rate sensitivity of flow stress was observed in DSA regime. The analysis suggests that the ordering of the substitutional solutes around some defects like mobile dislocations and stacking faults due to the thermal activated process may cause the serrations on the tensile curves.展开更多
基金support from the National Key Research and Development Program of China(Grant No.2019YFA0705300)the National Natural Science Foundation of China(GrantNo.52004051)the Innovation Team Projectfor Key Fields of Dalian(Grant No.2019RT13).
文摘The prevention of hot cracking formation is of utmost importance in the production of the new Ni-Co based superalloys through the utilization of the electron beam smelting layered solidification technique(EBSL),as it ensures exceptional homogeneity and dependable consistency of the specimens.In contrast to previous studies that focused on minimizing the liquid film and solidification range,our methodology adopts a distinct approach.In this research,a novel methodology was employed to mitigate internal stresses through the implementation of equiaxed grain layers via an alternately reduced cooling method.This ultimately resulted in the elimination of hot cracking.To be more specific,the transition from a columnar to an equiaxed structure was observed during the layer-by-layer construction process in the fabrication of the new Ni-Co based superalloy in EBSL.The EBSL-Ni-Co superalloy,when subjected to the alternating reduction cooling method,exhibited an internal stress of 49 MPa.This value represents a significant reduction of 83.8%compared to the internal stress observed when employing the linear reduction cooling method.Additionally,the solvus temperature of theγ-γ’eutectic phases in EBSL-Ni-Co superalloys produced by the alternating reduction cooling method is significantly higher.Intriguingly,the Nth layer of the EBSL-Ni-Co based superalloys produced by EBSL simultaneously heats treated with the preceding layers.And the low melting point phase gradually dissolved back into the matrix.The implementation of an alternating reduced cooling method successfully mitigated the formation of the liquid film in theγ-γ’eutectic phase and the buildup of internal stresses in the EBSL-Ni-Co superalloy during its manufacturing process.These discoveries open up a novel preparation procedure pathway for the manufacture of crack-free superalloys with superior mechanical characteristics using EBSL.
基金financially supported by the National Key Research and Development Program(No.2018YFA0702900)the National Natural Science Foundation of China(Nos.52173305,52101061,52233017 and52203384)+6 种基金the National Science and Technology Major Project of China(No.2019ZX06004010)the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDC04000000)the China Postdoctoral Science Foundation(Nos.2020M681004 and 2021M703276)the IMR Innovation Foundation(No.2022-PY12)the Ling Chuang Research Project of China National Nuclear CorporationCNNC Science Fund for Talented Young ScholarsYouth Innovation Promotion Association,CAS.
文摘The interface healing mechanism of fine-grained Ni-Co-based superalloy during hot-compression bonding(HCB)is investigated.During HCB,the incompatibility of deformation between theγand the primary γ′leads to a large number of dislocation pairs(DP),stacking faults(SF),and micro-twins(MT)in the primary γ′.These defects act as fast channels for elemental diffusion,leading to supersaturation of the primary γ′and promoting the growth of the γ-shell.On the one hand,the primary γ′with a γ-shell moves towards the bonding interface due to anomalous yielding phenomena of the primary γ′and plastic flow during HCB process.The increase in the number of defects leads to the growth of γ-γ′heterogeneous epitaxial recrystallization(HERX)grain with coherent structure at the bonding interface,which promotes the bulge of the interface grain boundaries(IGBs).On the other hand,the nucleation and growth of a necklace-like distribution of discontinuous dynamic recrystallization(DDRX)grain at the interface lead to the healing of IGBs.With the synergistic action of DDRX and HERX,the mechanical properties of Ni-Co-based superalloy joints through HCB achieve the same level as the base material.This finding further enriches the theory of interface healing in HCB.
基金supported by the National Key R&D Program of China(Nos.2021YFB3700601 and 2019YFA0705304)the IMR Innovation Fund(No.2023-PY08).
文摘The hot deformation behavior of a newly developed Ni–W–Cr superalloy for use in 800℃molten salt reactors(MSRs)was looked into by isothermal compression tests in the temperature range of 1050–1200℃with a strain rate of 0.001–1 s^(−1)under a true strain of 0.693.An Arrhenius-type model for the Ni–W–Cr superalloy was constructed by fitting the corrected flow stress data.In this model,the effect of dispersion of solid solution elements during thermal deformation on microstructure evolution was considered,as well as the effects of friction and adiabatic heating on the temperature and strain rate-dependent variation of flow stresses.The hot deformation activation energy of the Ni–W–Cr superalloy was 323 kJ/mol,which was less than that of the Hastelloy N alloy(currently used in MSRs).According to the rectified flow stress data,processing maps were created.In conjunction with the corresponding deformation microstructures,the flow instability domains of the Ni–W–Cr superalloy were determined to be 1050–1160℃/0.03–1 s^(−1)and 1170–1200℃/0.001–0.09 s^(−1).In these deformation conditions,a locally inhomogeneous microstructure was caused by flow-i.e.,incomplete dynamic recrystallization and hot working parameters should avoid sliding into these domains.The ideal processing hot deformation domain for the Ni–W–Cr superalloy was determined to be 1170–1200℃/0.6–1 s^(−1).
基金financial support from the National Key R&D Program of China(2019YFA0705300)the Youth Innovation Promotion Association,CAS(No.2023202)the Natural Science Foundation Project of Liaoning Province(No.2023-MS-024).
文摘The mechanism behind void formation during superplasticity remains a subject of uncertainty.This study presented a novel insight into the void formation in a fine-grained Ni-Co-based superalloy during superplasticity.It was observed that the dissolution ofγ′-particles resulted in the creation of vacancies due to differences in atomic size between the matrix and the particles.These vacancies acted as inclusions,leading to the formation of micro-voids.Notably,excessive void formation correlated with higher particle dissolution was experimentally observed,highlighting a direct relationship between void formation and particle dissolution.
基金the Shenzhen Technology Innovation Plan(CXZZ20140731091722497 and CXZZ20140419114548507)the Shenzhen Basic Research Project(JCYJ20150529162228734,JCYJ20160407090231002,JCYJ20150625155931806 and JCYJ20160427100211076)
文摘The Ni-based K417G superalloy is extensively applied as aeroengine components for its low cost and good mid-temperature （600-900 ~C） properties. Since used in as-cast state, the comprehensive under-standing on its mechanical properties and microstructure evolution is necessary. In the present research, the tensile, creep behavior and microstructure evolution of the as-cast K417G superalloy under differ-ent conditions were investigated. The results exhibit that tensile cracks tend to initiate at MC carbide and γ＇/γ＇ eutectic structure and then propagate along grain boundary. As the temperature for tensile tests increases from 21 ℃ to 700 ℃, the yield strength and ultimate tensile strength of K417G superalloy decreases slightly, while the elongation to failure decreases greatly because of the intermediate tem- perature embrittlement. When the temperature rises to 900 ℃, the yield strength and ultimate tensile strength would decrease significantly. The creep deformation mechanism varies under different test-ing conditions. At 760 ℃/645 MPa, the creep cracks initiate at MC carbides and γ/γ＇ eutectic structures, and propagate transgranularly. While at 900℃/315 MPa and 950℃/235 MPa, the creep cracks initiate at grain boundary and propagate intergranularly. As the creep condition changes from 760 ℃/645 MPa to 900 ℃/315 MPa and 950 ℃/235 MPa, the γ＇ phase starts to raft, which reduces the creep deformation resistance and increases the steady-state deformation rate.
基金financially supported by the National Natural Science Foundation of China(Nos.51601192,51671188,51671189and 11332010)the High Technology Research and Development Program of China(No.2014AA041701)
文摘The Portevin-Le Chatelier(PLC) effects in a wrought Ni-base superalloy with different γ' precipitates contents have been investigated. Detailed analysis on the serration type of the tensile curves indicates that the γ' precipitates have a decisive influence on the transformation from normal to inverse PLC behavior, which is rarely proposed in other works. It is considered that the γ' precipitates play the same role in PLC effect as temperature and strain rate for the investigated wrought Ni-base superalloy.
基金the National Science and Technology Major Project(No.2017-VI-0002-0072)the National Key R&D Program of China(No.2017YFA0700704)+1 种基金the National Natural Science Foundation of China(Nos.51601192 and 51671188)the State Key Lab of Advanced Metals and Materials Open Fund(No.2018-Z07)。
文摘The effect of thermal exposure on microstructure and creep properties of a fourth-generation nickelbased single crystal superalloy was investigated.The thermal exposure of samples after the full heat treatment was carried out at 1000℃,1100℃ and 1140℃ for 100 h and 200 h.The γ’ coarsening,γ’ rafting and γ channel widening were observed in samples after thermal exposure.When the thermal exposure time was constant,the morphology of γ’ phase in the alloy evolved significantly with increasing aging temperature.The interracial dislocation networks in aged samples after creep ruptured gradually became irregular and sparse with the increase of exposure temperature.When the higher exposure temperature was used,enla rgement of the defect pores was observed in samples,the microcracks were more likely to initiate and propagate at the corner of these pores.After aging at 1000℃ for 100 h,the creep life at 1140℃/137 MPa was slightly longer than that of heat-treated sample,which could be attributed to the slightly coarsened γ’ phase,homogenization of refractor elements.In contrast,the creep life of sample exposed at 1140℃ for 100 h was greatly decreased.The decrease of creep life was dominated by the rafting of γ’phase,the irregular interfacial dislocation networks as well as the enlargement of homogenization pores.
基金financially supported by the National Key R&D Program of China(Nos.2019YFA0705304 and 2017YFA0700703)the National Natural Science Foundation of China(No.51671189)+1 种基金Innovation Program of Institute of Metal Research,China Academy of Science(No.2021-PY09)the Doctoral Scientific Research Foundation of Liaoning Province(No.2020-BS-007)。
文摘To reduce microsegregation,a series of homogenization treatments were carried out on a Ni-Co based superalloy prepared through directional solidification(DS).The element segregation characteristics and microstructural evolution were investigated by optical microscopy(OM),scanning electron microscopy(SEM),and electron probe microanalysis(EPMA).The results show that the elements are non-uniformly distributed in the solidified superalloy,in which W and Ti have the greatest tendency of microsegregation.Furthermore,severe microsegregation leads to complicated precipitations,includingη-Ni_(3) Ti and eutectic(γ+γ’).EPMA results show that Al and Mo are uniformly distributed between the eutectic(γ+γ’)andγmatrix,whereas Ti is segregated in the eutectic(γ+γ’)andηphases.The positive segregation element Ti,which is continuously rejected into the remaining liquid duringγmatrix solidification,promotes the formation of eutectic(γ+γ’)and the transformation of theηphase.According to the homogenization effect,the optimal single-stage homogenization process of this alloy is 1180℃for 2 h because of the sufficient diffusion segregation of the elements.In the present study,a kinetic diffusion model was built to reflect the degree of element segregation during homogenization,and the diffusion coefficients of W and Ti were estimated.
基金the financial support from the National Natural Science Foundation of China(No.51671189)the Ministry of Science and Technology of China(Nos.2017YFA0700703 and 2019YFA0705304)。
文摘The effects of strain rate on the microstructural evolution and deformation mechanism of a Ni-Co based superalloy were investigated by isothermal compression tests performed atγ'sub-solvus(1090℃)andγ'super-solvus temperatures(1150℃)with a wide strain rate range from 0.001 to 10 s^(-1)under a true strain of 0.693.Electron backscatter diffraction(EBSD),electron channeling contrast imaging(ECCI)and transmission electron microscope(TEM)techniques were used to characterize the microstructures.The results revealed that the dynamic recrystallization(DRX)volume fraction increased and stored energy of theγ'matrix grains decreased with increasing the strain rate duringγ'sub-solvus temperature deformation,while the opposite phenomena were observed duringγ'super-solvus temperature deformation.The comprehensive effect of initial grain size,primaryγ'phase,twins and adiabatic temperature rise led to these results.The primaryγ'particles undergone the deformation behavior within itself and obviously accelerated the DRX of the matrix.The microstructural evolution proved that discontinuous dynamic recrystallization(DDRX)was the dominant mechanism during the hot deformation carried out at bothγ'sub-solvus andγ'super-solvus temperatures.Primaryγ'particles obviously accelerated the nucleation step and retarded the growth step of DDRX duringγ'sub-solvus temperature deformation.Besides,the acceleration effect of primaryγ'particles on DDRX increased with the increase of strain rate.Continuous dynamic recrystallization(CDRX)was confirmed to be an assistant mechanism duringγ'super-solvus temperature deformation and was promoted with the increase of strain rate.
基金financially supported by the National Natural Science Foundation of China(Nos.51671189 and 51271174)the Ministry of Science and Technology of China(Nos.2017YFA0700703 and 2019YFA0705304)。
文摘The Portevin-Le Chatelier(PLC)effect is a plastic instability in alloys at certain strain rates and deformation temperatures.This plastic instability exhibits serrated yielding in the temporal domain and strain localization in the spatial domain.Wrought Ni-based superalloys often exhibit the PLC effect.To guarantee the safe and stable operation of equipment,it is important to study the PLC effect in wrought Ni-based superalloys.This paper provides a review of various experimental phenomena and micromechanisms related to the PLC effect in wrought Ni-based superalloys,which have been reported in various publications in recent years and include work from our own group.The influences of stacking fault energy andγ’precipitates on the PLC effect in wrought Ni-based superalloys are also discussed in detail.Additionally,several suggestions for the future study of the PLC effect in wrought Ni-based superalloys are provided.
基金supported by the National Natural Science Foundation of China(Grant Nos.11335010,51271174,11802080 and 11627803)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB22040502)。
文摘The macroscopically localized deformation behaviors of Ni–Co-based superalloys with differentγ’precipitate content were investigated at 500?C and 1×10-4 s-1 via an in situ method namely,digital image correlation(DIC).The DIC results showed that the serrated flow of the stress–strain curves was accompanied by localized deformation of the specimens.The fracture morphology was characterized mainly by transgranular fracture with numerous dimples in the lowγ’content alloy,and intergranular fracture with large fracture section in the highγ’content alloy.The Portevin–Le Chatelier(PLC)effect occurred in the investigated Ni–Co-based superalloys.Furthermore,the localized deformation of the highγ’content alloy was more severe than that of the lowγ’content alloy,and the band width was slightly larger.Moreover,for the first-time ever,a special propagation feature,namely±60?zigzag bands characterized by head-to-tail connections,was observed in the highγ’content alloy.
基金the financial support from the National Key Research and Development Program of China(Grant No.2019YFA0705300)the National Natural Science Foundation of China(Grant No.52004051)the Innovation Team Project for Key Fields of Dalian(Grant No.2019RT13).
文摘The new Ni-Co-based superalloy featuring a"fusion structure"was produced utilizing electron beam smelting layered solidification technology(EBSL).Experimental examination of hot compression deformation with varied settings for EBSL and conventional duplex process melting Ni-Co superalloys was performed.As per the study,EBSL-Ni-Co superalloys exhibited enhanced recrystallization susceptibility during hot deformation.Furthermore,elevating deformation temperature,lowering strain rate,and augmenting strain collectively contribute to enlarging the volume fraction of dynamically recrystallized grains.Aberrant growth of grains occurred when the deformation temperature equaledγ′sub-solvus temperature and the strain rate was slower.Moreover,exceeding theγ′solvus temperature during deformation significantly increases the particle size of dynamic recrystallization(DRX)grains.Theγ′phase can effectively modulate the DRX grain size through the pegging effect.Additionally,it was revealed that the presence of the fusion structure aids in the generation of continuous dynamic recrystallization,discontinuous dynamic recrystallization,and twinning-induced dynamic recrystallization while the alloy undergoes hot deformation.This mechanism promotes DRX granule formation and permits complete recrystallization.Ultimately,the fusion structure was identified as playing a catalytic role in the dynamic recrystallization process of the new Ni-Co superalloy.
基金financially supported by the National Key R&D Program of China (Nos.2017YFA0700703 and 2019YFA0705300)the National Natural Science Foundation of China (Grant Nos.11872354 and 11627803)+1 种基金the National Science and Technology Major Project (Grant Nos.J2019-V-0006-0100)the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant Nos.XDB22040502)。
文摘The trade-off between strength and ductility has been an enormous difficulty in the field of materials for an extended time due to their inverse correlation. In this work, friction stir processing(FSP) was for the first time performed to high-strength and high-melting-point Ni-Co based superalloy(GH4068),and enhanced strength and ductility were achieved in FSP samples. At room temperature, the FSP sample demonstrated significantly higher yield strength and ultimate tensile strength(1290 and 1670 MPa)than that of the base material(BM, 758 and 904 MPa) and advanced wrought GH4068 alloy(982 and 1291 MPa), concurrent with high tensile ductility(~24%). Compared with the BM, 70% higher yield strength of the FSP sample results from the remarkable contribution of grain-boundary and nanotwin strengthening, which has been confirmed by the multimechanistic model studied in this work. More importantly, with increasing temperature, an excellent strength-ductility synergy was obtained at 400 ℃,i.e., the yield strength of the FSP sample was increased by more than 50% compared with the BM(from789 to 1219 MPa);more interestingly, the elongation was also significantly increased from 17.9% in the BM to 28.5% in the FSP sample. Meanwhile, the Portevin-Le Chatelier effect was observed in the engineering stress-strain curve. The occurrence of this effect may be attributed to the interaction between solutes and defects like twins and mobile dislocations. Moreover, the grain refinement mechanism of FSP samples was proved to be discontinuous dynamic recrystallization.
文摘In the Original publication of the article,the Chinese title and author names appeared inadvertently in the Ref.[24].The corrected Ref.[24]is given below.
基金financially supported by the National Key R&D Program of China (No.2019YFA0705300)the National Natural Science Foundation of China (No.52004051)+1 种基金the Doctoral Start-up Foundation of Liaoning Province (No.2021-BS-069)Support Plan for Innovation Teams in Key Areas of Dalian (No.2019RT13).
文摘A turbine disk alloy was prepared by electron beam sheet lamination(EBSL),giving a refined microstruc-ture and high purity,and the microstructure-property relationship of this alloy has been developed.The alloy showed an outstanding creep life of 1266.3 h at 953 K/500 MPa.Compared with the conventional vacuum induction melted and vacuum arc re-melted alloy,a smaller dendrite arm spacing of less than 23μm was obtained through the EBSL method,which restricted the formation of large inter-dendritic carbides.As a result,the typical intergranular failure mode was observed in the EBSL alloy,whereas the transgranular fracture mode was dominant in the conventional alloy.The inter-dendritic MC carbides formed from the reverse diffusion of Nb are believed to either impede grain boundary sliding or initi-ate cracks,depending on their size and morphology.The tiny grain boundary precipitates of theδphase in the EBSL alloy could reduce the critical stress for microvoid nucleation to 161.07 MPa by decoher-ing the particle/matrix interface,or allowing vacancy condensation near theδinterface,resulting in the formation of grain boundary microcracks.In the conventional alloy,however,the larger-sized MC car-bides which were formed during the solidification process(0.36 vol.%)nucleated the microcracks within the particles,leading to the transgranular fracture.Furthermore,the results indicated that the nanoscaleγ′andγ″precipitates contributed primarily to strengthening and coordinating intragranular deforma-tion during creep,in which the Orowan mechanism and shearing of a/6<211>partial dislocations and a/2<110>doublets were active forγ′andγ″precipitates,respectively.
基金the National Key R&D Program of China(Nos.2019YFA0705300 and 2017YFA0700703)the National Science and Technology Major Project of China(No.2019-VI-0006-0120)+1 种基金the IMR Innovation Fund(No.2021-PY09)the Doctoral Start-up Foundation of Liaoning Province(No.2020-BS-007).
文摘Deformation twinning is an important deformation mechanism in nickel-based superalloys. For superalloys, deformation twins are generally observed at low or intermediate temperatures and high strain rates;however, the appearance of microtwins(MTs) at high temperatures has rarely been reported. In this study, transmission electron microscopy(TEM) was used to study MT formation in Ni-Co-based superalloys following compression at 1120 °C/1 s. The deformation behavior was discussed in detail to reveal the mechanism of MT formation. The twinning mechanism at elevated temperatures was theoretically attributed to the low stacking fault energy(SFE) and poor dislocation-driven deformations caused by the high strain rate in specific directions.
基金partly supported by the High Technology Research and Development Program of China (No. 2014AA041701)the National Natural Science Foundation of China (Nos. 51171179, 51271174, 51331005, and 11332010)China Postdoctoral Science Foundation under Grant No. 2015M580923
文摘The grain boundary microstructures of a heat-treated Ni-based cast superalloy IN792 were investigated. The results show that M5B3 boride precipitates at the grain boundary. A special orientation relationship between M5B3 phase and the matrix at one side of the grain boundary is found. At the same time, two M5B3 borides with different orientations could co-exist in a single M5B3 particle as an intergrowth besides existing alone, thus forming orientation relationship between the two M5B3 phases and matrix. This phenomenon could be attributed to the special orientation relationship between M5B3 phase and the matrix.
基金partly supported by "Hundred of Talents Projects"the National Basic Research Program (973 Program) of China under grant No. 2010CB631206the National Natural Science Foundation of China (NSFC) under Grant Nos. 51171179, 51128101 and 51271174
文摘Characteristics of dynamic strain aging （DSA） in a Ni-Co-base superalloy were studied by tensile tests at temperatures ranging from 250 ℃ to 550 ℃ and strain rates ranging from 3 x 10-5 to 8 x 10-4 s-1. Serrated flow in the tensile stress-strain curves was observed in the temperature range from 300 ℃ to 500 ℃. Normal DSA behavior was found at temperatures ranging from 300 ℃ to 350 ℃, while inverse DSA behavior was observed at temperatures ranging from 400 ℃ to 500 ℃. The yield strength, ultimate tensile strength, elongation, work hardening index, and fracture features were not affected by temperature and strain rates in DSA regime. Negative strain-rate sensitivity of flow stress was observed in DSA regime. The analysis suggests that the ordering of the substitutional solutes around some defects like mobile dislocations and stacking faults due to the thermal activated process may cause the serrations on the tensile curves.
