Co-Ni-based superalloys are known for their capability to function at elevated temperatures and superior hot corrosion and thermal fatigue resistance.Therefore,these alloys show potential as crucial high-temperature s...Co-Ni-based superalloys are known for their capability to function at elevated temperatures and superior hot corrosion and thermal fatigue resistance.Therefore,these alloys show potential as crucial high-temperature structural materials for aeroengine and gas turbine hot-end components.Our previous work elucidated the influence of Ti and Ta on the high-temperature mechanical properties of alloys.However,the intricate interaction among elements considerably affects the oxidation resistance of alloys.In this paper,Co-35Ni-10Al-2W-5Cr-2Mo-1Nb-xTi-(5−x)Ta alloys(x=1,2,3,4)with varying Ti and Ta contents were designed and compounded,and their oxidation resistance was investigated at the temperature range from 800 to 1000℃.After oxidation at three test conditions,namely,800℃for 200 h,900℃for 200 h,and 1000℃for 50 h,the main structure of the oxide layer of the alloy consisted of spinel,Cr_(2)O_(3),and Al_(2)O_(3)from outside to inside.Oxides consisting of Ta,W,and Mo formed below the Cr_(2)O_(3)layer.The interaction of Ti and Ta imparted the highest oxidation resistance to 3Ti2Ta alloy.Conversely,an excessive amount of Ti or Ta resulted in an adverse effect on the oxidation resistance of the alloys.This study reports the volatilization of W and Mo oxides during the oxidation process of Co-Ni-based cast superalloys with a high Al content for the first time and explains the formation mechanism of holes in the oxide layer.The results provide a basis for gaining insights into the effects of the interaction of alloying elements on the oxidation resistance of the alloys they form.展开更多
The additive manufacturing(AM)of Ni-based superalloys has attracted extensive interest from both academia and industry due to its unique capabilities to fabricate complex and high-performance components for use in hig...The additive manufacturing(AM)of Ni-based superalloys has attracted extensive interest from both academia and industry due to its unique capabilities to fabricate complex and high-performance components for use in high-end industrial systems.However,the intense temperature gradient induced by the rapid heating and cooling processes of AM can generate high levels of residual stress and metastable chemical and structural states,inevitably leading to severe metallurgical defects in Ni-based superalloys.Cracks are the greatest threat to these materials’integrity as they can rapidly propagate and thereby cause sudden and non-predictable failure.Consequently,there is a need for a deeper understanding of residual stress and cracking mechanisms in additively manufactured Ni-based superalloys and ways to potentially prevent cracking,as this knowledge will enable the wider application of these unique materials.To this end,this paper comprehensively reviews the residual stress and the various mechanisms of crack formation in Ni-based superalloys during AM.In addition,several common methods for inhibiting crack formation are presented to assist the research community to develop methods for the fabrication of crack-free additively manufactured components.展开更多
The strengthening effects of alloying elements Re,Ta,and W in the[110](001)dislocation core of theγ/γ'interface are studied by first-principles calculations.From the level of energy the substitution formation en...The strengthening effects of alloying elements Re,Ta,and W in the[110](001)dislocation core of theγ/γ'interface are studied by first-principles calculations.From the level of energy the substitution formation energies and the migration energies of alloying elements are computed and from the level of electron the differential charge density(DCD)and the partial density of states(PDOSs)are computed.Alloying elements above are found to tend to substitute for Al sitesγ'phase by analyzing the substitution formation energy.The calculation results for the migration energies of alloying elements indicate that the stability of the[110](001)dislocation core is enhanced by adding Ta,W,and Re and the strengthening effect of Re is the strongest.Our results agree with the relevant experiments.The electronic structure analysis indicates that the electronic interaction between Re-nearest neighbor(NN)Ni is the strongest.The reason why the doped atoms have different strengthening effects in the[110](001)dislocation core is explained at the level of electron.展开更多
The doping effects on the stacking fault energies(SFEs),including the superlattice intrinsic stacking fault and superlattice extrinsic stacking fault,were studied by first principles calculation of the γ' phase i...The doping effects on the stacking fault energies(SFEs),including the superlattice intrinsic stacking fault and superlattice extrinsic stacking fault,were studied by first principles calculation of the γ' phase in the Ni-based superalloys.The formation energy results show that the main alloying elements in Ni-based superalloys,such as Re,Cr,Mo,Ta,and W,prefer to occupy the Al-site in Ni3Al,Co shows a weak tendency to occupy the Ni-site,and Ru shows a weak tendency to occupy the Al-site.The SFE results show that Co and Ru could decrease the SFEs when added to fault planes,while other main elements increase SFEs.The double-packed superlattice intrinsic stacking fault energies are lower than superlattice extrinsic stacking fault energies when elements(except Co)occupy an Al-site.Furthermore,the SFEs show a symmetrical distribution with the location of the elements in the ternary model.A detailed electronic structure analysis of the Ru effects shows that SFEs correlated with not only the symmetry reduction of the charge accumulation but also the changes in structural energy.展开更多
The phase partition and site preference of Re atoms in a ternary Ni-Al-Re model alloy,including the electronic structure of different Re configurations,are investigated with first-principles calculations and atom prob...The phase partition and site preference of Re atoms in a ternary Ni-Al-Re model alloy,including the electronic structure of different Re configurations,are investigated with first-principles calculations and atom probe tomography.The Re distribution of single,nearest neighbor(NN),next-nearest neighbor(NNN),and cluster configurations are respectively designed in the models withγandγphases.The results show that the Re atoms tend to enteringγphase and the Re atoms prefer to occupy the Al sites inγphase.The Re cluster with a combination of NN and NNN Re-Re pair configuration is not preferred than the isolated Re atom in the Ni-based superalloys,and the configuration with isolated Re atom is more preferred in the system.Especially,the electronic states are analyzed and the energetic parameters are calculated.The electronic structure analyses show there exists strong Ni-Re electronic interaction and it is mainly contributed by the d-d hybridization.The characteristic features of the electronic states of the Re doping effects are also given.It is also found that Re atoms prefer the Al sites inγside at the interface.The density of states at or near the Fermi level and the d-d hybridizations of NN Ni-Re are found to be important in the systems.展开更多
Three kinds of superalloys were prepared by spray deposited process. The analysis results of microstructures and mechanical properties indicate that the spray deposited preforms with higher integral densification and ...Three kinds of superalloys were prepared by spray deposited process. The analysis results of microstructures and mechanical properties indicate that the spray deposited preforms with higher integral densification and the oxygen content in each kind of superalloy was very low. The microstructures are consisted of fine grain without dendritic equi-axed. The spray deposited superalloys possessed good ductility. The forging experiment displays that even though the once deformation of spray deposited GH742 alloy more than 60%, the crack can not be found. Meanwhile, the mechanical properties of spray deposited superalloys are significantly increased.展开更多
An analytical method to investigate the morphological evolution of the cellular microstructure is explored and proposed. The method is essentially based on the Eshelby's micromechanics theory, and it is extended s...An analytical method to investigate the morphological evolution of the cellular microstructure is explored and proposed. The method is essentially based on the Eshelby'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-4single crystal Ni-based superalloy.展开更多
A high thrust-to-weight ratio poses challenges to the high-temperature performance of Ni-based superalloys. The oxidation behavior of GH4738 at extreme temperatures has been investigated by isothermal and non-isotherm...A high thrust-to-weight ratio poses challenges to the high-temperature performance of Ni-based superalloys. The oxidation behavior of GH4738 at extreme temperatures has been investigated by isothermal and non-isothermal experiments. As a result of the competitive diffusion of alloying elements, the oxide scale included an outermost porous oxide layer (OOL), an inner relatively dense oxide layer (IOL), and an internal oxide zone (IOZ), depending on the temperature and time. A high temperature led to the formation of large voids at the IOL/IOZ interface. At 1200℃, the continuity of the Cr-rich oxide layer in the IOL was destroyed, and thus, spallation occurred. Extension of oxidation time contributed to the size of Al-rich oxide particles with the increase in the IOZ. Based on this finding,the oxidation kinetics of GH4738 was discussed, and the corresponding oxidation behavior at 900-1100℃ was predicted.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
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
A low-density single crystal(LDS) alloy with the composition of high Mo content was designed.The extra 1.5 wt% Mo was added in the Alloy A with the composition of Ni-6.5 Al-8.0 Mo-2.4 Cr-6.2 Ta-4.9 Co-1.5 Re-(0.01-0.0...A low-density single crystal(LDS) alloy with the composition of high Mo content was designed.The extra 1.5 wt% Mo was added in the Alloy A with the composition of Ni-6.5 Al-8.0 Mo-2.4 Cr-6.2 Ta-4.9 Co-1.5 Re-(0.01-0.05) Y(wt%) to study the influence of Mo on the lattice parameter and partitioning behavior.Scanning electron microscope(SEM) with energy-dispersive spectrometer(EDS),transmission electron microscopy(TEM)and high-temperature X-ray diffraction(HT-XRD) were used to observe the microstructure,analyze the elemental content and measure the lattice parameter of the alloys.The natural lattice misfit was calculated by lattice constants which were measured by HT-XRD at the temperature from 25 to 1150℃,and the results showed that the lattice misfit would be more and more negative with temperature increasing.It was found that 1.5 wt% addition of Mo will increase the absolute value of the lattice misfit of γ/γ’phases and the volume fraction of γ’,and at the same time,influence the elemental distribution in γ and γ’ phases,especially Re and Cr.Re has a higher partitioning ratio(k) after the addition of Mo.展开更多
Plastic deformation bonding(PDB)has emerged as a promising solid state bonding technique with limited risk of phase transformations and residual thermal stresses in the joint.In this study,the PDB behavior of IN718 su...Plastic deformation bonding(PDB)has emerged as a promising solid state bonding technique with limited risk of phase transformations and residual thermal stresses in the joint.In this study,the PDB behavior of IN718 superalloy was systematically investigated by performing a series of isothermal compression tests at various processing conditions.It was revealed that,with increasing PDB strain rate at 1000?C,different extents of dynamic recrystallization(DRX)occur in the bonding area of IN718 joints.The extent of DRX,average size of DRXed grains,and a newly proposed"interfacial bonding ratio(?Bonding)"parameter(to quantify the bond quality)were initially reduced with increase in the strain rate up to 0.1 s-1 and later increased at further higher strain rates.Electron backscattered diffraction(EBSD)and transmission electron microscopy(TEM)based interfacial microstructure analyses indicated that the quality of the bonded joints is closely related with the development of fine DRXed grains at the bonding interface with the increasing strain,which promotes adiabatic temperature rise.It was revealed that the initial bulging and subsequent migration of the original interfacial grain boundary(IGB)were the main mechanisms promoting DRX in the well bonded IN718 superalloy joints.Moreover,the mechanical properties of the bonded joints were not only controlled by the recrystallized microstructure but also depended upon the Bonding parameter of the joints.展开更多
The microstructure and partitioning behaviors of alloying elements in the γ and γ′ phases in Ni-based powder metallurgy superalloys with different Ti and Al contents were investigated. The results showed that Ti an...The microstructure and partitioning behaviors of alloying elements in the γ and γ′ phases in Ni-based powder metallurgy superalloys with different Ti and Al contents were investigated. The results showed that Ti and Al were mainly enriched in the γ′ phase, partially partitioned in the γ matrix, and slightly distributed in the carbides. Different Ti and Al contents in various alloys influenced the composition and amount of MC carbides but did not influence the MC carbides' morphology. With increasing Ti and Al contents, γ + γ′ fan-type structures formed at the grain boundary, eventually resulting in a coarsened γ′ phase. In addition, the morphology of the secondary γ′ phase transformed from nearly spherical to cuboidal. The saturation degrees of Cr, Co, and Mo in the γ matrix were substantially improved with increasing Ti and Al contents.展开更多
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 st...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 different inclusions of micromechanical model are calculated when applying a tensile or compressive loading along the[001] direction. The calculated results can successfully predict 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
Generating sufficient strains on metal surfaces are highly challenging owing to that most metals can deform plastically to relax the strains on the surfaces.In this work,we developed a facile but highly efficient stac...Generating sufficient strains on metal surfaces are highly challenging owing to that most metals can deform plastically to relax the strains on the surfaces.In this work,we developed a facile but highly efficient stacked deposition strategy to in situ activation and reconstruction of NiO/NiOOH on Ni matrix,following with the migration of Fe ions to NiOOH.The Fe sites on the Ni/NiO/NiOOH facilitate the formation of the stable*OH oxygenated intermediates,and the Ni matrix in the catalyst provides the catalyst excellent stability.The oxygen evolution reaction(OER)performance of the stacked NiFe-5 with compressive strain displays the strengthened binding to oxygenated intermediates and superior OER activity,the ultralow overpotentials of 162 versus reversible hydrogen electrode at 10 mA cm^(-2).On the other hand,the Ni-5 without the incorporation of Fe has shown an outstanding hydrogen evolution reaction(HER)activity,affording an overpotential of 47 mV at 10 mA cm^(-2).The NiFe-5‖Ni-5 enables the overall water splitting at a voltage of 1.508 V to achieve 20 mA cm^(-2) with remarkable durability.The stacked deposition strategy improves binding strength of Ni-based catalysts to oxygenated intermediates via generating compressive strain,causing high catalytic activities on OER and HER.展开更多
Steam reforming(SR)of fossil methane is already a well-known,documented and established expertise in the industrial sector as it accounts for the vast majority of global hydrogen production.From a sustainable developm...Steam reforming(SR)of fossil methane is already a well-known,documented and established expertise in the industrial sector as it accounts for the vast majority of global hydrogen production.From a sustainable development perspective,hydrogen production by SR of biomass-derived feedstock represents a promising alternative that could help to lower the carbon footprint of the traditional process.In this regard,bio-alcohols such as methanol,ethanol or glycerol are among the attractive candidates that could serve as green hydrogen carriers as they decompose at relatively low temperatures in the presence of water compared to methane,allowing for improved H_(2)yields.However,significant challenges remain regarding the activity and stability of nickel-based catalysts,which are most widely used in alcohol SR processes due to their affordability and ability to break C–C,O–H and C–H bonds,yet are prone to rapid deactivation primarily caused by coke deposition and metal particle sintering.In this state-of-the-art review,a portfolio of strategies to improve the performance of Ni-based catalysts used in alcohol SR processes is unfolded with the intent of pinpointing the critical issues in catalyst development.Close examination of the literature reveals that the efforts tackling these recurring issues can be directed at the active metal,either by tuning Ni dispersion and Ni-support interactions or by targeting synergistic effects in bimetallic systems,while others focus on the support,either by modifying acid-base character,oxygen mobility,or by embedding Ni in specific crystallographic structures.This review provides a very useful tool to orient future work in catalyst development.展开更多
The effects of Ta content(2.72wt.%,3.10wt.%and 4.00wt.%)on the solidification characteristics and mechanical properties of directionally solidified DZ411 Ni-based superalloys were investigated.It is found that the con...The effects of Ta content(2.72wt.%,3.10wt.%and 4.00wt.%)on the solidification characteristics and mechanical properties of directionally solidified DZ411 Ni-based superalloys were investigated.It is found that the content of Mo decreases with the increase of Ta in liquid phase after directional solidification,indicating the addition of Ta can reduce the element segregation in alloys.The primary and secondary dendrite arm spacings(PDAS and SDAS)of the DZ411 alloy increase with the addition of Ta,which are consistent with the models by Hunt and Wagner.The increase of PDAS and SDAS can provide enough space for the growth of tertiary dendrite arms,which hinders the growth of unfavorably oriented primary dendrites.As a result,the addition of Ta facilitates the growth of favorably oriented dendrites.More MC carbides andγ-γ'eutectics are formed in the interdendritic regions,which is attributed to the segregation of Ta in the liquid phase.Furthermore,the degree of supersaturation of W,Mo inγmatrix increases with the increase of Ta,thus,the addition of Ta promotes the formation of TCP phase.The addition of Ta also increases the microhardness in both the primary dendrite and interdendritic regions of the alloy,and the microhardness of the primary dendrite is closer to that in interdendritic regions with the increase of Ta.展开更多
This paper develops a Bayesian inference-based probabilistic crack nucleation model for the Ni-based superalloy René88DT under fatigue loading.A data-driven,machine learning approach is developed,identifying unde...This paper develops a Bayesian inference-based probabilistic crack nucleation model for the Ni-based superalloy René88DT under fatigue loading.A data-driven,machine learning approach is developed,identifying underlying mechanisms driving crack nucleation.An experimental set of fatigue-loaded microstructures is characterized near crack nucleation sites using scanning electron microscopy and electron backscatter diffraction images for correlating the grain morphology and crystallography to the location of crack nucleation sites.A concurrent multiscale model,embedding experimental polycrystalline microstructural representative volume elements(RVEs)in a homogenized material,is developed for fatigue simulations.The RVE domain is modeled by a crystal plasticity finite element model.An anisotropic continuum plasticity model,obtained by homogenization of the crystal plasticity model,is used for the exterior domain.A Bayesian classification method is introduced to optimally select informative state variable predictors of crack nucleation.From this principal set of state variables,a simple scalar crack nucleation indicator is formulated.展开更多
The formation and properties of precipitates in wrought Ni-based superalloys with different W contents during long-term exposure to high temperatures were investigated.The scanning electron microscope,transmission ele...The formation and properties of precipitates in wrought Ni-based superalloys with different W contents during long-term exposure to high temperatures were investigated.The scanning electron microscope,transmission electron microscope,and chemical phase analysis were used to investigate the formation and properties of precipitates.It is found that with increasing W content,the quantity and thermal stability of MC carbide in Ni-based superalloys increased,while the quantity of M_(23)C_(6)carbides decreased.As the results show,W has a higher partition coefficient in γ'-and γ-matrix,and the addition of W promotes the precipitation of γ'phase.W content has no significant effect on the morphology,size,crystal structure,and coarsening rate of γ'precipitates.The influence of W content on high-temperature tensile and creep properties of the alloys was investigated.The results showed that W content has no obvious influence on the high-temperature yield strength,but the elongation and area reduction decreased significantly when the addition of W was more than 4 wt.%.Because of the similar volume fractions of γ'phase,the creep fracture strengths in the tested alloys with lower W concentrations were not significantly different after long-term exposure at 700℃.展开更多
This study developed a new high-throughput strategy,designated as hot-isostatic-pres sing-based microsynthesis approach(HIP-MSA),to optimize high-performance nickel-based superalloys in a rapid,efficient,and cost-effe...This study developed a new high-throughput strategy,designated as hot-isostatic-pres sing-based microsynthesis approach(HIP-MSA),to optimize high-performance nickel-based superalloys in a rapid,efficient,and cost-effective manner.A specific honeycomb-array structure containing 106 discrete cells was designed and optimized using finite element analysis(FEA)and then applied to create a combinatorial library consisting of 106 Ni-based superalloys with various Co,Nb and Ta concentrations.By integration with high-throughput characterization tools,extensive composition and phase structure data were collected quickly and efficiently.In the superalloys with higher amounts of Nb and Ta,the detrimentalηphase displaying needle-like morphology was observed,and its content(wt%)increased drastically with Ta and Nb contents increasing.However,the increase of Co addition in those alloys was confirmed to be surprisingly beneficial by significantly suppressing the formation ofηphase that was induced by high Nb and Ta contents.The zero-phasefraction(ZPF)line ofηphase was established,which is critical to design superalloy chemistry for superior micros tructural stability at high-temperature service conditions.展开更多
基金the National Major Science and Technology Projects of China(Nos.J2019-VII-0010-0150 and J2019-VI-0009-0123)National Natural Science Foundation of China(Nos.52022011 and 52090041)+3 种基金Beijing Nova Program(No.Z211100002121170)Science Center for Gas Turbine Project(No.P2021-A-IV-001-002)Science and Technology on Advanced High Temperature Structural Materials Laboratory(No.6142903210306)Xiaomi Young Scholars Program.
文摘Co-Ni-based superalloys are known for their capability to function at elevated temperatures and superior hot corrosion and thermal fatigue resistance.Therefore,these alloys show potential as crucial high-temperature structural materials for aeroengine and gas turbine hot-end components.Our previous work elucidated the influence of Ti and Ta on the high-temperature mechanical properties of alloys.However,the intricate interaction among elements considerably affects the oxidation resistance of alloys.In this paper,Co-35Ni-10Al-2W-5Cr-2Mo-1Nb-xTi-(5−x)Ta alloys(x=1,2,3,4)with varying Ti and Ta contents were designed and compounded,and their oxidation resistance was investigated at the temperature range from 800 to 1000℃.After oxidation at three test conditions,namely,800℃for 200 h,900℃for 200 h,and 1000℃for 50 h,the main structure of the oxide layer of the alloy consisted of spinel,Cr_(2)O_(3),and Al_(2)O_(3)from outside to inside.Oxides consisting of Ta,W,and Mo formed below the Cr_(2)O_(3)layer.The interaction of Ti and Ta imparted the highest oxidation resistance to 3Ti2Ta alloy.Conversely,an excessive amount of Ti or Ta resulted in an adverse effect on the oxidation resistance of the alloys.This study reports the volatilization of W and Mo oxides during the oxidation process of Co-Ni-based cast superalloys with a high Al content for the first time and explains the formation mechanism of holes in the oxide layer.The results provide a basis for gaining insights into the effects of the interaction of alloying elements on the oxidation resistance of the alloys they form.
基金This work was supported by Shenzhen-Hong Kong Science and Technology Innovation Cooperation Zone Shenzhen Park Project:HZQB-KCZYB-2020030the National Natural Science Foundation of China(No.91860131and No.52074157)+2 种基金Guangdong Provincial Department of Science and Technology,Key-Area Research and Development Program of Guangdong Province(No.2020B090923002)the National Key Research and Development Program of China(No.2017YFB0702901)the Shenzhen Science and Technology Innovation Commission(No.JCYJ20170817111811303,No.KQTD20170328154443162and No.ZDSYS201703031748354).
文摘The additive manufacturing(AM)of Ni-based superalloys has attracted extensive interest from both academia and industry due to its unique capabilities to fabricate complex and high-performance components for use in high-end industrial systems.However,the intense temperature gradient induced by the rapid heating and cooling processes of AM can generate high levels of residual stress and metastable chemical and structural states,inevitably leading to severe metallurgical defects in Ni-based superalloys.Cracks are the greatest threat to these materials’integrity as they can rapidly propagate and thereby cause sudden and non-predictable failure.Consequently,there is a need for a deeper understanding of residual stress and cracking mechanisms in additively manufactured Ni-based superalloys and ways to potentially prevent cracking,as this knowledge will enable the wider application of these unique materials.To this end,this paper comprehensively reviews the residual stress and the various mechanisms of crack formation in Ni-based superalloys during AM.In addition,several common methods for inhibiting crack formation are presented to assist the research community to develop methods for the fabrication of crack-free additively manufactured components.
基金Project supported by the National Key Research and Development Program of China(Grant No.2017YFB0701503).
文摘The strengthening effects of alloying elements Re,Ta,and W in the[110](001)dislocation core of theγ/γ'interface are studied by first-principles calculations.From the level of energy the substitution formation energies and the migration energies of alloying elements are computed and from the level of electron the differential charge density(DCD)and the partial density of states(PDOSs)are computed.Alloying elements above are found to tend to substitute for Al sitesγ'phase by analyzing the substitution formation energy.The calculation results for the migration energies of alloying elements indicate that the stability of the[110](001)dislocation core is enhanced by adding Ta,W,and Re and the strengthening effect of Re is the strongest.Our results agree with the relevant experiments.The electronic structure analysis indicates that the electronic interaction between Re-nearest neighbor(NN)Ni is the strongest.The reason why the doped atoms have different strengthening effects in the[110](001)dislocation core is explained at the level of electron.
基金Project supported by the National Key Research and Development Program of China(Grant No.2017YFB0701502).
文摘The doping effects on the stacking fault energies(SFEs),including the superlattice intrinsic stacking fault and superlattice extrinsic stacking fault,were studied by first principles calculation of the γ' phase in the Ni-based superalloys.The formation energy results show that the main alloying elements in Ni-based superalloys,such as Re,Cr,Mo,Ta,and W,prefer to occupy the Al-site in Ni3Al,Co shows a weak tendency to occupy the Ni-site,and Ru shows a weak tendency to occupy the Al-site.The SFE results show that Co and Ru could decrease the SFEs when added to fault planes,while other main elements increase SFEs.The double-packed superlattice intrinsic stacking fault energies are lower than superlattice extrinsic stacking fault energies when elements(except Co)occupy an Al-site.Furthermore,the SFEs show a symmetrical distribution with the location of the elements in the ternary model.A detailed electronic structure analysis of the Ru effects shows that SFEs correlated with not only the symmetry reduction of the charge accumulation but also the changes in structural energy.
基金Project supported by the National Key Research and Development Program of China(Grant No.2017YFB0701503)。
文摘The phase partition and site preference of Re atoms in a ternary Ni-Al-Re model alloy,including the electronic structure of different Re configurations,are investigated with first-principles calculations and atom probe tomography.The Re distribution of single,nearest neighbor(NN),next-nearest neighbor(NNN),and cluster configurations are respectively designed in the models withγandγphases.The results show that the Re atoms tend to enteringγphase and the Re atoms prefer to occupy the Al sites inγphase.The Re cluster with a combination of NN and NNN Re-Re pair configuration is not preferred than the isolated Re atom in the Ni-based superalloys,and the configuration with isolated Re atom is more preferred in the system.Especially,the electronic states are analyzed and the energetic parameters are calculated.The electronic structure analyses show there exists strong Ni-Re electronic interaction and it is mainly contributed by the d-d hybridization.The characteristic features of the electronic states of the Re doping effects are also given.It is also found that Re atoms prefer the Al sites inγside at the interface.The density of states at or near the Fermi level and the d-d hybridizations of NN Ni-Re are found to be important in the systems.
基金Funded by the Innovation Fund for Outstanding Scholar of Henan Province(No. 0621000700)
文摘Three kinds of superalloys were prepared by spray deposited process. The analysis results of microstructures and mechanical properties indicate that the spray deposited preforms with higher integral densification and the oxygen content in each kind of superalloy was very low. The microstructures are consisted of fine grain without dendritic equi-axed. The spray deposited superalloys possessed good ductility. The forging experiment displays that even though the once deformation of spray deposited GH742 alloy more than 60%, the crack can not be found. Meanwhile, the mechanical properties of spray deposited superalloys are significantly increased.
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 microstructure is explored and proposed. The method is essentially based on the Eshelby'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-4single crystal Ni-based superalloy.
基金financially supported by the National Key R&D Program of China (No.2021YFB3700400)the National Natural Science Foundation of China (Nos.52074030,51904021,and 52174294)。
文摘A high thrust-to-weight ratio poses challenges to the high-temperature performance of Ni-based superalloys. The oxidation behavior of GH4738 at extreme temperatures has been investigated by isothermal and non-isothermal experiments. As a result of the competitive diffusion of alloying elements, the oxide scale included an outermost porous oxide layer (OOL), an inner relatively dense oxide layer (IOL), and an internal oxide zone (IOZ), depending on the temperature and time. A high temperature led to the formation of large voids at the IOL/IOZ interface. At 1200℃, the continuity of the Cr-rich oxide layer in the IOL was destroyed, and thus, spallation occurred. Extension of oxidation time contributed to the size of Al-rich oxide particles with the increase in the IOZ. Based on this finding,the oxidation kinetics of GH4738 was discussed, and the corresponding oxidation behavior at 900-1100℃ was predicted.
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financially supported by the National Natural Science Foundation of China(Nos.U1435207,51371007 and 51671015)the National Defense Basic Scientific Research Program of China(No.A2120132006)。
文摘A low-density single crystal(LDS) alloy with the composition of high Mo content was designed.The extra 1.5 wt% Mo was added in the Alloy A with the composition of Ni-6.5 Al-8.0 Mo-2.4 Cr-6.2 Ta-4.9 Co-1.5 Re-(0.01-0.05) Y(wt%) to study the influence of Mo on the lattice parameter and partitioning behavior.Scanning electron microscope(SEM) with energy-dispersive spectrometer(EDS),transmission electron microscopy(TEM)and high-temperature X-ray diffraction(HT-XRD) were used to observe the microstructure,analyze the elemental content and measure the lattice parameter of the alloys.The natural lattice misfit was calculated by lattice constants which were measured by HT-XRD at the temperature from 25 to 1150℃,and the results showed that the lattice misfit would be more and more negative with temperature increasing.It was found that 1.5 wt% addition of Mo will increase the absolute value of the lattice misfit of γ/γ’phases and the volume fraction of γ’,and at the same time,influence the elemental distribution in γ and γ’ phases,especially Re and Cr.Re has a higher partitioning ratio(k) after the addition of Mo.
基金supported by the National Key Research and Development Program[grant number 2018YFA0702900]the National Natural Science Foundation of China[grant numbers U1508215,51774265]+2 种基金the National Science and Technology Major Project of China[Grant No.2019ZX06004010]the Key Program of the Chinese Academy of Sciences[grant number ZDRW-CN-20171]Program of CAS Interdisciplinary Innovation Team.
文摘Plastic deformation bonding(PDB)has emerged as a promising solid state bonding technique with limited risk of phase transformations and residual thermal stresses in the joint.In this study,the PDB behavior of IN718 superalloy was systematically investigated by performing a series of isothermal compression tests at various processing conditions.It was revealed that,with increasing PDB strain rate at 1000?C,different extents of dynamic recrystallization(DRX)occur in the bonding area of IN718 joints.The extent of DRX,average size of DRXed grains,and a newly proposed"interfacial bonding ratio(?Bonding)"parameter(to quantify the bond quality)were initially reduced with increase in the strain rate up to 0.1 s-1 and later increased at further higher strain rates.Electron backscattered diffraction(EBSD)and transmission electron microscopy(TEM)based interfacial microstructure analyses indicated that the quality of the bonded joints is closely related with the development of fine DRXed grains at the bonding interface with the increasing strain,which promotes adiabatic temperature rise.It was revealed that the initial bulging and subsequent migration of the original interfacial grain boundary(IGB)were the main mechanisms promoting DRX in the well bonded IN718 superalloy joints.Moreover,the mechanical properties of the bonded joints were not only controlled by the recrystallized microstructure but also depended upon the Bonding parameter of the joints.
基金financially supported by the Guangdong Provincial Key Laboratory for Technology and Application of Metal Toughening (No. GKL201611)the National Natural Science Foundation of China (No. 51571020)the Fundamental Research Funds for the Central Universities (No. FRF-IC-17-002)
文摘The microstructure and partitioning behaviors of alloying elements in the γ and γ′ phases in Ni-based powder metallurgy superalloys with different Ti and Al contents were investigated. The results showed that Ti and Al were mainly enriched in the γ′ phase, partially partitioned in the γ matrix, and slightly distributed in the carbides. Different Ti and Al contents in various alloys influenced the composition and amount of MC carbides but did not influence the MC carbides' morphology. With increasing Ti and Al contents, γ + γ′ fan-type structures formed at the grain boundary, eventually resulting in a coarsened γ′ phase. In addition, the morphology of the secondary γ′ phase transformed from nearly spherical to cuboidal. The saturation degrees of Cr, Co, and Mo in the γ matrix were substantially improved with increasing Ti and Al contents.
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 different inclusions of micromechanical model are calculated when applying a tensile or compressive loading along the[001] direction. The calculated results can successfully predict 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 National Natural Science Foundations of China(21965024,22269016,51721002)the Inner Mongolia funding(2020JQ01,21300-5223601)the funding of Inner Mongolia University(10000-21311201/137,213005223601/003,21300-5223707)。
文摘Generating sufficient strains on metal surfaces are highly challenging owing to that most metals can deform plastically to relax the strains on the surfaces.In this work,we developed a facile but highly efficient stacked deposition strategy to in situ activation and reconstruction of NiO/NiOOH on Ni matrix,following with the migration of Fe ions to NiOOH.The Fe sites on the Ni/NiO/NiOOH facilitate the formation of the stable*OH oxygenated intermediates,and the Ni matrix in the catalyst provides the catalyst excellent stability.The oxygen evolution reaction(OER)performance of the stacked NiFe-5 with compressive strain displays the strengthened binding to oxygenated intermediates and superior OER activity,the ultralow overpotentials of 162 versus reversible hydrogen electrode at 10 mA cm^(-2).On the other hand,the Ni-5 without the incorporation of Fe has shown an outstanding hydrogen evolution reaction(HER)activity,affording an overpotential of 47 mV at 10 mA cm^(-2).The NiFe-5‖Ni-5 enables the overall water splitting at a voltage of 1.508 V to achieve 20 mA cm^(-2) with remarkable durability.The stacked deposition strategy improves binding strength of Ni-based catalysts to oxygenated intermediates via generating compressive strain,causing high catalytic activities on OER and HER.
基金The financial support of the Natural Sciences and Engineering Research Council of Canada(NSERC)the CIRCUIT Program(Centre for Innovation and Research on carbon utilization in industrial technologies,NSERC CREATE program)NSERC for the Alexander Graham Bell Canada Graduate Scholarship(BESCD)。
文摘Steam reforming(SR)of fossil methane is already a well-known,documented and established expertise in the industrial sector as it accounts for the vast majority of global hydrogen production.From a sustainable development perspective,hydrogen production by SR of biomass-derived feedstock represents a promising alternative that could help to lower the carbon footprint of the traditional process.In this regard,bio-alcohols such as methanol,ethanol or glycerol are among the attractive candidates that could serve as green hydrogen carriers as they decompose at relatively low temperatures in the presence of water compared to methane,allowing for improved H_(2)yields.However,significant challenges remain regarding the activity and stability of nickel-based catalysts,which are most widely used in alcohol SR processes due to their affordability and ability to break C–C,O–H and C–H bonds,yet are prone to rapid deactivation primarily caused by coke deposition and metal particle sintering.In this state-of-the-art review,a portfolio of strategies to improve the performance of Ni-based catalysts used in alcohol SR processes is unfolded with the intent of pinpointing the critical issues in catalyst development.Close examination of the literature reveals that the efforts tackling these recurring issues can be directed at the active metal,either by tuning Ni dispersion and Ni-support interactions or by targeting synergistic effects in bimetallic systems,while others focus on the support,either by modifying acid-base character,oxygen mobility,or by embedding Ni in specific crystallographic structures.This review provides a very useful tool to orient future work in catalyst development.
基金This study was funded by the National Natural Science Foundation of China(Grant No.51871118)the fund of the State Key Laboratory of Solidification Processing in NPU,(Grant No.SKLSP202204)the Fundamental Research Funds for the Central Universities(Grant No.lzujbky-2022-ey15).
文摘The effects of Ta content(2.72wt.%,3.10wt.%and 4.00wt.%)on the solidification characteristics and mechanical properties of directionally solidified DZ411 Ni-based superalloys were investigated.It is found that the content of Mo decreases with the increase of Ta in liquid phase after directional solidification,indicating the addition of Ta can reduce the element segregation in alloys.The primary and secondary dendrite arm spacings(PDAS and SDAS)of the DZ411 alloy increase with the addition of Ta,which are consistent with the models by Hunt and Wagner.The increase of PDAS and SDAS can provide enough space for the growth of tertiary dendrite arms,which hinders the growth of unfavorably oriented primary dendrites.As a result,the addition of Ta facilitates the growth of favorably oriented dendrites.More MC carbides andγ-γ'eutectics are formed in the interdendritic regions,which is attributed to the segregation of Ta in the liquid phase.Furthermore,the degree of supersaturation of W,Mo inγmatrix increases with the increase of Ta,thus,the addition of Ta promotes the formation of TCP phase.The addition of Ta also increases the microhardness in both the primary dendrite and interdendritic regions of the alloy,and the microhardness of the primary dendrite is closer to that in interdendritic regions with the increase of Ta.
基金This work has been supported through Grant No.CMMI-1825115 from the National Science Foundation awarded by the Mechanics of Materials and Structures(MOMS)Program(Program Manager:Dr.Siddiq Qidwai)Early stages of this work was supported through a grant No.FA9550-12-1-0445 to the Center of Excellence on Integrated Materials Modeling(CEIMM)at Johns Hopkins University awarded by the AFOSR/RSL Computational Mathematics Program(Managers Dr.Fariba Fahroo and Dr.A.Sayir).
文摘This paper develops a Bayesian inference-based probabilistic crack nucleation model for the Ni-based superalloy René88DT under fatigue loading.A data-driven,machine learning approach is developed,identifying underlying mechanisms driving crack nucleation.An experimental set of fatigue-loaded microstructures is characterized near crack nucleation sites using scanning electron microscopy and electron backscatter diffraction images for correlating the grain morphology and crystallography to the location of crack nucleation sites.A concurrent multiscale model,embedding experimental polycrystalline microstructural representative volume elements(RVEs)in a homogenized material,is developed for fatigue simulations.The RVE domain is modeled by a crystal plasticity finite element model.An anisotropic continuum plasticity model,obtained by homogenization of the crystal plasticity model,is used for the exterior domain.A Bayesian classification method is introduced to optimally select informative state variable predictors of crack nucleation.From this principal set of state variables,a simple scalar crack nucleation indicator is formulated.
基金the National Key Research and Develop Program,China(No.2017YFB0305203).
文摘The formation and properties of precipitates in wrought Ni-based superalloys with different W contents during long-term exposure to high temperatures were investigated.The scanning electron microscope,transmission electron microscope,and chemical phase analysis were used to investigate the formation and properties of precipitates.It is found that with increasing W content,the quantity and thermal stability of MC carbide in Ni-based superalloys increased,while the quantity of M_(23)C_(6)carbides decreased.As the results show,W has a higher partition coefficient in γ'-and γ-matrix,and the addition of W promotes the precipitation of γ'phase.W content has no significant effect on the morphology,size,crystal structure,and coarsening rate of γ'precipitates.The influence of W content on high-temperature tensile and creep properties of the alloys was investigated.The results showed that W content has no obvious influence on the high-temperature yield strength,but the elongation and area reduction decreased significantly when the addition of W was more than 4 wt.%.Because of the similar volume fractions of γ'phase,the creep fracture strengths in the tested alloys with lower W concentrations were not significantly different after long-term exposure at 700℃.
基金financially supported by the National Key Research and Development Program of China (No. 2016YFB0700300)the National Science and Technology Major Project of China (No.J2019-VI-0023-0140)+1 种基金Taishan Scholars Program of Shandong Province (No.tsqn201909081)Shandong Natural Science Foundation of China (No.ZR2020ZD05)
文摘This study developed a new high-throughput strategy,designated as hot-isostatic-pres sing-based microsynthesis approach(HIP-MSA),to optimize high-performance nickel-based superalloys in a rapid,efficient,and cost-effective manner.A specific honeycomb-array structure containing 106 discrete cells was designed and optimized using finite element analysis(FEA)and then applied to create a combinatorial library consisting of 106 Ni-based superalloys with various Co,Nb and Ta concentrations.By integration with high-throughput characterization tools,extensive composition and phase structure data were collected quickly and efficiently.In the superalloys with higher amounts of Nb and Ta,the detrimentalηphase displaying needle-like morphology was observed,and its content(wt%)increased drastically with Ta and Nb contents increasing.However,the increase of Co addition in those alloys was confirmed to be surprisingly beneficial by significantly suppressing the formation ofηphase that was induced by high Nb and Ta contents.The zero-phasefraction(ZPF)line ofηphase was established,which is critical to design superalloy chemistry for superior micros tructural stability at high-temperature service conditions.