The microstructure evolution and deformation mechanism of a DZ125 superalloy during high-temperature creep were studied by means of microstructure observation and creep-property tests.The results show that at the init...The microstructure evolution and deformation mechanism of a DZ125 superalloy during high-temperature creep were studied by means of microstructure observation and creep-property tests.The results show that at the initial stage of high-temperature creep,two sets of dislocations with different Burgers vectors move and meet inγmatrix channels,and react to form a quadrilateral dislocation network.Andγ′phases with raft-like microstructure are generated after the formation of dislocation networks.As creep progresses,the quadrilateral dislocation network is gradually transformed into hexagonal and quadrilateral dislocation networks.During steady stage of creep,the superalloy undergoes deformation with the mechanism that a great number of dislocations slip and climb in the matrix across the raft-likeγ′phases.At the later stage of creep,the raft-likeγ′phases are sheared by dislocations at the breakage of dislocation networks,and then alternate slip occurs,which distorts and breaks the raft-likeγ′/γphases,resulting in the accumulation of micropores at the raft-likeγ′/γinterfaces and the formation of microcracks.As creep continues,the microcracks continue to expand until creep fracture occurs,which is the damage and fracture mechanism of the alloy at the later stage of creep at high temperature.展开更多
The microstructure of single crystal superalloy is relatively simple,consisting primarily ofγdendrites andγ/γ′eutectics.During the directional solidification process of Ni-based single crystal superalloys,withdraw...The microstructure of single crystal superalloy is relatively simple,consisting primarily ofγdendrites andγ/γ′eutectics.During the directional solidification process of Ni-based single crystal superalloys,withdrawal rate is a critical parameter affecting the spatial distribution ofγ/γ′eutectic along gravity direction.The results show that theγ/γ′eutectic fraction of the upper platform surface is always higher than that of the lower one,regardless of withdrawal rate.As the withdrawal rate decreases,there is a significant increase inγ/γ′eutectic fraction on the upper surface,while it decreases on the lower surface.The upward accumulation ofγ/γ′eutectic becomes more severe as the withdrawal rate decreases.It is also found that the percentage of Al+Ta is positively correlated with theγ/γ′eutectic fraction.Thermo-solute convection of Al and Ta solutes in the solidification front is the prime reason for the non-uniform distribution of eutectic.The non-uniform distribution ofγ/γ′eutectic cannot be eliminated even after subsequent solution heat treatment,resulting in excess eutectic on the upper surface and thus leading to the scrapping of the blade.展开更多
With ongoing global warming and increasing energy demands,the CH_(4)-CO_(2)reforming reaction(dry reforming of methane,DRM)has garnered significant attention as a promising carbon capture and utilization technology.Ni...With ongoing global warming and increasing energy demands,the CH_(4)-CO_(2)reforming reaction(dry reforming of methane,DRM)has garnered significant attention as a promising carbon capture and utilization technology.Nickel-based catalysts are renowned for their outstanding activity and selectivity in this process.The impact of metal-support interaction(MSI),on Ni-based catalyst performance has been extensively researched and debated recently.This paper reviews the recent research progress of MSI on Ni-based catalysts and their characterization and modulation strategies in catalytic reactions.From the perspective of MSI,the effects of different carriers(metal oxides,carbon materials and molecular sieves,etc.)are introduced on the dispersion and surface structure of Ni active metal particles,and the effect of MSI on the activity and stability of DRM reactions on Ni-based catalysts is discussed in detail.Future research should focus on better understanding and controlling MSI to improve the performance and durability of nickel-based catalysts in CH_(4)-CO_(2)reforming,advancing cleaner energy technologies.展开更多
The effect of carbon content on the microstructures and stress rupture properties of a newly developed polycrystalline Ni-based superalloy with high Cr content has been studied.It was observed that both grain size and...The effect of carbon content on the microstructures and stress rupture properties of a newly developed polycrystalline Ni-based superalloy with high Cr content has been studied.It was observed that both grain size and the number of carbides increased with an increase in carbon content.After heat treatment,granular M_(23)C_(6)carbides were dispersed around MC carbides along grain boundaries and inside grains.The quantity of granular M_(23)C_(6)carbides increased while their sizes decreased.These findings can be verified with the results of thermodynamic calculation and differential scanning calorimetry analysis.The stress rupture times(975℃/225 MPa)increased from 13.3 to 25.5 h with the carbon content increased from 0.1 to 0.2 wt.%.The improvement can be attributed to two primary factors.Firstly,grain boundary is typically weak region during deformation process and the grain size increased as carbon content increased in the alloy.Secondly,carbides act as hindrances to impede dislocation movement,leading to dislocation entanglement.As carbon content rose,the quantity of carbides in interdendritic regions and grain boundaries increased,providing a certain degree of strengthening effect and resulting in a longer stress rupture time.展开更多
The creep behavior of two PM superalloys,U720Li and RR1000,each alloyed with trace amount of Sc,was systematically investigated.Findings reveal that RR1000 alloy with 0.064 wt.%Sc(R-0.064)demonstrates superior creep r...The creep behavior of two PM superalloys,U720Li and RR1000,each alloyed with trace amount of Sc,was systematically investigated.Findings reveal that RR1000 alloy with 0.064 wt.%Sc(R-0.064)demonstrates superior creep resistance compared to U720Li alloy with 0.043 wt.%Sc(U-0.043),at 650℃ and 1000 MPa,and the primary creep mechanisms in both alloys are identified as dislocation shearing and precipitate bypassing.When tested at 700℃ and 700 MPa,the U-0.043 alloy predominantly exhibits micro-twinning and dislocation bypassing,while the R-0.064 alloy engages in extended stacking fault shearing ofγ'precipitate,dislocation bypassing and climb.At 750℃ and 460 MPa,dislocation bypassing and climb emerge as the main creep mechanisms for both alloys.展开更多
The performance of welded Ni-based superalloys at high temperatures is essential to be evaluated due to their particular service environment for aero-engines and high-speed aircrafts.The tensile properties and related...The performance of welded Ni-based superalloys at high temperatures is essential to be evaluated due to their particular service environment for aero-engines and high-speed aircrafts.The tensile properties and related microstructural evolutions such as the carbide precipitate and grain of a laser-welded Ni-based alloy were experimentally and numerically investigated at different temperatures(20,300,500,800℃).The results show that at room temperature,the strength of the Base Material(BM)was slightly smaller,with a difference of less than 1%,than the Welded Material(WM),which can be attributed to the more uniformly distributed needle-shaped carbide precipitates in the WM than those nonuniformly coarser spherical ones in the BM.While at 300℃ and 500℃,the strength of WM decreased more obviously compared with that of BM due to the more apparent growth of grain:13.52%loss in yield strength in WM alloys as compared with BM alloys at 300℃,and 16.57% at 500℃.At 800℃,the strength of BM and WM both decreased to a similar level due to Dynamic Recrystallization(DRX).However,a much higher elongation was observed for the BM than WM(less than 50%of BM),which can be attributed to the enhanced dislocation accumulation capability of the large spherical carbides along grain boundaries on the fracture surface in BM.Furthermore,a unified model considering the welding effects on both microstructures(dislocation,carbides,and grain)and mechanical properties evolutions at different temperatures was developed and validated.Based on this model,the key temperature ranges(20–600℃)where apparent weakening of strength and uniform plasticity occurs for welded structures were identified,providing a direct guidance for potential structure and process design.展开更多
The coupling between heat and pressure is the kernel of inertia friction welding(IFW)and is still not fully understood.A novel 3D fully coupled finite element model based on a plastic friction pair was developed to si...The coupling between heat and pressure is the kernel of inertia friction welding(IFW)and is still not fully understood.A novel 3D fully coupled finite element model based on a plastic friction pair was developed to simulate the IFW process of a Ni-based superalloy and reveal the omnidirectional thermo-mechanical coupling mechanism of the friction interface.The numerical model successfully simulated the deceleration,deformation processes,and peak torsional moments in IFW and captured the evolution of temperature,contact pressure,and stress.The simulated results were validated through measured thermal history,optical macrography,and axial shortening.The results indicated that interfacial friction heat was the primary heat source,and plastic deformation energy only accounted for 4%of the total.The increase in initial rotational speed and friction pressure elevated the peak temperature,reaching a maximum of 1525.5K at an initial rotational speed of 2000 r/min and friction pressure of 400 MPa.The interface heat generation could form an axial temperature gradient exceeding 320K/mm.The radial inhomogeneities of heat generation and temperature were manifested in a concentric ring distribution with maximum heat flux and temperature ranging from 2/5 to 2/3 radius.The radial inhomogeneities were caused by increasing linear velocity along the radius and an opposite distribution of contact pressure,which could reach 1.7 times the set pressure at the center.The circumferential inhomogeneity of thermomechanical distribution during rotary friction welding was revealed for the first time,benefiting from the 3D model.The deflection and transformation of distribution in contact pressure and Mises stress were indicators of plastic deformation and transition of quasi-steady state welding.The critical Mises stress was 0.5 times the friction pressure in this study.The presented modeling provides a reliable insight into the thermo-mechanical coupling mechanism of IFW and lays a solid foundation for predicting the microstructures and mechanical properties of inertia friction welded joints.展开更多
Four powder metallurgy(PM)Ni-based superalloys with different Hf and Ta contents were creep-tested at 650℃ and 970 MPa,700℃ and 770 MPa,and 750℃ and 580 MPa,respectively.The effect of Hf and Ta on creep deformation...Four powder metallurgy(PM)Ni-based superalloys with different Hf and Ta contents were creep-tested at 650℃ and 970 MPa,700℃ and 770 MPa,and 750℃ and 580 MPa,respectively.The effect of Hf and Ta on creep deformation behaviors of the superalloys was studied from multiple scales by SEM,electron backscatter diffraction(EBSD),and aberration-corrected scanning transmission electron microscope(AC-STEM).The results showed that Hf and Ta suppressed the intergranular fracture and initiation of cracks during the acceleration creep stage,which prolonged the creep rupture time.Hf and Ta inhibited the stacking faults extending and the dislocation climbing and promoted the Suzuki segregation of W during the steady-state creep stage,which reduced the minimum creep rate and delayed the start time of the acceleration creep stage.The Suzuki segregation of Co,Cr,Mo,Ti,Nb,W,and Ta along stacking faults was observed after Hf and Ta addition,leading to the localized phase transformation in the γ′phase,and the stacking fault phase was chemically disordered.This study provided ideas for the composition design of novel PM Ni-based superalloys and theoretical foundations for the combined addition of Hf and Ta.展开更多
Surface recrystallization(RX) is a typical grain defect observed in directionally solidified(DS) Ni-based superalloys. Most studies have focused on the RX behavior and its impact on the mechanical properties of single...Surface recrystallization(RX) is a typical grain defect observed in directionally solidified(DS) Ni-based superalloys. Most studies have focused on the RX behavior and its impact on the mechanical properties of single-crystal(SC) superalloys, with limited research on its influence on the high-temperature mechanical properties of DS superalloys. This study systematically investigated the effect of RX on the high-temperature tensile properties of a DS DZ409 superalloy. The results show that at 650℃, the yield strength decreases almost linearly with an increase in RX fraction. A significant reduction in elongation is observed as the RX fraction increases from 0% to 4.9%. However, beyond this point, further increase in RX fraction leads to minimal changes in elongation. At 950℃, both yield strength and elongation decrease as the RX fraction increases from 0% to 4.9%. At 650℃, fractures in the RX DS superalloys exhibit a mixed mode of transgranular and intergranular cleavage fracture, while at 950℃, it features a combination of ductile and intergranular dimple fractures. The failure mechanism of the RX DS superalloy is associated with the introduction of transverse grain boundaries(GBs) during RX. In the early stages of tensile testing at intermediate and high temperatures, cracks can easily initiate at these GBs. Subsequently, the cracks propagate along the GBs into the DS matrix, ultimately leading to failure of the DS superalloy.展开更多
Photothermal catalytic methane dry reforming(DRM)technology can convert greenhouse gases(i.e.CH_(4)and CO_(2))into syngas(i.e.H_(2)and CO),providing more opportunities for reducing the greenhouse effect and achieving ...Photothermal catalytic methane dry reforming(DRM)technology can convert greenhouse gases(i.e.CH_(4)and CO_(2))into syngas(i.e.H_(2)and CO),providing more opportunities for reducing the greenhouse effect and achieving carbon neutrality.In the DRM field,Ni-based catalysts attract wide attention due to their low cost and high activity.However,the carbon deposition over Ni-based catalysts always leads to rapid deactivation,which is still a main challenge.To improve the long-term stability of Ni-based catalysts,this work proposes a carbon-atom-diffusion strategy under photothermal conditions and investigates its effect on a Zn-doped Ni-based photothermal catalyst(Ni_(3)Zn@CeO_(2)).The photothermal catalytic behavior of Ni_(3)Zn@CeO_(2)can maintain more than 70 h in DRM reaction.And the photocatalytic DRM activity of Ni_(3)Zn@CeO_(2)is 1.2 times higher than thermal catalytic activity.Density functional theory(DFT)calculation and experimental characterizations indicate that Ni_(3)Zn promotes the diffusion of carbon atoms into the Ni_(3)Zn to form the Ni_(3)ZnC0.7 phase with body-centered cubic(bcc)structure,thus inhibiting carbon deposition.Further,in-situ diffuse reflectance infrared Fourier transform(DRIFT)spectroscopy and DFT calculation prove Ni_(3)Zn@CeO_(2)benefits the CH_(4)activation and inhibits the carbon deposition during the DRM process.Through inducing carbon atoms diffusion within the Ni_(3)Zn lattice,this work provides a straightforward and feasible strategy for achieving efficient photothermal catalytic DRM and even other CH_(4)conversion implementations with long-term stability.展开更多
Nickel-based catalysts have emerged as crucial components in alkaline oxygen evolution reactions(OER)due to their exceptional catalytic performance and unique structural properties.However,the understanding of their c...Nickel-based catalysts have emerged as crucial components in alkaline oxygen evolution reactions(OER)due to their exceptional catalytic performance and unique structural properties.However,the understanding of their catalytic mechanisms remains incomplete.This review systematically explores the various types of Ni-based catalysts,including metal-organic frameworks(MOFs),perovskites,and layered double hydroxides(LDHs),while emphasizing their performance metrics.We critically assess the application of advanced in situ characterization techniques,such as in situ Raman spectroscopy and X-ray absorption spectroscopy(XAS),in elucidating the structural evolution and active species during the OER process.By addressing the interplay between catalyst structure and performance,this review aims to provide insights that drive future research efforts toward the optimization of Ni-based catalysts for sustainable hydrogen production.Key areas for potential research advancements are also identified.展开更多
For searching alternative strategies to improve reliability of titanium and steel dissimilar bimetallic joints manufactured by directed energy deposition with laser beam(DED-LB),pure titanium was considered as claddin...For searching alternative strategies to improve reliability of titanium and steel dissimilar bimetallic joints manufactured by directed energy deposition with laser beam(DED-LB),pure titanium was considered as cladding deposited on carbon steel substrate with Ni-based alloy interlayers in this work.Effect of different interlayer modification methods on the microstructure evolution and mechanical properties of joints was analyzed systematically.The distribution of intermetallic compounds(IMCs)such asβ-Ti,Ti_(2)Ni,TiNiFe_(0.2),Ti_(2)Ni_(3)Si and TiB_(2)in joints was revealed.The results showed that original deposition cracks caused by residual stress during processing could be alleviated by substrate preheating treatment while suppressed by the modified interlayer with Cr completely.Notably,additional Cr could reduce reaction activity between Ti and Ni atoms by raising laser molten pool liquidus,leading to fewer IMCs in joints.As a result,both bonding strength and toughness of joints were remarkably improved.The findings em-phasize more significance of optimizing Ni-based interlayer composition with Cr than preheating method to improve the mechanical performance of DED-LB joints.展开更多
A practical process method for precise integration of SiC_(f)/SiC composite(CMC)and a Ni-based superalloy(K403)was proposed in this study.It involves Nb coating pretreatment of the CMC via the chemical vapor depositio...A practical process method for precise integration of SiC_(f)/SiC composite(CMC)and a Ni-based superalloy(K403)was proposed in this study.It involves Nb coating pretreatment of the CMC via the chemical vapor deposition(CVD)at 1000℃and subsequent integral precision casting between the pretreated CMC and the K403 superalloy melt.The method solves the difficulty for the dissimilar material to be cast together,forming a robust bonding interface with an average shear strength of 94.8 MPa at room temperature.During the pretreatment process,the Nb reacted with the CMC,forming a reactive coating with the microstructure composed of NbC,Nb2C and Nb5Si3 phases.In the following integral casting,the Nb reactive coating effectively blocked detrimental graphitization reaction between the Ni element in the superalloy melt and the CMC,and mitigated the interface thermal stress generated by both the mismatch of thermal expansion coefficients and temperature difference,resulting in the increase of interfacial strength.The typical interfacial microstructure consists of the CMC,NbC,NbSi_(2)/NbC,SiC,NbSi_(2),Nb_(2)C,Nb_(5)Si_(3),Al_(4)C_(3),Nb_(2)Al/γ/γ'and MC(M=W,Mo,Ti).A formula for estimating the interfacial thermal stress of an integrated cast was derived.展开更多
In this study,a novel Ni-based superalloy,ZGH451,has been fabricated using direct energy deposition(DED).The thermal fatigue resistance of ZGH451 is systematically evaluated at 900,1000,and 1100℃,primarily focusing o...In this study,a novel Ni-based superalloy,ZGH451,has been fabricated using direct energy deposition(DED).The thermal fatigue resistance of ZGH451 is systematically evaluated at 900,1000,and 1100℃,primarily focusing on the crack initiation and propagation behaviors.The results indicate that higher peak temperatures lead to earlier initiation and more rapid propagation of cracks.Cracks are initiated at the defects and grain boundaries in the vicinity of the notch,and different crack propagation mecha-nisms(γ'phase slip shearing,γ'phase distortion shearing,andγ'phase rafting shearing at 900,1000,and 1100℃,respectively)are the main reason for the different cracks propagation behaviors under the three temperatures.The main crack propagation paths are oriented at approximately 45°with respect to the build direction,suggesting activation of the{111}<110>slip system.Additionally,oxidation reduces the matrix strength and passivates the crack tips,leading to varying rates of crack propagation.At ele-vated temperatures,the synergistic effects of thermal stress and oxidative erosion are found to be the primary damage mechanisms of thermal fatigue.Overall,the proposed ZGH451 superalloy demonstrates exceptional thermal fatigue resistance,providing a crucial experimental reference for thermal fatigue in additively manufactured superalloys.展开更多
With the evolution of nickel-based single crystal superalloys,there is an increase in heavy elements such as Re and Ru.This has made solutal convection more pronounced during the directional solidification process,lea...With the evolution of nickel-based single crystal superalloys,there is an increase in heavy elements such as Re and Ru.This has made solutal convection more pronounced during the directional solidification process,leading to solute redistribution and increasing the risk of casting defects such as low-angle grain boundaries.To avoid casting defects,downward directional solidification(DWS)method is adopted to eliminate solutal convection and change solute redistribution.However,there is currently no in-situ characterization or quantitative simulation studying the solute redistribution during DWS and upward directional solidification(UWS)processes.A multicomponent phase field simulation coupled with lattice Boltzmann method was employed to quantitatively investigate changes in dendrite morphology,solutal convection and deviation of dendrite tips from the perspective of solute redistribution during UWS and DWS processes.The simulation of microstructure agrees well with the experimental results.The mechanism that explains how solutal convection affects side branching behavior is depicted.A novel approach is introduced to characterize dendrite deviation,elucidating the reasons why defects are prone to occur under the influence of natural convection and solute redistribution.展开更多
The wear behavior of Ni-based single crystal(NBSC)superalloy SRR99 fabricated by laser-directed energy deposition(LDED)is investigated and compared with that of its cast counterpart.While γ'precipitate size in th...The wear behavior of Ni-based single crystal(NBSC)superalloy SRR99 fabricated by laser-directed energy deposition(LDED)is investigated and compared with that of its cast counterpart.While γ'precipitate size in the latter is>400 nm,that in the former is an order of magnitude lower.Dry sliding wear tests reveal that the wear rate and coefficient of friction of the LDED alloy are 75% and 20%lower than that of its cast counterpart,respectively.Detailed transmission electron microscopy investigation of the wear-tested cast alloy indicates that there is orientation change and formation of nanoscale grains only at the top layer of the worn surface,whereas regions below undergo moderate plastic deformation via dislocation slip.In contrast,the sub-surface of the worn LDED alloy has a graded microstructure,with a composite of NiO/γ-Ni on the top,γ'free nano-grains in the middle,and a highly deformed nanoscale layer at the bottom.The improved wear behavior of the LDED alloy is attributed to its higher dislocation density,finerγ'precipitates,and the formation of this graded microstructure.Finally,a detailed description of mechanisms that lead to the formation of this unique graded microstructure is provided.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 precipitation of topologically close-packed(TCP)phases is the result of microstructure instabilities of Ni-based superalloys.This review seeks to comprehensively collate all the available information on TCP phases...The precipitation of topologically close-packed(TCP)phases is the result of microstructure instabilities of Ni-based superalloys.This review seeks to comprehensively collate all the available information on TCP phases in SX superalloys based on the latest findings.First,the thermodynamics and kinetics of the TCP phase precipitation are introduced.Meanwhile,the morphology,composition and orientation of TCP phases and their sequential transformation are summarized in detail.Further,the factors affecting the precipitation of these phases are sorted out.Besides,the proposed damage mechanisms of TCP phases are listed.Finally,several control and prediction methods of the TCP phase precipitation are reviewed,so the alloy designer can better balance the relationship between microstructure stabilities and properties of the superalloy.展开更多
A novel Ni-based superalloy GH4151,with a γ′ volume fraction of about 55%and a service temperature capability up to 8oo oC,was investigated.Due to the different cooling conditions of various regions during the solid...A novel Ni-based superalloy GH4151,with a γ′ volume fraction of about 55%and a service temperature capability up to 8oo oC,was investigated.Due to the different cooling conditions of various regions during the solidification of ingots,significant cooling rate variations may lead to the occurrence of hot cracking.Conventional scanning laser microscope was utilised to investigate the solidification process and phase precipitation behaviour of the GH4151 under wide range cooling rates.The characteristics of L→γ transformation were analysed,and the growth rates of at each stage were calculated.The segregation behaviour was predicted using the Scheil equation,and the predicted results match well with the experimental results.The sensitivity coefficient for hot cracking was modified,and cracking sensitivity coefficient values for the alloy under different cooling rates were computed,revealing that the alloy is most susceptible to hot cracking at 10℃/min cooling rate.Therefore,controlling the cooling rate can reduce the possibility of hot cracking in ingot.展开更多
Alloy composition design usually contributes to eliminating cracking in Ni-based superalloys during addi-tive manufacturing(AM).However,a detailed understanding of each solid solution element in the crack-ing suscepti...Alloy composition design usually contributes to eliminating cracking in Ni-based superalloys during addi-tive manufacturing(AM).However,a detailed understanding of each solid solution element in the crack-ing susceptibility of Ni-based superalloys during AM is still missing.Thirteen newly designed alloys are considered to investigate the combined effect of solid solution elements on cracking susceptibility.The behaviors of solidification cracking,liquation cracking,and solid-state cracking were analyzed by the microstructural characterization and thermodynamic calculations.The results showed that W and Mo cause the formation of high melting-point carbides at grain boundaries(GBs),which increase solidifica-tion cracking susceptibility.Moreover,W and Mo lead to a slightly higher solidification cracking index(SCI)compared to Co,Cr,and Re.In the successive solidification and remelting process,the borides en-riched in W,Mo,and B around GBs will cause grain boundary segregation and liquation cracking.W and Re extend the freezing range(FR)and exacerbate the segregation of Al and Ti in the inter-dendritic re-gions,contributing to the formation of eutectics.Similarly,complete or partial melting of the eutectic can induce liquation cracking during the thermal cycling in AM.The solid-state cracking susceptibility can be reduced by solid solution elements,especially Re and Co.In summary,compared to Co,Cr,and Re,W and Mo exacerbate the cracking susceptibility.展开更多
基金Guizhou Province Science and Technology Plan Project(QKHJC-ZK[2024]yiban604)Guizhou Province Science and Technology Plan Project(CXTD[2021]008)+4 种基金Bijie City Science and Technology Project(BKLH[2023]9)Technology Project of Bijie City(BKLH[2023]36)Natural Science Research Project of Guizhou Higher Education Institutions of China(QJJ[2023]047)Science and Technology Project of Guizhou Department of Transportation(2022-121-011)Sanmenxia City Science and Technology Bureau Science and Technology Research Project(2022002005)。
文摘The microstructure evolution and deformation mechanism of a DZ125 superalloy during high-temperature creep were studied by means of microstructure observation and creep-property tests.The results show that at the initial stage of high-temperature creep,two sets of dislocations with different Burgers vectors move and meet inγmatrix channels,and react to form a quadrilateral dislocation network.Andγ′phases with raft-like microstructure are generated after the formation of dislocation networks.As creep progresses,the quadrilateral dislocation network is gradually transformed into hexagonal and quadrilateral dislocation networks.During steady stage of creep,the superalloy undergoes deformation with the mechanism that a great number of dislocations slip and climb in the matrix across the raft-likeγ′phases.At the later stage of creep,the raft-likeγ′phases are sheared by dislocations at the breakage of dislocation networks,and then alternate slip occurs,which distorts and breaks the raft-likeγ′/γphases,resulting in the accumulation of micropores at the raft-likeγ′/γinterfaces and the formation of microcracks.As creep continues,the microcracks continue to expand until creep fracture occurs,which is the damage and fracture mechanism of the alloy at the later stage of creep at high temperature.
基金Shenzhen Science and Technology Program(JSGG20220831092800001)。
文摘The microstructure of single crystal superalloy is relatively simple,consisting primarily ofγdendrites andγ/γ′eutectics.During the directional solidification process of Ni-based single crystal superalloys,withdrawal rate is a critical parameter affecting the spatial distribution ofγ/γ′eutectic along gravity direction.The results show that theγ/γ′eutectic fraction of the upper platform surface is always higher than that of the lower one,regardless of withdrawal rate.As the withdrawal rate decreases,there is a significant increase inγ/γ′eutectic fraction on the upper surface,while it decreases on the lower surface.The upward accumulation ofγ/γ′eutectic becomes more severe as the withdrawal rate decreases.It is also found that the percentage of Al+Ta is positively correlated with theγ/γ′eutectic fraction.Thermo-solute convection of Al and Ta solutes in the solidification front is the prime reason for the non-uniform distribution of eutectic.The non-uniform distribution ofγ/γ′eutectic cannot be eliminated even after subsequent solution heat treatment,resulting in excess eutectic on the upper surface and thus leading to the scrapping of the blade.
基金supported by the Natural Science Foundation of Shanxi Province(202203021221155)the Foundation of National Key Laboratory of High Efficiency and Low Carbon Utilization of Coal(J23-24-902)。
文摘With ongoing global warming and increasing energy demands,the CH_(4)-CO_(2)reforming reaction(dry reforming of methane,DRM)has garnered significant attention as a promising carbon capture and utilization technology.Nickel-based catalysts are renowned for their outstanding activity and selectivity in this process.The impact of metal-support interaction(MSI),on Ni-based catalyst performance has been extensively researched and debated recently.This paper reviews the recent research progress of MSI on Ni-based catalysts and their characterization and modulation strategies in catalytic reactions.From the perspective of MSI,the effects of different carriers(metal oxides,carbon materials and molecular sieves,etc.)are introduced on the dispersion and surface structure of Ni active metal particles,and the effect of MSI on the activity and stability of DRM reactions on Ni-based catalysts is discussed in detail.Future research should focus on better understanding and controlling MSI to improve the performance and durability of nickel-based catalysts in CH_(4)-CO_(2)reforming,advancing cleaner energy technologies.
基金supported by the National Natural Science Foundation of China(No.52303394)the National Key Research and Development Program of China(No.2022YFB3705000)+1 种基金the Natural Science Foundation of Liaoning Province(No.2023-BS-015)the Science Center for Gas Turbine Project(No.P2022-C-IV-002-001).
文摘The effect of carbon content on the microstructures and stress rupture properties of a newly developed polycrystalline Ni-based superalloy with high Cr content has been studied.It was observed that both grain size and the number of carbides increased with an increase in carbon content.After heat treatment,granular M_(23)C_(6)carbides were dispersed around MC carbides along grain boundaries and inside grains.The quantity of granular M_(23)C_(6)carbides increased while their sizes decreased.These findings can be verified with the results of thermodynamic calculation and differential scanning calorimetry analysis.The stress rupture times(975℃/225 MPa)increased from 13.3 to 25.5 h with the carbon content increased from 0.1 to 0.2 wt.%.The improvement can be attributed to two primary factors.Firstly,grain boundary is typically weak region during deformation process and the grain size increased as carbon content increased in the alloy.Secondly,carbides act as hindrances to impede dislocation movement,leading to dislocation entanglement.As carbon content rose,the quantity of carbides in interdendritic regions and grain boundaries increased,providing a certain degree of strengthening effect and resulting in a longer stress rupture time.
基金supported by the Natural Science Foundation of China(No.52074366)the Top Ten Science and Technology Projects in Hunan Province,China(No.2024GK1080)+4 种基金the Aero Engine Corporation of China(No.HFZL2022CXY029)the Young Elite Scientists Sponsorship Program by CAST,China(No.2022QNRC001)the Natural Science Foundation of Hunan Province,China(No.2021JJ40757)the Science and Technology Innovation Program of Hunan Province,China(No.2021RC3131)the High Performance Computing Center of Central South University,and the Project supported by State Key Laboratory of Powder Metallurgy,Central South University,China.
文摘The creep behavior of two PM superalloys,U720Li and RR1000,each alloyed with trace amount of Sc,was systematically investigated.Findings reveal that RR1000 alloy with 0.064 wt.%Sc(R-0.064)demonstrates superior creep resistance compared to U720Li alloy with 0.043 wt.%Sc(U-0.043),at 650℃ and 1000 MPa,and the primary creep mechanisms in both alloys are identified as dislocation shearing and precipitate bypassing.When tested at 700℃ and 700 MPa,the U-0.043 alloy predominantly exhibits micro-twinning and dislocation bypassing,while the R-0.064 alloy engages in extended stacking fault shearing ofγ'precipitate,dislocation bypassing and climb.At 750℃ and 460 MPa,dislocation bypassing and climb emerge as the main creep mechanisms for both alloys.
基金co-supported by the financial support from the Fundamental Research Funds for the Central Universities,China(Nos.YWF-23-L-1012,YWF-22-L-1017)the National Natural Science Foundation of China(No.52005020)。
文摘The performance of welded Ni-based superalloys at high temperatures is essential to be evaluated due to their particular service environment for aero-engines and high-speed aircrafts.The tensile properties and related microstructural evolutions such as the carbide precipitate and grain of a laser-welded Ni-based alloy were experimentally and numerically investigated at different temperatures(20,300,500,800℃).The results show that at room temperature,the strength of the Base Material(BM)was slightly smaller,with a difference of less than 1%,than the Welded Material(WM),which can be attributed to the more uniformly distributed needle-shaped carbide precipitates in the WM than those nonuniformly coarser spherical ones in the BM.While at 300℃ and 500℃,the strength of WM decreased more obviously compared with that of BM due to the more apparent growth of grain:13.52%loss in yield strength in WM alloys as compared with BM alloys at 300℃,and 16.57% at 500℃.At 800℃,the strength of BM and WM both decreased to a similar level due to Dynamic Recrystallization(DRX).However,a much higher elongation was observed for the BM than WM(less than 50%of BM),which can be attributed to the enhanced dislocation accumulation capability of the large spherical carbides along grain boundaries on the fracture surface in BM.Furthermore,a unified model considering the welding effects on both microstructures(dislocation,carbides,and grain)and mechanical properties evolutions at different temperatures was developed and validated.Based on this model,the key temperature ranges(20–600℃)where apparent weakening of strength and uniform plasticity occurs for welded structures were identified,providing a direct guidance for potential structure and process design.
基金supported by the National Key Research and Development Program of China(Grant No.2022YFB3404904)。
文摘The coupling between heat and pressure is the kernel of inertia friction welding(IFW)and is still not fully understood.A novel 3D fully coupled finite element model based on a plastic friction pair was developed to simulate the IFW process of a Ni-based superalloy and reveal the omnidirectional thermo-mechanical coupling mechanism of the friction interface.The numerical model successfully simulated the deceleration,deformation processes,and peak torsional moments in IFW and captured the evolution of temperature,contact pressure,and stress.The simulated results were validated through measured thermal history,optical macrography,and axial shortening.The results indicated that interfacial friction heat was the primary heat source,and plastic deformation energy only accounted for 4%of the total.The increase in initial rotational speed and friction pressure elevated the peak temperature,reaching a maximum of 1525.5K at an initial rotational speed of 2000 r/min and friction pressure of 400 MPa.The interface heat generation could form an axial temperature gradient exceeding 320K/mm.The radial inhomogeneities of heat generation and temperature were manifested in a concentric ring distribution with maximum heat flux and temperature ranging from 2/5 to 2/3 radius.The radial inhomogeneities were caused by increasing linear velocity along the radius and an opposite distribution of contact pressure,which could reach 1.7 times the set pressure at the center.The circumferential inhomogeneity of thermomechanical distribution during rotary friction welding was revealed for the first time,benefiting from the 3D model.The deflection and transformation of distribution in contact pressure and Mises stress were indicators of plastic deformation and transition of quasi-steady state welding.The critical Mises stress was 0.5 times the friction pressure in this study.The presented modeling provides a reliable insight into the thermo-mechanical coupling mechanism of IFW and lays a solid foundation for predicting the microstructures and mechanical properties of inertia friction welded joints.
基金financially supported by the National Science and Technology Major Project of China(No.2017-Ⅵ-0008-0078)。
文摘Four powder metallurgy(PM)Ni-based superalloys with different Hf and Ta contents were creep-tested at 650℃ and 970 MPa,700℃ and 770 MPa,and 750℃ and 580 MPa,respectively.The effect of Hf and Ta on creep deformation behaviors of the superalloys was studied from multiple scales by SEM,electron backscatter diffraction(EBSD),and aberration-corrected scanning transmission electron microscope(AC-STEM).The results showed that Hf and Ta suppressed the intergranular fracture and initiation of cracks during the acceleration creep stage,which prolonged the creep rupture time.Hf and Ta inhibited the stacking faults extending and the dislocation climbing and promoted the Suzuki segregation of W during the steady-state creep stage,which reduced the minimum creep rate and delayed the start time of the acceleration creep stage.The Suzuki segregation of Co,Cr,Mo,Ti,Nb,W,and Ta along stacking faults was observed after Hf and Ta addition,leading to the localized phase transformation in the γ′phase,and the stacking fault phase was chemically disordered.This study provided ideas for the composition design of novel PM Ni-based superalloys and theoretical foundations for the combined addition of Hf and Ta.
基金supported by the National Science and Technology Major Project(No.HT-J2019-VI-0020-0136)the National Youth Talent Support Program,and the Fundamental Research Funds for the Central Universities(No.xtr072024004).
文摘Surface recrystallization(RX) is a typical grain defect observed in directionally solidified(DS) Ni-based superalloys. Most studies have focused on the RX behavior and its impact on the mechanical properties of single-crystal(SC) superalloys, with limited research on its influence on the high-temperature mechanical properties of DS superalloys. This study systematically investigated the effect of RX on the high-temperature tensile properties of a DS DZ409 superalloy. The results show that at 650℃, the yield strength decreases almost linearly with an increase in RX fraction. A significant reduction in elongation is observed as the RX fraction increases from 0% to 4.9%. However, beyond this point, further increase in RX fraction leads to minimal changes in elongation. At 950℃, both yield strength and elongation decrease as the RX fraction increases from 0% to 4.9%. At 650℃, fractures in the RX DS superalloys exhibit a mixed mode of transgranular and intergranular cleavage fracture, while at 950℃, it features a combination of ductile and intergranular dimple fractures. The failure mechanism of the RX DS superalloy is associated with the introduction of transverse grain boundaries(GBs) during RX. In the early stages of tensile testing at intermediate and high temperatures, cracks can easily initiate at these GBs. Subsequently, the cracks propagate along the GBs into the DS matrix, ultimately leading to failure of the DS superalloy.
文摘Photothermal catalytic methane dry reforming(DRM)technology can convert greenhouse gases(i.e.CH_(4)and CO_(2))into syngas(i.e.H_(2)and CO),providing more opportunities for reducing the greenhouse effect and achieving carbon neutrality.In the DRM field,Ni-based catalysts attract wide attention due to their low cost and high activity.However,the carbon deposition over Ni-based catalysts always leads to rapid deactivation,which is still a main challenge.To improve the long-term stability of Ni-based catalysts,this work proposes a carbon-atom-diffusion strategy under photothermal conditions and investigates its effect on a Zn-doped Ni-based photothermal catalyst(Ni_(3)Zn@CeO_(2)).The photothermal catalytic behavior of Ni_(3)Zn@CeO_(2)can maintain more than 70 h in DRM reaction.And the photocatalytic DRM activity of Ni_(3)Zn@CeO_(2)is 1.2 times higher than thermal catalytic activity.Density functional theory(DFT)calculation and experimental characterizations indicate that Ni_(3)Zn promotes the diffusion of carbon atoms into the Ni_(3)Zn to form the Ni_(3)ZnC0.7 phase with body-centered cubic(bcc)structure,thus inhibiting carbon deposition.Further,in-situ diffuse reflectance infrared Fourier transform(DRIFT)spectroscopy and DFT calculation prove Ni_(3)Zn@CeO_(2)benefits the CH_(4)activation and inhibits the carbon deposition during the DRM process.Through inducing carbon atoms diffusion within the Ni_(3)Zn lattice,this work provides a straightforward and feasible strategy for achieving efficient photothermal catalytic DRM and even other CH_(4)conversion implementations with long-term stability.
基金supported by the Fundamental Research Funds for the Central Universities(20822041H4082).
文摘Nickel-based catalysts have emerged as crucial components in alkaline oxygen evolution reactions(OER)due to their exceptional catalytic performance and unique structural properties.However,the understanding of their catalytic mechanisms remains incomplete.This review systematically explores the various types of Ni-based catalysts,including metal-organic frameworks(MOFs),perovskites,and layered double hydroxides(LDHs),while emphasizing their performance metrics.We critically assess the application of advanced in situ characterization techniques,such as in situ Raman spectroscopy and X-ray absorption spectroscopy(XAS),in elucidating the structural evolution and active species during the OER process.By addressing the interplay between catalyst structure and performance,this review aims to provide insights that drive future research efforts toward the optimization of Ni-based catalysts for sustainable hydrogen production.Key areas for potential research advancements are also identified.
基金supported by the National Natural Science Foundation of China(No.5230010216)2022 Annual Nanjing New R&D Institutions Joint Technical Tackling Project(No.202208019)+1 种基金Jiangsu Provincial Excellent Postdoctoral Talent Program(No.2022ZB385)the technical support of Nanjing Shangi Institute for Advanced Materials Co.,Ltd.
文摘For searching alternative strategies to improve reliability of titanium and steel dissimilar bimetallic joints manufactured by directed energy deposition with laser beam(DED-LB),pure titanium was considered as cladding deposited on carbon steel substrate with Ni-based alloy interlayers in this work.Effect of different interlayer modification methods on the microstructure evolution and mechanical properties of joints was analyzed systematically.The distribution of intermetallic compounds(IMCs)such asβ-Ti,Ti_(2)Ni,TiNiFe_(0.2),Ti_(2)Ni_(3)Si and TiB_(2)in joints was revealed.The results showed that original deposition cracks caused by residual stress during processing could be alleviated by substrate preheating treatment while suppressed by the modified interlayer with Cr completely.Notably,additional Cr could reduce reaction activity between Ti and Ni atoms by raising laser molten pool liquidus,leading to fewer IMCs in joints.As a result,both bonding strength and toughness of joints were remarkably improved.The findings em-phasize more significance of optimizing Ni-based interlayer composition with Cr than preheating method to improve the mechanical performance of DED-LB joints.
基金the financial support from the Fundamental Research Funds for the Central Universities,China(No.FRF-GF-18-006A)。
文摘A practical process method for precise integration of SiC_(f)/SiC composite(CMC)and a Ni-based superalloy(K403)was proposed in this study.It involves Nb coating pretreatment of the CMC via the chemical vapor deposition(CVD)at 1000℃and subsequent integral precision casting between the pretreated CMC and the K403 superalloy melt.The method solves the difficulty for the dissimilar material to be cast together,forming a robust bonding interface with an average shear strength of 94.8 MPa at room temperature.During the pretreatment process,the Nb reacted with the CMC,forming a reactive coating with the microstructure composed of NbC,Nb2C and Nb5Si3 phases.In the following integral casting,the Nb reactive coating effectively blocked detrimental graphitization reaction between the Ni element in the superalloy melt and the CMC,and mitigated the interface thermal stress generated by both the mismatch of thermal expansion coefficients and temperature difference,resulting in the increase of interfacial strength.The typical interfacial microstructure consists of the CMC,NbC,NbSi_(2)/NbC,SiC,NbSi_(2),Nb_(2)C,Nb_(5)Si_(3),Al_(4)C_(3),Nb_(2)Al/γ/γ'and MC(M=W,Mo,Ti).A formula for estimating the interfacial thermal stress of an integrated cast was derived.
基金supported by the Defense Indus-trial Technology Development Program(No.JCKY2020130C024)the National Key R&D Program of China(No.2021YFB3702503)+1 种基金the Science Center for Gas Turbine Project(No.P2022-C-Ⅳ-002-001)the National Science and Technology Major Project(No.Y2019-VII-0011-0151).
文摘In this study,a novel Ni-based superalloy,ZGH451,has been fabricated using direct energy deposition(DED).The thermal fatigue resistance of ZGH451 is systematically evaluated at 900,1000,and 1100℃,primarily focusing on the crack initiation and propagation behaviors.The results indicate that higher peak temperatures lead to earlier initiation and more rapid propagation of cracks.Cracks are initiated at the defects and grain boundaries in the vicinity of the notch,and different crack propagation mecha-nisms(γ'phase slip shearing,γ'phase distortion shearing,andγ'phase rafting shearing at 900,1000,and 1100℃,respectively)are the main reason for the different cracks propagation behaviors under the three temperatures.The main crack propagation paths are oriented at approximately 45°with respect to the build direction,suggesting activation of the{111}<110>slip system.Additionally,oxidation reduces the matrix strength and passivates the crack tips,leading to varying rates of crack propagation.At ele-vated temperatures,the synergistic effects of thermal stress and oxidative erosion are found to be the primary damage mechanisms of thermal fatigue.Overall,the proposed ZGH451 superalloy demonstrates exceptional thermal fatigue resistance,providing a crucial experimental reference for thermal fatigue in additively manufactured superalloys.
基金supported by the stable support project and the Major National Science and Technology Project(2017-VII-0008-0101).
文摘With the evolution of nickel-based single crystal superalloys,there is an increase in heavy elements such as Re and Ru.This has made solutal convection more pronounced during the directional solidification process,leading to solute redistribution and increasing the risk of casting defects such as low-angle grain boundaries.To avoid casting defects,downward directional solidification(DWS)method is adopted to eliminate solutal convection and change solute redistribution.However,there is currently no in-situ characterization or quantitative simulation studying the solute redistribution during DWS and upward directional solidification(UWS)processes.A multicomponent phase field simulation coupled with lattice Boltzmann method was employed to quantitatively investigate changes in dendrite morphology,solutal convection and deviation of dendrite tips from the perspective of solute redistribution during UWS and DWS processes.The simulation of microstructure agrees well with the experimental results.The mechanism that explains how solutal convection affects side branching behavior is depicted.A novel approach is introduced to characterize dendrite deviation,elucidating the reasons why defects are prone to occur under the influence of natural convection and solute redistribution.
基金supported by the National Key R&D Program of China(Grant Nos.2023YFB3712002 and 2021YFB3702503)the National Natural Science Foundation of China(Grant Nos.51927801 and U2032205)the National Science and Technology Major Project(Grant Nos.Y2019-VII-0011-0151 and 2019-VII-0019-0161)。
文摘The wear behavior of Ni-based single crystal(NBSC)superalloy SRR99 fabricated by laser-directed energy deposition(LDED)is investigated and compared with that of its cast counterpart.While γ'precipitate size in the latter is>400 nm,that in the former is an order of magnitude lower.Dry sliding wear tests reveal that the wear rate and coefficient of friction of the LDED alloy are 75% and 20%lower than that of its cast counterpart,respectively.Detailed transmission electron microscopy investigation of the wear-tested cast alloy indicates that there is orientation change and formation of nanoscale grains only at the top layer of the worn surface,whereas regions below undergo moderate plastic deformation via dislocation slip.In contrast,the sub-surface of the worn LDED alloy has a graded microstructure,with a composite of NiO/γ-Ni on the top,γ'free nano-grains in the middle,and a highly deformed nanoscale layer at the bottom.The improved wear behavior of the LDED alloy is attributed to its higher dislocation density,finerγ'precipitates,and the formation of this graded microstructure.Finally,a detailed description of mechanisms that lead to the formation of this unique graded microstructure is provided.
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financially supported by the National Science and Technology Major Project(No.2019-VII-0019-0161)Science Center for Gas Turbine Project(No.P2021-A-Ⅳ-001-002)+1 种基金National Key Research and Development Program of China under Grant(No.2017YFA0700704)National Natural Science Foundation of China(No.51971214).
文摘The precipitation of topologically close-packed(TCP)phases is the result of microstructure instabilities of Ni-based superalloys.This review seeks to comprehensively collate all the available information on TCP phases in SX superalloys based on the latest findings.First,the thermodynamics and kinetics of the TCP phase precipitation are introduced.Meanwhile,the morphology,composition and orientation of TCP phases and their sequential transformation are summarized in detail.Further,the factors affecting the precipitation of these phases are sorted out.Besides,the proposed damage mechanisms of TCP phases are listed.Finally,several control and prediction methods of the TCP phase precipitation are reviewed,so the alloy designer can better balance the relationship between microstructure stabilities and properties of the superalloy.
基金supported by the National Science and Technology Major Project(J2019-VI-0006-0120)National Natural Science Foundation of China(52074092).
文摘A novel Ni-based superalloy GH4151,with a γ′ volume fraction of about 55%and a service temperature capability up to 8oo oC,was investigated.Due to the different cooling conditions of various regions during the solidification of ingots,significant cooling rate variations may lead to the occurrence of hot cracking.Conventional scanning laser microscope was utilised to investigate the solidification process and phase precipitation behaviour of the GH4151 under wide range cooling rates.The characteristics of L→γ transformation were analysed,and the growth rates of at each stage were calculated.The segregation behaviour was predicted using the Scheil equation,and the predicted results match well with the experimental results.The sensitivity coefficient for hot cracking was modified,and cracking sensitivity coefficient values for the alloy under different cooling rates were computed,revealing that the alloy is most susceptible to hot cracking at 10℃/min cooling rate.Therefore,controlling the cooling rate can reduce the possibility of hot cracking in ingot.
基金supported by the National Science and Technology Major Project,China(Project No.Y2019-Ⅶ-0011-0151)and the Science Center for Gas Turbine Project(Project No.P2022-C-Ⅳ-002-001).
文摘Alloy composition design usually contributes to eliminating cracking in Ni-based superalloys during addi-tive manufacturing(AM).However,a detailed understanding of each solid solution element in the crack-ing susceptibility of Ni-based superalloys during AM is still missing.Thirteen newly designed alloys are considered to investigate the combined effect of solid solution elements on cracking susceptibility.The behaviors of solidification cracking,liquation cracking,and solid-state cracking were analyzed by the microstructural characterization and thermodynamic calculations.The results showed that W and Mo cause the formation of high melting-point carbides at grain boundaries(GBs),which increase solidifica-tion cracking susceptibility.Moreover,W and Mo lead to a slightly higher solidification cracking index(SCI)compared to Co,Cr,and Re.In the successive solidification and remelting process,the borides en-riched in W,Mo,and B around GBs will cause grain boundary segregation and liquation cracking.W and Re extend the freezing range(FR)and exacerbate the segregation of Al and Ti in the inter-dendritic re-gions,contributing to the formation of eutectics.Similarly,complete or partial melting of the eutectic can induce liquation cracking during the thermal cycling in AM.The solid-state cracking susceptibility can be reduced by solid solution elements,especially Re and Co.In summary,compared to Co,Cr,and Re,W and Mo exacerbate the cracking susceptibility.
