A composite coating of nitrogen-doped carbon dots(N–CDs)and polydopamine(PDA)was prepared on magnesium alloy by combining electrodeposition with dip coating methods.The microstructure of the N–CDs/PDA composite coat...A composite coating of nitrogen-doped carbon dots(N–CDs)and polydopamine(PDA)was prepared on magnesium alloy by combining electrodeposition with dip coating methods.The microstructure of the N–CDs/PDA composite coating,including composition,surface morphology,and crystalline structure,is characterized by Raman spectroscopy,scanning electron microscopy,transmission electron microscopy,and X-ray photoelectron spectroscopy,respectively.The corrosion protection performances of the composite coating are evaluated by potentiodynamic polarization tests,electrochemical impedance spectroscopy,and salt spray tests.The effect of the particle size of the N–CDs on the corrosion performance is also investigated.The results show that the corrosion performance of the N–CDs coatings are enhanced with the increase of the particle sizes.Furthermore,an obvious self-healing performance is observed on the surface of the N–CDs/PDA composite coating.These results indicate that N–CDs/PDA composite coating can improve the corrosion performance of the Mg alloy,and open a new design direction for the protective coating of metallic materials.展开更多
In order to clarify the effect of strain rate on hot deformation characteristics of GH690superalloy,the hot deformationbehavior of this superalloy was investigated by isothermal compression in the temperature range of...In order to clarify the effect of strain rate on hot deformation characteristics of GH690superalloy,the hot deformationbehavior of this superalloy was investigated by isothermal compression in the temperature range of1000?1200°C and strain raterange of0.001?10s?1on a Gleeble?3800thermo-mechanical simulator.The results reveal that the flow stress is sensitive to the strainrate,and the dynamic recrystallization(DRX)is the principal softening mechanism.The strain rate of0.1s?1is considered to be thecritical point during the hot deformation at1000°C.The DRX process is closely related to the strain rate due to the adiabatictemperature rise.The strain rate has an important influence on DDRX and CDRX during hot deformation.The nucleation of DRXcan be activated by twin boundaries,and there is a lower fraction ofΣ3n(n=1,2,3)boundaries at the intermediate strain rate of0.1s?1.展开更多
Cr is the most important element in nickel-based alloys to prevent high temperature oxidation and corrosion. However, high-Cr content will lead to a decline of hot workability which limits the addition of Cr for most ...Cr is the most important element in nickel-based alloys to prevent high temperature oxidation and corrosion. However, high-Cr content will lead to a decline of hot workability which limits the addition of Cr for most nickel-based superalloys. In order to add more Cr into Ni-based alloy for improving high temperature oxidation and corrosion resistance, the poor hot workability of high-Cr alloy must be first solved. Deformation characteristic of a high-Cr nickel-based alloy （40 wt% Cr） under hot compression conditions at 800-1200 ℃ has been investigated by using a Gleeble 3500 machine, and the microstructural evolution during hot working process has been observed by optical microscopy and scanning electron microscopy. The results show that a high-temperature low-plasticity （HTLP） region exists in this high-Cr nickel-based alloy. This phenomenon can be attributed to its non-uniform interdendritic microstructure at high temperatures. These results can explain the poor hot workability of high-Cr nickel-based alloy.展开更多
Single-phase face-centered cubic(fcc)high/medium-entropy alloys(H/MEAs)exhibit a much higher tendency to form nanoscale deformation twins than conventional fcc metals with similar low stacking fault energies(SFEs).Thi...Single-phase face-centered cubic(fcc)high/medium-entropy alloys(H/MEAs)exhibit a much higher tendency to form nanoscale deformation twins than conventional fcc metals with similar low stacking fault energies(SFEs).This extraordinary propensity for nanotwin formation in H/MEAs cannot therefore be ex-plained by their low SFEs alone.Here,using in situ compression tests of CrCoNi in comparison with Ag nanopillars inside a transmission electron microscope,we found that in the CrCoNi MEA,a high density of nanoscale twins continuously formed with an average thickness of 4.6 nm.In contrast,for similar experiments on Ag with almost identical SFE,following the nucleation of a few twins,they could further thicken to above one hundred nanometers by twin boundary migration.Molecular dynamics calculations indicated that in the highly-concentrated CrCoNi solid solution,the magnitude of the energy barriers for nucleating a stacking fault as a twin precursor in the pristine lattice and for the thickening of an existing twin both span a wide range and largely overlap with each other.Therefore,twin thickening through successive addition of atomic layers is prone to discontinuation,giving way to the nucleation of new twins at other sites where a lower energy barrier is encountered for partial-dislocation mediated fault formation.展开更多
This paper reports a synergistic design of high-performance BCC high-entropy alloy based on the combined consideration of the principles of intrinsic ductility of elements,maximum atomic size difference for solid solu...This paper reports a synergistic design of high-performance BCC high-entropy alloy based on the combined consideration of the principles of intrinsic ductility of elements,maximum atomic size difference for solid solution strengthening and the valence electron concentration criterion for ductility.The single-phase BCC HfNbTaTiV alloy thus designed exhibited a high compressive yield strength of 1350 MPa and a high compressive ductility of>45%at the room temperature.This represents a 50%increase in yield strength relative to a HfNbTaTiZr alloy.This is attributed to the maximized solid solution strengthening effect caused by lattice distortion,which is estimated to be 1094 MPa.The alloy was also able to retain 53%of its yield strength and 77%of its ductility at 700℃.These properties are superior to those of most refractory BCC high-entropy alloys reported in the literature.展开更多
As an attractive class of metallic materials,single-phase CrCoNi medium-entropy alloy(MEA)has drawn much attention recently regarding their deformation behaviors,but the dynamically mechanical responses of this alloy ...As an attractive class of metallic materials,single-phase CrCoNi medium-entropy alloy(MEA)has drawn much attention recently regarding their deformation behaviors,but the dynamically mechanical responses of this alloy at high strain rates remain less studied,especially coupled with extremely low temperatures.In this study,the dynamic deformation behaviors of this CrCoNi MEA were systematically investigated at room temperature(RT)of 298 K and liquid nitrogen temperature(LNT)of 77 K using the split Hopkinson pressure bar(SHPB).This alloy exhibited a combination of higher yield strength and stronger hardening rate upon dynamic compressive deformation when the loading conditions become much harsher(higher strain rate or lower temperature).Detailed microstructure analyses indicated that the strong strain hardening ability during dynamic deformation was mainly attributed to the continuous formation of nanoscale deformation twins.Furthermore,as loaded at LNT,multi-directional deformation twins were activated.Meanwhile,due to the interaction between Shockley partial dislocations and twin boundaries,large-sized deformation-induced FCC-HCP phase transformations at a micrometer scale were also observed within the grains,which not only accommodated the plasticity but also played an important role in improving the hardening capability owing to the appearance of newly generated interfaces.展开更多
Metallic amorphous/crystalline(A/C)nanolaminates exhibit excellent ductility while retaining their high strength.However,the underlying physical mechanisms and the resultant structural changes during plastic deformati...Metallic amorphous/crystalline(A/C)nanolaminates exhibit excellent ductility while retaining their high strength.However,the underlying physical mechanisms and the resultant structural changes during plastic deformation still remain unclear.In the present work,the structure-property relationship of CuZr/Cu A/C nanolaminates is established through integrated high-throughput micro-compression tests and molecular dynamics simulations together with high-resolution transmission electron microcopy.The serrated flow of nanolaminates results from the formation of hexagonal-close-packed(HCP)-type stacking faults and twins inside the face-centered-cubic(FCC)Cu nano-grains,the body-centered-cubic(BCC)-type ordering at their grain boundaries,and the crystallization of the amorphous CuZr layers.The serration behavior of CuZr/Cu A/C nanolaminates is determined by several factors,including the formation of dense dislocation networks from the multiplication of initial dislocations that formed after yielding,weak-spots-related configurational-transitions and shear-transition-zone activities,and deformation-induced devitrification.The present work provides an insight into the heterogeneous deformation mechanism of A/C nanolaminates at the atomic scale,and mechanistic base for the microstructural design of self-toughening metallic-glass(MG)-based composites and A/C nanolaminates.展开更多
Increasing the print quality is the critical requirement for the additive manufactured complex part of aero-engines of nickel-based superalloys.A study of the effects of Co and Nb on the crack is performed focusing on...Increasing the print quality is the critical requirement for the additive manufactured complex part of aero-engines of nickel-based superalloys.A study of the effects of Co and Nb on the crack is performed focusing on the selective laser melting(SLM)nickel-based superalloy.In this paper,the solvus temperature of γ',crack characteristics,microstructure,thermal expansion,and mechanical properties of SLM nickel-based superalloy are investigated by varying the content of Co and Nb.The alloy with 15Co/0Nb shows the highest comprehensive quality.Nb increases the crack risk and thermal deformation,and then Co accelerates the stress release.Therefore,Co is an extremely important alloying element for improving the quality of SLM nickel-based superalloy.Finally,the crack growth kinetics and the strain difference are discussed to reveal the SLM crack regular that is affected by time or temperature.The analysis work on the effect of alloying elements can obtain an effective foundational theory to guide the composition optimization of SLM nickel-based superalloys.展开更多
To provide insight into the effect of grain size on the precipitation behavior ofγstrengthening super-alloy Inconel 718,a gradient nanostructure with a large grain size span(from 9 nm to tens of microns)along the dep...To provide insight into the effect of grain size on the precipitation behavior ofγstrengthening super-alloy Inconel 718,a gradient nanostructure with a large grain size span(from 9 nm to tens of microns)along the depth direction was achieved by mean of surface mechanical grinding treatment,followed by annealing upon 700-1000℃ for 1 h.The results reveal significant differences in the type and size of precipitates in samples with different grain sizes.Noγprecipitate was detected inside the grains as the grain size was refined down to 40 nm(NG-40)and 9 nm(NG-9).Forδphase,a significantly accelerated precipitation along grain boundary was observed in NG-40 upon 700℃ annealing.Interestingly,with the grain size drops to 9 nm,the precipitation ofδwas suppressed,with some nanosized MC carbides appearing upon annealing.The grain size effect of precipitation behavior endows NG-9 an ultra-high RT-hardness(5.2 GPa)after 1000℃ thermal exposure and an ultra-high hot-hardness(3.2 GPa)at 800℃.展开更多
GH4169 alloy has been widely used in fields such as aviation, aerospace, and petrochemical, because of its excellent combination of mechanical and processing properties. These properties include good high-temperature ...GH4169 alloy has been widely used in fields such as aviation, aerospace, and petrochemical, because of its excellent combination of mechanical and processing properties. These properties include good high-temperature strength, excellent creep and fatigue resistance, and good processing and welding performance. The requirement for high performance, high reliability, and long service life of modem engines has led to the incentive to develop GH4169 alloys with improved performance, such as increased temperature-bearing capacity, improved creep endurance, and better fatigue resistance. Advances during the past thirty years in ba- sic research and industrial technology related to GH4169 alloy were systematically summarized, including advances in alloy modi- fication, melting process optimization, and hot deformation technology.展开更多
Four experimental FGH96 alloys with various contents of Hf and Zr （0 and 0.04%, 0.3% and 0.04%, 0.6% and 0. 04%, 0. 3% and 0.06%, respectively） were produced using PREP （plasma rotating electrode process）＋ HIP （...Four experimental FGH96 alloys with various contents of Hf and Zr （0 and 0.04%, 0.3% and 0.04%, 0.6% and 0. 04%, 0. 3% and 0.06%, respectively） were produced using PREP （plasma rotating electrode process）＋ HIP （hot isostatic pressing） route. The unnotched and notched stress-rupture properties and fatigue crack growth rate （FCGR） of all the experimental alloys were investigated to study the effect of Hf and Zr. Relevant fracture morphol ogy and microstructure were observed by scanning electron microscopy and transmission electron microscopy. The results revealed that appropriate content of Hf could lengthen stress-rupture life, eliminate notch sensitivity and slo wer FCGR. Microstructure analysis showed that the amount of ＂f phase should be increased or decreased by adjusting Hf and Zr contents, and MC carbide and oxide coupled growth should be increased by adding Hf content, which caused oxycarbide to precipitate along grain boundary and strengthen the alloy. It was found that excessive Zr in Hf- containing FGH96 alloy had certain deleterious effects on stress-rupture property because there was strong Zr segre- gation at prior particle boundary, leaving a long chain of large-size oxides along the boundary. The optimal content of Hf and Zr in FGH96 alloy was 0.6% and 0. 04%, respectively.展开更多
Phase stability and its effect on tensile properties of MAR-M247 alloy have been investigated during thermal exposure at 800–900°C for up to 10,000 h.Detailed investigations reveal that the larger secondaryγ′p...Phase stability and its effect on tensile properties of MAR-M247 alloy have been investigated during thermal exposure at 800–900°C for up to 10,000 h.Detailed investigations reveal that the larger secondaryγ′phase has no obvious growth,but the smaller tertiaryγ′phase obviously coarsens and the coalescence occurs during thermal exposure at 850°C and below.γ′coarsening behavior is consistent with the description of Ostwald ripening theory beforeγ′coalescence.Hf-rich blocky MC carbide shows excellent thermal stability,but Ta-rich script-type MC carbide gradually degenerates via reaction,MC+γ→M_(23)C_(6)+γ′and finally formsγ film around MC and M_(23)C_(6) carbides.With increasing thermal exposure time,the tensile strength decreases.The ductility first increases and then decreases during exposure at 800°C,but it decreases continuously at 900°C.In addition,the ductility keeps almost constant when the exposure time is longer than 5000 h.展开更多
The phase evolution and thermal expansion behavior in superalloy during heating play an essential role in controlling the size and distribution of precipitates,as well as optimizing thermomechanical properties.Synchro...The phase evolution and thermal expansion behavior in superalloy during heating play an essential role in controlling the size and distribution of precipitates,as well as optimizing thermomechanical properties.Synchrotron X-ray diffraction is able to go through the interior of sample and can be carried out with in situ environment,and thus,it can obtain more statistics information in real time comparing with traditional methods,such as electron and optical microscopies.In this study,in situ heating synchrotron X-ray diffraction was carried out to study the phase evolution in a typicalγ′phase precipitation strengthened Ni-based superalloy,Waspaloy,from 29 to 1050°C.Theγ′,γ,M_(23)C_(6)and M C phases,including their lattice parameters,misfits,dissolution behavior and thermal expansion coefficients,were mainly investigated.Theγ′phase and M_(23)C_(6)carbides appeared obvious dissolution during heating and re-precipitated when the temperature dropped to room temperature.Combining with the microscopy results,we can indicate that the dissolution of M_(23)C_(6)leads to the growth of grain andγ′phase cannot be completely dissolved for the short holding time above the solution temperature.Besides,the coefficients of thermal expansions of all the phases are calculated and fitted as polynomials.展开更多
Two TiAl alloys,Ti-47.5Al-3.7(Cr,V,Zr)and Ti-47.5Al-3.7(Cr,V,Zr)-0.1C(at.%),were prepared by cold crucible levitation melting to couple the hard-oriented directional lamellar microstructure with carbon microalloying s...Two TiAl alloys,Ti-47.5Al-3.7(Cr,V,Zr)and Ti-47.5Al-3.7(Cr,V,Zr)-0.1C(at.%),were prepared by cold crucible levitation melting to couple the hard-oriented directional lamellar microstructure with carbon microalloying strengthening.The creep behavior and mechanism for the improvement in creep properties by carbon addition were investigated by mechanical tests and electron microscopy characterizations.The results show that obvious improvements on the creep properties at 760°C and 276 MPa are achieved by 0.1 at.%C addition into TiAl alloy with directional lamellar microstructure,which promotes the creep strain and minimum creep rate decreasing with a large content.The minimum creep rate is reduced from 4.37×10^(-8) to 3.97×10^(-9) s^(-1),and the duration entering into creep acceleration is prolonged for more than 10 times.The mechanism for creep property improvement by 0.1%C addition is attributed to two aspects.The first one is that Ti_(2) AlC is found to be strong obstacles of 1/2[110]dislocations when moving across the lamellar interface in the carbon containing alloy.The other one is that the in terfacial dislocatio ns are effectively impeded and the release process is hindered by dynamic precipitation of Ti_(3) AlC,which is proposed to be the special mechanism for creep resistance improvement of this hard-oriented directional lamellar microstructure.展开更多
The hot deformation behavior of GH4945 superalloy was investigated by isothermal compression test in the temperature range of 1000--1200 ℃with strain rates of 0.001 10.000 s 1 toa total strain of 0.7. Dynamic recryst...The hot deformation behavior of GH4945 superalloy was investigated by isothermal compression test in the temperature range of 1000--1200 ℃with strain rates of 0.001 10.000 s 1 toa total strain of 0.7. Dynamic recrystallization is the primary softening mechanism for GH4945 superalloy during hot deformation. The constitutive equation is established, and the calculated apparent activation energy is 458. 446 kJ/moh The processing maps at true strains of 0.2, 0.4 and 0.6 are generally similar, dem- onstrating that strain has little influence on processing map. The power dissipation efficiency and in- stability factors are remarkably influenced by deformation temperature and strain rate. The optimal hot working conditions are determined in temperature range of 1082 -1131 ℃ with strain rates of 0.004--0.018 s-1. Another domain of1134--1150 ℃ and 0. 018 0.213s ^- can also be selected as the optimal hot working conditions. The initial grains are replaced by dynamically reerystallized ones in optimal domains. The unsafe domains locate in the zone with strain rates above 0, 274 s^- 1, mainly characterized by uneven microstructure. Hot working is not recommended in the unsafe domains.展开更多
Strengthening in Inconel 718 superalloy is derived from dislocation interaction withγ"precipitates,which exist in disk-shaped three possible orientation variants with their{100}habit plane normal to each other.T...Strengthening in Inconel 718 superalloy is derived from dislocation interaction withγ"precipitates,which exist in disk-shaped three possible orientation variants with their{100}habit plane normal to each other.The interactions between dislocations andγ"precipitates vary according to theγ"orienta-tion variants,which makes the deformation behaviour complicated and difficult to reveal experimentally.In this work,γ"variant distributions of Inconel 718 samples were tailored by ageing heat treatment under either tensile or compressive stress.Theγ"variant-sensitive deformation behaviours were then studied by in situ tensile tests via neutron diffraction at room temperature.It is demonstrated that yield-ing first takes place in grains oriented with<110>parallel to the loading direction.An identical lattice strain response to applied stress of both theγmatrix and theγ"precipitates was observed during yield-ing,suggesting that dislocations shearing through theγ"precipitates is predominant at this stage.Vari-ations in yield strength for samples with differentγ"variant distributions were observed,which can be attributed to different strengthening that arises from interactions between dislocation and differentγ"variants.展开更多
The precipitation behavior of topological close-packed（TCP）μphase in powder metallurgy（P/M）nickelbased superalloy FGH97 was investigated.The results showed that proper addition of solution strengthening elements,...The precipitation behavior of topological close-packed（TCP）μphase in powder metallurgy（P/M）nickelbased superalloy FGH97 was investigated.The results showed that proper addition of solution strengthening elements,such as Co,Cr,W,Mo,improved tensile strength,while excessive addition of those elements facilitated the precipitation ofμphase,which seriously aggravated the plasticity of the P/M superalloy.For the heat-treated specimens,the relationship between critical aging time（whenμstarted to precipitate）,aging temperature,and the average electron vacancy number ofγmatrix was established.展开更多
Two TiAl alloys,Ti^47.5Al-3.7(Cr,V,Zr)and Ti77.5Al-3.7(Cr,V,Zr)-0.1C(at.%),were melted and cast with the same process,respectively.Microstructures with strongly oriented lamellae were both observed in these two alloys...Two TiAl alloys,Ti^47.5Al-3.7(Cr,V,Zr)and Ti77.5Al-3.7(Cr,V,Zr)-0.1C(at.%),were melted and cast with the same process,respectively.Microstructures with strongly oriented lamellae were both observed in these two alloys followed by hot isostatic pressing and heat treatment.Ti2AlC carbides were identified in the alloy with C addition.Stress rupture tests were carried out at 800 and 850°C,with tensile stress from 220 to 400 MPa,respectively.It was shown that the alloy with C experienced much longer lives than the other,especially under the condition of 800°C/260 MPa,800°C/300 MPa,850°C/220 MPa,850°C/240 MPa and 850°C/260 MPa.Observation of ruptured specimens revealed that the microstructure stability was improved significantly in the alloy with C addition which is attributed to the strengthening effect of Ti-Al-C carbides.The Ti2AlC carbides mainly increased the resistance of dislocation passing through the interfaces and kept the integrity of the interfaces.And Ti3AlC carbide was formed during stress rupture process,which could not only effectively act as the barrier of dislocation movement inside the lamellae,but also strengthen the lamellae itself.展开更多
In this study,TiC/CM247LC nickel-based composite was successfully prepared by selective laser melting,then was heat treated at a solid solution temperature of 1260℃and different aging temperature of 840℃,870℃,900℃...In this study,TiC/CM247LC nickel-based composite was successfully prepared by selective laser melting,then was heat treated at a solid solution temperature of 1260℃and different aging temperature of 840℃,870℃,900℃and 930℃respectively.Effects of aging temperatures on the microstructures and mechanical properties were systematically studied.The results show that the microstructures of all the heat treated samples are composed ofγmatrix,carbides andγ′phase.Theγgrains remain a columnar shape after treatments,but the size ofγ′phase grows up gradually with the increasing aging temperature.The composite treated at an aging temperature of 870℃exhibits the best mechanical properties with the tensile strength of 1073 MPa,yield strength of 1004 MPa and elongation of 7.57%.The plastic deformation and strengthening mechanisms of heat treated composite were systematically investigated.展开更多
Alloy synthesis and processing determine the design of alloys with desired microstructure and properties.However,using data science to identify optimal synthesis-design routes from a specified set of starting material...Alloy synthesis and processing determine the design of alloys with desired microstructure and properties.However,using data science to identify optimal synthesis-design routes from a specified set of starting materials has been limited by large-scale data acquisition.Text mining has made it possible to convert scientific text into structured data collections.Still,the complexity,diversity,and flexibility of synthesis and processing expressions,and the lack of annotated corpora with a gold standard severely hinder accurate and efficient extraction.Here we introduce a semi-supervised text mining method to extract the parameters corresponding to the sequence of actions of synthesis and processing.We automatically extract a total of 9853 superalloy synthesis and processing actions with chemical compositions from a corpus of 16,604 superalloy articles published up to 2022.These have then been used to capture an explicitly expressed synthesis factor for predictingγ′phase coarsening.The synthesis factor derived from text mining significantly improves the performance of the data-drivenγ′size prediction model.The method thus complements the use of data-driven approaches in the search for relationships between synthesis and structures.展开更多
基金National Natural Science Foundation of China(grants 51771121)the fund provided by Science and Technology Committee of Shanghai Municipality(20ZR1437500)financial supports from Shanghai Municipal Education Commission(2019-01-07-00-07-E00015)。
文摘A composite coating of nitrogen-doped carbon dots(N–CDs)and polydopamine(PDA)was prepared on magnesium alloy by combining electrodeposition with dip coating methods.The microstructure of the N–CDs/PDA composite coating,including composition,surface morphology,and crystalline structure,is characterized by Raman spectroscopy,scanning electron microscopy,transmission electron microscopy,and X-ray photoelectron spectroscopy,respectively.The corrosion protection performances of the composite coating are evaluated by potentiodynamic polarization tests,electrochemical impedance spectroscopy,and salt spray tests.The effect of the particle size of the N–CDs on the corrosion performance is also investigated.The results show that the corrosion performance of the N–CDs coatings are enhanced with the increase of the particle sizes.Furthermore,an obvious self-healing performance is observed on the surface of the N–CDs/PDA composite coating.These results indicate that N–CDs/PDA composite coating can improve the corrosion performance of the Mg alloy,and open a new design direction for the protective coating of metallic materials.
基金Special Project(2013) supported by China’s National Development and Reform Commission for R&D and Industrialization of New Materials
文摘In order to clarify the effect of strain rate on hot deformation characteristics of GH690superalloy,the hot deformationbehavior of this superalloy was investigated by isothermal compression in the temperature range of1000?1200°C and strain raterange of0.001?10s?1on a Gleeble?3800thermo-mechanical simulator.The results reveal that the flow stress is sensitive to the strainrate,and the dynamic recrystallization(DRX)is the principal softening mechanism.The strain rate of0.1s?1is considered to be thecritical point during the hot deformation at1000°C.The DRX process is closely related to the strain rate due to the adiabatictemperature rise.The strain rate has an important influence on DDRX and CDRX during hot deformation.The nucleation of DRXcan be activated by twin boundaries,and there is a lower fraction ofΣ3n(n=1,2,3)boundaries at the intermediate strain rate of0.1s?1.
基金support from the National Natural Science Foundation of China, No.50771011
文摘Cr is the most important element in nickel-based alloys to prevent high temperature oxidation and corrosion. However, high-Cr content will lead to a decline of hot workability which limits the addition of Cr for most nickel-based superalloys. In order to add more Cr into Ni-based alloy for improving high temperature oxidation and corrosion resistance, the poor hot workability of high-Cr alloy must be first solved. Deformation characteristic of a high-Cr nickel-based alloy （40 wt% Cr） under hot compression conditions at 800-1200 ℃ has been investigated by using a Gleeble 3500 machine, and the microstructural evolution during hot working process has been observed by optical microscopy and scanning electron microscopy. The results show that a high-temperature low-plasticity （HTLP） region exists in this high-Cr nickel-based alloy. This phenomenon can be attributed to its non-uniform interdendritic microstructure at high temperatures. These results can explain the poor hot workability of high-Cr nickel-based alloy.
基金supported by the National Natural Science Foundation of China(Nos.52231001,51971167,and 52031011)the Xi’an Science and Technology Plan(No.2017xasjl014)+4 种基金B.G.gratefully acknowledges the financial support of the project from the Ministry of Science and Technology of China(No.2017YFA0700703)the support by the National Natural Science Foundation of China(No.92060102)E.M.and J.D.acknowledge the support at CAID by XJTU.J.D.acknowledges support from the National Natural Science Foundation of China(No.12004294)the HPC platform of Xi’an Jiaotong Universitysupported by the Office of Science,Office of Basic Energy Sciences,Materials Sciences and Engineering Division,of the U.S.Department of Energy under Contract No.DE-AC02-05-CH11231.
文摘Single-phase face-centered cubic(fcc)high/medium-entropy alloys(H/MEAs)exhibit a much higher tendency to form nanoscale deformation twins than conventional fcc metals with similar low stacking fault energies(SFEs).This extraordinary propensity for nanotwin formation in H/MEAs cannot therefore be ex-plained by their low SFEs alone.Here,using in situ compression tests of CrCoNi in comparison with Ag nanopillars inside a transmission electron microscope,we found that in the CrCoNi MEA,a high density of nanoscale twins continuously formed with an average thickness of 4.6 nm.In contrast,for similar experiments on Ag with almost identical SFE,following the nucleation of a few twins,they could further thicken to above one hundred nanometers by twin boundary migration.Molecular dynamics calculations indicated that in the highly-concentrated CrCoNi solid solution,the magnitude of the energy barriers for nucleating a stacking fault as a twin precursor in the pristine lattice and for the thickening of an existing twin both span a wide range and largely overlap with each other.Therefore,twin thickening through successive addition of atomic layers is prone to discontinuation,giving way to the nucleation of new twins at other sites where a lower energy barrier is encountered for partial-dislocation mediated fault formation.
基金This work was financially supported by the Basic Science Center Program for Multiphase Evolution in Hyper-gravity of the National Natural Science Foundation of China(No.51988101)the National Natural Science Foundation of China(Nos.52071003,91860202,11604006)+4 种基金the Beijing Municipal Education Commission Project(Nos.PXM2020-014204-000021and PXM2019-014204-500032)the Beijing Outstanding Young Scientists Projects(No.BJJWZYJH01201910005018)the Beijing Natural Science Foundation(No.Z180014)the“111”project(No.DB18015)supported by the Australian Research Council(No.DP190102990)。
文摘This paper reports a synergistic design of high-performance BCC high-entropy alloy based on the combined consideration of the principles of intrinsic ductility of elements,maximum atomic size difference for solid solution strengthening and the valence electron concentration criterion for ductility.The single-phase BCC HfNbTaTiV alloy thus designed exhibited a high compressive yield strength of 1350 MPa and a high compressive ductility of>45%at the room temperature.This represents a 50%increase in yield strength relative to a HfNbTaTiZr alloy.This is attributed to the maximized solid solution strengthening effect caused by lattice distortion,which is estimated to be 1094 MPa.The alloy was also able to retain 53%of its yield strength and 77%of its ductility at 700℃.These properties are superior to those of most refractory BCC high-entropy alloys reported in the literature.
基金supported by the National Natural Science Foundation of China(Grant No.12102363)the China National Funds for Distinguished Young Scientists(Grant No.12025205).
文摘As an attractive class of metallic materials,single-phase CrCoNi medium-entropy alloy(MEA)has drawn much attention recently regarding their deformation behaviors,but the dynamically mechanical responses of this alloy at high strain rates remain less studied,especially coupled with extremely low temperatures.In this study,the dynamic deformation behaviors of this CrCoNi MEA were systematically investigated at room temperature(RT)of 298 K and liquid nitrogen temperature(LNT)of 77 K using the split Hopkinson pressure bar(SHPB).This alloy exhibited a combination of higher yield strength and stronger hardening rate upon dynamic compressive deformation when the loading conditions become much harsher(higher strain rate or lower temperature).Detailed microstructure analyses indicated that the strong strain hardening ability during dynamic deformation was mainly attributed to the continuous formation of nanoscale deformation twins.Furthermore,as loaded at LNT,multi-directional deformation twins were activated.Meanwhile,due to the interaction between Shockley partial dislocations and twin boundaries,large-sized deformation-induced FCC-HCP phase transformations at a micrometer scale were also observed within the grains,which not only accommodated the plasticity but also played an important role in improving the hardening capability owing to the appearance of newly generated interfaces.
基金financially supported by the National Natural Science Foundation of China(Nos.51690163 and 51601147)the Science Challenge Project(No.TZZT2019-D1.5)+4 种基金the Ministry of Science and Technology of China(No.2017YFA0700700)the United States National Science Foundation(Nos.DMR-1006557,1611180,and 1809640)the Fundamental Research Funds for the Central Universities in China(No.G2016KY0302)the CyberStar cluster funded by NSF through grant No.OCI-0821527the XSEDE clusters supported by NSF through Grant No.ACI-1053575。
文摘Metallic amorphous/crystalline(A/C)nanolaminates exhibit excellent ductility while retaining their high strength.However,the underlying physical mechanisms and the resultant structural changes during plastic deformation still remain unclear.In the present work,the structure-property relationship of CuZr/Cu A/C nanolaminates is established through integrated high-throughput micro-compression tests and molecular dynamics simulations together with high-resolution transmission electron microcopy.The serrated flow of nanolaminates results from the formation of hexagonal-close-packed(HCP)-type stacking faults and twins inside the face-centered-cubic(FCC)Cu nano-grains,the body-centered-cubic(BCC)-type ordering at their grain boundaries,and the crystallization of the amorphous CuZr layers.The serration behavior of CuZr/Cu A/C nanolaminates is determined by several factors,including the formation of dense dislocation networks from the multiplication of initial dislocations that formed after yielding,weak-spots-related configurational-transitions and shear-transition-zone activities,and deformation-induced devitrification.The present work provides an insight into the heterogeneous deformation mechanism of A/C nanolaminates at the atomic scale,and mechanistic base for the microstructural design of self-toughening metallic-glass(MG)-based composites and A/C nanolaminates.
基金financially supported by the National Natural Science Foundation of China(Grant No.12205055)the National Key Research and Development Program of China(Grant No.2021YFB3702500).
文摘Increasing the print quality is the critical requirement for the additive manufactured complex part of aero-engines of nickel-based superalloys.A study of the effects of Co and Nb on the crack is performed focusing on the selective laser melting(SLM)nickel-based superalloy.In this paper,the solvus temperature of γ',crack characteristics,microstructure,thermal expansion,and mechanical properties of SLM nickel-based superalloy are investigated by varying the content of Co and Nb.The alloy with 15Co/0Nb shows the highest comprehensive quality.Nb increases the crack risk and thermal deformation,and then Co accelerates the stress release.Therefore,Co is an extremely important alloying element for improving the quality of SLM nickel-based superalloy.Finally,the crack growth kinetics and the strain difference are discussed to reveal the SLM crack regular that is affected by time or temperature.The analysis work on the effect of alloying elements can obtain an effective foundational theory to guide the composition optimization of SLM nickel-based superalloys.
基金supported by the Strategic Pri-ority Research Program of the Chinese Academy of Sciences(No.XDB0510400)the National Natural Science Foundation of China(No.52225102)the Youth Innovation Promotion Association CAS(No.2023201).
文摘To provide insight into the effect of grain size on the precipitation behavior ofγstrengthening super-alloy Inconel 718,a gradient nanostructure with a large grain size span(from 9 nm to tens of microns)along the depth direction was achieved by mean of surface mechanical grinding treatment,followed by annealing upon 700-1000℃ for 1 h.The results reveal significant differences in the type and size of precipitates in samples with different grain sizes.Noγprecipitate was detected inside the grains as the grain size was refined down to 40 nm(NG-40)and 9 nm(NG-9).Forδphase,a significantly accelerated precipitation along grain boundary was observed in NG-40 upon 700℃ annealing.Interestingly,with the grain size drops to 9 nm,the precipitation ofδwas suppressed,with some nanosized MC carbides appearing upon annealing.The grain size effect of precipitation behavior endows NG-9 an ultra-high RT-hardness(5.2 GPa)after 1000℃ thermal exposure and an ultra-high hot-hardness(3.2 GPa)at 800℃.
文摘GH4169 alloy has been widely used in fields such as aviation, aerospace, and petrochemical, because of its excellent combination of mechanical and processing properties. These properties include good high-temperature strength, excellent creep and fatigue resistance, and good processing and welding performance. The requirement for high performance, high reliability, and long service life of modem engines has led to the incentive to develop GH4169 alloys with improved performance, such as increased temperature-bearing capacity, improved creep endurance, and better fatigue resistance. Advances during the past thirty years in ba- sic research and industrial technology related to GH4169 alloy were systematically summarized, including advances in alloy modi- fication, melting process optimization, and hot deformation technology.
基金Sponsored by National Basic Research Program of China(2010CB631204)
文摘Four experimental FGH96 alloys with various contents of Hf and Zr （0 and 0.04%, 0.3% and 0.04%, 0.6% and 0. 04%, 0. 3% and 0.06%, respectively） were produced using PREP （plasma rotating electrode process）＋ HIP （hot isostatic pressing） route. The unnotched and notched stress-rupture properties and fatigue crack growth rate （FCGR） of all the experimental alloys were investigated to study the effect of Hf and Zr. Relevant fracture morphol ogy and microstructure were observed by scanning electron microscopy and transmission electron microscopy. The results revealed that appropriate content of Hf could lengthen stress-rupture life, eliminate notch sensitivity and slo wer FCGR. Microstructure analysis showed that the amount of ＂f phase should be increased or decreased by adjusting Hf and Zr contents, and MC carbide and oxide coupled growth should be increased by adding Hf content, which caused oxycarbide to precipitate along grain boundary and strengthen the alloy. It was found that excessive Zr in Hf- containing FGH96 alloy had certain deleterious effects on stress-rupture property because there was strong Zr segre- gation at prior particle boundary, leaving a long chain of large-size oxides along the boundary. The optimal content of Hf and Zr in FGH96 alloy was 0.6% and 0. 04%, respectively.
基金financially supported by the National Natural Science Foundation of China (Nos. 51971216 and 51301171)the National Science and Technology Major Project of China (No. 2017-VI-0018-0090)+1 种基金the fund of State Key Laboratory of Long-life High Temperature Materials (No. DTCC28EE190231)the LiaoNing Revitalization Talents Program (No. XLYC1807038)。
文摘Phase stability and its effect on tensile properties of MAR-M247 alloy have been investigated during thermal exposure at 800–900°C for up to 10,000 h.Detailed investigations reveal that the larger secondaryγ′phase has no obvious growth,but the smaller tertiaryγ′phase obviously coarsens and the coalescence occurs during thermal exposure at 850°C and below.γ′coarsening behavior is consistent with the description of Ostwald ripening theory beforeγ′coalescence.Hf-rich blocky MC carbide shows excellent thermal stability,but Ta-rich script-type MC carbide gradually degenerates via reaction,MC+γ→M_(23)C_(6)+γ′and finally formsγ film around MC and M_(23)C_(6) carbides.With increasing thermal exposure time,the tensile strength decreases.The ductility first increases and then decreases during exposure at 800°C,but it decreases continuously at 900°C.In addition,the ductility keeps almost constant when the exposure time is longer than 5000 h.
基金supported by the National Natural Science Foundation of China(NSFC)(Grant Nos.11805009 and 51921001)the Fundamental Research Funds for the Central Universities(Grant No.06111020)。
文摘The phase evolution and thermal expansion behavior in superalloy during heating play an essential role in controlling the size and distribution of precipitates,as well as optimizing thermomechanical properties.Synchrotron X-ray diffraction is able to go through the interior of sample and can be carried out with in situ environment,and thus,it can obtain more statistics information in real time comparing with traditional methods,such as electron and optical microscopies.In this study,in situ heating synchrotron X-ray diffraction was carried out to study the phase evolution in a typicalγ′phase precipitation strengthened Ni-based superalloy,Waspaloy,from 29 to 1050°C.Theγ′,γ,M_(23)C_(6)and M C phases,including their lattice parameters,misfits,dissolution behavior and thermal expansion coefficients,were mainly investigated.Theγ′phase and M_(23)C_(6)carbides appeared obvious dissolution during heating and re-precipitated when the temperature dropped to room temperature.Combining with the microscopy results,we can indicate that the dissolution of M_(23)C_(6)leads to the growth of grain andγ′phase cannot be completely dissolved for the short holding time above the solution temperature.Besides,the coefficients of thermal expansions of all the phases are calculated and fitted as polynomials.
基金National Natural Science Foundation of China(51788104,51390471,51527803 and 51761135131)National 973 Project of China(2015CB654902)National Key Research and Development Pro gram(2016YFB0700402)。
文摘Two TiAl alloys,Ti-47.5Al-3.7(Cr,V,Zr)and Ti-47.5Al-3.7(Cr,V,Zr)-0.1C(at.%),were prepared by cold crucible levitation melting to couple the hard-oriented directional lamellar microstructure with carbon microalloying strengthening.The creep behavior and mechanism for the improvement in creep properties by carbon addition were investigated by mechanical tests and electron microscopy characterizations.The results show that obvious improvements on the creep properties at 760°C and 276 MPa are achieved by 0.1 at.%C addition into TiAl alloy with directional lamellar microstructure,which promotes the creep strain and minimum creep rate decreasing with a large content.The minimum creep rate is reduced from 4.37×10^(-8) to 3.97×10^(-9) s^(-1),and the duration entering into creep acceleration is prolonged for more than 10 times.The mechanism for creep property improvement by 0.1%C addition is attributed to two aspects.The first one is that Ti_(2) AlC is found to be strong obstacles of 1/2[110]dislocations when moving across the lamellar interface in the carbon containing alloy.The other one is that the in terfacial dislocatio ns are effectively impeded and the release process is hindered by dynamic precipitation of Ti_(3) AlC,which is proposed to be the special mechanism for creep resistance improvement of this hard-oriented directional lamellar microstructure.
基金financially supported by the National Natural Science Foundation of China(Grant Nos. 51601041and 51301085)
文摘The hot deformation behavior of GH4945 superalloy was investigated by isothermal compression test in the temperature range of 1000--1200 ℃with strain rates of 0.001 10.000 s 1 toa total strain of 0.7. Dynamic recrystallization is the primary softening mechanism for GH4945 superalloy during hot deformation. The constitutive equation is established, and the calculated apparent activation energy is 458. 446 kJ/moh The processing maps at true strains of 0.2, 0.4 and 0.6 are generally similar, dem- onstrating that strain has little influence on processing map. The power dissipation efficiency and in- stability factors are remarkably influenced by deformation temperature and strain rate. The optimal hot working conditions are determined in temperature range of 1082 -1131 ℃ with strain rates of 0.004--0.018 s-1. Another domain of1134--1150 ℃ and 0. 018 0.213s ^- can also be selected as the optimal hot working conditions. The initial grains are replaced by dynamically reerystallized ones in optimal domains. The unsafe domains locate in the zone with strain rates above 0, 274 s^- 1, mainly characterized by uneven microstructure. Hot working is not recommended in the unsafe domains.
基金support from the Guangdong Introducing Innovative and Entrepreneurial Teams(No.2016ZT06G025)and the financial support from the Centre for Doctoral Training in Innovative Metal Processing(IMPaCT)funded by the UK Engineering and Physical Sciences Research Council(EPSRC,No.EP/L016206/1).The authors also acknowledge useful discussions by Dr.Xingzhong Liang and the allocation of beam time(RB1820207)at ENGIN-X,ISIS,Rutherford Appleton Labora-tory.Chinnapat Panwisawas would like to acknowledge the funding from Innovation Fellowship by EPSRC,UK Research and Innovation(UKRI,No.EP/S000828/2).Shuyan Zhang gratefully acknowledges the support from the Guangdong Major Project of Basic and Ap-plied Basic Research(No.2020B0301030001)and the Strategic Pri-ority Research Program of the Chinese Academy of Sciences(No.XDC04000000).
文摘Strengthening in Inconel 718 superalloy is derived from dislocation interaction withγ"precipitates,which exist in disk-shaped three possible orientation variants with their{100}habit plane normal to each other.The interactions between dislocations andγ"precipitates vary according to theγ"orienta-tion variants,which makes the deformation behaviour complicated and difficult to reveal experimentally.In this work,γ"variant distributions of Inconel 718 samples were tailored by ageing heat treatment under either tensile or compressive stress.Theγ"variant-sensitive deformation behaviours were then studied by in situ tensile tests via neutron diffraction at room temperature.It is demonstrated that yield-ing first takes place in grains oriented with<110>parallel to the loading direction.An identical lattice strain response to applied stress of both theγmatrix and theγ"precipitates was observed during yield-ing,suggesting that dislocations shearing through theγ"precipitates is predominant at this stage.Vari-ations in yield strength for samples with differentγ"variant distributions were observed,which can be attributed to different strengthening that arises from interactions between dislocation and differentγ"variants.
基金Item Sponsored by International Science and Technology Cooperation Program of China(2014DFR50330)
文摘The precipitation behavior of topological close-packed（TCP）μphase in powder metallurgy（P/M）nickelbased superalloy FGH97 was investigated.The results showed that proper addition of solution strengthening elements,such as Co,Cr,W,Mo,improved tensile strength,while excessive addition of those elements facilitated the precipitation ofμphase,which seriously aggravated the plasticity of the P/M superalloy.For the heat-treated specimens,the relationship between critical aging time（whenμstarted to precipitate）,aging temperature,and the average electron vacancy number ofγmatrix was established.
基金National 973 Project of China(2015CB654902)Chinese National Natural Science Foundation(11374174,51390471 and 51527803).
文摘Two TiAl alloys,Ti^47.5Al-3.7(Cr,V,Zr)and Ti77.5Al-3.7(Cr,V,Zr)-0.1C(at.%),were melted and cast with the same process,respectively.Microstructures with strongly oriented lamellae were both observed in these two alloys followed by hot isostatic pressing and heat treatment.Ti2AlC carbides were identified in the alloy with C addition.Stress rupture tests were carried out at 800 and 850°C,with tensile stress from 220 to 400 MPa,respectively.It was shown that the alloy with C experienced much longer lives than the other,especially under the condition of 800°C/260 MPa,800°C/300 MPa,850°C/220 MPa,850°C/240 MPa and 850°C/260 MPa.Observation of ruptured specimens revealed that the microstructure stability was improved significantly in the alloy with C addition which is attributed to the strengthening effect of Ti-Al-C carbides.The Ti2AlC carbides mainly increased the resistance of dislocation passing through the interfaces and kept the integrity of the interfaces.And Ti3AlC carbide was formed during stress rupture process,which could not only effectively act as the barrier of dislocation movement inside the lamellae,but also strengthen the lamellae itself.
基金he financial supports provided by the Shandong Provincial Natural Science Foundation General Program under Grant No.ZR2023ME062.
文摘In this study,TiC/CM247LC nickel-based composite was successfully prepared by selective laser melting,then was heat treated at a solid solution temperature of 1260℃and different aging temperature of 840℃,870℃,900℃and 930℃respectively.Effects of aging temperatures on the microstructures and mechanical properties were systematically studied.The results show that the microstructures of all the heat treated samples are composed ofγmatrix,carbides andγ′phase.Theγgrains remain a columnar shape after treatments,but the size ofγ′phase grows up gradually with the increasing aging temperature.The composite treated at an aging temperature of 870℃exhibits the best mechanical properties with the tensile strength of 1073 MPa,yield strength of 1004 MPa and elongation of 7.57%.The plastic deformation and strengthening mechanisms of heat treated composite were systematically investigated.
基金This work is financially supported by the National Key Research and Development Program of China(2021YFB3702403,2022YFB3707502)National Natural Science Foundation of China(52201061,U22A20106)+1 种基金Fundamental Research Funds for the Central Universities(FRF-TP-22-008A1)USTB MatCom of Beijing Advanced Innova-tion Center for Materials Genome Engineering,and the CNNC Science Fund for Talented Young Scholars(FY222506000902).
文摘Alloy synthesis and processing determine the design of alloys with desired microstructure and properties.However,using data science to identify optimal synthesis-design routes from a specified set of starting materials has been limited by large-scale data acquisition.Text mining has made it possible to convert scientific text into structured data collections.Still,the complexity,diversity,and flexibility of synthesis and processing expressions,and the lack of annotated corpora with a gold standard severely hinder accurate and efficient extraction.Here we introduce a semi-supervised text mining method to extract the parameters corresponding to the sequence of actions of synthesis and processing.We automatically extract a total of 9853 superalloy synthesis and processing actions with chemical compositions from a corpus of 16,604 superalloy articles published up to 2022.These have then been used to capture an explicitly expressed synthesis factor for predictingγ′phase coarsening.The synthesis factor derived from text mining significantly improves the performance of the data-drivenγ′size prediction model.The method thus complements the use of data-driven approaches in the search for relationships between synthesis and structures.
