GH4350(AEREX 350)is a Ni-based wrought superalloy for high-performance fasteners,with a maximum service temperature of 750℃.It has high tensile strength,fatigue resistance,stress rupture and relaxation resistance,cor...GH4350(AEREX 350)is a Ni-based wrought superalloy for high-performance fasteners,with a maximum service temperature of 750℃.It has high tensile strength,fatigue resistance,stress rupture and relaxation resistance,corrosion resistance,low thermal expansion,and notch sensitivity.The high strength of GH4350 is largely derived through solid solution strengthening and the γ′phase precipitation strengthening.During the precipitation of γ′phase,a minor amount ofηphase also precipitates.However,it is reported that the microstructure of alloy is sensitive to heat treatment parameters,including temperature and time.The γ′phases can be transformed intoηphases under certain conditions,potentially degrading the performance of the alloy.The chemical composition characteristics,heat treatment strategies,and strengthening mechanism of GH4350 were reviewed in this research,aiming to understand the factors behind its remarkable high-temperature performance,to guide the development of new alloys,and to further enhance its heat resistance.展开更多
The influence of V contents(0.6 wt%,0.8 wt%and 1.0 wt%)on the microstructure and creep behavior of a Nickel-based superalloy was investigated.The results revealed that the V content exerted a significant impact on the...The influence of V contents(0.6 wt%,0.8 wt%and 1.0 wt%)on the microstructure and creep behavior of a Nickel-based superalloy was investigated.The results revealed that the V content exerted a significant impact on the morphology of carbide.Notably,in the alloy containing 0.8 wt%V,coarse blocky M_(6)C carbides formed adjacent to MC carbides,while in the 1.0 wt%V alloy,fine granular M_(6)C carbides exhibited a nearly continuous distribution along grain boundaries(GBs).The influence of V content on creep properties exhibited significant variations depending on temperature.At 650℃/1010 MPa,the 1.0 wt%V alloy,containing a high density of granular M_(6)C carbides,demonstrated enhanced intergranular bonding strength,which contributed to prolonged creep life.In contrast,at higher temperatures(750℃/620 MPa and 800℃/500 MPa),GB mobility was activated,making GB slip the dominant creep mechanism.The near-continuous distribution of M_(6)C carbides in the 1.0 wt%V alloy restricted GB deformation compatibility,promoting stress localization and an increased density of micropores along GBs.As a result,the 0.8 wt%V alloy,with its discrete M_(6)C carbide distribution,exhibited superior creep resistance at elevated temperatures.展开更多
Alloy selection and alloy design both require consideration of an array of material attributes, including in-service properties, weldability and fabricability. Critical properties of advanced wrought superalloys for g...Alloy selection and alloy design both require consideration of an array of material attributes, including in-service properties, weldability and fabricability. Critical properties of advanced wrought superalloys for gas turbine applications include high temperature strength, thermal stability, oxidation resistance and fatigue resistance. In this paper, the properties of twelve wrought solid-solution-strengthened and six age-hardenable superalloys are compared. Weldability is an important attribute and can be a major limiting factor in the use of certain alloys. Weldability test methods are discussed and the resistance of alloys to solidification cracking and strain-age cracking is compared. The use of weldability testing in the development of modern wrought su-peralloys is discussed with several examples cited. Finally, alloy selection for gas turbine components is outlined, taking into account both alloy properties and fabricability.展开更多
Wrought magnesium alloys attract special interests as lightweight structural material due to their homogeneous microstructure and enhanced mechanical properties compared to as-cast alloys.In this contribution,recent r...Wrought magnesium alloys attract special interests as lightweight structural material due to their homogeneous microstructure and enhanced mechanical properties compared to as-cast alloys.In this contribution,recent research and developments on wrought magnesium alloys are reviewed from the viewpoint of the alloy design,focusing on Mg-Al,Mg-Zn and Mg-rare earth(RE)systems.The effects of different alloying elements on the microstructure and mechanical properties are described considering their strengthening mechanisms,e.g.grain refinement,precipitation and texture hardening effect.Finally,the new alloy design and also the future research of wrought magnesium alloys to improve their mechanical properties are discussed.展开更多
The Portevin-Le Chatelier(PLC) effects in a wrought Ni-base superalloy with different γ' precipitates contents have been investigated. Detailed analysis on the serration type of the tensile curves indicates that ...The Portevin-Le Chatelier(PLC) effects in a wrought Ni-base superalloy with different γ' precipitates contents have been investigated. Detailed analysis on the serration type of the tensile curves indicates that the γ' precipitates have a decisive influence on the transformation from normal to inverse PLC behavior, which is rarely proposed in other works. It is considered that the γ' precipitates play the same role in PLC effect as temperature and strain rate for the investigated wrought Ni-base superalloy.展开更多
Many researchers in China are actively engaged in the development of new types of wrought magnesium alloys with low cost or with high-performances and novel plastic processing technologies.The research activities are ...Many researchers in China are actively engaged in the development of new types of wrought magnesium alloys with low cost or with high-performances and novel plastic processing technologies.The research activities are funded primarily through four government-supported programs:the Key Technologies R&D Program of China,the National Basic Research Program of China,the National High-tech R&D Program of China,and the National Natural Science Foundation of China.The key R&D activities for the development of new wrought magnesium alloys in China are reviewed,and typical properties of some new alloys are summarized. More attentions are paid to high-strength wrought magnesium alloys and high-plasticity wrought magnesium alloys.Some novel plastic processing technologies,emerging in recent years,which aim to control deformation texture and to improve plasticity and formability especially at room temperature,are also introduced.展开更多
In this paper, the relationship between anisotropic mechanical properties and the corresponding microstructure evolution of wrought magnesium alloys is critically reviewed. Experimental observations of the strong anis...In this paper, the relationship between anisotropic mechanical properties and the corresponding microstructure evolution of wrought magnesium alloys is critically reviewed. Experimental observations of the strong anisotropy(including the strength differential effect) induced by texture and twinning are discussed under different loading conditions(i.e., monotonic, cyclic and multiaxial loading). An accurate constitutive model is essential to describe the mechanical responses and to predict the forming performance considering engineering applications. Therefore, macroscale constitutive modeling of the anisotropy of magnesium alloys with directional distortional hardening are comprehensively reviewed with different approaches. To clarify the origin of the anisotropic behavior, physics-based mesoscale modeling of the anisotropy is also compared in detail.展开更多
One important problem in casting wrought aluminum alloys is the high tendency to the formation of hot tears in the solidification process.By using semi-solid metal(SSM) processing,the hot tearing tendency of alloys ca...One important problem in casting wrought aluminum alloys is the high tendency to the formation of hot tears in the solidification process.By using semi-solid metal(SSM) processing,the hot tearing tendency of alloys can be minimized during casting.In the present research,the semi-solid slurry of wrought aluminum alloy 2024 was firstly prepared with a novel self-inoculation method(SIM),and then the microstructure characteristics of the semi-solid slurry and the rheo-diecastings cast with the semi-solid slurry were investigated.The results indicate that finer and more uniform globular primary α-Al particles can be obtained when the semi-solid slurry are isothermally held for a short period within the semi-solid temperature range,and the primary α-Al particles without entrapped liquid are uniformly fine,globular grains in the rheo-diecastings.The holding temperature and time affect the solid fraction,particle size,and shape factor.After the semi-solid slurry is held at 625 ℃ for 3 min and 5 min,the optimal values for the average equivalent diameter are 70.80 μm and 74.15 μm,and for the shape factor are 1.32 and 1.42,respectively.The solidification process of the rheo-diecastings is composed of the following two distinct stages:primary solidification process and secondary solidification process.The secondary solidification process consists further of the following three stages:(1) direct growth of secondary primary(α 2) phase from the surface of the primary α-Al phase particles without re-nucleation,(2) independent nucleation and growth of α 3 phase from the residual liquid,and(3) eutectic reaction at the end.展开更多
Some existing wrought Ni-Cr-Co-based superalloys are being evaluated as the candidate materials for advanced ultra-supercritical power plant applications beyond 700 ℃ due to their high creep strength. But they are al...Some existing wrought Ni-Cr-Co-based superalloys are being evaluated as the candidate materials for advanced ultra-supercritical power plant applications beyond 700 ℃ due to their high creep strength. But they are all prohibitively expensive due to the addition of Co, Mo and W. Here we developed a new Ni-Fe-Cr-based superalloy （named as HT700 alloy） with low cost and high strength. This paper reports the mechanical properties and fracture modes of HT700 alloy to support its high temperature applications and to understand prospective failure mechanism. Fracto- graphic examinations indicate that the fracture modes shift with test condition change. In addition, the HT700 alloy has relatively stable microstructure at 750 ℃. Compared with IN740 and GH2984 alloys, this new alloy has higher yield strength in the temperature range from room temperature to 800 ℃. The creep life of this new alloy is much longer than that of the Ni-Fe-based superaUoy GH2984. The results suggest that this new alloy is a promising material for advanced ultra-supercritical power plant applications beyond 700 ℃.展开更多
Empirical improvements made in cast alloys have led to gamma alloys which are a viable materials technology, and to the development of various applications for gas turbine engines, as well as automotive engines. For w...Empirical improvements made in cast alloys have led to gamma alloys which are a viable materials technology, and to the development of various applications for gas turbine engines, as well as automotive engines. For wrougth alloys, over the last seven years the author et al have made extensive efforts to remove their deficiencies, and to achieve an improved balance of properties, across three interrelated task areas. The first effort was directed toward understanding fundamentals, such as phase relations, microstructure evolution, and microstructure property relationships. The second task was then directed to improve the balance of properties through designing refined lamellar microstructures and microalloying. The third effort was to explore the production methods to develop desired microstructures and to optimize the alloy compositions. This paper discusses the progress made from the last two efforts.展开更多
Effects of hot plastic deformation on microstructures and tensile propertiesof AZ91 alloy were investigated. Compared with as-T4 microstructures, the as-extruded samples ofAZ91 alloy with fine grains exhibit better st...Effects of hot plastic deformation on microstructures and tensile propertiesof AZ91 alloy were investigated. Compared with as-T4 microstructures, the as-extruded samples ofAZ91 alloy with fine grains exhibit better strength and ductility due to dynamic recrystallization.The succeeded rotation forging also provides finer grains while the strength increases, but theelongation decreases. Simultaneously, wrought AZ91 alloy shows more balance properties than as-T4condition ones. An interesting elongation of 228.5% is attained in the as-extruded AZ91 alloy inspite of the coarse grains with the size of 85 μm. The two-step method enhances the superplasticproperty of AZ91 alloy. The microstructure is still keeping the same scale of grains aftersuperplastic testing.展开更多
The semisolid slurry of the 6061 wrought aluminum alloy was prepared by the self-inoculation method（SIM）. The effects of the isothermal holding parameters on microstructures of rheo-diecastings were investigated, an...The semisolid slurry of the 6061 wrought aluminum alloy was prepared by the self-inoculation method（SIM）. The effects of the isothermal holding parameters on microstructures of rheo-diecastings were investigated, and the solidification behavior of 6061 wrought aluminum alloy during the rheo-diecasting process was analyzed using OM, SEM, EDS and EBSD. The results indicate that the isothermal holding process during slurry preparation has great effect on primary α（Al） particles（α1）, but has little effect on the microstructure of secondary solidification in the process of thin-walled rheo-diecasting. Nucleation is expected to take place in the entire remaining liquid when the remaining liquid fills the die cavity, and the secondary solidification particles（α2） are formed after the process of stable growth, unstable growth and merging. The solute concentration of remaining liquid is higher than that of the original alloy due to the existence of α1 particles, hence the contents of Mg and Si in α2 particles are higher than those in α1 particles.展开更多
A novel low-cost Mg-Al-Ca-Zn-Mn-based alloy was developed to simultaneously improve its strength and ductility.The high yield strength of 411 MPa and the high elongation to failure of~8.9%have been achieved in the as-...A novel low-cost Mg-Al-Ca-Zn-Mn-based alloy was developed to simultaneously improve its strength and ductility.The high yield strength of 411 MPa and the high elongation to failure of~8.9%have been achieved in the as-extruded Mg-1.3Al-1.2Ca-0.5Zn-0.6Mn(wt%)sample.Microstructure characterizations showed that the high strength is mainly associated with the ultra-fined dynamically recrystallized(DRXed)grains.Moreover,high-density dislocations in the un-DRXed region and nano-precipitates are distributed among theα-Mg matrix.The high ductility property can be ascribed to the high volume fraction of DRXed grains with a much randomized texture,as well as the formations of high-density subgrains in the un-DRXed grain regions.展开更多
A new method was exploited using solution treatment and aging process as a pretreatment in preparing semi-solid slurry with fine microstructure before isothermal treatment of wrought aluminum alloy 7A09.Parameters of ...A new method was exploited using solution treatment and aging process as a pretreatment in preparing semi-solid slurry with fine microstructure before isothermal treatment of wrought aluminum alloy 7A09.Parameters of pretreatment were optimized by orthogonal experiment design and proper precursor was prepared.The evolution of microstructure of semi-solid slurry during isothermal treatment was analyzed and the mechanism of microstructure refining was discussed.The result of orthogonal experiment design shows that the optimum parameters are 462 ℃for solution temperature,40min for solution time,132 ℃for aging temperature and 14 h for aging time.Microstructure of isothermal treatment is fine,homogenous,with globular solid grains and a solid fraction between 50%and 70%,which is qualified for later semi-solid forming process.Mechanism of microstructure evolution includes the agglomeration ofα-phase and Ostwald ripening.Precipitations prepared by solution and aging treatment prevent the grains from coarsening and promote the grain ripening to globular shape.展开更多
Inclusions in wrought superalloys significantly affect the stability of the alloy properties and limit their use and devel-opment in aeroengines and other applications.The types and sources of inclusions in wrought su...Inclusions in wrought superalloys significantly affect the stability of the alloy properties and limit their use and devel-opment in aeroengines and other applications.The types and sources of inclusions in wrought superalloys were reviewed with analysis of the conditions of inclusion formation from the viewpoints of thermodynamics and kinetics.The ther-modynamic data for inclusion formation in nickel-based and cobalt-based alloys were summarized and improved.The damage of inclusions to the fatigue and tensile properties and workability of these alloys and the mechanisms of crack initiation and propagation caused by inclusions were also discussed,and the effects of inclusions with different charac-teristics on crack propagation were reviewed.In addition,the control methods and mechanisms of inclusions in the triple smelting process(vacuum induction melting+protective electroslag remelting+vacuum arc remelting)were covered,providing a reference for improving the control technology of inclusions in wrought superalloys.Finally,the difficulties and development trends for inclusion control in wrought superalloys were discussed.展开更多
The Portevin-Le Chatelier(PLC)effect is a plastic instability in alloys at certain strain rates and deformation temperatures.This plastic instability exhibits serrated yielding in the temporal domain and strain locali...The Portevin-Le Chatelier(PLC)effect is a plastic instability in alloys at certain strain rates and deformation temperatures.This plastic instability exhibits serrated yielding in the temporal domain and strain localization in the spatial domain.Wrought Ni-based superalloys often exhibit the PLC effect.To guarantee the safe and stable operation of equipment,it is important to study the PLC effect in wrought Ni-based superalloys.This paper provides a review of various experimental phenomena and micromechanisms related to the PLC effect in wrought Ni-based superalloys,which have been reported in various publications in recent years and include work from our own group.The influences of stacking fault energy andγ’precipitates on the PLC effect in wrought Ni-based superalloys are also discussed in detail.Additionally,several suggestions for the future study of the PLC effect in wrought Ni-based superalloys are provided.展开更多
The recent advances in the microstructure modifications of wrought and cast TiAl alloys in CISRI were presented. The contributed results and discussions included the aspects and mechanisms of the refinement and homoge...The recent advances in the microstructure modifications of wrought and cast TiAl alloys in CISRI were presented. The contributed results and discussions included the aspects and mechanisms of the refinement and homogenization of the FL microstructure in wrought TiAl alloy and the microstructure adjustment of cast TiAl alloy. The mechanical properties of the modified microstructures of wrought and cast Ti 46.5 Al 2.5 V 1.0 Cr (mole fraction,%) alloys have been experimentally evaluated as well.展开更多
Microstructures and mechanical properties of （Mg-2.0%Ce-0.7%Zn-0.7%Zr） alloy were studied. The results of scanning electron microscopy show that Mg12Ce phase mainly distributes at the grain boundaries. The fine (Mg1...Microstructures and mechanical properties of （Mg-2.0%Ce-0.7%Zn-0.7%Zr） alloy were studied. The results of scanning electron microscopy show that Mg12Ce phase mainly distributes at the grain boundaries. The fine (Mg12Ce) phase can apparently elevate recrystallization temperature by preventing the grain boundary migration. No dynamic recrystallization occurs during the hot-extrusion. The mechanical properties of as extruded specimens are （σb=278.5 MPa,） δ=12.0%, while those of the specimens annealed at 250 ℃ for 100 h are σb=（272.6 MPa,） δ=（11.3%,） which indicate that the alloy has good mechanical properties at room temperature.展开更多
Microstructure evolution of wrought aluminum alloy extruded rods and the mechanism of liquid phase formation during reheating were investigated. And the relation between the volume fraction of liquid phase and the rec...Microstructure evolution of wrought aluminum alloy extruded rods and the mechanism of liquid phase formation during reheating were investigated. And the relation between the volume fraction of liquid phase and the recrystallization microstructure was proposed. The results show that increase in reheating temperature and time can augment the volume fraction of liquid phase and accelerate the grain spheroidization, as a result of which the requirement of semi-solid forming can be satisfied. Due to the higher aberration energy of grain boundary, the melting point is lowered as a result of the easy diffusion of atoms. At higher reheating temperature the grain boundary melts, the growth of the recrystallized grain is inhibited and the grain is refined. The composition of the low melt-point phase along the recrystallized grains was determined using EDS. It can be seen from the experimental results that when the extrusion rod of the wrought aluminum alloy is reheated at 610℃ for 20min, perfect fine equiaxial grains can be obtained, the average grain size is about 66.34μm and the volume fraction of solid phase is about 68%.展开更多
In the precipitation-hardened Ni-based superalloy,typified by ATI 718 Plus,the nano-scaleγandγphase in duplet or triple coprecipitate morphology can provide superior high-temperature strength.Thus,it is of great sen...In the precipitation-hardened Ni-based superalloy,typified by ATI 718 Plus,the nano-scaleγandγphase in duplet or triple coprecipitate morphology can provide superior high-temperature strength.Thus,it is of great sense to study the evolution ofγ’/γ’’coprecipitate during long term service at elevated temperature.In this study,the new-typeγ’/γ’’coprecipitates with a sandwich or compact configuration were found firstly in wrought ATI 718 Plus superalloy during long term thermal exposure at 705℃.These co-structure of theγ’/γ’’precipitates evidently inhibit the coarsening ofγ’phase.The increase of thermal exposure time evidently leads to the increase of the volume fraction ofγ’/γ’’coprecipitate and transformation of sandwich-typeγ’/γ’’coprecipitate to compact-typeγ’/γ’’coprecipitate,which is characterized asγphase precipitate at several faces of theγphase.The main evolution mechanism ofγ’/γ’’coprecipitates is element segregation,especially the composition variations of Al+Ti and Nb and their ratio of Al+Ti/Nb.In addition,the interfacial energy betweenγ’’phase andγmatrix also plays a key role on theγ’/γ’’coprecipitates evolution.The calculated results show that the longer thermal exposure time leads to the higher interfacial energy,which is beneficial for nucleation and precipitation ofγ’’phase on the faces ofγ’phase.展开更多
文摘GH4350(AEREX 350)is a Ni-based wrought superalloy for high-performance fasteners,with a maximum service temperature of 750℃.It has high tensile strength,fatigue resistance,stress rupture and relaxation resistance,corrosion resistance,low thermal expansion,and notch sensitivity.The high strength of GH4350 is largely derived through solid solution strengthening and the γ′phase precipitation strengthening.During the precipitation of γ′phase,a minor amount ofηphase also precipitates.However,it is reported that the microstructure of alloy is sensitive to heat treatment parameters,including temperature and time.The γ′phases can be transformed intoηphases under certain conditions,potentially degrading the performance of the alloy.The chemical composition characteristics,heat treatment strategies,and strengthening mechanism of GH4350 were reviewed in this research,aiming to understand the factors behind its remarkable high-temperature performance,to guide the development of new alloys,and to further enhance its heat resistance.
基金support from the National Science and Technology Major Project(No.J2019-VI-0006-0120)the National Key R&D Program of China(No.2019YFA0705300)+2 种基金the Youth Innovation Promotion Association,CAS(No.2023202)the Natural Science Foundation Project of Liaoning Province(No.2023-MS-024)the Innovation Program of Institute of Metal Research,Chinese Academy of Sciences(No.2023-PY08).
文摘The influence of V contents(0.6 wt%,0.8 wt%and 1.0 wt%)on the microstructure and creep behavior of a Nickel-based superalloy was investigated.The results revealed that the V content exerted a significant impact on the morphology of carbide.Notably,in the alloy containing 0.8 wt%V,coarse blocky M_(6)C carbides formed adjacent to MC carbides,while in the 1.0 wt%V alloy,fine granular M_(6)C carbides exhibited a nearly continuous distribution along grain boundaries(GBs).The influence of V content on creep properties exhibited significant variations depending on temperature.At 650℃/1010 MPa,the 1.0 wt%V alloy,containing a high density of granular M_(6)C carbides,demonstrated enhanced intergranular bonding strength,which contributed to prolonged creep life.In contrast,at higher temperatures(750℃/620 MPa and 800℃/500 MPa),GB mobility was activated,making GB slip the dominant creep mechanism.The near-continuous distribution of M_(6)C carbides in the 1.0 wt%V alloy restricted GB deformation compatibility,promoting stress localization and an increased density of micropores along GBs.As a result,the 0.8 wt%V alloy,with its discrete M_(6)C carbide distribution,exhibited superior creep resistance at elevated temperatures.
文摘Alloy selection and alloy design both require consideration of an array of material attributes, including in-service properties, weldability and fabricability. Critical properties of advanced wrought superalloys for gas turbine applications include high temperature strength, thermal stability, oxidation resistance and fatigue resistance. In this paper, the properties of twelve wrought solid-solution-strengthened and six age-hardenable superalloys are compared. Weldability is an important attribute and can be a major limiting factor in the use of certain alloys. Weldability test methods are discussed and the resistance of alloys to solidification cracking and strain-age cracking is compared. The use of weldability testing in the development of modern wrought su-peralloys is discussed with several examples cited. Finally, alloy selection for gas turbine components is outlined, taking into account both alloy properties and fabricability.
文摘Wrought magnesium alloys attract special interests as lightweight structural material due to their homogeneous microstructure and enhanced mechanical properties compared to as-cast alloys.In this contribution,recent research and developments on wrought magnesium alloys are reviewed from the viewpoint of the alloy design,focusing on Mg-Al,Mg-Zn and Mg-rare earth(RE)systems.The effects of different alloying elements on the microstructure and mechanical properties are described considering their strengthening mechanisms,e.g.grain refinement,precipitation and texture hardening effect.Finally,the new alloy design and also the future research of wrought magnesium alloys to improve their mechanical properties are discussed.
基金financially supported by the National Natural Science Foundation of China(Nos.51601192,51671188,51671189and 11332010)the High Technology Research and Development Program of China(No.2014AA041701)
文摘The Portevin-Le Chatelier(PLC) effects in a wrought Ni-base superalloy with different γ' precipitates contents have been investigated. Detailed analysis on the serration type of the tensile curves indicates that the γ' precipitates have a decisive influence on the transformation from normal to inverse PLC behavior, which is rarely proposed in other works. It is considered that the γ' precipitates play the same role in PLC effect as temperature and strain rate for the investigated wrought Ni-base superalloy.
基金Project(50725413)supported by the National Natural Science Foundation of ChinaProject(2007CB613704)supported by the National Basic Research Program of ChinaProject(2008DFR50040)supported by the International Cooperation Program of Ministry of Science and Technology of China
文摘Many researchers in China are actively engaged in the development of new types of wrought magnesium alloys with low cost or with high-performances and novel plastic processing technologies.The research activities are funded primarily through four government-supported programs:the Key Technologies R&D Program of China,the National Basic Research Program of China,the National High-tech R&D Program of China,and the National Natural Science Foundation of China.The key R&D activities for the development of new wrought magnesium alloys in China are reviewed,and typical properties of some new alloys are summarized. More attentions are paid to high-strength wrought magnesium alloys and high-plasticity wrought magnesium alloys.Some novel plastic processing technologies,emerging in recent years,which aim to control deformation texture and to improve plasticity and formability especially at room temperature,are also introduced.
基金Financial support from the projects by the NSFC [51771166]Chongqing Special Project of Science and Technology Innovation (cstc2020yszx-jcyj X0001)+5 种基金the Hebei Natural Science Foundation [E2019203452, E2021203011]the talent project of human resources and social security department of Hebei province [A202002002]the key project of department of education of Hebei province [ZD2021107]project of the central government guiding local science and technology development [216Z1001G]Cultivation Project for Basic Research and Innovation of Yanshan University [2021LGZD002]supported by the State Key Laboratory of Materials Processing and Die & Mould Technology, Huazhong University of Science and Technology [P2020-013]。
文摘In this paper, the relationship between anisotropic mechanical properties and the corresponding microstructure evolution of wrought magnesium alloys is critically reviewed. Experimental observations of the strong anisotropy(including the strength differential effect) induced by texture and twinning are discussed under different loading conditions(i.e., monotonic, cyclic and multiaxial loading). An accurate constitutive model is essential to describe the mechanical responses and to predict the forming performance considering engineering applications. Therefore, macroscale constitutive modeling of the anisotropy of magnesium alloys with directional distortional hardening are comprehensively reviewed with different approaches. To clarify the origin of the anisotropic behavior, physics-based mesoscale modeling of the anisotropy is also compared in detail.
基金financially supported by the National Natural Science Foundation of China(No.50964010)the Basic Scientific Research Fund for the Universities in Gansu Province(No.1201ZTC056)
文摘One important problem in casting wrought aluminum alloys is the high tendency to the formation of hot tears in the solidification process.By using semi-solid metal(SSM) processing,the hot tearing tendency of alloys can be minimized during casting.In the present research,the semi-solid slurry of wrought aluminum alloy 2024 was firstly prepared with a novel self-inoculation method(SIM),and then the microstructure characteristics of the semi-solid slurry and the rheo-diecastings cast with the semi-solid slurry were investigated.The results indicate that finer and more uniform globular primary α-Al particles can be obtained when the semi-solid slurry are isothermally held for a short period within the semi-solid temperature range,and the primary α-Al particles without entrapped liquid are uniformly fine,globular grains in the rheo-diecastings.The holding temperature and time affect the solid fraction,particle size,and shape factor.After the semi-solid slurry is held at 625 ℃ for 3 min and 5 min,the optimal values for the average equivalent diameter are 70.80 μm and 74.15 μm,and for the shape factor are 1.32 and 1.42,respectively.The solidification process of the rheo-diecastings is composed of the following two distinct stages:primary solidification process and secondary solidification process.The secondary solidification process consists further of the following three stages:(1) direct growth of secondary primary(α 2) phase from the surface of the primary α-Al phase particles without re-nucleation,(2) independent nucleation and growth of α 3 phase from the residual liquid,and(3) eutectic reaction at the end.
基金financially supported by the High Technology Research and Development Program of China (No. 2014AA041701)the National Natural Science Foundation of China (Nos. 51171179, 51271174, 51331005, and 11332010)
文摘Some existing wrought Ni-Cr-Co-based superalloys are being evaluated as the candidate materials for advanced ultra-supercritical power plant applications beyond 700 ℃ due to their high creep strength. But they are all prohibitively expensive due to the addition of Co, Mo and W. Here we developed a new Ni-Fe-Cr-based superalloy （named as HT700 alloy） with low cost and high strength. This paper reports the mechanical properties and fracture modes of HT700 alloy to support its high temperature applications and to understand prospective failure mechanism. Fracto- graphic examinations indicate that the fracture modes shift with test condition change. In addition, the HT700 alloy has relatively stable microstructure at 750 ℃. Compared with IN740 and GH2984 alloys, this new alloy has higher yield strength in the temperature range from room temperature to 800 ℃. The creep life of this new alloy is much longer than that of the Ni-Fe-based superaUoy GH2984. The results suggest that this new alloy is a promising material for advanced ultra-supercritical power plant applications beyond 700 ℃.
文摘Empirical improvements made in cast alloys have led to gamma alloys which are a viable materials technology, and to the development of various applications for gas turbine engines, as well as automotive engines. For wrougth alloys, over the last seven years the author et al have made extensive efforts to remove their deficiencies, and to achieve an improved balance of properties, across three interrelated task areas. The first effort was directed toward understanding fundamentals, such as phase relations, microstructure evolution, and microstructure property relationships. The second task was then directed to improve the balance of properties through designing refined lamellar microstructures and microalloying. The third effort was to explore the production methods to develop desired microstructures and to optimize the alloy compositions. This paper discusses the progress made from the last two efforts.
基金This project is financially supported by China Postdoctoral Science Foundation (No. 2003033090)
文摘Effects of hot plastic deformation on microstructures and tensile propertiesof AZ91 alloy were investigated. Compared with as-T4 microstructures, the as-extruded samples ofAZ91 alloy with fine grains exhibit better strength and ductility due to dynamic recrystallization.The succeeded rotation forging also provides finer grains while the strength increases, but theelongation decreases. Simultaneously, wrought AZ91 alloy shows more balance properties than as-T4condition ones. An interesting elongation of 228.5% is attained in the as-extruded AZ91 alloy inspite of the coarse grains with the size of 85 μm. The two-step method enhances the superplasticproperty of AZ91 alloy. The microstructure is still keeping the same scale of grains aftersuperplastic testing.
基金Project(51464031)supported by the National Natural Science Foundation of China
文摘The semisolid slurry of the 6061 wrought aluminum alloy was prepared by the self-inoculation method（SIM）. The effects of the isothermal holding parameters on microstructures of rheo-diecastings were investigated, and the solidification behavior of 6061 wrought aluminum alloy during the rheo-diecasting process was analyzed using OM, SEM, EDS and EBSD. The results indicate that the isothermal holding process during slurry preparation has great effect on primary α（Al） particles（α1）, but has little effect on the microstructure of secondary solidification in the process of thin-walled rheo-diecasting. Nucleation is expected to take place in the entire remaining liquid when the remaining liquid fills the die cavity, and the secondary solidification particles（α2） are formed after the process of stable growth, unstable growth and merging. The solute concentration of remaining liquid is higher than that of the original alloy due to the existence of α1 particles, hence the contents of Mg and Si in α2 particles are higher than those in α1 particles.
基金supported by National Key Research and Development Program of China (No. 2021 YFB3701000)the National Natural Science Foundation of China (Nos. U2167213 and 51971053)+1 种基金the Young Elite Scientists Sponsorship Program by China Association for Science and Technology (Nos. 2019-2021QNRC001, 20192021QNRC002, and 2019-2021QNRC003)and the Fundamental Research Funds for the Central Universities (No. N2202020)
文摘A novel low-cost Mg-Al-Ca-Zn-Mn-based alloy was developed to simultaneously improve its strength and ductility.The high yield strength of 411 MPa and the high elongation to failure of~8.9%have been achieved in the as-extruded Mg-1.3Al-1.2Ca-0.5Zn-0.6Mn(wt%)sample.Microstructure characterizations showed that the high strength is mainly associated with the ultra-fined dynamically recrystallized(DRXed)grains.Moreover,high-density dislocations in the un-DRXed region and nano-precipitates are distributed among theα-Mg matrix.The high ductility property can be ascribed to the high volume fraction of DRXed grains with a much randomized texture,as well as the formations of high-density subgrains in the un-DRXed grain regions.
基金Project(2007-83)supported by Science and Technology Development Projects of Weihai,Shandong Province。
文摘A new method was exploited using solution treatment and aging process as a pretreatment in preparing semi-solid slurry with fine microstructure before isothermal treatment of wrought aluminum alloy 7A09.Parameters of pretreatment were optimized by orthogonal experiment design and proper precursor was prepared.The evolution of microstructure of semi-solid slurry during isothermal treatment was analyzed and the mechanism of microstructure refining was discussed.The result of orthogonal experiment design shows that the optimum parameters are 462 ℃for solution temperature,40min for solution time,132 ℃for aging temperature and 14 h for aging time.Microstructure of isothermal treatment is fine,homogenous,with globular solid grains and a solid fraction between 50%and 70%,which is qualified for later semi-solid forming process.Mechanism of microstructure evolution includes the agglomeration ofα-phase and Ostwald ripening.Precipitations prepared by solution and aging treatment prevent the grains from coarsening and promote the grain ripening to globular shape.
基金supported by the National Natural Science Foundation of China[Grant Nos.52074030,51874103,and 51974020].
文摘Inclusions in wrought superalloys significantly affect the stability of the alloy properties and limit their use and devel-opment in aeroengines and other applications.The types and sources of inclusions in wrought superalloys were reviewed with analysis of the conditions of inclusion formation from the viewpoints of thermodynamics and kinetics.The ther-modynamic data for inclusion formation in nickel-based and cobalt-based alloys were summarized and improved.The damage of inclusions to the fatigue and tensile properties and workability of these alloys and the mechanisms of crack initiation and propagation caused by inclusions were also discussed,and the effects of inclusions with different charac-teristics on crack propagation were reviewed.In addition,the control methods and mechanisms of inclusions in the triple smelting process(vacuum induction melting+protective electroslag remelting+vacuum arc remelting)were covered,providing a reference for improving the control technology of inclusions in wrought superalloys.Finally,the difficulties and development trends for inclusion control in wrought superalloys were discussed.
基金financially supported by the National Natural Science Foundation of China(Nos.51671189 and 51271174)the Ministry of Science and Technology of China(Nos.2017YFA0700703 and 2019YFA0705304)。
文摘The Portevin-Le Chatelier(PLC)effect is a plastic instability in alloys at certain strain rates and deformation temperatures.This plastic instability exhibits serrated yielding in the temporal domain and strain localization in the spatial domain.Wrought Ni-based superalloys often exhibit the PLC effect.To guarantee the safe and stable operation of equipment,it is important to study the PLC effect in wrought Ni-based superalloys.This paper provides a review of various experimental phenomena and micromechanisms related to the PLC effect in wrought Ni-based superalloys,which have been reported in various publications in recent years and include work from our own group.The influences of stacking fault energy andγ’precipitates on the PLC effect in wrought Ni-based superalloys are also discussed in detail.Additionally,several suggestions for the future study of the PLC effect in wrought Ni-based superalloys are provided.
文摘The recent advances in the microstructure modifications of wrought and cast TiAl alloys in CISRI were presented. The contributed results and discussions included the aspects and mechanisms of the refinement and homogenization of the FL microstructure in wrought TiAl alloy and the microstructure adjustment of cast TiAl alloy. The mechanical properties of the modified microstructures of wrought and cast Ti 46.5 Al 2.5 V 1.0 Cr (mole fraction,%) alloys have been experimentally evaluated as well.
文摘Microstructures and mechanical properties of （Mg-2.0%Ce-0.7%Zn-0.7%Zr） alloy were studied. The results of scanning electron microscopy show that Mg12Ce phase mainly distributes at the grain boundaries. The fine (Mg12Ce) phase can apparently elevate recrystallization temperature by preventing the grain boundary migration. No dynamic recrystallization occurs during the hot-extrusion. The mechanical properties of as extruded specimens are （σb=278.5 MPa,） δ=12.0%, while those of the specimens annealed at 250 ℃ for 100 h are σb=（272.6 MPa,） δ=（11.3%,） which indicate that the alloy has good mechanical properties at room temperature.
文摘Microstructure evolution of wrought aluminum alloy extruded rods and the mechanism of liquid phase formation during reheating were investigated. And the relation between the volume fraction of liquid phase and the recrystallization microstructure was proposed. The results show that increase in reheating temperature and time can augment the volume fraction of liquid phase and accelerate the grain spheroidization, as a result of which the requirement of semi-solid forming can be satisfied. Due to the higher aberration energy of grain boundary, the melting point is lowered as a result of the easy diffusion of atoms. At higher reheating temperature the grain boundary melts, the growth of the recrystallized grain is inhibited and the grain is refined. The composition of the low melt-point phase along the recrystallized grains was determined using EDS. It can be seen from the experimental results that when the extrusion rod of the wrought aluminum alloy is reheated at 610℃ for 20min, perfect fine equiaxial grains can be obtained, the average grain size is about 66.34μm and the volume fraction of solid phase is about 68%.
基金the National Natural Science Foundation of China(Nos.52034004,51974201 and 52122409)for grant and financial support。
文摘In the precipitation-hardened Ni-based superalloy,typified by ATI 718 Plus,the nano-scaleγandγphase in duplet or triple coprecipitate morphology can provide superior high-temperature strength.Thus,it is of great sense to study the evolution ofγ’/γ’’coprecipitate during long term service at elevated temperature.In this study,the new-typeγ’/γ’’coprecipitates with a sandwich or compact configuration were found firstly in wrought ATI 718 Plus superalloy during long term thermal exposure at 705℃.These co-structure of theγ’/γ’’precipitates evidently inhibit the coarsening ofγ’phase.The increase of thermal exposure time evidently leads to the increase of the volume fraction ofγ’/γ’’coprecipitate and transformation of sandwich-typeγ’/γ’’coprecipitate to compact-typeγ’/γ’’coprecipitate,which is characterized asγphase precipitate at several faces of theγphase.The main evolution mechanism ofγ’/γ’’coprecipitates is element segregation,especially the composition variations of Al+Ti and Nb and their ratio of Al+Ti/Nb.In addition,the interfacial energy betweenγ’’phase andγmatrix also plays a key role on theγ’/γ’’coprecipitates evolution.The calculated results show that the longer thermal exposure time leads to the higher interfacial energy,which is beneficial for nucleation and precipitation ofγ’’phase on the faces ofγ’phase.
