Morphology and crystal structure of β precipitate phase in Mg-7Gd-5Y-1Nd-0.5Zr (mass fraction, %) alloy were characterized by optical microscopy, scanning electron microscopy and transmission electron microscopy. Com...Morphology and crystal structure of β precipitate phase in Mg-7Gd-5Y-1Nd-0.5Zr (mass fraction, %) alloy were characterized by optical microscopy, scanning electron microscopy and transmission electron microscopy. Compositions were determined for β phase using thin foil energy dispersive spectroscopy. Precipitation at 400 ℃ involves formation of platelet and block-shaped β phase. The orientation relationship is and between β precipitate phase and α-Mg matrix with habit planes parallel to , and a composition of Mg5(Y0.4Gd0.4Nd0.2) is suggested for the β phase in Mg-7Gd-5Y-1Nd-0.5Zr alloy.展开更多
As reported in our previous works, a Mg-7Gd-5Y-1Nd-0.5Zr alloy recently developed exhibited remarkable age-hardening responses and excellent mechanical properties at both room and elevated temperatures. In Mg-7Gd-5Y-1...As reported in our previous works, a Mg-7Gd-5Y-1Nd-0.5Zr alloy recently developed exhibited remarkable age-hardening responses and excellent mechanical properties at both room and elevated temperatures. In Mg-7Gd-5Y-1Nd-0.5Zr alloy, the β pre- cipitate phase was assumed to he one of the main strengthening phases in peak-aged samples. This study aimed to determine the crys- tal structure and orientation relationship of the β precipitate phase in Mg-7Gd-5Y-INd-0.5Zr alloy using transmission electron mi- croscopy and high-resolution electron microscopy. The results indicated that the β precipitate had a face-centered cubic structure with a lattice parameter of a=2.22 nm. The orientation relationship between the β precipitate phase and the ct-Mg matrix was （i-12）β（1-100）α, [110]β[0001 ]α. Theβ plates formed on prismatic planes could play an important role in alloy strengthening by proving effective barriers to gliding dislocations. A single β plate often contained several domains of （1 11）β twin-related variants. A composition of Mgs（Y0.4Gdo.4Nd0.2） was suggested for the β phase in Mg-7Gd-5Y-1Nd-0.5Zr alloy.展开更多
Precipitates in an 11% Cr ferritic/martensitic steel containing Nd with tempering and creep conditions were investigated using transmission electron microscope with energy-dispersive X-ray spectroscopy. The precipitat...Precipitates in an 11% Cr ferritic/martensitic steel containing Nd with tempering and creep conditions were investigated using transmission electron microscope with energy-dispersive X-ray spectroscopy. The precipitates in the steel with a tempering condition were identified to be Cr-rich M23C6 carbide, Nb-rich/V-rich/Ta–Nb-rich MX carbides, Nbrich MX carbonitride, and Fe-rich M5C2 carbide. Nd-rich carbonitride, which is not known to have been reported previously in steels, was also detected in the steel after tempering. Most of the Nb-rich MX precipitates were dissolved, whereas the amount of Ta-rich MX precipitates was increased significantly in the steel after a creep test at 600 °C at an applied stress of180 MPa for 1,100 h. No Fe2 W Laves phase has been detected in the steel after tempering.（Fe, Cr）2W Laves phase with a relatively large size was observed in the steel after the creep test.展开更多
1.Introduction.Ni-Mn-X(X=Ga,In,Sn,or Sb)Heusler alloys have versatile properties[1-4],such as shape memory effect[1],superelastic-ity[5],magnetocaloric effect[3],elastocaloric effect[6],and even multicaloric effect[7]...1.Introduction.Ni-Mn-X(X=Ga,In,Sn,or Sb)Heusler alloys have versatile properties[1-4],such as shape memory effect[1],superelastic-ity[5],magnetocaloric effect[3],elastocaloric effect[6],and even multicaloric effect[7],that indicate their potential for use in actu-ators,sensors,micropumps,energy harvesters,and solid-state re-frigeration[8-10].Among the alloys,Ni-Mn-Sn-based alloys are environment-friendly and cost-effective[6,7,11],and hence,they have received widespread attention.展开更多
To explain the precipitation mechanism ofχphase in Co-based superalloys,the microstructural evolution of Co−Ti−Mo superalloys subjected to aging was investigated by X-ray diffraction(XRD),scanning electron microscope...To explain the precipitation mechanism ofχphase in Co-based superalloys,the microstructural evolution of Co−Ti−Mo superalloys subjected to aging was investigated by X-ray diffraction(XRD),scanning electron microscope(SEM)and transmission electron microscope(TEM).The results show that the needle-likeχphase is mainly composed ofD0_(19)-Co_(3)(Ti,Mo),which is transformed from L1_(2-γ′)phase,and a specific orientation relationship exists between them.χphase is nucleated through the shearing ofγ′phase due to the influence of stacking fault.The crystal orientation relationship between L1_(2) andD0_(19)can be confirmed as{111}L1_(2)//{0001}_(D0_(19)),and<112>_(L1_(2))//<1100>_(D0_(19)).The growth ofD0_(19-χ)phase depends on the diffusions of Ti and Mo,and consumes a large number of elements.This progress leads to the appearance ofγ′precipitation depletion zone(PDZ)aroundD0_(19-χ)phase.The addition of Ni improves the stability of L1_(2-γ′)phase and the mechanical properties of Co-based superalloys.展开更多
The microstructure and phase precipitate behavior and their effects on the room temperature hardness and impact toughness of Inconel 740H aged at 750 ℃ for 10000 h were investigated by SEM, TEM and mechanical analys...The microstructure and phase precipitate behavior and their effects on the room temperature hardness and impact toughness of Inconel 740H aged at 750 ℃ for 10000 h were investigated by SEM, TEM and mechanical analysis. The as-received alloy shows a low hardness value of HB 168 and a highest toughness value of 96 J. After an aging treatment at 800 ℃ for 16 h and cooled in air （standard heat-treated condition）, fine γ′ phase particles precipitate within the grains and small carbide particles are located at the grain boundaries. The hardness increases to HB 304 and the impact toughness decreases to 15 J after standard heat treatment. A maximum hardness value of HB 331 is achieved for the alloy aged at 750 ℃ for 300 h. With increasing the aging time from 300 to 10000 h, a decrease of the hardness and toughness is observed along with an enhanced quantity of M23C6 particles and the coarsening of γ′ phase.展开更多
Through independently developed stress-loading equipment,stress corrosion tests on Mg-Gd-Y alloy were conducted in a 3.5 wt%NaCl solution.The effects of plastic compressive stress on the corrosion behavior of the allo...Through independently developed stress-loading equipment,stress corrosion tests on Mg-Gd-Y alloy were conducted in a 3.5 wt%NaCl solution.The effects of plastic compressive stress on the corrosion behavior of the alloy were thoroughly investigated using scanning electron microscopy(SEM)and transmission electron microscopy(TEM)among other microscopic analysis techniques.The results indicate that the alloy mainly consists of a-Mg grains,Mg24Y5 phase,Mg5Gd phase,and LPSO phase.The corrosion behavior of the Mg-Gd-Y alloy is significantly influenced by the microstructure of the interface between the precipitates and the matrix,the potential difference,and the stress state.In the unstressed state,the Mg24Y5 phase first induces corrosion at the edges of the a-Mg grain boundaries,which then spreads internally.Upon the application of plastic stress,the corrosion-inducing capability of the LPSO phase on a-Mg grains notably increases.This discovery provides new insights into the mechanisms by which plastic compressive stress affects the corrosion behavior of Mg-Gd-Y alloys and offers an important basis for the theoretical research and anti-corrosion design in the engineering applications of this alloy.展开更多
The excellent thermal stability of magnetic properties of Sm_(2)Co_(17)-based magnets is their most impor-tant feature.However,this stability is reduced when the maximum energy product of Sm_(2)Co_(17)-based magnets i...The excellent thermal stability of magnetic properties of Sm_(2)Co_(17)-based magnets is their most impor-tant feature.However,this stability is reduced when the maximum energy product of Sm_(2)Co_(17)-based magnets is improved,which is mainly determined by the Fe/Cu distribution of the 2:17R cell and 1:5H cell boundary phases.During the demagnetization process,the Cu-rich 1:5H cell boundary phase with a width of 2-15 nm obstructs the motion of the domain walls,yielding coercivity.Herein,we report a micron-scale Cu/Zr-rich and Fe-lean 1:5H-based precipitated phase with a lamellar structure,probably induced by Sm_(2)O_(3) doping.This structure enables the separate regulation of Fe and Cu distribution for Sm_(2)Co_(17)-based magnets with Fe-rich 2:17R cell phases and Cu-rich 1:5H cell boundary phases,consid-erably optimizing the thermal stability of magnetic properties.This discovery can be further developed to produce Sm_(2)Co_(17)-based magnets with high performance and excellent thermal stability of magnetic properties.展开更多
The phase diagram of superaustenitic stainless steel 654SMO was calculated by thermodynamic software and the precipitated phases in the specimens aged at 800-1100°C for 1hwere studied by methods of physicochemica...The phase diagram of superaustenitic stainless steel 654SMO was calculated by thermodynamic software and the precipitated phases in the specimens aged at 800-1100°C for 1hwere studied by methods of physicochemical phase analysis,scanning electron microscopy and transmission electron microscopy.The results showed that the size of precipitated particles increased with increasing the temperature.The amount of second phases reached the maximum value at 900°C,but decreased above 900°C.There were about eight kinds of precipitated phases in 654SMO includingσphase,Cr_2N,μphase,χphase,Laves phase,M_（23）C_6,M_6C and M_3C,in which theσphase and Cr_2N were the dominant precipitated phases.展开更多
Understanding the influence of purities on the electrochemical performance of pure aluminum(Al)in alkaline media for Al–air batteries is significant.Herein,we comprehensively investigate secondary phase precipitate(S...Understanding the influence of purities on the electrochemical performance of pure aluminum(Al)in alkaline media for Al–air batteries is significant.Herein,we comprehensively investigate secondary phase precipitate(SPP)-induced localized corrosion of pure Al in NaOH solution mainly based on quasi-in-situ and cross-section observations under scanning electron microscopy coupled with finite element simulation.The experimental results indicate that Al–Fe SPPs appear as clusters and are coherent with the Al substrate.In alkaline media,Al–Fe SPPs exhibit more positive potentials than the substrate,thus aggravating localized galvanic corrosion as cathodic phases.Moreover,finite element simulation indicates that the irregular geometry coupled with potential difference produces the non-uniform current density distribution inside the SPP cluster,and the current density on the Al substrate gradually decreases with distance.展开更多
Fe–Ga sheets with large magnetostriction are required for improving the conversion efficiency under the ultra-high frequencymagnetic field. Trace Tb element doping can simultaneously improve the magnetostriction and ...Fe–Ga sheets with large magnetostriction are required for improving the conversion efficiency under the ultra-high frequencymagnetic field. Trace Tb element doping can simultaneously improve the magnetostriction and ductility of Fe–Ga alloy. However, the im-pact of trace Tb doping on the microstructure and magnetostriction of Fe–Ga thin sheets is an open question. In this paper, the effects oftrace Tb addition on the secondary recrystallization and magnetostriction of Fe–Ga thin sheets are systematically studied by comparing thecharacteristics evolution of precipitation, texture, and nanoinclusions. The results indicate that trace Tb addition accelerates the secondaryrecrystallization of Goss texture due to the combined action of the bimodal size distributed precipitates, smaller grains, and more HEGBsin primary recrystallization. After quenching at 900℃, the magnetostriction value in 0.07 at %Tb-doped Fe_(81)Ga_(19) thin sheets increases by 30% to that of Fe_(81)Ga_(19) thin sheets. The increase in magnetostriction is attributed to the decrease in the number of Tb-rich precipitates andthe higher density of the nanometer-sized modified-D0_(3) inclusions induced by the dissolving of trace Tb elements after quenching. Theseresults demonstrate a simple and efficient approach for preparing Fe–Ga thin sheets with a large magnetostrictive coefficient by a combin-ation of trace RE element addition and conventional rolling method.展开更多
To enhance the high-temperature oxidation resistance and mechanical properties of a secondgeneration nickel-based superalloy,various concentrations of lanthanum(La)ranging from 5.0×10^(-5)wt.%to 3.4×10^(-4)w...To enhance the high-temperature oxidation resistance and mechanical properties of a secondgeneration nickel-based superalloy,various concentrations of lanthanum(La)ranging from 5.0×10^(-5)wt.%to 3.4×10^(-4)wt.%are added to the alloy.The microstructure of the nickel-based single crystal superalloy with trace of La was examined by means of SEM,EDS and TEM.Results show the addition of La decreases the segregation of elements and increases the amount ofγ/γ′eutectics of the as-cast alloy,and in the interdendritic region,the growth of eutectics is accompanied by the growth of strip clusters composed of Ni_(5)La and Ni_(3)Ta.As the La content in the alloy increases,the proportion of Ni_(5)La in the cluster increases.After heat treatment,incipient melting occurs in the cluster regions,leading to an increase in microporosity compared to the original as-cast samples.Furthermore,the heat treatment alters the shape of the clusters from a strip morphology to an elliptical one,and it changes their composition from Ni_(5)La and Ni_(3)Ta to a combination of Ni_(5)La,Ni_(3)Ta,and MC carbides.展开更多
Scanning electron microscopy and X-ray energy dispersive spectrum analysis show that the clusters of intermetallic AlFeSi particle are distributed on or near the aluminum foil stock surfaces heterogeneously. 3D finite...Scanning electron microscopy and X-ray energy dispersive spectrum analysis show that the clusters of intermetallic AlFeSi particle are distributed on or near the aluminum foil stock surfaces heterogeneously. 3D finite element modeling shows that these clusters of hard particles induce the fracture of the nano-scale lubricant oil film at first and further lead to severe deformation in the nearby aluminum foil substrate along the rolling direction. Consequently, the optical property in this region differs from that in the surroundings, resulting in surface defects.展开更多
The effects of different aging processes on the precipitated phase,mechanical properties,molten salt corrosion resistance and post-weld microstructure of 347H stainless steel were studied.The results show that a large...The effects of different aging processes on the precipitated phase,mechanical properties,molten salt corrosion resistance and post-weld microstructure of 347H stainless steel were studied.The results show that a large number of precipitated phases appear in the crystal after aging at 700℃for 400 h.After aging for 3000 h,the number of precipitated phases increases and most of them are gathered at the grain boundaries.There are two forms of precipitates,one is the coarse precipitate rich in Cr,and the other is the smaller precipitates mainly consisting of NbC.After aging at 700℃for 30 min,the yield strength and tensile strength of the samples at room temperature and 593℃increase,but the elongation decreases.The corrosion results in nitrate at 565℃show that the corrosion products of the aged samples are the same as that of the original samples,which are Fe_(2)O_(3),Fe_(3)O_(4),MgCr_(2)O_(4),MgFe_(2)O_(4),FeCr_(2)O_(4) and NaFeO_(2).The proportion of Fe_(3)O_(4) that is dense and well bonded to the subtrate in the original sample is higher than that in the aged sample,so the corrosion resistance is better.At 700℃,the aging time has no obvious effect on the microstructure after welding.展开更多
A ZM51 magnesium alloy joint with high intensity and thermal conductivity was fabricated using friction stir welding(FSW)followed by aging heat treatment(AG).During the FSW process,β_(1)'andβ_(2)'phases form...A ZM51 magnesium alloy joint with high intensity and thermal conductivity was fabricated using friction stir welding(FSW)followed by aging heat treatment(AG).During the FSW process,β_(1)'andβ_(2)'phases formed in the heat-affected zone(HAZ),yet new phases were absent in both the stirring zone(SZ)and thermal mechanical affected zone(TMAZ).After AG,numerousβ_(1)'andβ_(2)'phases emerged in the SZ and the TMAZ of the joint,while only theβ_(2)'phase precipitated in the HAZ.Due to precipitation strengthening,the average microhardness,yield strength and ultimate tensile strength of the joint reached up to 98%,94%and 88%those of the base metal(BM),respectively.Notably,basal slip{0001}<1120>,and twinning at 60°/<1010>and 86°/<1120>were more prevalent in TMAZ,contributing to the joint’s fracture.Furthermore,the precipitation ofβ_(1)'andβ_(2)'phases enhanced the joint’s thermal conductivity,averaging 121.7 W/(m·K),being 112%that of BM.展开更多
A method of pre-regulating the lamellar long-period stacking ordered(LPSO)phase was introduced to enhance the hot plasticity of rare earth magnesium alloys.Additionally,low-temperature extrusion was used to achieve a ...A method of pre-regulating the lamellar long-period stacking ordered(LPSO)phase was introduced to enhance the hot plasticity of rare earth magnesium alloys.Additionally,low-temperature extrusion was used to achieve a comprehensive improvement of alloy performance with small deformation,providing a new approach for the preparation of high-performance large components.The strengthening−toughening mechanism under low-temperature extrusion with an extrusion ratio of 3.6꞉1 was investigated by comparing the microstructure and performance of pre-regulated Mg−Gd−Y−Zn−Zr alloy at three different extrusion temperatures(420,450,and 480℃).Results show that the alloy extruded at 420℃exhibits a yield strength of 341 MPa,tensile strength of 419 MPa,and elongation of 7.2%.The increase in strength is mainly caused by the strong texture and internal dislocation pinning of the undynamic recrystallization(un-DRX)zone,and a lower volume fraction ofβdynamic precipitation phase is beneficial to improving the ductility of the alloy.展开更多
The effects of heat treatment on microstructure and creep properties of β high-strength titanium alloy,Ti-3.5Al-5Mo-6V-3Cr-2Sn-0.5Fe,were studied.After solution treatment at 790℃ and aging treatment(HT1),the microst...The effects of heat treatment on microstructure and creep properties of β high-strength titanium alloy,Ti-3.5Al-5Mo-6V-3Cr-2Sn-0.5Fe,were studied.After solution treatment at 790℃ and aging treatment(HT1),the microstructure is composed of equiaxedαp phase,β phase,α_(p) phase,and becomes β phase and α_(s) phases after solution treatment at 840℃ and aging treatment(HT2).The creep behavior at 400℃ was analyzed.The stress exponents of both alloys are between 1 and 2,indicating that the diffusional creep mechanism is one of the dominant creep mechanisms.The alloy after HT2 treatment has better creep resistance and a subsequent creep test on this alloy was performed at 450℃ under 400 MPa.The creep fracture has the mixed ductile-brittle characteristics.The phase interfaces can hinder the dislocation movement,and theαs phase can coordinate with the matrix to deform,thereby reducing the occurrence of intragranular cracks.展开更多
Ti−1Al−8V−5Fe(Ti-185)alloy with different iron contents was additively manufactured by electron beam powder bed fusion(EB-PBF),and its microstructure and mechanical properties were investigated.The results show that i...Ti−1Al−8V−5Fe(Ti-185)alloy with different iron contents was additively manufactured by electron beam powder bed fusion(EB-PBF),and its microstructure and mechanical properties were investigated.The results show that increasing the Fe powder content from 4.56 wt.%to 5.98 wt.%(within the specification range)converted coarse columnar prior-βgrains in as-printed alloy into fine equiaxed ones((54.2±32.4)μm)by EB-PBF.However,due to subsequent in-situ precipitation,a micron-thick low-solute weakα-phase became prevalent along each equiaxed grain boundary(GB).This drastically decreased the tensile deformation energy of Ti-185 from 6.2×10^(7)J/m^(3)(columnar grains)to 4.8×10^(7)J/m^(3)(equiaxed grains),despite a mild increase in strength.Fracture characteristics unveiled that the weak GBα-phase is the main crack initiation site and propagation path.展开更多
The phase precipitation behavior and tensile properties of an as-cast Ni-based alloy,IN617B alloy,after solution heat treatment and long-term aging treatment were investigated.Ti(C,N),M6C and M23C6 are the primary pre...The phase precipitation behavior and tensile properties of an as-cast Ni-based alloy,IN617B alloy,after solution heat treatment and long-term aging treatment were investigated.Ti(C,N),M6C and M23C6 are the primary precipitates in as-cast microstructure.After solution heat treatment,most of carbides dissolve into the matrix except a few fine Ti(C,N)within grains.During long-term aging at 700°C,the phase precipitation behaviors of the alloy are characterized as follows:(1)M23C6 carbides at grain boundaries(GBs)transform from film-like shape to cellular shape and gradually coarsen due to the decrease of the surface energy and element aggregation to GBs;(2)M23C6 carbides within grains have a bar-like morphology with a preferential growth direction[110]and have a cube-on-cube coherent orientation relationship with the matrixγ;(3)γ?particles inhibit the coarsening of M23C6 within grains by constraining the diffusion of formation elements.Furthermore,the tensile strength of the alloy obviously increases,but the ductility significantly decreases after the aging for 5000 h.The alloy has a relatively stable microstructure which guarantees the excellent tensile properties during long-term aging.展开更多
A high strength Mg-5.1Zn-3.2Y-0.4Zr-0.4Ca （wt%） alloy containing W phase （Mg3Y2Zn3） prepared by permanent mold direct-chill casting is indirectly extruded at 350 ℃ and 400 ℃, respectively. The extruded alloys sh...A high strength Mg-5.1Zn-3.2Y-0.4Zr-0.4Ca （wt%） alloy containing W phase （Mg3Y2Zn3） prepared by permanent mold direct-chill casting is indirectly extruded at 350 ℃ and 400 ℃, respectively. The extruded alloys show bimodal grain structure consisting of fine dynamic recrystallized （DRXed） grains and unre- crystallized coarse regions containing fine W phase and β2′ precipitates. The fragmented W phase particles induced by extrusion stimulate nucleation of DRXed grains, leading to the formation of fine DRXed grains, which are mainly distributed near the W particle bands along the extrusion direction. The alloy extruded at 350 ℃ exhibits yield strength of 373 MPa, ultimate tensile strength of 403 MPa and elongation to failure of 5.1%. While the alloy extruded at 400 ℃ shows lower yield strength of 332 MPa, ultimate tensile strength of 352 MPa and higher elongation to failure of 12%. The mechanical properties of the as-extruded alloys vary with the distribution and size of W phase. A higher fraction of DRXed grains is obtained due to the homogeneous distribution of micron-scale broken W phase particles in the alloy extruded at 400 ℃, which can lead to higher ductility. In addition, the nano-scale dynamic W phase precipitates distributed in the unDRXed regions are refined at lower extrusion temperature. The smaller size of nano-scale W phase precipitates leads to a higher fraction of unDRXed regions which contributes to higher strength of the alloy extruded at 350 ℃.展开更多
基金Project (2011DAE22B01) supported by the Key Technologies Program of China during the 12th Fire-Year Plan Period
文摘Morphology and crystal structure of β precipitate phase in Mg-7Gd-5Y-1Nd-0.5Zr (mass fraction, %) alloy were characterized by optical microscopy, scanning electron microscopy and transmission electron microscopy. Compositions were determined for β phase using thin foil energy dispersive spectroscopy. Precipitation at 400 ℃ involves formation of platelet and block-shaped β phase. The orientation relationship is and between β precipitate phase and α-Mg matrix with habit planes parallel to , and a composition of Mg5(Y0.4Gd0.4Nd0.2) is suggested for the β phase in Mg-7Gd-5Y-1Nd-0.5Zr alloy.
基金supported by the National "Twelfth Five-Year Plan" Key Technologies Program of China (2011DAE22B01)
文摘As reported in our previous works, a Mg-7Gd-5Y-1Nd-0.5Zr alloy recently developed exhibited remarkable age-hardening responses and excellent mechanical properties at both room and elevated temperatures. In Mg-7Gd-5Y-1Nd-0.5Zr alloy, the β pre- cipitate phase was assumed to he one of the main strengthening phases in peak-aged samples. This study aimed to determine the crys- tal structure and orientation relationship of the β precipitate phase in Mg-7Gd-5Y-INd-0.5Zr alloy using transmission electron mi- croscopy and high-resolution electron microscopy. The results indicated that the β precipitate had a face-centered cubic structure with a lattice parameter of a=2.22 nm. The orientation relationship between the β precipitate phase and the ct-Mg matrix was （i-12）β（1-100）α, [110]β[0001 ]α. Theβ plates formed on prismatic planes could play an important role in alloy strengthening by proving effective barriers to gliding dislocations. A single β plate often contained several domains of （1 11）β twin-related variants. A composition of Mgs（Y0.4Gdo.4Nd0.2） was suggested for the β phase in Mg-7Gd-5Y-1Nd-0.5Zr alloy.
基金financially supported by Key Program of National Natural Science Foundation of China (No. 51034011)ITER-National Magnetic Confinement Fusion Program (No.2011GB113001)National Science and Technology Major Project (No.2011ZX06004-009)
文摘Precipitates in an 11% Cr ferritic/martensitic steel containing Nd with tempering and creep conditions were investigated using transmission electron microscope with energy-dispersive X-ray spectroscopy. The precipitates in the steel with a tempering condition were identified to be Cr-rich M23C6 carbide, Nb-rich/V-rich/Ta–Nb-rich MX carbides, Nbrich MX carbonitride, and Fe-rich M5C2 carbide. Nd-rich carbonitride, which is not known to have been reported previously in steels, was also detected in the steel after tempering. Most of the Nb-rich MX precipitates were dissolved, whereas the amount of Ta-rich MX precipitates was increased significantly in the steel after a creep test at 600 °C at an applied stress of180 MPa for 1,100 h. No Fe2 W Laves phase has been detected in the steel after tempering.（Fe, Cr）2W Laves phase with a relatively large size was observed in the steel after the creep test.
基金supported by the National Key R&D Pro-gram of China(No.2022YFB3805701)National Natural Science Foundation of China(NSFC)(No.52371182,51701052,52192592,52192593)+1 种基金Young Elite Scientists Sponsorship Program by CAST(No.2019QNRC001)the Heilongjiang Touyan Innovation Team Program.
文摘1.Introduction.Ni-Mn-X(X=Ga,In,Sn,or Sb)Heusler alloys have versatile properties[1-4],such as shape memory effect[1],superelastic-ity[5],magnetocaloric effect[3],elastocaloric effect[6],and even multicaloric effect[7],that indicate their potential for use in actu-ators,sensors,micropumps,energy harvesters,and solid-state re-frigeration[8-10].Among the alloys,Ni-Mn-Sn-based alloys are environment-friendly and cost-effective[6,7,11],and hence,they have received widespread attention.
基金The financial supports from the National Natural Science Foundation of China(Nos.52171107,52201203)the National Natural Science Foundation of China-Joint Fund of Iron and Steel Research(No.U1960204)the“333”Talent Project of Hebei Province,China(No.B20221001)are gratefully acknowledged.
文摘To explain the precipitation mechanism ofχphase in Co-based superalloys,the microstructural evolution of Co−Ti−Mo superalloys subjected to aging was investigated by X-ray diffraction(XRD),scanning electron microscope(SEM)and transmission electron microscope(TEM).The results show that the needle-likeχphase is mainly composed ofD0_(19)-Co_(3)(Ti,Mo),which is transformed from L1_(2-γ′)phase,and a specific orientation relationship exists between them.χphase is nucleated through the shearing ofγ′phase due to the influence of stacking fault.The crystal orientation relationship between L1_(2) andD0_(19)can be confirmed as{111}L1_(2)//{0001}_(D0_(19)),and<112>_(L1_(2))//<1100>_(D0_(19)).The growth ofD0_(19-χ)phase depends on the diffusions of Ti and Mo,and consumes a large number of elements.This progress leads to the appearance ofγ′precipitation depletion zone(PDZ)aroundD0_(19-χ)phase.The addition of Ni improves the stability of L1_(2-γ′)phase and the mechanical properties of Co-based superalloys.
基金Project(TN-15-TYK05) supported by the Research and Development Fund of Thermal Power Research Institute(TPRI),ChinaProject(2012AA050501)supported by the National High-tech Research and Development Program of China
文摘The microstructure and phase precipitate behavior and their effects on the room temperature hardness and impact toughness of Inconel 740H aged at 750 ℃ for 10000 h were investigated by SEM, TEM and mechanical analysis. The as-received alloy shows a low hardness value of HB 168 and a highest toughness value of 96 J. After an aging treatment at 800 ℃ for 16 h and cooled in air （standard heat-treated condition）, fine γ′ phase particles precipitate within the grains and small carbide particles are located at the grain boundaries. The hardness increases to HB 304 and the impact toughness decreases to 15 J after standard heat treatment. A maximum hardness value of HB 331 is achieved for the alloy aged at 750 ℃ for 300 h. With increasing the aging time from 300 to 10000 h, a decrease of the hardness and toughness is observed along with an enhanced quantity of M23C6 particles and the coarsening of γ′ phase.
基金Project supported by the National Natural Science Foundation of China(52271066)Basic Research and Innovation Project for Vehicle Power+2 种基金Key Project of“Two-Chain Integration”in Shaanxi Province(2023-LL-QY-33-3)Xi'an Key Laboratory of Corrosion Protection and Functional Coating Technology for Military and Civil Light AlloyKey Project of Shaanxi Natural Science Foundation Research Program(2021JZ-54)。
文摘Through independently developed stress-loading equipment,stress corrosion tests on Mg-Gd-Y alloy were conducted in a 3.5 wt%NaCl solution.The effects of plastic compressive stress on the corrosion behavior of the alloy were thoroughly investigated using scanning electron microscopy(SEM)and transmission electron microscopy(TEM)among other microscopic analysis techniques.The results indicate that the alloy mainly consists of a-Mg grains,Mg24Y5 phase,Mg5Gd phase,and LPSO phase.The corrosion behavior of the Mg-Gd-Y alloy is significantly influenced by the microstructure of the interface between the precipitates and the matrix,the potential difference,and the stress state.In the unstressed state,the Mg24Y5 phase first induces corrosion at the edges of the a-Mg grain boundaries,which then spreads internally.Upon the application of plastic stress,the corrosion-inducing capability of the LPSO phase on a-Mg grains notably increases.This discovery provides new insights into the mechanisms by which plastic compressive stress affects the corrosion behavior of Mg-Gd-Y alloys and offers an important basis for the theoretical research and anti-corrosion design in the engineering applications of this alloy.
基金supported by the National Key R&D Program of China (No.2021YFB3501600)the Key R&D Program of Zhejiang Province (Nos.2021C01191 and 2021C01190).
文摘The excellent thermal stability of magnetic properties of Sm_(2)Co_(17)-based magnets is their most impor-tant feature.However,this stability is reduced when the maximum energy product of Sm_(2)Co_(17)-based magnets is improved,which is mainly determined by the Fe/Cu distribution of the 2:17R cell and 1:5H cell boundary phases.During the demagnetization process,the Cu-rich 1:5H cell boundary phase with a width of 2-15 nm obstructs the motion of the domain walls,yielding coercivity.Herein,we report a micron-scale Cu/Zr-rich and Fe-lean 1:5H-based precipitated phase with a lamellar structure,probably induced by Sm_(2)O_(3) doping.This structure enables the separate regulation of Fe and Cu distribution for Sm_(2)Co_(17)-based magnets with Fe-rich 2:17R cell phases and Cu-rich 1:5H cell boundary phases,consid-erably optimizing the thermal stability of magnetic properties.This discovery can be further developed to produce Sm_(2)Co_(17)-based magnets with high performance and excellent thermal stability of magnetic properties.
文摘The phase diagram of superaustenitic stainless steel 654SMO was calculated by thermodynamic software and the precipitated phases in the specimens aged at 800-1100°C for 1hwere studied by methods of physicochemical phase analysis,scanning electron microscopy and transmission electron microscopy.The results showed that the size of precipitated particles increased with increasing the temperature.The amount of second phases reached the maximum value at 900°C,but decreased above 900°C.There were about eight kinds of precipitated phases in 654SMO includingσphase,Cr_2N,μphase,χphase,Laves phase,M_（23）C_6,M_6C and M_3C,in which theσphase and Cr_2N were the dominant precipitated phases.
基金financially supported by the National Natural Science Foundation of China(No.51901018)the Young Elite Scientists Sponsorship Program by the China Association for Science and Technology(YESS,No.2019 QNRC001)+3 种基金the Fundamental Research Funds for the Central Universities,China(No.FRF-AT-20-07,06500119)the Natural Science Foundation of Beijing Municipality,China(No.2212037)the National Science and Technology Resources Investigation Program of China(No.2019FY 101400)the Southwest Institute of Technology and Engineering Cooperation Fund,China(No.HDHDW5902020107)。
文摘Understanding the influence of purities on the electrochemical performance of pure aluminum(Al)in alkaline media for Al–air batteries is significant.Herein,we comprehensively investigate secondary phase precipitate(SPP)-induced localized corrosion of pure Al in NaOH solution mainly based on quasi-in-situ and cross-section observations under scanning electron microscopy coupled with finite element simulation.The experimental results indicate that Al–Fe SPPs appear as clusters and are coherent with the Al substrate.In alkaline media,Al–Fe SPPs exhibit more positive potentials than the substrate,thus aggravating localized galvanic corrosion as cathodic phases.Moreover,finite element simulation indicates that the irregular geometry coupled with potential difference produces the non-uniform current density distribution inside the SPP cluster,and the current density on the Al substrate gradually decreases with distance.
基金financially supported by the National Natural Science Foundation of China (No. 52004164)the Funding Program of Science and Technology Department of Liaoning Province, China (No. 2023-MSLH-249)the Funding Program of Education Department of Liaoning P rovince, China (No. LMGD2023018)。
文摘Fe–Ga sheets with large magnetostriction are required for improving the conversion efficiency under the ultra-high frequencymagnetic field. Trace Tb element doping can simultaneously improve the magnetostriction and ductility of Fe–Ga alloy. However, the im-pact of trace Tb doping on the microstructure and magnetostriction of Fe–Ga thin sheets is an open question. In this paper, the effects oftrace Tb addition on the secondary recrystallization and magnetostriction of Fe–Ga thin sheets are systematically studied by comparing thecharacteristics evolution of precipitation, texture, and nanoinclusions. The results indicate that trace Tb addition accelerates the secondaryrecrystallization of Goss texture due to the combined action of the bimodal size distributed precipitates, smaller grains, and more HEGBsin primary recrystallization. After quenching at 900℃, the magnetostriction value in 0.07 at %Tb-doped Fe_(81)Ga_(19) thin sheets increases by 30% to that of Fe_(81)Ga_(19) thin sheets. The increase in magnetostriction is attributed to the decrease in the number of Tb-rich precipitates andthe higher density of the nanometer-sized modified-D0_(3) inclusions induced by the dissolving of trace Tb elements after quenching. Theseresults demonstrate a simple and efficient approach for preparing Fe–Ga thin sheets with a large magnetostrictive coefficient by a combin-ation of trace RE element addition and conventional rolling method.
基金funded by the National Science and Technology Major Project of China(Grant No.J2019-Ⅵ-0023-0139)。
文摘To enhance the high-temperature oxidation resistance and mechanical properties of a secondgeneration nickel-based superalloy,various concentrations of lanthanum(La)ranging from 5.0×10^(-5)wt.%to 3.4×10^(-4)wt.%are added to the alloy.The microstructure of the nickel-based single crystal superalloy with trace of La was examined by means of SEM,EDS and TEM.Results show the addition of La decreases the segregation of elements and increases the amount ofγ/γ′eutectics of the as-cast alloy,and in the interdendritic region,the growth of eutectics is accompanied by the growth of strip clusters composed of Ni_(5)La and Ni_(3)Ta.As the La content in the alloy increases,the proportion of Ni_(5)La in the cluster increases.After heat treatment,incipient melting occurs in the cluster regions,leading to an increase in microporosity compared to the original as-cast samples.Furthermore,the heat treatment alters the shape of the clusters from a strip morphology to an elliptical one,and it changes their composition from Ni_(5)La and Ni_(3)Ta to a combination of Ni_(5)La,Ni_(3)Ta,and MC carbides.
基金Project(51074117)supported by the National Natural Science Foundation of ChinaProject(2009CDA044)supported by the Foundation for Distinguished Young Scientists of Hubei Province,ChinaProjects(201104493,20100471161)supported by the China Postdoctoral Science Foundation
文摘Scanning electron microscopy and X-ray energy dispersive spectrum analysis show that the clusters of intermetallic AlFeSi particle are distributed on or near the aluminum foil stock surfaces heterogeneously. 3D finite element modeling shows that these clusters of hard particles induce the fracture of the nano-scale lubricant oil film at first and further lead to severe deformation in the nearby aluminum foil substrate along the rolling direction. Consequently, the optical property in this region differs from that in the surroundings, resulting in surface defects.
基金Science and Technology Program Project of Gansu Province(21ZD3GB001)。
文摘The effects of different aging processes on the precipitated phase,mechanical properties,molten salt corrosion resistance and post-weld microstructure of 347H stainless steel were studied.The results show that a large number of precipitated phases appear in the crystal after aging at 700℃for 400 h.After aging for 3000 h,the number of precipitated phases increases and most of them are gathered at the grain boundaries.There are two forms of precipitates,one is the coarse precipitate rich in Cr,and the other is the smaller precipitates mainly consisting of NbC.After aging at 700℃for 30 min,the yield strength and tensile strength of the samples at room temperature and 593℃increase,but the elongation decreases.The corrosion results in nitrate at 565℃show that the corrosion products of the aged samples are the same as that of the original samples,which are Fe_(2)O_(3),Fe_(3)O_(4),MgCr_(2)O_(4),MgFe_(2)O_(4),FeCr_(2)O_(4) and NaFeO_(2).The proportion of Fe_(3)O_(4) that is dense and well bonded to the subtrate in the original sample is higher than that in the aged sample,so the corrosion resistance is better.At 700℃,the aging time has no obvious effect on the microstructure after welding.
基金supported by the Key Research and Development Program of Shaanxi Province,China(No.2017ZDXM-GY-037)the National Natural Science Fund for Excellent Young Scholars,China(No.52222410)+3 种基金the National Natural Science Foundation of China(Key Program)(No.52034005)the National Natural Science Foundation of China(No.52227807)the National Key Research and Development Program of China(No.2021YFB3700902)the Shaanxi Province Qinchuangyuan“Scientist+Engineer”Team Program,China(No.2022KXJ-072).
文摘A ZM51 magnesium alloy joint with high intensity and thermal conductivity was fabricated using friction stir welding(FSW)followed by aging heat treatment(AG).During the FSW process,β_(1)'andβ_(2)'phases formed in the heat-affected zone(HAZ),yet new phases were absent in both the stirring zone(SZ)and thermal mechanical affected zone(TMAZ).After AG,numerousβ_(1)'andβ_(2)'phases emerged in the SZ and the TMAZ of the joint,while only theβ_(2)'phase precipitated in the HAZ.Due to precipitation strengthening,the average microhardness,yield strength and ultimate tensile strength of the joint reached up to 98%,94%and 88%those of the base metal(BM),respectively.Notably,basal slip{0001}<1120>,and twinning at 60°/<1010>and 86°/<1120>were more prevalent in TMAZ,contributing to the joint’s fracture.Furthermore,the precipitation ofβ_(1)'andβ_(2)'phases enhanced the joint’s thermal conductivity,averaging 121.7 W/(m·K),being 112%that of BM.
基金financial support by the Innovative Talents Support Program of Higher Education Institutions in Shanxi Province,China,and Project of Science and Technology by the North University of China in 2022(No.20221878).
文摘A method of pre-regulating the lamellar long-period stacking ordered(LPSO)phase was introduced to enhance the hot plasticity of rare earth magnesium alloys.Additionally,low-temperature extrusion was used to achieve a comprehensive improvement of alloy performance with small deformation,providing a new approach for the preparation of high-performance large components.The strengthening−toughening mechanism under low-temperature extrusion with an extrusion ratio of 3.6꞉1 was investigated by comparing the microstructure and performance of pre-regulated Mg−Gd−Y−Zn−Zr alloy at three different extrusion temperatures(420,450,and 480℃).Results show that the alloy extruded at 420℃exhibits a yield strength of 341 MPa,tensile strength of 419 MPa,and elongation of 7.2%.The increase in strength is mainly caused by the strong texture and internal dislocation pinning of the undynamic recrystallization(un-DRX)zone,and a lower volume fraction ofβdynamic precipitation phase is beneficial to improving the ductility of the alloy.
基金supported by the National Natural Science Foundation of China(No.51975147)。
文摘The effects of heat treatment on microstructure and creep properties of β high-strength titanium alloy,Ti-3.5Al-5Mo-6V-3Cr-2Sn-0.5Fe,were studied.After solution treatment at 790℃ and aging treatment(HT1),the microstructure is composed of equiaxedαp phase,β phase,α_(p) phase,and becomes β phase and α_(s) phases after solution treatment at 840℃ and aging treatment(HT2).The creep behavior at 400℃ was analyzed.The stress exponents of both alloys are between 1 and 2,indicating that the diffusional creep mechanism is one of the dominant creep mechanisms.The alloy after HT2 treatment has better creep resistance and a subsequent creep test on this alloy was performed at 450℃ under 400 MPa.The creep fracture has the mixed ductile-brittle characteristics.The phase interfaces can hinder the dislocation movement,and theαs phase can coordinate with the matrix to deform,thereby reducing the occurrence of intragranular cracks.
基金supported by the National Natural Science Foundation of China(No.51829401)the Australian Research Council(No.DP220103407).
文摘Ti−1Al−8V−5Fe(Ti-185)alloy with different iron contents was additively manufactured by electron beam powder bed fusion(EB-PBF),and its microstructure and mechanical properties were investigated.The results show that increasing the Fe powder content from 4.56 wt.%to 5.98 wt.%(within the specification range)converted coarse columnar prior-βgrains in as-printed alloy into fine equiaxed ones((54.2±32.4)μm)by EB-PBF.However,due to subsequent in-situ precipitation,a micron-thick low-solute weakα-phase became prevalent along each equiaxed grain boundary(GB).This drastically decreased the tensile deformation energy of Ti-185 from 6.2×10^(7)J/m^(3)(columnar grains)to 4.8×10^(7)J/m^(3)(equiaxed grains),despite a mild increase in strength.Fracture characteristics unveiled that the weak GBα-phase is the main crack initiation site and propagation path.
基金Project(51571191)supported by the National Natural Science Foundation of ChinaProject(NY 20150102)supported by the National Energy Administration Program of China
文摘The phase precipitation behavior and tensile properties of an as-cast Ni-based alloy,IN617B alloy,after solution heat treatment and long-term aging treatment were investigated.Ti(C,N),M6C and M23C6 are the primary precipitates in as-cast microstructure.After solution heat treatment,most of carbides dissolve into the matrix except a few fine Ti(C,N)within grains.During long-term aging at 700°C,the phase precipitation behaviors of the alloy are characterized as follows:(1)M23C6 carbides at grain boundaries(GBs)transform from film-like shape to cellular shape and gradually coarsen due to the decrease of the surface energy and element aggregation to GBs;(2)M23C6 carbides within grains have a bar-like morphology with a preferential growth direction[110]and have a cube-on-cube coherent orientation relationship with the matrixγ;(3)γ?particles inhibit the coarsening of M23C6 within grains by constraining the diffusion of formation elements.Furthermore,the tensile strength of the alloy obviously increases,but the ductility significantly decreases after the aging for 5000 h.The alloy has a relatively stable microstructure which guarantees the excellent tensile properties during long-term aging.
基金supported financially by the National Key Research and Development Program of China (No. 2016YFB0301102)the National Natural Science Foundation of China (No. 51571068)
文摘A high strength Mg-5.1Zn-3.2Y-0.4Zr-0.4Ca （wt%） alloy containing W phase （Mg3Y2Zn3） prepared by permanent mold direct-chill casting is indirectly extruded at 350 ℃ and 400 ℃, respectively. The extruded alloys show bimodal grain structure consisting of fine dynamic recrystallized （DRXed） grains and unre- crystallized coarse regions containing fine W phase and β2′ precipitates. The fragmented W phase particles induced by extrusion stimulate nucleation of DRXed grains, leading to the formation of fine DRXed grains, which are mainly distributed near the W particle bands along the extrusion direction. The alloy extruded at 350 ℃ exhibits yield strength of 373 MPa, ultimate tensile strength of 403 MPa and elongation to failure of 5.1%. While the alloy extruded at 400 ℃ shows lower yield strength of 332 MPa, ultimate tensile strength of 352 MPa and higher elongation to failure of 12%. The mechanical properties of the as-extruded alloys vary with the distribution and size of W phase. A higher fraction of DRXed grains is obtained due to the homogeneous distribution of micron-scale broken W phase particles in the alloy extruded at 400 ℃, which can lead to higher ductility. In addition, the nano-scale dynamic W phase precipitates distributed in the unDRXed regions are refined at lower extrusion temperature. The smaller size of nano-scale W phase precipitates leads to a higher fraction of unDRXed regions which contributes to higher strength of the alloy extruded at 350 ℃.
