Effects of different volume fraction of long-period stacking ordered(LPSO)phase on the microstructure,mechanical property and anisotropy of the as-extruded Mg-xZn-yY-0.1Mn(x=1 wt%,2 wt%,4 wt%and y=2 wt%,4 wt%,8 wt%)al...Effects of different volume fraction of long-period stacking ordered(LPSO)phase on the microstructure,mechanical property and anisotropy of the as-extruded Mg-xZn-yY-0.1Mn(x=1 wt%,2 wt%,4 wt%and y=2 wt%,4 wt%,8 wt%)alloys were studied by an optical microscope,a scanning electron microscope,texture analysis,a transmission electron microscope and tensile testing.The results reveal that the volume fraction of LPSO phase increases from ZW12 to ZW24 to ZW48 alloys with the elevating Zn and Y content but constant Y/Zn value,and the mechanical strength of the LPSO-containing Mg-Zn-Y-Mn system is gradually improved when increasing LPSO phases.With the highest volume fraction of LPSO phase,ZW48 alloy presents the highest ultimate tensile strength(UTS)of 427 MPa along the extrusion direction(ED)when compared with those of ZW12 alloy with the UTS of 307 MPa and ZW24 alloy with the UTS of 347 MPa.Moreover,the elongation ratio of ZW48 alloy is maintained to moderate 9.9%,which is also the highest among three studied alloys.On the other hand,texture analysis demonstrates that the basal texture of the a-Mg phase in the ZW48 alloy is significantly weakened by the generation of more LPSO phases.On the contrary,a high texture intensity of a-Mg phase and obvious mechanical anisotropy can be observed for the ZW12 alloy.However,mechanical anisotropy still exists in the ZW48 alloy containing massive LPSO phases,which is attributed primarily to the zonal distribution of large LPSO along the ED.展开更多
The LPSO phase can effectively enhance the mechanical properties of Mg alloys.To investigate the impact of different LPSO phase contents and morphologies on the mechanical properties and strengthening mechanisms of Mg...The LPSO phase can effectively enhance the mechanical properties of Mg alloys.To investigate the impact of different LPSO phase contents and morphologies on the mechanical properties and strengthening mechanisms of Mg-Y-Al alloys under room temperature deformation,this study prepared Mg-12Y-1Al(WA121)alloys containing Bulk-LPSO(B-LPSO),Lattice-LPSO(L-LPSO),and Needle-like LPSO(N-LPSO)with different contents through different heat-treatment processes.The results indicate that with the increase in heat treatment time,the contents of B-LPSO phases remain essentially unchanged,and the contents of L-LPSO and N-LPSO phases gradually increase.The increase in N-LPSO phase content is the most pronounced,with the highest content(7.29%)observed in the alloy treated for 4.5 h.Moreover,the alloy treated for 4.5 h exhibits the best mechanical properties,with ultimate tensile strength(UTS),tensile yield strength(TYS),and elongation(EL)values of 177 MPa,139 MPa,and 4.27%,respectively.Compared to the as-cast alloy,UTS,TYS,and EL increased by 9.94%,11.2%,and 27.1%,respectively.The study reveals that all three LPSO phases exhibit excellent dislocation hindering effects,effectively enhancing strength of the alloy.Additionally,the N-LPSO phase,due to its dense distribution,forms numerous dislocation channels within the grains,dispersing stress concentration within the grains to improve plasticity of the alloy.Furthermore,the interaction between the N-LPSO phase and the other phases in the alloy can also enhance plasticity of the alloy.Therefore,the alloy treated for 4.5 h demonstrates a synergistic improvement in strength and plasticity.Research has revealed that the precipitation mechanism of the N-LPSO phase in the as-cast WA121 alloy involves the formation of an Al-rich region adjacent to the needle-like Mg_(24)Y_(5) phase.Subsequently,the Y element provided by the dissolving Mg_(24)Y_(5) phase reacts with this region,ultimately leading to the formation of the needle-like LPSO phase.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 homogenized Mg−5.6Gd−0.8Zn(wt.%)alloys were treated with water cooling and furnace cooling to obtain specimens without and with the 14H long-period stacking ordered(LPSO)phase.Subsequently,multi-directional forgin...The homogenized Mg−5.6Gd−0.8Zn(wt.%)alloys were treated with water cooling and furnace cooling to obtain specimens without and with the 14H long-period stacking ordered(LPSO)phase.Subsequently,multi-directional forging(MDF)experiments were carried out.The microstructure and mechanical properties of different regions(the center,middle and edge regions)in the MDFed alloys were systematically investigated,and the effect of LPSO phase on them was discussed.The results show that the alloys in different regions undergo significant grain refinement during the MDF process.Inhomogeneous microstructures with different degrees of dynamic recrystallization(DRX)are formed,resulting in microhardness heterogeneity.The alloy with the LPSO phase has higher microstructure homogeneity,a higher degree of recrystallization,and better comprehensive mechanical properties than the alloy without the LPSO phase.The furnace-cooled alloy after 18 passes of MDF has the best comprehensive mechanical properties,with an ultimate compressive strength of 488 MPa,yield strength of 258 MPa,and fracture strain of 21.2%.DRX behavior is closely related to the LPSO phase and deformation temperature.The kinked LPSO phase can act as a potential nucleation site for DRX grains,while the fragmented LPSO phase promotes DRX nucleation through the particle-stimulated nucleation mechanism.展开更多
It is extremely difficult to introduce high-density nano twins during the solidification process of TiAl alloy.In this study,high-density nanotwins are inducted in the as-cast Ti48Al2Cr alloyed by adding Re element.Ph...It is extremely difficult to introduce high-density nano twins during the solidification process of TiAl alloy.In this study,high-density nanotwins are inducted in the as-cast Ti48Al2Cr alloyed by adding Re element.Phase transformation,morphology characteristics of nano twins,compressive and tensile proper-ties,and the related mechanisms have been studied.Results show that B2 phase enriched with Re tends to precipitate along theα_(2)/γinterface within lamellar colony.The stacking fault energy(SFE)ofγphase decreases from 43 mJ/m^(2) to 16 mJ/m^(2) as Re content increases from 0 at.%to 0.6 at.%,decreasing the crit-ical shear stress for twin formation.Compared to the mismatch value ofα_(2)/γinterface(0.004),which of B2/α_(2) and B2/γinterfaces increase to 0.247 and 0.149,respectively.Driven by high interfacial stress,high-density dislocations are generated at the B2/α_(2) interface,providing the dislocation slip channel for the formation of stacking faults(SFs)and nanotwins at the B2/γinterface.Therefore,the mechanism of inducting high-density nanotwins is to reduce the stacking fault energy ofγphase by Re and form highly mismatched B2/α_(2) interface.Compressive strength and the strain increase from 1723 MPa to 2398 MPa and 29%to 39%as Re content increases from 0 at.%to 0.6 at.%,respectively.Tensile strength increases from 356 MPa to 452 MPa without sacrificing plasticity.The improvement in strength and plasticity are attributed to the nano-twinning strengthening and interfacial thermal mismatch strengthening.Forming nanotwins during solidification process serve as the nucleation sites for newly formed twins during de-formation process,increasing the deformation tolerance of TiAl alloy.展开更多
The lower Yarlung Tsangpo River basin of the Qinghai-Tibet Plateau frequently experiences geo-hazardous occurrences such as landslides,ice/rock avalanches and debris flows,causing loss of human lives and damage to inf...The lower Yarlung Tsangpo River basin of the Qinghai-Tibet Plateau frequently experiences geo-hazardous occurrences such as landslides,ice/rock avalanches and debris flows,causing loss of human lives and damage to infrastructure.However,a comprehensive inventory map of geohazards is lacking for this region,due to the extreme challenges of the geomorphological and environmental conditions(i.e.,steep terrain,dense vegetation cover,and the presence of ice and snow).To this end,we propose a novel approach for mapping active geohazards in complex mountainous regions through InSAR phase gradient measurements based on a deep learning algorithm,which is then applied to the lower Yarlung Tsangpo River basin for the first time,in order to prepare an inventory map of active geohazards using ascending and descending Sentinel-1 SAR images acquired between March 2017 and July 2023.First,the InSAR phase gradient stacking method was introduced to estimate ground deformation,which offers significant advantages in minimizing the influence of InSAR decorrelation and effectively suppressing topographic residuals and atmospheric delays.InSAR phase gradient rates effectively retrieve patterns of localized ground deformation associated with geohazard activity.Then,a DeepLabv3 deep learning model was established and trained with phase gradient rate maps of manually labeled geohazards,in order to achieve the automatic identification of active geohazards.Our results show that there are 277 active geohazards within the lower Yarlung Tsangpo River basin,encompassing an area of~25600 km^(2).The DeepLabv3 model achieved good precision,recall rate and F1 scores at 92,86 and 90%,respectively.The distribution of detected geohazards is closely correlated with the topographic factors,faults and river system.Compared to the results derived from Small Baseline Subset InSAR(SBAS-InSAR)and optical images,the proposed approach can obtain high density pixels of InSAR measurement in low-coherence scenarios,thus enabling high-accuracy mapping of active geohazards in complex mountainous areas.展开更多
Suitable heat treatment processes were adopted to regulate the precipitation of the lamellar LPSO phase andβ′phase in Mg−Gd−Y−Zn−Zr−Nd alloy.The effects of lamellar LPSO phase andβ′phase on the mechanical properti...Suitable heat treatment processes were adopted to regulate the precipitation of the lamellar LPSO phase andβ′phase in Mg−Gd−Y−Zn−Zr−Nd alloy.The effects of lamellar LPSO phase andβ′phase on the mechanical properties and damping capacity of the alloy were studied systematically.Experimental results demonstrate that the lamellar LPSO phase is more conducive to dynamic recrystallization processes,leading to a high degree of recrystallization and a weak texture intensity,resulting in a higher plasticity and damping capacity.After aging treatment,theβ′precipitates exhibit pronounced aging strengthening and increase the number of mobile interfaces,thus enhancing the strength and damping capacity at the same time.Through regulating lamellar LPSO and agedβ′phase,the alloy achieves high strength and high damping capacity:ultimate tensile strength of 498 MPa,yield strength of 371 MPa and damping capacity of 0.02 at strain amplitude of 1×10^(−3).展开更多
The mechanical properties of two main precipitating phases(LPSO and MgRE)and matrix in Mg-Gd-Y-Nd-Zn bioalloy were examined using nanoindentation method.A new is suggested for characterizing the elastic-plastic behavi...The mechanical properties of two main precipitating phases(LPSO and MgRE)and matrix in Mg-Gd-Y-Nd-Zn bioalloy were examined using nanoindentation method.A new is suggested for characterizing the elastic-plastic behavior,fracture toughness and strain rate sensitivity(SRS)of materials within micro/nanoscale.Firstly,a nanomechanical model was developed for extracting hardness(H),young’s modulus(E)and yield stress(σY)from the characteristic load points which were subsequently analyzed by atomic force microscope(AFM)images.The elasticity data and AFM data were then utilized for determination of plastic deformation in constituent phases.The displacement of the indentation gets the highest value for Mg matrix and between precipitates,depth is more in LPSO rather than that of MgRE.The serrated flow or the behavior of shear bands may originate from the side effect of the interface region in Mg alloys with precipitates.It can be deduced that the KIC produced by both L method and energy-based calculation are both reliable for KIC approximation.The maximum load in simulation withμ=0.2 friction is marginally lesser than that of the frictionless(μ=0)one while elastic recovery of indentation withμ=0.2 is higher to some extent.展开更多
As-extruded Mg-Er-Ni alloys with different volume fractions of long-period stacking ordered(LPSO)phase and density of lamellar γ' phase were prepared,and the microstructure,mechanical,and degradation properties w...As-extruded Mg-Er-Ni alloys with different volume fractions of long-period stacking ordered(LPSO)phase and density of lamellar γ' phase were prepared,and the microstructure,mechanical,and degradation properties were investigated.Coupling the bulk LPSO phase and the lamellar γ' phase,and controlling the dynamic recrystallization processes during deformation by adjusting the volume fraction of LPSO and the density of the γ' phase,a synergistic increase in strength and degradation rate can be achieved.On the one hand,the increase in corrosion rate was related to the increased volume fraction of the bulk LPSO phase and the densities of the lamellar γ' phase,which provide more galvanic corrosion.Moreover,high densities of the lamellar γ' phase can provide more corrosion interface by inhibiting the recrystallization process to refine dynamic recrystallized(DRXed)grains during the hot extrusion.On the other hand,the ultimate tensile strength(UTS)and tensile yield strength(TYS)of the Mg-Er-Ni alloy increased from 345 and 265 MPa to 514 MPa and 358 MPa,respectively,which was mainly attributed to grain boundary and texture strengthening,bulk LPSO phase and lamellar γ' phase strengthening.Overall,Mg^(-1)4Er-4Ni alloy,which contains the highest volume fraction bulk LPSO phase and the densities of lamellar γ' phase,re-alized a synergistic enhancement of strength and degradation rate.The UTS,TYS,and degradation rate of Mg^(-1)4Er-4Ni were 514 MPa,358 MPa,and 142.5 mg cm^(-2)h^(-1)(3 wt%KCl solution at 93◦C),respectively.This research provides new insight into developing Mg alloys with high strength and degradation rates for fracturing tool materials in the application of oil and gas exploitation in harsh environments.展开更多
The deformation behavior of the as-extruded Mg-Y-Ni alloys with different volume fraction of long period stacking ordered(LPSO)phase during tension and compression was investigated by in-situ synchrotron diffraction.T...The deformation behavior of the as-extruded Mg-Y-Ni alloys with different volume fraction of long period stacking ordered(LPSO)phase during tension and compression was investigated by in-situ synchrotron diffraction.The micro-yielding,macro-yielding,tension-compression asymmetry and strain hardening behavior of the alloys were explored by combining with deformation mechanisms.The micro-yielding is dominated by basal slip of dynamic recrystallized(DRXed)grains in tension,while it is dominated by extension twinning of non-dynamic recrystallized(non-DRXed)grains in compression.At macro-yielding,the non-DRXed grains are still elastic deformed in tension and the basal slip of DRXed grains in compression are activated.Meanwhile,the LPSO phase still retains elastic deformation,but can bear more load,so the higher the volume fraction of hard LPSO phase,the higher the tensile/compressive macro-yield strength of the alloys.Benefiting from the low volume fraction of the non-DRXed grains and the delay effect of LPSO andγphases on extension twinning,the as-extruded alloys exhibit excellent tension-compression symmetry.When the volume fraction of LPSO phase reaches∼50%,tension-compression asymmetry is reversed,which is due to the fact that the LPSO phase is stronger in compression than in tension.The tensile strain hardening behavior is dominated by dislocation slip,while the dominate mechanism for compressive strain hardening changes from twinning in theα-Mg grains to kinking of the LPSO phase with increasing volume fraction of LPSO phase.The activation of kinking leads to the constant compressive strain hardening rate of∼2500 MPa,which is significantly higher than the tensile strain hardening rate.展开更多
This work studied the microstructure,mechanical properties and damping properties of Mg_(95.34)Ni_(2)Y_(2.66) and Mg_(95.34)Zn_(1)Ni_(1)Y_(2.66)alloys systematically.The difference in the evolution of the long-period ...This work studied the microstructure,mechanical properties and damping properties of Mg_(95.34)Ni_(2)Y_(2.66) and Mg_(95.34)Zn_(1)Ni_(1)Y_(2.66)alloys systematically.The difference in the evolution of the long-period stacked ordered(LPSO)phase in the two alloys during heat treatment was the focus.The morphology of the as-cast Mg_(95.34)Ni_(2)Y_(2.66)presented a disordered network.After heat treatment at 773 K for 2 hours,the eutectic phase was integrated into the matrix,and the LPSO phase maintained the 18R structure.As Zn partially replaced Ni,the crystal grains became rounded in the cast alloy,and lamellar LPSO phases and more solid solution atoms were contained in the matrix after heat treatment of the Mg_(95.34)Zn_(1)Ni_(1)Y_(2.66)alloy.Both Zn and the heat treatment had a significant effect on damping.Obvious dislocation internal friction peaks and grain boundary internal friction peaks were found after temperature-dependent damping of the Mg_(95.34)Ni_(2)Y_(2.66)and Mg_(95.34)Zn_(1)Ni_(1)Y_(2.66)alloys.After heat treatment,the dislocation peak was significantly increased,especially in the alloy Mg_(95.34)Ni_(2)Y_(2).66.The annealed Mg_(95.34)Ni_(2)Y_(2.66)alloy with a rod-shaped LPSO phase exhibited a good damping performance of 0.14 atε=10^(−3),which was due to the difference between the second phase and solid solution atom content.These factors also affected the dynamic modulus of the alloy.The results of this study will help in further development of high-damping magnesium alloys.展开更多
A large-scale fine-grained Mg-Gd-Y-Zn-Zr alloy plate with high strength and ductility was successfully prepared by multi-pass friction stir processing(MFSP)technology in this work.The structure of grains and long peri...A large-scale fine-grained Mg-Gd-Y-Zn-Zr alloy plate with high strength and ductility was successfully prepared by multi-pass friction stir processing(MFSP)technology in this work.The structure of grains and long period stacking ordered(LPSO)phase were characterized,and the mechanical properties uniformity was investigated.Moreover,a quantitative relationship between the microstructure and tensile yield strength was established.The results showed that the grains in the processed zone(PZ)and interfacial zone(IZ)were refined from 50μm to 3μm and 4μm,respectively,and numerous original LPSO phases were broken.In IZ,some block-shaped 18R LPSO phases were transformed into needle-like 14H LPSO phases due to stacking faults and the short-range diffusion of solute atoms.The severe shear deformation in the form of kinetic energy caused profuse stacking fault to be generated and move rapidly,greatly increasing the transformation rate of LPSO phase.After MFSP,the ultimate tensile strength,yield strength and elongation to failure of the large-scale plate were 367 MPa,305 MPa and 18.0% respectively.Grain refinement and LPSO phase strengthening were the major strengthening mechanisms for the MFSP sample.In particularly,the strength of IZ was comparable to that of PZ because the strength contribution of the 14H LPSO phase offsets the lack of grain refinement strengthening in IZ.This result opposes the widely accepted notion that IZ is a weak region in MFSP-prepared large-scale fine-grained plate.展开更多
Although extensive research has been conducted on the strengthening mechanism of rare-earth magnesium alloys,achieving a balance between strength and toughness has proven challenging.This paper introduces a method for...Although extensive research has been conducted on the strengthening mechanism of rare-earth magnesium alloys,achieving a balance between strength and toughness has proven challenging.This paper introduces a method for regulating the overlapping structure of the lamellar long-period stacking ordered(LPSO)phase andβ′phase to achieve a balance between strength and toughness in the alloy.By focusing on the extruded VW93A alloy cabin component,the study delves into the mechanism of the alloy's strength and toughness through a comparative analysis of the microstructure characteristics and room-temperature mechanical properties of the alloys in various states.Additionally,the molecular dynamics simulation is employed to clarify the mechanism of the alloy's strength and toughness balance induced by the overlapping structure.The findings reveal that when theβ′phase precipitates in the alloy alone,a significant increase in strength is achieved by pinning dislocations,albeit at the expense of reduced plasticity.Conversely,the presence of the lamellar LPSO phase disperses dislocations between the LPSO phase lamellae,thereby enhancing plasticity by avoiding stress concentration resulting from dislocation stacking.When both phases coexist in the alloy and form an overlapping structure,the dispersion of dislocations due to the lamellar LPSO phase weakens the pinning effect of theβ′phase,further reducing dislocation stacking and resulting in a balance of strength and toughness in the alloy.Ultimately,the alloy with the overlapping structure exhibits an ultimate tensile strength and elongation of 421 MPa and 20.1%,respectively.展开更多
In this study,the high-temperature stability and the generation mechanism of the Portevin-Le Chatelier(PLC)effect in solid-solution Mg-1Al-12Y alloy with different heat treatment processes were investigated by adjusti...In this study,the high-temperature stability and the generation mechanism of the Portevin-Le Chatelier(PLC)effect in solid-solution Mg-1Al-12Y alloy with different heat treatment processes were investigated by adjusting the content of long-period stacking ordered(LPSO)phases.It was found that the content of LPSO phases in the alloys differed the most after heat treatment at 530℃for 16 h and 24 h,with values of 13.56%and 3.93%respectively.Subsequently,high-temperature tensile experiments were conducted on these two alloys at temperatures of 150℃,200℃,250℃,and 300℃.The results showed that both alloys exhibited the PLC effect at temperatures ranging from 150 to 250℃.However,at a temperature 300℃,only the alloy with a greater concentration of LPSO phases exhibited the PLC effect,whereas the alloy with a lower proportion of LPSO phases did not exhibit this phenomenon.Additionally,both alloys exhibited remarkable high-temperature stability,with the alloy containing a greater percentage of LPSO phases also demonstrating superior strength.The underlying mechanism for this phenomenon lies in the exceptional high-temperature stability exhibited by the second phase within the alloy.Furthermore,the LPSO phase effectively obstructs the movement of dislocations,and it also undergoing kinking to facilitate plastic deformation of the alloy.The results indicate that the PLC effect can be suppressed by reducing dislocation pile-up at grain boundaries,which leads to a decrease in alloy plasticity but an increase in strength.The presence of the PLC effect in the WA121 alloy is attributed to the abundant dispersed second phase within the alloy,which initially hinders the movement of dislocations,leading to an increase in stress,and subsequently releases the dislocations,allowing them to continue their movement and thereby reducing in stress.展开更多
The solidification methods of electromagnetic stirring(EMS)and non-electromagnetic stirring were employed to prepare Mg–6Gd–3Y–xZn–0.6Zr(x=1,1.5,2,3)alloys.The evolution of alloy microstructures and the changes in...The solidification methods of electromagnetic stirring(EMS)and non-electromagnetic stirring were employed to prepare Mg–6Gd–3Y–xZn–0.6Zr(x=1,1.5,2,3)alloys.The evolution of alloy microstructures and the changes in properties were analyzed for different Zn contents.It has been observed that in alloys without electromagnetic stirring,as the Zn content increases,the alloy structure gradually refines.The primary second phase transitions from Mg5RE phase to long-period stacking ordered(LPSO)phase,resulting in improved hardness and elongation.In alloys subjected to electromagnetic stirring,there is a relatively higher content of the second phase,primarily consisting of LPSO phase.After applying electromagnetic stirring,the quantity and the type of LPSO phase in the alloy change.The alloy structure becomes more uniform with electromagnetic stirring,resulting in increased hardness and reduced hardness gradients within the grains.The mechanical properties of alloys with electromagnetic stirring are superior to those without electromagnetic stirring.展开更多
We have systematically investigated the microstructures of as-cast Mg_(97.49)Ho_(1.99)Cu_(0.43)Zr_(0.09)alloy by atomic resolution high-angle annular dark field scanning transmission electron microscopy(HAADF-STEM), r...We have systematically investigated the microstructures of as-cast Mg_(97.49)Ho_(1.99)Cu_(0.43)Zr_(0.09)alloy by atomic resolution high-angle annular dark field scanning transmission electron microscopy(HAADF-STEM), revealing the coexistence of 18R, 14H and 24R long period stacking/order(LPSO) phases with fully coherent interfaces along step-like composition gradient in a blocky intermetallic compound distributed at grain boundary. The short-range order(SRO) L1_(2)-type Cu_(6)Ho_(8)clusters embedded across AB’C’A-stacking fault layers are directly revealed at atomic scale. Importantly, the order degree of SRO clusters in the present dilute alloy is significant lower than previous 6M and 7M in-plane order reported in ternary Mg-TM(transition metal)-RE(rare earth) alloys, which can be well matched by 9M in-plane order. This directly demonstrates that SRO in-plane L1_(2)-type clusters can be expanded into more dilute composition regions bounded along the definite TM/RE ratio of 3/4. In addition, the estimated chemical compositions of solute enriched stacking fault(SESF) in all LPSO variants are almost identical with the ideal SESF composition of 9M in-plane order, regardless of the type of LPSO phases. The results further support the viewpoint that robust L1_(2)-type TM_(6)RE_(8)clusters play an important role in governing LPSO phase formation.展开更多
In this study,we investigated the oxidation of the Mg-11Y-1Al alloy at 500℃in an Ar-20%O2environment.Multiscale analysis showed the network-like long-period stacking ordered(LPSO)phase transformed into needle-like LP...In this study,we investigated the oxidation of the Mg-11Y-1Al alloy at 500℃in an Ar-20%O2environment.Multiscale analysis showed the network-like long-period stacking ordered(LPSO)phase transformed into needle-like LPSO and polygonal Mg24Y5 phases,leading to the formation of a high-dense network of needle-like oxides at the oxidation front.These oxides grew laterally along the oxide/matrix interfaces,forming a thicker,continuous scale that effectively blocked elemental diffusion.Hence,the preferential oxidation along the needle-like LPSO is believed to accelerate the formation of a thicker and continuous oxide scale,further improving the oxidation resistance of the Mg-11Y-1Al alloy.展开更多
基金Project supported by Guangdong Basic and Applied Basic Research Foundation(2024A1515030065,2023A1515012299)Guangzhou Science and Technology Planning Project(2024A04J6299,202201011454)+2 种基金Young Talent Support Project of Guangzhou Association for Science and Technology(QT2024-012)the National Natural Science Foundation of China(52101283)National College Students Innovation and Entrepreneurship Training Program(xj2023118450625)。
文摘Effects of different volume fraction of long-period stacking ordered(LPSO)phase on the microstructure,mechanical property and anisotropy of the as-extruded Mg-xZn-yY-0.1Mn(x=1 wt%,2 wt%,4 wt%and y=2 wt%,4 wt%,8 wt%)alloys were studied by an optical microscope,a scanning electron microscope,texture analysis,a transmission electron microscope and tensile testing.The results reveal that the volume fraction of LPSO phase increases from ZW12 to ZW24 to ZW48 alloys with the elevating Zn and Y content but constant Y/Zn value,and the mechanical strength of the LPSO-containing Mg-Zn-Y-Mn system is gradually improved when increasing LPSO phases.With the highest volume fraction of LPSO phase,ZW48 alloy presents the highest ultimate tensile strength(UTS)of 427 MPa along the extrusion direction(ED)when compared with those of ZW12 alloy with the UTS of 307 MPa and ZW24 alloy with the UTS of 347 MPa.Moreover,the elongation ratio of ZW48 alloy is maintained to moderate 9.9%,which is also the highest among three studied alloys.On the other hand,texture analysis demonstrates that the basal texture of the a-Mg phase in the ZW48 alloy is significantly weakened by the generation of more LPSO phases.On the contrary,a high texture intensity of a-Mg phase and obvious mechanical anisotropy can be observed for the ZW12 alloy.However,mechanical anisotropy still exists in the ZW48 alloy containing massive LPSO phases,which is attributed primarily to the zonal distribution of large LPSO along the ED.
基金supported by the Qinghai Provincial Science and Technology Department Basic Research Program(No.2025ZY029).
文摘The LPSO phase can effectively enhance the mechanical properties of Mg alloys.To investigate the impact of different LPSO phase contents and morphologies on the mechanical properties and strengthening mechanisms of Mg-Y-Al alloys under room temperature deformation,this study prepared Mg-12Y-1Al(WA121)alloys containing Bulk-LPSO(B-LPSO),Lattice-LPSO(L-LPSO),and Needle-like LPSO(N-LPSO)with different contents through different heat-treatment processes.The results indicate that with the increase in heat treatment time,the contents of B-LPSO phases remain essentially unchanged,and the contents of L-LPSO and N-LPSO phases gradually increase.The increase in N-LPSO phase content is the most pronounced,with the highest content(7.29%)observed in the alloy treated for 4.5 h.Moreover,the alloy treated for 4.5 h exhibits the best mechanical properties,with ultimate tensile strength(UTS),tensile yield strength(TYS),and elongation(EL)values of 177 MPa,139 MPa,and 4.27%,respectively.Compared to the as-cast alloy,UTS,TYS,and EL increased by 9.94%,11.2%,and 27.1%,respectively.The study reveals that all three LPSO phases exhibit excellent dislocation hindering effects,effectively enhancing strength of the alloy.Additionally,the N-LPSO phase,due to its dense distribution,forms numerous dislocation channels within the grains,dispersing stress concentration within the grains to improve plasticity of the alloy.Furthermore,the interaction between the N-LPSO phase and the other phases in the alloy can also enhance plasticity of the alloy.Therefore,the alloy treated for 4.5 h demonstrates a synergistic improvement in strength and plasticity.Research has revealed that the precipitation mechanism of the N-LPSO phase in the as-cast WA121 alloy involves the formation of an Al-rich region adjacent to the needle-like Mg_(24)Y_(5) phase.Subsequently,the Y element provided by the dissolving Mg_(24)Y_(5) phase reacts with this region,ultimately leading to the formation of the needle-like LPSO phase.
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the financial supports from the Key Research and Development Program of Hunan Province,China(No.2023GK2020)。
文摘The homogenized Mg−5.6Gd−0.8Zn(wt.%)alloys were treated with water cooling and furnace cooling to obtain specimens without and with the 14H long-period stacking ordered(LPSO)phase.Subsequently,multi-directional forging(MDF)experiments were carried out.The microstructure and mechanical properties of different regions(the center,middle and edge regions)in the MDFed alloys were systematically investigated,and the effect of LPSO phase on them was discussed.The results show that the alloys in different regions undergo significant grain refinement during the MDF process.Inhomogeneous microstructures with different degrees of dynamic recrystallization(DRX)are formed,resulting in microhardness heterogeneity.The alloy with the LPSO phase has higher microstructure homogeneity,a higher degree of recrystallization,and better comprehensive mechanical properties than the alloy without the LPSO phase.The furnace-cooled alloy after 18 passes of MDF has the best comprehensive mechanical properties,with an ultimate compressive strength of 488 MPa,yield strength of 258 MPa,and fracture strain of 21.2%.DRX behavior is closely related to the LPSO phase and deformation temperature.The kinked LPSO phase can act as a potential nucleation site for DRX grains,while the fragmented LPSO phase promotes DRX nucleation through the particle-stimulated nucleation mechanism.
基金supported by the National Natural Science Foundation of China(No.U21A2042)the National Nature Fund Youth Fund Project of China(No.52101038)Young Elite Scientists Sponsorship Program by CAST(No.2021QNRC001).
文摘It is extremely difficult to introduce high-density nano twins during the solidification process of TiAl alloy.In this study,high-density nanotwins are inducted in the as-cast Ti48Al2Cr alloyed by adding Re element.Phase transformation,morphology characteristics of nano twins,compressive and tensile proper-ties,and the related mechanisms have been studied.Results show that B2 phase enriched with Re tends to precipitate along theα_(2)/γinterface within lamellar colony.The stacking fault energy(SFE)ofγphase decreases from 43 mJ/m^(2) to 16 mJ/m^(2) as Re content increases from 0 at.%to 0.6 at.%,decreasing the crit-ical shear stress for twin formation.Compared to the mismatch value ofα_(2)/γinterface(0.004),which of B2/α_(2) and B2/γinterfaces increase to 0.247 and 0.149,respectively.Driven by high interfacial stress,high-density dislocations are generated at the B2/α_(2) interface,providing the dislocation slip channel for the formation of stacking faults(SFs)and nanotwins at the B2/γinterface.Therefore,the mechanism of inducting high-density nanotwins is to reduce the stacking fault energy ofγphase by Re and form highly mismatched B2/α_(2) interface.Compressive strength and the strain increase from 1723 MPa to 2398 MPa and 29%to 39%as Re content increases from 0 at.%to 0.6 at.%,respectively.Tensile strength increases from 356 MPa to 452 MPa without sacrificing plasticity.The improvement in strength and plasticity are attributed to the nano-twinning strengthening and interfacial thermal mismatch strengthening.Forming nanotwins during solidification process serve as the nucleation sites for newly formed twins during de-formation process,increasing the deformation tolerance of TiAl alloy.
基金financially supported by the Joint Funds of the National Natural Science Foundation of China(Grant No.U2244226)the National Key R&D Program of China(No.2022YFC3004302)+7 种基金Chinese Geological Survey Project(No.DD20230538)the Science Foundation of Gansu Province(No.23JRRA830)the Science and Technology Major Project of Gansu Province(No.23ZDFA007)the Foundation for Innovation Groups of Basic Research in Gansu Province(24JRRA169)Power China Project(No.CD2C20230228)the Lanzhou Youth Science and Technology Talent Innovation Project(No.2024-QN-170)supported by the ESA-MOST China DRAGON-5(Grant No.59339)DRAGON-6 project(Grant No.95355).
文摘The lower Yarlung Tsangpo River basin of the Qinghai-Tibet Plateau frequently experiences geo-hazardous occurrences such as landslides,ice/rock avalanches and debris flows,causing loss of human lives and damage to infrastructure.However,a comprehensive inventory map of geohazards is lacking for this region,due to the extreme challenges of the geomorphological and environmental conditions(i.e.,steep terrain,dense vegetation cover,and the presence of ice and snow).To this end,we propose a novel approach for mapping active geohazards in complex mountainous regions through InSAR phase gradient measurements based on a deep learning algorithm,which is then applied to the lower Yarlung Tsangpo River basin for the first time,in order to prepare an inventory map of active geohazards using ascending and descending Sentinel-1 SAR images acquired between March 2017 and July 2023.First,the InSAR phase gradient stacking method was introduced to estimate ground deformation,which offers significant advantages in minimizing the influence of InSAR decorrelation and effectively suppressing topographic residuals and atmospheric delays.InSAR phase gradient rates effectively retrieve patterns of localized ground deformation associated with geohazard activity.Then,a DeepLabv3 deep learning model was established and trained with phase gradient rate maps of manually labeled geohazards,in order to achieve the automatic identification of active geohazards.Our results show that there are 277 active geohazards within the lower Yarlung Tsangpo River basin,encompassing an area of~25600 km^(2).The DeepLabv3 model achieved good precision,recall rate and F1 scores at 92,86 and 90%,respectively.The distribution of detected geohazards is closely correlated with the topographic factors,faults and river system.Compared to the results derived from Small Baseline Subset InSAR(SBAS-InSAR)and optical images,the proposed approach can obtain high density pixels of InSAR measurement in low-coherence scenarios,thus enabling high-accuracy mapping of active geohazards in complex mountainous areas.
基金financially supported by the National Key Research and Development Program of China(No.2021YFB3701100)the National Natural Science Foundation of China(Nos.U20A20234,51874062)+1 种基金the Postdoctoral Science Foundation of China(Nos.2023M730390,2022M710563)the Natural Science Foundation Commission,China(Nos.CSTB2023NSCQ-BHX0164,CSTB2022NSCQ-BHX0029)。
文摘Suitable heat treatment processes were adopted to regulate the precipitation of the lamellar LPSO phase andβ′phase in Mg−Gd−Y−Zn−Zr−Nd alloy.The effects of lamellar LPSO phase andβ′phase on the mechanical properties and damping capacity of the alloy were studied systematically.Experimental results demonstrate that the lamellar LPSO phase is more conducive to dynamic recrystallization processes,leading to a high degree of recrystallization and a weak texture intensity,resulting in a higher plasticity and damping capacity.After aging treatment,theβ′precipitates exhibit pronounced aging strengthening and increase the number of mobile interfaces,thus enhancing the strength and damping capacity at the same time.Through regulating lamellar LPSO and agedβ′phase,the alloy achieves high strength and high damping capacity:ultimate tensile strength of 498 MPa,yield strength of 371 MPa and damping capacity of 0.02 at strain amplitude of 1×10^(−3).
文摘The mechanical properties of two main precipitating phases(LPSO and MgRE)and matrix in Mg-Gd-Y-Nd-Zn bioalloy were examined using nanoindentation method.A new is suggested for characterizing the elastic-plastic behavior,fracture toughness and strain rate sensitivity(SRS)of materials within micro/nanoscale.Firstly,a nanomechanical model was developed for extracting hardness(H),young’s modulus(E)and yield stress(σY)from the characteristic load points which were subsequently analyzed by atomic force microscope(AFM)images.The elasticity data and AFM data were then utilized for determination of plastic deformation in constituent phases.The displacement of the indentation gets the highest value for Mg matrix and between precipitates,depth is more in LPSO rather than that of MgRE.The serrated flow or the behavior of shear bands may originate from the side effect of the interface region in Mg alloys with precipitates.It can be deduced that the KIC produced by both L method and energy-based calculation are both reliable for KIC approximation.The maximum load in simulation withμ=0.2 friction is marginally lesser than that of the frictionless(μ=0)one while elastic recovery of indentation withμ=0.2 is higher to some extent.
基金support from the National Key Research and Development Program of China(No.2021YFB3701100)the Natural Science Foundation Commission of China(Grant Nos.U20A20234 and 51874062)+1 种基金the Fundamental Re-search Funds for Central Universities(No.2022CDJKYJH004C)the Science and Technology Major Project of Shanxi Province(No.20191102008).
文摘As-extruded Mg-Er-Ni alloys with different volume fractions of long-period stacking ordered(LPSO)phase and density of lamellar γ' phase were prepared,and the microstructure,mechanical,and degradation properties were investigated.Coupling the bulk LPSO phase and the lamellar γ' phase,and controlling the dynamic recrystallization processes during deformation by adjusting the volume fraction of LPSO and the density of the γ' phase,a synergistic increase in strength and degradation rate can be achieved.On the one hand,the increase in corrosion rate was related to the increased volume fraction of the bulk LPSO phase and the densities of the lamellar γ' phase,which provide more galvanic corrosion.Moreover,high densities of the lamellar γ' phase can provide more corrosion interface by inhibiting the recrystallization process to refine dynamic recrystallized(DRXed)grains during the hot extrusion.On the other hand,the ultimate tensile strength(UTS)and tensile yield strength(TYS)of the Mg-Er-Ni alloy increased from 345 and 265 MPa to 514 MPa and 358 MPa,respectively,which was mainly attributed to grain boundary and texture strengthening,bulk LPSO phase and lamellar γ' phase strengthening.Overall,Mg^(-1)4Er-4Ni alloy,which contains the highest volume fraction bulk LPSO phase and the densities of lamellar γ' phase,re-alized a synergistic enhancement of strength and degradation rate.The UTS,TYS,and degradation rate of Mg^(-1)4Er-4Ni were 514 MPa,358 MPa,and 142.5 mg cm^(-2)h^(-1)(3 wt%KCl solution at 93◦C),respectively.This research provides new insight into developing Mg alloys with high strength and degradation rates for fracturing tool materials in the application of oil and gas exploitation in harsh environments.
基金supported by National Natural Science Foundation of China(no.U21A2047,no.51971076 and no.52001069).
文摘The deformation behavior of the as-extruded Mg-Y-Ni alloys with different volume fraction of long period stacking ordered(LPSO)phase during tension and compression was investigated by in-situ synchrotron diffraction.The micro-yielding,macro-yielding,tension-compression asymmetry and strain hardening behavior of the alloys were explored by combining with deformation mechanisms.The micro-yielding is dominated by basal slip of dynamic recrystallized(DRXed)grains in tension,while it is dominated by extension twinning of non-dynamic recrystallized(non-DRXed)grains in compression.At macro-yielding,the non-DRXed grains are still elastic deformed in tension and the basal slip of DRXed grains in compression are activated.Meanwhile,the LPSO phase still retains elastic deformation,but can bear more load,so the higher the volume fraction of hard LPSO phase,the higher the tensile/compressive macro-yield strength of the alloys.Benefiting from the low volume fraction of the non-DRXed grains and the delay effect of LPSO andγphases on extension twinning,the as-extruded alloys exhibit excellent tension-compression symmetry.When the volume fraction of LPSO phase reaches∼50%,tension-compression asymmetry is reversed,which is due to the fact that the LPSO phase is stronger in compression than in tension.The tensile strain hardening behavior is dominated by dislocation slip,while the dominate mechanism for compressive strain hardening changes from twinning in theα-Mg grains to kinking of the LPSO phase with increasing volume fraction of LPSO phase.The activation of kinking leads to the constant compressive strain hardening rate of∼2500 MPa,which is significantly higher than the tensile strain hardening rate.
基金funded by the National Natural Science Foundation of China(Nos.51801189)The Central Guidance on Local Science and Technology Development Fund of Shanxi Province(Nos.YDZJTSX2021A027)+2 种基金The National Natural Science Foundation of China(Nos.51801189)The Science and Technology Major Project of Shanxi Province(No.20191102008,20191102007)The North University of China Youth Academic Leader Project(No.11045505).
文摘This work studied the microstructure,mechanical properties and damping properties of Mg_(95.34)Ni_(2)Y_(2.66) and Mg_(95.34)Zn_(1)Ni_(1)Y_(2.66)alloys systematically.The difference in the evolution of the long-period stacked ordered(LPSO)phase in the two alloys during heat treatment was the focus.The morphology of the as-cast Mg_(95.34)Ni_(2)Y_(2.66)presented a disordered network.After heat treatment at 773 K for 2 hours,the eutectic phase was integrated into the matrix,and the LPSO phase maintained the 18R structure.As Zn partially replaced Ni,the crystal grains became rounded in the cast alloy,and lamellar LPSO phases and more solid solution atoms were contained in the matrix after heat treatment of the Mg_(95.34)Zn_(1)Ni_(1)Y_(2.66)alloy.Both Zn and the heat treatment had a significant effect on damping.Obvious dislocation internal friction peaks and grain boundary internal friction peaks were found after temperature-dependent damping of the Mg_(95.34)Ni_(2)Y_(2.66)and Mg_(95.34)Zn_(1)Ni_(1)Y_(2.66)alloys.After heat treatment,the dislocation peak was significantly increased,especially in the alloy Mg_(95.34)Ni_(2)Y_(2).66.The annealed Mg_(95.34)Ni_(2)Y_(2.66)alloy with a rod-shaped LPSO phase exhibited a good damping performance of 0.14 atε=10^(−3),which was due to the difference between the second phase and solid solution atom content.These factors also affected the dynamic modulus of the alloy.The results of this study will help in further development of high-damping magnesium alloys.
基金supported by the National Key Research and Development Program of China(2021YFB3501002)State Key Program of National Natural Science Foundation of China(5203405)+3 种基金National Natural Science Foundation of China(51974220,52104383)National Key Research and Development Program of China(2021YFB3700902)Key Research and Development Program of Shaanxi Province(2020ZDLGY13-06,2017ZDXM-GY-037)Shaanxi Province National Science Fund for Distinguished Young Scholars(2022JC-24)。
文摘A large-scale fine-grained Mg-Gd-Y-Zn-Zr alloy plate with high strength and ductility was successfully prepared by multi-pass friction stir processing(MFSP)technology in this work.The structure of grains and long period stacking ordered(LPSO)phase were characterized,and the mechanical properties uniformity was investigated.Moreover,a quantitative relationship between the microstructure and tensile yield strength was established.The results showed that the grains in the processed zone(PZ)and interfacial zone(IZ)were refined from 50μm to 3μm and 4μm,respectively,and numerous original LPSO phases were broken.In IZ,some block-shaped 18R LPSO phases were transformed into needle-like 14H LPSO phases due to stacking faults and the short-range diffusion of solute atoms.The severe shear deformation in the form of kinetic energy caused profuse stacking fault to be generated and move rapidly,greatly increasing the transformation rate of LPSO phase.After MFSP,the ultimate tensile strength,yield strength and elongation to failure of the large-scale plate were 367 MPa,305 MPa and 18.0% respectively.Grain refinement and LPSO phase strengthening were the major strengthening mechanisms for the MFSP sample.In particularly,the strength of IZ was comparable to that of PZ because the strength contribution of the 14H LPSO phase offsets the lack of grain refinement strengthening in IZ.This result opposes the widely accepted notion that IZ is a weak region in MFSP-prepared large-scale fine-grained plate.
基金financially supported by the Special Project of Science and Technology Cooperation and Exchange of Shanxi Province(No.202104041101033)the special fund for Science and Technology Innovation Teams of Shanxi Province.
文摘Although extensive research has been conducted on the strengthening mechanism of rare-earth magnesium alloys,achieving a balance between strength and toughness has proven challenging.This paper introduces a method for regulating the overlapping structure of the lamellar long-period stacking ordered(LPSO)phase andβ′phase to achieve a balance between strength and toughness in the alloy.By focusing on the extruded VW93A alloy cabin component,the study delves into the mechanism of the alloy's strength and toughness through a comparative analysis of the microstructure characteristics and room-temperature mechanical properties of the alloys in various states.Additionally,the molecular dynamics simulation is employed to clarify the mechanism of the alloy's strength and toughness balance induced by the overlapping structure.The findings reveal that when theβ′phase precipitates in the alloy alone,a significant increase in strength is achieved by pinning dislocations,albeit at the expense of reduced plasticity.Conversely,the presence of the lamellar LPSO phase disperses dislocations between the LPSO phase lamellae,thereby enhancing plasticity by avoiding stress concentration resulting from dislocation stacking.When both phases coexist in the alloy and form an overlapping structure,the dispersion of dislocations due to the lamellar LPSO phase weakens the pinning effect of theβ′phase,further reducing dislocation stacking and resulting in a balance of strength and toughness in the alloy.Ultimately,the alloy with the overlapping structure exhibits an ultimate tensile strength and elongation of 421 MPa and 20.1%,respectively.
基金supported by the Qinghai Provincial Science and Technology Department Basic Research Program(No.2023-ZJ-913M).
文摘In this study,the high-temperature stability and the generation mechanism of the Portevin-Le Chatelier(PLC)effect in solid-solution Mg-1Al-12Y alloy with different heat treatment processes were investigated by adjusting the content of long-period stacking ordered(LPSO)phases.It was found that the content of LPSO phases in the alloys differed the most after heat treatment at 530℃for 16 h and 24 h,with values of 13.56%and 3.93%respectively.Subsequently,high-temperature tensile experiments were conducted on these two alloys at temperatures of 150℃,200℃,250℃,and 300℃.The results showed that both alloys exhibited the PLC effect at temperatures ranging from 150 to 250℃.However,at a temperature 300℃,only the alloy with a greater concentration of LPSO phases exhibited the PLC effect,whereas the alloy with a lower proportion of LPSO phases did not exhibit this phenomenon.Additionally,both alloys exhibited remarkable high-temperature stability,with the alloy containing a greater percentage of LPSO phases also demonstrating superior strength.The underlying mechanism for this phenomenon lies in the exceptional high-temperature stability exhibited by the second phase within the alloy.Furthermore,the LPSO phase effectively obstructs the movement of dislocations,and it also undergoing kinking to facilitate plastic deformation of the alloy.The results indicate that the PLC effect can be suppressed by reducing dislocation pile-up at grain boundaries,which leads to a decrease in alloy plasticity but an increase in strength.The presence of the PLC effect in the WA121 alloy is attributed to the abundant dispersed second phase within the alloy,which initially hinders the movement of dislocations,leading to an increase in stress,and subsequently releases the dislocations,allowing them to continue their movement and thereby reducing in stress.
基金supported by Postgraduate Research&Practice Innovation Program of Jiangsu Province(Project No.KYCX22_3792)Basic Science(Natural Science)Research General Project of Jiangsu Province Universities,China(22KJB430003).
文摘The solidification methods of electromagnetic stirring(EMS)and non-electromagnetic stirring were employed to prepare Mg–6Gd–3Y–xZn–0.6Zr(x=1,1.5,2,3)alloys.The evolution of alloy microstructures and the changes in properties were analyzed for different Zn contents.It has been observed that in alloys without electromagnetic stirring,as the Zn content increases,the alloy structure gradually refines.The primary second phase transitions from Mg5RE phase to long-period stacking ordered(LPSO)phase,resulting in improved hardness and elongation.In alloys subjected to electromagnetic stirring,there is a relatively higher content of the second phase,primarily consisting of LPSO phase.After applying electromagnetic stirring,the quantity and the type of LPSO phase in the alloy change.The alloy structure becomes more uniform with electromagnetic stirring,resulting in increased hardness and reduced hardness gradients within the grains.The mechanical properties of alloys with electromagnetic stirring are superior to those without electromagnetic stirring.
基金supported by JSPS KAKENHI for Scientific Research on Innovative Areas “Materials Science of a Millefeuille Structure (Grant Nos. JP18H05475, JP18H05479)”“Nanotechnology Platform” of the MEXT, Japan+1 种基金supported by Grant-in-Aid for JSPS Fellows (JP19F19775)the Open Funds of the State Key Laboratory of Rare Earth Resource Utilization (RERU2020012)。
文摘We have systematically investigated the microstructures of as-cast Mg_(97.49)Ho_(1.99)Cu_(0.43)Zr_(0.09)alloy by atomic resolution high-angle annular dark field scanning transmission electron microscopy(HAADF-STEM), revealing the coexistence of 18R, 14H and 24R long period stacking/order(LPSO) phases with fully coherent interfaces along step-like composition gradient in a blocky intermetallic compound distributed at grain boundary. The short-range order(SRO) L1_(2)-type Cu_(6)Ho_(8)clusters embedded across AB’C’A-stacking fault layers are directly revealed at atomic scale. Importantly, the order degree of SRO clusters in the present dilute alloy is significant lower than previous 6M and 7M in-plane order reported in ternary Mg-TM(transition metal)-RE(rare earth) alloys, which can be well matched by 9M in-plane order. This directly demonstrates that SRO in-plane L1_(2)-type clusters can be expanded into more dilute composition regions bounded along the definite TM/RE ratio of 3/4. In addition, the estimated chemical compositions of solute enriched stacking fault(SESF) in all LPSO variants are almost identical with the ideal SESF composition of 9M in-plane order, regardless of the type of LPSO phases. The results further support the viewpoint that robust L1_(2)-type TM_(6)RE_(8)clusters play an important role in governing LPSO phase formation.
基金the financial support from the National Key Research and Development Program of China(No.2022YFB3708400)the National Science and Technology Major Project(J2019-VIII-0003-0165)the Space Utilization System of China Manned Space Engineering(No.KJZ-YY-WCL04).
文摘In this study,we investigated the oxidation of the Mg-11Y-1Al alloy at 500℃in an Ar-20%O2environment.Multiscale analysis showed the network-like long-period stacking ordered(LPSO)phase transformed into needle-like LPSO and polygonal Mg24Y5 phases,leading to the formation of a high-dense network of needle-like oxides at the oxidation front.These oxides grew laterally along the oxide/matrix interfaces,forming a thicker,continuous scale that effectively blocked elemental diffusion.Hence,the preferential oxidation along the needle-like LPSO is believed to accelerate the formation of a thicker and continuous oxide scale,further improving the oxidation resistance of the Mg-11Y-1Al alloy.
