The T_(1)(Al_(2) CuLi)phase is one of the most effective strengthening nanoscale-precipitate in Al-Cu alloys with Li.However,its formation and evolution still need to be further clarified during aging due to the compl...The T_(1)(Al_(2) CuLi)phase is one of the most effective strengthening nanoscale-precipitate in Al-Cu alloys with Li.However,its formation and evolution still need to be further clarified during aging due to the complex precipitation sequences.Here,a detailed investigation has been carried out on the atomic struc-tural evolution of T_(1) precipitate in an aged Al-Cu-Li-Mg-Ag alloy using state-of-the-art Cs-corrected high-angle annular dark field(HAADF)-coupled with integrated differential phase contrast(iDPC)-scanning transmission electron microscopy(STEM)and energy-dispersive X-ray spectroscopy(EDXS)techniques.An intermediate T_(1)’phase between T_(1p) and T_(1) phase,with a crystal structure and orientation rela-tionship consistent with T_(1),but exhibiting different atomic occupancy and chemical composition was found.We observed the atomic structural transformation from T_(1p) to T_(1)’phase(fcc→hcp),involving only 1/12<112>Al shear component.DFT calculation results validated our proposed structural models and the precipitation sequence.Besides,the distributions of minor solute elements(Ag,Mg,and Zn)in the pre-cipitates exhibited significant differences.These findings may contribute to a further understanding of the nucleation mechanism of T_(1) precipitate.展开更多
Introducing B2 ordering can effectively improve the mechanical properties of lightweight refractory high-entropy alloys(LRHEAs).However,(Zr,Al)-enriched B2 precipitates generally reduce the ductility because their ord...Introducing B2 ordering can effectively improve the mechanical properties of lightweight refractory high-entropy alloys(LRHEAs).However,(Zr,Al)-enriched B2 precipitates generally reduce the ductility because their ordering characteristic is destroyed after dislocation shearing.Meanwhile,the local chemical order(LCO)cannot provide an adequate strengthening effect due to its small size.展开更多
An increase in RE element content in Mg alloys promotes the grain boundary precipitate,which affects the mechanical properties.However,the influence of grain boundary precipitates on microstructure of Mg-RE alloys dur...An increase in RE element content in Mg alloys promotes the grain boundary precipitate,which affects the mechanical properties.However,the influence of grain boundary precipitates on microstructure of Mg-RE alloys during ageing and their role on ductility of the aged alloy is unclear.In this work,hot extrusion and ageing treatment were performed for Mg-9Gd-2Y-xNd-0.2Zr(x=1 wt.%and 3 wt.%)alloys,and grain boundary precipitates were formed in the extruded Mg-9Gd-2Y-3Nd-0.2Zr alloy due to the increase of Nd content.The extruded alloys exhibit a complete dynamic recrystallization(DRX)microstructure and a texture with the<0001>orientation parallel to the extrusion direction(ED).In addition,a large amount of fiber microstructures distributed by the second phase along the ED were formed in the Mg-9Gd-2Y-3Nd-0.2Zr alloy,while only a small amount of the second phase was observed in the Mg-9Gd-2Y-1Nd-0.2Zr alloy.After ageing treatment,a large amount ofβ'phase precipitated inside the grains.The strength of the Mg-9Gd-2Y-1Nd-0.2Zr alloy increased from 202 MPa to 275 MPa but the elongation decreased from 12.8%to 2.6%,and the strength of the Mg-9Gd-2Y-3Nd-0.2Zr alloy increased from 212 MPa to 281 MPa but the elongation decreased from 13.7%to 6.2%.Among them,the Mg-9Gd-2Y-3Nd-0.2Zr alloy showed good overall mechanical properties,especially the elongation of the aged alloy was 58%higher than that of the Mg-9Gd-2Y-1Nd-0.2Zr alloy.The increase in ductility of the aged Mg-9Gd-2Y-3Nd-0.2Zr alloy attributed to the grain boundary precipitate promotes the formation of a large number of precipitation free zones(PFZs)with widths of 130-150 nm during ageing treatment.展开更多
The effect of high welding heat inputs in the range of 50–200 kJ/cm on the microstructural evolution,MX(M=Ti,Nb and V;X=N and C)precipitation and mechanical properties was investigated in the coarse-grained heat-affe...The effect of high welding heat inputs in the range of 50–200 kJ/cm on the microstructural evolution,MX(M=Ti,Nb and V;X=N and C)precipitation and mechanical properties was investigated in the coarse-grained heat-affected zone(CGHAZ)of a high-Nb(0.10 wt.%)structural steel.The results showed that the primary microconstituents varied from lath bainite(LB)to intragranular acicular ferrite(IAF)+intragranular polygonal ferrite(IPF),and the most content of IAF was acquired at 100 kJ/cm.Moreover,the submicron Ti-and Nb-rich MX precipitates not only pinned prior austenite grain boundaries but also facilitated IAF and IPF nucleation with the Kurdjumov–Sachs orientation relationship of[011]_(MX)//[111]_(Ferrite);the nanoscale V-rich MX precipitates hindered dislocation movement and followed the Baker–Nutting orientation relationship of[001]_(MX)//[001]_(Ferrite)with ferrite matrix,synergistically strengthening and toughening the CGHAZ.In addition,the−20℃impact absorbed energy firstly elevated from 93±5.2 J at 50 kJ/cm to 131±5.4 J at 100 kJ/cm and finally decreased to 59±3.0 J at 200 kJ/cm,being related to the IAF content,while the microhardness decreased from 312±26.1 to 269±12.9 HV0.1,because of the coarsened microstructure and the decreased content of LB and martensite.Compared to the CGHAZ properties with 0.05 wt.%Nb,a higher Nb content produced better low-temperature toughness,as more solid dissolved Nb atoms and precipitated Nb-rich MX particles in austenite limited prior austenite grain growth and promoted IAF formation.Furthermore,the welding process at 100 kJ/cm was most applicable for the high-Nb steel.展开更多
Nickel-based alloys are the primary structural materials in steam generators of high-temperature gas reactors.To understand the irradiation effect of nickel-based alloys,it is necessary to examine dislocation movement...Nickel-based alloys are the primary structural materials in steam generators of high-temperature gas reactors.To understand the irradiation effect of nickel-based alloys,it is necessary to examine dislocation movement and its interaction with irradiation defects at the microscale.Hardening due to voids and Ni_(3)Al precipitates may significantly impact irradiation damage in nickel-based alloys.This paper employs the molecular dynamics method to analyze the interaction between edge dislocations and irradiation defects(void and Ni_(3)Al precipitates)in face-centered cubic nickel.The effects of temperature and defect size on the interaction are also explored.The results show that the interaction process of the edge dislocation and irradiation defects can be divided into four stages:dislocation free slip,dislocation attracted,dislocation pinned,and dislocation unpinned.Interaction modes include the formation of stair-rod dislocations and the climbing of extended dislocation bundles for voids,as well as the generation of stair-rod dislocation and dislocation shear for precipitates.Besides,the interactions of edge dislocations with voids and Ni_(3)Al precipitates are strongly influenced by temperature and defect size.展开更多
In a typical sintered multi-component Sm_(2)Co_(17)-type magnet with strong fiber texture,we show that the distributions of grain boundary precipitates(GBPs)are heavily dependent on the grain boundary(GB)geometry with...In a typical sintered multi-component Sm_(2)Co_(17)-type magnet with strong fiber texture,we show that the distributions of grain boundary precipitates(GBPs)are heavily dependent on the grain boundary(GB)geometry with respect to the texture direction,which has significant effects on domain wall pinning.Re-sults demonstrate that the continuous GBPs turn into discrete upon the angle between{0001}planes and GB increases from 0°to 90°,meanwhile the GBPs thickness and precipitation free zones(PFZs)width both increase linearly by a factor of 2.5-4.Transmission electron microscopy(TEM)reveals that the GBPs are alternatively stacked Cu-rich SmCo_(5)and Zr-rich Sm_(n+1)Co_(5n-1)(n=2,3,4)compounds,while the PFZs are composed of 2:17R and intermediate 2:17R’phases.Atomic-level elemental mappings and first-principles calculations indicate that Cu exists at the Co-2c site in the SmCo_(5)forming SmCo_(3)Cu_(2)and Zr locates at the dumbbell Sm-6c sites in the Sm_(n+1)Co_(5n-1).The symbiotic GBPs have orientation relationships of[0001]GBPs//[0001]2:17R and[1010]GBPs//[2110]2:17R.The formation of anisotropic GBPs is owing to the strong fiber texture,i.e.,the larger angle between{0001}planes and GBs,the more{0001}diffusion channels for atoms to GBs,resulting in discrete and thick GBPs.In-situ Lorentz TEM shows that the domain walls interrupted by GBPs migrate easily under applied magnetic fields.Possible approaches to enhance the magnetic hardness via tuning the GBs are proposed.展开更多
The orientation effect of θʹ precipitates in stress-aged Al-Cu alloys has ambiguous interpretations. One view is that θʹ precipitates prefer to grow on the habit planes perpendicular to the applied compressive stres...The orientation effect of θʹ precipitates in stress-aged Al-Cu alloys has ambiguous interpretations. One view is that θʹ precipitates prefer to grow on the habit planes perpendicular to the applied compressive stress, while the other view suggests growth on habit planes parallel to the applied stress. In this study, stress-aged Al-4 wt.%Cu single crystal was sampled from three different <100>Al zone axes to observe the distribution of θʹ precipitates. A hybrid Monte-Carlo/ molecular dynamics simulations were used to investigate the orientation effect of θʹ precipitates. The simulation results are consistent with experimental observations and indicate that θʹ precipitates prefer to grow on the habit planes that are parallel to the direction of the applied compressive stress, not along the planes perpendicular to it. It is also found that 1/2<110> perfect dislocations are generated as θʹ precipitates plates grow thicker, and the reaction of 1/2<110> perfect dislocations decomposing into 1/6<112> Shockley dislocations lead to an increase in the length of θʹ precipitates. The former does not enhance the orientation effect, whereas the latter leads to a more significant orientation effect. Additionally, the degree of the orientation effect of θʹ precipitates is determined by the reduction of 1/2<110> dislocations with a positive correlation between them.展开更多
This work focuses on the influence of Al content on the precipitation of nanoprecipitates,growth of prior austenite grains(PAGs),and impact toughness in simulated coarse-grained heat-affected zones (CGHAZs) of two exp...This work focuses on the influence of Al content on the precipitation of nanoprecipitates,growth of prior austenite grains(PAGs),and impact toughness in simulated coarse-grained heat-affected zones (CGHAZs) of two experimental shipbuilding steels after being subjected to high-heat input welding at 400 kJ·cm^(-1).The base metals (BMs) of both steels contained three types of precipitates Type Ⅰ:cubic (Ti,Nb)(C,N),Type Ⅱ:precipitate with cubic (Ti,Nb)(C,N) core and Nb-rich cap,and Type Ⅲ:ellipsoidal Nb-rich precipitate.In the BM of 60Al and 160Al steels,the number densities of the precipitates were 11.37×10^(5) and 13.88×10^(5) mm^(-2),respectively The 60Al and 160Al steel contained 38.12% and 6.39% Type Ⅲ precipitates,respectively.The difference in the content of Type Ⅲ precipitates in the 60Al steel reduced the pinning effect at the elevated temperature of the CGHAZ,which facilitated the growth of PAGs The average PAG sizes in the CGHAZ of the 60Al and 160Al steels were 189.73 and 174.7μm,respectively.In the 60Al steel,the low lattice mismatch among Cu_(2)S,TiN,and γ-Al_(2)O_(3)facilitated the precipitation of Cu_(2)S and TiN onto γ-Al_(2)O_(3)during welding,which decreased the number density of independently precipitated (Ti,Nb)(C,N) particles but increased that of γ-Al_(2)O_(3)–Ti N–Cu_(2)S particles.Thus abnormally large PAGs formed in the CGHAZ of the 60Al steel,and they reached a maximum size of 1 mm.These PAGs greatly reduced the microstructural homogeneity and consequently decreased the impact toughness from 134 (0.016wt%Al) to 54 J (0.006wt%Al)at-40℃.展开更多
Face-centered cubic(FCC)-structured multicomponent alloys typically exhibit good ductility but low strength.To simultaneously improve strength and ductility,a multicomponent alloy,Ni_(43.9)Co_(22.4)Fe_(8.8)Al_(10.7)Ti...Face-centered cubic(FCC)-structured multicomponent alloys typically exhibit good ductility but low strength.To simultaneously improve strength and ductility,a multicomponent alloy,Ni_(43.9)Co_(22.4)Fe_(8.8)Al_(10.7)Ti_(11.7)B_(2.5)(at%)with a unique microstructure was developed in this work.The microstructure,which includes 17.8%nanosized L12 precipitates and 26.6%micron-sized annealing twins distributed within~8μm fine FCC grains,was achieved through cryogenic rolling and subsequent annealing.The alloy exhibits a yield strength(YS)of 1063 MPa,ultimate tensile strength(UTS)of 1696 MPa,and excellent elongation of~26%.The L1_(2) precipitates and high-density grain boundaries act as a barrier to the dislocation movement,resulting in a substantial strengthening effect.In addition,the dislocations can cut through the L1_(2) precipitates that are coherent with the FCC matrix,whereas the twin boundaries can effectively absorb and store dislocations,leading to a high work-hardening rate.Furthermore,the stacking faults,Lomer-Cottrell locks,and 9-layer rhombohedral stacking sequence(9R)structures formed during tensile deformation significantly enhance strain hardening by blocking dislocation movement and accumulating dislocations,resulting in excellent comprehensive tensile properties.Theoretical calculations reveal that the grain boundaries,L1_(2)precipitates,and twin boundaries contribute the strengths of 263.8,412.6,and 68.7 MPa,respectively,accounting for 71.9%of the YS.This study introduces a promising strategy for developing multicomponent alloys with significant strength-ductility synergies.展开更多
How to achieve high-entropy alloys(HEAs)with ultrahigh strength and ductility is a challenging issue.Precipitation strengthening is one of the methods to significantly enhance strength,but unfortunately,ductility will...How to achieve high-entropy alloys(HEAs)with ultrahigh strength and ductility is a challenging issue.Precipitation strengthening is one of the methods to significantly enhance strength,but unfortunately,ductility will be lost.To overcome the strength-ductility trade-off,the strategy of this study is to induce the formation of high-density nanoprecipitates through dual aging(DA),triggering multiple deformation mechanisms,to obtain HEAs with ultrahigh strength and ductility.First,the effect of precold deformation on precipitation behavior was studied using Ni_(35)(CoFe)_(55)V_(5)Nb_(5)(at.%)HEAas the object.The results reveal that the activation energy of recrystallization is 112.2 kJ/mol.As the precold-deformation amount increases from 15%to 65%,the activation energy of precipitation gradually decreases from 178.8 to 159.7 kJ/mol.The precipitation time shortens,the size of the nanoprecipitate decreases,and the density increases.Subsequently,the thermal treatment parameters were optimized,and the DA process was customized based on the effect of precold deformation on precipitation behavior.High-density L1_(2) nanoprecipitates(~3.21×10^(25) m^(-3))were induced in the 65% precold-deformed HEA,which led to the simultaneous formation of twins and stacking fault(SF)networks during deformation.The yield strength(YS),ultimate tensile strength,and ductility of the DA-HEA are~2.0 GPa,~2.2 GPa,and~12.3%,respectively.Compared with the solid solution HEA,the YS of the DA-HEA increased by 1,657 MPa,possessing an astonishing increase of~440%.The high YS stems from the precipitation strengthening contributed by the L1_(2) nanoprecipitates and the dislocation strengthening contributed by precold deformation.The synergistically enhanced ductility stems from the high strain-hardening ability under the dual support of twinning-induced plasticity and SF-induced plasticity.展开更多
The development of low-cost,high-performance Mg alloys is crucial to the industrial applications of large-scale production of Mg alloys.In this work,extruded Mg-5Bi-3Al alloy with excellent mechanical properties is su...The development of low-cost,high-performance Mg alloys is crucial to the industrial applications of large-scale production of Mg alloys.In this work,extruded Mg-5Bi-3Al alloy with excellent mechanical properties is successfully prepared by modifying the extrusion temperatures(240℃and 300℃).The extruded alloy obtained ultra-high strength(yield strength=380 MPa,ultimate tensile strength=418 MPa)and excellent plasticity(elongation=10.2%)at the extrusion temperature of 240℃,the main contributing factors are primarily attributed to the synergistic effect of ultrafine recrystallized grain size(~0.5µm)and high density of Mg_(3)Bi_(2)precipitates.Stacking faults within the sub-micron Mg_(3)Bi_(2)phase are observed in the E240 alloy,confirming the plastic deformation capability of Mg_(3)Bi_(2)phase.The effects of extrusion temperature on the microstructure,mechanical properties,and work-hardening behavior of the extruded Mg-5Bi-3Al alloys at room temperature are systematically investigated.The results suggest that decreasing the extrusion temperature can refine recrystallized grain size and Mg_(3)Bi_(2)phase size,and the quantity of Mg_(3)Bi_(2)phase is increased,while increasing the extrusion temperature can improve the degree of recrystallization and weaken texture.The work hardening rate is increased with the increased extrusion temperature,mainly due to the coarsening of grains and precipitates,and the weakening of texture.This work provides an experimental basis for preparing high-performance wrought Mg-5Bi-3Al alloys.展开更多
Precipitation via thermal treatments is among the most effective approaches to strengthening and is widely applied in the Al industry. Thermal treatments combined with deformation are capable of finely regulating the ...Precipitation via thermal treatments is among the most effective approaches to strengthening and is widely applied in the Al industry. Thermal treatments combined with deformation are capable of finely regulating the process of precipitation and distribution of precipitates. Deformation-induced defects exert significant impacts on the precipitation and already present precipitates, which however is often overlooked. In this study, the interactions between deformation and precipitation/precipitates, and their impacts on mechanical properties were systematically investigated in the solution-treated (ST) Al-0.61Mg-1.17Si-0.5Cu (wt.%), processed by multi-pass equal channel angular pressing (ECAP) and thermal treatments. Novel deformation-mediated cyclic evolution of precipitates is discovered: ST→ (1,2 passes: deformation induced precipitation) Guinier Preston (GP) zones→ (An250/30) Q’ and L phases→ (3-pass: deformation induced fragmentation/resolution) spherical precipitates→ (4-pass: deformation induced further fragmentation/resolution) GP zones. On this basis, we extend the quasi-binary phase diagram of Al-Mg_(2)Si along deformation as the third dimension and construct an innovative defect phase diagram for the Al-Mg-Si-based system. To testify to the effect of deformation-mediated cyclic evolution of precipitation/precipitates on the optimum mechanical properties, peak-aging treatments were performed in samples of ST and 3-pass states. Based on the microscopic characterizations, a distinctive mechanism of peak-aging strengthening is proposed. Notably in the 3-pass ECAPed and peak-aged sample the dominant strengthening phases become the L precipitates that thrived from the segmented and spherical L phases, rather than β’’ precipitates in the solely peak-aged ST sample. Our work provides a feasible example for exploring the combined processing technique of multi-step deformation and thermal treatments, to optimize the mechanical properties.展开更多
For the traditional peak-aged (PA) AA2024 alloy, the formation of large S-phase precipitates within the grains, wide precipitate-free zones (PFZs) near the grain boundaries (GBs), and continuous distribution of grain ...For the traditional peak-aged (PA) AA2024 alloy, the formation of large S-phase precipitates within the grains, wide precipitate-free zones (PFZs) near the grain boundaries (GBs), and continuous distribution of grain boundary precipitates (GBPs) can be observed. As a result, the PA alloy exhibits relatively high strength but poor corrosion resistance. However, with the application of cyclic plasticity treatment, high-density 1–2 nm clusters form within the matrix, and no PFZs form near GBs. In this study, this treatment yields the optimal balance between strength–elongation characteristics and corrosion resistance. By combining cyclic plasticity and ageing heat treatment with different heating rates, the nanoscale clusters play a crucial role as heterogeneous nucleation sites, resulting in the formation of finer and higher number density of S precipitates within the matrix. Additionally, the presence of these clusters reduces the formation of GBPs and minimizes the width of PFZs. Consequently, compared to the traditional PA sample, this approach achieves a significantly higher yield strength (increased by 46 %) and ultimate tensile strength (increased by 18 %), along with superior corrosion resistance. Although the influence of ageing heat treatment with different rates on mechanical properties is not significant, it notably affects the formation of GBPs and corrosion resistance. Specifically, a slower heating rate leads to an increase in the spacing between adjacent GBPs, resulting in improved corrosion resistance. In summary, cyclic strengthening, as a novel method for alloy strengthening, when combined with ageing heat treatment, modulates the distribution of S precipitates within the matrix and GBs. This optimization maximizes the effects of precipitation strengthening and breaks the inverse relationship between strength and corrosion resistance.展开更多
The effect of precipitation aging on the fracture behavior of cast Mg-14.23Gd-0.45Zr(wt.%)alloy at room temperature has been studied in this work.Uniaxial tensile and three-point bending tests were conducted on sample...The effect of precipitation aging on the fracture behavior of cast Mg-14.23Gd-0.45Zr(wt.%)alloy at room temperature has been studied in this work.Uniaxial tensile and three-point bending tests were conducted on samples peak-aged at 175,200,225,and 250 ℃.Notably,samples aged at 175 ℃ and 200 ℃ exhibited premature fracture during the uniaxial tensile test.Through fractographic observations of the tensile test samples and electron backscattered diffraction(EBSD)analysis on the samples sub-jected to three-point bending tests,a preferential formation of cleavage cracks in samples aged at 175 ℃ and 200 ℃ was identified as the reason for their premature fracture.The X-ray diffraction(XRD)results and transmission electron microscopy(TEM)observations of precipitates indicate that the dominant strengthening precipitates in all peak-aged samples are of theβ'phase,and their size significantly influences the formation of cleavage cracks.This phenomenon is attributed to the shearing mechanism of precipitates.Specifically,the smaller β'precipitates formed under the aging temperature of 175-200 ℃ are susceptible to dislocation shearing,leading to the formation of cleavage cracks.In contrast,the larger size of β'precipitates formed under the aging temperature of 225-250 ℃ provides resistance to shearing,resulting in the restrained formation of cleavage cracks and ultimately contributing to the enhancement of the ultimate tensile strength.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
Through an understanding of diffusion,precise control of the size distribution of nano-precipitates can be essential to developing superior properties in precipitation-strengthened alloys.Although a significant influe...Through an understanding of diffusion,precise control of the size distribution of nano-precipitates can be essential to developing superior properties in precipitation-strengthened alloys.Although a significant influence of crystallographic orientation on the diffusion process is known to exist in low-symmetry hexagonal close-packed alloys,such anisotropic diffusion is still unidentified in high-symmetry cubic alloys.In this work,we reveal the diffusion-controlled coarsening induced anisotropic growth process of nano-precipitates in an Al-Zn-Mg-Cu alloy.Our experimental and theoretical studies demonstrate that with an increase in the residual stress,the diffusion-controlled coarsening rate is slow along the<112>fiber texture in the alloy matrix with smaller grain sizes.As such,we find that the diffusion activation energy will be increased along the preferred orientation with largest residual stress,which leads to a reduced diffusion-controlled coarsening rate.Specifically,we demonstrate that the increase in the volume fraction of nano-precipitates originates from the rapid grain-boundary controlled coarsening of the grainboundary precipitates.Based on these results,an underlying microstructural design strategy is proposed,involving the crystallographic orientation,the residual stress and the grain boundaries to manipulate the precipitate size distribution in this class of alloys.展开更多
In-situ electron irradiation and aging are applied to introduce high-density precipitates in an Mg-10Gd-3Y-1Zn-0.5Zr(GWZ1031K,wt.%)alloy to improve the hardness.The results show that the hardness of the Mg alloy after...In-situ electron irradiation and aging are applied to introduce high-density precipitates in an Mg-10Gd-3Y-1Zn-0.5Zr(GWZ1031K,wt.%)alloy to improve the hardness.The results show that the hardness of the Mg alloy after irradiation for 10 h and aging for 9 h at 250℃ is 1.64 GPa,which is approximately 64% higher than that of the samples before being treated.It is mainly attributed to γ'precipitates on the basal plane after irradiation and the high-density nanoscale β'precipitates on the prismatic plane after aging,which should be closely related to the irradiation-induced homogenous clusters.The latter plays a key role in precipitation hardening.This result paves a way to improve the mechanical properties of metallic materials by tailoring the precipitation through irradiation and aging.展开更多
The chemical boundaries inside the ultrafine spinodal decomposition structure in metastable β-Ti alloys can act as a new feature to architect heterogeneous microstructures.In this work,we combined two semi-empirical ...The chemical boundaries inside the ultrafine spinodal decomposition structure in metastable β-Ti alloys can act as a new feature to architect heterogeneous microstructures.In this work,we combined two semi-empirical methods,i.e.,the d-electron theory and the e/a electron concentration,to achieve the spinodal decomposition structure in a metastable β Ti-4.5Al-4.5Mo-7V-1.5Cr-1.5Zr(wt.%)alloy.Utilizing the spinodal decomposition structure,the aged Ti-Al-Mo-V-Cr-Zr alloys showed multi-architectured α precipitates spanning from micron-scale(primary α_(p))to nano-scale(secondary α_(s))that were uniformly distributed in the β-domains.Being compared with the forged sample,the multi-scale heterogeneous microstructure enables the aged β-Ti alloy to have ultra-high strength(yield strength ~1366 MPa and ultimate tensile strength ~1424 MPa)and an appreciable ductility(~9.3%).Strengthening models were proposed for the present alloys to estimate the contribution of various microstructural features to the measured yield strength.While the solid solution strengthening,β-spinodal strengthening,and back stress strengthening made comparable contributions to the strength of the forged alloy,the back stress strengthening was the predominant strengthening effect in the aged alloy.This alloy design approach based on chemical boundary engineering to construct multi-architectured α precipitates provided an effective strategy for achieving an outstanding combination of ultra-high strength and ductility in metastable β-Ti alloys.展开更多
One of the most intriguing methods of mitigating the hydrogen embrittlement of steels entails nano-precipitates that can trap H from enriching at vulnerable locations.However,controversial findings have been reported ...One of the most intriguing methods of mitigating the hydrogen embrittlement of steels entails nano-precipitates that can trap H from enriching at vulnerable locations.However,controversial findings have been reported on whether the incoherent NbC precipitates trap hydrogen.Here,by using in-situ scan-ning Kelvin probe force microscopy(SKPFM),we reveal the dynamic interaction of H with the border area of incoherent NbC nanoprecipitates in steel.Results indicate that the interaction between H flux and the interfaces varies amongst different precipitates,implying that H-trapping behaviours of incoherent NbC precipitates could be intrinsically diverse.Potential origins underlying the distinct behaviours are analyzed.展开更多
The coarsening behavior and strengthening effect of L1_(2)-Ni_(3)(Ti,Al)precipitates in a face-centered-cubic(FCC)(FeCoNi)_(92)Al_(2.5)Ti_(5.5) high entropy alloy have been systematically investigated.The coherent L1_...The coarsening behavior and strengthening effect of L1_(2)-Ni_(3)(Ti,Al)precipitates in a face-centered-cubic(FCC)(FeCoNi)_(92)Al_(2.5)Ti_(5.5) high entropy alloy have been systematically investigated.The coherent L1_(2) precipitates,uniformly distributed throughout the FCC matrix,consistently retain a spherical shape.The coarsening rate coefficient of precipitate is determined by employing the Philippe-Voorhees(PV)model,suggesting excellent thermal stability.Furthermore,the elemental partitioning and compositional evolution of the L1_(2) precipitates is analyzed by atom probe tomography,which identify aluminum(Al)as the slowest diffusion species during the coarsening process.In addition,the precipitation strengthening effect is quantified to ascertain the optimal size of the precipitates.Our study enhances the understanding of precipitate coarsening in high entropy alloys,presenting valuable insights into their thermal stability and mechanical properties.展开更多
基金supported by the Pre-research fund(No.412130024).
文摘The T_(1)(Al_(2) CuLi)phase is one of the most effective strengthening nanoscale-precipitate in Al-Cu alloys with Li.However,its formation and evolution still need to be further clarified during aging due to the complex precipitation sequences.Here,a detailed investigation has been carried out on the atomic struc-tural evolution of T_(1) precipitate in an aged Al-Cu-Li-Mg-Ag alloy using state-of-the-art Cs-corrected high-angle annular dark field(HAADF)-coupled with integrated differential phase contrast(iDPC)-scanning transmission electron microscopy(STEM)and energy-dispersive X-ray spectroscopy(EDXS)techniques.An intermediate T_(1)’phase between T_(1p) and T_(1) phase,with a crystal structure and orientation rela-tionship consistent with T_(1),but exhibiting different atomic occupancy and chemical composition was found.We observed the atomic structural transformation from T_(1p) to T_(1)’phase(fcc→hcp),involving only 1/12<112>Al shear component.DFT calculation results validated our proposed structural models and the precipitation sequence.Besides,the distributions of minor solute elements(Ag,Mg,and Zn)in the pre-cipitates exhibited significant differences.These findings may contribute to a further understanding of the nucleation mechanism of T_(1) precipitate.
基金supported by the National Natural Science Foundation of China(Nos.52171166 and U20A20231)the Natural Science Foundation of Hunan Province,China(Nos.2024JJ2060 and 2024JJ5406)+1 种基金the Key Laboratory of Materials in Dynamic Extremes of Sichuan Province(No.2023SCKT1102)the Postgraduate Scientific Research Innovation Project of National University of Defense Technology(No.XJJC2024065).
文摘Introducing B2 ordering can effectively improve the mechanical properties of lightweight refractory high-entropy alloys(LRHEAs).However,(Zr,Al)-enriched B2 precipitates generally reduce the ductility because their ordering characteristic is destroyed after dislocation shearing.Meanwhile,the local chemical order(LCO)cannot provide an adequate strengthening effect due to its small size.
基金Project(2021YFB3701103) supported by the National Key R&D Program of China。
文摘An increase in RE element content in Mg alloys promotes the grain boundary precipitate,which affects the mechanical properties.However,the influence of grain boundary precipitates on microstructure of Mg-RE alloys during ageing and their role on ductility of the aged alloy is unclear.In this work,hot extrusion and ageing treatment were performed for Mg-9Gd-2Y-xNd-0.2Zr(x=1 wt.%and 3 wt.%)alloys,and grain boundary precipitates were formed in the extruded Mg-9Gd-2Y-3Nd-0.2Zr alloy due to the increase of Nd content.The extruded alloys exhibit a complete dynamic recrystallization(DRX)microstructure and a texture with the<0001>orientation parallel to the extrusion direction(ED).In addition,a large amount of fiber microstructures distributed by the second phase along the ED were formed in the Mg-9Gd-2Y-3Nd-0.2Zr alloy,while only a small amount of the second phase was observed in the Mg-9Gd-2Y-1Nd-0.2Zr alloy.After ageing treatment,a large amount ofβ'phase precipitated inside the grains.The strength of the Mg-9Gd-2Y-1Nd-0.2Zr alloy increased from 202 MPa to 275 MPa but the elongation decreased from 12.8%to 2.6%,and the strength of the Mg-9Gd-2Y-3Nd-0.2Zr alloy increased from 212 MPa to 281 MPa but the elongation decreased from 13.7%to 6.2%.Among them,the Mg-9Gd-2Y-3Nd-0.2Zr alloy showed good overall mechanical properties,especially the elongation of the aged alloy was 58%higher than that of the Mg-9Gd-2Y-1Nd-0.2Zr alloy.The increase in ductility of the aged Mg-9Gd-2Y-3Nd-0.2Zr alloy attributed to the grain boundary precipitate promotes the formation of a large number of precipitation free zones(PFZs)with widths of 130-150 nm during ageing treatment.
基金financially supported by the National Natural Science Foundation of China(Grant No.52104333)the Natural Science Foundation of Inner Mongolia(Grant No.2024MS05029)+1 种基金the Program for Young Talents of Science and Technology in Universities of Inner Mongolia Autonomous Region(Grant No.NJYT24070)the Research Project of Carbon Peak and Carbon Neutrality in Universities of Inner Mongolia Autonomous Region(Grant No.STZX202316).
文摘The effect of high welding heat inputs in the range of 50–200 kJ/cm on the microstructural evolution,MX(M=Ti,Nb and V;X=N and C)precipitation and mechanical properties was investigated in the coarse-grained heat-affected zone(CGHAZ)of a high-Nb(0.10 wt.%)structural steel.The results showed that the primary microconstituents varied from lath bainite(LB)to intragranular acicular ferrite(IAF)+intragranular polygonal ferrite(IPF),and the most content of IAF was acquired at 100 kJ/cm.Moreover,the submicron Ti-and Nb-rich MX precipitates not only pinned prior austenite grain boundaries but also facilitated IAF and IPF nucleation with the Kurdjumov–Sachs orientation relationship of[011]_(MX)//[111]_(Ferrite);the nanoscale V-rich MX precipitates hindered dislocation movement and followed the Baker–Nutting orientation relationship of[001]_(MX)//[001]_(Ferrite)with ferrite matrix,synergistically strengthening and toughening the CGHAZ.In addition,the−20℃impact absorbed energy firstly elevated from 93±5.2 J at 50 kJ/cm to 131±5.4 J at 100 kJ/cm and finally decreased to 59±3.0 J at 200 kJ/cm,being related to the IAF content,while the microhardness decreased from 312±26.1 to 269±12.9 HV0.1,because of the coarsened microstructure and the decreased content of LB and martensite.Compared to the CGHAZ properties with 0.05 wt.%Nb,a higher Nb content produced better low-temperature toughness,as more solid dissolved Nb atoms and precipitated Nb-rich MX particles in austenite limited prior austenite grain growth and promoted IAF formation.Furthermore,the welding process at 100 kJ/cm was most applicable for the high-Nb steel.
基金supported by the Ministry of Industry and Information Technology of China(grant number TC220A04W-7,203)CNNC Youth Elite Scientific Research Project,the National Key R&D Plan of China(grant number 2020YFB1901600)the National Science Technology Major Project of China(grant numbers 2017ZX06902012 and 2017ZX06901024).
文摘Nickel-based alloys are the primary structural materials in steam generators of high-temperature gas reactors.To understand the irradiation effect of nickel-based alloys,it is necessary to examine dislocation movement and its interaction with irradiation defects at the microscale.Hardening due to voids and Ni_(3)Al precipitates may significantly impact irradiation damage in nickel-based alloys.This paper employs the molecular dynamics method to analyze the interaction between edge dislocations and irradiation defects(void and Ni_(3)Al precipitates)in face-centered cubic nickel.The effects of temperature and defect size on the interaction are also explored.The results show that the interaction process of the edge dislocation and irradiation defects can be divided into four stages:dislocation free slip,dislocation attracted,dislocation pinned,and dislocation unpinned.Interaction modes include the formation of stair-rod dislocations and the climbing of extended dislocation bundles for voids,as well as the generation of stair-rod dislocation and dislocation shear for precipitates.Besides,the interactions of edge dislocations with voids and Ni_(3)Al precipitates are strongly influenced by temperature and defect size.
基金the financial support by the National Nat-ural Science Foundation of China(No.52201032)the Science and Technology Innovation Program of Hunan Province(No.2023RC1013)+2 种基金supported by the Advanced Research Center(for FIB and Talos F200X usages)the State Key Laboratory of Powder Metallurgy(for Spectra 300 usage)the High Performance Computing Center(for supercomputing usage)of Central South University.
文摘In a typical sintered multi-component Sm_(2)Co_(17)-type magnet with strong fiber texture,we show that the distributions of grain boundary precipitates(GBPs)are heavily dependent on the grain boundary(GB)geometry with respect to the texture direction,which has significant effects on domain wall pinning.Re-sults demonstrate that the continuous GBPs turn into discrete upon the angle between{0001}planes and GB increases from 0°to 90°,meanwhile the GBPs thickness and precipitation free zones(PFZs)width both increase linearly by a factor of 2.5-4.Transmission electron microscopy(TEM)reveals that the GBPs are alternatively stacked Cu-rich SmCo_(5)and Zr-rich Sm_(n+1)Co_(5n-1)(n=2,3,4)compounds,while the PFZs are composed of 2:17R and intermediate 2:17R’phases.Atomic-level elemental mappings and first-principles calculations indicate that Cu exists at the Co-2c site in the SmCo_(5)forming SmCo_(3)Cu_(2)and Zr locates at the dumbbell Sm-6c sites in the Sm_(n+1)Co_(5n-1).The symbiotic GBPs have orientation relationships of[0001]GBPs//[0001]2:17R and[1010]GBPs//[2110]2:17R.The formation of anisotropic GBPs is owing to the strong fiber texture,i.e.,the larger angle between{0001}planes and GBs,the more{0001}diffusion channels for atoms to GBs,resulting in discrete and thick GBPs.In-situ Lorentz TEM shows that the domain walls interrupted by GBPs migrate easily under applied magnetic fields.Possible approaches to enhance the magnetic hardness via tuning the GBs are proposed.
基金Project(2023YFB3710503) supported by the National Key R&D Program of ChinaProject(52305439) supported by the National Natural Science Foundation of China。
文摘The orientation effect of θʹ precipitates in stress-aged Al-Cu alloys has ambiguous interpretations. One view is that θʹ precipitates prefer to grow on the habit planes perpendicular to the applied compressive stress, while the other view suggests growth on habit planes parallel to the applied stress. In this study, stress-aged Al-4 wt.%Cu single crystal was sampled from three different <100>Al zone axes to observe the distribution of θʹ precipitates. A hybrid Monte-Carlo/ molecular dynamics simulations were used to investigate the orientation effect of θʹ precipitates. The simulation results are consistent with experimental observations and indicate that θʹ precipitates prefer to grow on the habit planes that are parallel to the direction of the applied compressive stress, not along the planes perpendicular to it. It is also found that 1/2<110> perfect dislocations are generated as θʹ precipitates plates grow thicker, and the reaction of 1/2<110> perfect dislocations decomposing into 1/6<112> Shockley dislocations lead to an increase in the length of θʹ precipitates. The former does not enhance the orientation effect, whereas the latter leads to a more significant orientation effect. Additionally, the degree of the orientation effect of θʹ precipitates is determined by the reduction of 1/2<110> dislocations with a positive correlation between them.
基金support from the National Natural Science Foundation of China (No. U1960202)the Opening Foundation from Shanghai Engineering Research Center of Hot Manufacturing, China (No. 18DZ2253400)。
文摘This work focuses on the influence of Al content on the precipitation of nanoprecipitates,growth of prior austenite grains(PAGs),and impact toughness in simulated coarse-grained heat-affected zones (CGHAZs) of two experimental shipbuilding steels after being subjected to high-heat input welding at 400 kJ·cm^(-1).The base metals (BMs) of both steels contained three types of precipitates Type Ⅰ:cubic (Ti,Nb)(C,N),Type Ⅱ:precipitate with cubic (Ti,Nb)(C,N) core and Nb-rich cap,and Type Ⅲ:ellipsoidal Nb-rich precipitate.In the BM of 60Al and 160Al steels,the number densities of the precipitates were 11.37×10^(5) and 13.88×10^(5) mm^(-2),respectively The 60Al and 160Al steel contained 38.12% and 6.39% Type Ⅲ precipitates,respectively.The difference in the content of Type Ⅲ precipitates in the 60Al steel reduced the pinning effect at the elevated temperature of the CGHAZ,which facilitated the growth of PAGs The average PAG sizes in the CGHAZ of the 60Al and 160Al steels were 189.73 and 174.7μm,respectively.In the 60Al steel,the low lattice mismatch among Cu_(2)S,TiN,and γ-Al_(2)O_(3)facilitated the precipitation of Cu_(2)S and TiN onto γ-Al_(2)O_(3)during welding,which decreased the number density of independently precipitated (Ti,Nb)(C,N) particles but increased that of γ-Al_(2)O_(3)–Ti N–Cu_(2)S particles.Thus abnormally large PAGs formed in the CGHAZ of the 60Al steel,and they reached a maximum size of 1 mm.These PAGs greatly reduced the microstructural homogeneity and consequently decreased the impact toughness from 134 (0.016wt%Al) to 54 J (0.006wt%Al)at-40℃.
基金supported by the Major Science and Technology Project of Gansu Province(Nos.23ZDGA010 and 22ZD6GA008)the National Natural Science Foundation of China(No.51564035).
文摘Face-centered cubic(FCC)-structured multicomponent alloys typically exhibit good ductility but low strength.To simultaneously improve strength and ductility,a multicomponent alloy,Ni_(43.9)Co_(22.4)Fe_(8.8)Al_(10.7)Ti_(11.7)B_(2.5)(at%)with a unique microstructure was developed in this work.The microstructure,which includes 17.8%nanosized L12 precipitates and 26.6%micron-sized annealing twins distributed within~8μm fine FCC grains,was achieved through cryogenic rolling and subsequent annealing.The alloy exhibits a yield strength(YS)of 1063 MPa,ultimate tensile strength(UTS)of 1696 MPa,and excellent elongation of~26%.The L1_(2) precipitates and high-density grain boundaries act as a barrier to the dislocation movement,resulting in a substantial strengthening effect.In addition,the dislocations can cut through the L1_(2) precipitates that are coherent with the FCC matrix,whereas the twin boundaries can effectively absorb and store dislocations,leading to a high work-hardening rate.Furthermore,the stacking faults,Lomer-Cottrell locks,and 9-layer rhombohedral stacking sequence(9R)structures formed during tensile deformation significantly enhance strain hardening by blocking dislocation movement and accumulating dislocations,resulting in excellent comprehensive tensile properties.Theoretical calculations reveal that the grain boundaries,L1_(2)precipitates,and twin boundaries contribute the strengths of 263.8,412.6,and 68.7 MPa,respectively,accounting for 71.9%of the YS.This study introduces a promising strategy for developing multicomponent alloys with significant strength-ductility synergies.
基金supported by the National Key Research and Development Project(No.2023YFA1600082)the National Natural Science Foundation of China(Nos.U2141207,52001083,52171111)+3 种基金Natural Science Foundation of Heilongjiang(No.YQ2023E026)the Fundamental Research Funds for the Central Universities(No.3072022JIP1002)Key Laboratory Found of the Ministry of Industry and Information Technology(No.GXB202201)Youth Talent Project of China National Nuclear Corporation(No.CNNC2021YTEP-HEU01).
文摘How to achieve high-entropy alloys(HEAs)with ultrahigh strength and ductility is a challenging issue.Precipitation strengthening is one of the methods to significantly enhance strength,but unfortunately,ductility will be lost.To overcome the strength-ductility trade-off,the strategy of this study is to induce the formation of high-density nanoprecipitates through dual aging(DA),triggering multiple deformation mechanisms,to obtain HEAs with ultrahigh strength and ductility.First,the effect of precold deformation on precipitation behavior was studied using Ni_(35)(CoFe)_(55)V_(5)Nb_(5)(at.%)HEAas the object.The results reveal that the activation energy of recrystallization is 112.2 kJ/mol.As the precold-deformation amount increases from 15%to 65%,the activation energy of precipitation gradually decreases from 178.8 to 159.7 kJ/mol.The precipitation time shortens,the size of the nanoprecipitate decreases,and the density increases.Subsequently,the thermal treatment parameters were optimized,and the DA process was customized based on the effect of precold deformation on precipitation behavior.High-density L1_(2) nanoprecipitates(~3.21×10^(25) m^(-3))were induced in the 65% precold-deformed HEA,which led to the simultaneous formation of twins and stacking fault(SF)networks during deformation.The yield strength(YS),ultimate tensile strength,and ductility of the DA-HEA are~2.0 GPa,~2.2 GPa,and~12.3%,respectively.Compared with the solid solution HEA,the YS of the DA-HEA increased by 1,657 MPa,possessing an astonishing increase of~440%.The high YS stems from the precipitation strengthening contributed by the L1_(2) nanoprecipitates and the dislocation strengthening contributed by precold deformation.The synergistically enhanced ductility stems from the high strain-hardening ability under the dual support of twinning-induced plasticity and SF-induced plasticity.
基金supported by the National Natural Science Foundation of China[grant nos.52371005,52022017,and 51927801]Fundamental Research Funds for the Central Universities.E.G.thanks Xiaomi Foundation for support.
文摘The development of low-cost,high-performance Mg alloys is crucial to the industrial applications of large-scale production of Mg alloys.In this work,extruded Mg-5Bi-3Al alloy with excellent mechanical properties is successfully prepared by modifying the extrusion temperatures(240℃and 300℃).The extruded alloy obtained ultra-high strength(yield strength=380 MPa,ultimate tensile strength=418 MPa)and excellent plasticity(elongation=10.2%)at the extrusion temperature of 240℃,the main contributing factors are primarily attributed to the synergistic effect of ultrafine recrystallized grain size(~0.5µm)and high density of Mg_(3)Bi_(2)precipitates.Stacking faults within the sub-micron Mg_(3)Bi_(2)phase are observed in the E240 alloy,confirming the plastic deformation capability of Mg_(3)Bi_(2)phase.The effects of extrusion temperature on the microstructure,mechanical properties,and work-hardening behavior of the extruded Mg-5Bi-3Al alloys at room temperature are systematically investigated.The results suggest that decreasing the extrusion temperature can refine recrystallized grain size and Mg_(3)Bi_(2)phase size,and the quantity of Mg_(3)Bi_(2)phase is increased,while increasing the extrusion temperature can improve the degree of recrystallization and weaken texture.The work hardening rate is increased with the increased extrusion temperature,mainly due to the coarsening of grains and precipitates,and the weakening of texture.This work provides an experimental basis for preparing high-performance wrought Mg-5Bi-3Al alloys.
基金supported by the National Natural Science Foundation of China(Grant Nos.U22A20187,52171007,52371111,and 52371177).
文摘Precipitation via thermal treatments is among the most effective approaches to strengthening and is widely applied in the Al industry. Thermal treatments combined with deformation are capable of finely regulating the process of precipitation and distribution of precipitates. Deformation-induced defects exert significant impacts on the precipitation and already present precipitates, which however is often overlooked. In this study, the interactions between deformation and precipitation/precipitates, and their impacts on mechanical properties were systematically investigated in the solution-treated (ST) Al-0.61Mg-1.17Si-0.5Cu (wt.%), processed by multi-pass equal channel angular pressing (ECAP) and thermal treatments. Novel deformation-mediated cyclic evolution of precipitates is discovered: ST→ (1,2 passes: deformation induced precipitation) Guinier Preston (GP) zones→ (An250/30) Q’ and L phases→ (3-pass: deformation induced fragmentation/resolution) spherical precipitates→ (4-pass: deformation induced further fragmentation/resolution) GP zones. On this basis, we extend the quasi-binary phase diagram of Al-Mg_(2)Si along deformation as the third dimension and construct an innovative defect phase diagram for the Al-Mg-Si-based system. To testify to the effect of deformation-mediated cyclic evolution of precipitation/precipitates on the optimum mechanical properties, peak-aging treatments were performed in samples of ST and 3-pass states. Based on the microscopic characterizations, a distinctive mechanism of peak-aging strengthening is proposed. Notably in the 3-pass ECAPed and peak-aged sample the dominant strengthening phases become the L precipitates that thrived from the segmented and spherical L phases, rather than β’’ precipitates in the solely peak-aged ST sample. Our work provides a feasible example for exploring the combined processing technique of multi-step deformation and thermal treatments, to optimize the mechanical properties.
基金support of the National Natural Science Foundation for Young Scholars of China(No.52001063)the National Natural Science Foundation of China(No.52371103)+2 种基金the Fundamental Research Funds for the Central Universities(No.2242023K40028)the Open Research Fund of Jiangsu Key Laboratory for Advanced Metallic Materials(No.AMM2023B01)X.L.An gratefully acknowledges the support of the Natural Science Foundation for Young Scholars of Jiangsu Province(No.BK20220628).
文摘For the traditional peak-aged (PA) AA2024 alloy, the formation of large S-phase precipitates within the grains, wide precipitate-free zones (PFZs) near the grain boundaries (GBs), and continuous distribution of grain boundary precipitates (GBPs) can be observed. As a result, the PA alloy exhibits relatively high strength but poor corrosion resistance. However, with the application of cyclic plasticity treatment, high-density 1–2 nm clusters form within the matrix, and no PFZs form near GBs. In this study, this treatment yields the optimal balance between strength–elongation characteristics and corrosion resistance. By combining cyclic plasticity and ageing heat treatment with different heating rates, the nanoscale clusters play a crucial role as heterogeneous nucleation sites, resulting in the formation of finer and higher number density of S precipitates within the matrix. Additionally, the presence of these clusters reduces the formation of GBPs and minimizes the width of PFZs. Consequently, compared to the traditional PA sample, this approach achieves a significantly higher yield strength (increased by 46 %) and ultimate tensile strength (increased by 18 %), along with superior corrosion resistance. Although the influence of ageing heat treatment with different rates on mechanical properties is not significant, it notably affects the formation of GBPs and corrosion resistance. Specifically, a slower heating rate leads to an increase in the spacing between adjacent GBPs, resulting in improved corrosion resistance. In summary, cyclic strengthening, as a novel method for alloy strengthening, when combined with ageing heat treatment, modulates the distribution of S precipitates within the matrix and GBs. This optimization maximizes the effects of precipitation strengthening and breaks the inverse relationship between strength and corrosion resistance.
基金National Natural Science Foundation of China(Nos.52271107,and 51701218)Natural Science Foundation of Shandong Province(No.ZR2021ME241)+1 种基金Natural Science Foundation of Liaoning Province(No.2020-MS-004)Bintech-IMR R&D Program(GYY-JSBU-2022-012).
文摘The effect of precipitation aging on the fracture behavior of cast Mg-14.23Gd-0.45Zr(wt.%)alloy at room temperature has been studied in this work.Uniaxial tensile and three-point bending tests were conducted on samples peak-aged at 175,200,225,and 250 ℃.Notably,samples aged at 175 ℃ and 200 ℃ exhibited premature fracture during the uniaxial tensile test.Through fractographic observations of the tensile test samples and electron backscattered diffraction(EBSD)analysis on the samples sub-jected to three-point bending tests,a preferential formation of cleavage cracks in samples aged at 175 ℃ and 200 ℃ was identified as the reason for their premature fracture.The X-ray diffraction(XRD)results and transmission electron microscopy(TEM)observations of precipitates indicate that the dominant strengthening precipitates in all peak-aged samples are of theβ'phase,and their size significantly influences the formation of cleavage cracks.This phenomenon is attributed to the shearing mechanism of precipitates.Specifically,the smaller β'precipitates formed under the aging temperature of 175-200 ℃ are susceptible to dislocation shearing,leading to the formation of cleavage cracks.In contrast,the larger size of β'precipitates formed under the aging temperature of 225-250 ℃ provides resistance to shearing,resulting in the restrained formation of cleavage cracks and ultimately contributing to the enhancement of the ultimate tensile strength.
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 Research and Development Program of China(No.2017YFF0210002)the National Science and Technology Major Projects of China(No.J2019VII-0015-0155).
文摘Through an understanding of diffusion,precise control of the size distribution of nano-precipitates can be essential to developing superior properties in precipitation-strengthened alloys.Although a significant influence of crystallographic orientation on the diffusion process is known to exist in low-symmetry hexagonal close-packed alloys,such anisotropic diffusion is still unidentified in high-symmetry cubic alloys.In this work,we reveal the diffusion-controlled coarsening induced anisotropic growth process of nano-precipitates in an Al-Zn-Mg-Cu alloy.Our experimental and theoretical studies demonstrate that with an increase in the residual stress,the diffusion-controlled coarsening rate is slow along the<112>fiber texture in the alloy matrix with smaller grain sizes.As such,we find that the diffusion activation energy will be increased along the preferred orientation with largest residual stress,which leads to a reduced diffusion-controlled coarsening rate.Specifically,we demonstrate that the increase in the volume fraction of nano-precipitates originates from the rapid grain-boundary controlled coarsening of the grainboundary precipitates.Based on these results,an underlying microstructural design strategy is proposed,involving the crystallographic orientation,the residual stress and the grain boundaries to manipulate the precipitate size distribution in this class of alloys.
基金supported by the National Natural Science Foundation of China(Grant Nos.51871222,52171021,and 51801214)Liaoning Provincial Natural Science Foundation(2019-MS-335)the research fund of SYNL。
文摘In-situ electron irradiation and aging are applied to introduce high-density precipitates in an Mg-10Gd-3Y-1Zn-0.5Zr(GWZ1031K,wt.%)alloy to improve the hardness.The results show that the hardness of the Mg alloy after irradiation for 10 h and aging for 9 h at 250℃ is 1.64 GPa,which is approximately 64% higher than that of the samples before being treated.It is mainly attributed to γ'precipitates on the basal plane after irradiation and the high-density nanoscale β'precipitates on the prismatic plane after aging,which should be closely related to the irradiation-induced homogenous clusters.The latter plays a key role in precipitation hardening.This result paves a way to improve the mechanical properties of metallic materials by tailoring the precipitation through irradiation and aging.
基金supported by the National Natural Science Foundation of China(Grant Nos.92163201 and U2067219)Shaanxi Province Youth Innovation Team Project(No.22JP042)+1 种基金Shaanxi Province Innovation Team Project(No.2024RS-CXTD-58)the Fundamental Research Funds for the Central Universities(No.xtr022019004).
文摘The chemical boundaries inside the ultrafine spinodal decomposition structure in metastable β-Ti alloys can act as a new feature to architect heterogeneous microstructures.In this work,we combined two semi-empirical methods,i.e.,the d-electron theory and the e/a electron concentration,to achieve the spinodal decomposition structure in a metastable β Ti-4.5Al-4.5Mo-7V-1.5Cr-1.5Zr(wt.%)alloy.Utilizing the spinodal decomposition structure,the aged Ti-Al-Mo-V-Cr-Zr alloys showed multi-architectured α precipitates spanning from micron-scale(primary α_(p))to nano-scale(secondary α_(s))that were uniformly distributed in the β-domains.Being compared with the forged sample,the multi-scale heterogeneous microstructure enables the aged β-Ti alloy to have ultra-high strength(yield strength ~1366 MPa and ultimate tensile strength ~1424 MPa)and an appreciable ductility(~9.3%).Strengthening models were proposed for the present alloys to estimate the contribution of various microstructural features to the measured yield strength.While the solid solution strengthening,β-spinodal strengthening,and back stress strengthening made comparable contributions to the strength of the forged alloy,the back stress strengthening was the predominant strengthening effect in the aged alloy.This alloy design approach based on chemical boundary engineering to construct multi-architectured α precipitates provided an effective strategy for achieving an outstanding combination of ultra-high strength and ductility in metastable β-Ti alloys.
基金supported by the National Natural Science Foun-dation of China under grant Nos.52231003,52301073,52271049,and 52201063.
文摘One of the most intriguing methods of mitigating the hydrogen embrittlement of steels entails nano-precipitates that can trap H from enriching at vulnerable locations.However,controversial findings have been reported on whether the incoherent NbC precipitates trap hydrogen.Here,by using in-situ scan-ning Kelvin probe force microscopy(SKPFM),we reveal the dynamic interaction of H with the border area of incoherent NbC nanoprecipitates in steel.Results indicate that the interaction between H flux and the interfaces varies amongst different precipitates,implying that H-trapping behaviours of incoherent NbC precipitates could be intrinsically diverse.Potential origins underlying the distinct behaviours are analyzed.
基金supported by the National Key Research and Development Program of China(No.2022YFE0134400)the State Key Laboratory for Advanced Metals and Materials(No.2023-Z05)+1 种基金the National Key Laboratory Foundation of Science and Technology on Materials under Shock and Impact(No.6142902220101)the Hunan Provincial Postgraduate Scientific Research Innovation Project(No.CX20230181).
文摘The coarsening behavior and strengthening effect of L1_(2)-Ni_(3)(Ti,Al)precipitates in a face-centered-cubic(FCC)(FeCoNi)_(92)Al_(2.5)Ti_(5.5) high entropy alloy have been systematically investigated.The coherent L1_(2) precipitates,uniformly distributed throughout the FCC matrix,consistently retain a spherical shape.The coarsening rate coefficient of precipitate is determined by employing the Philippe-Voorhees(PV)model,suggesting excellent thermal stability.Furthermore,the elemental partitioning and compositional evolution of the L1_(2) precipitates is analyzed by atom probe tomography,which identify aluminum(Al)as the slowest diffusion species during the coarsening process.In addition,the precipitation strengthening effect is quantified to ascertain the optimal size of the precipitates.Our study enhances the understanding of precipitate coarsening in high entropy alloys,presenting valuable insights into their thermal stability and mechanical properties.
