Recent studies have confirmed the critical and essential role of elemental hydrolysis in metallogenic processes,such as metal migration and precipitation.However,the kinetic processes,characteristics,and formation mec...Recent studies have confirmed the critical and essential role of elemental hydrolysis in metallogenic processes,such as metal migration and precipitation.However,the kinetic processes,characteristics,and formation mechanisms of hydrolyzed precipitates require further comprehensive investigation.This paper is based on a systematic investigation of the hydrolysis mechanisms of Pb and Zn in various systems under ambient temperature and pressure,the storage conditions of the hydrolyzed precipitates,and the characterization of these precipitates.The results indicate that the hydrolysis behaviors of Pb and Zn exhibit significant differences across various systems.Within the monometallic regime,there is a pronounced disparity in the hydrolysis rates between Pb ions and Zn ions.Pb ions demonstrate a substantially higher degree of hydrolysis,a trend that persists over time and remains largely unaffected by the fluid retention or isolation"phenomenon in the surrounding environment.Both hydrolytic precipitation rates were observed to decrease in the mixed system,with Zn ions exhibiting less reduction than Pb ions.After hydrolysis,hydrolyzed precipitates can remain in the fluid environment for extended periods of time,which can lead to re-dissolution.Over time,this re-dissolution can increase,eventually leading to significant loss of hydrolyzed precipitates.The hydrolyzed precipitates obtained from the experiments primarily consisted of alkaline carbonates of Pb and Zn.Notably,the crystalline characteristics of the hydrolysis products of Pb and Zn ions exhibited significant differences across various experimental systems;however,the crystallographic characteristics of the primary hydrolysis products are essentially identical to those of their corresponding natural counterparts.Based on the findings from physical phase analysis and previous research,it is concluded that the hydrolysis process consists of three main stages:oxides/hydroxides,carbonates,and alkali carbonates.In the Pb-Zn-NaCl-H_(2)O system,the proportion of the basic carbonate products of Pb and Zn is 6:2.This research offers an in-depth analysis of the hydrolysis dynamics of lead and zinc under ambient temperature and pressure conditions.Furthermore,it characterizes the crystallization features of the hydrolyzed precipitates and reconstructs the three stages of the formation process.This study holds significant scientific value for understanding the metallogenic mechanisms of Pb and Zn.展开更多
The nano-scale L1_(2)-Ni_(3)Al precipitates significantly contribute to thermal stability of alumina-forming austenitic(AFA)steels.The coarsening behavior of L1_(2)-Ni_(3)Al precipitates in AFA steels during isotherma...The nano-scale L1_(2)-Ni_(3)Al precipitates significantly contribute to thermal stability of alumina-forming austenitic(AFA)steels.The coarsening behavior of L1_(2)-Ni_(3)Al precipitates in AFA steels during isothermal aging with considering the influence of alloying elements was investigated.The results show that the coarsening rate of L1_(2)-Ni_(3)Al precipitates increases with co-additions of Ni and Cu,and especially,the increase of Cu content promotes the nucleation of L1_(2)-Ni_(3)Al precipitates.A dynamic competition exists between Lifshitz-Slyozov-Wagner theory and transient interface diffusion-controlled theory for coarsening behavior of L1_(2)-Ni_(3)Al precipitates with duration of isothermal aging.Additionally,the transition from L1_(2)-Ni_(3)Al precipitates to B2-NiAl precipitates during isothermal aging results in the formation of a depleted zone of L1_(2)-Ni_(3)Al precipitates around B2-NiAl precipitates,which inhibits the growth of L1_(2)-Ni_(3)Al precipitates.The coarsening of L1_(2)-Ni_(3)Al precipitates significantly contributes to the yield strength of AFA steels.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
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
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
High-strength Al-Zn-Mg-Cu alloys are widely utilized,but their strength deteriorates as strengthening precipitates coarsen rapidly at elevated temperatures,limiting their applications above 150℃.This study systematic...High-strength Al-Zn-Mg-Cu alloys are widely utilized,but their strength deteriorates as strengthening precipitates coarsen rapidly at elevated temperatures,limiting their applications above 150℃.This study systematically investigates the microstructure evolution and its impact on the properties of peak-aged Al-Zn-Mg-Cu alloys with varying Zn/Mg ratios during thermal exposure at a series of temperatures from 150 to 300℃ for 500 h.The results reveal that alloys A1 and A2 with an optimal Zn/Mg ratio(1.50-2.14)and relatively lower(Zn+Mg)content(7.0-8.8 wt.%),exhibit superior heat resistance properties compared to the other three alloys.Despite having lower strength relative to alloys with higher solute content,peak-aged alloys A1 and A2 retain the highest strength after thermal exposure.This performance is attributed to the high proportion(over 80%)of T'/T phases in the precipitates for alloys A1 and A2,which demonstrate better thermal stability in comparison to η'/η phases.Additionally,the lower solute content reduces the driving force for diffusion of Zn and Mg atoms,thus inhibiting the coarsening of precipitates.Moreover,the study elucidates that the coarsening mechanism of precipitates transitions from interfacial diffusion control at 150℃ to matrix diffusion control at 200-300℃.These insights into the composition-dependent coarsening behavior of precipitates in dual-phase strengthened Al-Zn-Mg-Cu alloys offer valuable guidance for designing heat-resistant aluminum alloys with enhanced performance at elevated temperatures.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
Precipitation strengthening is a critical strategy for developing high-performance Cu alloys that combine exceptional strength with high conductivity.However,this method often loses effectiveness at elevated temperatu...Precipitation strengthening is a critical strategy for developing high-performance Cu alloys that combine exceptional strength with high conductivity.However,this method often loses effectiveness at elevated temperatures due to the poor thermal stability of the precipitates,which tend to coarsen rapidly,leading to accelerated mechanical degradation.In this study,we introduce a CuCrZrY alloy that demonstrates remarkable structural and mechanical stability at high temperatures.Notably,after annealing at 550℃ for 500 h,only 18.8%of the grains were recrystallized.Through a combination of experimental investigations and first-principles calculations,we discovered that the strong solute-vacancy binding energy of Y in Cu significantly impedes bulk diffusion of solute,thereby inhibiting precipitate coarsening and recrystallization.The coarsening rate constant for the CuCrZrY alloy was found to be approximately half that of the CuCrZr alloy.During prolonged annealing,the formation of sub-grains via recovery enhances boundary diffusion,leading to a layered distribution of precipitates.The recrystallization model further elucidates the interplay between eutectic phases,precipitates,and the migration of recrystallization boundaries.Initially,eutectic phases contribute to the accumulation of geometrically necessary dislocations during rolling,which triggers recrystallization in the early stages of annealing.Additionally,the triple junctions of sub-grain and recrystallization boundaries facilitate precipitate coarsening,thereby reducing the pinning force.Consequently,the CuCrZrY alloy undergoes a unique recrystallization process characterized by discontinuous precipitate coarsening and a cycle of pinning-depinning-repinning of recrystallized grain boundaries.These insights provide valuable guidance for designing Cu alloys with stable microstructural and mechanical properties under prolonged high-temperature conditions.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
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 addition of Ce significantly enhances cleanliness of steel and modifies precipitation phases.However,there are differences in the effects of different alloy systems,especially its role in M54 steel is insufficient...The addition of Ce significantly enhances cleanliness of steel and modifies precipitation phases.However,there are differences in the effects of different alloy systems,especially its role in M54 steel is insufficiently understood.This study investigates the evolution of inclusions and precipitation phases in M54 steel ingots with varying Ce additions.Results indicate that the addition of Ce reduces the content of impurity elements(O and S)and transforms Mg and Al inclusions into Ce inclusions,which is due to the stronger affinity between Ce and impurity elements such as O and S.Ce inclusions serve as nucleation sites for dendrites,reducing secondary dendrite arm spacing.In addition,these inclusions and Cecontaining precipitated phase also act as nucleation sites for carbide precipitates,effectively refining their distribution by reducing growth spaces and increasing nucleation density.Notably,as Ce content increases from 0 to 0.01 wt%,the precipitation phase content decreases significantly but rises slightly with further increases in Ce content due to the formation of additional Ce-containing precipitates.By quantitatively comparing the dendrite arm spacing,cleanliness,content and size of precipitated phase,it is determined that the optimum addition amount of Ce for M54 steel is about 0.01 wt%.展开更多
A mathematical model coupling flow,solidification,strain-stress,and interface failure was developed.Following identification of crack source type through thermal tensile experiment and validation by strain-stress comp...A mathematical model coupling flow,solidification,strain-stress,and interface failure was developed.Following identification of crack source type through thermal tensile experiment and validation by strain-stress comparison,the model was used to investigate slab cracking tendency near precipitated phases,considering various locations,sizes and shapes of them.The results show that the jet from submerged entry nozzle creates a“double roll”flow pattern during continuous casting,resulting in more uniform temperature distributions at slab corner and wide surface center compared with narrow surface center.Consequently,precipitated phases,particularly those located on the narrow surface,readily induce stress concentration and thus increase cracking tendency.A smaller precipitated phase size can reduce the stress concentration zone,while a more spherical shape can distribute surrounding stress along its surface and lower the internal stress within it,thereby decreasing the risk of slab cracking during continuous casting.The optimal precipitated phase exhibits a spherical or ellipsoidal shape with a major axis of less than 5µm,minimizing its potential to initiate cracks.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
Non-oriented silicon steels with both excellent magnetic properties and high strength are essential for the drive motors of new energy vehicles.However,achieving a balance between strength and magnetic properties is a...Non-oriented silicon steels with both excellent magnetic properties and high strength are essential for the drive motors of new energy vehicles.However,achieving a balance between strength and magnetic properties is a challenging task.This study successfully developed non-oriented silicon steel that met these demanding requirements by utilizing the coherent nano-Cu-rich phases precipitated during aging.In the current investigation,the evolution of precipitation during the aging process of Cu-alloyed non-oriented silicon steel is revealed as:BCC Cu-rich cluster(Fe:Cu>1)→B2 FeCu cluster(Fe:Cu approaches 1)→BCC Cu cluster(Fe:Cu<1)→Twinned 9R Cu→Detwinned 9R Cu.Notably,the 9R Cu precipitated in the later stage of aging was coarse and incoherent with the matrix,offering minimal strengthening benefits while considerably deteriorated the magnetic properties.Conversely,the other three phases that formed in the early stage of aging were fine,dispersed,and coherent with the matrix,effectively enhancing the yield strength of the steel with minimal negative impact on its magnetic properties.The total increment of yield strength attributed to BCC Cu-rich clusters,B2 FeCu clusters,and BCC Cu clusters were 207,304,and 374 MPa,respectively.The strengthening mechanism operated primarily through the cutting mechanism,which was dominated by the modulus difference strengthening and coherent strain strengthening.Moreover,a unique ordered strengthening of approximately 207 MPa arose from the ordered B2 FeCu clusters.Thus,the steel aged for 3–30 min with the precipitation of B2 FeCu clusters and BCC Cu clusters exhibited the most favorable overall performance with a yield strength of 750–800 MPa,P1.0/400 of 16.3–18.3 W kg^(−1),and B5000 of 1.641–1.656 T.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
Boundary engineering has proven effective in enhancing the thermoelectric performance of materials.SnSe,known for its low thermal conductivity,has garnered significant interest;however,its application is hindered by p...Boundary engineering has proven effective in enhancing the thermoelectric performance of materials.SnSe,known for its low thermal conductivity,has garnered significant interest;however,its application is hindered by poor electrical conductivity.Herein,the Ag_(8)GeSe_(6) is introduced into the p-type polycrystalline SnSe matrix to optimize the thermoelectric performance,and the in-situ Ag_(2)Se precipitates are formed in grain boundaries,which play dual roles,acting as an electron attraction center for improving hole concentration and a phonon scattering center for reducing lattice thermal conductivity.It effectively decouples the thermal and electrical transport properties to optimize the thermoelectric performance.Importantly,the amount of Ag_(2)Se can be controlled by adjusting the amount of Ag_(8)GeSe_(6) added to the SnSe matrix.The introduction of Ag_(8)GeSe_(6) enhances electrical conductivity due to the increased hole carrier caused by the introduced Ag+and the formed electron attraction center(in-situ Ag_(2)Se precipitates).Based on the DFT calculations,the band gap of the Ag_(8)GeSe_(6)-doped samples is considerably decreased,facilitating carrier transport.As a result,the electrical transport properties increase to 808μW m^(−1) K^(−2) at 823 K for SnSe+0.5 wt%Ag_(8)GeSe_(6).In addition,in-situ Ag_(2)Se precipitates in grain boundaries strongly enhance phonon scattering,causing a decrease in lattice thermal conductivity.Furthermore,the presence of defects contributes to a reduction in lattice thermal conductivity.Specifically,the thermal conductivity of SnSe+1.0 wt%Ag_(8)GeSe_(6) decreases to 0.29 W m^(−1) K^(−1) at 823 K.Consequently,SnSe+0.5 wt%Ag_(8)GeSe_(6) obtains a high ZT value of 1.7 at 823 K and maintains a high average ZT value of 0.57 over the temperature range of 323−773 K.Additionally,the mechanical properties of Ag_(8)GeSe_(6)-doped also show an improvement.These advancements can be applied to energy supply applications during deep space exploration.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
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
基金financed jointly by the National Natural Science Foundation of China(42472127,42172086)the Yunnan Major Science and Technological Projects(202202AG050014)+2 种基金the Yunnan Major Project of Basic Research(202401BN070001-002)Yunnan Mineral Resources Prediction and Evaluation Engineering Research Center(2011)Innovation Team Program of Kunming University of Science and Technology,Yunnan Province。
文摘Recent studies have confirmed the critical and essential role of elemental hydrolysis in metallogenic processes,such as metal migration and precipitation.However,the kinetic processes,characteristics,and formation mechanisms of hydrolyzed precipitates require further comprehensive investigation.This paper is based on a systematic investigation of the hydrolysis mechanisms of Pb and Zn in various systems under ambient temperature and pressure,the storage conditions of the hydrolyzed precipitates,and the characterization of these precipitates.The results indicate that the hydrolysis behaviors of Pb and Zn exhibit significant differences across various systems.Within the monometallic regime,there is a pronounced disparity in the hydrolysis rates between Pb ions and Zn ions.Pb ions demonstrate a substantially higher degree of hydrolysis,a trend that persists over time and remains largely unaffected by the fluid retention or isolation"phenomenon in the surrounding environment.Both hydrolytic precipitation rates were observed to decrease in the mixed system,with Zn ions exhibiting less reduction than Pb ions.After hydrolysis,hydrolyzed precipitates can remain in the fluid environment for extended periods of time,which can lead to re-dissolution.Over time,this re-dissolution can increase,eventually leading to significant loss of hydrolyzed precipitates.The hydrolyzed precipitates obtained from the experiments primarily consisted of alkaline carbonates of Pb and Zn.Notably,the crystalline characteristics of the hydrolysis products of Pb and Zn ions exhibited significant differences across various experimental systems;however,the crystallographic characteristics of the primary hydrolysis products are essentially identical to those of their corresponding natural counterparts.Based on the findings from physical phase analysis and previous research,it is concluded that the hydrolysis process consists of three main stages:oxides/hydroxides,carbonates,and alkali carbonates.In the Pb-Zn-NaCl-H_(2)O system,the proportion of the basic carbonate products of Pb and Zn is 6:2.This research offers an in-depth analysis of the hydrolysis dynamics of lead and zinc under ambient temperature and pressure conditions.Furthermore,it characterizes the crystallization features of the hydrolyzed precipitates and reconstructs the three stages of the formation process.This study holds significant scientific value for understanding the metallogenic mechanisms of Pb and Zn.
基金financial supports from the National Natural Science Foundation of China(Nos.52471004,52171107,52201203)the Industry-University-Research Cooperation Project of Hebei Based Universities and Shijiazhuang City(No.241791237A)the Fundamental Research Funds for the Central Universities(No.N2423030)。
文摘The nano-scale L1_(2)-Ni_(3)Al precipitates significantly contribute to thermal stability of alumina-forming austenitic(AFA)steels.The coarsening behavior of L1_(2)-Ni_(3)Al precipitates in AFA steels during isothermal aging with considering the influence of alloying elements was investigated.The results show that the coarsening rate of L1_(2)-Ni_(3)Al precipitates increases with co-additions of Ni and Cu,and especially,the increase of Cu content promotes the nucleation of L1_(2)-Ni_(3)Al precipitates.A dynamic competition exists between Lifshitz-Slyozov-Wagner theory and transient interface diffusion-controlled theory for coarsening behavior of L1_(2)-Ni_(3)Al precipitates with duration of isothermal aging.Additionally,the transition from L1_(2)-Ni_(3)Al precipitates to B2-NiAl precipitates during isothermal aging results in the formation of a depleted zone of L1_(2)-Ni_(3)Al precipitates around B2-NiAl precipitates,which inhibits the growth of L1_(2)-Ni_(3)Al precipitates.The coarsening of L1_(2)-Ni_(3)Al precipitates significantly contributes to the yield strength of AFA steels.
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 Natural Science Foundation of Chongqing(Nos.CSTB2022NSCQ-LZX0002 and CSTB2022NSCQ-BHX0624)the Chongqing Key Project for Technological Innovation and Application(No.CSTB2022TIAD-KPX0073)+1 种基金the Opening Project of State Key Laboratory for Advanced Metals and Materials(No.2022-Z03)the Science and Technology Research Program of Chongqing Municipal Education Commission(No.KJQN202200810).
文摘High-strength Al-Zn-Mg-Cu alloys are widely utilized,but their strength deteriorates as strengthening precipitates coarsen rapidly at elevated temperatures,limiting their applications above 150℃.This study systematically investigates the microstructure evolution and its impact on the properties of peak-aged Al-Zn-Mg-Cu alloys with varying Zn/Mg ratios during thermal exposure at a series of temperatures from 150 to 300℃ for 500 h.The results reveal that alloys A1 and A2 with an optimal Zn/Mg ratio(1.50-2.14)and relatively lower(Zn+Mg)content(7.0-8.8 wt.%),exhibit superior heat resistance properties compared to the other three alloys.Despite having lower strength relative to alloys with higher solute content,peak-aged alloys A1 and A2 retain the highest strength after thermal exposure.This performance is attributed to the high proportion(over 80%)of T'/T phases in the precipitates for alloys A1 and A2,which demonstrate better thermal stability in comparison to η'/η phases.Additionally,the lower solute content reduces the driving force for diffusion of Zn and Mg atoms,thus inhibiting the coarsening of precipitates.Moreover,the study elucidates that the coarsening mechanism of precipitates transitions from interfacial diffusion control at 150℃ to matrix diffusion control at 200-300℃.These insights into the composition-dependent coarsening behavior of precipitates in dual-phase strengthened Al-Zn-Mg-Cu alloys offer valuable guidance for designing heat-resistant aluminum alloys with enhanced performance at elevated temperatures.
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 National Natural Science Foundation of China(No.U21B2066).
文摘Precipitation strengthening is a critical strategy for developing high-performance Cu alloys that combine exceptional strength with high conductivity.However,this method often loses effectiveness at elevated temperatures due to the poor thermal stability of the precipitates,which tend to coarsen rapidly,leading to accelerated mechanical degradation.In this study,we introduce a CuCrZrY alloy that demonstrates remarkable structural and mechanical stability at high temperatures.Notably,after annealing at 550℃ for 500 h,only 18.8%of the grains were recrystallized.Through a combination of experimental investigations and first-principles calculations,we discovered that the strong solute-vacancy binding energy of Y in Cu significantly impedes bulk diffusion of solute,thereby inhibiting precipitate coarsening and recrystallization.The coarsening rate constant for the CuCrZrY alloy was found to be approximately half that of the CuCrZr alloy.During prolonged annealing,the formation of sub-grains via recovery enhances boundary diffusion,leading to a layered distribution of precipitates.The recrystallization model further elucidates the interplay between eutectic phases,precipitates,and the migration of recrystallization boundaries.Initially,eutectic phases contribute to the accumulation of geometrically necessary dislocations during rolling,which triggers recrystallization in the early stages of annealing.Additionally,the triple junctions of sub-grain and recrystallization boundaries facilitate precipitate coarsening,thereby reducing the pinning force.Consequently,the CuCrZrY alloy undergoes a unique recrystallization process characterized by discontinuous precipitate coarsening and a cycle of pinning-depinning-repinning of recrystallized grain boundaries.These insights provide valuable guidance for designing Cu alloys with stable microstructural and mechanical properties under prolonged high-temperature conditions.
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 supported by the National Natural Science Foundation of China(52374330,52325406)。
文摘The addition of Ce significantly enhances cleanliness of steel and modifies precipitation phases.However,there are differences in the effects of different alloy systems,especially its role in M54 steel is insufficiently understood.This study investigates the evolution of inclusions and precipitation phases in M54 steel ingots with varying Ce additions.Results indicate that the addition of Ce reduces the content of impurity elements(O and S)and transforms Mg and Al inclusions into Ce inclusions,which is due to the stronger affinity between Ce and impurity elements such as O and S.Ce inclusions serve as nucleation sites for dendrites,reducing secondary dendrite arm spacing.In addition,these inclusions and Cecontaining precipitated phase also act as nucleation sites for carbide precipitates,effectively refining their distribution by reducing growth spaces and increasing nucleation density.Notably,as Ce content increases from 0 to 0.01 wt%,the precipitation phase content decreases significantly but rises slightly with further increases in Ce content due to the formation of additional Ce-containing precipitates.By quantitatively comparing the dendrite arm spacing,cleanliness,content and size of precipitated phase,it is determined that the optimum addition amount of Ce for M54 steel is about 0.01 wt%.
基金supported by National Natural Science Foundation of China(Nos.52325406 and 52374330)Fundamental Research Funds for the Central Universities(No.N2225046).
文摘A mathematical model coupling flow,solidification,strain-stress,and interface failure was developed.Following identification of crack source type through thermal tensile experiment and validation by strain-stress comparison,the model was used to investigate slab cracking tendency near precipitated phases,considering various locations,sizes and shapes of them.The results show that the jet from submerged entry nozzle creates a“double roll”flow pattern during continuous casting,resulting in more uniform temperature distributions at slab corner and wide surface center compared with narrow surface center.Consequently,precipitated phases,particularly those located on the narrow surface,readily induce stress concentration and thus increase cracking tendency.A smaller precipitated phase size can reduce the stress concentration zone,while a more spherical shape can distribute surrounding stress along its surface and lower the internal stress within it,thereby decreasing the risk of slab cracking during continuous casting.The optimal precipitated phase exhibits a spherical or ellipsoidal shape with a major axis of less than 5µm,minimizing its potential to initiate cracks.
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supported by the National Natural Science Foundation of China(Nos.52074200,52274393,and 12102310)the Key R&D Program of Hubei Province(No.2023BAB141)the State Key Laboratory for Advanced Metals and Materials(No.2023-ZD03).
文摘Non-oriented silicon steels with both excellent magnetic properties and high strength are essential for the drive motors of new energy vehicles.However,achieving a balance between strength and magnetic properties is a challenging task.This study successfully developed non-oriented silicon steel that met these demanding requirements by utilizing the coherent nano-Cu-rich phases precipitated during aging.In the current investigation,the evolution of precipitation during the aging process of Cu-alloyed non-oriented silicon steel is revealed as:BCC Cu-rich cluster(Fe:Cu>1)→B2 FeCu cluster(Fe:Cu approaches 1)→BCC Cu cluster(Fe:Cu<1)→Twinned 9R Cu→Detwinned 9R Cu.Notably,the 9R Cu precipitated in the later stage of aging was coarse and incoherent with the matrix,offering minimal strengthening benefits while considerably deteriorated the magnetic properties.Conversely,the other three phases that formed in the early stage of aging were fine,dispersed,and coherent with the matrix,effectively enhancing the yield strength of the steel with minimal negative impact on its magnetic properties.The total increment of yield strength attributed to BCC Cu-rich clusters,B2 FeCu clusters,and BCC Cu clusters were 207,304,and 374 MPa,respectively.The strengthening mechanism operated primarily through the cutting mechanism,which was dominated by the modulus difference strengthening and coherent strain strengthening.Moreover,a unique ordered strengthening of approximately 207 MPa arose from the ordered B2 FeCu clusters.Thus,the steel aged for 3–30 min with the precipitation of B2 FeCu clusters and BCC Cu clusters exhibited the most favorable overall performance with a yield strength of 750–800 MPa,P1.0/400 of 16.3–18.3 W kg^(−1),and B5000 of 1.641–1.656 T.
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 Outstanding Youth Fund of Yunnan Province(Grant No.202201AV070005)the National Natural Science Foundation of China(Grant No.52162029)the National Key R&D Program of China(Grant No.2022YFF0503804).
文摘Boundary engineering has proven effective in enhancing the thermoelectric performance of materials.SnSe,known for its low thermal conductivity,has garnered significant interest;however,its application is hindered by poor electrical conductivity.Herein,the Ag_(8)GeSe_(6) is introduced into the p-type polycrystalline SnSe matrix to optimize the thermoelectric performance,and the in-situ Ag_(2)Se precipitates are formed in grain boundaries,which play dual roles,acting as an electron attraction center for improving hole concentration and a phonon scattering center for reducing lattice thermal conductivity.It effectively decouples the thermal and electrical transport properties to optimize the thermoelectric performance.Importantly,the amount of Ag_(2)Se can be controlled by adjusting the amount of Ag_(8)GeSe_(6) added to the SnSe matrix.The introduction of Ag_(8)GeSe_(6) enhances electrical conductivity due to the increased hole carrier caused by the introduced Ag+and the formed electron attraction center(in-situ Ag_(2)Se precipitates).Based on the DFT calculations,the band gap of the Ag_(8)GeSe_(6)-doped samples is considerably decreased,facilitating carrier transport.As a result,the electrical transport properties increase to 808μW m^(−1) K^(−2) at 823 K for SnSe+0.5 wt%Ag_(8)GeSe_(6).In addition,in-situ Ag_(2)Se precipitates in grain boundaries strongly enhance phonon scattering,causing a decrease in lattice thermal conductivity.Furthermore,the presence of defects contributes to a reduction in lattice thermal conductivity.Specifically,the thermal conductivity of SnSe+1.0 wt%Ag_(8)GeSe_(6) decreases to 0.29 W m^(−1) K^(−1) at 823 K.Consequently,SnSe+0.5 wt%Ag_(8)GeSe_(6) obtains a high ZT value of 1.7 at 823 K and maintains a high average ZT value of 0.57 over the temperature range of 323−773 K.Additionally,the mechanical properties of Ag_(8)GeSe_(6)-doped also show an improvement.These advancements can be applied to energy supply applications during deep space exploration.
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.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.
