Aging prior to twinning deformation was proposed to alter the precipitate orientation of the plate-shapedβ-MgAlfrom(0002)basal planes(named basal plates)to■prismatic planes(named prismatic plates)in AZ31 Mg alloy.Th...Aging prior to twinning deformation was proposed to alter the precipitate orientation of the plate-shapedβ-MgAlfrom(0002)basal planes(named basal plates)to■prismatic planes(named prismatic plates)in AZ31 Mg alloy.The experimental results showed that the compressive yield strength(CYS)of the sample containing prismatic plates increased 40 MPa and the compression ratio raised by 22%compared to that containing basal plates.The underlying strengthening mechanism was analyzed via a yield strengthen(YS)model with a function of grain size,precipitate characters(size,oritention,fraction)and Schmid factor(SF).It revealed that the improvement of CYS was mainly attributed to the altered precipitate orientation and refined grain size produced by twinning deformation.Particularly,the prismatic plates always have a stronger hardening effect on basal slip than basal plates under the same varites of precipitate diameter and SF.Besides,the decreased CRSS ratio of prismatic slip to basal slip revealed that the activity of non-basal slip in Mg alloy might be enhanced.More activated slip systems provided more mobile dislocations,contributing to the large compression ratio of the Mg rolled sheet with prismatic plates.展开更多
The effects of heat treatment on the precipitates and strengthening mechanism in AISI H13 steel were investigated. The results showed that the presence of nanoscale precipitates favorably affected grain refinement and...The effects of heat treatment on the precipitates and strengthening mechanism in AISI H13 steel were investigated. The results showed that the presence of nanoscale precipitates favorably affected grain refinement and improved the yield strength. The volume fraction of precipitates increased from 1.05% to 2.85% during tempering, whereas the average precipitate size first decreased then increased during tempering. Contributions to the yield strength arising from the various mechanisms were calculated quantificationally, and the results demonstrated that grain refinement and dislocation density most strongly influenced the yield strength. In addition, under the interaction of average size and volume fraction, precipitates' contribution to the yield strength ranged from 247.9 to 378.5 MPa. Finally, a root-mean-square summation law of σ = σg + σs +(σd^2 + σp^2)^1/2, where σg, σs, σd, and σp represent the contributions of fine-grain strengthening, solid-solution strengthening, dislocation strengthening, and precipitation strengthening, respectively, was confirmed as the most applicable for AISI H13 steel, which indicates a strong link between precipitates and dislocations in AISI H13 steel.展开更多
Metallic alloys for a given application are usually designed to achieve the desired properties by devising experimentsbased on experience, thermodynamic and kinetic principles, and various modeling and simulation exer...Metallic alloys for a given application are usually designed to achieve the desired properties by devising experimentsbased on experience, thermodynamic and kinetic principles, and various modeling and simulation exercises.However, the influence of process parameters and material properties is often non-linear and non-colligative. Inrecent years, machine learning (ML) has emerged as a promising tool to dealwith the complex interrelation betweencomposition, properties, and process parameters to facilitate accelerated discovery and development of new alloysand functionalities. In this study, we adopt an ML-based approach, coupled with genetic algorithm (GA) principles,to design novel copper alloys for achieving seemingly contradictory targets of high strength and high electricalconductivity. Initially, we establish a correlation between the alloy composition (binary to multi-component) andthe target properties, namely, electrical conductivity and mechanical strength. Catboost, an ML model coupledwith GA, was used for this task. The accuracy of the model was above 93.5%. Next, for obtaining the optimizedcompositions the outputs fromthe initial model were refined by combining the concepts of data augmentation andPareto front. Finally, the ultimate objective of predicting the target composition that would deliver the desired rangeof properties was achieved by developing an advancedMLmodel through data segregation and data augmentation.To examine the reliability of this model, results were rigorously compared and verified using several independentdata reported in the literature. This comparison substantiates that the results predicted by our model regarding thevariation of conductivity and evolution ofmicrostructure and mechanical properties with composition are in goodagreement with the reports published in the literature.展开更多
Considering the components produced by high pressure die casting(HPDC)process usually with ultra-large sizes and complex morphologies,high temperature solid solution treatment is not a suitable method to further impro...Considering the components produced by high pressure die casting(HPDC)process usually with ultra-large sizes and complex morphologies,high temperature solid solution treatment is not a suitable method to further improve their mechanical properties.In this study,two-stage aging treatment with different pre-aging times was designed and employed to further improve the mechanical properties of HPDC Al8SiMgCuZn alloy.The characteristics of precipitates were evaluated by a transmission electron microscope(TEM),and the precipitation strengthening mechanism was discussed.The results reveal that the strengthening is mainly contributed by the precipitation ofβ″phase after two-stage aging,and the number density and size of the precipitates are significantly depended on the pre-aging time.The number density of precipitates is increased with the pre-aging time prolonged from 0 h to 4 h,and then decreases with the further increase of pre-aging time from 4 h to 6 h.The precipitates with the highest density and smallest size are observed after pre-aging for 4 h.After pre-aged at 100℃for 4 h and then artificial aged at 200℃for 30 min,the yield strength of 207 MPa,ultimate tensile strength of 325 MPa and elongation of 7.6%are achieved.展开更多
Precipitation strengthening is a crucial microscopic mechanism for enhancing the strength of magnesium alloys. In order to elucidate the influence of precipitation on the microscopic deformation mechanisms and macrosc...Precipitation strengthening is a crucial microscopic mechanism for enhancing the strength of magnesium alloys. In order to elucidate the influence of precipitation on the microscopic deformation mechanisms and macroscopic mechanical response of magnesium alloys under cyclic loading conditions, we employed a crystal plasticity model to analyze the stress-strain curves, specific crystal plane diffraction intensities, and the temporal evolution of various microscopic deformation mechanisms and twinning volume fractions for an extruded magnesium alloy, AXM10304, containing coherent precipitates. The research findings indicate that precipitation does not fundamentally alter the microscopic mechanisms of this alloy. However, it hinders twinning during the compression stage, mildly promotes detwinning during the tension stage, and enhances tension secondary hardening by elevating the difficulty of activation of the prismatic slip.展开更多
Mg-rare earth(RE)based systems provide several important commercial alloys and many alloy development opportunities for high strength applications,especially in aerospace and defense industries.The phase diagrams,micr...Mg-rare earth(RE)based systems provide several important commercial alloys and many alloy development opportunities for high strength applications,especially in aerospace and defense industries.The phase diagrams,microstructure,and strengthening mechanisms of these multicomponent systems are very complex and often not well understood in literature.We have calculated phase diagrams of important binary,ternary,and multicomponent RE-containing alloy systems,using CALPHAD(CALculation of PHAse Diagrams).Based on these phase diagrams,this paper offers a critical overview on phase equilibria and strengthening mechanisms in these alloy systems,including precipitation,long period stacking order(LPSO),and other intermetallic phases.This review also summarized several promising Mg-RE based cast alloys in comparison with commercial WE54 and WE43 alloys;and explored new strategies for future alloy development for high strength applications.It is pointed out that the combination of precipitation and LPSO phases can lead to superior strength and ductility in Mg-RE based cast alloys.The precipitates and LPSO phases can form a complex three-dimensional network that effectively impedes dislocation motion on the basal and non-basal planes.The LPSO phases can also prevent the coarsening of precipitates when they interact,thus providing good thermal stability at elevated temperatures.Future research is needed to determine how the combination of these two types of phases can be used in alloy design and industrial scale applications.展开更多
Precipitation strengthening provides one of the most widely-used mechanisms for strengthen-ing multi-principal-element alloys(MPEAs).Here,we report dual-morphology B2 precipitates in Co_(36)Cr_(15)Fe_(18)Ni_(18)Al_(8)...Precipitation strengthening provides one of the most widely-used mechanisms for strengthen-ing multi-principal-element alloys(MPEAs).Here,we report dual-morphology B2 precipitates in Co_(36)Cr_(15)Fe_(18)Ni_(18)Al_(8)Ti_(4)Mo_(1)MPEA obtained by thermo-mechanical processing.Electron microscopy charac-terization reveals that the dual-morphology B2 precipitates are either recrystallized B2 particles formed at the grain boundaries or triple junctions with recrystallization process,or rod-like within the non-recrystallized FCC matrix.The dual-morphology B2 precipitates enhance the yield strength and ultimate tensile strength up to 1120 MPa and 1480 MPa,respectively.This work suggests the mechanical proper-ties of the alloy can be optimized by B2 precipitation strengthening to meet the needs of engineering applications.展开更多
The effects of solution and ageing treatment (T6) on microstructure and tensile properties of as-extruded Mg-10Gd-3Y-0.6Zr (mass fraction. %) alloy were investigated. The results show that after T6 treatment, the diam...The effects of solution and ageing treatment (T6) on microstructure and tensile properties of as-extruded Mg-10Gd-3Y-0.6Zr (mass fraction. %) alloy were investigated. The results show that after T6 treatment, the diameter of grain increases to 20 μm. As the second phases dissolve into the matrix, the smaller and denser β′ phases precipitate inside the grains. After T6-treatment, both yield strength (TYS) and ultimate tensile strength (UTS) are increased. Comparing with that in only ageing condition (T5), the UTS and TYS increased from 365 MPa,285 MPa to 400 MPa,310 MPa, respectively, but the elongation decreased from 7.0% to 3.5%. It has been found that the effects of precipitates on the strength are stronger than that of the growth of grain size.展开更多
Phase analysis of titanium in steel has been carried out on thirty samples with different Ticontent from 0. 036 %-0. 204% . The various heat treatments for the samples are to anneal at 1050-1200 ℃ for a while ,follo...Phase analysis of titanium in steel has been carried out on thirty samples with different Ticontent from 0. 036 %-0. 204% . The various heat treatments for the samples are to anneal at 1050-1200 ℃ for a while ,followed by cooling at a rate of 1 . 10, 20 ℃/s ,respectively.It is achieved to separate and determine fine particle TiC ,coarse particle Ti_2CS and TiN ex-tracted from steel by controlling the oxidation potential and acidity of solutions.The results of quantrtative analysis of the individual phase show that 0. 09 %- 0. 13 % Ti-contentis enough to eliminate free nitrogen and transform MnS into Yi_2CS in steel effectively. In the case of0. 06 %- 0. 10 % Ti-content combined with annealing at 1050℃. and quick cooling at 20 ℃/s ,a prop-er amount of fine particle TiC can be precipitated and the rate of TiC (fine )/TiC (total )is high ,which arebeneficial to increase strength and toughness of steel. More Ti-content or cooling slowly will preciprtatemore coarse particle TiC which decreaces toughness severely. The proposed methods for quantitativephase analysis of titanium in steel are given in detail.展开更多
Recent studies have indicated that precipitation-strengthened high-entropy alloys(HEAs)show superior mechanical performance and have been successfully fabricated by additive manufacturing.However,the lack of fatigue a...Recent studies have indicated that precipitation-strengthened high-entropy alloys(HEAs)show superior mechanical performance and have been successfully fabricated by additive manufacturing.However,the lack of fatigue and fracture research has limited the engineering applications of additive manufacturing HEAs.This work explored a dual precipitation-strengthened(FeCoNi)_(86)Al_(7)Ti_(7) HEA with excellent tensile and fatigue strength,prepared through selective laser melting and heat treatment.Compared with the as-built samples,the tensile properties and fatigue endurance limit improved through aging by 48.7%and 30%,respectively.The strengthening mechanism and enhanced fatigue performance were clarified in detail.The improvement in fatigue strength was attributed to the improved resistance of the L1_(2) and L2_(1) precipitates.During deformation,the dislocation shear coherent L1_(2) precipitates reduced slip band energy and inhibited slip band expansion,while the L2_(1) particles acted as obstructions for further slip band propagation,severely limiting the rapid formation and propagation of crack growth.In-situ TEM cyclic tensile-tensile testing also clarified the fatigue crack growth behavior,demonstrating that crack deflection due to L2_(1) precipitate obstruction slowed down the crack growth rate and efficiently promoted the closure of the microcrack tips.This work offers im plications for a new strategy to develop additive manufacturing HEAs.展开更多
Multiphase CrMnFeCoNi high-entropy alloys(HEAs)were prepared by a powder metallurgy process com-bining mechanical alloying(MA)and vacuum hot-pressing sintering(HPS).The single-phase face-centered cubic(FCC)HEA powder ...Multiphase CrMnFeCoNi high-entropy alloys(HEAs)were prepared by a powder metallurgy process com-bining mechanical alloying(MA)and vacuum hot-pressing sintering(HPS).The single-phase face-centered cubic(FCC)HEA powder prepared by MA was sintered into a bulk HEA specimen containing FCC phase matrix along with precipitated M 23 C 6 phase and nanoscaleσphase particles.When the sintering temper-ature was 1223 K,the ultimate strength reaches 1300±11.6 MPa,and the elongation exceeds 4%±0.6%.Microstructural characterization reveals that the formation of nanoscale particles and deformation twins play critical roles in improving the strain hardening(SH)ability.Prolonging the MA time promoted the formation of the precipitated phase and enhanced the SH ability by increasing the number of precip-itated particles.The SH capacity increases significantly with increasing sintering temperature,which is attributed to a significant enhancement in the twinning capacity due to grain growth and the reduced number ofσphase particles.Through systematic studies,the planar glide of dislocations was found to be the main mode of deformation,while deformation twinning appeared as an auxiliary deformation mode when the twinning stress was reached.Although the formation of precipitates leads to grain bound-ary and precipitation strengthening effects,crack initiation is more prominent owing to increased grain boundary brittleness around the precipitated M 23 C 6 phase.The prominence of crack initiation is a contra-diction that must be reconciled with regard to precipitation strengthening.This work serves as a useful reference for the preparation of high-strength HEA parts by powder metallurgy.展开更多
Effect of microstructure on the mechanical properties of a precipitation strengthening Fe-Ni-Co based low expansion alloy,Incoloy 907.has been investigated under different heat treatments.The dispersed γ-phase is fou...Effect of microstructure on the mechanical properties of a precipitation strengthening Fe-Ni-Co based low expansion alloy,Incoloy 907.has been investigated under different heat treatments.The dispersed γ-phase is found to be the principal strengthening phase in the alloy.The microstructure of the alloy with even dispersed fine γ′-phase seems to have the best mechanical properties.However,it will be worsened if the alloy was aged at some higher tem- perature or overaged to precipitate needle-like ε-phase.展开更多
In this article, a quantitative equation was established to determine the relationship between yield strength and composition in nickel base SC superalloys based on Copley Kear precipitation strengthening model. The ...In this article, a quantitative equation was established to determine the relationship between yield strength and composition in nickel base SC superalloys based on Copley Kear precipitation strengthening model. The yield strength of two well known commercial SC superalloys calculated by this equation was compared with experimental data. It was found that the calculated yield strength of these two alloys was fairly correspondent with experimental results reported in the references. This model accurately described the solution strengthening of alloying elements and precipitation strengthening of γ′ phase. Yield strength of SC superalloys can be successfully predicted by this equation.展开更多
Since the 21^(st) century,great attention has been paid to ultra fast cooling(UFC) technology in the whole world.The industries and the research institutions began to carry out investigations on basic theories and ind...Since the 21^(st) century,great attention has been paid to ultra fast cooling(UFC) technology in the whole world.The industries and the research institutions began to carry out investigations on basic theories and industrial applications.Since 2003,the RAL of Northeastern University has made some progresses on microstructure control theories,understanding of strengthening mechanisms and their industrial applications.In this paper,these achievements since the last Baosteel BAC in 2008 will be reported on the industrialization of UFC, strengthening mechanism,development of new steel grades,and so on.展开更多
Recently,researchers have explored the use of precipitation strengthening and finer microstructures with high-density dislocations in additive manufacturing to produce high-entropy alloys(HEAs)with adjustable properti...Recently,researchers have explored the use of precipitation strengthening and finer microstructures with high-density dislocations in additive manufacturing to produce high-entropy alloys(HEAs)with adjustable properties.However,the inherent surface roughness and lack of machinability research in AMed HEAs limit their engineering applications.In this study,we systematically investigated the microstructural characteristics,mechanical properties,and machinability of Fe_(29.3)Co_(28.7)Ni_(28.6)Al_(6.8)Ti_(6.6)(at.%)HEAs with three different structures:single FCC phase cellular(SPC),dual precipitation-strengthened(DPS),and single precipitation-strengthened(SPS).These structures were fabricated by selective laser melting and isothermally annealing at 780 and 940℃.Compared to SPC HEA,DPS HEA exhibits a significant increase in yield strength and ultimate tensile strength but with a dramatic sacrifice in ductility.SPS HEA exhibits similar mechanical properties to SPC HEA due to the pronounced coarsening of L21 precipitates.The ultraprecision machining micro-cutting test showed that SPC HEA had a significant mechanochem-ical effect,as evidenced by a sharp drop in cutting force for inked workpieces,but not DPS HEA.An abnormal finding was that the negligible reflection of cutting force for SPS HEAs suggested a negative mechanochemical effect,even though SPS HEA had equally excellent plasticity like SPC HEA.It was found that nanocrystallization-induced strength enhancement and ductility reduction of SPS HEA lead to chips’deformation dominated by shear avalanche rather than chip folding of SPC HEA,which involves the reduction of surface energy and friction of chips’interfaces.Overall,these results and our research findings may guide the machining of AMed precipitation-strengthened HEAs and accelerate their engineering ap-plication.展开更多
The Cu-containing austenitic heat-resistant steel 18Cr9Ni3CuNbN, which is being used as superheater and reheater tube material for modern ultra-super-critical (USC) power plants all over the world, has been investig...The Cu-containing austenitic heat-resistant steel 18Cr9Ni3CuNbN, which is being used as superheater and reheater tube material for modern ultra-super-critical (USC) power plants all over the world, has been investigated at 650 ℃ long time aging till 10 000 h. SEM, TEM and 3DAP (three dimensional atom probe) have been used to follow microstructural changes with mechanical property variations. Experimental results show that Cu-rich phase and MX precipitate in the grains as well as M 23 C 6 precipitates at grain boundaries are the main precipitation strengthening phases in this steel. Among them Cu-rich phase is the most important strengthening phase. Homogeneous distribution of very fine nano-size Cu-rich phase has been formed at very early stage of 650 ℃ aging (less than 1 h). Cu atoms gradually concentrate to Cu-rich particles and the other elements (such as Fe, Cr, Ni etc) diffuse away from Curich particles to γ-matrix with the increasing of aging time at 650 ? C. The growth rate of Cu-rich phase at 650 ℃ long time aging is very slow and the average diameters of Cu-rich phase have been determined by TEM method. Cu-rich phase keeps in about 30 nm till 650 ℃ aging for 10 000 h. It shows that nano-size Cu-rich phase precipitation strengthening can be kept for long time aging at 650 ℃ because of its excellent stability at high temperatures. According to structure stability study and mechanical properties determination results the Cu-rich phase precipitation sequence and its strengthening mechanism model have been suggested and discussed.展开更多
In the current work,a parallel comparison of the influence of Al,Mo and Ti,on the microstructure and strengthening of the CoCrFeNi alloy was conducted.To achieve this,inconsistencies on variables including the extent ...In the current work,a parallel comparison of the influence of Al,Mo and Ti,on the microstructure and strengthening of the CoCrFeNi alloy was conducted.To achieve this,inconsistencies on variables including the extent of alloying,thermomechanical processing and property-evaluation method were avoided.Microstructurally,following cold-rolling,annealing of the 4 at.%Al-doped alloys at 800-1000℃ did not result in phase separation;nevertheless,that of the 4 at.%Mo-and Ti-doped alloys led to the respective formation ofσandηphase and,consequently,caused extra strengthening through the Orowan dislocation bypassing mechanism.Our systematic qualitative analysis and DFT calculations showed that Al and Ti are more effective than Mo in reducing the stacking fault energy(SFE)of the CoCrFeNi alloy,because they can induce more considerable deformation of electronic density,making the gliding of atomic layers easier.Following identical thermomechnical processing,Al-,Mo-,and Ti-doping causes different extent of solid solution strengthening and grain boundary strengthening.Mo causes the most pronounced solid solution strengthening but does not benefit the grain boundary strengthening;in contrast,the effectiveness of grain boundary strengthening is boosted by the doping Al and Ti.Current analyses support that Labusch instead of Fleischer mechanism is applicable to explain the differences in solid solution strengthening,and the observed differences in grain boundary strengthening arise from the different tendency of Al,Mo and Ti to reduce the SFE of CoCrFeNi.In addition,we determined the value of the dimensionless parameter f in the Labusch model for CoCrFeNi-based alloys and observed a close relation between Hall-Petch slope and SFE.Although more in-depth studies are needed to provide full and mechanistic understandings,both these findings in fact presents significant values toward designing novel singlephase high-strength CoCrFeNi-based alloys through manipulating the solid solution and grain boundary strengthening by compositional tuning.展开更多
Magnesium-lithium(Mg-Li) alloy,as the lightest metal structure material,has unparalleled market prospects in aerospace,weapons and equipment,electronic technology,transportation,and many other fields.However,it is har...Magnesium-lithium(Mg-Li) alloy,as the lightest metal structure material,has unparalleled market prospects in aerospace,weapons and equipment,electronic technology,transportation,and many other fields.However,it is hard to balance the superlight and high strength of Mg-Li alloy,and the inferior high-temperature strength and poor high-temperature stability limit the wide application of Mg-Li alloy.At present,the main methods to improve the mechanical properties of Mg-Li alloy are alloying,grain refinement,and compound strengthening.The domestic and overseas research progress in the strengthening and toughening methods and mechanisms of Mg-Li alloy are reviewed,and the future development of the high strength and high toughness Mg-Li alloy is prospected.展开更多
In this work,the effects of Ce addition(0,0.1 wt%,0.3 wt%,0.5 wt%and 0.7 wt%)on the evolution of microstructure and mechanical properties of 6111 Al alloy and strengthening mechanism of 6111 Al-Ce alloy were systemati...In this work,the effects of Ce addition(0,0.1 wt%,0.3 wt%,0.5 wt%and 0.7 wt%)on the evolution of microstructure and mechanical properties of 6111 Al alloy and strengthening mechanism of 6111 Al-Ce alloy were systematically investigated by a polarizing microscope,a scanning electronic microscope,an energy dispersive spectroscope and a high-resolution transmission electron microscope.The results indicate that with 0.3 wt%Ce addition,theα-Al grains show the equiaxed crystal morphology with the average size decreasing from 137 to 57μm and numerous small AlCeSi phases with lump-like or platelike morphology are distributed closely along the grain boundary.The peak yield strength,ultimate tensile strength and elongation of 6111 Al-Ce alloy reach to 279 MPa,316 MPa and 12.1%,respectively,which is attributed to the grain refinement strengthening and the formation of nanosized Al11Ce3 precipitates.Eventually,this investigation gives us instructive suggestion to prepare the new kind of aluminum alloy with high strength and high ductility.展开更多
The mechanical properties of the hot-rolled plates of Ti steel and Ti-Mo steel after isothermal transformation in a temperature range of 600 700 ℃ for 60 min have been tested, and the microstructures of the matrix an...The mechanical properties of the hot-rolled plates of Ti steel and Ti-Mo steel after isothermal transformation in a temperature range of 600 700 ℃ for 60 min have been tested, and the microstructures of the matrix and the characteristics of precipitated nanometer-sized carbides have also been examined by scanning electron microscopy and transmission electron microscopy. The precipitation regularity of nanometer-sized carbides has been studied by thermodynamic method and the contributions of corresponding strengthening mechanisms to the total yield strength have been calculated. The tensile strength of hot-rolled Ti-Mo ferritie steel can achieve 780 MPa with an elongation of 20.0% after being isothermally treated at 600 ℃ for 60 rain, and the tensile strength of Ti steel is 605 MPa with an elongation of 22.7%, according to the results of tensile tests. The critical nucleation size of (Ti,Mo)C is smaller than that of TiC at a given isothermal temperature, but the nucleation rate of (Ti, Mo)C is larger than that of TiC. The grainrefinement strengthening and precipitation strengthening contribute the main amount of the total yield strength. The major increase in yield strength with the decrease of isothermal temperature results from the contribution of precipi tation strengthening. The contribution of precipitation strengthening to the yield strength of the steels has been esti mated. The ferrite phase can be strengthened by about 400 MPa through precipitation strengthening in Ti-Mo steel isothermally treated at 600 ℃ for 60 rain, which is about 200 MPa higher than that of Ti steel under the same conditions.展开更多
基金the Fundamental Research Funds for the Project of Science&Technology Department of Sichuan Province(2018HH0026)National Natural Science Foundation of China(51701132,U1764253)China Scholarship Council(201907005018)。
文摘Aging prior to twinning deformation was proposed to alter the precipitate orientation of the plate-shapedβ-MgAlfrom(0002)basal planes(named basal plates)to■prismatic planes(named prismatic plates)in AZ31 Mg alloy.The experimental results showed that the compressive yield strength(CYS)of the sample containing prismatic plates increased 40 MPa and the compression ratio raised by 22%compared to that containing basal plates.The underlying strengthening mechanism was analyzed via a yield strengthen(YS)model with a function of grain size,precipitate characters(size,oritention,fraction)and Schmid factor(SF).It revealed that the improvement of CYS was mainly attributed to the altered precipitate orientation and refined grain size produced by twinning deformation.Particularly,the prismatic plates always have a stronger hardening effect on basal slip than basal plates under the same varites of precipitate diameter and SF.Besides,the decreased CRSS ratio of prismatic slip to basal slip revealed that the activity of non-basal slip in Mg alloy might be enhanced.More activated slip systems provided more mobile dislocations,contributing to the large compression ratio of the Mg rolled sheet with prismatic plates.
基金financially supported by the National Natural Science Foundation of China(No.51274031)
文摘The effects of heat treatment on the precipitates and strengthening mechanism in AISI H13 steel were investigated. The results showed that the presence of nanoscale precipitates favorably affected grain refinement and improved the yield strength. The volume fraction of precipitates increased from 1.05% to 2.85% during tempering, whereas the average precipitate size first decreased then increased during tempering. Contributions to the yield strength arising from the various mechanisms were calculated quantificationally, and the results demonstrated that grain refinement and dislocation density most strongly influenced the yield strength. In addition, under the interaction of average size and volume fraction, precipitates' contribution to the yield strength ranged from 247.9 to 378.5 MPa. Finally, a root-mean-square summation law of σ = σg + σs +(σd^2 + σp^2)^1/2, where σg, σs, σd, and σp represent the contributions of fine-grain strengthening, solid-solution strengthening, dislocation strengthening, and precipitation strengthening, respectively, was confirmed as the most applicable for AISI H13 steel, which indicates a strong link between precipitates and dislocations in AISI H13 steel.
文摘Metallic alloys for a given application are usually designed to achieve the desired properties by devising experimentsbased on experience, thermodynamic and kinetic principles, and various modeling and simulation exercises.However, the influence of process parameters and material properties is often non-linear and non-colligative. Inrecent years, machine learning (ML) has emerged as a promising tool to dealwith the complex interrelation betweencomposition, properties, and process parameters to facilitate accelerated discovery and development of new alloysand functionalities. In this study, we adopt an ML-based approach, coupled with genetic algorithm (GA) principles,to design novel copper alloys for achieving seemingly contradictory targets of high strength and high electricalconductivity. Initially, we establish a correlation between the alloy composition (binary to multi-component) andthe target properties, namely, electrical conductivity and mechanical strength. Catboost, an ML model coupledwith GA, was used for this task. The accuracy of the model was above 93.5%. Next, for obtaining the optimizedcompositions the outputs fromthe initial model were refined by combining the concepts of data augmentation andPareto front. Finally, the ultimate objective of predicting the target composition that would deliver the desired rangeof properties was achieved by developing an advancedMLmodel through data segregation and data augmentation.To examine the reliability of this model, results were rigorously compared and verified using several independentdata reported in the literature. This comparison substantiates that the results predicted by our model regarding thevariation of conductivity and evolution ofmicrostructure and mechanical properties with composition are in goodagreement with the reports published in the literature.
基金financially supported by the Natural Science Foundation of Guangdong Province(Nos.2021A151510042,2021A1515011728)the China Postdoctoral Science Foundation(2022M711190)+1 种基金the National Natural Science Foundation of China(No.51875211)the Key Area Research and Development Program of Guangdong Province(No.2020B010186002)。
文摘Considering the components produced by high pressure die casting(HPDC)process usually with ultra-large sizes and complex morphologies,high temperature solid solution treatment is not a suitable method to further improve their mechanical properties.In this study,two-stage aging treatment with different pre-aging times was designed and employed to further improve the mechanical properties of HPDC Al8SiMgCuZn alloy.The characteristics of precipitates were evaluated by a transmission electron microscope(TEM),and the precipitation strengthening mechanism was discussed.The results reveal that the strengthening is mainly contributed by the precipitation ofβ″phase after two-stage aging,and the number density and size of the precipitates are significantly depended on the pre-aging time.The number density of precipitates is increased with the pre-aging time prolonged from 0 h to 4 h,and then decreases with the further increase of pre-aging time from 4 h to 6 h.The precipitates with the highest density and smallest size are observed after pre-aging for 4 h.After pre-aged at 100℃for 4 h and then artificial aged at 200℃for 30 min,the yield strength of 207 MPa,ultimate tensile strength of 325 MPa and elongation of 7.6%are achieved.
文摘Precipitation strengthening is a crucial microscopic mechanism for enhancing the strength of magnesium alloys. In order to elucidate the influence of precipitation on the microscopic deformation mechanisms and macroscopic mechanical response of magnesium alloys under cyclic loading conditions, we employed a crystal plasticity model to analyze the stress-strain curves, specific crystal plane diffraction intensities, and the temporal evolution of various microscopic deformation mechanisms and twinning volume fractions for an extruded magnesium alloy, AXM10304, containing coherent precipitates. The research findings indicate that precipitation does not fundamentally alter the microscopic mechanisms of this alloy. However, it hinders twinning during the compression stage, mildly promotes detwinning during the tension stage, and enhances tension secondary hardening by elevating the difficulty of activation of the prismatic slip.
基金partially funded by the United States Army Research Laboratory (ARL)Terves LLC。
文摘Mg-rare earth(RE)based systems provide several important commercial alloys and many alloy development opportunities for high strength applications,especially in aerospace and defense industries.The phase diagrams,microstructure,and strengthening mechanisms of these multicomponent systems are very complex and often not well understood in literature.We have calculated phase diagrams of important binary,ternary,and multicomponent RE-containing alloy systems,using CALPHAD(CALculation of PHAse Diagrams).Based on these phase diagrams,this paper offers a critical overview on phase equilibria and strengthening mechanisms in these alloy systems,including precipitation,long period stacking order(LPSO),and other intermetallic phases.This review also summarized several promising Mg-RE based cast alloys in comparison with commercial WE54 and WE43 alloys;and explored new strategies for future alloy development for high strength applications.It is pointed out that the combination of precipitation and LPSO phases can lead to superior strength and ductility in Mg-RE based cast alloys.The precipitates and LPSO phases can form a complex three-dimensional network that effectively impedes dislocation motion on the basal and non-basal planes.The LPSO phases can also prevent the coarsening of precipitates when they interact,thus providing good thermal stability at elevated temperatures.Future research is needed to determine how the combination of these two types of phases can be used in alloy design and industrial scale applications.
基金supported by the Central Guidance on Local Science and Technology Development Fund of Hebei Province(No.216Z1012G)the National Natural Science Foundation of China(No.12174274).
文摘Precipitation strengthening provides one of the most widely-used mechanisms for strengthen-ing multi-principal-element alloys(MPEAs).Here,we report dual-morphology B2 precipitates in Co_(36)Cr_(15)Fe_(18)Ni_(18)Al_(8)Ti_(4)Mo_(1)MPEA obtained by thermo-mechanical processing.Electron microscopy charac-terization reveals that the dual-morphology B2 precipitates are either recrystallized B2 particles formed at the grain boundaries or triple junctions with recrystallization process,or rod-like within the non-recrystallized FCC matrix.The dual-morphology B2 precipitates enhance the yield strength and ultimate tensile strength up to 1120 MPa and 1480 MPa,respectively.This work suggests the mechanical proper-ties of the alloy can be optimized by B2 precipitation strengthening to meet the needs of engineering applications.
基金Project supported by program for Changjiang Scholars and Innovative Research Teamin University(IRT0713)National Basic Research Program ofChina (2007CB613702, 2007CB613701)
文摘The effects of solution and ageing treatment (T6) on microstructure and tensile properties of as-extruded Mg-10Gd-3Y-0.6Zr (mass fraction. %) alloy were investigated. The results show that after T6 treatment, the diameter of grain increases to 20 μm. As the second phases dissolve into the matrix, the smaller and denser β′ phases precipitate inside the grains. After T6-treatment, both yield strength (TYS) and ultimate tensile strength (UTS) are increased. Comparing with that in only ageing condition (T5), the UTS and TYS increased from 365 MPa,285 MPa to 400 MPa,310 MPa, respectively, but the elongation decreased from 7.0% to 3.5%. It has been found that the effects of precipitates on the strength are stronger than that of the growth of grain size.
文摘Phase analysis of titanium in steel has been carried out on thirty samples with different Ticontent from 0. 036 %-0. 204% . The various heat treatments for the samples are to anneal at 1050-1200 ℃ for a while ,followed by cooling at a rate of 1 . 10, 20 ℃/s ,respectively.It is achieved to separate and determine fine particle TiC ,coarse particle Ti_2CS and TiN ex-tracted from steel by controlling the oxidation potential and acidity of solutions.The results of quantrtative analysis of the individual phase show that 0. 09 %- 0. 13 % Ti-contentis enough to eliminate free nitrogen and transform MnS into Yi_2CS in steel effectively. In the case of0. 06 %- 0. 10 % Ti-content combined with annealing at 1050℃. and quick cooling at 20 ℃/s ,a prop-er amount of fine particle TiC can be precipitated and the rate of TiC (fine )/TiC (total )is high ,which arebeneficial to increase strength and toughness of steel. More Ti-content or cooling slowly will preciprtatemore coarse particle TiC which decreaces toughness severely. The proposed methods for quantitativephase analysis of titanium in steel are given in detail.
基金financially supported by the National Natural Sci-ence Foundation of China(Nos.51971123 and 51925103)the In-novation Program of Shanghai Municipal Education Commission(No.2021-01-07-00-09-E00114)+3 种基金the Program 173(No.2020-JCIQ-ZD-186-01)the Key Program of Science and Technology of Yun nan Province(No.202002AB080001-2)the 111 Project(No.D16002)the Space Utilization System of China Manned Space Engineer-ing(No.KJZ-YY-NCL08)。
文摘Recent studies have indicated that precipitation-strengthened high-entropy alloys(HEAs)show superior mechanical performance and have been successfully fabricated by additive manufacturing.However,the lack of fatigue and fracture research has limited the engineering applications of additive manufacturing HEAs.This work explored a dual precipitation-strengthened(FeCoNi)_(86)Al_(7)Ti_(7) HEA with excellent tensile and fatigue strength,prepared through selective laser melting and heat treatment.Compared with the as-built samples,the tensile properties and fatigue endurance limit improved through aging by 48.7%and 30%,respectively.The strengthening mechanism and enhanced fatigue performance were clarified in detail.The improvement in fatigue strength was attributed to the improved resistance of the L1_(2) and L2_(1) precipitates.During deformation,the dislocation shear coherent L1_(2) precipitates reduced slip band energy and inhibited slip band expansion,while the L2_(1) particles acted as obstructions for further slip band propagation,severely limiting the rapid formation and propagation of crack growth.In-situ TEM cyclic tensile-tensile testing also clarified the fatigue crack growth behavior,demonstrating that crack deflection due to L2_(1) precipitate obstruction slowed down the crack growth rate and efficiently promoted the closure of the microcrack tips.This work offers im plications for a new strategy to develop additive manufacturing HEAs.
基金supported by the National Natu-ral Science Foundation of China(Nos.52061021,51861016,and 51871132)the Science and Technology Major Project of Yun-nan Province(Nos.202202AG050004,202002AB080001)+2 种基金the Young and Middle-Aged Academic and Technical Leaders Reserve Talent Project(No.202005AC160039)support by the Ministry of Science and Higher Educa-tion of the Russian Federation in the framework of the Increase Competitiveness Program of NUST«MISiS»(No.K2-2020-046)financial support from the China Scholarship Council(CSC,No.201906220226).
文摘Multiphase CrMnFeCoNi high-entropy alloys(HEAs)were prepared by a powder metallurgy process com-bining mechanical alloying(MA)and vacuum hot-pressing sintering(HPS).The single-phase face-centered cubic(FCC)HEA powder prepared by MA was sintered into a bulk HEA specimen containing FCC phase matrix along with precipitated M 23 C 6 phase and nanoscaleσphase particles.When the sintering temper-ature was 1223 K,the ultimate strength reaches 1300±11.6 MPa,and the elongation exceeds 4%±0.6%.Microstructural characterization reveals that the formation of nanoscale particles and deformation twins play critical roles in improving the strain hardening(SH)ability.Prolonging the MA time promoted the formation of the precipitated phase and enhanced the SH ability by increasing the number of precip-itated particles.The SH capacity increases significantly with increasing sintering temperature,which is attributed to a significant enhancement in the twinning capacity due to grain growth and the reduced number ofσphase particles.Through systematic studies,the planar glide of dislocations was found to be the main mode of deformation,while deformation twinning appeared as an auxiliary deformation mode when the twinning stress was reached.Although the formation of precipitates leads to grain bound-ary and precipitation strengthening effects,crack initiation is more prominent owing to increased grain boundary brittleness around the precipitated M 23 C 6 phase.The prominence of crack initiation is a contra-diction that must be reconciled with regard to precipitation strengthening.This work serves as a useful reference for the preparation of high-strength HEA parts by powder metallurgy.
文摘Effect of microstructure on the mechanical properties of a precipitation strengthening Fe-Ni-Co based low expansion alloy,Incoloy 907.has been investigated under different heat treatments.The dispersed γ-phase is found to be the principal strengthening phase in the alloy.The microstructure of the alloy with even dispersed fine γ′-phase seems to have the best mechanical properties.However,it will be worsened if the alloy was aged at some higher tem- perature or overaged to precipitate needle-like ε-phase.
文摘In this article, a quantitative equation was established to determine the relationship between yield strength and composition in nickel base SC superalloys based on Copley Kear precipitation strengthening model. The yield strength of two well known commercial SC superalloys calculated by this equation was compared with experimental data. It was found that the calculated yield strength of these two alloys was fairly correspondent with experimental results reported in the references. This model accurately described the solution strengthening of alloying elements and precipitation strengthening of γ′ phase. Yield strength of SC superalloys can be successfully predicted by this equation.
文摘Since the 21^(st) century,great attention has been paid to ultra fast cooling(UFC) technology in the whole world.The industries and the research institutions began to carry out investigations on basic theories and industrial applications.Since 2003,the RAL of Northeastern University has made some progresses on microstructure control theories,understanding of strengthening mechanisms and their industrial applications.In this paper,these achievements since the last Baosteel BAC in 2008 will be reported on the industrialization of UFC, strengthening mechanism,development of new steel grades,and so on.
基金the National Natural Science Foundation of China(Nos.52271149,51971123,and 51925103)the Innovation Program of Shanghai Municipal Edu-cation Commission(No.2021-01-07-00-09-E00114)+4 种基金the financial support from Program 173(No.2020-JCIQ-ZD-186-01)111project(No.D16002)the Space Utilization System of China Manned Space Engineering(No.KJZ-YY-NCL08)the Singapore Ministry of Education Academic Research Funds(Grant Nos.MOE-T2EP50120-0010,MOE-T2EP50220-0010,and A-8001225-00-00)Long Xu thanks the China Scholarship Council(CSC)Scholarship,China(CSC No.202106890047).
文摘Recently,researchers have explored the use of precipitation strengthening and finer microstructures with high-density dislocations in additive manufacturing to produce high-entropy alloys(HEAs)with adjustable properties.However,the inherent surface roughness and lack of machinability research in AMed HEAs limit their engineering applications.In this study,we systematically investigated the microstructural characteristics,mechanical properties,and machinability of Fe_(29.3)Co_(28.7)Ni_(28.6)Al_(6.8)Ti_(6.6)(at.%)HEAs with three different structures:single FCC phase cellular(SPC),dual precipitation-strengthened(DPS),and single precipitation-strengthened(SPS).These structures were fabricated by selective laser melting and isothermally annealing at 780 and 940℃.Compared to SPC HEA,DPS HEA exhibits a significant increase in yield strength and ultimate tensile strength but with a dramatic sacrifice in ductility.SPS HEA exhibits similar mechanical properties to SPC HEA due to the pronounced coarsening of L21 precipitates.The ultraprecision machining micro-cutting test showed that SPC HEA had a significant mechanochem-ical effect,as evidenced by a sharp drop in cutting force for inked workpieces,but not DPS HEA.An abnormal finding was that the negligible reflection of cutting force for SPS HEAs suggested a negative mechanochemical effect,even though SPS HEA had equally excellent plasticity like SPC HEA.It was found that nanocrystallization-induced strength enhancement and ductility reduction of SPS HEA lead to chips’deformation dominated by shear avalanche rather than chip folding of SPC HEA,which involves the reduction of surface energy and friction of chips’interfaces.Overall,these results and our research findings may guide the machining of AMed precipitation-strengthened HEAs and accelerate their engineering ap-plication.
基金supported by the National Natural Science Foundation of China (No.50931003)
文摘The Cu-containing austenitic heat-resistant steel 18Cr9Ni3CuNbN, which is being used as superheater and reheater tube material for modern ultra-super-critical (USC) power plants all over the world, has been investigated at 650 ℃ long time aging till 10 000 h. SEM, TEM and 3DAP (three dimensional atom probe) have been used to follow microstructural changes with mechanical property variations. Experimental results show that Cu-rich phase and MX precipitate in the grains as well as M 23 C 6 precipitates at grain boundaries are the main precipitation strengthening phases in this steel. Among them Cu-rich phase is the most important strengthening phase. Homogeneous distribution of very fine nano-size Cu-rich phase has been formed at very early stage of 650 ℃ aging (less than 1 h). Cu atoms gradually concentrate to Cu-rich particles and the other elements (such as Fe, Cr, Ni etc) diffuse away from Curich particles to γ-matrix with the increasing of aging time at 650 ? C. The growth rate of Cu-rich phase at 650 ℃ long time aging is very slow and the average diameters of Cu-rich phase have been determined by TEM method. Cu-rich phase keeps in about 30 nm till 650 ℃ aging for 10 000 h. It shows that nano-size Cu-rich phase precipitation strengthening can be kept for long time aging at 650 ℃ because of its excellent stability at high temperatures. According to structure stability study and mechanical properties determination results the Cu-rich phase precipitation sequence and its strengthening mechanism model have been suggested and discussed.
基金financially supported by the National Natural Science Foundation of China(No.51901077)the Science and Technology Innovation Platform and Talent Plan of Hunan Province(No.2019RS1020)+1 种基金the open project of State Key Laboratory of Advanced Design and Manufacturing for Vehicle Body(No.71865003)Hunan University,Changsha,China.YG acknowledges support from NSF DMR 1809640。
文摘In the current work,a parallel comparison of the influence of Al,Mo and Ti,on the microstructure and strengthening of the CoCrFeNi alloy was conducted.To achieve this,inconsistencies on variables including the extent of alloying,thermomechanical processing and property-evaluation method were avoided.Microstructurally,following cold-rolling,annealing of the 4 at.%Al-doped alloys at 800-1000℃ did not result in phase separation;nevertheless,that of the 4 at.%Mo-and Ti-doped alloys led to the respective formation ofσandηphase and,consequently,caused extra strengthening through the Orowan dislocation bypassing mechanism.Our systematic qualitative analysis and DFT calculations showed that Al and Ti are more effective than Mo in reducing the stacking fault energy(SFE)of the CoCrFeNi alloy,because they can induce more considerable deformation of electronic density,making the gliding of atomic layers easier.Following identical thermomechnical processing,Al-,Mo-,and Ti-doping causes different extent of solid solution strengthening and grain boundary strengthening.Mo causes the most pronounced solid solution strengthening but does not benefit the grain boundary strengthening;in contrast,the effectiveness of grain boundary strengthening is boosted by the doping Al and Ti.Current analyses support that Labusch instead of Fleischer mechanism is applicable to explain the differences in solid solution strengthening,and the observed differences in grain boundary strengthening arise from the different tendency of Al,Mo and Ti to reduce the SFE of CoCrFeNi.In addition,we determined the value of the dimensionless parameter f in the Labusch model for CoCrFeNi-based alloys and observed a close relation between Hall-Petch slope and SFE.Although more in-depth studies are needed to provide full and mechanistic understandings,both these findings in fact presents significant values toward designing novel singlephase high-strength CoCrFeNi-based alloys through manipulating the solid solution and grain boundary strengthening by compositional tuning.
基金the National Natural Science Foundation of China(Nos.51771115,51775334,51821001 and U2037601)the Joint Fund for Space Science and Technology(No.6141B06310106)。
文摘Magnesium-lithium(Mg-Li) alloy,as the lightest metal structure material,has unparalleled market prospects in aerospace,weapons and equipment,electronic technology,transportation,and many other fields.However,it is hard to balance the superlight and high strength of Mg-Li alloy,and the inferior high-temperature strength and poor high-temperature stability limit the wide application of Mg-Li alloy.At present,the main methods to improve the mechanical properties of Mg-Li alloy are alloying,grain refinement,and compound strengthening.The domestic and overseas research progress in the strengthening and toughening methods and mechanisms of Mg-Li alloy are reviewed,and the future development of the high strength and high toughness Mg-Li alloy is prospected.
基金Project supported by the National Natural Science Foundation of China(U1664254,51701085,51801074,52071158)the Natural Science Foundation for Young of Jiangsu Province,China(BK20160516,BK20170543)the Six Talents Peak Project of Jiangsu Province(2018-XCL-202)。
文摘In this work,the effects of Ce addition(0,0.1 wt%,0.3 wt%,0.5 wt%and 0.7 wt%)on the evolution of microstructure and mechanical properties of 6111 Al alloy and strengthening mechanism of 6111 Al-Ce alloy were systematically investigated by a polarizing microscope,a scanning electronic microscope,an energy dispersive spectroscope and a high-resolution transmission electron microscope.The results indicate that with 0.3 wt%Ce addition,theα-Al grains show the equiaxed crystal morphology with the average size decreasing from 137 to 57μm and numerous small AlCeSi phases with lump-like or platelike morphology are distributed closely along the grain boundary.The peak yield strength,ultimate tensile strength and elongation of 6111 Al-Ce alloy reach to 279 MPa,316 MPa and 12.1%,respectively,which is attributed to the grain refinement strengthening and the formation of nanosized Al11Ce3 precipitates.Eventually,this investigation gives us instructive suggestion to prepare the new kind of aluminum alloy with high strength and high ductility.
基金Sponsored by National Natural Science Foundation of China(51271035)
文摘The mechanical properties of the hot-rolled plates of Ti steel and Ti-Mo steel after isothermal transformation in a temperature range of 600 700 ℃ for 60 min have been tested, and the microstructures of the matrix and the characteristics of precipitated nanometer-sized carbides have also been examined by scanning electron microscopy and transmission electron microscopy. The precipitation regularity of nanometer-sized carbides has been studied by thermodynamic method and the contributions of corresponding strengthening mechanisms to the total yield strength have been calculated. The tensile strength of hot-rolled Ti-Mo ferritie steel can achieve 780 MPa with an elongation of 20.0% after being isothermally treated at 600 ℃ for 60 rain, and the tensile strength of Ti steel is 605 MPa with an elongation of 22.7%, according to the results of tensile tests. The critical nucleation size of (Ti,Mo)C is smaller than that of TiC at a given isothermal temperature, but the nucleation rate of (Ti, Mo)C is larger than that of TiC. The grainrefinement strengthening and precipitation strengthening contribute the main amount of the total yield strength. The major increase in yield strength with the decrease of isothermal temperature results from the contribution of precipi tation strengthening. The contribution of precipitation strengthening to the yield strength of the steels has been esti mated. The ferrite phase can be strengthened by about 400 MPa through precipitation strengthening in Ti-Mo steel isothermally treated at 600 ℃ for 60 rain, which is about 200 MPa higher than that of Ti steel under the same conditions.