The differences in damage values,residual stresses,microstructure and mechanical properties of Ti–6Al–4V alloy under hammer forging and press forging were explored through physical experiments and numerical simulati...The differences in damage values,residual stresses,microstructure and mechanical properties of Ti–6Al–4V alloy under hammer forging and press forging were explored through physical experiments and numerical simulations.The results showed that the temperature field and equivalent strain field of forgings under the hammer forging process were more uniformly distributed,resulting in smaller surface cracks and better residual stress distribution.The impact dynamic loading of hammer forging leads to forgings with higher dislocation densities,while the stabilized strain rate of press forging results in forgings exhibiting finer grain sizes.In this context,the yield strength enhancement of forgings by both processes was nearly identical,while the forgings demonstrated more excellent elongation under the hammer forging process.Additionally,increasing the number of blows in the hammer forging process or enhancing the loading rate in the press forging process can optimize the residual stress distribution of the forgings while simultaneously promoting dislocation multiplication and grain refinement.展开更多
This study systematically investigated the microstructure,mechanical properties,and corrosion behavior of an extruded Zn-0.2Mg alloy processed by multi-directional forging(MDF)at 100℃.The mean grain size was remarkab...This study systematically investigated the microstructure,mechanical properties,and corrosion behavior of an extruded Zn-0.2Mg alloy processed by multi-directional forging(MDF)at 100℃.The mean grain size was remarkably decreased from 17.2±0.5µm to 1.9±0.3µm,and 84.4%of the microstructure was occupied by grains of below 1µm in size after applying three MDF passes.Electron backscattered difraction examinations revealed that continuous dynamic recrystallization,progressive lattice rotation,and particle-stimulated nucleation mechanisms were recognized as contributing to microstructural evolution.Furthermore,transmission electron microscopy results showed that nanoparticles of Mg/Zn dynamically formed under high strain MDF,while the initial extrusion fber texture was altered to be<0001>parallel to the fnal forging axis.A synergistic efect of grain refnement,texture evolution,second-phase precipitates,and dislocation strengthening resulted in an increased ultimate tensile strength of 232±5 MPa after three MDF passes.However,this was accompanied by a reduction in the elongation(8±2.1%).Additionally,a high corrosion rate of 0.59 mm/year was measured for the experimental alloy fabricated by 3 MDF passes.In agreement with the latter,electrochemical impedance spectroscopy results indicated that the grain refnement improved the passivation kinetics of the oxide layer.展开更多
Digital modeling and autonomous control of the die forging process are significant challenges in realizing high-quality intelli-gent forging of components.Using the die forging of AA2014 aluminum alloy as a case study...Digital modeling and autonomous control of the die forging process are significant challenges in realizing high-quality intelli-gent forging of components.Using the die forging of AA2014 aluminum alloy as a case study,a machine-learning-assisted method for di-gital modeling of the forging force and autonomous control in response to forging parameter disturbances was proposed.First,finite ele-ment simulations of the forging processes were conducted under varying friction factors,die temperatures,billet temperatures,and for-ging velocities,and the sample data,including process parameters and forging force under different forging strokes,were gathered.Pre-diction models for the forging force were established using the support vector regression algorithm.The prediction error of F_(f),that is,the forging force required to fill the die cavity fully,was as low as 4.1%.To further improve the prediction accuracy of the model for the ac-tual F_(f),two rounds of iterative forging experiments were conducted using the Bayesian optimization algorithm,and the prediction error of F_(f) in the forging experiments was reduced from 6.0%to 1.5%.Finally,the prediction model of F_(f) combined with a genetic algorithm was used to establish an autonomous optimization strategy for the forging velocity at each stage of the forging stroke,when the billet and die temperatures were disturbed,which realized the autonomous control in response to disturbances.In cases of−20 or−40℃ reductions in the die and billet temperatures,forging experiments conducted with the autonomous optimization strategy maintained the measured F_(f) around the target value of 180 t,with the relative error ranging from−1.3%to+3.1%.This work provides a reference for the study of di-gital modeling and autonomous optimization control of quality factors in the forging process.展开更多
Magnesium alloy thin-walled cylindrical components with the advantages of high specific stiffness and strength present broad prospect for the lightweight of aerospace components.However,poor formability resulting from...Magnesium alloy thin-walled cylindrical components with the advantages of high specific stiffness and strength present broad prospect for the lightweight of aerospace components.However,poor formability resulting from the hexagonal close-packed crystal structure in magnesium alloy puts forwards a great challenge for thin-walled cylindrical components fabrication,especially for extreme structure with the thicknesschanging web and the high thin-wall.In this research,an ZK61 magnesium alloy thin-walled cylindrical component was successfully fabricated by two-step forging,i.e.,the pre-forging and final-forging is mainly used for wed and thin-wall formation,respectively.Microstructure and mechanical properties at the core,middle and margin of the web and the thin-wall of the pre-forged and final-forged components are studied in detail.Due to the large strain-effectiveness and metal flow along the radial direction(RD),the grains of the web are all elongated along RD for the pre-forged component,where an increasingly elongated trend is found from the core to the margin of the wed.A relatively low recrystallized degree occurs during pre-forging,and the web at different positions are all with prismatic and pyramid textures.During finalforging,the microstructures of the web and the thin-wall are almost equiaxed due to the remarkable occurrence of dynamic recrystallization.Similarity,except for few basal texture of the thin-wall,only prismatic and pyramid textures are found for the final-forged component.Compared with the initial billet,an obviously improved mechanical isotropy is achieved during pre-forging,which is well-maintained during final-forging.展开更多
The mechanical properties,microstructure and second phase precipitation behavior of flange forgings for high-pressure hydrogen storage vessels at different tempering temperatures(620–700℃)were studied.The results sh...The mechanical properties,microstructure and second phase precipitation behavior of flange forgings for high-pressure hydrogen storage vessels at different tempering temperatures(620–700℃)were studied.The results showed that when tempered at 620–680°C,the main microstructure of the test steel was tempered sorbite,and the main microstructure of tempered steel changed to martensite at 700℃.At 700℃,the dislocation density increased and some retained austenite existed.With the tempering temperature increasing,the yield strength showed a decreasing trend,the formation of fresh martensite made the tensile strength first decrease and then increase slightly,the impact energy at−40℃increased first and then decreased,and the impact energy at 660℃had the maximum value.The precipitates of MC type were mainly(Mo,V,Ti)C.The test steel had excellent strength and toughness matching at 660℃tempering,the tensile strength at different cross section locations was above 750 MPa,the impact energy was above 200 J at−40℃,and the relative percentage reduction of area(ZH2/ZN2)was above 75%at hydrogen environment of 6.3 MPa.展开更多
The homogenized Mg−5.6Gd−0.8Zn(wt.%)alloys were treated with water cooling and furnace cooling to obtain specimens without and with the 14H long-period stacking ordered(LPSO)phase.Subsequently,multi-directional forgin...The homogenized Mg−5.6Gd−0.8Zn(wt.%)alloys were treated with water cooling and furnace cooling to obtain specimens without and with the 14H long-period stacking ordered(LPSO)phase.Subsequently,multi-directional forging(MDF)experiments were carried out.The microstructure and mechanical properties of different regions(the center,middle and edge regions)in the MDFed alloys were systematically investigated,and the effect of LPSO phase on them was discussed.The results show that the alloys in different regions undergo significant grain refinement during the MDF process.Inhomogeneous microstructures with different degrees of dynamic recrystallization(DRX)are formed,resulting in microhardness heterogeneity.The alloy with the LPSO phase has higher microstructure homogeneity,a higher degree of recrystallization,and better comprehensive mechanical properties than the alloy without the LPSO phase.The furnace-cooled alloy after 18 passes of MDF has the best comprehensive mechanical properties,with an ultimate compressive strength of 488 MPa,yield strength of 258 MPa,and fracture strain of 21.2%.DRX behavior is closely related to the LPSO phase and deformation temperature.The kinked LPSO phase can act as a potential nucleation site for DRX grains,while the fragmented LPSO phase promotes DRX nucleation through the particle-stimulated nucleation mechanism.展开更多
This study investigates the differences in microstructural control between cryogenic forging combined with pre-deformation(PCF)and traditional thermal forging(TTF)for 7050 aluminum forgings intended for aerospace appl...This study investigates the differences in microstructural control between cryogenic forging combined with pre-deformation(PCF)and traditional thermal forging(TTF)for 7050 aluminum forgings intended for aerospace applications.The PCF process,utilizing cryogenic deformation,significantly refines the coarse grains at the surface of the forgings,resulting in a finer and more uniform microstructure,thereby effectively addressing the issue of surface coarse grains associated with traditional methods.The findings indicate that the PCF process can accumulate higher stored energy,facilitating static recrystallization(SRX)during subsequent heat treatment and enhancing the microstructural uniformity.Utilizing various analytical techniques,including optical microscopy(OM),electron backscatter diffraction(EBSD),and transmission electron microscopy(TEM).This study reveals the superiority of the PCF process in terms of strain accumulation,dislocation density,and grain refinement.In conclusion,this method offers advantages in enhancing the performance and microstructural uniformity of 7050 aluminum forgings,presenting new opportunities for applications in the aluminum forging industry.展开更多
In-situ TiB_(2)/Al–Cu composite was processed by multidirectional forging(MDF)for six passes.The microstructure evolution of the forged workpiece was examined across various regions.The mechanical properties of the a...In-situ TiB_(2)/Al–Cu composite was processed by multidirectional forging(MDF)for six passes.The microstructure evolution of the forged workpiece was examined across various regions.The mechanical properties of the as-cast and MDFed composites were compared,and their strengthening mechanisms were analyzed.Results indicate that the grain refinement achieved through the MDF process is mainly due to the subdivision of the original grains through mechanical geometric fragmentation and the occurrence of dynamic recrystallization(DRX).DRX grains are formed through discontinuous DRX,continuous DRX,and recrystallization induced by particle-stimulated nucleation.A rise in accumulated equivalent strain(Σ?ε)results in finerα-Al grains and a more uniform distribution of TiB_(2)particles,which enhance the Vickers hardness of the composite.In addition,the tensile properties of the MDFed composite significantly improve compared with those of the as-cast composites,with ultimate tensile strength and yield strength increasing by 51.2%and 54%,respectively.This enhancement is primarily due to grain refinement strengthening and dislocation strengthening achieved by the MDF process.展开更多
The superplasticity of the Mg−8.59Gd−3.85Y−1.14Zn−0.49Zr alloy was investigated before and after multi-directional forging(MDF)and the mechanisms affecting superplastic deformation were analyzed.The results indicate t...The superplasticity of the Mg−8.59Gd−3.85Y−1.14Zn−0.49Zr alloy was investigated before and after multi-directional forging(MDF)and the mechanisms affecting superplastic deformation were analyzed.The results indicate that after MDF at a temperature of 350℃and strain rates of 0.1 and 0.01 s^(−1)(1-MDFed and 2-MDFed),the superplasticity of the alloy can be significantly improved.The elongations of the MDFed alloys exceed 400%under the strain rate of 6.06×10^(−4)s^(−1)and temperatures of 350,375,and 400℃,and reach the maximum values of 766%(1-MDFed)and 693%(2-MDFed)at 375℃.The grain boundary sliding of the MDFed alloy is sufficient,and the energy barrier of deformation decreases.Theβphase limits the grain growth and promotes dynamic recrystallization,maintaining the stability of the fine-grained structure during superplastic deformation.Several Y-rich phases nucleate in the high-strain region(i.e.,the final fracture region)at high temperatures,accelerating the fracture of the specimen.展开更多
The microstructure and mechanical properties of the Ti-5Al-5Mo-5V-1Cr-1Fe(Ti-55511)alloy under different strains were investigated through the design of step-shaped die forging.The results indicate that continuous dyn...The microstructure and mechanical properties of the Ti-5Al-5Mo-5V-1Cr-1Fe(Ti-55511)alloy under different strains were investigated through the design of step-shaped die forging.The results indicate that continuous dynamic recrystallization(CDRX)and discontinuous dynamic recrystallization(DDRX)occur in the high strain region.The orientation of the grains produced by CDRX is random and does not weaken the fiber texture.<100>-oriented grains expand gradually with increasing strain,thereby enhancing the strength of{100}texture.Significant anisotropic mechanical properties are observed in the large strain region and analyzed through in-situ tensile experiments.When the loading direction is parallel to the longitudinal(L)direction,strain concentration is observed near the dynamically recrystallized(DRXed)grains and inside grains oriented along<100>,leading to crack initiation.Furthermore,the small angle between the loading direction and the c-axis hinders the activation of prismatic and basal slip,thereby enhancing the strength.When the loading direction is parallel to the short transverse(ST)direction,cracks are initiated not only within grains oriented along<100>,but also at the grain boundaries.Regarding impact toughness,the elongatedβgrains in the L direction enhance the resistance to crack propagation.展开更多
Today,I want to share how international standards can forge trust and fuel innovation,laying the foundation for a future where AI benefits everyone,everywhere.First,AI standards,developed jointly by ISO and IEC-the In...Today,I want to share how international standards can forge trust and fuel innovation,laying the foundation for a future where AI benefits everyone,everywhere.First,AI standards,developed jointly by ISO and IEC-the International Electrotechnical Commission-help build global trust and enable responsible innovation by bringing clarity and coherence to an ever-changing AI landscape.As developments in AI continue to emerge at speed,regulation is struggling to keep up and the proliferation of competing standards has created confusion rather than clarity.ISO and our partner IEC are addressing this challenge through the work of our expert committee on AI,SC 42,which takes a holistic,cohesive approach to AI standardization.展开更多
The deformation mechanism,microstructure evolution,and precipitation behavior of a Mg-8.9Gd-1.8Y-0.5Zr-0.2Ag(wt.%)alloy multi-directionally forged at three different temperatures were investigated.As the forging tempe...The deformation mechanism,microstructure evolution,and precipitation behavior of a Mg-8.9Gd-1.8Y-0.5Zr-0.2Ag(wt.%)alloy multi-directionally forged at three different temperatures were investigated.As the forging temperature increases,the particle-stimulated nucleation(PSN)effect diminishes as the num-ber of dynamic precipitates decreases,pyramidal slip is activated,grain boundary migration accelerates,and continuous dynamic recrystallization(CDRX)dominates.The microstructures varied greatly,although fine-grained structures were formed at all different forging temperatures.Competitive precipitation be-tween dynamic precipitate growth,dislocation-induced precipitation,and homogeneous precipitation was observed after aging treatment.Among them,the medium temperature(748 K)forged and aged alloy ex-hibits the best mechanical performance,with an ultimate tensile strength of 436 MPa,and elongation of 16.3%.The calculation indicates that the mixed precipitation structure containing theβprecipitate band provides a 35%higher strengthening contribution than the typical homogeneously distributed precipi-tates.The formation of precipitation-free zones(PFZs)ensures that aging will not cause a dramatic de-crease in ductility,which provides a reference for the industrial preparation of high-performance wrought Mg-Gd series alloys.展开更多
The effect of forging on the microstructure and texture evolution of a high Nb containing Ti-45Al-7Nb-0.3W(at.%)alloy was investigated by X-ray diffractometer(XRD),scanning electron microscopy(SEM),and transmission el...The effect of forging on the microstructure and texture evolution of a high Nb containing Ti-45Al-7Nb-0.3W(at.%)alloy was investigated by X-ray diffractometer(XRD),scanning electron microscopy(SEM),and transmission electron microscopy(TEM).The results show that the as-cast alloy is mainly composed of α_(2)/γ lamellar colonies with a mean size of 70μm,but the hot-forged pancake displays a near duplex microstructure(DP).Kinking and bending of lamellar colonies,deformation twinning and dynamic recrystallization(DRX)occur during hot forging.Meanwhile,dense dislocations in theβphase after forging suggest that the high-temperature β phase with a disordered structure is favorable for improving the hot-workability of the alloy.Unlike the common TiAl casting texture,the solidification process of the investigated as-cast alloy with high Nb content is completely via the β phase region,resulting in the formation of a<110>γ fiber texture where the<110>γ aligns parallel to the heat-flow direction.In comparison,the relatively strong<001>and weak<302>texture components in the as-forged alloy are attributed to the deformation twinning.After annealing,static recrystallization occurs at the twin boundary and intersections,which weakens the deformation texture.展开更多
The effect of die forging on the microstructure evolution and deformation behavior of metastable β-titanium alloy Ti55511 was investigated by electron backscatter diffraction.Before die forging,the alloy Ti55511 was ...The effect of die forging on the microstructure evolution and deformation behavior of metastable β-titanium alloy Ti55511 was investigated by electron backscatter diffraction.Before die forging,the alloy Ti55511 was subjected to multi-pass forging to optimize the microstructural heterogeneity(texture)which can cause mechanical behavior anisotropy of titanium alloys.Results show that after die forging,Ti55511 components exhibit different microstructures and textures in different local areas.No<100>fiber texture is found in all areas with different degrees of deformation.Dynamic recrystallization occurs in the area where large strain occurs during the early stage of die forging.Basket-weave microstructure forms in most local areas.展开更多
Gradient microstructure modification is a cost-efficient strategy for high strength without compromising ductility,which is urgently needed in the fundamental science of engineering materials.In this study,heterogeneo...Gradient microstructure modification is a cost-efficient strategy for high strength without compromising ductility,which is urgently needed in the fundamental science of engineering materials.In this study,heterogeneous structures of AZ61 alloy bars with anisotropic gradients(with different grain size distributions from the surface to the center)were observed to exhibit strong strength-ductility synergies under different deformation tem peratures.The results reveal that the grain refinement process under mediumlow temperature deformation conditions(≤350℃)consists of four transition stages along the radial direction,i.e.,twin activations and deformation band formations,dislocation cells and pile-ups,ultrafine sub-grains,and randomly orientated quasi-micron grains.Different deformation temperatures have a great influence on twin activations and deformation band formations,and the high temperature can easily provoke the initiation of non-basal slip.The deformation bands were determined as a primary nucleation site due to their highly unstable dislocation hindrance ability.Analysis in combination with the Radial forging(RF)deformation process,the differences of dynamic precipitates can be attributed to microstructural difference and solubility limit of Al at different tem peratures.By summarizing the tensile test results,the sample forged at 350℃exhibited the best strength-ductility synergy,exhibiting the highest elongation(EL)of 23.2%with a 251 MPa yield strength(YS)and 394 MPa ultimate tensile strength(UTS)in center region,and combined with the highest strength value of 256 MPa YS and 420 MPa UTS in the center region,while the EL was slightly degraded to 19.8%.展开更多
Mo element was added to cobalt-based alloy L605,and cold forging deformation was performed.The effects of the addition and cold forging deformation on the microstructure and mechanical properties of the alloy were stu...Mo element was added to cobalt-based alloy L605,and cold forging deformation was performed.The effects of the addition and cold forging deformation on the microstructure and mechanical properties of the alloy were studied by thermodynamic calculation,electron backscatter diffraction,transmission electron microscopy,and X-ray diffraction.The stacking fault energy(SFE)of the alloy decreased after the addition,and the formation of stacking faults and intersections were promoted to improve the strength and hardness.The tensile strength of the alloy with Mo increased from 1190 to 1702 MPa after 24%cold deformation,producing significant work hardening.The strengthening mechanism is strain-induced martensitic transformation(SIMT)and deformation twinning.The alloy,combined with Mo and after 24%deformation,had both high strength and ductility in comparison with the original cobalt-based alloy L605.This is attributed to the lower SFE which caused the increase in stacking fault density.During the tensile process,theε-hcp phase was easily generated at the stacking fault to reduce the stress concentration and increase the ductility.Controlling SIMT by adjusting the density of stacking faults can improve the mechanical properties of cobalt-based alloys.Theε-hcp phase,the interaction between deformation twins and dislocations,and the interaction between e-hcp phases during cold forging deformation caused local stress concentration,lowering ductility and toughness.展开更多
Understanding the non-equilibrium phase transition mechanism is critical to controlling the transform-ing microstructures and thus material performance.In order to improve the problem of low room-temperature ductility...Understanding the non-equilibrium phase transition mechanism is critical to controlling the transform-ing microstructures and thus material performance.In order to improve the problem of low room-temperature ductility of TiAl alloys with traditional microstructures,a two-step forging with an interme-diate heat preservation process is proposed to prepare a hybrid microstructure via non-equilibrium phase transition in this study.This hybrid microstructure is composed ofβ_(0)/γlamellar colony,a structure with innerα_(2)/γand outerβ_(0)/γlamellae surrounded byβ_(0)phase,a structure ofγgrains embedded withinα_(2)/γlamellar colony,and some granularβ_(0)withinγphase.This hybrid microstructure exhibits excellent room-temperature mechanical properties with a total elongation to failure of 2.15%and tensile strength of 920 MPa.Furthermore,the evolution mechanisms of these various structures are analyzed from the perspective of solute element diffusion and distribution in front of the phase transition interface.Aggre-gation of V element in front of theγgrowth interface induces the elemental reaction deviating from the equilibrium phase transitionα→α_(2)+γ,andα→β(β_(0))+γtransition occurs,resulting in the formation ofβ(β_(0))/γlamellar colony.During hot forging,α→α_(2)+γtransition occurs to generateα_(2)/γlamellae in the initial transition stage(I)of solute diffusion.In the stable stage(II),the content of V element in front of the growth interface ofγlamellae increases to∼18.41%,andα→β(β_(0))+γtransition occurs,soβ(β_(0))/γlamellae are formed outside theα_(2)/γlamellar colony.In the final stage(III),the remainingαphase is less,and the diffusion of the V element is hindered,causing a sudden increase of the V element inαphase,resulting in the remainingαphase transformed into irregularβ(β_(0))phase.Finally,the structure with innerα_(2)/γand outerβ_(0)/γlamellae surrounded byβ_(0)phase is formed.Moreover,adjusting the cooling rate realizes the precise controlling of theα_(2)/γ,β_(0)/γlamellar size and content of irregularβ_(0)phase based on the solute element distribution equation.Additionally,the structure ofγgrain embedded withinα_(2)/γlamellar colony is obtained.β(β_(0))grains nucleate and grow withinα_(2)/γlamellar colony throughα_(2)+γ→β(β_(0))+γphase transition and the coarseα_(2)lamellae are decomposed into fineα_(2)andγlamellae in parallel.Then,β(β_(0))→γphase transition occurs,resulting in the formation ofγgrains.Finally,the structure ofγgrains embedded withinα_(2)/γlamellar colony is formed,and someβ(β_(0))phases are mixed.This work clearly reveals the mystery of various complex phase transition processes and results inβ-γTiAl alloy.Moreover,this design strategy of forging process and controlling the microstructure should be extendable to other TiAl systems and provides a promising new route to solve the low room-temperature ductility of TiAl alloy.展开更多
In this work,we successfully fabricate an ultra-high strength Mg-11Gd-3Y-0.5Zr alloy with ultimate tensile strength of 523 MPa and enhanced ductility via cost-effective bi-directional forging (BDF) and subsequent anne...In this work,we successfully fabricate an ultra-high strength Mg-11Gd-3Y-0.5Zr alloy with ultimate tensile strength of 523 MPa and enhanced ductility via cost-effective bi-directional forging (BDF) and subsequent annealing heat treatments.To elucidate the role of BDF and gain a fundamental understanding of the remarkable simultaneous increase of strength and ductility,systematic microstructure characterization and analysis are performed.It is revealed that the double-peak basal texture,with basal poles located at the center of two mutually perpendicular forging directions,serves as an essential factor for the strength-ductility synergy of the Mg-11Gd-3Y-0.5Zr alloy processed with BDF.Roles of the double-peak basal texture in overcoming the strength-ductility trade-off include promoting non-basal slip,increasing ductility,and enlarging the Hall-Petch effect along the sample elongation direction while reducing the extent of anisotropy in critical resolved shear stresses of different slip systems.This study demonstrates that texture engineering is a powerful strategy to control magnesium alloy performance and BDF is a promising processing technique for enhancing mechanical properties of magnesium alloys.展开更多
In this work,a new strategy for achieving ultrahigh strength in the coarse-grained Mg-Gd binary alloy via utilizing recrystallization texture hardening and maximizing precipitation strengthening has been reported.Forg...In this work,a new strategy for achieving ultrahigh strength in the coarse-grained Mg-Gd binary alloy via utilizing recrystallization texture hardening and maximizing precipitation strengthening has been reported.Forging at a much high temperature suppresses dynamic precipitation,enabling the super-saturation of Gd atoms in Mg matrix.This facilitates the formation of fully recrystallized grains with strong texture and induces an exceptionally high precipitation hardening in the following ageing.Therefore,the forged Mg-13Gd sample exhibited extraordinary tensile yield strength(TYS)of∼430 MPa,in which ageing-induced TYS increment exceeds∼210 MPa,as the highest record so far in precipitation-hardened Mg communities.These results provide important theoretical guidance for fabricating the large section and high-strength Mg components for industrial applications.展开更多
In order to enhance the fatigue properties of metallic materials,a feasible rationale is to delay or prevent the interior and surface fatigue crack initiation.Based on this rationale,the study investigates the approac...In order to enhance the fatigue properties of metallic materials,a feasible rationale is to delay or prevent the interior and surface fatigue crack initiation.Based on this rationale,the study investigates the approach of improving the very high cycle fatigue properties of TC6 titanium alloys through near-βforging coupled with shot peening,conducted at 930℃and ambient temperature,respectively.To unveil the associated mechanisms,microstructure,microhardness,residual stress,and fatigue properties are thoroughly analyzed after each process.Results indicate a considerable refinement in microstructure and significant mitigation of the initially existed strong texture post near-βforging and annealing,efficiently delaying crack initiation and propagation.As a result,the very high cycle fatigue property of TC6 achieves remarkable enhancement after forging.Compared to near-βforging,shot peening might not necessarily improve the very high cycle fatigue performance,particularly beyond 10^(6)cycles.展开更多
基金supported by the National Natural Science Foundation of China(Nos.52175145 and 51775427)the Key Research and Development Projects of Shaanxi Province(Grant No.2023-YBGY-335).
文摘The differences in damage values,residual stresses,microstructure and mechanical properties of Ti–6Al–4V alloy under hammer forging and press forging were explored through physical experiments and numerical simulations.The results showed that the temperature field and equivalent strain field of forgings under the hammer forging process were more uniformly distributed,resulting in smaller surface cracks and better residual stress distribution.The impact dynamic loading of hammer forging leads to forgings with higher dislocation densities,while the stabilized strain rate of press forging results in forgings exhibiting finer grain sizes.In this context,the yield strength enhancement of forgings by both processes was nearly identical,while the forgings demonstrated more excellent elongation under the hammer forging process.Additionally,increasing the number of blows in the hammer forging process or enhancing the loading rate in the press forging process can optimize the residual stress distribution of the forgings while simultaneously promoting dislocation multiplication and grain refinement.
文摘This study systematically investigated the microstructure,mechanical properties,and corrosion behavior of an extruded Zn-0.2Mg alloy processed by multi-directional forging(MDF)at 100℃.The mean grain size was remarkably decreased from 17.2±0.5µm to 1.9±0.3µm,and 84.4%of the microstructure was occupied by grains of below 1µm in size after applying three MDF passes.Electron backscattered difraction examinations revealed that continuous dynamic recrystallization,progressive lattice rotation,and particle-stimulated nucleation mechanisms were recognized as contributing to microstructural evolution.Furthermore,transmission electron microscopy results showed that nanoparticles of Mg/Zn dynamically formed under high strain MDF,while the initial extrusion fber texture was altered to be<0001>parallel to the fnal forging axis.A synergistic efect of grain refnement,texture evolution,second-phase precipitates,and dislocation strengthening resulted in an increased ultimate tensile strength of 232±5 MPa after three MDF passes.However,this was accompanied by a reduction in the elongation(8±2.1%).Additionally,a high corrosion rate of 0.59 mm/year was measured for the experimental alloy fabricated by 3 MDF passes.In agreement with the latter,electrochemical impedance spectroscopy results indicated that the grain refnement improved the passivation kinetics of the oxide layer.
基金financially supported by the National Key Research and Development Program of China(No.2022YFB3706901)the National Natural Science Foundation of China(No.52090041)the Young Elite Scientists Sponsorship Program by CAST(No.2022QNRC 001).
文摘Digital modeling and autonomous control of the die forging process are significant challenges in realizing high-quality intelli-gent forging of components.Using the die forging of AA2014 aluminum alloy as a case study,a machine-learning-assisted method for di-gital modeling of the forging force and autonomous control in response to forging parameter disturbances was proposed.First,finite ele-ment simulations of the forging processes were conducted under varying friction factors,die temperatures,billet temperatures,and for-ging velocities,and the sample data,including process parameters and forging force under different forging strokes,were gathered.Pre-diction models for the forging force were established using the support vector regression algorithm.The prediction error of F_(f),that is,the forging force required to fill the die cavity fully,was as low as 4.1%.To further improve the prediction accuracy of the model for the ac-tual F_(f),two rounds of iterative forging experiments were conducted using the Bayesian optimization algorithm,and the prediction error of F_(f) in the forging experiments was reduced from 6.0%to 1.5%.Finally,the prediction model of F_(f) combined with a genetic algorithm was used to establish an autonomous optimization strategy for the forging velocity at each stage of the forging stroke,when the billet and die temperatures were disturbed,which realized the autonomous control in response to disturbances.In cases of−20 or−40℃ reductions in the die and billet temperatures,forging experiments conducted with the autonomous optimization strategy maintained the measured F_(f) around the target value of 180 t,with the relative error ranging from−1.3%to+3.1%.This work provides a reference for the study of di-gital modeling and autonomous optimization control of quality factors in the forging process.
基金supported by the National Natural Science Foundation of China(No.52405408,No.U21A20131,No.U2037204,No.52422510)the Natural Science Foundation of Hubei Province(No.2023AFB116)+1 种基金the State Key Laboratory of Materials Processing and Die&Mould TechnologyHuazhong University of Science and Technology(No.P2022-005)。
文摘Magnesium alloy thin-walled cylindrical components with the advantages of high specific stiffness and strength present broad prospect for the lightweight of aerospace components.However,poor formability resulting from the hexagonal close-packed crystal structure in magnesium alloy puts forwards a great challenge for thin-walled cylindrical components fabrication,especially for extreme structure with the thicknesschanging web and the high thin-wall.In this research,an ZK61 magnesium alloy thin-walled cylindrical component was successfully fabricated by two-step forging,i.e.,the pre-forging and final-forging is mainly used for wed and thin-wall formation,respectively.Microstructure and mechanical properties at the core,middle and margin of the web and the thin-wall of the pre-forged and final-forged components are studied in detail.Due to the large strain-effectiveness and metal flow along the radial direction(RD),the grains of the web are all elongated along RD for the pre-forged component,where an increasingly elongated trend is found from the core to the margin of the wed.A relatively low recrystallized degree occurs during pre-forging,and the web at different positions are all with prismatic and pyramid textures.During finalforging,the microstructures of the web and the thin-wall are almost equiaxed due to the remarkable occurrence of dynamic recrystallization.Similarity,except for few basal texture of the thin-wall,only prismatic and pyramid textures are found for the final-forged component.Compared with the initial billet,an obviously improved mechanical isotropy is achieved during pre-forging,which is well-maintained during final-forging.
基金supported by the National Key research and Development Program of China(No.2022YFB4003001).
文摘The mechanical properties,microstructure and second phase precipitation behavior of flange forgings for high-pressure hydrogen storage vessels at different tempering temperatures(620–700℃)were studied.The results showed that when tempered at 620–680°C,the main microstructure of the test steel was tempered sorbite,and the main microstructure of tempered steel changed to martensite at 700℃.At 700℃,the dislocation density increased and some retained austenite existed.With the tempering temperature increasing,the yield strength showed a decreasing trend,the formation of fresh martensite made the tensile strength first decrease and then increase slightly,the impact energy at−40℃increased first and then decreased,and the impact energy at 660℃had the maximum value.The precipitates of MC type were mainly(Mo,V,Ti)C.The test steel had excellent strength and toughness matching at 660℃tempering,the tensile strength at different cross section locations was above 750 MPa,the impact energy was above 200 J at−40℃,and the relative percentage reduction of area(ZH2/ZN2)was above 75%at hydrogen environment of 6.3 MPa.
基金the financial supports from the Key Research and Development Program of Hunan Province,China(No.2023GK2020)。
文摘The homogenized Mg−5.6Gd−0.8Zn(wt.%)alloys were treated with water cooling and furnace cooling to obtain specimens without and with the 14H long-period stacking ordered(LPSO)phase.Subsequently,multi-directional forging(MDF)experiments were carried out.The microstructure and mechanical properties of different regions(the center,middle and edge regions)in the MDFed alloys were systematically investigated,and the effect of LPSO phase on them was discussed.The results show that the alloys in different regions undergo significant grain refinement during the MDF process.Inhomogeneous microstructures with different degrees of dynamic recrystallization(DRX)are formed,resulting in microhardness heterogeneity.The alloy with the LPSO phase has higher microstructure homogeneity,a higher degree of recrystallization,and better comprehensive mechanical properties than the alloy without the LPSO phase.The furnace-cooled alloy after 18 passes of MDF has the best comprehensive mechanical properties,with an ultimate compressive strength of 488 MPa,yield strength of 258 MPa,and fracture strain of 21.2%.DRX behavior is closely related to the LPSO phase and deformation temperature.The kinked LPSO phase can act as a potential nucleation site for DRX grains,while the fragmented LPSO phase promotes DRX nucleation through the particle-stimulated nucleation mechanism.
基金Project(2021GK1040) supported by the Major Projects of Scientific and Technology Innovation of Hunan Province,ChinaProjects(52375398,52171018) supported by the National Natural Science Foundation of China+1 种基金Project(Kfkt2023-09) supported by the Open Research Fund of State Key Laboratory of Precision Manufacturing for Extreme Service Performance,Central South University,ChinaProject(E2021203059) supported by the Natural Science Foundation of Hebei Province,China。
文摘This study investigates the differences in microstructural control between cryogenic forging combined with pre-deformation(PCF)and traditional thermal forging(TTF)for 7050 aluminum forgings intended for aerospace applications.The PCF process,utilizing cryogenic deformation,significantly refines the coarse grains at the surface of the forgings,resulting in a finer and more uniform microstructure,thereby effectively addressing the issue of surface coarse grains associated with traditional methods.The findings indicate that the PCF process can accumulate higher stored energy,facilitating static recrystallization(SRX)during subsequent heat treatment and enhancing the microstructural uniformity.Utilizing various analytical techniques,including optical microscopy(OM),electron backscatter diffraction(EBSD),and transmission electron microscopy(TEM).This study reveals the superiority of the PCF process in terms of strain accumulation,dislocation density,and grain refinement.In conclusion,this method offers advantages in enhancing the performance and microstructural uniformity of 7050 aluminum forgings,presenting new opportunities for applications in the aluminum forging industry.
基金supported by the Key Program for International Cooperation of the Ministry of Science and Technology,China(No.ZCGX2022001L)。
文摘In-situ TiB_(2)/Al–Cu composite was processed by multidirectional forging(MDF)for six passes.The microstructure evolution of the forged workpiece was examined across various regions.The mechanical properties of the as-cast and MDFed composites were compared,and their strengthening mechanisms were analyzed.Results indicate that the grain refinement achieved through the MDF process is mainly due to the subdivision of the original grains through mechanical geometric fragmentation and the occurrence of dynamic recrystallization(DRX).DRX grains are formed through discontinuous DRX,continuous DRX,and recrystallization induced by particle-stimulated nucleation.A rise in accumulated equivalent strain(Σ?ε)results in finerα-Al grains and a more uniform distribution of TiB_(2)particles,which enhance the Vickers hardness of the composite.In addition,the tensile properties of the MDFed composite significantly improve compared with those of the as-cast composites,with ultimate tensile strength and yield strength increasing by 51.2%and 54%,respectively.This enhancement is primarily due to grain refinement strengthening and dislocation strengthening achieved by the MDF process.
基金supported by the National Natural Science Foundation of China(No.52127808)。
文摘The superplasticity of the Mg−8.59Gd−3.85Y−1.14Zn−0.49Zr alloy was investigated before and after multi-directional forging(MDF)and the mechanisms affecting superplastic deformation were analyzed.The results indicate that after MDF at a temperature of 350℃and strain rates of 0.1 and 0.01 s^(−1)(1-MDFed and 2-MDFed),the superplasticity of the alloy can be significantly improved.The elongations of the MDFed alloys exceed 400%under the strain rate of 6.06×10^(−4)s^(−1)and temperatures of 350,375,and 400℃,and reach the maximum values of 766%(1-MDFed)and 693%(2-MDFed)at 375℃.The grain boundary sliding of the MDFed alloy is sufficient,and the energy barrier of deformation decreases.Theβphase limits the grain growth and promotes dynamic recrystallization,maintaining the stability of the fine-grained structure during superplastic deformation.Several Y-rich phases nucleate in the high-strain region(i.e.,the final fracture region)at high temperatures,accelerating the fracture of the specimen.
基金funded by Department of Science and Technology of Sichuan Province,China(No.2022YFG0102)the China Postdoctoral Science Foundation(No.2023M733314).
文摘The microstructure and mechanical properties of the Ti-5Al-5Mo-5V-1Cr-1Fe(Ti-55511)alloy under different strains were investigated through the design of step-shaped die forging.The results indicate that continuous dynamic recrystallization(CDRX)and discontinuous dynamic recrystallization(DDRX)occur in the high strain region.The orientation of the grains produced by CDRX is random and does not weaken the fiber texture.<100>-oriented grains expand gradually with increasing strain,thereby enhancing the strength of{100}texture.Significant anisotropic mechanical properties are observed in the large strain region and analyzed through in-situ tensile experiments.When the loading direction is parallel to the longitudinal(L)direction,strain concentration is observed near the dynamically recrystallized(DRXed)grains and inside grains oriented along<100>,leading to crack initiation.Furthermore,the small angle between the loading direction and the c-axis hinders the activation of prismatic and basal slip,thereby enhancing the strength.When the loading direction is parallel to the short transverse(ST)direction,cracks are initiated not only within grains oriented along<100>,but also at the grain boundaries.Regarding impact toughness,the elongatedβgrains in the L direction enhance the resistance to crack propagation.
文摘Today,I want to share how international standards can forge trust and fuel innovation,laying the foundation for a future where AI benefits everyone,everywhere.First,AI standards,developed jointly by ISO and IEC-the International Electrotechnical Commission-help build global trust and enable responsible innovation by bringing clarity and coherence to an ever-changing AI landscape.As developments in AI continue to emerge at speed,regulation is struggling to keep up and the proliferation of competing standards has created confusion rather than clarity.ISO and our partner IEC are addressing this challenge through the work of our expert committee on AI,SC 42,which takes a holistic,cohesive approach to AI standardization.
基金supported by the National Key R&D Program of China(No.2021YFB3701100).
文摘The deformation mechanism,microstructure evolution,and precipitation behavior of a Mg-8.9Gd-1.8Y-0.5Zr-0.2Ag(wt.%)alloy multi-directionally forged at three different temperatures were investigated.As the forging temperature increases,the particle-stimulated nucleation(PSN)effect diminishes as the num-ber of dynamic precipitates decreases,pyramidal slip is activated,grain boundary migration accelerates,and continuous dynamic recrystallization(CDRX)dominates.The microstructures varied greatly,although fine-grained structures were formed at all different forging temperatures.Competitive precipitation be-tween dynamic precipitate growth,dislocation-induced precipitation,and homogeneous precipitation was observed after aging treatment.Among them,the medium temperature(748 K)forged and aged alloy ex-hibits the best mechanical performance,with an ultimate tensile strength of 436 MPa,and elongation of 16.3%.The calculation indicates that the mixed precipitation structure containing theβprecipitate band provides a 35%higher strengthening contribution than the typical homogeneously distributed precipi-tates.The formation of precipitation-free zones(PFZs)ensures that aging will not cause a dramatic de-crease in ductility,which provides a reference for the industrial preparation of high-performance wrought Mg-Gd series alloys.
基金Projects(52274402,52174381)supported by the National Natural Science Foundation of China。
文摘The effect of forging on the microstructure and texture evolution of a high Nb containing Ti-45Al-7Nb-0.3W(at.%)alloy was investigated by X-ray diffractometer(XRD),scanning electron microscopy(SEM),and transmission electron microscopy(TEM).The results show that the as-cast alloy is mainly composed of α_(2)/γ lamellar colonies with a mean size of 70μm,but the hot-forged pancake displays a near duplex microstructure(DP).Kinking and bending of lamellar colonies,deformation twinning and dynamic recrystallization(DRX)occur during hot forging.Meanwhile,dense dislocations in theβphase after forging suggest that the high-temperature β phase with a disordered structure is favorable for improving the hot-workability of the alloy.Unlike the common TiAl casting texture,the solidification process of the investigated as-cast alloy with high Nb content is completely via the β phase region,resulting in the formation of a<110>γ fiber texture where the<110>γ aligns parallel to the heat-flow direction.In comparison,the relatively strong<001>and weak<302>texture components in the as-forged alloy are attributed to the deformation twinning.After annealing,static recrystallization occurs at the twin boundary and intersections,which weakens the deformation texture.
基金National Science and Technology Project of China(JPPT-135-GH-2-017)Fellowship of China Postdoctoral Science Foundation(2022M720399)。
文摘The effect of die forging on the microstructure evolution and deformation behavior of metastable β-titanium alloy Ti55511 was investigated by electron backscatter diffraction.Before die forging,the alloy Ti55511 was subjected to multi-pass forging to optimize the microstructural heterogeneity(texture)which can cause mechanical behavior anisotropy of titanium alloys.Results show that after die forging,Ti55511 components exhibit different microstructures and textures in different local areas.No<100>fiber texture is found in all areas with different degrees of deformation.Dynamic recrystallization occurs in the area where large strain occurs during the early stage of die forging.Basket-weave microstructure forms in most local areas.
基金the financial support of the National Natural Science Foundation of China(Nos.U1910213 and 52205400)the China Postdoctoral Science Foundation(No.2021M692626)+2 种基金the Fundamental Research Program of Shanxi Province(No.202203021212321)Technological Innovation Talent Team Special Plan of Shanxi Province(No.202204051002002)the Doctoral Starting up Foundation of Taiyuan University of Science and Technology(No.20222046).
文摘Gradient microstructure modification is a cost-efficient strategy for high strength without compromising ductility,which is urgently needed in the fundamental science of engineering materials.In this study,heterogeneous structures of AZ61 alloy bars with anisotropic gradients(with different grain size distributions from the surface to the center)were observed to exhibit strong strength-ductility synergies under different deformation tem peratures.The results reveal that the grain refinement process under mediumlow temperature deformation conditions(≤350℃)consists of four transition stages along the radial direction,i.e.,twin activations and deformation band formations,dislocation cells and pile-ups,ultrafine sub-grains,and randomly orientated quasi-micron grains.Different deformation temperatures have a great influence on twin activations and deformation band formations,and the high temperature can easily provoke the initiation of non-basal slip.The deformation bands were determined as a primary nucleation site due to their highly unstable dislocation hindrance ability.Analysis in combination with the Radial forging(RF)deformation process,the differences of dynamic precipitates can be attributed to microstructural difference and solubility limit of Al at different tem peratures.By summarizing the tensile test results,the sample forged at 350℃exhibited the best strength-ductility synergy,exhibiting the highest elongation(EL)of 23.2%with a 251 MPa yield strength(YS)and 394 MPa ultimate tensile strength(UTS)in center region,and combined with the highest strength value of 256 MPa YS and 420 MPa UTS in the center region,while the EL was slightly degraded to 19.8%.
基金supported by Program for Young Talents of Science and Technology in Universities of Inner Mongolia Autonomous Region (Grant No.NJYT23115)the Inner Mongolia Natural Science Foundation (Grant No.2022MS05039).
文摘Mo element was added to cobalt-based alloy L605,and cold forging deformation was performed.The effects of the addition and cold forging deformation on the microstructure and mechanical properties of the alloy were studied by thermodynamic calculation,electron backscatter diffraction,transmission electron microscopy,and X-ray diffraction.The stacking fault energy(SFE)of the alloy decreased after the addition,and the formation of stacking faults and intersections were promoted to improve the strength and hardness.The tensile strength of the alloy with Mo increased from 1190 to 1702 MPa after 24%cold deformation,producing significant work hardening.The strengthening mechanism is strain-induced martensitic transformation(SIMT)and deformation twinning.The alloy,combined with Mo and after 24%deformation,had both high strength and ductility in comparison with the original cobalt-based alloy L605.This is attributed to the lower SFE which caused the increase in stacking fault density.During the tensile process,theε-hcp phase was easily generated at the stacking fault to reduce the stress concentration and increase the ductility.Controlling SIMT by adjusting the density of stacking faults can improve the mechanical properties of cobalt-based alloys.Theε-hcp phase,the interaction between deformation twins and dislocations,and the interaction between e-hcp phases during cold forging deformation caused local stress concentration,lowering ductility and toughness.
基金The authors are grateful for the financial support from the National Natural Science Foundation of China(Grant Nos.52201116,52301143,52071228,and 52271118)the State Key Labo-ratory of Advanced Welding and Joining,Harbin Institute of Tech-nology(Grant No.AWJ-23M24)the Heilongjiang Provincial Natural Science Foundation of China(Grant No.YQ2023E007).
文摘Understanding the non-equilibrium phase transition mechanism is critical to controlling the transform-ing microstructures and thus material performance.In order to improve the problem of low room-temperature ductility of TiAl alloys with traditional microstructures,a two-step forging with an interme-diate heat preservation process is proposed to prepare a hybrid microstructure via non-equilibrium phase transition in this study.This hybrid microstructure is composed ofβ_(0)/γlamellar colony,a structure with innerα_(2)/γand outerβ_(0)/γlamellae surrounded byβ_(0)phase,a structure ofγgrains embedded withinα_(2)/γlamellar colony,and some granularβ_(0)withinγphase.This hybrid microstructure exhibits excellent room-temperature mechanical properties with a total elongation to failure of 2.15%and tensile strength of 920 MPa.Furthermore,the evolution mechanisms of these various structures are analyzed from the perspective of solute element diffusion and distribution in front of the phase transition interface.Aggre-gation of V element in front of theγgrowth interface induces the elemental reaction deviating from the equilibrium phase transitionα→α_(2)+γ,andα→β(β_(0))+γtransition occurs,resulting in the formation ofβ(β_(0))/γlamellar colony.During hot forging,α→α_(2)+γtransition occurs to generateα_(2)/γlamellae in the initial transition stage(I)of solute diffusion.In the stable stage(II),the content of V element in front of the growth interface ofγlamellae increases to∼18.41%,andα→β(β_(0))+γtransition occurs,soβ(β_(0))/γlamellae are formed outside theα_(2)/γlamellar colony.In the final stage(III),the remainingαphase is less,and the diffusion of the V element is hindered,causing a sudden increase of the V element inαphase,resulting in the remainingαphase transformed into irregularβ(β_(0))phase.Finally,the structure with innerα_(2)/γand outerβ_(0)/γlamellae surrounded byβ_(0)phase is formed.Moreover,adjusting the cooling rate realizes the precise controlling of theα_(2)/γ,β_(0)/γlamellar size and content of irregularβ_(0)phase based on the solute element distribution equation.Additionally,the structure ofγgrain embedded withinα_(2)/γlamellar colony is obtained.β(β_(0))grains nucleate and grow withinα_(2)/γlamellar colony throughα_(2)+γ→β(β_(0))+γphase transition and the coarseα_(2)lamellae are decomposed into fineα_(2)andγlamellae in parallel.Then,β(β_(0))→γphase transition occurs,resulting in the formation ofγgrains.Finally,the structure ofγgrains embedded withinα_(2)/γlamellar colony is formed,and someβ(β_(0))phases are mixed.This work clearly reveals the mystery of various complex phase transition processes and results inβ-γTiAl alloy.Moreover,this design strategy of forging process and controlling the microstructure should be extendable to other TiAl systems and provides a promising new route to solve the low room-temperature ductility of TiAl alloy.
基金National Natural Science Foundation of China (11988102 and 52301146)Chinese Postdoctoral Science Foundation (8206300226)+1 种基金National Science and Technology Infrastructure Platform Development Plan-Young Backbone Talents Training Project (52001325)Fundamental Research Funds for the Central Universities (JB2023118)。
文摘In this work,we successfully fabricate an ultra-high strength Mg-11Gd-3Y-0.5Zr alloy with ultimate tensile strength of 523 MPa and enhanced ductility via cost-effective bi-directional forging (BDF) and subsequent annealing heat treatments.To elucidate the role of BDF and gain a fundamental understanding of the remarkable simultaneous increase of strength and ductility,systematic microstructure characterization and analysis are performed.It is revealed that the double-peak basal texture,with basal poles located at the center of two mutually perpendicular forging directions,serves as an essential factor for the strength-ductility synergy of the Mg-11Gd-3Y-0.5Zr alloy processed with BDF.Roles of the double-peak basal texture in overcoming the strength-ductility trade-off include promoting non-basal slip,increasing ductility,and enlarging the Hall-Petch effect along the sample elongation direction while reducing the extent of anisotropy in critical resolved shear stresses of different slip systems.This study demonstrates that texture engineering is a powerful strategy to control magnesium alloy performance and BDF is a promising processing technique for enhancing mechanical properties of magnesium alloys.
基金supported by National Key Research and Development Program of China(2021YFB3701002)National Natural Science Foundation of China(nos.U2167213,51971053 and 52201111)+2 种基金China Postdoctoral Science Foundation(no.2022M710628)H.C.Pan acknowledges the financial assistance from Young Elite Scientists Sponsorship Program by China Association for Science and Technology(2019-2021QNRC001-003)the fund from the Fundamental Research Funds for the Central Universities(N2202020).
文摘In this work,a new strategy for achieving ultrahigh strength in the coarse-grained Mg-Gd binary alloy via utilizing recrystallization texture hardening and maximizing precipitation strengthening has been reported.Forging at a much high temperature suppresses dynamic precipitation,enabling the super-saturation of Gd atoms in Mg matrix.This facilitates the formation of fully recrystallized grains with strong texture and induces an exceptionally high precipitation hardening in the following ageing.Therefore,the forged Mg-13Gd sample exhibited extraordinary tensile yield strength(TYS)of∼430 MPa,in which ageing-induced TYS increment exceeds∼210 MPa,as the highest record so far in precipitation-hardened Mg communities.These results provide important theoretical guidance for fabricating the large section and high-strength Mg components for industrial applications.
基金financial support from the National Science and Technology Major Project(Grant No.J2019-IV-0010-0078)the National Natural Science Foundation of China(Grant Nos.12172139 and 11972012)funding from the Fundamental Research Funds for the Central Universities(Grant No.2019kfyXJJS141).
文摘In order to enhance the fatigue properties of metallic materials,a feasible rationale is to delay or prevent the interior and surface fatigue crack initiation.Based on this rationale,the study investigates the approach of improving the very high cycle fatigue properties of TC6 titanium alloys through near-βforging coupled with shot peening,conducted at 930℃and ambient temperature,respectively.To unveil the associated mechanisms,microstructure,microhardness,residual stress,and fatigue properties are thoroughly analyzed after each process.Results indicate a considerable refinement in microstructure and significant mitigation of the initially existed strong texture post near-βforging and annealing,efficiently delaying crack initiation and propagation.As a result,the very high cycle fatigue property of TC6 achieves remarkable enhancement after forging.Compared to near-βforging,shot peening might not necessarily improve the very high cycle fatigue performance,particularly beyond 10^(6)cycles.
