The spheroidization of the Widmanstätten structure through thermo-mechanical processes,leading to the formation of fine recrystallized and sub-grain structures,is crucial for achieving a balance between strength ...The spheroidization of the Widmanstätten structure through thermo-mechanical processes,leading to the formation of fine recrystallized and sub-grain structures,is crucial for achieving a balance between strength and plasticity.This study systematically examined the spheroidization mechanism of the Widmanstätten structure in Ti-25Zr-4Al-1.5Mn(wt.%,TiZrAlMn)alloy under varying rolling temperatures and its influence on microstructure and mechanical properties.After rolling at 900℃,the specimen exhibited a mixed morphology of Widmanstätten and Basket-weave structures,with a high yield strength of approximately 1038 MPa but low plasticity(∼5.2%).While the rolling temperature was reduced to 850℃,the specimen exhibited refined prior-β grains,discontinuous grain boundaries and a small amount of equiaxed α grains,which collectively enhanced plasticity(∼12.4%)while preserving yield strength.As the rolling temperature further decreased,the dynamic recrystallization mechanism shifted from the discontinuous dynamic recrystallization(DDRX)to continuous dynamic recrystallization(CDRX).Specimens rolled at 800℃ and 750℃ showed excellent strength-plasticity synergy,with yield strengths of 1070 MPa and 1110 MPa,respectively,and total elongations of 15%and 18%,respectively.The enhanced yield strength is attributed to both fine-grain and sub-grain strengthening.Furthermore,the lower degree of recrystallization in the 750-AC specimen preserved a relatively high dislocation density,offering additional strengthening.The favorable plasticity results from a combination of equiaxedαgrains,“soft”barrier sub-grains,and a small number of twins.Additionally,the 750-AC specimen retained 6.4%of the fine β grains and the weak basal texture.These characteristics contribute to the enhanced plasticity.Therefore,750℃is the optimal rolling temperature for achieving the best strength-plasticity synergy in the hot-rolled TiZrAlMn alloy.These findings demonstrate that selecting the appropriate temperature during thermomechanical processing to optimize recrystallized grains and sub-grain content ensures excellent plasticity at high yield strength.This offers valuable guidance for developing near-α Ti alloys with superior mechanical properties.展开更多
Microstructure evolutions of the medium-manganese wear-resistant steel Fe-8Mn-1C-1.2Cr-0.2V (in wt.%) with stacking-fault energy of 22 mJ m-2 during deformation at strain rate ranging of 10^-2-1 s^-1 were analyzed by ...Microstructure evolutions of the medium-manganese wear-resistant steel Fe-8Mn-1C-1.2Cr-0.2V (in wt.%) with stacking-fault energy of 22 mJ m-2 during deformation at strain rate ranging of 10^-2-1 s^-1 were analyzed by means of X-ray diffraction, field emission scanning electron microscopy and high-resolution transmission electron microscopy. The results indicate that the twinning-induced plasticity effect is the main strengthening mechanism of the studied steel, whilst the transformation-induced plasticity effect only occurs at high strain rate. With an increase in strain rate, volume fraction of the deformation twins, in particular that of the secondary twins, increases significantly along with decreasing average size. When applied strain rate is higher than 10^-1 s^-1, the parallel deformation twins are turned into a crossing morphology, and the original straight twin boundaries exhibit a ladder feature, which is attributed to the interactions between regular dislocations and twin dislocations at the twin boundary. The critical strain, a key indicator of the initiation of deformation twin, decreases with increasing strain rate. In addition, the ductility and strength of medium-manganese wear-resistant steel Fe-8Mn-1C-1.2Cr-0.2V are mainly determined by the shape and volume fraction of deformation twins.展开更多
In this study, different welding param eters were selected to investigate the effects of heat-in put on the microstructure and corrosion resistance of the friction stir welded high nitrogen stainless steel joints. The...In this study, different welding param eters were selected to investigate the effects of heat-in put on the microstructure and corrosion resistance of the friction stir welded high nitrogen stainless steel joints. The results show ed that, the welding speed had major influence on the duration at elevated tem perature rather than the peak tem perature. The hardness distribution and tensile properties of the nugget zones (NZs) for various joints were very similar while the pitting corrosion behavior of various NZs showed major differences. Large heat-input resulted in the ferrite bands being the pitting location, while tool wear bands were sensitive to pitting corrosion in the low heat-input joints. Cr diffusion and tool wear were the main reasons for pitting. The mechanisms of pitting corrosion in the NZs were analyzed in detail.展开更多
Friction stir lap welding of a DP1180 advanced ultrahigh strength steel was successfully carried out by using three welding tools with different pin lengths. The effects of the welding heat input and material flow on ...Friction stir lap welding of a DP1180 advanced ultrahigh strength steel was successfully carried out by using three welding tools with different pin lengths. The effects of the welding heat input and material flow on the microstructure evolution of the joints were analyzed in detail. The relationship between pin length and mechanical properties of lap joints was studied. The results showed that the peak temperatures of all joints exceeded A c3, and martensite phases with similar morphologies were formed in the stir zones. These martensite retained good toughness due to the self-tempering effect. The formation of ferrite and tempered martensite was the main reason for the hardness reduction in heat-affected zone. The mechanical properties of the lap joints were determined by loading mode, features of lap interface and the joint defects. When the stir pin was inserted into the lower sheet with a depth of 0.4 mm, the lap joint exhibited the maximum tensile strength of 12.4 kN.展开更多
Strong metal/non-polar plastic dissimilar joints are highly demanded for the lightweight design in many fields,which,however,are rather challenging to achieve directly via welding.In this study,we designed a laser pro...Strong metal/non-polar plastic dissimilar joints are highly demanded for the lightweight design in many fields,which,however,are rather challenging to achieve directly via welding.In this study,we designed a laser processing pretreatment on the Al alloy to create a deep porous Al surface structure,which was successfully joined to the polypropylene(PP) via friction spot welding.A maximum joint strength of29 MPa was achieved,the same as that of the base PP(i.e.the joint efficiency reached 100%),much larger than ever reported.The joining mechanism of the Al alloy and the PP was mainly attributed to the large mechanical interlocking effect between the laser processed Al porous structure and the re-solidified PP and the formation of chemical bond at the interface.The deep porous Al surface structure modified by laser processing largely changed the Al-PP reaction feature.The evidence of the C-O-Al chemical bond was first time found at the non-polar plastic/Al joint interface,which was the reaction result between the oxide on the Al alloy surface and thermal oxidization products of the PP during welding.This study provides a new way for enhancing metal-plastic joints via surface laser treatment techniques.展开更多
A conventional multi-pass rolling is designed to form different microstructures in a Mg-2Ag alloy.The relationship between microstructure and mechanical property is investigated.The result shows that twin-induced nucl...A conventional multi-pass rolling is designed to form different microstructures in a Mg-2Ag alloy.The relationship between microstructure and mechanical property is investigated.The result shows that twin-induced nucleation plays a prominent role for the dynamic recrystallization(DRX)behavior of the rolled Mg-2Ag alloys.The DRXed grains distributed around elongated grains have random orientations but gradually turn to the concentrated orientation with strong basal texture when the rolling pass increases.The yield strength and ultimate tensile strength of rolled Mg-2Ag alloy gradually increase with increasing rolling pass.The elongation of rolled sample is gradually improved when the rolling pass increases from one to three,while a significant drop of elongation shows in the four-pass rolling sample.The strong basal texture,refined grains,high-density dislocations,and Ag segregation along grain boundaries are suggested to play a prominent role for enhancing the strength of Mg-Ag alloys,while the low-density dislocations,homogeneously fine-grained microstructure,and weak texture are critical for improving the ductility.展开更多
Ultrahigh-strength quenching and partitioning(Q&P) steels have attracted strong interests in the auto manufactory,while the comprehensive understanding in the microstructure and mechanical behavior of their welded...Ultrahigh-strength quenching and partitioning(Q&P) steels have attracted strong interests in the auto manufactory,while the comprehensive understanding in the microstructure and mechanical behavior of their welded joints is highly needed to enrich their applications.In the present work,it is designed to make an insight into these imperative conundrums.Equal strength Q&P 1180 steel joints to parent metal were successfully fabricated via friction stir welding(FSW) technique under different parameters. Apparent hardening and softening were observed in stir zone(SZ) and heat-affected zone(HAZ) respectively,whose microstructures strongly depended on the peak temperature and cooling rate during welding.The formation of fresh martensite was the main mechanism for the SZ hardening,while the decomposition of metastable phases played key roles in the microhardness drop of the HAZ.A heat source zone-isothermal phase transition layer model was proposed to clarify the impregnability of the joint strength under parameter variation.The dual-phase structure,nano-carbide particles,tempered initial martensite,and ultrafine-grained ferrite synergistically improved the strain hardening ability of the HAZ,which eventually resulted in the equal strength FSW joints.展开更多
For additive manufactured aluminum alloys,the inferior mechanical properties along the building direction have been a serious weakness.In this study,an optimized heat treatment was developed as a simple and effective ...For additive manufactured aluminum alloys,the inferior mechanical properties along the building direction have been a serious weakness.In this study,an optimized heat treatment was developed as a simple and effective solution.The effects of direct aging on microstructure and mechanical properties along the building direction of AlSi10Mg samples produced via selective laser melting(SLM)were investigated.The results showed that,compared with the conventional heat treatment at elevated temperatures,direct aging at temperatures of 130-190℃ could retain the fine grain microstructure of SLM samples and promote further precipitation of Si phase,however,the growth of pores occurred during direct aging.With increasing aging temperature,while finer cell structures were obtained,more and larger pores were developed,resulting in decreased density of the samples.Two types of pore formation mechanisms were identified.Considering the balance between the refinement of cell structure and the growth of pores,aging at 130℃ was determined as the optimized heat treatment for SLM AlSi10Mg samples.The tensile strength along the building direction of the 130℃ aged sample was increased from 403 MPa to 451 MPa,with relatively high elongation of 6.5%.展开更多
Nanolaminated Ti3AlC2honeycomb monolith with parallel and uniform holes has been prepared through a facile extrusion route by using Ti3AlC2powder as the main raw material.The fabricated honeycomb monolith has high com...Nanolaminated Ti3AlC2honeycomb monolith with parallel and uniform holes has been prepared through a facile extrusion route by using Ti3AlC2powder as the main raw material.The fabricated honeycomb monolith has high compressive strength of 133 ± 11 and 59 ± 9 MPa,along and perpendicular to the extrusion direction,respectively.It also has good electrical conductivity,and excellent match of thermal expansion coefficient with the washcoat material of γ-AI2O3.These combined properties endow the honeycomb monolith a promising candidate as catalysis substrate for cleaning vehicle exhaust.展开更多
The microstructure and properties of water-cooled and air-cooled friction stir welded（FSW） ultra-high strength high nitrogen stainless steel joints were comparatively studied. With additional rapid cooling by flowin...The microstructure and properties of water-cooled and air-cooled friction stir welded（FSW） ultra-high strength high nitrogen stainless steel joints were comparatively studied. With additional rapid cooling by flowing water, the peak temperature and duration at elevated temperature during FSW were significantly reduced. Compared to those in the air-cooled joint, nugget zone with finer grains（900 nm） and heat affected zone with higher dislocation density were successfully obtained in the water-cooled joint,leading to significantly improved mechanical properties. The wear of the welding tool was significantly reduced with water cooling, resulting in better corrosion resistance during the immersion corrosion test.展开更多
We analyzed the relationship between several basic parameters describing supermassive black holes such as jet power,black hole spin,accretion disk magnetic field,black hole mass,etc.We found that there is a general co...We analyzed the relationship between several basic parameters describing supermassive black holes such as jet power,black hole spin,accretion disk magnetic field,black hole mass,etc.We found that there is a general correlation between these parameters,such as jet power is significantly positively correlated with black hole spin,while black hole mass is significantly negatively correlated with black hole spin.To apprehend these relationships,we consider the Blandford–Znajek model to be superior to the Blandford–Payne model.It is also found that the intrinsic gamma luminosity of the FSRQs has a positive correlation with the accretion disk magnetic field,while the intrinsic gamma luminosity of the BL Lacs has a negative correlation with the accretion disk magnetic field.A feedback effect may exist between accretion disk accretion rate and magnetic field,which may be the key to the evolution between BL Lacs and FSRQs.There is no significant difference in the jet power and jet generation efficiency of FSRQs and BL Lacs,which suggests that the jets are generated by the same mechanism.The contribution rate of accretion rate to jet generation efficiency is high,while the contribution rate of accretion rate to jet power is very low.展开更多
The spheroidization of the lamellar structure can greatly contribute to the superplasticity of the nugget zone(NZ)of Ti alloy welds,which is the key to achieve the integral superplastic forming of welds for the fabric...The spheroidization of the lamellar structure can greatly contribute to the superplasticity of the nugget zone(NZ)of Ti alloy welds,which is the key to achieve the integral superplastic forming of welds for the fabrication of large-scale complex components.However,the spheroidization process is complex and costly since it cannot be obtained generally,unless the lamellae suffers from a large deformation.In this study,the static spheroidization was achieved for the fine lamellae structure in the nugget of a friction stir welded(FSW)Ti-6Al-4V joint,particularly by the annealing without any deformation.The specialα/βinterface obeying a Burgers orientation relationship(BOR)after FSW was first time directly observed,whose effect on the spheroidization was discussed.A new static spheroidization mechanism with the gradual coalescence of the adjacent lamellae was discovered,which we named as“termination coalescence”.There was a slower coarsening rate in the lamellar structure than in the classical equiaxed one,due to the BOR in the lamellae,although both of them exhibited a volume diffusion character during annealing.Consequently,the similar superplasticity can be achieved for the base material and NZ after annealing.This study can provide a new way to the spheroidization and a theoretical basis for the integral superplastic forming of welds during production.展开更多
Large-scale components of steel and aluminum alloys(Fe-Al)with high bonding strength are highly needed from space exploration to the fabrication of transportation systems.The formation of detrimental intermetallic com...Large-scale components of steel and aluminum alloys(Fe-Al)with high bonding strength are highly needed from space exploration to the fabrication of transportation systems.The formation of detrimental intermetallic compounds at the Al-Fe interface has limited the application range of the Fe-Al components.The modified friction stir additive manufacturing was developed for fabricating large-scale Fe-Al compo-nents with homogenously distributed interfacial amorphous layers rather than detrimental intermetallic compounds.The interfacial amorphous layers comprised an Mg-O rich amorphous layer<20 nm in thick-ness and an Al-Fe-Si amorphous layer<120 nm in thickness.The interfacial amorphous layers exhibited high thermal stability and did not change even after the post-processing heat treatment of heating at 500℃ for 20 min and aging at 170℃ for 7 h.The tensile strengths of the Fe-Al tensile specimens were increased from 160 to 250 MPa after the application of the post-processing heat treatment.The fracture occurred in the aluminum alloys instead of at the dissimilar metal interface,demonstrating that high bonding strength at the Al-Fe interface was enabled by the formation of homogenously distributed interfacial amorphous layers.展开更多
The chemical boundaries inside the ultrafine spinodal decomposition structure in metastable β-Ti alloys can act as a new feature to architect heterogeneous microstructures.In this work,we combined two semi-empirical ...The chemical boundaries inside the ultrafine spinodal decomposition structure in metastable β-Ti alloys can act as a new feature to architect heterogeneous microstructures.In this work,we combined two semi-empirical methods,i.e.,the d-electron theory and the e/a electron concentration,to achieve the spinodal decomposition structure in a metastable β Ti-4.5Al-4.5Mo-7V-1.5Cr-1.5Zr(wt.%)alloy.Utilizing the spinodal decomposition structure,the aged Ti-Al-Mo-V-Cr-Zr alloys showed multi-architectured α precipitates spanning from micron-scale(primary α_(p))to nano-scale(secondary α_(s))that were uniformly distributed in the β-domains.Being compared with the forged sample,the multi-scale heterogeneous microstructure enables the aged β-Ti alloy to have ultra-high strength(yield strength ~1366 MPa and ultimate tensile strength ~1424 MPa)and an appreciable ductility(~9.3%).Strengthening models were proposed for the present alloys to estimate the contribution of various microstructural features to the measured yield strength.While the solid solution strengthening,β-spinodal strengthening,and back stress strengthening made comparable contributions to the strength of the forged alloy,the back stress strengthening was the predominant strengthening effect in the aged alloy.This alloy design approach based on chemical boundary engineering to construct multi-architectured α precipitates provided an effective strategy for achieving an outstanding combination of ultra-high strength and ductility in metastable β-Ti alloys.展开更多
Analytical solutions for the flexural-gravity wave resistances due to a line source steadily moving on the surface of an infinitely deep fluid are investigated within the framework of the linear po- tential theory. Th...Analytical solutions for the flexural-gravity wave resistances due to a line source steadily moving on the surface of an infinitely deep fluid are investigated within the framework of the linear po- tential theory. The homogenous fluid, covered by a thin elastic plate, is assumed to be incompressible and inviscid, and the motion to be irrotational. The solution in integral form for the wave resistance is obtained by means of the Fourier transform and the explicitly analytical solutions are derived with the aid of the residue theorem. The dispersion relation shows that there is a minimal phase speed cmin, a threshold for the existence of the wave resistance. No wave is generated when the moving speed of the source V is less than emin while the wave resistances firstly increase to their peak values and then decrease when V ~〉 Crnin. The effects of the flexural rigidity and the inertia of the plate are studied. @ 2013 The Chinese Society of Theoretical and Applied Mechanics. [doi：10.1063/2.1302202]展开更多
A good understanding of melting and resolidification of the substrate will help us to achieve better bonding.Anumerical model is developed to investigate the solidification of the droplet,and melting and resolidificat...A good understanding of melting and resolidification of the substrate will help us to achieve better bonding.Anumerical model is developed to investigate the solidification of the droplet,and melting and resolidification of thesubstrate.The molybdenum powder spraying onto three different substrates:a stainless steel,brass(70%Cu)andaluminum by atmospheric plasma spraying has been investigated.The maximum melting depth of the substrate hasbeen measured and compared with the numerical prediction.Experimental results show that the material propertiesof the splat and substrate and melting temperature of the substrate play the important roles on substrate melting.A dimensionless parameter,temperature factor,has been proposed and served as an indicator for substrate melting.展开更多
Branched flow is an interesting phenomenon that can occur in diverse systems.It is usually linear in the sense that the flow does not alter the properties of the medium.Branched flow of light on thin films has recentl...Branched flow is an interesting phenomenon that can occur in diverse systems.It is usually linear in the sense that the flow does not alter the properties of the medium.Branched flow of light on thin films has recently been discovered.It is therefore of interest to know whether nonlinear light branching can also occur.Here,using particle-in-cell simulations,we find that in the case of an intense laser propagating through a randomly uneven medium,cascading local photoionization by the incident laser,together with the response of freed electrons in the strong laser fields,triggers space–time-dependent optical unevenness.The resulting branching pattern depends dramatically on the laser intensity.That is,the branching here is distinct from the existing linear ones.The observed branching properties agree well with theoretical analyses based on the Helmholtz equation.Nonlinear branched propagation of intense lasers potentially opens up a new area for laser–matter interaction and may be relevant to other branching phenomena of a nonlinear nature.展开更多
基金financially supported by the National Natural Science Foundation of China(Nos.52125405,52127808,52071278,U22A20108 and 52471148)the Science Research Project of Hebei Education Department(No.KJZX202201)+2 种基金Natural Science Foundation of Hebei Province(No.242Q9906Z/E2021402002)Basic Research Project of Shijiazhuang City for Universities in Hebei Province(No.241791027A)the Hebei Provincial Department of Education Funding Project for Cultivating Innovative Ability of Graduate Students(Grant no.CXZZBS2025057/CXZZBS2025056).
文摘The spheroidization of the Widmanstätten structure through thermo-mechanical processes,leading to the formation of fine recrystallized and sub-grain structures,is crucial for achieving a balance between strength and plasticity.This study systematically examined the spheroidization mechanism of the Widmanstätten structure in Ti-25Zr-4Al-1.5Mn(wt.%,TiZrAlMn)alloy under varying rolling temperatures and its influence on microstructure and mechanical properties.After rolling at 900℃,the specimen exhibited a mixed morphology of Widmanstätten and Basket-weave structures,with a high yield strength of approximately 1038 MPa but low plasticity(∼5.2%).While the rolling temperature was reduced to 850℃,the specimen exhibited refined prior-β grains,discontinuous grain boundaries and a small amount of equiaxed α grains,which collectively enhanced plasticity(∼12.4%)while preserving yield strength.As the rolling temperature further decreased,the dynamic recrystallization mechanism shifted from the discontinuous dynamic recrystallization(DDRX)to continuous dynamic recrystallization(CDRX).Specimens rolled at 800℃ and 750℃ showed excellent strength-plasticity synergy,with yield strengths of 1070 MPa and 1110 MPa,respectively,and total elongations of 15%and 18%,respectively.The enhanced yield strength is attributed to both fine-grain and sub-grain strengthening.Furthermore,the lower degree of recrystallization in the 750-AC specimen preserved a relatively high dislocation density,offering additional strengthening.The favorable plasticity results from a combination of equiaxedαgrains,“soft”barrier sub-grains,and a small number of twins.Additionally,the 750-AC specimen retained 6.4%of the fine β grains and the weak basal texture.These characteristics contribute to the enhanced plasticity.Therefore,750℃is the optimal rolling temperature for achieving the best strength-plasticity synergy in the hot-rolled TiZrAlMn alloy.These findings demonstrate that selecting the appropriate temperature during thermomechanical processing to optimize recrystallized grains and sub-grain content ensures excellent plasticity at high yield strength.This offers valuable guidance for developing near-α Ti alloys with superior mechanical properties.
基金The authors gratefully appreciate the financial support by the National Natural Science Foundation of China (Grant Nos. 51471048 and U1860201)the Basic Research Program of Key Laboratory of Liaoning Province (LZ2015035).
文摘Microstructure evolutions of the medium-manganese wear-resistant steel Fe-8Mn-1C-1.2Cr-0.2V (in wt.%) with stacking-fault energy of 22 mJ m-2 during deformation at strain rate ranging of 10^-2-1 s^-1 were analyzed by means of X-ray diffraction, field emission scanning electron microscopy and high-resolution transmission electron microscopy. The results indicate that the twinning-induced plasticity effect is the main strengthening mechanism of the studied steel, whilst the transformation-induced plasticity effect only occurs at high strain rate. With an increase in strain rate, volume fraction of the deformation twins, in particular that of the secondary twins, increases significantly along with decreasing average size. When applied strain rate is higher than 10^-1 s^-1, the parallel deformation twins are turned into a crossing morphology, and the original straight twin boundaries exhibit a ladder feature, which is attributed to the interactions between regular dislocations and twin dislocations at the twin boundary. The critical strain, a key indicator of the initiation of deformation twin, decreases with increasing strain rate. In addition, the ductility and strength of medium-manganese wear-resistant steel Fe-8Mn-1C-1.2Cr-0.2V are mainly determined by the shape and volume fraction of deformation twins.
基金supported financially by the National Natural Science Foundation of China (Nos. 51671190 and 51471171)
文摘In this study, different welding param eters were selected to investigate the effects of heat-in put on the microstructure and corrosion resistance of the friction stir welded high nitrogen stainless steel joints. The results show ed that, the welding speed had major influence on the duration at elevated tem perature rather than the peak tem perature. The hardness distribution and tensile properties of the nugget zones (NZs) for various joints were very similar while the pitting corrosion behavior of various NZs showed major differences. Large heat-input resulted in the ferrite bands being the pitting location, while tool wear bands were sensitive to pitting corrosion in the low heat-input joints. Cr diffusion and tool wear were the main reasons for pitting. The mechanisms of pitting corrosion in the NZs were analyzed in detail.
基金supported by the National Natural Science Foundation of China (Nos. 51671190, 51774085 and 51471171).
文摘Friction stir lap welding of a DP1180 advanced ultrahigh strength steel was successfully carried out by using three welding tools with different pin lengths. The effects of the welding heat input and material flow on the microstructure evolution of the joints were analyzed in detail. The relationship between pin length and mechanical properties of lap joints was studied. The results showed that the peak temperatures of all joints exceeded A c3, and martensite phases with similar morphologies were formed in the stir zones. These martensite retained good toughness due to the self-tempering effect. The formation of ferrite and tempered martensite was the main reason for the hardness reduction in heat-affected zone. The mechanical properties of the lap joints were determined by loading mode, features of lap interface and the joint defects. When the stir pin was inserted into the lower sheet with a depth of 0.4 mm, the lap joint exhibited the maximum tensile strength of 12.4 kN.
基金supported by the National Natural Science Foundation of China (Nos. 51975553 and 51931009)IMR SYNL-T.S. Kê Research Fellowship。
文摘Strong metal/non-polar plastic dissimilar joints are highly demanded for the lightweight design in many fields,which,however,are rather challenging to achieve directly via welding.In this study,we designed a laser processing pretreatment on the Al alloy to create a deep porous Al surface structure,which was successfully joined to the polypropylene(PP) via friction spot welding.A maximum joint strength of29 MPa was achieved,the same as that of the base PP(i.e.the joint efficiency reached 100%),much larger than ever reported.The joining mechanism of the Al alloy and the PP was mainly attributed to the large mechanical interlocking effect between the laser processed Al porous structure and the re-solidified PP and the formation of chemical bond at the interface.The deep porous Al surface structure modified by laser processing largely changed the Al-PP reaction feature.The evidence of the C-O-Al chemical bond was first time found at the non-polar plastic/Al joint interface,which was the reaction result between the oxide on the Al alloy surface and thermal oxidization products of the PP during welding.This study provides a new way for enhancing metal-plastic joints via surface laser treatment techniques.
基金supported by the National Natural Science Foundation of China(Nos.52171121,51971151,and 51971053)the Liao Ning XingLiao Program(No.XLYC1907083)+4 种基金the Science Research Project of Liaoning Province Education Department(No.LQ2019002)the Fundamental Research Funds for the Central Universities(No.N2202020)the Science Research Project of Liaoning Province Education Department(No.LJ2020015)Natural Science Foundation of Liaoning Province of China(2022-NLTS-18-01)the Open Foundation of Key Laboratory of Superlight Materials&Surface Technology of Ministry of Education(HEU10202205).
文摘A conventional multi-pass rolling is designed to form different microstructures in a Mg-2Ag alloy.The relationship between microstructure and mechanical property is investigated.The result shows that twin-induced nucleation plays a prominent role for the dynamic recrystallization(DRX)behavior of the rolled Mg-2Ag alloys.The DRXed grains distributed around elongated grains have random orientations but gradually turn to the concentrated orientation with strong basal texture when the rolling pass increases.The yield strength and ultimate tensile strength of rolled Mg-2Ag alloy gradually increase with increasing rolling pass.The elongation of rolled sample is gradually improved when the rolling pass increases from one to three,while a significant drop of elongation shows in the four-pass rolling sample.The strong basal texture,refined grains,high-density dislocations,and Ag segregation along grain boundaries are suggested to play a prominent role for enhancing the strength of Mg-Ag alloys,while the low-density dislocations,homogeneously fine-grained microstructure,and weak texture are critical for improving the ductility.
基金supported by the National Natural Science Foundation of China under Grant Nos. 51671190, 51901225, 51774085 and 52034005the Open Research Fund from the State Key Laboratory of Rolling and Automation, Northeastern University (2020RALKFKT009)the Youth Innovation Promotion Association of the Chinese Academy of Sciences (2017236)。
文摘Ultrahigh-strength quenching and partitioning(Q&P) steels have attracted strong interests in the auto manufactory,while the comprehensive understanding in the microstructure and mechanical behavior of their welded joints is highly needed to enrich their applications.In the present work,it is designed to make an insight into these imperative conundrums.Equal strength Q&P 1180 steel joints to parent metal were successfully fabricated via friction stir welding(FSW) technique under different parameters. Apparent hardening and softening were observed in stir zone(SZ) and heat-affected zone(HAZ) respectively,whose microstructures strongly depended on the peak temperature and cooling rate during welding.The formation of fresh martensite was the main mechanism for the SZ hardening,while the decomposition of metastable phases played key roles in the microhardness drop of the HAZ.A heat source zone-isothermal phase transition layer model was proposed to clarify the impregnability of the joint strength under parameter variation.The dual-phase structure,nano-carbide particles,tempered initial martensite,and ultrafine-grained ferrite synergistically improved the strain hardening ability of the HAZ,which eventually resulted in the equal strength FSW joints.
基金financially supported by the National Key R&D Program of China(No.2017YFB0703104)。
文摘For additive manufactured aluminum alloys,the inferior mechanical properties along the building direction have been a serious weakness.In this study,an optimized heat treatment was developed as a simple and effective solution.The effects of direct aging on microstructure and mechanical properties along the building direction of AlSi10Mg samples produced via selective laser melting(SLM)were investigated.The results showed that,compared with the conventional heat treatment at elevated temperatures,direct aging at temperatures of 130-190℃ could retain the fine grain microstructure of SLM samples and promote further precipitation of Si phase,however,the growth of pores occurred during direct aging.With increasing aging temperature,while finer cell structures were obtained,more and larger pores were developed,resulting in decreased density of the samples.Two types of pore formation mechanisms were identified.Considering the balance between the refinement of cell structure and the growth of pores,aging at 130℃ was determined as the optimized heat treatment for SLM AlSi10Mg samples.The tensile strength along the building direction of the 130℃ aged sample was increased from 403 MPa to 451 MPa,with relatively high elongation of 6.5%.
基金supported by the National Natural Science Foundation of China(Nos.50802097 and 50832008)the Scientific Research Foundation for the Returned Overseas Chinese Scholars,State Education Ministrythe support of K.C.Wang Education Foundation, Hong Kong
文摘Nanolaminated Ti3AlC2honeycomb monolith with parallel and uniform holes has been prepared through a facile extrusion route by using Ti3AlC2powder as the main raw material.The fabricated honeycomb monolith has high compressive strength of 133 ± 11 and 59 ± 9 MPa,along and perpendicular to the extrusion direction,respectively.It also has good electrical conductivity,and excellent match of thermal expansion coefficient with the washcoat material of γ-AI2O3.These combined properties endow the honeycomb monolith a promising candidate as catalysis substrate for cleaning vehicle exhaust.
基金supported by the National Natural Science Foundation of China under grant Nos.51201163,51331008 and 51671190
文摘The microstructure and properties of water-cooled and air-cooled friction stir welded（FSW） ultra-high strength high nitrogen stainless steel joints were comparatively studied. With additional rapid cooling by flowing water, the peak temperature and duration at elevated temperature during FSW were significantly reduced. Compared to those in the air-cooled joint, nugget zone with finer grains（900 nm） and heat affected zone with higher dislocation density were successfully obtained in the water-cooled joint,leading to significantly improved mechanical properties. The wear of the welding tool was significantly reduced with water cooling, resulting in better corrosion resistance during the immersion corrosion test.
基金supported by the National Natural Science Foundation of China(NSFC,grant No.11063004)。
文摘We analyzed the relationship between several basic parameters describing supermassive black holes such as jet power,black hole spin,accretion disk magnetic field,black hole mass,etc.We found that there is a general correlation between these parameters,such as jet power is significantly positively correlated with black hole spin,while black hole mass is significantly negatively correlated with black hole spin.To apprehend these relationships,we consider the Blandford–Znajek model to be superior to the Blandford–Payne model.It is also found that the intrinsic gamma luminosity of the FSRQs has a positive correlation with the accretion disk magnetic field,while the intrinsic gamma luminosity of the BL Lacs has a negative correlation with the accretion disk magnetic field.A feedback effect may exist between accretion disk accretion rate and magnetic field,which may be the key to the evolution between BL Lacs and FSRQs.There is no significant difference in the jet power and jet generation efficiency of FSRQs and BL Lacs,which suggests that the jets are generated by the same mechanism.The contribution rate of accretion rate to jet generation efficiency is high,while the contribution rate of accretion rate to jet power is very low.
基金supported by the National Natural Science Foundation of China(Nos.51601194,51471171,and U1760201)the Chinese Academy of Sciences Youth Innovation Promotion Association(No.2021193)+1 种基金the Liaoning Provincial Natural Science Foundation(No.2021-YQ-01)the Liaoning Revitalization Talents Program(No.XLYC2002099)。
文摘The spheroidization of the lamellar structure can greatly contribute to the superplasticity of the nugget zone(NZ)of Ti alloy welds,which is the key to achieve the integral superplastic forming of welds for the fabrication of large-scale complex components.However,the spheroidization process is complex and costly since it cannot be obtained generally,unless the lamellae suffers from a large deformation.In this study,the static spheroidization was achieved for the fine lamellae structure in the nugget of a friction stir welded(FSW)Ti-6Al-4V joint,particularly by the annealing without any deformation.The specialα/βinterface obeying a Burgers orientation relationship(BOR)after FSW was first time directly observed,whose effect on the spheroidization was discussed.A new static spheroidization mechanism with the gradual coalescence of the adjacent lamellae was discovered,which we named as“termination coalescence”.There was a slower coarsening rate in the lamellar structure than in the classical equiaxed one,due to the BOR in the lamellae,although both of them exhibited a volume diffusion character during annealing.Consequently,the similar superplasticity can be achieved for the base material and NZ after annealing.This study can provide a new way to the spheroidization and a theoretical basis for the integral superplastic forming of welds during production.
基金supported by the National Natu-ral Science Foundation of China(Nos.52375396,52034005,and 51975553)the Liaoning Provincial Department of Science and Technology(No.2023JH2/101300149)+4 种基金the Shenyang Science and Technology Bureau(No.22-315-6-03)and Institute of Metal Re-search,Chinese Academy of Sciences(No.2023-ZD02-01)the Liaoning Province Excellent Youth Foundation(No.2021-YQ-01)the Program of the Youth Innovation Promotion Association of the Chi-nese Academy of Sciences(No.Y2021061)the Bintech-IMR R&D Program(No.GYY-JSBU-2022-002).
文摘Large-scale components of steel and aluminum alloys(Fe-Al)with high bonding strength are highly needed from space exploration to the fabrication of transportation systems.The formation of detrimental intermetallic compounds at the Al-Fe interface has limited the application range of the Fe-Al components.The modified friction stir additive manufacturing was developed for fabricating large-scale Fe-Al compo-nents with homogenously distributed interfacial amorphous layers rather than detrimental intermetallic compounds.The interfacial amorphous layers comprised an Mg-O rich amorphous layer<20 nm in thick-ness and an Al-Fe-Si amorphous layer<120 nm in thickness.The interfacial amorphous layers exhibited high thermal stability and did not change even after the post-processing heat treatment of heating at 500℃ for 20 min and aging at 170℃ for 7 h.The tensile strengths of the Fe-Al tensile specimens were increased from 160 to 250 MPa after the application of the post-processing heat treatment.The fracture occurred in the aluminum alloys instead of at the dissimilar metal interface,demonstrating that high bonding strength at the Al-Fe interface was enabled by the formation of homogenously distributed interfacial amorphous layers.
基金supported by the National Natural Science Foundation of China(Grant Nos.92163201 and U2067219)Shaanxi Province Youth Innovation Team Project(No.22JP042)+1 种基金Shaanxi Province Innovation Team Project(No.2024RS-CXTD-58)the Fundamental Research Funds for the Central Universities(No.xtr022019004).
文摘The chemical boundaries inside the ultrafine spinodal decomposition structure in metastable β-Ti alloys can act as a new feature to architect heterogeneous microstructures.In this work,we combined two semi-empirical methods,i.e.,the d-electron theory and the e/a electron concentration,to achieve the spinodal decomposition structure in a metastable β Ti-4.5Al-4.5Mo-7V-1.5Cr-1.5Zr(wt.%)alloy.Utilizing the spinodal decomposition structure,the aged Ti-Al-Mo-V-Cr-Zr alloys showed multi-architectured α precipitates spanning from micron-scale(primary α_(p))to nano-scale(secondary α_(s))that were uniformly distributed in the β-domains.Being compared with the forged sample,the multi-scale heterogeneous microstructure enables the aged β-Ti alloy to have ultra-high strength(yield strength ~1366 MPa and ultimate tensile strength ~1424 MPa)and an appreciable ductility(~9.3%).Strengthening models were proposed for the present alloys to estimate the contribution of various microstructural features to the measured yield strength.While the solid solution strengthening,β-spinodal strengthening,and back stress strengthening made comparable contributions to the strength of the forged alloy,the back stress strengthening was the predominant strengthening effect in the aged alloy.This alloy design approach based on chemical boundary engineering to construct multi-architectured α precipitates provided an effective strategy for achieving an outstanding combination of ultra-high strength and ductility in metastable β-Ti alloys.
基金supported by the National Natural Science Foundation of China (11072140)the State Key Laboratory of Ocean Engineering (Shanghai Jiao Tong University) (0803)The Shanghai Program for Innovative Research Team in Universities
文摘Analytical solutions for the flexural-gravity wave resistances due to a line source steadily moving on the surface of an infinitely deep fluid are investigated within the framework of the linear po- tential theory. The homogenous fluid, covered by a thin elastic plate, is assumed to be incompressible and inviscid, and the motion to be irrotational. The solution in integral form for the wave resistance is obtained by means of the Fourier transform and the explicitly analytical solutions are derived with the aid of the residue theorem. The dispersion relation shows that there is a minimal phase speed cmin, a threshold for the existence of the wave resistance. No wave is generated when the moving speed of the source V is less than emin while the wave resistances firstly increase to their peak values and then decrease when V ~〉 Crnin. The effects of the flexural rigidity and the inertia of the plate are studied. @ 2013 The Chinese Society of Theoretical and Applied Mechanics. [doi：10.1063/2.1302202]
基金This work was supported by the National Science Foundation under award No.CTS-9876198MRSEC program under award No.DMR-00800221.
文摘A good understanding of melting and resolidification of the substrate will help us to achieve better bonding.Anumerical model is developed to investigate the solidification of the droplet,and melting and resolidification of thesubstrate.The molybdenum powder spraying onto three different substrates:a stainless steel,brass(70%Cu)andaluminum by atmospheric plasma spraying has been investigated.The maximum melting depth of the substrate hasbeen measured and compared with the numerical prediction.Experimental results show that the material propertiesof the splat and substrate and melting temperature of the substrate play the important roles on substrate melting.A dimensionless parameter,temperature factor,has been proposed and served as an indicator for substrate melting.
基金supported by the National Natural Science Foundation of China(Grant Nos.12205201,12175154,11875092,and 12005149)the Natural Science Foundation of Top Talent of SZTU(Grant Nos.2019010801001 and 2019020801001)+1 种基金GCS Jülich(Project No.QED20)in GermanyThe EPOCH code is used under a UK EPSRC contract(Grant Nos.EP/G055165/1 and EP/G056803/1).
文摘Branched flow is an interesting phenomenon that can occur in diverse systems.It is usually linear in the sense that the flow does not alter the properties of the medium.Branched flow of light on thin films has recently been discovered.It is therefore of interest to know whether nonlinear light branching can also occur.Here,using particle-in-cell simulations,we find that in the case of an intense laser propagating through a randomly uneven medium,cascading local photoionization by the incident laser,together with the response of freed electrons in the strong laser fields,triggers space–time-dependent optical unevenness.The resulting branching pattern depends dramatically on the laser intensity.That is,the branching here is distinct from the existing linear ones.The observed branching properties agree well with theoretical analyses based on the Helmholtz equation.Nonlinear branched propagation of intense lasers potentially opens up a new area for laser–matter interaction and may be relevant to other branching phenomena of a nonlinear nature.
