For a long time,the large loss of the strength and toughness of fusion welded joints for thick nearβtitanium alloys has largely hindered their engineering application,which results from the few precipitations of the ...For a long time,the large loss of the strength and toughness of fusion welded joints for thick nearβtitanium alloys has largely hindered their engineering application,which results from the few precipitations of the strengtheningαphase during welding cooling.In this study,double annealing treatment was designed for electron beam welded joints of 30-mm-thick nearβTi-5Al-5Mo-5V-1Cr-1Fe alloy,with the aim of regulating the proportion of multi-level lamellar microstructures and enhancing the joint properties.Among various annealing temperatures(first annealing at 750–880 ℃+second annealing at 580 ℃),the 750 ℃+580 ℃ annealed joint exhibited simultaneously enhanced strength and toughness,with the increase in tensile strength and impact energy from 844 MPa and 8.8 J for the as-welded joint to 1129 MPa and 14.5 J for annealed joint,respectively,which were superior to those of the joints of Ti5Al-5Mo-5V-1Cr-1Fe alloy as reported.The great increases in the strength and toughness were mainly attributed to the excellent proportion matching of formed multi-level lamellar microstructures(76.1%of primaryα(αp)lamellae and 7.9%of secondaryα(αs)lamellae),among which theαp phase andαs phase mainly affected the joint toughness and strength,respectively.The good coupling ofαp phase andαs phase improved the precipitation strengthening and the resistance to crack propagation.The modified strengthening mechanism models were proposed by introducing the thickness and proportion parameters of the precipitated phase.It was indicated that the theoretical calculation values were in good agreement with the experimental ones,and the solution strengthening and precipitation strengthening provided a large contribution(a sum of about 75%)to the yield strength of the annealed joints.This study provides a novel method via designing proper multi-level lamellar microstructures to simultaneously improve the strength and toughness of nearβtitanium alloy joints.展开更多
Electron beam powder bed fusion(EB-PBF)offers a promising route for producing Ti_(6)Al_(4)V alloys with tailored microstructures and superior mechanical properties.Herein,EB-PBF produced nearly fully dense Ti 6Al 4V a...Electron beam powder bed fusion(EB-PBF)offers a promising route for producing Ti_(6)Al_(4)V alloys with tailored microstructures and superior mechanical properties.Herein,EB-PBF produced nearly fully dense Ti 6Al 4V alloys(≥98.5%)with basketweave microstructures containing fine equilibriumαlamellae,different from typicalα′acicular observed in materials produced via laser-PBF.The as-printed horizontal material has a yield strength(YS)of 992 MPa,an ultimate tensile strength(UTS)of 1053 MPa,and a fracture strain(ε)of 10.9%.Meanwhile,the as-printed longitudinal material shows inferior mechanical properties(YS of 934 MPa,UTS of 979 MPa,andεof 2.4%).The horizontal and longitudinal samples show notable hysteresis loops in the loading unloading reloading curves,indicating substantial heterogeneous-induced strengthening.Flow stress,back stress,and effective stress increase with increasing strain,where back stress is comparable to effective stress during the overall deformation.Furthermore,a monotonically decreased strain hardening rate with increasing strain can be attributed to dislocation activities,whose failure is related to the strain localization at theαlamellae boundary.展开更多
The microstructures and mechanical properties of 550 MPa grade lightweight high strength thin-walled H-beam steel were experimentally studied. The experimental results show that the microstructure of the air-cooled H-...The microstructures and mechanical properties of 550 MPa grade lightweight high strength thin-walled H-beam steel were experimentally studied. The experimental results show that the microstructure of the air-cooled H-beam steel sample is consisted of ferrite, pearlite and a small amount of granular bainites as well as fine and dispersive V（C,N） precipitates. The microstructure of the water-cooled steel sample is consisted of ferrite and bainite as well as a small amount of fine pearlites. The microstructure of the water-cooled sample is finer than that of the air-cooled sample with the average intercept size of the surface grains reaching to 3.5 gna. The finish rolling temperature of the thin-walled high strength H-beam steel is in the range of 750 ~C-850 ~C. The lower the finish rolling temperature and the faster the cooling rate, the finer the ferrite grains, the volume fraction of bainite is increased through water cooling process. Grain refinement strengthening and precipitation strengthening are used as major strengthening means to develop 550 MPa grade lightweight high strength thin- walled H-beam steel. Vanadium partially soluted in the matrix and contributes to the solution strengthening. The 550 MPa grade high-strength thin-walled H-beam steel could be developed by direct air cooling after hot rolling to fully meet the requirements of the target properties.展开更多
TiAl alloys fabricated by electron beam powder bed fusion(EB-PBF)usually exhibit special microstructures with alternating fine-grained(FG)regions and coarse-grained(CG)bands.In previous studies,the CG microstructures ...TiAl alloys fabricated by electron beam powder bed fusion(EB-PBF)usually exhibit special microstructures with alternating fine-grained(FG)regions and coarse-grained(CG)bands.In previous studies,the CG microstructures were equiaxed γ phases,and the FG microstructures presented three types:near gamma,duplex,and nearly lamellar.However,the rule for controlling FG microstructures has not been found.Hence,a method needs to be built to find the rule for controlling FG microstructures.Here,we established a normalized process diagram by combining Al-equivalent and dimensionless process parameters.Based on the normalized process diagram,we successfully control the FG microstructures and customize three FG microstructures of the Ti-48Al-2Cr-2Nb alloy.Meanwhile,the average tensile yield strength reaches 756 MPa when the FG microstructure is near gamma.The yield strength is higher than the previous data for the Ti-48Al-2Cr-2Nb alloy.This is attributed to the strong interface-strengthening effect between FG near γ microstructures and CG γ bands.These findings can help shorten the research time of the other TiAl alloys fabricated by EB-PBF,improving the mechanical properties of the other EBPBF-built TiAl alloys in the future.展开更多
It is rather difficult for titanium alloy ultra-thick plates to achieve superior weld formation and excellent mechanical properties along the weld penetration direction due to the large fluctuations of the molten pool...It is rather difficult for titanium alloy ultra-thick plates to achieve superior weld formation and excellent mechanical properties along the weld penetration direction due to the large fluctuations of the molten pool,largely limiting their engineering application.In this study,106-mm-thick Ti-6Al-4V ELI alloy plates were successfully butt welded via electron beam welding(EBW).The defect-free EBW joint with full penetration was obtained.The precipitated secondary α(α_(s))in heat affected zone(HAZ),αlamellae in fusion line(FL)and α′martensite in fusion zone(FZ)increased the α_(s)/β,α/β and α′/β interfaces,respectively,resulting in the higher microhardness and impact energy values(57 J in the HAZ,62 J in the FL and 51.9 J in the FZ)than those in the base material(BM).The impact energy of the joint in this study was higher than that for Ti-6Al-4V ELI alloy joints as reported,which was mainly attributed to the formation of the relatively thickerαphase and finer interlamellar spacing in this study,enhancing the resistance to crack propagation.Furthermore,the average fracture toughness(90.2 MPa m^(1/2))of the FZ was higher than that of the BM(74.2 MPa m^(1/2)).This study provides references for the welding application of titanium alloy ultra-thick plates in the manufacture of large-sized components.展开更多
Nearly undamaged joints of electron beam welded(EBW)dual-phase Mg-8Li-3Al-2Zn-0.5Y alloy were achieved with joint coefficients exceeding 95%.All specimens were fractured at the base metal(BM),implying a significant de...Nearly undamaged joints of electron beam welded(EBW)dual-phase Mg-8Li-3Al-2Zn-0.5Y alloy were achieved with joint coefficients exceeding 95%.All specimens were fractured at the base metal(BM),implying a significant departure from conventional fracture modes of welded joints.The fusion zone(FZ)consists of ultrafine acicular α-Mg and equiaxed β-Li,with grain sizes reduced by approximately 90% and 80%,respectively,compared to the base metal.This results in a significant increase in microhardness of about 40%.A unique multiphase mixture was observed in the heat-affected zone(HAZ),which mainly consists of lamellar eutectoid structures,fine precipitates zone,and numerous fine Mg_(3)(Al,Zn)particles.This mixture was transformed from typical Li(Al,Zn)(a common softening phase)undergoing atomic diffusion and solid-state phase transformation during welding.It introduces a synergistic strengthening effect,making the heat-affected zone no longer the weakest part of the joint.This study provides valuable insights into the electron beam welding technology for Mg-Li alloys and offers theoretical support for manufacturing high-quality joints.展开更多
The T-joints of Ti?6Al?4V alloy were manufactured by double-sided synchronized laser beam welding with the homologous filler wire. The formation, microstructure and mechanical properties of welded joints as well as th...The T-joints of Ti?6Al?4V alloy were manufactured by double-sided synchronized laser beam welding with the homologous filler wire. The formation, microstructure and mechanical properties of welded joints as well as the correlations of each other were investigated. The results indicate that the quality of weld seams is good without defects such as discontinuity, beading, visible cracks or porosity, which is linked to the steady molten pool behavior and droplet transition. The morphologies of the heat affected zone (HAZ) located on the skin and stringer are disparate. The microstructure of the HAZ and fusion zone (FZ) is mainly comprised of acicular martensiticα′ phases. The microhardness of the HAZ and FZ is higher than that of the base metal (BM) and reaches a maximum value at the HAZ near FZ on the stringer. The tensile specimens along the skin and stringer fractured at the BM with ductile fracture surfaces.展开更多
To improve the microstructure and properties of the electron beam welded joints, the vacuum or furnace whole post weld heat treatment (FWPWHT) usually should be done on it. The electron beam local post weld heat treat...To improve the microstructure and properties of the electron beam welded joints, the vacuum or furnace whole post weld heat treatment (FWPWHT) usually should be done on it. The electron beam local post weld heat treatment (EBLPWHT) is a rather new heat treatment procedure that provides the advantages of high precision, flexibility and efficiency, energy saving and higher productivity. In this paper, the microstructure, mechanical properties, fracture toughness and fatigue properties of electron beam welded joints of 30CrMnSiNi2A steel in as-welded (AW) and EBLPWHT conditions have been investigated respectively. The results show that the microstructures of different zones of joints in as-welded condition are changed by EBLPWHT procedure, in which the welds from coarse needle martensite into lath-shaped martensite; the main structures of heat affected zones (HAZ) from lath-shaped martensite into lower bainite. The properties of welded joints can be improved by the EBLPWHT in some extent, especially the fracture toughness of the welds and the fatigue crack resistance of welded joints can be sufficiently improved. However, more appropriate heat treatment parameters of the EBLPWHT have to be studied in order to increase the mechanical properties of base metal near by the HAZ.展开更多
With the development of the manufacturing technology, electron beam welding（EBW） is capable of producing titanium alloy large parts in aero fields. To increase the applications and improve the properties, EBW with b...With the development of the manufacturing technology, electron beam welding（EBW） is capable of producing titanium alloy large parts in aero fields. To increase the applications and improve the properties, EBW with beam oscillation was investigated on TC4-DT alloy with50 mm thickness. We detected the welding samples by X-ray NDT, observed the microstructures of the welds, and tested the fatigue properties of the joints. The results showed that EBW with beam oscillation improved the weld morphology as well as welding quality, and the microstructure homogeneity of the welds and HAZ along the weld penetration were also improved. The fatigue properties of the joints with beam oscillation were more excellent than those of conventional EBW, even equal to those of the base metal under high stresses. The influences of the processing and the microstructure on the properties with beam oscillation were discussed.展开更多
The Ti-24Al-15Nb-1.5Mo alloy, in the as-forged and heat-treated states, was joined to the as-forged TC 11 titanium alloy by electron beam welding with the heat inputs of 135 and 150 kJ/m. Then the microstructure and p...The Ti-24Al-15Nb-1.5Mo alloy, in the as-forged and heat-treated states, was joined to the as-forged TC 11 titanium alloy by electron beam welding with the heat inputs of 135 and 150 kJ/m. Then the microstructure and property of the Ti-24Al-15Nb- 1.5Mo/TC 11 welding interface were investigated. The results show that the phase constitution of the weld is not related to the heat input, and is mainly composed of α＇ phase. Moreover, the intermetallic phases of TiEAlNb, MoNb, NbaAl, and TiAl3 are formed in the weld zone. Therefore, the microhardness value of the weld zone is higher than that of the other portions in the same sample. The profile of the weld is asymmetrically fimnel-like. The grain sizes of the weld and its heat-affected zones are increased with increasing heat input. There is an obvious difference in the element content of the welding interface; only the alloying elements in the fusion zone reach a new balance during solidification.展开更多
Electron beam welding （EBW） was applied to a 10-mm-thick plate cut from Ti-6246 compressor disk. The microstructural characteristics, microhardness and room temperature tensile properties were investigated. Microstr...Electron beam welding （EBW） was applied to a 10-mm-thick plate cut from Ti-6246 compressor disk. The microstructural characteristics, microhardness and room temperature tensile properties were investigated. Microstructure observations indicated that there existed plenty of thin needle-like α platelets studding in the matrix of the columnar β grains in the as-welded fusion zone （FZ）. Post-weld heat treat- ment （PWHT） led to the precipitation of small secondary α platelets in the β matrix in heat affected zone and FZ. The thickness and the density of α platelets increased as the temperature of PWHT increased from 545 to 645 C. The microhardness across the Ti-6246 EBWjoint exhibited a nonuniform distribution. The hardness increased with the decrease of distance to the weld center, and reached the maximum of 467 HV in FZ when PWHT was carried out at 595 C. All the weldments tested with tension were fractured at the base material （BM） and exhibited a ductile fracture mode. The major deformation barrier in BM was the platelet α/β interfaces, however, the major deformation barrier in FZ was found to be β grain boundaries and secondary α/β interfaces. The BM with thicker platelet α phases had lower strength than the other two zones in the joint, and the BM deformed first and led to fracture in this zone.展开更多
Post-weld single aging treatment（solution treatment at 510 ℃ for 1 h, water quenching,and aging at 155 ℃ for 16 h） and post-weld double aging treatment（solution treatment at 510 ℃ for 1 h, water quenching, aging...Post-weld single aging treatment（solution treatment at 510 ℃ for 1 h, water quenching,and aging at 155 ℃ for 16 h） and post-weld double aging treatment（solution treatment at 510 ℃ for 1 h, water quenching, aging at 155 ℃ for 16 h, and aging at 130 ℃ for 12 h） are carried out on Al-Cu-Li alloy joints by electron beam welding（EBW） respectively. The effects of aging treatments on microstructures and mechanical properties of welded joints are investigated. Results show that the mechanical properties of welded joints are obviously improved after both aging treatments. The strength coefficient of joints is increased from 0.64 in an as-welded condition（AW） to 0.90 after post-weld double aging treatment. Microstructure analysis shows that the precipitates of the fusion zone within grains and grain boundaries are less in the AW condition. After post-weld heat treatment（PWHT）, a lot of fine needle-like phases T_1（Al_2 Cu Li） precipitate in grain boundaries of the fusion zone, and more horseshoe-shaped β＇ （Al_3 Zr） particles precipitate within grains. In addition,grains of the fusion zone are refined after post-weld double aging treatment, which leads to an effect of grain refinement strengthening. Consequently, the mechanical properties of welded joints are greatly improved.展开更多
The microstructure and mechanical properties of laser beam welded dissimilar joints in TC4 and TA15 titanium alloyswere investigated.The results showed that the coarse columnar grains containing a large amount of acic...The microstructure and mechanical properties of laser beam welded dissimilar joints in TC4 and TA15 titanium alloyswere investigated.The results showed that the coarse columnar grains containing a large amount of acicularαand martensiteα′werepresent in the fusion zone(FZ),some residualαphases and martensite structure were formed in the heat-affected zone(HAZ)onTC4 side,and bulk equiaxedαphase of the HAZ was on TA15 side.An asymmetrical microhardness profile across the dissimilarjoint was observed with the highest microhardness in the FZ and the lowest microhardness in TA15 BM.The orders of yield strengthand ultimate tensile strength were as follows:TC4 BM>TC4/TC4 similar joint>TA15 BM>TA15/TA15 similar joint>TC4/TA15dissimilar joint,and increased while hardening capacity and strain hardening exponent decreased with increasing strain rate from1×10?4 s?1 to 1×10?2 s?1.The TC4/TA15 dissimilar joints failed in the TA15 BM,and had characteristics of ductile fracture atdifferent strain rates.展开更多
Electron beam welding experiments of TZM alloy and 30CrMnSiA steel butt joints were carried out with different beam currents.Microstructures and chemical compositions of typical zones were analyzed by optical microsco...Electron beam welding experiments of TZM alloy and 30CrMnSiA steel butt joints were carried out with different beam currents.Microstructures and chemical compositions of typical zones were analyzed by optical microscopy,scanning electron microscopy and X-ray diffraction.The mechanical properties of the joints were evaluated by tensile strength tests.Besides,nanoindentation tests were carried out to compare the brittleness of the reaction layer and other typical microstructures.The results illustrated that the reaction layer at the interface between fusion zone(FZ)and TZM alloy was the weak position of the joint,which was divided into Fe2Mo layer and a mixture layer of Fe2Mo and a-Fe phases.As the beam current increased,the thickness of the Fe2Mo layer decreased,which resulted in the increasing of the tensile strength of the joints.When the beam current exceeded 24 m A,the formation of the joint was poor with a low tensile strength.When the beam current was 24 mA,the joint presented the highest strength of 191.3 MPa and the joint fractured along the Fe2Mo layer near the TZM alloy side with a brittle fracture mode.展开更多
Effects of welding parameters on the microstructure and mechanical properties of Ti/Cu/Ni joint welded by electron beam were investigated.High welding heat input increased the melting quantity of Ti60 titanium alloy a...Effects of welding parameters on the microstructure and mechanical properties of Ti/Cu/Ni joint welded by electron beam were investigated.High welding heat input increased the melting quantity of Ti60 titanium alloy and promoted the formation of Ti-Cu intermetallic compounds(IMC)such as Ti_(2)Cu and Ti_(3)Cu_(4),increasing the brittleness of the joints.Low welding heat input was not conducive to the complete melting of the copper interlayer,and the unmelted copper reduced the performance of the joints.Under the optimal welding parameters,Ti-Ni IMCs in the weld would be replaced by(Cu,Ni)solid solutions((Cu,Ni)_(ss)).However,Ti-Cu IMC layers cannot be eliminated entirely by changing the welding parameters.The maximum tensile strength of the joints was 201 MPa.The fracture of the joints occurred at the Ti-Cu IMC layer,which was a typical brittle fracture.展开更多
Two post weld heat treatments (PWHT), 900 ℃ oil quenched and low temperature tempered (PWHTA) and high temperature tempered and then 900 ℃ oil quenched and low temperature tempered (PWHTB), are employed to t...Two post weld heat treatments (PWHT), 900 ℃ oil quenched and low temperature tempered (PWHTA) and high temperature tempered and then 900 ℃ oil quenched and low temperature tempered (PWHTB), are employed to treat the weldment. Then the effect of two post weld heat treatment processes on the microstructure,mechanical properties and fracture toughness of electron beam welded joints of 30CrMnSiNi2A steel have been discussed. The results show that, after two kinds of PWHT the microstructure and hardness at every zones of EBW joints are nearly same. Although the welds have good mechanical properties, fracture toughness of both weld and heat affected zone (HAZ) is low, the CTOD values of welds are comparatively higher than that of HAZ. Microstructure and fracture toughness of two EBW joints have no evident differences.展开更多
The effects of two post-weld heat treatment processes on the microstructure and fatigue properties of the electron beam welded joints of 30CrMnSiNi2A steel were studied. Electron beam local post-weld heat treatment (E...The effects of two post-weld heat treatment processes on the microstructure and fatigue properties of the electron beam welded joints of 30CrMnSiNi2A steel were studied. Electron beam local post-weld heat treatment (EBLPWHT), in a vacuum chamber, immediately after welding and a traditional furnace whole post-weld heat treatment (FWPWHT) were accepted. The experimental results show that, after EBLPWHT, the main microstructure of weld is changed from coarse acicular martensite into lath martensite, and base metal is changed from ferrite and perlite into upper bainite and residual austenite, however the microstructures of different zones of joints in FWPWHT conditions are tempered sorbite. The fatigue crack growth rate da/dN of welds and base metal are not obviously changed among EBLPWHT, FWPWHT test and as-welded (AW) test, as the mechanical properties of materials have a certain but not large effect on the da/dN of welded joints. The resistance to near threshold fatigue crack growth data of welded joints can be largely improved by EBLPWHT and it is related to microstructure and crack closure effect.展开更多
In this paper,the effects of rare earth oxides on the micro structure and mechanical properties of nickelbased superalloys prepared by high-energy beam processing technology were critically studied.The focus is on the...In this paper,the effects of rare earth oxides on the micro structure and mechanical properties of nickelbased superalloys prepared by high-energy beam processing technology were critically studied.The focus is on the optimal amount of rare earth oxides that can produce ideal results.Special attention was paid to their main strengthening mechanisms,including solid solution strengthening mainly in the form of solid solution dissolved in the nickel-based alloy and improving the microstructure of the alloy by grain refinement or fine grain strengthening produced by homogenizing the distribution phase.Y_(2)O_(3),La_(2)O_(3) and CeO_(2) rare earth oxides can also improve the fluidity of the alloy molten pool and reduce the segregation of alloying elements.These advantages can significantly improve the mechanical properties of the alloy.Thereafter,this paper outlines the future research directions of rare earth oxides,aiming to expand their application potential.展开更多
The effects of microstructure inhomogeneity on the mechanical properties of different zones in TA15 electron beam welded joints were investigated using a micromechanics-based finite element method.Considering the inde...The effects of microstructure inhomogeneity on the mechanical properties of different zones in TA15 electron beam welded joints were investigated using a micromechanics-based finite element method.Considering the indentation size effect,the mechanical properties for constituent phases of the base metal(BM) and heat affected zone(HAZ) were determined by the instrumented nano-indentation test.The macroscopic mechanical properties of BM and HAZ obtained from the tensile test agree well with the numerical results.The incompatible deformation between the constituent phases tends to localize along the softer primary phase a where failure usually initiates in form of localized plastic strain.Compared with the BM,the mechanical properties of constituent phases in the HAZ differ substantially,leading to more serious strain localization behavior.展开更多
Electron beam welding of titanium alloy to aluminum alloy was carried out by melting and melt-brazing to investigate the effects of welding parameters on microstructure of the joint. The results indicated that the joi...Electron beam welding of titanium alloy to aluminum alloy was carried out by melting and melt-brazing to investigate the effects of welding parameters on microstructure of the joint. The results indicated that the joint of the specimen welded by melting was well-formed but contained a large amount of intermetallic compounds. These intermetallic compounds were mainly composed of brittle phases such as TiAl and TiAl3 that decreased the ductility of the joints and resulted in a tensile strength 50 % lower than that of the base metal. In the melt-brazing experiment, direct heat was applied to the aluminum alloy to melt the aluminum rather than the titanium alloy, creating a well-formed joint. The weld was mainly composed of Al element and only a 3 ~m thickness of intermetallic compounds formed near the fusion line at the Ti side. The ductility and the performauce of the joint were significantly improved compared with those of the melting-only joint. In addition, the tensile strength of the joint reached 80 % of that of the aluminum base metal.展开更多
基金supported by the National Key Re-search and Development Program of China(No.2023YFC2810700)the Youth Innovation Promotion Association of the Chinese Academy of Sciences(No.2021193)+2 种基金Liaoning Province Excellent Youth Foundation(No.2024JH3/10200021)the Liaoning Revital-ization Talents Program(No.XLYC2403094)the Scientific In-strument Developing Project of the Chinese Academy of Sciences(No.PTYQ2024YZ0009).
文摘For a long time,the large loss of the strength and toughness of fusion welded joints for thick nearβtitanium alloys has largely hindered their engineering application,which results from the few precipitations of the strengtheningαphase during welding cooling.In this study,double annealing treatment was designed for electron beam welded joints of 30-mm-thick nearβTi-5Al-5Mo-5V-1Cr-1Fe alloy,with the aim of regulating the proportion of multi-level lamellar microstructures and enhancing the joint properties.Among various annealing temperatures(first annealing at 750–880 ℃+second annealing at 580 ℃),the 750 ℃+580 ℃ annealed joint exhibited simultaneously enhanced strength and toughness,with the increase in tensile strength and impact energy from 844 MPa and 8.8 J for the as-welded joint to 1129 MPa and 14.5 J for annealed joint,respectively,which were superior to those of the joints of Ti5Al-5Mo-5V-1Cr-1Fe alloy as reported.The great increases in the strength and toughness were mainly attributed to the excellent proportion matching of formed multi-level lamellar microstructures(76.1%of primaryα(αp)lamellae and 7.9%of secondaryα(αs)lamellae),among which theαp phase andαs phase mainly affected the joint toughness and strength,respectively.The good coupling ofαp phase andαs phase improved the precipitation strengthening and the resistance to crack propagation.The modified strengthening mechanism models were proposed by introducing the thickness and proportion parameters of the precipitated phase.It was indicated that the theoretical calculation values were in good agreement with the experimental ones,and the solution strengthening and precipitation strengthening provided a large contribution(a sum of about 75%)to the yield strength of the annealed joints.This study provides a novel method via designing proper multi-level lamellar microstructures to simultaneously improve the strength and toughness of nearβtitanium alloy joints.
基金support from the National Key Research and Development Program of China(No.2022YFB3705600)the Shanghai Science and Technology Innovation Action Plan(No.22SQBS00600).
文摘Electron beam powder bed fusion(EB-PBF)offers a promising route for producing Ti_(6)Al_(4)V alloys with tailored microstructures and superior mechanical properties.Herein,EB-PBF produced nearly fully dense Ti 6Al 4V alloys(≥98.5%)with basketweave microstructures containing fine equilibriumαlamellae,different from typicalα′acicular observed in materials produced via laser-PBF.The as-printed horizontal material has a yield strength(YS)of 992 MPa,an ultimate tensile strength(UTS)of 1053 MPa,and a fracture strain(ε)of 10.9%.Meanwhile,the as-printed longitudinal material shows inferior mechanical properties(YS of 934 MPa,UTS of 979 MPa,andεof 2.4%).The horizontal and longitudinal samples show notable hysteresis loops in the loading unloading reloading curves,indicating substantial heterogeneous-induced strengthening.Flow stress,back stress,and effective stress increase with increasing strain,where back stress is comparable to effective stress during the overall deformation.Furthermore,a monotonically decreased strain hardening rate with increasing strain can be attributed to dislocation activities,whose failure is related to the strain localization at theαlamellae boundary.
基金Funded by the "11th Five" National Science and Technology Support Project(No.2006BAE03A13)
文摘The microstructures and mechanical properties of 550 MPa grade lightweight high strength thin-walled H-beam steel were experimentally studied. The experimental results show that the microstructure of the air-cooled H-beam steel sample is consisted of ferrite, pearlite and a small amount of granular bainites as well as fine and dispersive V（C,N） precipitates. The microstructure of the water-cooled steel sample is consisted of ferrite and bainite as well as a small amount of fine pearlites. The microstructure of the water-cooled sample is finer than that of the air-cooled sample with the average intercept size of the surface grains reaching to 3.5 gna. The finish rolling temperature of the thin-walled high strength H-beam steel is in the range of 750 ~C-850 ~C. The lower the finish rolling temperature and the faster the cooling rate, the finer the ferrite grains, the volume fraction of bainite is increased through water cooling process. Grain refinement strengthening and precipitation strengthening are used as major strengthening means to develop 550 MPa grade lightweight high strength thin- walled H-beam steel. Vanadium partially soluted in the matrix and contributes to the solution strengthening. The 550 MPa grade high-strength thin-walled H-beam steel could be developed by direct air cooling after hot rolling to fully meet the requirements of the target properties.
基金financially supported by the National Science Foundation of China(Nos.92163215,52305379,52322101,52174364,52101143,51771093,and 12202201)the Fundamental Research Funds for the Central Universities(Nos.30922010202,and 30922010711)+4 种基金the Key Laboratory Funds for the Science and Technology of National Defense(No.6142212210103)the Natural Science Foundation of Jiangsu Province Major Project(No.BK20212009)the Xi’an Qinchuangyuan Construction of Two-Chain Integration Major Special Projects(No.23LLRHZDZX0015)the Aviation Science Foundation of AVIC(No.2024M0530S8002)the Natural Science Basic Research Program of Shaanxi Province(No.2024JC-YBQN-0579).
文摘TiAl alloys fabricated by electron beam powder bed fusion(EB-PBF)usually exhibit special microstructures with alternating fine-grained(FG)regions and coarse-grained(CG)bands.In previous studies,the CG microstructures were equiaxed γ phases,and the FG microstructures presented three types:near gamma,duplex,and nearly lamellar.However,the rule for controlling FG microstructures has not been found.Hence,a method needs to be built to find the rule for controlling FG microstructures.Here,we established a normalized process diagram by combining Al-equivalent and dimensionless process parameters.Based on the normalized process diagram,we successfully control the FG microstructures and customize three FG microstructures of the Ti-48Al-2Cr-2Nb alloy.Meanwhile,the average tensile yield strength reaches 756 MPa when the FG microstructure is near gamma.The yield strength is higher than the previous data for the Ti-48Al-2Cr-2Nb alloy.This is attributed to the strong interface-strengthening effect between FG near γ microstructures and CG γ bands.These findings can help shorten the research time of the other TiAl alloys fabricated by EB-PBF,improving the mechanical properties of the other EBPBF-built TiAl alloys in the future.
基金supported by the National Key Research and Development Program of China(No.2023YFC2810700)the Youth Innovation Promotion Association of the Chinese Academy of Sciences(No.2021193)+2 种基金the Liaoning Province Excellent Youth Foundation(No.2024JH3/10200021)the Liaoning Revitalization Talents Program(No.XLYC2403094)the Scientific Instrument Developing Project of the Chinese Academy of Sciences(No.PTYQ2024YZ0009).
文摘It is rather difficult for titanium alloy ultra-thick plates to achieve superior weld formation and excellent mechanical properties along the weld penetration direction due to the large fluctuations of the molten pool,largely limiting their engineering application.In this study,106-mm-thick Ti-6Al-4V ELI alloy plates were successfully butt welded via electron beam welding(EBW).The defect-free EBW joint with full penetration was obtained.The precipitated secondary α(α_(s))in heat affected zone(HAZ),αlamellae in fusion line(FL)and α′martensite in fusion zone(FZ)increased the α_(s)/β,α/β and α′/β interfaces,respectively,resulting in the higher microhardness and impact energy values(57 J in the HAZ,62 J in the FL and 51.9 J in the FZ)than those in the base material(BM).The impact energy of the joint in this study was higher than that for Ti-6Al-4V ELI alloy joints as reported,which was mainly attributed to the formation of the relatively thickerαphase and finer interlamellar spacing in this study,enhancing the resistance to crack propagation.Furthermore,the average fracture toughness(90.2 MPa m^(1/2))of the FZ was higher than that of the BM(74.2 MPa m^(1/2)).This study provides references for the welding application of titanium alloy ultra-thick plates in the manufacture of large-sized components.
基金financially supported by the National Defense Basic Research Program(No.JCKY2023204A005)Project of High Modulus Magnesium Alloy Forgings(JXXT-2023-014hbza)+1 种基金Research Program of Joint Research Center of Advanced Spaceflight Technologies(No.USCAST2023-3)Major Scientific and Technological Innovation Project of Luoyang(No.2201029A).
文摘Nearly undamaged joints of electron beam welded(EBW)dual-phase Mg-8Li-3Al-2Zn-0.5Y alloy were achieved with joint coefficients exceeding 95%.All specimens were fractured at the base metal(BM),implying a significant departure from conventional fracture modes of welded joints.The fusion zone(FZ)consists of ultrafine acicular α-Mg and equiaxed β-Li,with grain sizes reduced by approximately 90% and 80%,respectively,compared to the base metal.This results in a significant increase in microhardness of about 40%.A unique multiphase mixture was observed in the heat-affected zone(HAZ),which mainly consists of lamellar eutectoid structures,fine precipitates zone,and numerous fine Mg_(3)(Al,Zn)particles.This mixture was transformed from typical Li(Al,Zn)(a common softening phase)undergoing atomic diffusion and solid-state phase transformation during welding.It introduces a synergistic strengthening effect,making the heat-affected zone no longer the weakest part of the joint.This study provides valuable insights into the electron beam welding technology for Mg-Li alloys and offers theoretical support for manufacturing high-quality joints.
基金Project supported by Science and Technology on Power Beam Processes Laboratory at Beijing Aeronautical Manufacturing Technology Research Institute,China
文摘The T-joints of Ti?6Al?4V alloy were manufactured by double-sided synchronized laser beam welding with the homologous filler wire. The formation, microstructure and mechanical properties of welded joints as well as the correlations of each other were investigated. The results indicate that the quality of weld seams is good without defects such as discontinuity, beading, visible cracks or porosity, which is linked to the steady molten pool behavior and droplet transition. The morphologies of the heat affected zone (HAZ) located on the skin and stringer are disparate. The microstructure of the HAZ and fusion zone (FZ) is mainly comprised of acicular martensiticα′ phases. The microhardness of the HAZ and FZ is higher than that of the base metal (BM) and reaches a maximum value at the HAZ near FZ on the stringer. The tensile specimens along the skin and stringer fractured at the BM with ductile fracture surfaces.
文摘To improve the microstructure and properties of the electron beam welded joints, the vacuum or furnace whole post weld heat treatment (FWPWHT) usually should be done on it. The electron beam local post weld heat treatment (EBLPWHT) is a rather new heat treatment procedure that provides the advantages of high precision, flexibility and efficiency, energy saving and higher productivity. In this paper, the microstructure, mechanical properties, fracture toughness and fatigue properties of electron beam welded joints of 30CrMnSiNi2A steel in as-welded (AW) and EBLPWHT conditions have been investigated respectively. The results show that the microstructures of different zones of joints in as-welded condition are changed by EBLPWHT procedure, in which the welds from coarse needle martensite into lath-shaped martensite; the main structures of heat affected zones (HAZ) from lath-shaped martensite into lower bainite. The properties of welded joints can be improved by the EBLPWHT in some extent, especially the fracture toughness of the welds and the fatigue crack resistance of welded joints can be sufficiently improved. However, more appropriate heat treatment parameters of the EBLPWHT have to be studied in order to increase the mechanical properties of base metal near by the HAZ.
基金financially supported by the National Natural Science Foundation of China(No.50935008)Special Major Science and Technology of China(No.2010ZX04007041)the National Key Laboratory of High Energy Density Beam Processing Technology of China
文摘With the development of the manufacturing technology, electron beam welding（EBW） is capable of producing titanium alloy large parts in aero fields. To increase the applications and improve the properties, EBW with beam oscillation was investigated on TC4-DT alloy with50 mm thickness. We detected the welding samples by X-ray NDT, observed the microstructures of the welds, and tested the fatigue properties of the joints. The results showed that EBW with beam oscillation improved the weld morphology as well as welding quality, and the microstructure homogeneity of the welds and HAZ along the weld penetration were also improved. The fatigue properties of the joints with beam oscillation were more excellent than those of conventional EBW, even equal to those of the base metal under high stresses. The influences of the processing and the microstructure on the properties with beam oscillation were discussed.
基金supported by the National Natural Science Foundation of China (No.50775187)
文摘The Ti-24Al-15Nb-1.5Mo alloy, in the as-forged and heat-treated states, was joined to the as-forged TC 11 titanium alloy by electron beam welding with the heat inputs of 135 and 150 kJ/m. Then the microstructure and property of the Ti-24Al-15Nb- 1.5Mo/TC 11 welding interface were investigated. The results show that the phase constitution of the weld is not related to the heat input, and is mainly composed of α＇ phase. Moreover, the intermetallic phases of TiEAlNb, MoNb, NbaAl, and TiAl3 are formed in the weld zone. Therefore, the microhardness value of the weld zone is higher than that of the other portions in the same sample. The profile of the weld is asymmetrically fimnel-like. The grain sizes of the weld and its heat-affected zones are increased with increasing heat input. There is an obvious difference in the element content of the welding interface; only the alloying elements in the fusion zone reach a new balance during solidification.
文摘Electron beam welding （EBW） was applied to a 10-mm-thick plate cut from Ti-6246 compressor disk. The microstructural characteristics, microhardness and room temperature tensile properties were investigated. Microstructure observations indicated that there existed plenty of thin needle-like α platelets studding in the matrix of the columnar β grains in the as-welded fusion zone （FZ）. Post-weld heat treat- ment （PWHT） led to the precipitation of small secondary α platelets in the β matrix in heat affected zone and FZ. The thickness and the density of α platelets increased as the temperature of PWHT increased from 545 to 645 C. The microhardness across the Ti-6246 EBWjoint exhibited a nonuniform distribution. The hardness increased with the decrease of distance to the weld center, and reached the maximum of 467 HV in FZ when PWHT was carried out at 595 C. All the weldments tested with tension were fractured at the base material （BM） and exhibited a ductile fracture mode. The major deformation barrier in BM was the platelet α/β interfaces, however, the major deformation barrier in FZ was found to be β grain boundaries and secondary α/β interfaces. The BM with thicker platelet α phases had lower strength than the other two zones in the joint, and the BM deformed first and led to fracture in this zone.
基金project was supported by the Aeronautical Science Foundation of China (No. 2015ZE52048)A Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions
文摘Post-weld single aging treatment（solution treatment at 510 ℃ for 1 h, water quenching,and aging at 155 ℃ for 16 h） and post-weld double aging treatment（solution treatment at 510 ℃ for 1 h, water quenching, aging at 155 ℃ for 16 h, and aging at 130 ℃ for 12 h） are carried out on Al-Cu-Li alloy joints by electron beam welding（EBW） respectively. The effects of aging treatments on microstructures and mechanical properties of welded joints are investigated. Results show that the mechanical properties of welded joints are obviously improved after both aging treatments. The strength coefficient of joints is increased from 0.64 in an as-welded condition（AW） to 0.90 after post-weld double aging treatment. Microstructure analysis shows that the precipitates of the fusion zone within grains and grain boundaries are less in the AW condition. After post-weld heat treatment（PWHT）, a lot of fine needle-like phases T_1（Al_2 Cu Li） precipitate in grain boundaries of the fusion zone, and more horseshoe-shaped β＇ （Al_3 Zr） particles precipitate within grains. In addition,grains of the fusion zone are refined after post-weld double aging treatment, which leads to an effect of grain refinement strengthening. Consequently, the mechanical properties of welded joints are greatly improved.
基金Project(51405392)supported by the National Natural Science Foundation of ChinaProject(20136102120022)supported by the Research Fund for the Doctoral Program of Higher Education of ChinaProject(3102015ZY023)supported by the Fundamental Research Funds for the Central Universities,China
文摘The microstructure and mechanical properties of laser beam welded dissimilar joints in TC4 and TA15 titanium alloyswere investigated.The results showed that the coarse columnar grains containing a large amount of acicularαand martensiteα′werepresent in the fusion zone(FZ),some residualαphases and martensite structure were formed in the heat-affected zone(HAZ)onTC4 side,and bulk equiaxedαphase of the HAZ was on TA15 side.An asymmetrical microhardness profile across the dissimilarjoint was observed with the highest microhardness in the FZ and the lowest microhardness in TA15 BM.The orders of yield strengthand ultimate tensile strength were as follows:TC4 BM>TC4/TC4 similar joint>TA15 BM>TA15/TA15 similar joint>TC4/TA15dissimilar joint,and increased while hardening capacity and strain hardening exponent decreased with increasing strain rate from1×10?4 s?1 to 1×10?2 s?1.The TC4/TA15 dissimilar joints failed in the TA15 BM,and had characteristics of ductile fracture atdifferent strain rates.
基金supported by Shandong Provincial Key Research and Development Program of China(No.2019JZZY010439)International Science&Technology Cooperation Program of China(No.2011DFR50760)。
文摘Electron beam welding experiments of TZM alloy and 30CrMnSiA steel butt joints were carried out with different beam currents.Microstructures and chemical compositions of typical zones were analyzed by optical microscopy,scanning electron microscopy and X-ray diffraction.The mechanical properties of the joints were evaluated by tensile strength tests.Besides,nanoindentation tests were carried out to compare the brittleness of the reaction layer and other typical microstructures.The results illustrated that the reaction layer at the interface between fusion zone(FZ)and TZM alloy was the weak position of the joint,which was divided into Fe2Mo layer and a mixture layer of Fe2Mo and a-Fe phases.As the beam current increased,the thickness of the Fe2Mo layer decreased,which resulted in the increasing of the tensile strength of the joints.When the beam current exceeded 24 m A,the formation of the joint was poor with a low tensile strength.When the beam current was 24 mA,the joint presented the highest strength of 191.3 MPa and the joint fractured along the Fe2Mo layer near the TZM alloy side with a brittle fracture mode.
基金supported by Shandong Provincial Key Research and Development Program of China(2019JZZY010439)。
文摘Effects of welding parameters on the microstructure and mechanical properties of Ti/Cu/Ni joint welded by electron beam were investigated.High welding heat input increased the melting quantity of Ti60 titanium alloy and promoted the formation of Ti-Cu intermetallic compounds(IMC)such as Ti_(2)Cu and Ti_(3)Cu_(4),increasing the brittleness of the joints.Low welding heat input was not conducive to the complete melting of the copper interlayer,and the unmelted copper reduced the performance of the joints.Under the optimal welding parameters,Ti-Ni IMCs in the weld would be replaced by(Cu,Ni)solid solutions((Cu,Ni)_(ss)).However,Ti-Cu IMC layers cannot be eliminated entirely by changing the welding parameters.The maximum tensile strength of the joints was 201 MPa.The fracture of the joints occurred at the Ti-Cu IMC layer,which was a typical brittle fracture.
文摘Two post weld heat treatments (PWHT), 900 ℃ oil quenched and low temperature tempered (PWHTA) and high temperature tempered and then 900 ℃ oil quenched and low temperature tempered (PWHTB), are employed to treat the weldment. Then the effect of two post weld heat treatment processes on the microstructure,mechanical properties and fracture toughness of electron beam welded joints of 30CrMnSiNi2A steel have been discussed. The results show that, after two kinds of PWHT the microstructure and hardness at every zones of EBW joints are nearly same. Although the welds have good mechanical properties, fracture toughness of both weld and heat affected zone (HAZ) is low, the CTOD values of welds are comparatively higher than that of HAZ. Microstructure and fracture toughness of two EBW joints have no evident differences.
基金thefoundationoftheNationalDefenseTechnologyKeyLaboratory (No .99JS5 0 .3 .2JW14 0 2 )
文摘The effects of two post-weld heat treatment processes on the microstructure and fatigue properties of the electron beam welded joints of 30CrMnSiNi2A steel were studied. Electron beam local post-weld heat treatment (EBLPWHT), in a vacuum chamber, immediately after welding and a traditional furnace whole post-weld heat treatment (FWPWHT) were accepted. The experimental results show that, after EBLPWHT, the main microstructure of weld is changed from coarse acicular martensite into lath martensite, and base metal is changed from ferrite and perlite into upper bainite and residual austenite, however the microstructures of different zones of joints in FWPWHT conditions are tempered sorbite. The fatigue crack growth rate da/dN of welds and base metal are not obviously changed among EBLPWHT, FWPWHT test and as-welded (AW) test, as the mechanical properties of materials have a certain but not large effect on the da/dN of welded joints. The resistance to near threshold fatigue crack growth data of welded joints can be largely improved by EBLPWHT and it is related to microstructure and crack closure effect.
基金Project supported by China Postdoctoral Science Foundation(2021M7010380)the Natural Science Foundation of Shanghai (20ZR1422700)Class Ⅲ Peak Discipline of Shanghai-Materials Science and Engineering (High-Energy Beam Intelligent Processing and Green Manufacturing)。
文摘In this paper,the effects of rare earth oxides on the micro structure and mechanical properties of nickelbased superalloys prepared by high-energy beam processing technology were critically studied.The focus is on the optimal amount of rare earth oxides that can produce ideal results.Special attention was paid to their main strengthening mechanisms,including solid solution strengthening mainly in the form of solid solution dissolved in the nickel-based alloy and improving the microstructure of the alloy by grain refinement or fine grain strengthening produced by homogenizing the distribution phase.Y_(2)O_(3),La_(2)O_(3) and CeO_(2) rare earth oxides can also improve the fluidity of the alloy molten pool and reduce the segregation of alloying elements.These advantages can significantly improve the mechanical properties of the alloy.Thereafter,this paper outlines the future research directions of rare earth oxides,aiming to expand their application potential.
基金Project(51875402)supported by the National Natural Science Foundation of China
文摘The effects of microstructure inhomogeneity on the mechanical properties of different zones in TA15 electron beam welded joints were investigated using a micromechanics-based finite element method.Considering the indentation size effect,the mechanical properties for constituent phases of the base metal(BM) and heat affected zone(HAZ) were determined by the instrumented nano-indentation test.The macroscopic mechanical properties of BM and HAZ obtained from the tensile test agree well with the numerical results.The incompatible deformation between the constituent phases tends to localize along the softer primary phase a where failure usually initiates in form of localized plastic strain.Compared with the BM,the mechanical properties of constituent phases in the HAZ differ substantially,leading to more serious strain localization behavior.
文摘Electron beam welding of titanium alloy to aluminum alloy was carried out by melting and melt-brazing to investigate the effects of welding parameters on microstructure of the joint. The results indicated that the joint of the specimen welded by melting was well-formed but contained a large amount of intermetallic compounds. These intermetallic compounds were mainly composed of brittle phases such as TiAl and TiAl3 that decreased the ductility of the joints and resulted in a tensile strength 50 % lower than that of the base metal. In the melt-brazing experiment, direct heat was applied to the aluminum alloy to melt the aluminum rather than the titanium alloy, creating a well-formed joint. The weld was mainly composed of Al element and only a 3 ~m thickness of intermetallic compounds formed near the fusion line at the Ti side. The ductility and the performauce of the joint were significantly improved compared with those of the melting-only joint. In addition, the tensile strength of the joint reached 80 % of that of the aluminum base metal.
