Twinning-induced plasticity(TWIP)steel was processed using electrically assisted friction stir welding(EFSW).The microstructure,mechanical properties,and deformation behavior of the welded joints were systematically i...Twinning-induced plasticity(TWIP)steel was processed using electrically assisted friction stir welding(EFSW).The microstructure,mechanical properties,and deformation behavior of the welded joints were systematically investigated.The results show that the average grain size was refined from 3.67μm in the base material(BM)to 1.39μm in the stir zone(SZ),while it increased to 4.19μm in the heat-affected zone(HAZ).The fraction of twin boundaries(TBs)decreased from 20.7%in the BM to 6.9%in the SZ and increased to24.5%in the HAZ.The ultimate tensile strength,yield strength,and elongation of the BM were 1021 MPa,505 MPa,and 65.8%,respectively.In comparison,the EFSW joint exhibited values of 1055 MPa,561 MPa,and 60.8%,corresponding to 103.3%,111.1%,and 92.4%of those of the BM,respectively.During tensile testing,plastic deformation was primarily concentrated in the BM,although both the SZ and HAZ also exhibited notable plastic deformation.Fracture ultimately occurred in the BM.展开更多
In this work,the effect of microstructure features on the high-cycle fatigue behavior of Ti-7Mo-3Nb-3Cr-3Al(Ti-7333)alloy is investigated.Fatigue tests were carried out at room temperature in lab air atmosphere using ...In this work,the effect of microstructure features on the high-cycle fatigue behavior of Ti-7Mo-3Nb-3Cr-3Al(Ti-7333)alloy is investigated.Fatigue tests were carried out at room temperature in lab air atmosphere using a sinusoidal wave at a frequency of 120 Hz and a stress ratio of 0.1.Results show that the fatigue strength is closely related to the microstructure features,especially theα_(p) percentage.The Ti-7333 alloy with a lowerα_(p) percentage exhibits a higher scatter in fatigue data.The bimodal fatigue behavior and the duality of the S-N curve are reported in the Ti-7333 alloy with relatively lowerα_(p) percentage.Crack initiation region shows the compoundα_(p)/βfacets.Facetedα_(p) particles show crystallographic orientation and morphology dependence characteristics.Crack-initiation was accompanied by faceting process across elongatedα_(p) particles or multiple adjacentα_(p) particles.These particles generally oriented for basal slip result in near basal facets.Fatigue crack can also initiate at elongatedα_(p) particle well oriented for prismatic slip.Theβfacet is in close correspondence to{110}or{112}plane with high Schmid factor.Based on the fracture observation and FIB-CS analysis,three classes of fatigue-critical microstructural configurations are deduced.A phenomenological model for the formation ofα_(p) facet in the bimodal microstructure is proposed.This work provides an insight into the fatigue damage process of theβprecipitate strengthened metastableβtitanium alloys.展开更多
The coarse as-cast lamellar microstructure in TiAl alloys is difficult to be broken completely by thermomechanical processing. Some remnant lamellar colonies in the deformed microstructure seriously affect the microst...The coarse as-cast lamellar microstructure in TiAl alloys is difficult to be broken completely by thermomechanical processing. Some remnant lamellar colonies in the deformed microstructure seriously affect the microstructural homogeneity and deteriorate the properties. In this study, it is found that by isothermal compression at 1230 °C and 1250 °C, the lamellar colonies of Ti-43.5Al-4Nb-1Mo-0.1B (TNM) alloys can be completely broken. This is attributed to the weakened anisotropic deformation behavior of the lamellar colonies due to the isothermal holding treatment before deformation. The deformation behavior at 1230 °C was investigated by quasi-in-situ experiments. It is observed that the regions near lamellar colony boundaries first undergo dynamic recrystallization at small strain, while the lamellar colonies gradually break down with increasing strain. The adequate fragmentation of lamellar colonies mainly depends on the recrystallization of α lamellae (αL). The isothermal holding at 1230 °C leads to an increase in the content and thickness of αL, which allows it to assume more deformation and promotes its recrystallization by reaching critical strain. The interrupted γ lamellae (γL) formed by decomposition during isothermal holding facilitates the occurrence of α recrystallization within the lamellar colonies by hindering dislocation movement. In addition, recrystallized γ grains (γR) are gradually dissolved by the formation of α precipitates inside them through the γ → α phase transformation and the subsequent consumption of α precipitates by the recrystallized α grains.展开更多
The restoration mechanism of twin-induced plasticity(TWIP)steel during friction stir welding(FSW)changed with the degree of the deformation,and the microstructure evolution and dynamic recrystallization are complex an...The restoration mechanism of twin-induced plasticity(TWIP)steel during friction stir welding(FSW)changed with the degree of the deformation,and the microstructure evolution and dynamic recrystallization are complex and unclear.In this paper,the electron backscattered diffraction and transmission electron microscopy techniques were used to evaluate the dynamic grain structure of FSW joint of TWIP steel.The results showed that the dynamic recrystallization mechanisms in TWIP steel during FSW contained discontinuous dynamic recrystallization(DDRX)and continuous dynamic recrystallization(CDRX).The recrystallization mechanism transitioned from DDRX at the initial deformation stage to DDRX and CDRX at the middle deformation stage,eventually becoming primarily CDRX at the end deformation stage.Numerous annealing twin boundaries(ATBs)were formed within the joint,and the straight ATBs primarily resulted from grain growth accidents,while cluster-shaped ATBs were formed through re-excitations and decomposition of specific grain boundaries.展开更多
This study successfully achieved the welding of Ti-4.5Al-3V-2Mo-2Fe alloy using double side-friction stir welding.The microstructure of the nugget was characterized using a scanning electron microscope,electron backsc...This study successfully achieved the welding of Ti-4.5Al-3V-2Mo-2Fe alloy using double side-friction stir welding.The microstructure of the nugget was characterized using a scanning electron microscope,electron backscatter diffraction,and transmission electron microscope.High-temperature tensile tests were conducted to evaluate the superplastic deformation behavior of the nugget at temperatures ranging from 700℃ to 800℃ and strain rates of 1×10^(-3)s^(-1)-3×10^(-2) s^(-1).Results revealed that the nugget predominantly consisted of coarseβgrains,a small amount of grain boundaryα,and a large number of lamellarαwithin the coarseβgrains.An excellent superplasticity of 1400% was achieved at 750℃ and 3×10^(-3)s^(-1) in the nugget.This was mainly because the lamellar microstructure underwent significant dynamic spheroidization during the initial stage of superplastic deformation.During the dynamic spheroidization process,some lamellarαgrains grow abnormally,absorbing a large number of low-angle grain boundaries and thus providing a favorable condition for their subsequent continuous dynamic recrystallization.Meanwhile,the abnormally grownαgrains quickly engulf the β phase,reducing the size and proportion of the β phase in the tensile specimen.These fine grained and moderate proportions of the β phase effectively coordinated the grain boundary sliding at the later stages of superplastic deformation.Therefore,the dynamic spheroidization mechanism in the initial stage of superplastic deformation was continuous dynamic recrystallization,and the superplastic deformation mechanism was continuous dynamic recrystallization coordinated with grain boundary sliding.Based on these findings,a novel method was proposed to enhance high strain rate superplasticity by introducing prestrain to induce continuous dynamic recrystallization in the lamellar microstructure.This approach increased the superplastic elongation of the nugget from 345%to 520%at 750℃ and a high strain rate of 1×10^(-2)s^(-1).The study offers valuable insights for achieving superior superplastic forming of Ti-4.5Al-3V-2Mo-2Fe alloy joints.展开更多
基金financially supported by the National Natural Science Foundation of China(Nos.52034005,52227807,52104383,and 52222410)the Shaanxi Province National Science Fund for Distinguished Young Scholars,China(No.2022JC-24)+1 种基金the Key Research and Development Program of Shaanxi Province,China(No.2022JBGS2-01)the Central Guidance on Local Science and TechnologyDevelopment Fund of Shaanxi Province,China(No.2024ZY-JCYJ-04-09).
文摘Twinning-induced plasticity(TWIP)steel was processed using electrically assisted friction stir welding(EFSW).The microstructure,mechanical properties,and deformation behavior of the welded joints were systematically investigated.The results show that the average grain size was refined from 3.67μm in the base material(BM)to 1.39μm in the stir zone(SZ),while it increased to 4.19μm in the heat-affected zone(HAZ).The fraction of twin boundaries(TBs)decreased from 20.7%in the BM to 6.9%in the SZ and increased to24.5%in the HAZ.The ultimate tensile strength,yield strength,and elongation of the BM were 1021 MPa,505 MPa,and 65.8%,respectively.In comparison,the EFSW joint exhibited values of 1055 MPa,561 MPa,and 60.8%,corresponding to 103.3%,111.1%,and 92.4%of those of the BM,respectively.During tensile testing,plastic deformation was primarily concentrated in the BM,although both the SZ and HAZ also exhibited notable plastic deformation.Fracture ultimately occurred in the BM.
基金financially supported by the Major State Research Development Program of China(No.2016YFB0701303)the National Natural Science Foundation of China(No.51801156)the Natural Science Basic Research Plan in Shaanxi Province of China(No.2019JM-584)。
文摘In this work,the effect of microstructure features on the high-cycle fatigue behavior of Ti-7Mo-3Nb-3Cr-3Al(Ti-7333)alloy is investigated.Fatigue tests were carried out at room temperature in lab air atmosphere using a sinusoidal wave at a frequency of 120 Hz and a stress ratio of 0.1.Results show that the fatigue strength is closely related to the microstructure features,especially theα_(p) percentage.The Ti-7333 alloy with a lowerα_(p) percentage exhibits a higher scatter in fatigue data.The bimodal fatigue behavior and the duality of the S-N curve are reported in the Ti-7333 alloy with relatively lowerα_(p) percentage.Crack initiation region shows the compoundα_(p)/βfacets.Facetedα_(p) particles show crystallographic orientation and morphology dependence characteristics.Crack-initiation was accompanied by faceting process across elongatedα_(p) particles or multiple adjacentα_(p) particles.These particles generally oriented for basal slip result in near basal facets.Fatigue crack can also initiate at elongatedα_(p) particle well oriented for prismatic slip.Theβfacet is in close correspondence to{110}or{112}plane with high Schmid factor.Based on the fracture observation and FIB-CS analysis,three classes of fatigue-critical microstructural configurations are deduced.A phenomenological model for the formation ofα_(p) facet in the bimodal microstructure is proposed.This work provides an insight into the fatigue damage process of theβprecipitate strengthened metastableβtitanium alloys.
基金financially supported by the National Science and Technology Major Project of China(Grant No.J2019-VI-0011-0125)the China Postdoctoral Science Foundation(Grant No.2023MD734201)+1 种基金the ND Basic Research Funds of China(Grant No.G2022WD)the Shaanxi Province Innovation Capability Support Program(Grant No.2023-CX-TD-47).
文摘The coarse as-cast lamellar microstructure in TiAl alloys is difficult to be broken completely by thermomechanical processing. Some remnant lamellar colonies in the deformed microstructure seriously affect the microstructural homogeneity and deteriorate the properties. In this study, it is found that by isothermal compression at 1230 °C and 1250 °C, the lamellar colonies of Ti-43.5Al-4Nb-1Mo-0.1B (TNM) alloys can be completely broken. This is attributed to the weakened anisotropic deformation behavior of the lamellar colonies due to the isothermal holding treatment before deformation. The deformation behavior at 1230 °C was investigated by quasi-in-situ experiments. It is observed that the regions near lamellar colony boundaries first undergo dynamic recrystallization at small strain, while the lamellar colonies gradually break down with increasing strain. The adequate fragmentation of lamellar colonies mainly depends on the recrystallization of α lamellae (αL). The isothermal holding at 1230 °C leads to an increase in the content and thickness of αL, which allows it to assume more deformation and promotes its recrystallization by reaching critical strain. The interrupted γ lamellae (γL) formed by decomposition during isothermal holding facilitates the occurrence of α recrystallization within the lamellar colonies by hindering dislocation movement. In addition, recrystallized γ grains (γR) are gradually dissolved by the formation of α precipitates inside them through the γ → α phase transformation and the subsequent consumption of α precipitates by the recrystallized α grains.
基金supported by the National Natural Science Foundation of China(Nos.52034005,52227807,52104383,and 52222410)the Shaanxi Province National Science Fund for Distinguished Young Scholars(2022JC-24)+1 种基金the Key Research and Development Program of Shaanxi Province(2020ZDLGY13-06 and 2022JBGS2-01)the Scientific Research Program for Youth Innovation Team Construction of Shaanxi Provincial Department of Education(No.21JP058).
文摘The restoration mechanism of twin-induced plasticity(TWIP)steel during friction stir welding(FSW)changed with the degree of the deformation,and the microstructure evolution and dynamic recrystallization are complex and unclear.In this paper,the electron backscattered diffraction and transmission electron microscopy techniques were used to evaluate the dynamic grain structure of FSW joint of TWIP steel.The results showed that the dynamic recrystallization mechanisms in TWIP steel during FSW contained discontinuous dynamic recrystallization(DDRX)and continuous dynamic recrystallization(CDRX).The recrystallization mechanism transitioned from DDRX at the initial deformation stage to DDRX and CDRX at the middle deformation stage,eventually becoming primarily CDRX at the end deformation stage.Numerous annealing twin boundaries(ATBs)were formed within the joint,and the straight ATBs primarily resulted from grain growth accidents,while cluster-shaped ATBs were formed through re-excitations and decomposition of specific grain boundaries.
基金the China's National Defense Science and Technology(173 Program)(No.2021-JCJQ-JJ-0190)the National Natural Science Foundation of China(Nos.52227807,52374400)+3 种基金the National Natural Science Fund for Excellent Young Scholars(No.52222410)the Key Research and Development Program of Shaanxi Province(No.2025CY-YBXM-117)the Open Research Fund of Shaanxi Laboratory of Advanced Materials(No.2024ZY-JCYJ-04-09)the Qinchuangyuan"Scientist+Engineer"Team Development Program of Shaanxi Province(Nos.2022KXJ-099,2022KXJ-105,2024QCY-KXJ-012).
文摘This study successfully achieved the welding of Ti-4.5Al-3V-2Mo-2Fe alloy using double side-friction stir welding.The microstructure of the nugget was characterized using a scanning electron microscope,electron backscatter diffraction,and transmission electron microscope.High-temperature tensile tests were conducted to evaluate the superplastic deformation behavior of the nugget at temperatures ranging from 700℃ to 800℃ and strain rates of 1×10^(-3)s^(-1)-3×10^(-2) s^(-1).Results revealed that the nugget predominantly consisted of coarseβgrains,a small amount of grain boundaryα,and a large number of lamellarαwithin the coarseβgrains.An excellent superplasticity of 1400% was achieved at 750℃ and 3×10^(-3)s^(-1) in the nugget.This was mainly because the lamellar microstructure underwent significant dynamic spheroidization during the initial stage of superplastic deformation.During the dynamic spheroidization process,some lamellarαgrains grow abnormally,absorbing a large number of low-angle grain boundaries and thus providing a favorable condition for their subsequent continuous dynamic recrystallization.Meanwhile,the abnormally grownαgrains quickly engulf the β phase,reducing the size and proportion of the β phase in the tensile specimen.These fine grained and moderate proportions of the β phase effectively coordinated the grain boundary sliding at the later stages of superplastic deformation.Therefore,the dynamic spheroidization mechanism in the initial stage of superplastic deformation was continuous dynamic recrystallization,and the superplastic deformation mechanism was continuous dynamic recrystallization coordinated with grain boundary sliding.Based on these findings,a novel method was proposed to enhance high strain rate superplasticity by introducing prestrain to induce continuous dynamic recrystallization in the lamellar microstructure.This approach increased the superplastic elongation of the nugget from 345%to 520%at 750℃ and a high strain rate of 1×10^(-2)s^(-1).The study offers valuable insights for achieving superior superplastic forming of Ti-4.5Al-3V-2Mo-2Fe alloy joints.
