Dissimilar fusion welding of austenitic stainless steels to carbon steels has some metallurgical and technical problems. It was suggested that the solid-state nature of friction stir welding （FSW） can overcome these...Dissimilar fusion welding of austenitic stainless steels to carbon steels has some metallurgical and technical problems. It was suggested that the solid-state nature of friction stir welding （FSW） can overcome these problems and produce a sound weld with reliable mechanical properties. In this study, plates of 304 stainless steel and st37 steel were welded together by FSW at tool rotational speed of 600 r/rain and welding speed of 50 ram/rain. In the stir zone （SZ） of 304 stainless steel, the results showed a refined grain structure with some features of metadynamic recrystallization. In the SZ of st37 steel, the hot deformation of material in the austenite region produced small austenite grains. These grains transformed to fine ferrite and pearlite by cooling the material after FSW. The production of fine grains increased the hardness and tensile strength in the SZ of both sides with respect to their base metals （BMs）.展开更多
Increasingly harsh service conditions place higher requirements for the high strain-rate performance of titanium alloys.Adiabatic shear band(ASB),a phenomenon prone to dynamic loading,is often accom-panied by catastro...Increasingly harsh service conditions place higher requirements for the high strain-rate performance of titanium alloys.Adiabatic shear band(ASB),a phenomenon prone to dynamic loading,is often accom-panied by catastrophic damage.Yet,it is unclear how the internal nanostructures are related to shear instability.Here we report detailed microstructural evolution in the ASB of a titanium alloy via in-depth focused ion beam(FIB),transmission Kikuchi diffraction(TKD),and high-resolution transmission electron microscope(HRTEM)analyses,with the deformation instability phenomenon discussed from the energy perspective.The ASB interior undergoes multifaceted changes,namely deformation-induced beta-to-alpha transformation and deformation-induced martensitic transformation to form substantially refined and heterogeneous structures.Meanwhile,two types of extremely fine twins are identified to occur within both nano-sized martensite and alpha phase.The critical plastic work representing the onset of adiabatic shear instability and dynamic equilibrium is observed to be constant for a specific structure in the same deformation mode.The energy analysis could be extended to other materials subjected to high strain-rate dynamic deformation.展开更多
The interaction between{112}<111>deformation twinning and grain boundary in coaxial polycrystalline tantalum under shock compression was studied with molecular dynamics simulation under different grain pair miso...The interaction between{112}<111>deformation twinning and grain boundary in coaxial polycrystalline tantalum under shock compression was studied with molecular dynamics simulation under different grain pair misorientation angles(MA)and geometric compatibility factor(m’).Generally,in the coaxial polycrystal,the value of MA determines the occurrence of twin transfer(TT)or twin blockage(TB),i.e.,twin transfer occurs at MA≤29°with twin blockage otherwise.Under TT,the value of m’affects the selection of twin variants.,i.e.,the twin system with a larger m’is easier to active.The morphology of twin pairs is ruler-shaped and lenticular under TT and TB,respectively,with different thickening mechanisms,including grain boundary dislocation emission.展开更多
Additive manufacturing features rapid production of complicated shapes and has been widely employed in biomedical,aeronautical and aerospace applications.However,additive manufactured parts generally exhibit deteriora...Additive manufacturing features rapid production of complicated shapes and has been widely employed in biomedical,aeronautical and aerospace applications.However,additive manufactured parts generally exhibit deteriorated fatigue resistance due to the presence of random defects and anisotropy,and the prediction of fatigue properties remains challenging.In this paper,recent advances in fatigue life prediction of additive manufactured metallic alloys via machine learning models are reviewed.Based on artificial neural network,support vector machine,random forest,etc.,a number of models on various systems were proposed to reveal the relationships between fatigue life/strength and defect/microstructure/parameters.Despite the success,the predictability of the models is limited by the amount and quality of data.Moreover,the supervision of physical models is pivotal,and machine learning models can be well enhanced with appropriate physical knowledge.Lastly,future challenges and directions for the fatigue property prediction of additive manufactured parts are discussed.展开更多
The mechanical response of a single crystal titanium sample against(0001)α surface impact was investigated using molecular dynamics simulation.Remarkably,non-uniform plastic deformation was observed in the sample.At ...The mechanical response of a single crystal titanium sample against(0001)α surface impact was investigated using molecular dynamics simulation.Remarkably,non-uniform plastic deformation was observed in the sample.At high strain rates,amorphization occurred near the edge of the contact region where severe shear strain induced a large number of stacking faults(SFs)and dislocations.In contrast,the central part of the contact region underwent less deformation with significantly fewer dislocations.Moreover,instead of amorphization by consuming SFs and dislocations,there was a gradual increase in the density of dislocations and SFs during the process of amorphization.These local amorphous regions eventually grew into shear bands.展开更多
Microstructural evolution and strain hardening behavior of a friction stir welded（FSWed） high-strength7075Al-T651 alloy were evaluated.The nugget zone was observed to consist of fine and equiaxed recrystallized grai...Microstructural evolution and strain hardening behavior of a friction stir welded（FSWed） high-strength7075Al-T651 alloy were evaluated.The nugget zone was observed to consist of fine and equiaxed recrystallized grains with a low dislocation density and free of original precipitates,but containing uniformly distributed dispersoids.The strength,joint efficiency,and ductility of the FSWed joints increased with increasing welding speed.A joint efficiency of ＊91% was achieved at a welding speed of 400 mm/min and rotational rate of 800 r/min,while the ductility remained basically the same as that of the base metal.There was no obvious strain rate sensitivity observed in both base metal and welded joints.While both the base metal and FSWed joints exhibited stage III and IV hardening characteristics,the hardening capacity,strain hardening exponent,and strain hardening rate all increased after friction stir welding.展开更多
The rapidly increasing scientific interest in 3D-printed high-entropy alloys(HEAs)necessitates the understanding of their deformation mechanisms.Here,we present the grain rotation behavior of a nearly equiatomic CrMnF...The rapidly increasing scientific interest in 3D-printed high-entropy alloys(HEAs)necessitates the understanding of their deformation mechanisms.Here,we present the grain rotation behavior of a nearly equiatomic CrMnFeCoNi HEA fabricated with laser-beam powder bed fusion via quasi in-situ electron backscatter diffraction(EBSD)observations during compressive deformation.The rotation paths of grains can be predicted via a new lattice reorientation factor(m_(A)),defined as the average of primary and secondary slip Schmid factors.The grains that initially have their〈111〉directions oriented close to the loading direction with low-to-intermediate m_(A)values tend to rotate towards the〈101〉pole.The grains initially oriented in the center of inverse pole figures with high m_(A)values develop multiple rotation paths pointing away from the〈001〉pole.The cube-oriented grains with their〈001〉directions close to the loading direction undergo face-centered cubic(FCC)-to-hexagonal close-packed(HCP)phase transformation due to the activation of octahedral slip involving multiple slip systems.This transformation can be well elucidated via a modified parameter,defined as the average of four maximum Schmid factors on each of four{111}slip/twinning planes in FCC crystals.The findings provide new insights into the underlying mechanisms for deformation-induced grain rotation and phase transformation,and help pave the way for developing advanced HEAs via transformation-induced plasticity.展开更多
基金the support from Harbin Institute of Technology(HIT) for the experimental assistance
文摘Dissimilar fusion welding of austenitic stainless steels to carbon steels has some metallurgical and technical problems. It was suggested that the solid-state nature of friction stir welding （FSW） can overcome these problems and produce a sound weld with reliable mechanical properties. In this study, plates of 304 stainless steel and st37 steel were welded together by FSW at tool rotational speed of 600 r/rain and welding speed of 50 ram/rain. In the stir zone （SZ） of 304 stainless steel, the results showed a refined grain structure with some features of metadynamic recrystallization. In the SZ of st37 steel, the hot deformation of material in the austenite region produced small austenite grains. These grains transformed to fine ferrite and pearlite by cooling the material after FSW. The production of fine grains increased the hardness and tensile strength in the SZ of both sides with respect to their base metals （BMs）.
基金supported by the National Natural Science Foundation of China (NSFC) (Nos.51871168,52271012)the Natural Sciences and Engineering Research Council of Canada (NSERC)in the form of international research collaboration.Q.C.,A.H.F.,and S.J.Q.are grateful to the Southwest Institute of Technology and Engineering Cooperation Fund (No.HDHDW5902020102)H.W.acknowledges the financial support of the National Key Laboratory Foundation of Science and Technology on Materials under Shock and Impact (No.6142902220301).
文摘Increasingly harsh service conditions place higher requirements for the high strain-rate performance of titanium alloys.Adiabatic shear band(ASB),a phenomenon prone to dynamic loading,is often accom-panied by catastrophic damage.Yet,it is unclear how the internal nanostructures are related to shear instability.Here we report detailed microstructural evolution in the ASB of a titanium alloy via in-depth focused ion beam(FIB),transmission Kikuchi diffraction(TKD),and high-resolution transmission electron microscope(HRTEM)analyses,with the deformation instability phenomenon discussed from the energy perspective.The ASB interior undergoes multifaceted changes,namely deformation-induced beta-to-alpha transformation and deformation-induced martensitic transformation to form substantially refined and heterogeneous structures.Meanwhile,two types of extremely fine twins are identified to occur within both nano-sized martensite and alpha phase.The critical plastic work representing the onset of adiabatic shear instability and dynamic equilibrium is observed to be constant for a specific structure in the same deformation mode.The energy analysis could be extended to other materials subjected to high strain-rate dynamic deformation.
基金financially supported by the Key-Area Re-search and Development Program of GuangDong Province(No.2019B010941001)National Key Laboratory Foundation of Science and Technology on Materials under Shock and Impact(No.6142902220301)+1 种基金Shanghai Engineering Research Center of High-Performance Medical Device Materials(No.20DZ2255500)the Major Science and Technology Infrastructure Project of Material Genome Bigscience Facilities Platform supported by Municipal Development and Reform Commission of Shenzhen.
文摘The interaction between{112}<111>deformation twinning and grain boundary in coaxial polycrystalline tantalum under shock compression was studied with molecular dynamics simulation under different grain pair misorientation angles(MA)and geometric compatibility factor(m’).Generally,in the coaxial polycrystal,the value of MA determines the occurrence of twin transfer(TT)or twin blockage(TB),i.e.,twin transfer occurs at MA≤29°with twin blockage otherwise.Under TT,the value of m’affects the selection of twin variants.,i.e.,the twin system with a larger m’is easier to active.The morphology of twin pairs is ruler-shaped and lenticular under TT and TB,respectively,with different thickening mechanisms,including grain boundary dislocation emission.
基金support of National Natural Science Foundation of China(No.U2241245)support of National Natural Science Foundation of China(No.91960202)+4 种基金National Key Laboratory Foundation of Science and Technology on Materials under Shock and Impact(No.6142902220301)Natural Science Foundation of Shenyang(No.23-503-6-05)support of Opening Project of National Key Laboratory of Shock Wave and Detonation Physics(No.2022JCJQLB05702)Aeronautical Science Foundation of China(No.2022Z053092001)support of Shanghai Engineering Research Center of High-Performance Medical Device Materials(No.20DZ2255500).
文摘Additive manufacturing features rapid production of complicated shapes and has been widely employed in biomedical,aeronautical and aerospace applications.However,additive manufactured parts generally exhibit deteriorated fatigue resistance due to the presence of random defects and anisotropy,and the prediction of fatigue properties remains challenging.In this paper,recent advances in fatigue life prediction of additive manufactured metallic alloys via machine learning models are reviewed.Based on artificial neural network,support vector machine,random forest,etc.,a number of models on various systems were proposed to reveal the relationships between fatigue life/strength and defect/microstructure/parameters.Despite the success,the predictability of the models is limited by the amount and quality of data.Moreover,the supervision of physical models is pivotal,and machine learning models can be well enhanced with appropriate physical knowledge.Lastly,future challenges and directions for the fatigue property prediction of additive manufactured parts are discussed.
基金the National Natural Science Foundation of China(U2241245,91960202 and 52271012)the National Key Laboratory Foundation of Science and Technology on Materials under Shock and Impact(6142902220301)+2 种基金the Aeronautical Science Foundation of China(2022Z053092001)the Shanghai Engineering Research Center of High-Performance Medical Device Materials(20DZ2255500)the Opening Project of National Key Laboratory of Shock Wave and Detonation Physics(2022JCJQLB05702).
文摘The mechanical response of a single crystal titanium sample against(0001)α surface impact was investigated using molecular dynamics simulation.Remarkably,non-uniform plastic deformation was observed in the sample.At high strain rates,amorphization occurred near the edge of the contact region where severe shear strain induced a large number of stacking faults(SFs)and dislocations.In contrast,the central part of the contact region underwent less deformation with significantly fewer dislocations.Moreover,instead of amorphization by consuming SFs and dislocations,there was a gradual increase in the density of dislocations and SFs during the process of amorphization.These local amorphous regions eventually grew into shear bands.
基金financially supported by Natural Sciences and Engineering Research Council of Canada (NSERC)Premier’s Research Excellence Award (PREA),NSERC-DAS Award,Canada Foundation for Innovation (CFI)+2 种基金Ryerson Research Chair (RRC) programNational Outstanding Young Scientist Foundation of China (No.50525103)Hundred Talents Program of the Chinese Academy of Sciences
文摘Microstructural evolution and strain hardening behavior of a friction stir welded（FSWed） high-strength7075Al-T651 alloy were evaluated.The nugget zone was observed to consist of fine and equiaxed recrystallized grains with a low dislocation density and free of original precipitates,but containing uniformly distributed dispersoids.The strength,joint efficiency,and ductility of the FSWed joints increased with increasing welding speed.A joint efficiency of ＊91% was achieved at a welding speed of 400 mm/min and rotational rate of 800 r/min,while the ductility remained basically the same as that of the base metal.There was no obvious strain rate sensitivity observed in both base metal and welded joints.While both the base metal and FSWed joints exhibited stage III and IV hardening characteristics,the hardening capacity,strain hardening exponent,and strain hardening rate all increased after friction stir welding.
基金the Natural Sciences and Engineering Research Council of Canada(NSERC),Natural Resources Canada(NRCan),Alberta Innovates,and the National Natural Science Foundation of China(NSFC)(Grant Nos.52271012 and 51871168)for the financial support.
文摘The rapidly increasing scientific interest in 3D-printed high-entropy alloys(HEAs)necessitates the understanding of their deformation mechanisms.Here,we present the grain rotation behavior of a nearly equiatomic CrMnFeCoNi HEA fabricated with laser-beam powder bed fusion via quasi in-situ electron backscatter diffraction(EBSD)observations during compressive deformation.The rotation paths of grains can be predicted via a new lattice reorientation factor(m_(A)),defined as the average of primary and secondary slip Schmid factors.The grains that initially have their〈111〉directions oriented close to the loading direction with low-to-intermediate m_(A)values tend to rotate towards the〈101〉pole.The grains initially oriented in the center of inverse pole figures with high m_(A)values develop multiple rotation paths pointing away from the〈001〉pole.The cube-oriented grains with their〈001〉directions close to the loading direction undergo face-centered cubic(FCC)-to-hexagonal close-packed(HCP)phase transformation due to the activation of octahedral slip involving multiple slip systems.This transformation can be well elucidated via a modified parameter,defined as the average of four maximum Schmid factors on each of four{111}slip/twinning planes in FCC crystals.The findings provide new insights into the underlying mechanisms for deformation-induced grain rotation and phase transformation,and help pave the way for developing advanced HEAs via transformation-induced plasticity.
