The evolution of microstructure and texture for drawn polycrystalline Ag was investigated by transmission electron microscopy and electron backscattering diffraction.The results show that there are deformation twins a...The evolution of microstructure and texture for drawn polycrystalline Ag was investigated by transmission electron microscopy and electron backscattering diffraction.The results show that there are deformation twins and some un-tangled discrete dislocations at low strains.When the strain is increased to 0.58,a lot of high density dislocation walls and microbands come into being.At the same time,some twins lose the twinning relationship of 60°<111>.At a strain of 0.94,both dislocation boundaries and twin boundaries will rotate to the axis direction of wires and the shear bands start to appear.When the strain is higher than 1.96,most of the boundaries are parallel to the drawn direction.Texture analysis indicates that with the strain increasing,the volume fraction of complex texture component decreases,but<111>and<100>texture components increase.However,the variation in the volume fraction of each texture component as strains is not evident when the strains are higher than 0.58.For polycrystalline Ag with low stacking fault energy,complex texture components are easily formed.展开更多
Deformation twinning is an important deformation mechanism in nickel-based superalloys. For superalloys, deformation twins are generally observed at low or intermediate temperatures and high strain rates;however, the ...Deformation twinning is an important deformation mechanism in nickel-based superalloys. For superalloys, deformation twins are generally observed at low or intermediate temperatures and high strain rates;however, the appearance of microtwins(MTs) at high temperatures has rarely been reported. In this study, transmission electron microscopy(TEM) was used to study MT formation in Ni-Co-based superalloys following compression at 1120 °C/1 s. The deformation behavior was discussed in detail to reveal the mechanism of MT formation. The twinning mechanism at elevated temperatures was theoretically attributed to the low stacking fault energy(SFE) and poor dislocation-driven deformations caused by the high strain rate in specific directions.展开更多
研究了合金元素Al对3种不同Al含量的Fe-28Mn-x Al-1C(x=8,10,12)系低密度钢层错能的影响。结果表明,3种实验钢的层错能范围为67.76~90.64 m J/m^2,Al对层错能的影响呈多项式分布。与28Mn-10Al及28Mn-8Al合金相比,28Mn-12Al合金层错能较...研究了合金元素Al对3种不同Al含量的Fe-28Mn-x Al-1C(x=8,10,12)系低密度钢层错能的影响。结果表明,3种实验钢的层错能范围为67.76~90.64 m J/m^2,Al对层错能的影响呈多项式分布。与28Mn-10Al及28Mn-8Al合金相比,28Mn-12Al合金层错能较高,抗拉强度高但伸长率低,在相同变形量下,28Mn-8Al与28Mn-10Al合金均出现了孪晶组织,且28Mn-8Al中孪晶更明显,而28Mn-12Al合金中未发现孪晶。3种合金的变形机制均为平面滑移变形,这归因于Fe-Mn-Al-C系合金中存在的短程有序会导致"滑移面软化现象",使高层错能的28Mn-12Al合金变形机制也为平面滑移。展开更多
The microstructure characteristics of an Fe-Mn-C TWIP steel after deformation are investigated. The results show that the hot-rolled, cold-rolled and then annealed sample of the Fe-Mn-C TWIP steel has excellent mechan...The microstructure characteristics of an Fe-Mn-C TWIP steel after deformation are investigated. The results show that the hot-rolled, cold-rolled and then annealed sample of the Fe-Mn-C TWIP steel has excellent mechanical properties, and the true stress-true strain curve from tension tests exhibits repeated serrations. The deformed microstructure exhibits the typical planar glide characteristics such as no cell formation, dislocation pile-ups on a single slip plane, mechanical twins and stacking faults. There are equiaxial and deep dimple structures in the fractograph, indicative of a ductile fracture. Microcracks initiate from inclusions and twin-twin intersections. Deformation and fracture processes are the formation, growth and coalescence of microvoids.展开更多
Molybdenum(Mo)has been recognized as an essential alloying element of the MP35N(Co_(35.4)Cr_(22.9)Ni_(35.5)Mo_(6.2),at.%)superalloy for enhancing strength and corrosion resistance.However,a full understanding of the a...Molybdenum(Mo)has been recognized as an essential alloying element of the MP35N(Co_(35.4)Cr_(22.9)Ni_(35.5)Mo_(6.2),at.%)superalloy for enhancing strength and corrosion resistance.However,a full understanding of the addition of Mo on microstructure and mechanical properties of the Mo-free parent alloy is lacking.In this work,we consider five(Co_(37.7)Cr_(24.4)Ni_(37.9))_(100-x)Mo_(x)(x=0,0.7,2.0,3.2,and 6.2)alloys,and reveal that yield/tensile strength and ductility are continuously increased for these alloys with increasing Mo content while a single-phase face-centered cubic structure remains unchanged.It is found that strong solid solution strengthening(SSS)is a main domain to the improved yield strength,whereas grain boundaries are found to soften by the Mo addition.The first-principles calculations demonstrate that a severe local lattice distortion contributes to the enhanced SSS,and the grain boundary softening effect is mostly associated with the decreased shear modulus.Both first-principles calculations and scanning transmission electron microscopy observations reveal that the stacking fault energy(SFE)reduces by the Mo addition.The calculated SFE value decreases from 0.4 mJ/m^(2) to-11.8 mJ/m^(2) at 0 K as Mo content increases from 0 at.%to 6.2 at.%,and experimentally measured values of SFE at room temperature for both samples are about 18 mJ/m^(2) and 9 mJ/m^(2),respectively.The reduction of SFE promoted the generation of stacking faults and deformation twins,which sustain a high strain hardening rate,thus postponing necking instability and enhancing tensile strength and elongation.展开更多
A nanocrystalline layer was synthesized on the surface of TWIP steel samples by surface mechanical attri- tion treatment （SMAT） under varying durations. Microhardness variation was examined along the depth of the de...A nanocrystalline layer was synthesized on the surface of TWIP steel samples by surface mechanical attri- tion treatment （SMAT） under varying durations. Microhardness variation was examined along the depth of the de- formation layer. Microstructural characteristics of the surface at the TWIP steel SMATed for 90 min were observed and analyzed by optical microscope, x-ray diffraction, transmission and high-resolution electron microscope. The re- sults show that the orientation of austenite grains weakens, and a-martensite transformation occurs during SMAT. During the process of SMAT, the deformation twins generate and divide the austenite grains firstly~ then a-martens- ite transformation occurs beside and between the twin bundles~ after that the martensite and austenite grains rotate to accommodate deformation, and the orientations of martensite and between martensite and residual austenite increase; lastly the randomly oriented and uniform-sized nanocrystallir^e layers are formed under continuous deformation.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.51471123,51171135)the Natural Science Foundation of Shaanxi Province(Grant Nos.2012K07-08,2013KJXX-61)the Industrialization Program of Shaanxi Province(Grant No.2013JC14)
文摘The evolution of microstructure and texture for drawn polycrystalline Ag was investigated by transmission electron microscopy and electron backscattering diffraction.The results show that there are deformation twins and some un-tangled discrete dislocations at low strains.When the strain is increased to 0.58,a lot of high density dislocation walls and microbands come into being.At the same time,some twins lose the twinning relationship of 60°<111>.At a strain of 0.94,both dislocation boundaries and twin boundaries will rotate to the axis direction of wires and the shear bands start to appear.When the strain is higher than 1.96,most of the boundaries are parallel to the drawn direction.Texture analysis indicates that with the strain increasing,the volume fraction of complex texture component decreases,but<111>and<100>texture components increase.However,the variation in the volume fraction of each texture component as strains is not evident when the strains are higher than 0.58.For polycrystalline Ag with low stacking fault energy,complex texture components are easily formed.
基金the National Key R&D Program of China(Nos.2019YFA0705300 and 2017YFA0700703)the National Science and Technology Major Project of China(No.2019-VI-0006-0120)+1 种基金the IMR Innovation Fund(No.2021-PY09)the Doctoral Start-up Foundation of Liaoning Province(No.2020-BS-007).
文摘Deformation twinning is an important deformation mechanism in nickel-based superalloys. For superalloys, deformation twins are generally observed at low or intermediate temperatures and high strain rates;however, the appearance of microtwins(MTs) at high temperatures has rarely been reported. In this study, transmission electron microscopy(TEM) was used to study MT formation in Ni-Co-based superalloys following compression at 1120 °C/1 s. The deformation behavior was discussed in detail to reveal the mechanism of MT formation. The twinning mechanism at elevated temperatures was theoretically attributed to the low stacking fault energy(SFE) and poor dislocation-driven deformations caused by the high strain rate in specific directions.
文摘研究了合金元素Al对3种不同Al含量的Fe-28Mn-x Al-1C(x=8,10,12)系低密度钢层错能的影响。结果表明,3种实验钢的层错能范围为67.76~90.64 m J/m^2,Al对层错能的影响呈多项式分布。与28Mn-10Al及28Mn-8Al合金相比,28Mn-12Al合金层错能较高,抗拉强度高但伸长率低,在相同变形量下,28Mn-8Al与28Mn-10Al合金均出现了孪晶组织,且28Mn-8Al中孪晶更明显,而28Mn-12Al合金中未发现孪晶。3种合金的变形机制均为平面滑移变形,这归因于Fe-Mn-Al-C系合金中存在的短程有序会导致"滑移面软化现象",使高层错能的28Mn-12Al合金变形机制也为平面滑移。
基金Item Sponsored by National High-Technology Research and Development Program(2008AA03E502)National Natural Science Foundation of China(50575022)
文摘The microstructure characteristics of an Fe-Mn-C TWIP steel after deformation are investigated. The results show that the hot-rolled, cold-rolled and then annealed sample of the Fe-Mn-C TWIP steel has excellent mechanical properties, and the true stress-true strain curve from tension tests exhibits repeated serrations. The deformed microstructure exhibits the typical planar glide characteristics such as no cell formation, dislocation pile-ups on a single slip plane, mechanical twins and stacking faults. There are equiaxial and deep dimple structures in the fractograph, indicative of a ductile fracture. Microcracks initiate from inclusions and twin-twin intersections. Deformation and fracture processes are the formation, growth and coalescence of microvoids.
基金financially supported by the Young Scientists Fund of the National Natural Science Foundation of China(No.52001120)the Hunan Provincial National Science Fund for Distin-guished Young Scholars(No.2022JJ10015)+2 种基金the State Key Labora-tory of Advanced Metals and Materials(No.2021-Z09)the Univer-sity of Science&Technology Beijing,China.X.Q.Li was supported by the Swedish Research Council(No.2020-03736)funded by the Swedish Research Council through grant agreement(No.2018-05973)。
文摘Molybdenum(Mo)has been recognized as an essential alloying element of the MP35N(Co_(35.4)Cr_(22.9)Ni_(35.5)Mo_(6.2),at.%)superalloy for enhancing strength and corrosion resistance.However,a full understanding of the addition of Mo on microstructure and mechanical properties of the Mo-free parent alloy is lacking.In this work,we consider five(Co_(37.7)Cr_(24.4)Ni_(37.9))_(100-x)Mo_(x)(x=0,0.7,2.0,3.2,and 6.2)alloys,and reveal that yield/tensile strength and ductility are continuously increased for these alloys with increasing Mo content while a single-phase face-centered cubic structure remains unchanged.It is found that strong solid solution strengthening(SSS)is a main domain to the improved yield strength,whereas grain boundaries are found to soften by the Mo addition.The first-principles calculations demonstrate that a severe local lattice distortion contributes to the enhanced SSS,and the grain boundary softening effect is mostly associated with the decreased shear modulus.Both first-principles calculations and scanning transmission electron microscopy observations reveal that the stacking fault energy(SFE)reduces by the Mo addition.The calculated SFE value decreases from 0.4 mJ/m^(2) to-11.8 mJ/m^(2) at 0 K as Mo content increases from 0 at.%to 6.2 at.%,and experimentally measured values of SFE at room temperature for both samples are about 18 mJ/m^(2) and 9 mJ/m^(2),respectively.The reduction of SFE promoted the generation of stacking faults and deformation twins,which sustain a high strain hardening rate,thus postponing necking instability and enhancing tensile strength and elongation.
基金Sponsored by National Natural Science Foundation of China(51044007,51001079)Scientific Research Plan of Shanxi Province of China(20090321072)National High-Tech Research and Development Program(863Program)of China(2007AA03Z555)
文摘A nanocrystalline layer was synthesized on the surface of TWIP steel samples by surface mechanical attri- tion treatment （SMAT） under varying durations. Microhardness variation was examined along the depth of the de- formation layer. Microstructural characteristics of the surface at the TWIP steel SMATed for 90 min were observed and analyzed by optical microscope, x-ray diffraction, transmission and high-resolution electron microscope. The re- sults show that the orientation of austenite grains weakens, and a-martensite transformation occurs during SMAT. During the process of SMAT, the deformation twins generate and divide the austenite grains firstly~ then a-martens- ite transformation occurs beside and between the twin bundles~ after that the martensite and austenite grains rotate to accommodate deformation, and the orientations of martensite and between martensite and residual austenite increase; lastly the randomly oriented and uniform-sized nanocrystallir^e layers are formed under continuous deformation.
