A superior strength-ductility synergy of Al_(0.1)CrFeCoNi high-entropy alloy with fully recrystallized ultrafine grains and annealing twins

Grain refinement usually makes the materials stronger,while ductility has a dramatic loss.Here,a superior tensile strength–ductility synergy in a fully recrystallized ultrafine-grained(UFG)Al_(0.1)CrFeCoNi with abundant annealing twins was achieved by cold rolling at room temperature and short-time annealing.The microstructure characterization using electron backscattered scattering diffraction demonstrates that abundant geometrically necessary dislocations(GNDs)gather around the grain boundaries and twin boundaries after tensile deformation.Although coarse-grained(CG)samples undergo a larger plastic deformation than UFG samples,the GND density decreases with grain size ranging from UFG to CG.Transmission electron microscopy results reveal that the annealing twin boundary,which effectively hinders the dislocation slip and stores dislocation in grain interior,and the activation of multiple deformation twins are responsible for the superior strength–ductility synergy and work hardening ability.In addition,the yield strength of fully recrystallized Al_(0.1)CrFeCoNi follows a Hall–Petch relationship(σ_y=24+676d^(–1/2)),where d takes into account both grain boundaries and annealing twin boundaries.The strengthening effects of grain boundaries and annealing twin boundaries were also evaluated separately.

Evolution of Annealing Twins and Recrystallization Texture in Thin-Walled Copper Tube During Heat Treatment

Thin-walled copper tubes are usually produced by multi-pass float-plug drawing deformation.In general,the annealing treatment subsequently is necessary to release the stored energy and adjusts the microstructure.In this study,an investigation on the evolution of annealing twins as well as textures in the thin-walled(Φ6 mm×0.3 mm)copper tube underwent holding time-free heat treatment was reported.Electron backscattered diffraction analysis reveals that a large number ofΣ3 boundaries(600<111>twin relationship)are produced at the early stage of heat treatment,which is due to the lower boundary energy.With the recrystallization proceeding,the migration rate of grain boundaries decreases on account of the grain growth;meanwhile,the uniqueΣ9 boundaries(38.9°<110>relationship)are formed due to the interaction of theΣ3 boundaries.As a result,the number fractions ofΣ3 boundaries and high-angle grain boundaries decrease rapidly.During the grain growth stage,a strong recrystallization texture was formed due to the fact that the grains of Goss orientation have a growth advantage over the others.As a result,the initial copper texture was transferred into the Goss texture in domination.

Effects of annealing temperature on the microstructure and properties of the 25Mn-3Si-3Al TWIP steel

Microstructures and mechanical properties of the 25Mn twinning induced plasticity （TWIP） steel at different annealing temperatures were investigated. The results indicated that when the annealing temperature was 1000℃, the 25Mn steel showed excellent comprehensive mechanical properties, the tensile strength was about 640 MPa, the yield strength was higher than 255 MPa, and the elongation was above 82%. The microstructure was analyzed by optical microscopy （OM）, X-ray diffraction （XRD）, and transmission electron microscopy （TEM）. Before deformation the microstructure was composed of austenitic matrix and annealing twins at room temperature; at the same time, a significant amount of annealing twins and stacking faults were observed by TEM. Mechanical twins played a dominant role in deformation and as a result the mechanical properties were found to be excellent.

Annealing twin mechanism for 304 stainless steel solution treatment process

The texture evolution,twin crystallographic nature and grain orientation variation during the solution heat treatment process of the 304 stainless steel pipe were studied.It was found that after the solution heat treatment,the texture type clearly changed,and the texture strength was greatly increased.During the solution heat treatment process,grain boundaries migrated along the orientation available for grain growth,giving rise to abnormal growth of some grains through merging with the adjacent small grains.After the solution heat treatment,more<111>60°twins formed in the microstructures of the 304 stainless steel pipe,and the fraction of the twin boundaries showed a pronounced increase.Analysis of the twin crystallographic nature of the FCC crystals showed that four kinds of twin variants can be formed within austenite parent grains,and twelve kinds of misorientations can be formed between the austenite parent grains and the secondary twins.

Mechanical Properties and Microstructure Evolution of Cold-deformed High-nitrogen Nickel-free Austenitic Stainless Steel during Annealing

The mechanical properties and microstructure evolution of cold-deformed CrMnN austenitic stainless steel annealed in a temperature ranging from 50 ℃ to 650 ℃ for 90 min and at 550 ℃ for different time were investigated by tensile test, micro hardness test, and Transmission Electron Microscope （TEM）. The steel was strengthened when it got annealed at temperatures ranging from 100 ℃ to 550 ℃, while it was softened when it got annealed at temperatures ranging from 550 ℃ to 650 ℃. Annealing temperature had stronger effect on mechanical properties than annealing time. TEM observations showed that nano-sized precipitates formed when the steel was annealed at 150 ℃ for 90 min, but the size and density of precipitates had no noticeable change with annealing temperature and time. Recrystallization occurred when the steel was annealed at temperatures above 550 ℃ for 90 min, and its scale increased with annealing temperature. Nano-sized annealing twins were observed. The mechanisms that controlled the mechanical behaviors of the steel were discussed.

Oxidation behavior of Hastelloy C-2000 superalloy at 800 °C and 1000 °C

The oxidation behavior of Hastelloy C-2000 alloy was investigated in air at 800 °C and 1000 °C for 100 h, respectively. Oxidation kinetics and oxide scales morphologies were examined by mass gain measurement, scanning electron microscopy（SEM）, X-ray diffraction（XRD） and X-ray photoelectron spectroscopy（XPS）. The oxidation behavior of the alloy approximately follows a parabolic rate law. Moreover, annealing twins defect structure in matrix deteriorates the oxidation resistance of alloy due to the improvement of diffusion rates for alloying elements and oxygen atoms. At 800 °C, the microstructure is primarily composed of Ni O and Cr1.3Fe0.7O6 and the initial annealing twins structure is visible and Mo-rich phases are emerged to approach boundary of oxide scales. At 1000 °C, however, the morphology microstructure of oxide scales consists of oxide particle with fine Cr oxides and large Ni oxides by inlaying each other, whilst Mo-rich phases hardly appear closing to the interface of oxide scales.

Effects of electric-field treatment on a Ni-base superalloy

The effects of electric-field treatment on the microstructure and deformation behavior of a nickel-base superalloy were summarized.The results show that the electric-field treatment increases the ductility of the superalloy but has no evident influence on its static strength at both room and elevated temperatures,while,the strength increases but elongation changes weekly with the increasing tensile strain rate.It is found that the direction of microcrack propagation can be changed by the presence of the annealing twins during the tensile deformation,and it causes the increasing of the plastic deformation energy and delay of the fracture,which is considered as the reason for the increasing the ductility.

Study on Microstructure and Performance of Advanced Bush Strip

The strain induced ferrite formed under different conditions was observed with SEM and optical microscope. The nucleation sites of strain induced ferrite include grain boundary, grain inside, deformed band and annealing twin boundary. The shapes of the ferrite accordingly are equiaxed irregular polygonal, strip shaped and acicular.

Characteristics of Strain-Induced Ferrite in Low Carbon Steel

The strain-induced ferrite formed under different conditions was observed with SEM and optical microscope.The nucleation sites of strain-induced ferrite include grain boundary,grain inside,deformed band and annealing twin boundary.The shapes of the ferrite accordingly are equiaxed irregular polygonal,strip-shaped and acicular.

Evolution of Goss texture in thin-walled copper tube at different heat treatment temperatures

The evolution of microstructure,textures,and mechanical properties of thin-walled copper tube during heat treatment was investigated using EBSD technique and tensile test.The results show that the initial deformation textures of pre-drawn thin-walled copper tube are mainly composed of Copper and Y components,while with the increase of temperatures,the textures are transformed into a strong Goss texture gradually.The high-resolution microstructural characterizations indicate that the new Goss recrystallized grains nucleate and grow up within the deformed Copper grains and Y grains in different mechanisms,respectively.The tensile strength of the thin-walled copper tube decreases gradually with the increase of the temperature,while the elongation increases first and then decreases sharply due to the action of grain sizes and texture components.

Effect of Microstructures on Corrosion Behavior of Nickel Coatings:(Ⅱ) Competitive Effect of Grain Size and Twins Density on Corrosion Behavior

Nanocrystalline nickel coatings with grain size of 50 nm were annealed in vacuum at 200 ℃ and 400 ℃ for 10 min, Their microstructures were investigated by transmission electron microscopy （TEM）. And their corrosion behaviors were studied by means of polarization and electrochemical impedance spectroscopy （EIS）, The results showed that their grain size grew up to about 60 nm （200 ℃） and 500 nm （400 ℃）, respectively, The specimen annealed at 200 ℃ possessed higher density of twins in compared with the counterparts of as-deposited and annealed at 400 ℃, The normal grain size effect on the corrosion behavior was not observed, However, it was found that the corrosion resistance of the coating linearly changed with the density of twins.

Microstructure Evolution and Recrystallized Behavior of Friction Stir Welding Twin-Induced Plasticity Steel

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.

Nucleation mechanisms of dynamic recrystallization for G3 alloy during hot compression

Dynamic recrystallization （DRX） mechanisms of a nickel-based corrosion-resistant alloy, G3, were investigated by hot compression tests with temperatures from 1050 to 1200 ℃ and strain rates from 0.1 to 5.0 s-1. Deformation microstructure was observed at the strain from 0.05 to 0.75 by electron backscatter diffraction （EBSD） and transmission electron microscope （TEM）. Work hardening rate curves were calculated to analyze the effect of deformation parameters on the nucleation process. Results indicate that strain-induced grain boundary migration is the principal mechanism of DRX. Large annealing twins promote nucleation by accumulating dis- locations and fragmenting into cell blocks. Continuous dynamic recrystallization is also detected to be an effective supplement mechanism, especially at low temperature and high strain rate.

Tensile deformation behavior of nickel-free high-manganese austenitic cryogenic-temperature steel

Nickel-free high-manganese austenitic Fe–24.4Mn–4.04Al–0.057C steel was produced by smelting,and the homogenized forged billet was hot-rolled.The plastic deformation mechanism was investigated through tensile testing of the hot-rolled sample.Different characterization techniques such as scanning electron microscopy,transmission electron microscopy,electron backscattered diffraction,and X-ray diffraction were used to analyze the microstructural evolution of steel under different strain levels.The steel had a single austenite phase,which was stable during deformation.After hot rolling,annealing twins were observed in the microstructure of the steel.The steel showed an excellent combination of mechanical properties,like a tensile strength of 527 MPa,impact energy of 203 J at−196℃,and an elongation of 67%till fracture.At the initial deformation stage,the dislocations were generated within the austenite grains,entangled and accumulated at the grain boundaries and annealing twin boundaries.Annealing twins participated in plastic deformation and hindered the dislocation movement.As the deformation progressed,the dislocation slip was hindered and produced stress concentration,and the stacking faults evolved into mechanical twins,which released the stress concentration and delayed the necking.