高纯钽板异步轧制及后续退火过程中微观组织及织构演变研究

采用1.2的轧速比对高纯钽板材进行异步轧制,获得了变形量分别为60%、70%和80%的异步轧制钽样品。采用电子背散射衍射(EBSD)对样品进行显微组织分析,研究了异步轧制过程中高纯钽板沿整个板厚方向的微观组织及织构演变规律。结果表明:变形量为60%时,钽板近表面区域的晶粒主要为{100}(〈100〉//ND,ND为板法向)和{110}(〈110〉//ND)取向,而中心区域的晶粒主要为{111}(〈111〉//ND)取向。随着变形量的增大,轧制变形组织逐渐变得均匀,同时沿板厚方向的织构分布也愈发均匀。当变形量为80%时,形成了γ织构(〈111〉//ND)与θ织构(〈100〉//ND)交替、均匀分布的现象。这种特殊的织构变化与异步轧制过程中沿厚度方向引入的剪切变形有关。对上述不同变形量的异步轧制高纯钽板的退火微观组织的对比研究发现,80%变形量样品表现出更为细小均匀的再结晶组织。80%变形量的样品经1 200℃退火30 min后,获得了平均晶粒尺寸为53.4μm的再结晶组织,同时{111}取向的晶粒与{100}取向的晶粒均匀分布。

脱碳退火保温时间对取向硅钢组织、织构及磁性能的影响

通过研究脱碳退火保温时间对取向硅钢初次再结晶组织、织构及高温退火样品磁性能的影响,探讨了有利于Goss晶粒异常长大的初次再结晶环境。结果表明,在820℃进行脱碳退火,当保温时间从2 min增加到6 min时,初次再结晶织构中Goss晶粒相对于{111}<112>和{111}<110>晶粒的尺寸优势逐渐增加,{111}<110>含量逐渐升高,且1/8层中Goss相对于其他取向晶粒尺寸优势稳定,使取向硅钢二次再结晶晶粒尺寸逐渐增大、磁性能逐渐提高。

Effect of forging on the microstructure and texture of a high Nb containing γ-TiAl alloy

The effect of forging on the microstructure and texture evolution of a high Nb containing Ti-45Al-7Nb-0.3W(at.%)alloy was investigated by X-ray diffractometer(XRD),scanning electron microscopy(SEM),and transmission electron microscopy(TEM).The results show that the as-cast alloy is mainly composed of α_(2)/γ lamellar colonies with a mean size of 70μm,but the hot-forged pancake displays a near duplex microstructure(DP).Kinking and bending of lamellar colonies,deformation twinning and dynamic recrystallization(DRX)occur during hot forging.Meanwhile,dense dislocations in theβphase after forging suggest that the high-temperature β phase with a disordered structure is favorable for improving the hot-workability of the alloy.Unlike the common TiAl casting texture,the solidification process of the investigated as-cast alloy with high Nb content is completely via the β phase region,resulting in the formation of a<110>γ fiber texture where the<110>γ aligns parallel to the heat-flow direction.In comparison,the relatively strong<001>and weak<302>texture components in the as-forged alloy are attributed to the deformation twinning.After annealing,static recrystallization occurs at the twin boundary and intersections,which weakens the deformation texture.

Grain structure and microtexture evolution during superplastic deformation of 5A90 Al-Li alloy

The microstructural evolution of banded 5A90 A1-Li alloy during superplastic deformation at 475℃ with an initial strain rate of 8× 10^-4 S^-1 was studied using EBSD technique. The results showed that, before deformation, the grain shape appeared to be banded, the most grain boundaries belonged to low-angle boundaries, and the initial sheet had a dominate of { 110}（112） brass texture. During deformation, there were grain growth, grain shape change, misorientation increasing and textural weakening. The fraction of high-angle boundaries increased rapidly once the flow stress reached the peak value. Corresponding deformation mechanism for various stages of deformation was suggested. Dislocation activity was the dominant mechanism in the first stage, then dynamic recrystallization occurred, and grain rotation was expected as an accommodation for grain boundary sliding （GBS）. At large strains, GBS was the main mechanism.

Influence of microstructure and texture on formability of AZ31B magnesium alloy sheets

The effect of the repeated unidirectional bending （RUB） process and annealing on the formability of magnesium alloy sheets was investigated. The RUB process and annealing treatments produce two effects on microstructure： grain coarsening and weakening of the texture. The sheet that underwent RUB and was annealed at 300 ℃exhibits the best formability owing to the reduction of the （0002） basal texture intensity, which results in low yield strength, large fracture elongation, small Lankford value （r-value） and large strain hardening exponent （n-value）. Compared with the as-received sheet, the coarse-grain sheet produced by RUB and annealing at 400 ℃ exhibits lower tensile properties but higher formability. The phenomenon is because the deformation twin enhanced by grain coarsening can accommodate the strain of thickness.

Influence of thermomechanical processing on microstructure,texture evolution and mechanical properties of Al-Mg-Si-Cu alloy sheets

Influence of thermomechanical processing on the microstructure, texture evolution and mechanical properties of A1-Mg-Si-Cu alloy sheets was studied systematically. The quite weak mechanical properties anisotropy was obtained in the alloy sheet through thermomechanical processing optimizing. The highly elongated microstmcture is the main structure for the hot or cold-rolled alloy sheets. H {001 } （110） and E { 111 } （110） are the main texture components in the surface layer of hot-rolled sheet, while ]/-fibre is dominant in quarter and center layers. Compared with the hot-rolled sheet, the intensities offl-fibre components are higher after the first cold rolling, but H {001 }（110） component in the surface layer decreases greatly. Almost no deformation texatre can be observed after intermediate annealing. And fl-fibre becomes the main texture again after the final cold rolling. With the reduction of the thickness, the through-thickness texture gradients become much weaker. The through-thickness recrystallization texture in the solution treated sample only has cubeyD {001 }（310） component. The relationship among thermomechanical processing, microstructure, texture and mechanical orouerties was analyzed.

Microstructure evolution of alumina dispersion strengthened copper alloy deformed under different conditions

Microstructure and texture evolution of Cu-0.23%Al2O3 dispersion strengthened copper alloy, deformed at room temperature or cryogenic temperature, were investigated. The main textures in hot-extruded specimen were Brass {011} 〈211〉 and Cube {100} 〈100〉. Textures of Brass {011} 〈211〉 and Goss {011} 〈100〉 were observed in specimen after deformation at room temperature; while textures of Brass {011} 〈211〉, Goss {011} 〈100〉 and S {123} 〈634〉 were detected after deformation at cryogenic temperature. It is believed that the additional Al2O3 nanoparticles can result in dislocation pinning effect, which can further lead to the suppression of dislocations cross-slip. While in the specimen deformed at cryogenic temperature, both pinning effect and cryogenic temperature are responsible for the formation of Brass, Goss and S textures.

Compressive anisotropy of extruded Mg-Dy-Zn alloy sheet

Compressive anisotropy of extruded Mg-2Dy-0.5Zn （mole fraction, %） alloy sheet was investigated. The alloy sheet was mainly composed ofα-Mg, （Mg, Zn）xDy phase and a large number of long period stacking ordered （LPSO） phases distributed along the extrusion direction. The compressive experimental results show that the alloy sheet exhibits an obvious compressive anisotropy. The compressive strength of the specimen in the extrusion direction （ED） is higher than those of the specimens in the transverse direction （TD） and 45° inclined to the extrusion direction. The compressive yield strength （CYS）, ultimate compressive strength （UCS） and compressive strain of the specimen in the ED are 274.65 MPa, 518.94 MPa and 12.93%, respectively. The compressive anisotropy is mainly attributed to the distribution of LPSO phase and formation of〈10 10〉//ED fiber texture in the deformed grains.

Enhanced ductility and reduced asymmetry of Mg-2Al-1Zn alloy plate processed by torsion and annealing

The ductility and plastic asymmetry of an as-annealed magnesium alloy plate were studied in compression through combined process of torsion and subsequent annealing by optical microscope and EBSD. The yield strength（YS） and ultimate compression strength（UCS） as well as the compression ductility（CD） were simultaneously raised by prior torsion at room temperature. The CD was further enhanced by subsequent annealing. Also, the torqued sample followed by annealing experienced a rising CD with the increase in prior strain, leading to the maximum true strain of 0.279, which is twice that of the as-annealed original one. The sample showed a largely reduced tension-compression yield asymmetry by subjecting to pre-torsion alone or combined with a subsequent annealing. The enhanced ductility and reduced asymmetry are attributed to the development of a gradient microstructure with refined grains, and also randomization of the weakened texture due to torsion and subsequent annealing.

Microstructural evolution and delayed hydride cracking of FSW-AZ31 magnesium alloy during SSRT

Evolution of microstructure including texture and fractography in a friction-stir welded（FSW） AZ31 magnesium alloy was investigated. The texture was measured using a neutron diffractometer. The microstructure and fractography of stress corrosion cracking（SCC） samples were observed by optical and scanning electron microscopy, respectively. An X-ray diffraction study was carried out on the fractured surfaces of the SCC specimens. The results indicated that a strong basal fiber was formed on the base material, whereas the grains in the stir zone were reoriented with their most basal planes tilted 25 o to the welding direction. Feather-like twins and hydride formed under slow strain rate tensile（SSRT） stress in air and aggressive solutions, respectively. Transgranular cracks propagated and finally failed on the retreating side in the solution. The hydride phase confirmed to sit on the fracture surface demonstrated the delayed hydride cracking（DHC） mechanism of the alloy.

Microstructure and texture evolution of AZ31 magnesium alloy during large strain hot rolling

Commercial AZ31 magnesium alloy sheets were rolled by nearly 70% thickness reduction in one rolling pass at 823 K. The results show that ultrafine grains are distributed in both shear bands and surfaces of the rolled sheets. The grain size of the refined grain in the shear bands is 0.4-1 μm. The outstanding grain refinement is attained by dynamic recrystallization due to flow localization. The texture in middle layer of the sheet is basal texture with little change in intensity throughout the rolling process, while the texture on surface becomes a double-peak texture with basal poles splitting in the transverse direction（TD）. The relative intensity of the double-peak texture is 26.6, which is quite higher than that of the texture in the middle layer. The inhomogeneous strain distribution is responsible for the exceptional grain refinement and texture evolution.

Microstructure and mechanical properties of as-extruded Mg-Sn-Zn-Ca alloy with different extrusion ratios

The effect of extrusion ratio on microstructure and mechanical properties of as-extruded Mg-6Sn-2Zn-1Ca （TZX621）（mass fraction, %） alloy was investigated. It is found that incomplete dynamic recrystallization （DRX） took place in as-extrudedTZX621 alloy. As the extrusion ratio was increased from 6 to 16, both fraction of un-DRXed grains and average size of DRXedgrains in as-extruded TZX621 alloy decreased and the basal texture was weakened. Coarse CaMgSn phase was broken into particlesand fine Mg2Sn phase precipitated from α-Mg matrix during hot extrusion. Yield strength, ultimate tensile strength and elongation ofas-extruded TZX621 alloy with extrusion ratio of 16 reached 226.9 MPa, 295.6 MPa and 18.1%, which were improved by 36.0%,17.7% and 13.5%, respectively, compared to those of as-extruded TZX621 alloy with extrusion ratio of 6.

Microstructure, texture and mechanical properties of Mg-8Gd-4Y-1Nd-0.5Zr alloy prepared by pre-deformation annealing, hot compression and ageing

An extruded Mg-8Gd-4Y-1Nd-0.5Zr alloy was pre-heated at 470℃ for 1 h and subsequently compressed at 470℃ and two strain rates of 0.2 and 0.0003 s^-1. Microstructure, texture and mechanical properties of the alloy were examined by optical microscopy (OM), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), hardness test and tensile test. The results show that the post-deformed microstructures of alloy are non-uniform at both strain rates due to the dissolution of RE-rich particles and the occurrence of DRX. The textures of post-deformed alloy are affected by strain rate. The alloy exhibits a strong basal texture of (0001)//ND (normal direction) after compression at 0.2 s^-1, while a weak texture component of (0001)//ED (extrusion direction) is formed in the compression obtained at 0.0003 s^-1. Compared with the alloy compressed at 0.0003 s^-1, the compressed alloy obtained at 0.2 s^-1 presents better comprehensive mechanical properties with the ultimate tensile strength of 426 MPa, yield strength of 345 MPa and ductility of 2.1% when being aged at 225℃ for 8 h.

Evaluation of microstructure and texture formation during annealing of cold-rolled FeCrCuMnNi multiphase high-entropy alloy

Microstructure and texture variations of a cold-rolled multiphase FeCrCuMnNi high-entropy alloy were studied after different annealing treatments.Samples were heat-treated at different temperatures and for different time,and then,subjected to different tests including XRD and SEM-EBSD.The results reveal that the FCC1 phase,which goes through more strain,has lower melting temperature,and recrystallizes earlier(lower temperature and shorter time).In addition,it is seen that particle stimulated nucleation is more effective on the recrystallization of this phase compared to FCC2 phase.A significant number of FCC1 nuclei form around the BCC particles.Nucleation of FCC2 phase initiated at 800℃mostly at the grain boundaries and the inhomogeneities.The FCC1 phase was almost fully recrystallized at this temperature.The annealing process led to the elimination of rolling textures,while the Brass component remained a major component in the recrystallized samples.Increasing annealing temperature as well as annealing time led to the formation of Cube texture component,which is a major component of recrystallized low stacking fault energy materials.Furthermore,D and Rt-Co components formed during recrystallization as a result of the formation of annealing twins.

Effects of strain rate on mechanical properties, microstructure and texture of Al-Mg-Si-Cu alloy under tensile loading

The effects of strain rate on the mechanical properties,microstructure and texture of Al-Mg-Si-Cu alloy were investigated through tensile test,microstructure and texture characterization.The results show that strain rate has some influences on the mechanical properties and microstructure,but a slight influence on the texture.Overall,yield strength,ultimate tensile strength and elongation increase first,then remain unchanged,and finally increase with increasing strain rate.Independent of strain rate,microstructure in the vicinities of the fracture regions of all the specimens is composed of the slightly elongated grains.However,some differences in misorientation angle distributions can be observed.As strain rate increases,the low angle grain boundaries(LAGBs)increase first,and then decrease.Textures in the vicinities of the fracture regions are almost identical with increasing strain rate.

Relationship among solution heating rate,mechanical properties,microstructure and texture of Al−Mg−Si−Cu alloy

The relationship among heating rate, mechanical properties, microstructure and texture of Al-Mg-Si-Cu alloy during solution treatment was investigated through tensile test, scanning electron microscope, X-ray diffractometer and EBSD technology. The experimental results reveal that there is a non-monotonic relationship among solution heating rate, mechanical properties, microstructure and texture. As the solution heating rate increases, the strength variations are dependent on the tensile direction;work hardening exponent n decreases first, and then increases;plastic strain ratio r increases first, and then decreases, and finally increases. The final microstructure and texture are also affected by heating rate. As heating rate increases, the microstructure transforms from elongated grain structure to equiaxed grain structure, and the average grain size decreases first, and then increases, and decreases finally. Although the texture components including CubeND{001}<310> and P{011}<122> orientations almost have no change with the increase of heating rate, the texture intensity and volume fraction decrease first, and then increase, and finally decrease. Both microstructure and texture evolutions are weakly affected by heating rate. Improving heating rate is not always favorable for the development of fine equiaxed grain structure, weak texture and high average r value, which may be related to the recrystallization behavior.

Microstructure evolution and recrystallization behavior of cold-rolled Zr-1Sn-0.3Nb-0.3Fe-0.1Cr alloy during annealing

The effects of cold-rolling reduction,annealing temperature,and time on recrystallization behavior and kinetics of cold-rolled Zr-1Sn-0.3Nb-0.3Fe-0.1Cr alloy were investigated using the Vickers hardness test,scanning electronic microscopy(SEM),transmission electron microscopy(TEM)and electron backscatter diffractometry(EBSD).The results show that the rate of the recrystallization increased with increasing annealing temperature and rolling reduction.Recrystallized grains nucleated preferentially at sites with high density dislocation and deformation stored energy and then grew into integral grains.Recrystallization texture changed from-1010-//RD to-1120-//RD.The grain orientation changed from random orientation to the orientation with the maximum misorientation around 30°.Recrystallization kinetics and maps were constructed based on the Johnson-Mehl-Avrami-Kolmogorov(JMAK)equation to derive parameters sensitive to the microstructure.The activation energies for recrystallization of 30%,50%and 70%cold-rolling reductions were determined to be 240,249 and 180 kJ/mol,respectively.

Ti-6Al-4V合金的疲劳性能

简要综述了Ti-6Al-4V合金的显微组织和织构对其疲劳性能的影响及其机理.

Influence of roll speed difference on microstructure, texture and mechanical properties of 7075 aluminum plates produced via combined continuous casting and rolling process

The influences of the dissimilarity in the roll speeds on the microstructure, texture and mechanical properties of 7075 aluminum plates produced via combined continuous casting and rolling(CCCR) process were investigated. Several experiments were conducted with three different upper/lower roll rotational speed ratios(ω/ω0, ω is the upper roll rotational speed and ω0 is the lower roll rotational speed), namely 1:1, 1:1.2 and 1:1.4. It was found that the greatest dissimilarity in the roll speed(ω/ω0=1:1.4) improved the yield strength and ultimate tensile strength of 7075 Al plate in the rolling direction by 41.5% and 21.9%, respectively. Moreover, at a roll speed ratio of ω/ω0=1:1.4, the average grain size was decreased by 36% whereas the mean hardness of the transverse cross-section of the finally rolled plate was increased by about 9.2%. Texture studies also revealed that the more the difference in the roll speeds was, the greater the isotropy and the hardness of the final product were. Nevertheless, conducting CCCR operation with different roll speeds resulted in about 6% reduction in the elongation of the deformed plate.

Effect of large strain cross rolling on microstructure and properties of Al-Li alloy plates with high magnesium content

Transmission electron microscopy(TEM),electron backscattered diffraction imaging(EBSD)and X-ray diffractometry were used to analyze the microstructure and texture characteristics of Al-9.8Mg-1.5Li-0.4Mn alloy cross-rolled and extruded plates,and the tensile properties and deep drawing performance were measured.The results show that the occurrence of dynamic recrystallization was promoted,the grains were refined and the preferred orientation of the recrystallized grains was improved by large strain cross rolling.Compared with CBA and CCB rolling methods,CBB rolling method significantly reduced the orientation density of the typical Brass texture{110}?112?in the extruded plates.The orientation densities of Copper texture{112}?111?and Brass texture{110}?112?on theβorientation line in the CBB rolled plates were the lowest,and there were no typical texture features in the plates.Meanwhile,better deep drawing could be gained in the CBB rolled plates,and the mechanical properties of the 0°,45°and 90°directions were basically the same.The tensile strength,yield strength and elongation at room temperature for the CBB rolled plates were 617 MPa,523 MPa and over 20.1%,respectively.The deviation of the mechanical properties at different directions was less than 3%.