Texture evolution and fraction of favorably oriented fibers in commercially pure aluminum processed to 16 ECAP passes

Texture evolution in 1050 commercial purity aluminum severely deformed by equal channel angular pressing (ECAP) is investigated by electron back scattered diffraction (EBSD). Pole figures and orientation distribution function (ODF) plots are generated for samples processed to 1, 2, 4, 8, 12 and 16 passes. The processing was done using route B_C, in which the samples were rotated by 90° in the same sense between subsequent pressings. Two different sized scans were performed on the flow plane of the processed samples. The orientations constituting the favorably oriented fibers are depicted and crystal orientation maps are generated. The spatial distribution of grains having these orientations are revealed through these maps. The fraction of the main texture fibers for a 5° spread around the specified orientations is experimentally calculated and a quantitative idea on the evolution of texture is presented. The results ascertained that the texture intensity around the main fibers generally weakens with number of ECAP passes.     

Equal channel angular pressing of a TWIP steel: microstructure and mechanical response

A Fe–20.1Mn–1.23Si–1.72Al–0.5C TWIP steel with ultrafine grain structure was successfully processed through equal channel angular pressing (ECAP) at warm temperature up to four passes following the B _C route. The microstructure evolution was characterized by electron backscattered diffraction to obtain the grain maps, which revealed an obvious reduction in grain size, as well as a decrease in the twin fraction, with increasing number of ECAP passes. The texture evolution during ECAP was analyzed by orientation distribution function. The results show that the annealed material presents brass (B) as dominant component. After ECAP, the one pass sample presents A ₁* and A ₂* as the strongest components, while the two passes and four passes samples change gradually toward \( B/\bar{B} \) components. TEM analysis shows that all samples present twins. The twin thickness is reduced with increasing the number of ECAP passes. Nano-twins, as a result of secondary twinning, are also observed in the one and two passes samples. In the four passes sample, the microstructure is extensively refined by the joint action of ultrafine subgrains, grains and twins. The mechanical behavior was studied by tensile samples, and it was found that the yield strength and the ultimate tensile strength are significantly enhanced at increasing number of ECAP passes. Although the ductility and strain hardening capability are reduced with ECAP process, the present TWIP steel shows significant uniform deformation periods with positive work hardening rates.     

Evolution of microstructure and texture in an ultrafine-grained Al6082 alloy during severe plastic deformation

The evolution of microstructure and texture in Al6082 precipitation-hardened alloy during equal-channel angular pressing (ECAP) was studied. It was found that although the dislocation density and the subgrain size saturated after 1 pass, the size of grains bounded by high angle boundaries reached its minimum value only after 4 passes. Furthermore, the grain orientation distribution changes between 4 and 8 passes, indicating the development of grain boundary structure even after the saturation of the parameters of the microstructure. As a result of this evolution, the initial texture of the commercial alloy was diminished after 8 passes and the grain orientation distribution became to be close to random case.     

Texture and mechanical properties of EUROFER 97 steel processed by ECAP

The EUROFER 97 steel was processed by equal channel angular pressing (ECAP) at 550 °C for four passes via route C. The starting material consisted of ferrite-martensite dual phase composed by small subgrains of about 0.5 μm and low angle boundaries less than 5°. The volume fraction of second phase particles was around 10 vol.%, besides a texture formed by several fibers orientations belonging to the zone axes 〈1 1 0〉, 〈1 1 1〉 and 〈1 1 2〉. Increasing ECAP deformation, this microstructure became into equiaxed grain structures of less than 1 μm, and the misorientation between contiguous grains increased. This refinement of the microstructure was accompanied by the development of a new texture described by a family of fiber orientations related by rotations around axes 〈1 1 0〉 and 〈1 1 1〉. Tensile tests have revealed that an ECAP treatment at 550 °C for two passes could significantly strengthen the tempered material still maintaining good ductility.     

Modelling microstructure evolution towards ultrafine crystallinity produced by severe plastic deformation

The significance of severe plastic deformation by equal channel angular pressing (ECAP) as a promising technique for extreme grain refinement down to sub-micrometer and sometimes nanometer scale is generally recognised. We present a modelling frame for describing ECAP based on microstructure evolution. Following a particular scenario of grain refinement, in which a dislocation cell structure is considered as a ‘precursor’ of the developing grain structure, the variation of the cell size with the number of ECAP passes is traced. Finite element simulations based on the model compare favourably with the experimental data. Further features of the model such as a provision for modelling the variation of the misorientation angle distribution and texture evolution are also discussed.     

Modelling microstructure evolution toward ultrafine crystallinity produced by severe plastic deformation

The significance of severe plastic deformation by equal channel angular pressing (ECAP) as a promising technique for extreme grain refinement down to sub-micrometer and sometimes nanometer scale is generally recognised. We present a modelling frame for describing ECAP based on microstructure evolution. Following a particular scenario of grain refinement, in which a dislocation cell structure is considered as a ‘precursor’ of the developing grain structure, the variation of the cell size with the number of ECAP passes is traced. Finite element simulations based on the model compare favourably with the experimental data. Further features of the model such as a provision for modelling the variation of the misorientation angle distribution and texture evolution are also discussed. An erratum to this article can be found at     

Effect of equal channel angular pressing on grain refinement and texture evolution in a biomedical alloy Ti13Nb13Zr

Evolution of texture and concomitant grain refinement during Equal Channel Angular Pressing (ECAP) of Ti13Nb13Zr alloy has been presented. Sub-micron sized equiaxed grains with narrow grain size distribution could be achieved after eight pass at 873 K. A characteristic ECAP texture evolved in α phase till four passes while the evolution of characteristic ECAP texture in the β phase could be observed only beyond the fourth pass. On increasing the deformation up to eight passes, the texture in α phase weakens while the β phase shows an ideal ECAP texture. A weaker texture, low dislocation density and high crystallite size values in α phase suggest the occurrence of dynamic recrystallization. The absence of texture evolution in β phase till four passes can be attributed to local lattice rotations. The characteristic ECAP texture in the eight pass deformed sample is attributed to delayed dynamic recrystallization in the β phase.     

Microstructure and mechanical properties of equal channel angular pressed Mg–Y–RE–Zr alloy

The microstructure and mechanical properties of equal channel angular pressed (ECAP) Mg–Y–RE–Zr alloy (WE43) are examined. Results show that after ECAP, the average grain size remarkably decreases from ～50?µm at initial state to ～1.5?µm through ECAP for four passes and the homogeneity of microstructure also improves gradually. Meanwhile the secondary-phase β-Mg₅RE morphology has obvious transformation from plate-like to spherical. Moreover, the initial random texture is converted to the strong (0002) basal texture. The ultimate tensile strength and yield strength increase in all passes. However, the ductility exhibits a tendency of increase from 1 to 4 passes then decrease from 4 to 12 passes. The variation in strength and ductility is attributed to the effect of specific microstructure evolution.     

Microstructure and mechanical properties of ultrafine grain ZK60 alloy processed by equal channel angular pressing

The microstructure evolution and tensile properties of ZK60 magnesium alloy after equal channel angular pressing (ECAP) have been investigated. The results show that the two-step ECAP process is more effective in grain refinement than the single-step ECAP process due to the lower deformation temperature, a mean grain size of ~0.8 μm was obtained after two-step ECAP process at 513 K for four passes and 453 K for four passes. The EBSD examination reveals that ZK60 alloy after two-step ECAP process exhibits a more homogeneous grain size and misorientation distribution than single-step ECAP process. Both alloys after ECAP process present similar strong {0002} texture. The tensile strength of two-step ECAP alloy has also been improved compared with the single-step ECAP alloy. The strengthening effect was mainly ascribed to grain refinement.     

The role of grain orientation in microstructure evolution of pure aluminum processed by equal channel angular pressing

A new approach describing the role of crystallographic orientation in the microstructural refinement of commercially pure aluminum during the successive passes of equal channel angular pressing (ECAP) is introduced. The study is based on analysis of X-ray diffraction texture data that is used to calculate the geometrical position of crystallographic slip planes with respect to the shearing plane of the ECAP die. The angular deviations of {111} slip planes from the macroscopic deformation plane for different processing routes were calculated and compared. The microstructure evolution was investigated using electron back-scattered diffraction (EBSD). The grain size and grain boundary character distribution obtained for each processing route are related to the angles between {111} planes and the shearing plane. It was shown that the more effective routes in grain refinement have higher angles between {111} slip planes and the shearing plane.     

等通道挤压AZ80镁合金的析出行为和性能

研究了AZ80镁合金经300℃等通道挤压(ECAP)后的组织、织构与力学性能的演变规律以及第二相析出行为的影响。结果表明:ECAP显著促进了粒状连续析出,可有效节省后续热处理时间。A路径多道次挤压最终获得基面织构;Bc路径挤压后形成基面近似平行于剪切面的织构;第二相析出对ECAP织构特征的形成没有显著影响。用该工艺可获得较高的延伸率(13%-19%),但是抗拉强度过低(300 MPa),综合机械性能不理想。可通过抑制挤压前的未溶粗大粒子的析出、减少挤压道次和降低挤压温度等措施优化AZ80的析出控制。     

Investigation on nanocrystalline iron‐cobalt‐vanadium alloy processed by equal channel angular pressing (ECAP)

Nanocrystalline iron‐cobalt‐vanadium alloy was fabricated by Equal‐Channel Angular Pressing (ECAP). Microstructural evolution at different passes of ECAP and the effect of φ in the ECAP were researched. The results revealed that a phase slowly turned to γ phase and followed the form of dislocation cells in the iron‐cobalt‐vanadium alloy with the increase of severe plastic deformation. At last, it became reasonably finer bands of subgrains. The results with intersect at an angle φ of 90° was better than with at an angle φ of 120°. After three passes of ECAP, at an angle φ of 90°, the nanocrystalline microstructure could be obtained. The grain size was reduced from 30 μm in the initial state to 400nm.     

Investigation of texture and mechanical properties of copper processed by new route of equal channel angular pressing

The evolution of crystallographic texture and the mechanical properties of copper subjected to severe plastic deformation (SPD) using equal channel angular pressing (ECAP) were investigated. Samples were subjected to ECAP under two different processing routes: B₆₀ and B_C. As the cross sections of the samples were circular, a new route with a rotation angle of 60° in the same direction between consecutive passes was introduced. The material exhibited texture development similar to the simple shear texture in both routes and the most significant changes in texture strength in both processing routes took place after the second pass. Microstructure of ECAP processed samples were investigated using electron backscatter diffraction (EBSD) analysis. Comparison of the EBSD data with optical micrograph of the initial sample confirmed that ECAP process has led to a significant decrease in grain size. Significant increases in hardness and tensile strength were observed after the first pass of ECAP. Variations of tensile strength as a function of the number of passes were related to the dislocation densities and the average boundary spacing.     

Grain refinement in as cast Al–Mg–Mn alloy during high temperature equal channel angular pressing

Abstract

An as cast Al–Mg–Mn alloy with coarse equiaxed grain structure was processed by equal channel angular pressing (ECAP) at 350°C up to eight passes. Systematic studies were made on the microstructural evolution during ECAP by optical microscopy, electron backscattered diffraction and TEM. Equal channel angular pressing led to a considerable grain refinement, resulting in an average cell size of about 1 μm and a fraction of high angle boundaries of 75% after eight pressing passes. Deformation bands were not developed during the ECAP process, and a reasonably equiaxed substructure was obtained even after one pass. The main mechanism of grain refinement was attributed to the continuous dynamic recrystallisation based on the motion of deformation induced dislocations. Discontinuous recrystallisation at grain boundaries and triple junctions also contributed to the refinement, which played an important role especially at high strain of eight passes.     

Microstructural evolution during extrusion and ECAP of a spray-deposited Al–Zn–Mg–Cu–Sc–Zr alloy

The microstructural evolution of an Al–Zn–Mg–Cu–Sc–Zr alloy prepared by spray deposition via extrusion and equal-channel angular pressing (ECAP) was investigated in this study. Deformation route A for Al–11.5 wt% Zn–2 wt% Mg–1.5 wt% Cu–0.2 wt% Sc–0.15% Zr super-strength alloy was carried out at 573 K by ECAP. The microstructures of extruded and ECAP samples were investigated by means of Electron Backscatter Diffraction (EBSD), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). A large amount of dislocation tangles were formed inside grains during ECAP, which further evolved into sub-boundaries and high angle grain boundaries. Microstructure analyses showed that the grain size was refined to 800 nm after 8 passes ECAP from earlier 3.5 μm of sprayed and extruded alloy. A few finer MgZn₂ and Al₃(Sc,Zr) were dispersed uniformly after ECAP. The textures of 8 passes ECAPed sample were dominated by the strong Cu orientation and relatively weak S orientation.     

Texture and microstructure evolution in ultrafine-grained AZ31 processed by EX-ECAP

Extruded AZ31 alloy was processed by equal channel angular pressing (ECAP) up to 12 passes at 180 °C following route B_c, i.e. rotating the sample 90° between individual passes. Microstructure evolution was investigated using EBSD and TEM, as a function of strain imposed by ECAP. The first ECAP pass resulted in the formation of a new texture component which relates to the bimodal grain structure observed in this specimen. The grains larger than 10 μm show the orientation changes corresponding to the ECAP shear, which is characterised by the rotation of the basal poles by approximately 40° from the initial orientation. The fine grains with the average size of 1 μm maintain the initial orientation. The character of the bimodal grain structure and the distinct texture components between large and small grains remained unchanged up to 4 ECAP passes. Further ECAP pressing to 8 and 12 passes leads to a grain refinement through the whole sample volume and the orientation changes of all grains corresponding to the ECAP shear.     

Microstructural evolution in high purity aluminum processed by ECAP

High purity (99.99%) aluminum was processed by equal-channel angular pressing (ECAP) through 1–12 passes and examined using orientation imaging microscopy. The results reveal two distinct processing regimes: from 1 to 4 passes the microstructure evolves from elongated subgrains to an essentially equiaxed array of ultrafine grains and from 4 to 12 passes there is no measurable change in the average grain size and grain aspect ratio. The boundary misorientation angle and the fraction of high-angle boundaries increase rapidly up to 4 passes and at a slower rate from 4 to 12 passes. Anomalously large grains were visible in the central region of the billet pressed through 12 passes due to dynamic recovery and grain growth. The results suggest optimum processing is achieved by pressing through 4–8 passes.     

Cryogenic equal channel angular pressing of commercially pure titanium: microstructure and properties

Cylindrical samples of CP Titanium (Grade 2) were deformed by one, two and three passes of equal channel angular pressing (ECAP) each at temperatures 77, 300 and 575 K, respectively. The microstructure of samples processed at 77 K shows retardation of recrystallisation, high density of dislocations and deformation twins, diffuse and obscure grain boundaries compare to microstructure of samples processed at room and high temperature, where recrystallised ultrafine equiaxed grains are observed. Mechanical properties for all structural states of Ti were studied by microhardness measurements at 300 K and uniaxial compression at temperatures 300, 170, 77 and 4.2 K. Higher levels of ECAP deformation (more passes of ECAP) lead to higher values of strength and hardness at all studied temperatures. Decrease of ECAP temperature leads to increase of strength characteristics in all cases. Influence of ECAP and compression temperatures on possible changes of deformation mechanism are discussed.     

Texture evolution during hot-rolling and recrystallization in B2-type FeAl, NiAl and CoTi intermetallic compounds

The texture evolution during the hot-rolling and the recrystallization of B2-type Fe–48Al, Ni–50Al and Co–50Ti (expressed by at.%) intermetallic compounds were investigated. By hot-rolling at 973 K, Fe–48Al showed a microstructure with coarse grains elongated along rolling direction, while Ni–50Al and Co–50Ti showed a deformed microstructure featured by the heavily distorted (elongated) grains and/or the deformation bands. The hot-rolling texture of Fe–48Al was composed of {111}<uvw>, while those of Ni–50Al and Co–50Ti were composed of {111}<110> and {111}<112>, respectively. After annealing, the recrystallized grains were preferentially nucleated at the grain boundaries for Fe–48Al, and in the heavily distorted regions or the deformation bands for Ni–50Al and Co–50Ti. The orientations of the recrystallized grains were similar with those of the deformed matrix, especially for Ni–50Al and Co–50Ti. The recrystallization textures were generally more dispersive than the hot-rolling texture. Based on these results, the texture evolution during the hot rolling and the recrystallization of the B2-type intermetallic compounds were discussed.     

Effects of Heat Treatment on Microstructure and Mechanical Properties of an ECAPed Al–Zn–Mg–Cu Alloy

Equal‐channel angular pressing (ECAP) has a considerable advantage in the preparation of bulk fine‐grained alloys. To investigate the effect of solid solution treatment (SST) on the microstructure and mechanic properties of an Al–Zn–Mg–Cu alloy after ECAP, a comparative study is conducted using experimental techniques. It is shown that ECAP processing introduces a strong grain refinement, while the SST induces precipitation of skeleton‐like second phases distributed discontinuously at the grain boundary and needle‐like second phases in the grain. In addition, SST can also improve significantly the fractions of both high angle grain boundaries and recrystallization. The {110}<001> texture is introduced and the polar density is reduced during SST. Microstructural evolution involves three typical characteristics, namely, shear bands, substructure, and precipitates. The corresponding mechanism of microstructure evolution is proposed, considering the effect of dislocations, precipitates, and grain boundaries. After SST, the improvement of strength and hardness is not obvious, but significant in plasticity by 33.3%. Different strengthening mechanisms are also examined during ECAP and subsequent SST.