Static Recrystallization Research Articles

Effects of recrystallization on interfacial microstructure evolution and shear strength of TiAl alloy joints

The effects of dynamic recrystallization (DRX) and post-bonding heat treatment (PBHT) on the interfacial microstructure evolution and mechanical properties enhancement of Ti-43Al-4Nb-1Mo-0.2B alloy joints, subjected to various bonding parameters, were thoroughly investigated through detailed microstructural characterization and shear performance tests. A strip-like DRX area was observed at the interface when bonding at 1100 °C, ≥30 MPa, for 60 min. Equiaxial- γ grains underwent discontinuous dynamic recrystallization during the bonding process, and tended to form flat grains parallel to the lamellae direction during recrystallization annealing (1000 °C/6 h) owing to the hindrance imposed by the lamellae on both sides. The orientations of lamellae on the both sides of bonding interface affects the lamellae's stress distribution and deformation behavior at the bonding interface, subsequently influencing the DRX behavior and the width of the DRX zone. Static recrystallization (SRX) during the recrystallization annealing treatment can eliminate bonding defects of joints bonding at lower pressures or temperatures. Optimal joints with fully lamellar interfacial microstructure and excellent shear properties can be obtained through single-α phase annealing treatment. Lamellae microstructure tailored through PBHT can significantly enhance the quality of joints, attributed to the homogeneity of the microstructure between the interface and matrix. The highest shear strength of 478 MPa, accounting for 82 % of the matrix strength, was obtained under the bonding parameters of 1100 °C/30 MPa/60 min-1290 °C/15 min. This work provides important DB process parameters for fabricating of complex structural parts of TiAl alloy.

Regulating the grain refinement and rolling properties of coarse-crystalline Mg-Zn-Gd-Ca-Mn alloy through multi-pass cold rolling and annealing

The newly developed Mg–Zn-RE (rare earth) alloy sheet shows significant prospects for 3C applications due to its superior room-temperature malleability compared to the commercial AZ31 alloy. However, the casting ingots of these alloys often exhibit coarse grains due to low alloying element content and the absence of the grain-refining element Zr, making them susceptible to significant cracking while hot-rolling. This study applies a multi-pass cold rolling technique with minimal reduction to a cast Mg–Zn-Gd-system alloy characterized by coarse grains, followed by a static annealing process to enhance its rolling capability. The impact of cold rolling and annealing temperatures on microstructure, plastic deformation mechanism, and static recrystallization (SRX) behavior were studied. It was found that multi-pass cold rolling with minimal decrease promoted the generation of more twins and slip lines, resulting in more uniform deformation and a substantial accumulated rolling strain of 10 %. Consequently, the significant accumulated strain, coupled with stress concentration at positions such as grain boundaries, twin boundaries, and dislocation tangles, acted as nucleation sites for complete static recrystallization at a specific annealing temperature of 375 °C. As a result, the coarse cast grains were successfully refined from 400 μm to 37 μm. Fortunately, this improvement has significantly enhanced the hot-rolling qualities, removing fractures throughout the process. This advancement not only enables industrial-scale rolling but also enhances production efficiency.

New Insights into the Ingot Breakdown Mechanism of Near-β Titanium Alloy: An Orientation-Driven Perspective

The ingot breakdown behavior of a typical near-β titanium alloy, Ti-55511, was investigated by various multi-pass upsetting processes. Particular emphasis was placed on the breakdown mechanism of the ultra-large β grains. The results showed that the upsetting far above the β-transus yielded uniform and refined macrostructure with relatively coarse grain size. In contrast, subtransus deformation within the (α + β) dual-phase field caused severe strain localization and macroscale shear bands. It was found that the static recrystallization during the post-deformation annealing was determined by the preferential grain orientations, which were closely related to the processing conditions. During β-working, the stable <001>-oriented grains were predominant and fragmentized mainly via a so-called “low-angle grain boundary merging” mechanism, even under a fairly low deformation. However, the vast <001> grain area was unbeneficial for microstructural conversion since it provided minor nucleation sites for the subsequent annealing. In contrast, the α/β-working produced the majority <111>-orientated grains, which were strongly inclined to strain localization. Highly misoriented deformation/shear bands were massively produced within the <111> grains, providing abundant nucleation sites for static recrystallization and, hence, were favorable for microstructural refinement. Furthermore, the intrinsic causes for deformation nonuniformity were discussed in detail, as well as the competition between microstructural homogeneity and refinement.

Effect of strain path and short-term post-annealing on the microstructure, texture, and mechanical anisotropy of low-carbon steel

In this research, the effect of strain path and short-term post-annealing on the microstructure, texture, and mechanical anisotropy of low-carbon steel was investigated. Asymmetric unidirectional rolling (AUR) and asymmetric cross rolling (ACR) were applied on Fe-0.072C steel. The ACR-processed sheet revealed a very limited number of new grains compared to the AUR-processed sheet, which was due to the dynamic recovery induced by strain path change. The average ferrite grain size of the post-annealed AUR- and ACR-processed samples was 11.5 and 14.1 μm, respectively. The dominant recrystallization in the annealed AUR-processed sheet was discontinuous static recrystallization, while that in the annealed ACR-processed sheet was continuous static recrystallization. The weak typical rolling textures (γ-fiber and α-fiber) at the midthickness of both rolled sheets demonstrated that the shear deformation effectively contributed to the formation of the shear textures during asymmetric cold rolling. The ACR decreased the intensity of the overall texture more than the AUR process due to the changes in the reference frame of deformation after each pass, which destabilized ideal texture components. The results showed that Goss and {111}〈112〉 components were continuous and discontinuous static recrystallization textures in the asymmetrically cold-rolled low-carbon steel sheet during the annealing treatment, respectively. The annealed AUR-processed sheet revealed a weaker texture as compared to the annealed ACR-processed sheet. The significant changes in the preferred orientations of the annealed AUR-processed sample led to weaker texture intensity compared to the annealed ACR-processed sheet. The hardness of the annealed AUR-processed sheet (183.8 HV) was higher than that of the annealed ACR-processed steel (156.9 HV), which was owing to the larger grain size and also the elimination of the γ-fiber texture in the annealed ACR-processed sheet. The strength along the rolling direction was lower than that along the transverse direction in the AUR-processed sheet. However, in the ACR-processed sheet, the values of strength were similar along three different tensile directions. As an important conclusion, if both high-strength and low-anisotropy are needed in the low-carbon steel sheets, it's better to apply ACR rather than AUR. In addition, if both high toughness and low anisotropy are essential, it's better to use AUR followed by post-annealing rather than ACR + post-annealing. The length of the intermediate stage of work hardening in the annealed ACR-processed sample was much less than the annealed AUR-processed sheet due to the presence of harder orientations (〈111〉 and 〈110〉) along rolling and transverse directions in the annealed ACR-processed sample. Finally, the fracture behavior of deformed and post-annealed steel sheets for both strain paths was ductile and shear ductile.

High strength and elongation of Mg-Gd-Nd-Zr alloy obtained by synergistic action of high-speed extrusion and short-time aging treatment

Magnesium–gadolinium (Mg–Gd)-based alloys have excellent high-temperature properties and the addition of two heterogeneous rare earth (RE) elements may promote the formation of secondary phase for better-strengthened properties. Herein, novel Mg-7Gd-2Nd-0.5Zr (wt%) alloys were prepared by synergistic reaction induced by high-speed extrusion (EX) and short-time aging treatment (AT). The microstructures, textures, and mechanical properties of the resulting alloys were then comprehensively studied by various analytical methods. The result reveals that the as-cast Mg-7Gd-2Nd-0.5Zr (wt%) alloy is composed of α-Mg matrix and Mg5(Gd,Nd) phase with bony and continuous networks at grain boundaries. The microstructure presents coarse deformed grains and fine recrystallized grains after high-speed EX, and formation of typical (0001)∥ ED extruded fiber texture and [1¯21¯1] RE texture is observed. The EX22 sample exhibits more Mg5(Gd,Nd) precipitated phases, fuller DRXed grains, and shorter peak aging times than the EX9 sample. After the AT at 250 °C, the proportion of deformed grains decreases due to static recrystallization, which leads to a reduction in the average grain size and weakening of the texture intensity. Therefore, combined effect of all strengthening mechanisms aids in achieving balance of high-strength and high-elongation for Mg-7Gd-2Nd-0.5Zr (wt%) alloy. The values of yield strength (YS), ultimate tensile strength (UTS), and elongation (EL) of EX22-A sample at room temperature are found to be 292.5 MPa, 350.6 MPa, and 24.3%, respectively. Overall, this study provides relevant experimental basis and theoretical guidance for the development of high-strength Mg-RE alloys, which are useful for future consideration.

Electropulsing anisotropy of cold-rolled Grade 2 titanium sheet: Effect of electric current direction on recrystallization and hardness

This study investigated the effects of electropulsing treatment (EPT) condition on the microstructure and microhardness of cold-rolled Grade 2 Ti sheet. Particular attention was paid to the dependence of the material properties on the electric current direction, referred to as electropulsing anisotropy. Direct-current (DC) EPT was applied along either the rolling direction (RD) or transverse direction (TD) of the rolled sheet. EPT along the TD resulted in a higher heating rate and maximum temperature, whereas that along the RD accelerated the static recrystallization (SRX) process under identical electropulsing parameters. Such a discrepancy was interpreted using the elongated grain structure and basal texture in the cold-rolled Ti sheet. These results were further supported by microhardness measurements, confirming the presence of electropulsing anisotropy during DC EPT in Ti alloys for the first time. In addition, the employed EPT was compared to a traditional furnace heat treatment (FHT) with rigorous temperature and time control, wherein the optimum EPT process spent only 13% of the processing time to complete SRX with a lower thermal energy requirement. This indicates a significant athermal contribution of EPT to electropulsing anisotropy.

Experimental selection of rolling contact length to the average thickness (L\\have) ratio for producing fine-grain Incoloy 907 superalloy sheet by hot-rolling

The current study investigates the effects of L\\have values on the microstructure and tensile properties of the superalloy Incoloy 907. These effects are studied using hot-rolling at 84 % and 96 % thickness reductions. Microstructural examination of the received sample revealed a non-uniform coarse grain structure with precipitates of oxide phases rich in niobium and Laves. These precipitates are shredded and randomly distributed in the microstructure with elongated grains after hot-rolling under 84 % reduction. Following the solution-treatment, this sample's simultaneous static recrystallization and precipitation of secondary-phase particles has formed a banded structure of grain-size and secondary-phase particle bands. The particles of the secondary-phases are locally accumulated on the material's surface in the 96 % hot-rolled sample, creating a duplex grain and non-random microstructures with different cross-sectional conditions. The secondary-phase particle bands caused by the previous solution-treatment are retained in the pre-hot-rolled sample under 84 % reduction after aging. Furthermore, XRD analysis results show that the precipitation peak of γ'/γ phase was more visible and intense in this sample. Tensile tests conducted at room temperature and 649 °C indicate that the pre-hot-rolled sample with an 84 % reduction exhibited a 1 % improvement in cold ductility and an 8 % enhancement in hot ductility compared to the sample with a 96 % reduction.

Determination of Activation Energy For Static Re-Crystallization in Nb- Ti Low Carbon Micro Alloyed Steel

Data required for calculation the static re-crystallization kinetics have been evaluated from laboratory simulations. Series of two hit isothermal tests were conducted on high temperature torsion machine. These tests were conducted on four different temperatures and using inter-pass times between 0.5 and 5s with aim to investigate the influence of thermal activation on static re-crystallization. All tests were conducted on temperatures over TNR temperature, i.e. in temperature range in which all niobium is present only in solid solution. Method of evaluation of re-crystallization fraction was mechanical metallography, i.e. evaluation based on shape of each stress- strain curve. The fraction softening was calculated for all temperatures, together with avrami exponent, nA, and activation energy for re-crystallization, QSRX. Activation energy for static re-crystallization QSRX  281 KJ/mol and avrami exponent nA  1 determined in this work are in excellent agreement with previously reported data.

Effects of Crystal Orientation and External Stress on the Static Recrystallization Behavior of an Ni-Based Single-Crystal Superalloy.

The deformation mechanism and static recrystallization (SRX) behavior of an Ni-based single-crystal superalloy are investigated. Indentation tests were performed to investigate the effects of crystal orientation and external stress on SRX behavior. Following solution heat treatment, the depth of the SRX layer below the indentation increases with a deviation angle (β) from the [001] orientation. The slip analysis indicates that an increased deviation angle leads to an increase in the resolved shear stress on the slip plane and a decrease in the number of active slip systems. In addition, the variation pattern of the SRX layer depth with the deviation angle is consistent for different external stresses. The depth of the SRX layer also increases with external stress. The coarse γ' phases and residual γ/γ' eutectics obviously enhance the pinning effects on the expansion of recrystallized grain boundaries, resulting in slower growth rates of the recrystallized grains in interdendritic regions than those in dendrite core regions.

Recrystallization and grain growth activation energies in a hybrid magnesium material fabricated by high-pressure torsion

The recrystallization and grain growth activation energies of the hybrid AZ31/Mg-0.6Gd (wt.%) alloy were calculated using differential scanning calorimetry analyses and scanning electron microscopy, respectively, after fabricating by high-pressure torsion up to 20 turns and then subjecting to an isochronal annealing treatment from 423 to 723 K for 1 h. The DSC results show one exothermic peak belonging to the static recrystallization of the AZ31 region with an activation energy of 112 ± 10 kJ/mol. The grain growth kinetics for the AZ31 and Mg-0.6Gd regions were described by the Arrhenius equation. The calculation with a grain growth exponent equal to 4 gave values for the activation energies in both the AZ31 (146.2 ± 8.4 kJ/mol) and Mg-0.6Gd (90.9 ± 13.5 kJ/mol) regions. The present results reveal the heterogeneity of the thermal stability of the AZ31/Mg-0.6Gd hybrid material.

Delineating the role of dynamic and static recrystallization during hot working of nickel-based superalloy (IN600)

In the presented research, the dynamic working of nickel-based (IN600) superalloy was performed and the micro-mechanisms affecting the deformation behaviour were closely monitored, particularly the role of static and dynamic recrystallization. Hot deformation flow stress response indicated an increase in the true stress value with an increase in strain rate and decrease in temperature. The constitutive calculations indicated that deformation progressed mainly due to dislocation climb motion. The hot workability map indicated a peak power dissipation efficiency (PDE) of 0.39 in two working domains. The microstructural evolution in the hot deformed specimens depicted a consistent increase in dynamic softening at temperature ≥ 1000 °C, whereas, a steady decline in the extent of dynamic softening is observed with increase in strain rate from 0.01 s−1 to 1 s−1. The mechanism for microstructural evolution in this range (0.01–1 s−1) was identified as discontinuous dynamic recrystallization (DDRX). Moreover, at the highest strain rate of 10 s−1, a sudden surge in the recrystallization fraction was observed, which was attributed to the combined effect of DDRX and static recrystallization (SRX). Additionally, this study shows that the presence of twin boundaries (TBs) contributes to dynamic softening by serving as sites for nucleation of strain-free grains.

The Effect of Static Recrystallisation of Parent Austenite on the Lath Martensite Intervariant Boundary Network

The current study investigated the effect of static recrystallisation (SRX) of parent austenite microstructure on the lath martensite intervariant boundary network. In general, the misorientation angle distribution of lath martensite exhibited a bimodal distribution in the range of 10–22 deg and 47–60 deg for all thermomechanical conditions, closely matching the misorientations expected from the ideal Kurdjumov-Sachs orientation relationship. Nevertheless, the population of 60 deg misorientation angle initially reduced with the extent of softening up to 50 pct beyond which it progressively increased to a maximum in the fully recrystallised condition. This was closely consistent with the trend noticed for the 60 deg/[110] intervariant boundaries having twist character. This was explained through the distinct variant selection mechanism occurring due to the change in the parent austenite grain characteristics (i.e., size and deformed state) upon static recrystallisation. The recrystallisation initially led to the formation of fine dislocation-free parent austenite grains up to 50 pct softening, promoting a 4-variant (V1V2V3V4) clustering arrangement to decrease the strain related to the martensite transformation. In turn, this promoted the formation of symmetric tilt 60 deg/111¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\left[ {11\\overline{1}} \\right]$$\\end{document} intervariant boundaries, which ultimately reduced the 60 deg/110\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\left[ {110} \\right]$$\\end{document} boundaries. Further softening, accompanied with the growth and/or coalescence of parent austenite grains, altered the variant clustering to a 3-variant arrangement (V1V3V5) and the increase in 60 deg/110\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\left[ {110} \\right]$$\\end{document} twist intervariant boundaries. Indeed, the martensite boundary network was largely controlled by the SRX parent austenite characteristics (i.e., size), which can be controlled to enhance the materials performance for a given application.

Static recrystallization behavior of biomedical Co-29Cr-6Mo-0.16 N alloy with negative stacking fault energy

Static recrystallization (SRX) behavior of Co-29Cr-6Mo-0.16 N (CCMN) alloy subjected to a prior compression to 30% at room temperature and a subsequent annealing at 1000 °C was ex-situ observed by using an electron backscatter diffraction (EBSD). Ascribed to the large negative stacking fault energy of the alloy at room temperature, it was found that the microstructure of alloy compressed at room temperature is characterized by plenty of intersected strain-induced martensitic transformation (SIMT) ε phase bands with a mean interval of 2–3 μm, which divided the parent grains into fine pieces surrounded by high angle boundaries (HABs). The static recrystallization of CCMN alloy in the subsequent annealing at 1000 °C takes place in terms of transient transition of the HABs into Σ3n boundaries and reorientation of new grains.

Static recrystallization behavior and strengthening mechanism of a single-phase Cu–18Ni–17Zn alloy

The microstructural evolution and recrystallization behavior of a single-phase Cu–18Ni–17Zn alloy during annealing has been investigated. The strengthening effects of the solute atom concentration, grain size, and recrystallized volume fraction have also been studied. The results have shown that the difference in yield strengths for the fully recrystallized samples mainly depended on the grain boundary strengthening effect. This is attributed to a constant (∼41 MPa) solid-solution strengthening contribution in the completely recrystallized Cu–18Ni–17Zn alloy. When compared with pure copper, this alloy exhibited a high Hall-Petch constant (∼0.36 MPa m1/2), which is due to the higher grain boundary interface energy. A discontinuous recrystallization occurred in the alloy in the temperature range 400 °C–500 °C. Furthermore, the yield strength was linearly correlated to the recrystallized volume fraction in the partial recrystallized samples. Moreover, the addition of Ni and Zn increased the recrystallization temperature and slowed the recrystallization kinetics. The activation energy for the recrystallization was estimated as 92.6 ± 5.1 kJ/mol in the cold-rolled Cu–Ni–Zn alloy, which indicates that the grain boundary migration during recrystallization was mainly controlled by diffusion along the grain boundaries. In addition, the recrystallized grains preferentially nucleated at shear bands with high strain energies in the Cu–Ni–Zn alloy during annealing. As the regions of shear banding were completely consumed, new recrystallized nuclei formed at the grain corners. The limited number of nucleation sites resulted in a low Avrami exponent value that ranged from 0.41 to 0.61.

Effect of heat treatment processes on the Cu-electrodeposited through glass vias (TGV) plate

Based on laser-induced deep etching technology and through-hole filling techniques, TGV interposers were successfully fabricated. The residual stress in the Cu overburden film directly affects the yield improvement after subsequent grinding of the interposer. Therefore, we studied the evolution of residual stress, microstructural changes, and micro-nano mechanical properties within the Cu overburden film after heat treatment at different temperatures. Residual stress analysis using the sin2Ψ method with an X-ray diffractometer (XRD) indicates that during the process of increasing temperature from 100°C to 200°C, the internal residual stress in the Cu overburden film changes from compressive stress to tensile stress. Furthermore, the maximum absolute value of the residual stress, 70.09 MPa, appears at room temperature, and the minimum absolute value of the residual stress, 15.59 MPa, occurs after the heat treatment process at 200°C. Electron backscatter diffraction (EBSD) microstructural analysis shows that the application of heat treatment can effectively accelerate static recrystallization (SRX), promote a higher proportion of high-angle grain boundaries (HAGB), and refine grain size. Additionally, a (001) preferred orientation at high residual stress states and a (111) preferred orientation at low residual stress states are observed. Nanoindentation test results indicate that the Cu overburden film treated at 100°C has the most potential for removal during the grinding process.

Effect of nitrogen content on the static recrystallization and precipitation behaviors of vanadium–titanium microalloyed steels

Abstract Double compression tests were performed on vanadium–titanium microalloyed steels with different nitrogen contents by using a Gleeble-3800 thermo-mechanical simulator to study the softening behaviors of the deformed austenite during different time intervals between the two passes. The static recrystallization fractions were calculated by the stress offset method and static recrystallization diagrams for the tested steels were obtained. The effects of deformation temperature and interval time on the softening behaviors were analyzed. Especially, the effect of nitrogen on the softening behaviors of the tested steels is discussed in detail. The results showed that the softening behaviors of the tested steels with various nitrogen contents are different. As far as the steel with low nitrogen content is concerned, the softening fraction increases monotonically with increasing time interval, and higher temperature can promote the static recrystallization. However, with more nitrogen added into vanadium–titanium microalloyed steel, precipitated particles of vanadium titanium carbonitride can be observed in the tested steel at the temperature of 850 °C or 800 °C, which leads to the formation of plateaus on the softening curves. An increase in nitrogen content in the steel is favorable for vanadium titanium carbonitride precipitation, which leads to a stronger prohibition of static recrystallization and a longer plateau on the softening curves. Moreover, the precipitated particles in the tested steel will not play an inhibition role in static recrystallization until the nitrogen content in the steel reaches a critical value.

Structure refinement and performance balance of high-strength aluminum alloys using an improved thermomechanical treatment process

The microstructure of 7A85 aluminum alloy forgings often contains coarse second-phase particles and grains. To improve the microstructures and balance the properties, we used an enhanced thermomechanical treatment process that included multiaxial hot forging, multiaxial cryoforging (MACF), and three-step aging treatment. We thoroughly investigated the effects of MACF with 1–3 passes on the evolution of microstructure, three-dimensional (3D) mechanical properties at the center and edge, fracture toughness, and corrosion resistance of the alloy. Our findings revealed that multiaxial hot forging had a limited ability to crush the coarse second-phase particles. However, the higher flow stress and compound brittleness of MACF resulted in a significant increase in particle fragmentation and driving force for precipitation. Additionally, under MACF, massive dislocations proliferated due to the inhibition of dynamic recovery, forming large orientation gradient regions, which promote static recrystallization and grain refinement during solution treatment. As the number of MACF passes increased from one to three, the effect of particle crushing initially increased and then plateaued, the 3D grain sizes first decreased and then slightly increased, and the spacing of grain boundary precipitates (GBPs) increased. The dense and uniform precipitates, finest equiaxed grains, a low fraction of coarse particles, and large GBP spacing in MACF2 resulted in the higher strength, highest elongation with minimal anisotropy, superior fracture toughness, and enhanced corrosion resistance. Ultimately, MACF2 demonstrated the best overall performance and good homogeneity, with an average 3D ultimate tensile strength, average 3D yield strength, average 3D elongation, and fracture toughness at the center of 548 MPa, 476 MPa, 13.4%, and 42.5 MPa m1/2, respectively. These values were respectively 4.2%, 1.9%, 50.6%, and 13.9% higher than those of the uncompressed sample.

New understanding of static recrystallization from phase-field simulations

New understanding of static recrystallization from phase-field simulations

Low‐Temperature Annealing of Asymmetrically Cold‐Rolled Electrolytic Tough‐Pitch Copper: Anneal Hardening and Bimodal Microstructure

In this research, 90% asymmetric unidirectional rolling and post‐annealing are applied to electrolytic tough‐pitch (ETP) copper. The effect of low‐temperature (200 °C) annealing on the microstructure and texture evolution, mechanical, and electrical properties are investigated. Static recovery (SRV) is the main softening mechanism at the annealing time range of 1–5 min. In contrast, complete static recrystallization (SRX) is observed after annealing for 10 min. Bimodal microstructure, consisting of coarse and fine grains, is evolved for annealing times more than 10 min. With increasing the post‐annealing duration, the intensity of deformation and shear textures is continuously decreased; however, the recrystallization (Cube) orientation becomes stronger up to 11.2 × R. After 1, 2, and 5 min of post‐annealing, the hardness, yield strength, tensile strength, ductility, and toughness of copper are higher than those of the 90% rolled sample due to annealing hardening. After 10 min of annealing, the hardness, yield strength, and tensile strength suddenly decrease and the ductility and toughness significantly enhance owing to the complete recrystallization. With increasing the post‐annealing time, the fraction of flat surfaces is decreased and the fraction of ductile dimples is increased. With the post‐annealing time increasing from 1 to 120 min, the electrical conductivity gradually increases from 84.9%IACS to 96.7%IACS.

Revealing the inhomogeneous nature of microstructure and texture evolution in the cold-rolled CoCrFeMnNi alloy during static recrystallization

In the present investigation, equiatomic CoCrFeMnNi high entropy alloy (HEA) was subjected to 80% cold rolling (as-rolled) followed by isothermal annealing treatment at 700 °C for different time periods. Microstructural characterization was performed using electron back-scattered diffraction (EBSD) and electron channeling contrast imaging (ECCI) techniques on the as-rolled and annealed samples. The as-rolled microstructure consisted of elongated grains mainly composed of strong α-fiber and weak γ-fiber textures. The as-rolled sample showed the formation of ingrain SBs in the γ-fiber grains, which served as preferential sites for grain nucleation. The annealing treatment of as-rolled samples at 700 °C cause static recovery (SRV) before 5 minutes of heat-treatment, whereas static recrystallization (SRX) was observed after 5 minutes of heat-treatment in the CoCrFeMnNi alloy samples. A faster rate of recrystallization kinetics was observed after 15 minutes of heat-treatment. The annealing treatment reduced the intensity of α-fiber and enhanced the Copper, Cube and P ({011}<122>) texture components. Copper components originated from coarse recrystallized grains, which were the results of localized grain growth phenomena. Unusual behavior of banded featured α-fiber grains was observed during the annealing process. These banded grains in the partially annealed samples consisted of subgrain-boundaries and showed a delayed response to recrystallization as compared to grains with other orientations. Stored energy (SE) and Taylor factor (M) calculations were also used to understand the delayed recrystallization response of the banded featured/retained deformed grains. The microhardness value of the as-rolled sample was approximately 450 Hv, which decreased to around 230 Hv for the fully recrystallized grains.