Recrystallization Microstructure Research Articles

Simultaneously Improving Ductility and Stretch Formability of Mg-3Y Sheet via High Temperature Cross-Rolling and Subsequent Short-Term Annealing.

In this work, Mg-3Y sheet was prepared by high temperature cross-rolling and subsequent short-term annealing. The effect of annealing on microstructure, texture, mechanical properties, and stretch formability of Mg-3Y sheet was primarily investigated. Micro-nano size coexistence of β-Mg24Y5 phases can be well deformed with matrix. The as-rolled Mg-3Y sheet exhibited a homogeneous deformation microstructure consisting of deformed grains with extensive kink bands and dispersed β-Mg24Y5 phases. A double peak texture character appeared in as-rolled Mg-3Y sheet with a split of the texture peaks of about ±20° tilted to rolling direction. After annealing, the as-annealed Mg-3Y sheet presented complete static recrystallized (SRXed) microstructure consisting of uniform equiaxed grains. The texture orientation distribution was more dispersed and a weakened multiple-peak texture orientation distribution appeared. In addition, the maximum intensity of basal plane decreased from 5.2 to 3.1. The change of texture character was attributed to static recrystallization (SRX) induced by kink bands and grain boundaries. The as-annealed Mg-3Y sheet with high Schmid factor (SF) for basal <a> slip, prismatic <a> slip, pyramidal <a> slip, and pyramidal <c+a> slip exhibited high ductility (~25.6%). Simultaneously, enhanced activity of basal <a> slip and randomized grain orientation played a significant role in decreasing anisotropy for the as-annealed Mg-3Y sheet, which contributed to the formation of high stretch formability (~6.2 mm) at room temperature.

Study on the Microstructure and Mechanical Properties of Dynamic Recrystallization of Metastable β Titanium Alloy

A novel type of titanium alloy was investigated in this article. The microstructure and mechanical properties of Ti-3573 and Ti-3873 titanium alloys were observed and measured after 20% hot deformation, respectively. The results shown that both titanium alloys occurred dynamic recrystallization (DR) during hot deformation. The tensile strength of Ti-3873 titanium alloy was better than that of Ti-3573 titanium alloy. Both titanium alloys have fine secondary α-phase which appeared granular or acicular near the β-grain boundaries or within the β-grain after hot deformation. Better tensile strength (847 MPa) of Ti-3873 titanium alloy is contributed to the higher content of β-phase stable element (Mo). The improvement plasticity (12 %) of Ti-3573 titanium alloy is due to the occurrence of dynamic recrystallization during hot deformation.

Effect of Aging and Cooling Path on the Super β-Transus Heat-Treated Ti-6Al-4V Alloy Produced via Electron Beam Melting (EBM).

This work focuses on the effect of different heat treatments on the Ti-6Al-4V alloy processed by means of electron beam melting (EBM). Super β-transus annealing was conducted at 1050 °C for 1 h on Ti-6Al-4V samples, considering two different cooling paths (furnace cooling and water quenching). This heat treatment induces microstructural recrystallization, thus reducing the anisotropy generated by the EBM process (columnar prior-β grains). Subsequently, the annealed furnace-cooled and water-quenched samples were aged at 540 °C for 4 h. The results showed the influence of the aging treatment on the microstructure and the mechanical properties of the annealed EBM-produced Ti-6Al-4V. A comparison with the traditional processed heat-treated material was also conducted. In the furnace-cooled specimens consisting of lamellar α+β, the aging treatment improved ductility and strength by inducing microstructural thickening of the α laths and reducing the β fraction. The effect of the aging treatment was also more marked in the water-quenched samples, characterized by high tensile strengths but limited ductility due to the presence of martensite. In fact, the aging treatment was effective in the recovery of the ductility loss, maintaining high tensile strength properties due to the variation in the relative number of α/α’ interfaces resulting from α’ decomposition. This study, therefore, offers an in-depth investigation of the potential beneficial effects of the aging treatment on the microstructure and mechanical properties of the EBM-processed super β-transus heat-treated Ti-6Al-4V alloy under different cooling conditions.

Effect of Vacuum Heat Treatment on the Microstructure of a Laser Powder-Bed Fusion-Fabricated NiTa Alloy

The semiconductor industry uses a physical vapor-deposition process, with a nickel-tantalum (NiTa) alloy-sputtering target, to apply an amorphous NiTa thin film layer between the magnetic soft underlayer and substrate of a heat-assisted magnetic-recording hard disk drive. Currently, the alloy-sputtering target is produced through a hot-pressing (HP) process followed by a hot isostatic pressing (HIP). In this study, we demonstrate a better process for producing the sputtering targets, using laser powder-bed fusion (L-PBF) followed by vacuum heat treatment (VHT), to produce alloy targets with superior microstructural characteristics that will produce better-quality thin films. We compare as-fabricated (just L-PBF) specimens with specimens produced by L-PBF and then annealed at different conditions. Where the as-fabricated specimens are characterized by columnar dendrites, annealing at 1275 °C for 4 h produces a uniform equiaxed grain microstructure and a uniformly dispersed fcc Ta precipitate. In addition, the average microhardness value is reduced from 725 ± 40 to 594 ± 26 HV0.2 and the maximum compressive residual stress is reduced from 180 ± 50 MPa to 20 ± 10 MPa as the result of dislocation elimination during the recovery and recrystallization process. Finally, due to microstructure recrystallization, the VHT-treated L-PBF NiTa specimens exhibit a smaller grain size (2.1 ± 0.2 µm) than the traditional HIP-treated HP specimens (6.0 ± 0.6 µm).

Investigation of the Mechanical Properties of Inertia-Friction-Welded Joints of TC21 Titanium Alloy

TC21 titanium alloy is a new high damage-tolerant structural material for aerospace applications; its welding performance is very critical for the manufacturing of structural parts. In this research, the inertia friction welding (IFW) process of TC21 alloy was conducted, and the microstructure and mechanical properties of IFW joints were investigated. In tensile tests, specially designed tensile samples with grooves were utilized to achieve the tensile properties of IFW joints. The results show that the microhardness and tensile strength of IFW joints are higher than that of the base metal, but the plasticity of joints is worse compared with the base metal. The SEM results reveal that the weld zone has a dynamic recrystallization microstructure with uniform fine-needle α phases. The microstructure evolution in the weld is the key factor that results in the change of the mechanical properties of TC21 IFW joints.

Multi phase-field simulation study on microstructural grain development during inductive-based friction surfacing of aluminium

The computational solution is considered an effective tool for the analysis and a good understanding of the complex microstructural development that occurs during friction surfacing. In this article, ABACUS software was used to create a 3D-FE model of friction surfaced layering of AA 6063 aluminium on EN8 carbon steel, and the heat and strain rate collected throughout the operation were utilised for a computational investigation of microstructural recrystallization and grain development. The Multi-phase Field model (MFM) and constructive material model (CMM) were used for the prediction of the grain development during the process. A decrease in the incubation period from 0.839 sec to 0.578 sec was seen before recrystallization, after a temperature rises from 100°C to 300°C for substrate preheating. Validation of the reliability model obtained from the computational study was done using the image received from electron backscattered diffraction (EBSD) for grain size development and distribution. An appropriate assessment has been made between computational and experimental images which shows the maximum error of less than 10%. The development of grain structure during recrystallization was impacted extensively for increasing the coating strength, which was seen as inversely proportional to the average coating's grain diameter.

Plastic straining and concomitant microstructure recrystallization of Ni-Cu alloy in the undercooled condition

Microstructure and microtexture of rapidly solidified undercooled Ni-Cu alloys were investigated. The characteristic undercooling of Ni80Cu20 alloy was determined as 45K, 90K and 160K. Dendrite deformation due to rapid solidification led to strong deformation microtexture. Due to recrystallization upon annealing after recalescence, many subgrains were formed in the microstructure. Further, annealing the quenched alloy at 900°, new microtextures and subgrains were formed, which was due to recrystallization and dislocation network rearrangement. The results of comparative experiment proved the recrystallization mechanism of the microstructure refinement in the non-equilibrium solidification structure of the undercooled binary alloy

Fabrication of high-performance low silicon non-oriented electrical steels by a new method: Low-finishing-temperature hot rolling combined with batch annealing

The grain size prior to cold rolling plays an important role in the microstructural, textural evolution and magnetic properties of non-oriented silicon steel sheets. In this work, we proposed a new way to obtain large grain size before cold rolling and applied it to a 1.0 wt% Si-0.2 wt% Al non-oriented silicon steel, i.e., appropriate low-finishing-temperature hot rolling combined with batch annealing. The grain growth process during batch annealing was investigated using a quasi in-situ electron backscattered diffraction (EBSD) technique. It was demonstrated that significant grain growth took place through a strain-induced boundary migration mechanism. Then a large number of in-grain shear bands were formed in the cold rolled microstructure and could provide nucleation sites for Goss ({110} 〈001〉 ) and λ-fiber (〈001〉//ND) recrystallized grains, thus resulting in a coarse-grained and homogeneous recrystallization microstructure with weakened γ-fiber (〈111〉//ND) texture, strengthened Goss and λ-fiber texture. Consequently, superior magnetic properties (B50 = 1.763 T, P1.5/50 = 4.30 W/kg) were obtained. For comparison, the conventional processing route without batch annealing was also investigated. A small-grained and inhomogeneous recrystallization microstructure with pronounced γ-fiber texture was produced in the finally annealed sheet, which could significantly deteriorate both the magnetic induction and iron loss. This work provided a new way to enlarge the grains in hot rolled sheets by low temperature batch annealing instead of the conventional high temperature normalization. Thus a new processing route to fabricate low silicon non-oriented electrical steels with high permeability and low iron loss was established.

Effect of welding speed on microstructure and mechanical properties of Al−Mg−Mn−Zr−Tialloy sheet during friction stir welding

Effects of welding speed on the microstructure evolution in the stir zone (SZ) and mechanical properties of the friction stir welding (FSW) joints were studied by OM, XRD, SEM, TEM, EBSD and tensile testing. Compared with the base metal (BM), an obviously fine dynamic recrystallization (DRX) microstructure occurs in the SZ and the DRX grain size decreases from 5.6 to 4.4 μm with the increasing of welding speed. Fine DRX microstructure is mainly achieved by continuous dynamic recrystallization (CDRX) mechanism, strain induced boundary migration (SIBM) mechanism and particle stimulated nucleation (PSN) mechanism. Meanwhile, the geometric coalescence and the Burke−Turnbull mechanism are the main DRX grain growth mechanisms. Among all the welding speeds, the joint welded at rotation speed of 1500 r/min and welding speed of 75 mm/min has the greatest tensile properties, i.e. ultimate tensile strength (UTS) of (509±2) MPa, yield strength (YS) of (282±4) MPa, elongation (El) of (23±1)%, and the joint efficiency of 73%.

Effect of Holding Time of Decarbonization Annealing on Recrystallization in Fe-3.2%Si-0.047Nb% Low-Temperature Oriented Silicon Steel

In this study, the effects of decarburization annealing time on the primary recrystallization microstructure, the texture and the magnetic properties of the final product of 0.047% Nb low-temperature grain-oriented silicon steel were investigated by means of OM, EBSD and XRD. The results show that when the decarburization annealing condition is 850 °C for 5 min, the uniform fine primary recrystallization microstructure can be obtained, and the content of favorable texture {111} &lt;112&gt; is the highest while that of unfavorable texture {110} &lt;112&gt; is the lowest, which is mostly distributed near the central layer. At the same time, there are the most high-energy grain boundaries with high mobility in the primary recrystallization microstructure of the sample annealed at 850 °C for 5 min, and the ∑9 boundary has the highest percentage of grain boundaries. The samples with different decarburization annealing time were annealed at high temperature. It was found that perfect secondary recrystallization occurred after high-temperature annealing when the decarburization annealing condition was 850 °C for 5 min. The texture component was characterized by a single Goss texture, and the size of the Goss grain reached 4.6 mm. Under such annealing conditions, the sample obtained shows the optimal soft magnetic properties of B800 = 1.89 T and P1.7/50 = 1.33 w/kg.

The Influence of Annealing on the Optical Properties and Microstructure Recrystallization of the TiO2 Layers Produced by Means of the E-BEAM Technique.

Titanium dioxide films, about 200 nm in thickness, were deposited using the e-BEAM technique at room temperature and at 227 °C (500K) and then annealed in UHV conditions (as well as in the presence of oxygen (at 850 °C). The fabricated dielectric films were examined using X-ray powder diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, atomic force microscopy, scanning electron microscopy, transmission electron microscopy, and spectroscopic ellipsometry. The applied experimental techniques allowed us to characterize the phase composition and the phase transformation of the fabricated TiO2 coatings. The films produced at room temperature are amorphous but after annealing consist of anatase crystallites. The layers fabricated at 227 °C contain both anatase and rutile phases. In this case the anatase crystallites are accumulated near the substrate interface whilst the rutile crystallites were formed closer to the surface of the TiO2 film. It should be emphasized that these two phases of TiO2 are distinctly separated from each other.

Hot deformation behavior and processing map of low-alloy offshore steel

The hot deformation behavior of a low-alloy offshore steel was systematically investigated within the temperature range of 850–1150 °C and strain rate range of 0.01–10 s–1, via hot compression testing. The hot working equation, grain size model and recrystallization kinetic models of the steel were developed by fitting the experimental data. The results show that the decrease in Zener–Hollomon Z-parameter value (the increase in deformation temperature and the decrease in strain rate) is beneficial for the occurrence of dynamic recrystallization, and the grain size can be refined by increasing the Z-parameter value within the deformation range of dynamic recrystallization. However, when the Z-parameter value is higher than 3.43 × 1016, dynamic recrystallization will be difficult to occur within the range of experimental deformation conditions. Additionally, processing maps at different strains were constructed. According to the processing map and microstructural analysis, the optimal hot working conditions of the studied steel are within the temperature range of 1000–1100 °C and strain rate range of 0.1–1 s−1, and a complete recrystallization microstructure with fine homogeneous grains could be obtained.

Late Paleozoic Gondwanide deformation in the Central Andes: Insights from RSCM thermometry and thermal modeling, southern Bolivia

A widespread unconformity between Ordovician metasedimentary rocks and nonmetamorphosed Mesozoic sedimentary rocks across the Eastern Cordillera of Bolivia provides evidence for significant pre-Late Cretaceous deformation and erosion. In this paper, we refine the middle to late Paleozoic tectonic history of the central Andean segment of Gondwana's western margin. We combine Raman spectroscopy of carbonaceous material (RSCM) thermometry with semi-quantitative deformation temperature estimates from quartz recrystallization microstructures and published illite crystallinity values from Cambrian-Devonian sedimentary rocks that span the Eastern Cordillera of southern Bolivia at ~21°S. Estimates of peak temperature and deformation temperature range primarily between ~220 and ~ 400 °C and show a general increase with depth that defines a metamorphic field gradient between ~37 and ~ 47 °C/km. Temperatures obtained from Ordovician rocks directly below the unconformity require erosion of a > ~5 km overburden prior to the Late Cretaceous, which was likely accomplished by a combination of distributed cleavage development and Paleozoic folding and thrust faulting revealed from cross-section reconstructions. The peak temperature data are incorporated into thermal models along with published illite KAr, zircon (UTh)/He, and zircon fission-track cooling ages that refine the timing of Paleozoic orogenesis in the central Andes. We interpret shortening-related flexural subsidence driven by cratonward growth of a pre-Andean orogenic wedge along the western margin of Gondwana, with peak temperature conditions attained during eastward advance of a foreland basin between ~420 and ~ 318 Ma during the Devonian-Carboniferous Gondwanide Orogeny. Erosional exhumation between ~352 and ~ 294 Ma was the result of continued growth and eastward expansion of the associated Transpampean tectonic highland across the Eastern Cordillera. The growth of this pre-Andean contractional orogen coincided with global plate reorganization and the reestablishment of subduction and arc magmatism along the western margin of Gondwana, as indicated by a significant influx of Carboniferous arc-related detritus into the foreland basin system.

Dynamic recrystallization mechanisms of 2195 aluminum alloy during medium/high temperature compression deformation

The 2195 aluminum alloy has been widely utilized in the aerospace field, of which dynamic recrystallization microstructures have a substantial effect on the mechanical properties of aerospace parts. In this study, 2195 aluminum alloy was compressed at 300–520 °C using a Gleeble 3500-GTC thermo-mechanical testing system. The discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX) behavior of 2195 aluminum alloy at medium/high temperature was studied. The results demonstrated that during medium temperatures (300–360 °C) deformation the main softening mechanism was DDRX, and at high temperatures (420–520 °C), it was CDRX. CDRX of 2195 aluminum alloy involved three types of subgrain-forming mechanisms: dislocation tangling to form subgrains, microscopic shear bands to form subgrains, and the coalescence of two small subgrains to form larger subgrains. In addition, several recrystallized grains underwent geometric dynamic recrystallization (GDRX) at high temperature and extensive deformation (480 °C-80% or 520 °C-60%).

Primary Recrystallization Behaviors of Hi-B Steel with Lower Initial Nitrogen Produced by the Thin Slab Casting and Rolling Process

Based on low-temperature high-permeability grain-oriented silicon steel designed with an initial nitrogen content of 0.0055% and produced by the thin slab casting and rolling process, the effect of total nitrogen content and nitriding temperature on primary recrystallization microstructure and texture were studied by optical microscope, scanning electron microscope, transmission electron microscope, and electron backscatter diffraction. The nitriding temperature affects the primary recrystallization behaviors significantly, while the total nitrogen content has a small effect. As the nitriding temperature is 750–850 °C, the average primary grain size and its inhomogeneity factor are about 26.58–26.67 μm and 0.568–0.572, respectively. Moreover, the texture factor is mostly between 0.15 and 0.40. Because of the relatively sufficient inhibition ability of inherent inhibitors in a decarburized sheet, the nitriding temperature (750–850 °C) affects the primary recrystallization microstructure and texture slightly. However, as the nitriding temperature rises to 900–950 °C, the average primary grain size and its inhomogeneity factor increase to 27.75–28.26 μm and 0.575–0.578, respectively. Furthermore, because of the great increase on the area fraction of {112} &lt;110&gt; grains, part of texture factor is increased sharply. Therefore, in order to obtain better primary grain size and homogeneity, better texture composition, and stability of the decarburized sheet, the optimal nitriding temperature is 750–850 °C.

Influence of Severe Plastic Deformation on Static Recrystallization Microstructure of Pure Iron

In recent years, ultrafine-grained steel has been gaining increasing attention as a high-performance material. Accordingly, it is necessary to develop an efficient production method for ultrafine-grained steel. Severe plastic deformation is a critical factor that causes grain subdivision into ultrafine grains less than 1 µm in diameter. In this study, the effects of plastic deformation on the microstructure and static recrystallization of pure iron were studied by comparing orthogonal cutting and rolling. Orthogonal cutting yielded ultrafine grains with a diameter of 0.2 µm. It was found that a high strain rate in the thin shear plane generated during the cutting process caused a uniform subdivision of grains, and this uniform plastic deformation resulted in the uniform recrystallization of grains. In addition, a theoretical model was developed, and it was revealed that the number of recrystallized grains depended on the fraction of a large-misorientation area constructed with geometrically necessary boundaries (GNBs). It was suggested that the cutting process was more advantageous than rolling in producing ultrafine recrystallized grains because cutting could apply severe plastic strain uniformly on a work material, effectively generating GNBs.

Static Recrystallization Microstructure Evolution in a Cold-Deformed Ni-Based Superalloy during Electropulsing Treatment

The influence of electropulsing treatment (EPT) parameters on the static recrystallization (SRX) microstructure in a cold-deformed Ni-based superalloy was investigated. During EPT, both the volume fraction of SRX grains and the average grain size increased with the increasing EPT temperature, which was attributed to the thermal effect and athermal effect induced by EPT. The mobility of SRX grain boundaries was promoted at the higher temperature due to the thermal effect, while the nucleation rate would be increased by EPT through decreasing the thermodynamic barrier. The formation of parallel dislocations caused by electron wind force could also play an indirect role in promoting SRX process. Moreover, the volume fraction of SRX grains increased significantly with the extension of EPT time at 700 °C, while the EPT time had a trivial effect on the average grain size. In addition, the sufficient deformation was essential to the occurrence of SRX behavior during EPT, and the localized Joule heating effect could promote the SRX behavior in the samples with the larger strains. Besides that, the influence of twining and carbides on the SRX behaviors was also investigated.

Correlation between test temperature, applied load and wear transition of Mg97Zn1Y2 alloy

Dry sliding wear tests were performed on Mg97Zn1Y2 alloy at various temperatures of 20, 50, 100, 150 and 200°C using a pin-on-disc wear testing machine in order to reveal mild-severe (M-S) wear transition mechanism during elevated-temperature wear testing. It was shown that at each test temperature, the wear rate increased with increasing load, and all wear rate-load curves demonstrated two distinct stages i.e. mild and severe wear stages. The predominant wear mechanisms operating in mild and severe wear stages were analyzed, and they were indicated in the mild and severe wear regimes of a wear mechanism transition map, respectively. M-S wear transition mechanism was analyzed by comparison of microstructure transformation and hardness change in subsurfaces of samples tested in mild and severe wear stages, from which M-S wear transition mechanism was confirmed as softening of surface material arising from dynamic recrystallization (DRX) microstructure transformation. The M-S wear transition load was found to have a linear relationship with test temperature, and decreased with rising test temperature. M-S wear transition obeyed a critical surface DRX temperature (SDT) criterion under given conditions, and the transition loads were estimated at various test temperatures by using the criterion.

Correlations between Initial Goss Orientations with Different Deviation Angles and Evolution of Microstructure and Texture in Ultrathin Grain‐Oriented Silicon Steels

Herein, four kinds of initial Goss textures with different deviation angles (0°, 5°, 10°, and 15°) are obtained by controlling the included angles between the longitudinal directions of rectangular cutting specimens and the initial rolling direction of the raw material. Then, 0.05 mm thick grain‐oriented silicon steels are fabricated by cold rolling and primary recrystallization annealing. Effects of initial textures on the microstructure and texture evolutions and magnetic properties are investigated in detail. Compared with sharp {111}&lt;112&gt; in the cold rolling sheet with initial exact Goss, the deviated Goss favors the formation of strong {111}&lt;112&gt; + weak {h11}&lt;1/h 1 2&gt; textures. After annealing, sharp {210}&lt;001&gt; + medium {110}&lt;001&gt; textures develop as a result of the small initial deviation, while larger initial deviations contribute to the {310}&lt;001&gt; texture. In addition, the average grain sizes are also related to recrystallization textures. Consequently, the distinct recrystallization microstructures and textures result in the differences of magnetic properties.

Effect of Nb content on primary recrystallization microstructure, texture and magnetic properties of grain-oriented silicon steel manufactured by low-temperature slab reheating

The influence of Nb content on the primary recrystallization microstructure, crystallographic texture and magnetic properties of grain-oriented silicon steel manufactured by low-temperature slab reheating were studied. The results show that the effect of grain refining was enhanced with the increase of Nb content. With the increase of Nb content, the total contents of texture {111}〈112〉 and {114}〈481〉 in primary recrystallization which are beneficial to the secondary recrystallization increased, but the contents of deviated Goss component and adverse textures with abnormal growth ability in primary recrystallization also increased, which led to the deterioration of magnetic properties. By adding 0.005% Nb, the average size of the primary grain reduced to 23 μm, the content of {110}〈112〉 increased slightly and the least deviated Goss nuclei were obtained, therefore the final product had the sharpest {110}〈001〉 texture of secondary recrystallization and the best magnetic properties with B800 = 1.873 T , P1.7/50 = 1.21 W/kg.