Preferential Nucleation Research Articles

Novel core-layer-shell structured nano-composite precipitates formed in selective laser melted reduced activation ferritic-martensitic steel

A novel type of core-layer-shell structured nano-composite precipitates was identified for the first time in a typical reduced activation ferritic-martensitic steel fabricated via selective laser melting (SLM). Comprehensive characterization of morphology, composition and structure was achieved for them using high-resolution electron microscopy. Their formation mechanism is closely related to specific processing features of SLM: the core consists of a triclinic SiO2 nanoparticle (~10nm in diameter), resulting from the combination of Si and O in the powder melting stage; the middle layer corresponds to an MC-type carbide (~10-nm-thick) formed due to preferential nucleation at the SiO2/matrix interface during rapid cooling; the shell is an orthorhombic Cr7C3 carbide, which arises from thermally activated C and Cr diffused continuously to the MC/matrix interface due to the in-situ heat treatment during cyclic SLM scanning. This unique type of precipitate is believed to exert a significant influence on the mechanical properties of RAFM steels.

Study on high temperature tensile constitutive behavior and deformation mechanism of Ti-47.5Al-2.5 V-1.0Cr-0.2Zr alloy

The high temperature tensile test of Ti-47.5Al-2.5 V-1.0Cr-0.2Zr alloy was carried out by electronic universal testing machine under the condition of 750–900 °C/10−5–10−3 s−1. The hot tensile stress-strain curves were analyzed, and the constitutive model under hot tensile conditions was established. The microstructure transformation rule and deformation mechanism during tensile process were determined. The results show that the hot tensile curve is longer in the steady-state flow stage corresponding to lower strain rate and higher tensile temperature, the true stress declines and the elongation at break increases. The constitutive equation was established based on the tensile curve data, and the corresponding thermal activation energy was 310.3 kJ/mol. As the rise of tensile temperature and the decline of strain rate, the proportion about cross-layer fracture in the tensile fracture morphology decreases, the number of dimples increases, more lamellar structures change into recrystallized structures, and the softening effect of the alloy is more obvious. The dislocation deformation mechanism mainly includes the existence of dislocation slip and climb, dislocation intersection and dislocation ring or dislocation network formation. Twinning deformation is also another important mechanism of high temperature tensile deformation of TiAl alloy. Twins are formed in parallel with each other, so that the deformation can be further carried out. The dislocations and twins in the deformed microstructure will provide nucleation conditions for recrystallized grains. The dynamic recrystallization(DRX) grains are preferentially formed around the grain boundary and the vicinity of dislocation and twin is also preferred nucleation site for DRX. The DRX behavior is the main softening mechanism, and DRX size and volume fraction corresponding to lower tensile rate and higher tensile temperature are larger.

First-principles study on TiC/TiN heterogeneous nucleation interface in high-titanium steel

A systematic study using the first-principles method was conducted to investigate the interface relationship between TiC and TiN in high-titanium steel, where TiC nucleates and grows with TiN as the core. The results showed that the energy of the (111) surface depends on the type of terminal atoms, with the Ti-terminated surface exhibiting lower surface energy than the C(N)-terminated surface. In contrast, the energy of (100) and (110) surfaces was independent of the terminal atom type. The order of surface energy determined to be (111)-Ti<(100)<(110)<(111)-C(N), the work function exhibits the same trend, while the stability is exactly the opposite. Among all interface structures, the interface structure with Ti-C terminal atomic combination was identified as the most stable, which can be attributed to the formation of covalent, ionic, and metallic bonds at the interface. The bonding strength primarily arises from the hybridization between Ti-d orbitals and C(N)-p orbitals. Within the (111) interface structures, metallic bonds were formed in the interface structure with the Ti-Ti terminal atomic combination, leading to the lowest interface energy and making it thermodynamically the most stable. Consequently, TiC is capable of heterogeneously nucleating on TiN, with the preferred nucleation surface of TiN following the order of (111)>(100)>(110).

Interfacial Coupling Induced Discrete Orientation of Epitaxial Graphene on High‐Index Cu Substrates

AbstractControlled and precise synthesis of materials has been a central pursuit in academia and industry. With the rise of twistronics research, there is growing demand for synthesizing orientation‐controlled 2D materials with atomic precision. Previous theories for 2D materials can predict graphene (Gr) growth on low‐index metal substrates but fail to explain the discrete orientations on most high‐index substrates, inconsistent with experimental data. Using density functional theory (DFT) and ab‐initio molecular dynamics (AIMD), this study explores graphene growth on high‐index substrates, showing that atomic steps do not dominate in trapping C atoms or driving preferential graphene nucleation at high temperatures. Thus, the possibility of intrinsic atomic steps in inducing graphene orientation on high‐index substrates is ruled out. Interfacial coupling strength between graphene and substrates is quantified using a close contact index (CCI), linking atomic structure and electronic states. The coupling between graphene and high‐index Cu surfaces is generally weak, reducing substrate anchoring and increasing graphene orientation dispersion. The extension of this theory to bilayer graphene (BLG) reveals competition between Gr/Cu interfacial coupling and Gr/Gr interlayer coupling, offering insights for controlling twist angles. This theory explains the discrete orientations on high‐index substrates, providing a theoretical basis for synthesizing orientation‐controlled graphene.

Preparation of efficient and stable FA0.75MA0.25SnI3 perovskite solar cells using passivation materials with multiple F hydrophobic group

Although Sn-based perovskite solar cells (PSC) have impressive conversion efficiency, their stability needs to be improved. Herein, 3,4,5-trifluorophenol (C6H3F3O) containing –F and –OH groups was introduced to improve the film stability and quality of FA0.75MA0.25SnI3. –F groups with low surface energy cause C6H3F3O to spontaneously migrate to the air-solution interface and attract the SnI64− octahedron to the solution-air surface through hydrogen bond interactions between –OH and I. This leads to preferential nucleation of dense, high-quality perovskite films at the solution-air surface and orderly growth from top to bottom. Additionally, C6H3F3O is bonded to the surface of the film, and the outward-facing hydrophobic –F groups effectively shield FA0.75MA0.25SnI3 from water infiltration. The C6H3F3O-doped PSC exhibited a champion efficiency of 10.47 % and long-term stability of over 1000 h, retaining 80 % of its initial efficiency (in N2).

Microstructure and property alterations and toughening mechanism of cast TC4 alloy by solid state treatment with low-density DC electric field

In this paper, the impact of low-density DC electric field treatment (LDCT) on the microstructure and mechanical properties of cast TC4 titanium alloy (CTC4) was investigated. The findings indicate that the driving force for the current provided by LDCT enhances the texture of CTC4. When the current density is sufficiently high, the induced recrystallization effect weakens the texture, leading to an isotropic state. The polygonization of grain boundaries in the LDCT state CTC4 has been identified, along with the emergence of a secondary α phase due to recrystallization. Additionally, this study highlights the phenomenon of preferential nucleation and growth occurring at the grain boundaries. LDCT induces a grain refinement effect in the CTC4 material, whereby the average grain size of the LDCT3 sample decreases from 31.05 μm in the untreated sample to 28.93 μm. The observed reduction in dislocation density in the LDCT states is believed to result from the diffusion of impurity atoms and vacancies. The observation of dislocation plugging at the inner grain boundary of the LDCT3 sample suggests that the electron wind promotes dislocation slip toward the grain boundary. Furthermore, the simultaneous enhancement of strength and toughness in the LDCT state of the CTC4 alloy has been achieved. The LDCT3 sample demonstrates superior performance, exhibiting noteworthy increases of 7.7%, 22.0%, and 10.9% in tensile strength, elongation, and fracture energy, respectively, compared to the untreated sample. The significant role of non-thermal effects in LDCT and the mechanism of atomic diffusion induced by this effect are discussed. The origins of dislocation motion and phase transition are elucidated from the perspective of atomic diffusion.

Grain boundary sensitization kinetics of cold-rolled Al–Mg alloys

As super-saturated solid solutions of Al-Mg, 5XXX series aluminum alloys are susceptible to sensitization via intergranular precipitation of the anodic β-phase, which promotes intergranular corrosion, exfoliation and stress corrosion cracking under environmental conditions. This study presents important updates to a Johnson–Mehl–Avarami–Kolmogorov (JMAK) type model for low-temperature sensitization, correlating the intergranular corrosion response to impingement of locally sensitized regions surrounding discrete β-phase grain boundary precipitates. It is demonstrated that the sensitization response of these alloys can be approached as a combination of two independent contributions: the geometric configuration of grain boundaries passing through the microstructure that are most prone to sensitization, and the rate that these boundaries sensitize due to the formation of the β-phase. This allows for the large sensitization response variations found between nominally identical materials produced by different suppliers, which originate due to a lack of constraints within current cold-rolled plate tempers, to be removed as a sample-dependent linear scaling factor that is separate of the rate kinetics. The JMAK model describes the kinetics of 5xxx series sensitization with excellent accuracy across all data available in the literature. The results of the model imply that sensitization at environmental temperatures proceeds via a site-saturated process, with the β-phase forming on a set density of preferential nucleation sites. It is shown that site-saturation allows for extension of the JMAK model to non-isothermal aging profiles and supports a diffusion pathway dominated by pipe diffusion to the interface followed by precipitate growth via the collector plate mechanism.

Microstructure evolution and fracture characteristics of GH4079 superalloy during high-temperature tensile process

An investigation of the thermal deformation characteristics and fracture mechanisms of the GH4079 superalloy was conducted through a series of hot tensile experiments conducted across a range of strain rates (from 0.01 s−1 to 1 s−1) and temperatures (from 970 °C to 1160 °C). The impact of MC carbides on the thermal deformation characteristics and dynamic recrystallization (DRX) of GH4079 superalloys, which are known for their challenging deformability, was analyzed to provide insights into enhancing the thermal workability of these formidable superalloys. The results suggest that DRX consistently preferentially occurs near MC carbides. The MC carbide plays a nucleation role in the particle-induced dynamic recrystallization mechanism, as determined via EBSD analysis. In addition, the primary grain boundary is the preferred nucleation site for DRX initiation. The promotion of DRX within the GH4079 alloy is considerably facilitated by the increased stored energy and nucleation site density resulting from the larger and more numerous carbides present at the grain boundaries. Moreover, the presence of carbides leads to uncoordinated deformation of the alloy during tensile deformation, which is also the induction factor of alloy cracking. With increasing strain rates and temperatures, the window of control over the hot deformation structure of the alloy diminishes. During the high-temperature deformation process of the GH4079 alloy, it is necessary to control the temperature within the range of approximately 1120 °C–1140 °C and the strain rate within the range of 0.1 s−1 to 1 s−1 to obtain a fine and uniform grain structure, delay material failure, and thus enhance the thermal processing performance of the material.

Inkjet-Printed Silver Lithiophilic Sites on Copper Current Collectors: Tuning the Interfacial Electrochemistry for Anode-Free Lithium Batteries

Anode-free lithium batteries (AFLBs) present an opportunity to eliminate the need for conventional graphite electrodes or excess lithium–metal anodes, thus increasing the cell energy density and streamlining the manufacturing process. However, their attributed poor coulombic efficiency leads to rapid capacity decay, underscoring the importance of achieving stable plating and stripping of Li on the negative electrode for the success of this cell configuration. A promising approach is the utilization of lithiophilic coatings such as silver to mitigate the Li nucleation overpotential on the Cu current collector, thereby improving the process of Li plating/stripping. On the other hand, inkjet printing (IJP) emerges as a promising technique for electrode modification in the manufacturing process of lithium batteries, offering a fast and scalable technology capable of depositing both thin films and patterned structures. In this work, a Fujifilm Dimatix inkjet printer was used to deposit Ag sites on a Cu current collector, aiming to modulate the interfacial electrochemistry of the system. Samples were fabricated with varying areas of coverage and the electrochemical performance of the system was systematically evaluated from bare Cu (non-lithiophilic) to a designed pattern (partially lithiophilic) and the fully coated thin film case (lithiophilic). Increasing lithiophilicity resulted in lower charge transfer resistance, higher exchange current density and reduced Li nucleation overpotential (from 55.75 mV for bare Cu to 13.5 mV for the fully coated case). Enhanced half-cell cyclability and higher coulombic efficiency were also achieved (91.22% CE over 76 cycles for bare Cu, 97.01% CE over 250 cycles for the fully coated case), alongside more uniform lithium deposition and fewer macroscopic irregularities. Moreover, our observations demonstrated that surface patterning through inkjet printing could represent an innovative, easy and scalable strategy to provide preferential Li nucleation sites to guide the subsequent Li deposition.

Effect of magnesium on primary carbides in GCr15 bearing steel

GCr15 bearing steel has higher carbon and chromium content, large-size primary carbides tend to be easily precipitated during the solidification, which is harmful for the performance of steel. Hence, magnesium treatment was applied to refine primary carbides and the influence of magnesium on the size, distribution and morphology of primary carbides in GCr15 bearing steel was studied in this paper. The results indicated that M3C, M3C2, and M7C3 were precipitated during the solidification of GCr15 bearing steel. When magnesium was added into the steel, the area ratio and maximum size of primary carbide were decreased with the increase of magnesium content. The refinement of primary carbides was the most obvious when the magnesium content was 27 ppm. Compared with the steel without magnesium, the area ratio and maximum size of primary carbides were reduced by 2.41 % and 11.16μm respectively. In addition, for the steel without magnesium, MnS were likely to be attached with primary carbides. Once magnesium was added, smaller and two-layer structured composite inclusions (the inner layer was Mg-Al-O, and the outer layer was MnS) were formed and provided the preferred nucleation site for primary carbides, which ultimately promoted the refinement of primary carbides.

Toughening of a vacuum diffusion-bonded heterostructured AZ31/WE94/AZ31 alloy by interfacial reinforcement

Heterostructured materials have recently attracted extensive attentions from the materials community due to their superior combination of strength and ductility as compared to the conventional homogeneous counterparts. In the present study, the laminate AZ31/WE94/AZ31 Mg alloy was produced by vacuum diffusion bonding. The post annealing was carried out to improve the mechanical properties of the heterostructured Mg alloy. It is found the elemental diffusion and formation of interfacial phases enhance the interface bonding strength, thereby improving the comprehensive mechanical properties. The laminate sample annealed at 470 °C for 12 h shows a superior mechanical properties with a yield strength, ultimate tensile strength, and elongation of 158 MPa, 212 MPa and 12.9%, respectively. The higher annealing temperature leads to the growth of interfacial phase, which provides preferential nucleation sites for crack initiation and weakens the tensile properties.

Crystalline phase control of ferroelectric HfO2 thin film via heterogeneous co-doping

Our study investigates heterogeneous co-doped HfO2 thin films integrated into metal-ferroelectric-metal stacks, achieved by incorporating multiple layers doped with various species during the atomic layer deposition process. This approach creates an artificial crystallization temperature gradient across the HfO2 film, influencing the preferred nucleation sites of HfO2 during rapid thermal processing. Our findings demonstrate that the phase composition of the annealed HfO2 film is primarily determined by heterogeneous or homogeneous crystallization processes. In cases of heterogeneous crystallization, where crystallization initiates from nuclei formed at electrode/HfO2 interfaces, grains predominantly crystallize in the orthorhombic phase. Conversely, grains are more likely to crystallize in the monoclinic phase if they originate from nuclei formed at the center of the HfO2 film. Additionally, we observe correlations between the texture of the HfO2 film and the texture of the electrodes.

In-situ high-temperature EBSD study of austenite reversion from martensite, bainite and pearlite in a high-strength steel

The austenite (γ) reversely transformed from lath martensite (LM), lath bainite (LB), granular bainite (GB) and pearlite+ferrite (P+F) in a high-strength steel was studied at high temperatures using in-situ electron backscatter diffraction (EBSD). The memory effect of initial γ significantly affects the nucleation of the reverted γ in LM and GB structures, while a weak influence on that of LB and P+F structures. This results in a significant difference in γ grain size after complete austenitization, with the first two obtaining larger γ grains while the latter two are relatively small. Crystallographic analysis revealed that the reverted γ with acicular morphology (γA), most of which maintained the same orientation with the prior γ, dominated the reaustenitization behavior of LM and GB structures through preferential nucleation within γ grains and coalesced growth modes. Although globular reverted γ (γG) with random orientation or large deviation from the prior γ can nucleate at the grain boundaries or within the grains, it is difficult for it to grow and play a role in segmenting and refining the prior γ due to the inhibition of γA coalescing. For LB and P+F structures, the nucleation rate of intragranular γG increases with increasing temperature, and always shows a random orientation. These γG grains can coarsen simultaneously with the intergranular γG, ultimately playing a role in jointly dividing and refining the final γ grains. Research also found that the differences in the effects of four different microstructures on reverted γ nucleation are closely related to the variant selection of the matrix structure, as well as the content and size of cementite (θ). High density of block boundaries induced by weakening of variant selection and many fine θ formed in the lath are the key to promoting LB structure to obtain more intragranular γG formation, as well as the important role of the large-sized θ in P+F structure.

Directional self-assembly of organic vertically superposed nanowires

Organic crystal-based superimposed heterostructures with inherent multichannel characteristics demonstrate superior potential for manipulating excitons/photons at the micro/nanoscale for integrated optoelectronics. However, the precise construction of organic superimposed heterostructures with fixed superimposed sites remains challenging because of the random molecular nucleation process. Here, organic vertically superimposed heterostructures (OSHs) with fixed superimposed positions are constructed via semi-wrapped core/shell heterostructures with partially exposed cores, which provide preferential nucleation sites for further molecular epitaxial growth processes. Furthermore, the relative length ratio from 21.7% to 95.3% between interlayers is accurately adjusted by regulating the exposed area of the semi-wrapped core/shell heterostructures. Significantly, these OSHs with anisotropic optical characteristics demonstrate well regulation of excitation position-dependent waveguide behaviors and can function as photonic barcodes for information encryption. This strategy provides a facile approach for controlling the nucleation sites for the controllable preparation of organic heterostructures and advanced applications for integrated optoelectronics.

Theoretical analysis of the initial nucleation characteristics of trace water vapor frosting on a cryogenic surface

In certain extreme conditions characterized by ultra-low water vapor content and ultra-low temperatures (e.g. cryogenic wind tunnel), trace water vapor frosting can also pose significant hazards. Considering the crucial role of initial nucleation on subsequent frosting processes, this study firstly investigated and compared the nucleation characteristics of frosting at different water vapor contents (0.1−1000 ppmv) from humid air to trace water vapor based on classical nucleation theory. The preferred nucleation phase diagrams and critical nucleation conditions were analyzed. Sensitivity of the nucleation mass transfer rate, as well as the frosting pathways were further identified. Results show that the nucleation characteristics of trace water vapor frosting (<100 ppmv) is significantly different from that of humid air frosting (>1000 ppmv). Trace water vapor frosting is more inclined towards desublimation nucleation due to its lower nucleation temperature and larger critical contact angle. The critical contact angles for 1000 ppmv, 100 ppmv and 0.1 ppmv are 49°, 75° and 120°, respectively. Furthermore, trace water vapor nucleation requires a greater subcooling degree, has a smaller critical nucleation radius, and is highly sensitive to surface contact angle and further-subcooling degree. At a surface contact angle of 120°, the nucleation subcooling degree of 0.1 ppmv is 2.9 K greater than that of 1000 ppmv. This study helps understanding the nucleation characteristics under different water vapor content conditions, which indicates that reducing subcooling degree and increasing contact angle are more effective anti-frosting methods than reducing water vapor content for trace water vapor frosting.

Water‐Lean Inner Helmholtz Plane Enabled by Tetrahydropyran for Highly Reversible Zinc Metal Anode

AbstractThe reversibility and stability of zinc (Zn) metal anode are closely related to inner Helmholtz plane (IHP) chemistry. The H2O‐rich IHP raises severe parasitic reactions and irregular Zn deposition, impeding the practical utility of Zn anode in aqueous Zn‐ion batteries (AZIBs). In this study, tetrahydropyran (THP), a five‐carbon heterocyclic ether with permanent dipole moment and hydrophobic characteristic, is introduced as a self‐adsorptive additive to reshape the IHP. It squeezes out partial H2O molecules and forms a H2O‐lean IHP, benefitting for alleviating active H2O decomposition and improving the stability of Zn anode. Moreover, the adsorbed THP induces the preferential nucleation of Zn (002) plane, facilitating dendrite‐free growth and improving the reversibility of Zn anode. Consequently, the Zn||Zn symmetric cell enables to cycle over 3600 h at 5 mA cm−2@ 1 mAh cm−2. The Zn||Cu half‐cell can stably cycle over 400 cycles with 99.9% coulombic efficiency even under harsh test conditions (10 mA cm−2@5 mAh cm−2) with 30 µm Zn foil. The Zn||NH4V4O10 full cell maintains 92.6% capacity retention after 800 cycles at 1 A g−1 and the Zn||I2 full cell enables to perform steadily over 10000 cycles with a capacity decay rate of merely 0.003% per cycle at 5 C.

Exploiting Non-Classical Nucleation for Improved Gas Bubble Mitigation on Nickel Electrocatalysts for the Oxygen Evolution Reaction

The efficient transport of gas poses a significant challenge in the design of high-performance gas evolving electrocatalysts. Inefficiencies due to mass transport limitations become more pronounced at the high current densities required in industrial electrolyzers, largely as a result of gas bubbles that obstruct a portion of the electrochemically active surface area of the anode and/or cathode, while also hindering electrolyte transport to the electrode surfaces. One promising approach to mitigate these sources of inefficiency is to engineer micro-to-nanoscale surface textures that promote the favorable growth and release of these bubbles. A range of structures have been shown to improve electrocatalyst performance under both stagnant and induced convection conditions, particularly in applications for hydrogen production via electrocatalytic water splitting in alkaline water electrolyzers.1 Trends between surface texture and electrocatalyst performance have been observed for a range of features, such as pillars,2,3 ridges,4 dimples,5 “cracked” structures,6 and electrodeposited crystalline structures,7 however substantial work is still needed to optimize the designs of these materials. These textured surfaces can influence bubble evolution in various ways, such as by altering the wetting properties of a surface, or by providing preferential nucleation sites. Previous studies have noted that surface structures that provide good control over bubble nucleation can often be adversely affected by increased bubble retention.3–5 The present study investigates a method of fabricating patterned electrocatalysts that provides a fine, tunable control over the distribution of bubble nucleation sites on the surfaces of planar Ni electrocatalysts for the oxygen evolution reaction (OER). These textured surfaces are designed to take advantage of so-called “non-classical nucleation” or “type IV nucleation”, a scenario in which gas is trapped at specific surface sites with an effective radius larger than the critical radius for classical nucleation, thereby allowing spontaneous bubble growth without being required to overcome an activation energy barrier.8 The separation between these sites on the surface of the OER active material (i.e., Ni) is then varied to obtain the most favorable distribution of these non-classical nucleation sites. Chronoamperometry is used to compare the current densities achieved by these patterned Ni electrodes to that of a planar Ni electrode. High speed videography is used to directly measure how these textures influence processes such as bubble growth and detachment, and to determine how these processes influence performance. A better understanding of these gas evolution processes can help lower the energy requirements for electrolyzers and may have more general implications for the design of energy efficient gas evolving electrocatalysts relevant to a variety of industrially important reactions.

Adjusting Ion Diffusion Kinetics of Li Deposition Enabled by an Elastic Porous Melamine Sponge Host for Stable Lithium Metal Anodes.

Lithium (Li) dendritic growth and huge volume expansion seriously hamper Li-metal anode development. Herein, we design a lightweight 3D Li-ion-affinity host enabled by silver (Ag) nanoparticles fully decorating a porous melamine sponge (Ag@PMS) for dendrite-free and high-areal-capacity Li anodes. The compact Ag nanoparticles provide abundant preferred nucleation sites and give the host strong conductivity. Moreover, the high specific surface area and polar groups of the elastic, porous melamine sponge enhance the Li-ion diffusion kinetics, prompting homogeneity of Li deposition and stripping. As expected, the integrated 3D Ag@PMS-Li anode delivered a remarkable electrochemical performance, with a Coulombic efficiency (CE) of 97.14% after 450 cycles at 1 mA cm-2. The symmetric cell showed an ultralong lifespan of 3400 h at 1 mA cm-2 for 1 mAh cm-2. This study provides a facile and cost-effective strategy to design an advanced 3D framework for the preparation of a stable dendrite-free Li metal anode.

Effects of annealing time on microstructural characteristics and mechanical properties of cryo-rolled CoCrFeMnNi high entropy alloys

High-entropy CoCrFeMnNi alloy was subjected to cryo-rolling with a reduction ratio of 25 % and was then annealed at 1050 °C for 5, 25, and 45 min. The results of the recrystallization textures of the various annealed samples showed the presence of similar texture components, indicating that cryo-rolling had only a limited effect on the formation of the subsequent annealing texture. The volume fractions of the different texture components similarly showed no obvious dependence on the annealing temperature. The uniformity of the recrystallization texture suggests the absence of strong preferential nucleation and growth during annealing. The cryo-rolled samples processed with different holding times exhibited a remarkable ambient temperature strength-ductility combination.

Numerical modeling of shear band effect on Goss grain recrystallization in electrical steels: Crystal plasticity finite element and phase field modeling

This study investigates the effect of shear band evolution on the nucleation of Goss {110}<001> texture during the primary recrystallization of 3.24 wt% Si grain-oriented electrical steel. Nucleation at the early stage of primary recrystallization of the steel is explored both experimentally and numerically. The experimental approach involves cold rolling the steel specimens to obtain a thickness reduction ratio of 76 % and then applying heat treatment to them at 600 °C for less than 1 min. The numerical simulation employes crystal plasticity (CP) finite element model (FEM) to simulate the plastic deformation induced by the dislocation slips on predefined slip systems and non-crystallographic shear bands during cold rolling. Based on the CPFEM results, the generalized strain energy release maximization (GSERM) model is used to predict the preferential orientation probability of recrystallized nuclei for the steel by considering shear band formation. Subsequently, the microstructure evolution during the early stage of primary recrystallization of the steel is simulated using the phase field model (PFM). The developed CP model successfully predicted shear band activation and evolution in the γ-fibers centered on the {111}<112> texture component. The model also demonstrated that shear bands would be the preferred nucleation sites at the early stage of primary recrystallization because of their high stored energy. Moreover, by coupling with the GSERM model, the PFM could reproduce the nucleation of Goss grains at the beginning of primary recrystallization in shear bands.