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Deformation behavior as well as microstructural evolutions of a rolled AZ31 magnesium alloy with and without pre-existing extension twins were studied using compression tests which performed along different orientations at a temperature range of 25–350 °C. The results implied that the initial texture not only influence the evolution of flow stress, but also change the size and fraction of recrystallized grains. In contrast to samples parallel to rolling and transverse directions, compression along normal direction resulted in a respectful softening at 150 °C. The largest size and fraction of new grains at 250 °C were recorded after deformation along rolling direction, while the maximum flow softening was observed during deformation along normal direction. The anisotropy in microstructural evolutions was still retained at 350 °C. Pre-existing twins could reduce the anisotropy of material in respect of flow stress as well as DRX progression, where TD sample showed the lowest DRX fraction at 250 °C. Quaternion misorientation data obtained from EBSD analysis of pretwinned material implied that initial texture could not significantly influence final texture. A different misorientation distribution was realized after deformation of pretwinned material along ND and RD directions.

Abstract Zirconia-based shape memory ceramics (SMCs) exhibit anisotropic mechanical response when undergoing elastic deformations as well as during austenite–martensite phase transformation. This behavior results in different types of strain incompatibility at grain boundaries, which we study here using a micromechanical model. A single-crystal model is implemented to provide a full mechanistic three-dimensional description of the anisotropic elastic as well as martensitic transformation stress–strain response, including non-Schmid behavior caused by the significant volume change during martensitic transformation. This model was calibrated to and validated against compression tests of single-crystal zirconia micro-pillars conducted previously, and then used to model bi-crystals. Upon the introduction of a grain boundary, the simulation provides detailed information on the nucleation and evolution of martensite variants and stress distribution at grain boundaries. We identify bi-crystal configurations which result in very large stress concentrations at very low deformations due to elastic incompatibility, as well as others where the elastic incompatibility is relatively low and stress concentrations only occur at large transformation strains. We also show how this approach can be used to explore the misorientation space for quantifying the level of elastic and transformation incompatibility at SMCs grain boundaries. Graphical abstract Micromechanics models provide insights on grain boundary elastic and phase transformation strain incompatibility in shape memory zirconia

Compared to cold drawing, dieless drawing has shown great potential for manufacturing biodegradable Mg alloy microtubes due to the large reduction in area acquired in a single pass. However, owing to the local heating and local deformation, the deformation mechanism during dieless drawing is not clear, and thus causing difficulties in controlling the microstructure of dieless drawn tubes. For the purpose of acquiring a desired microstructure, in this study the deformation mechanism of ZM21 Mg alloy tube was clarified by conducting continuous observation of the microstructural evolution during dieless drawing. The results show that both SRX and DRX occurred during dieless drawing. SRX occurred before the plastic deformation to soften dieless drawn tubes. With increase of feeding speed, the deformation mechanism changed accordingly: (1) At the low-speed of 0.02 mm/s, the deformation mechanism was dominated by twin-slip sliding, during which {10–12} tension twins were generated inside grains to accommodate the plastic deformation by changing the crystal orientation. (2) At the intermediate-speed of 2 mm/s, a twin-DRX process related to {10–12} tension twin was observed, which was characterized by the generation of abundant {10–12} tension twins and the evolution of misorientation angle of {10–12} tension twins. Moreover, the transformation from twin-DRX to CDRX can be observed at the late stage of plastic deformation, which was attributed to the inhomogeneous conditions of dieless drawing. (3) At the high-speed of 5 mm/s, a CDRX process was observed, during which grain boundary sliding and grain tilting were observed, in addition to the gradual rotation of subgrains. These results show that during dieless drawing, DRX is not only a temperature-dependent phenomenon, but also influenced by the variation of feeding speed.

Heterogeneous metals and alloys are a new class of materials with superior mechanical properties. In this paper, we engineered sandwich-structured pure aluminum laminates composed of middle coarse-grained layer and outer fine-grained layer via extrusion, rolling and annealing. By controlling the post-annealing regimes, a larger degree of microstructure heterogeneities such as boundary spacing, misorientation and texture across the hetero-interface were obtained, which resulted in obvious mechanical differences. Tensile tests indicated that the 300 °C/30 min annealed laminates enabled a relatively high tensile ductility while simultaneously retaining a high strength, which was better than prediction by the rule-of-mixture. To explain the reasons behind it, the evolution of geometrically necessary dislocations and strain gradient at the hetero-interface zone were detected using in-situ tension and microscopic digital image correlation technique. It was found that with the increasing applied strain, a significant strain gradient was developed near the interface, which was accommodated by geometrically necessary dislocations, thereby contributing to higher hetero-deformation induced (HDI) strengthening and hardening.

Identification and evaluation of structural heterogeneity in spent cathode materials is crucial to developing appropriate remediation strategies for novel recycling processes. Native heterogeneities may be exacerbated during the cell's operational lifetime, as sub-particle-scale variations induce anisotropic expansion and contraction upon cycling. Structural transformations resulting from repeated cycling and calendar aging predominantly occur at the secondary particle surface and at the grain boundaries (GBs) between primary particles. However, the diffusion and stress build up around and across GBs are poorly understood. In this study, electron backscatter diffraction (EBSD) is employed to track sub-grain lattice structure across a statistically relevant number of Li(Ni0.33Mn0.33Co0.33)O2 (NMC-111) particles. Specifically, differences in lattice misorientation – measured as the deviation from the grain's average orientation – are tracked as a function of position within the electrode (near current collector, middle, and near separator) and as a function of electrochemical cycling. Further, a novel method of structural analysis is developed, offering insight into sub-grain diffusion behavior by comparing lattice misorientation near the grain boundary versus in the grain bulk. The present results suggest that electrode-scale spatial heterogeneity in lattice structure is induced by initial manufacturing conditions, and that radial gradients in lattice misorientation evolve at the primary particle scale with repeated electrochemical cycling.

Nowadays, thermal condition and solute field are considered as the potential dominant factors controlling competitive grain growth during directional solidification process. However, the controlling modes and critical conditions of competitive grain growth have been drastically debated over the past two decades. In this work, thermal condition and solute field are combined to study the competitive grain growth in the converging case by experimental observation and numerical simulation of bicrystal samples. We find the competitive grain growth is controlled by the cooperative effect of thermal condition and solute field, and the controlling modes are related to the bicrystal misorientation between favorably and unfavorably oriented grains. When the unfavorably oriented grain is low misoriented, unfavorably oriented grain dominates grain selection, and the competitive grain growth performs as solute field domination. However, with the increase of unfavorably oriented grain's misorientation, the grain selection converts into favorably oriented grain domination, and the competitive grain growth changes to thermal condition domination. To explain these abnormal transformation phenomena, we propose a misorientation dependent thermal condition-solute field cooperative domination model and identify the critical conditions by a critical misorientation (θcm). According to dynamic equation of dendrite growth, we calculate the critical misorientation θcm to prove this model. The theoretical calculation results agree well with the experimental results.

Ytterbium (Yb) containing magnesium alloys have aroused extensive interest due to their excellent mechanical properties after thermomechanical processing and heat treatment. Unfortunately, the sole effect of Yb addition on the microstructure and mechanical properties of pure Mg matrix remains uncertain to date. In this work, the effects of Yb concentration on the texture development and tensile properties of pure Mg matrix during hot extrusion and the subsequent annealing were systematically investigated. The results revealed that the constitutional supercooling induced by Yb addition refined the as-cast microstructure but exerted a negligible effect on the original columnar grain morphology. When extruded at 300 °C, the dynamic recrystallization (DRX) process was considerably retarded. The in-grain misorientation axes (IGMA) analysis combined with TEM observation indicated that non-basal slips operated with increasing Yb concentration. Specifically, the prismatic 〈a〉 slip should be robustly activated in Mg–1.0 Yb extrudate, promoting the formation of the texture with {10–10} plane normal to the extrusion direction (ED), while for the Mg–2.0 Yb counterpart, the increased activity of pyramidal 〈c + a〉 slip and the relaxation of basal/ dislocations generated an ED-tilted texture component. The preferential grain growth dominated the subsequent annealing texture development at 400 °C when a comparable grain size was achieved. An obvious ED-tilted texture intensity with the peak around 〈–12–13〉 was observed in Mg–2.0 Yb alloy, which was primarily caused by grains with the basal orientation vanished and with the non-basal orientations intensified due to a higher concentration of Yb solute. Favored by the grain refinement, the Mg–2.0 Yb extrudate exhibited a high tensile yield strength of 304 ± 3.5 MPa, while the subsequently annealed counterpart presented a favorable elongation to failure of 14.8 ± 1.2%, which mainly due to the homogeneous grain structure, weak ED-tilted texture, and dissolution of coarse phases after high-temperature annealing.

The capture efficiency describes the capability of a sink, such as a grain boundary (GB), dislocation, and void, to absorb point defects (PDs). The bias defines the difference in capture efficiency between the absorption of a vacancy and dumbbell at a sink. Complete kinetic information on PDs, including diffusion barriers and diffusion orientations, as well as accurate saddle points, are needed to determine the capture efficiency and bias at a sink accurately, which is computationally demanding. In the present study, the Self-Evolving Atomistic Kinetic Monte Carlo (SEAKMC) method was used to investigate the defect dynamics of PDs near different types of grain boundaries (GBs) (with both 〈100〉 and 〈110〉 families) accurately in body-centered cubic (BCC) iron (Fe). The capture efficiency, sink strength, and bias factor of different types of GBs were determined in Fe, which, different from traditional rate theory estimation, showed a distinct capture efficiency, sink strength, and bias in different GBs. The results demonstrate a strong positive correlation between the capture efficiency and the GB strain width, instead of the GB misorientation, GB energy, or GB-PD binding energy, which have been investigated previously. This work provides valuable insight into the radiation-induced microstructural evolution of GBs.

This research studied the mechanisms of Ca and Zn microalloying on the enhancement of ductility of extruded Mg-Gd sheet by combing electron backscattered diffraction and slip trace analysis. The ductility and microstructure of extruded Mg-0.6Gd and Mg-0.6Gd-0.3Ca-0.2Zn (wt%) sheets were investigated. Basal slip was the main deformation mode under investigation. Ca and Zn microalloying increased the frequency of grain boundaries (GBs) with misorientation angles (θs)

Detailed quasi-in-situ grain-by-grain slip trace analysis and EBSD analysis were performed on the as-extruded, under-aged, and peak-aged Mg–10Y (wt pct) sheets to investigate the precipitate effects on the individual slip activities and plastic heterogeneity during room temperature compression. The sheet exhibited a significant age-hardening response whose yield strength increased by 63 pct after the peak-aged treatment. In the as-extruded condition, deformation was dominated by pyramidal II $$\langle c + a\rangle$$ slip (42.3 pct) followed by basal $$\langle a\rangle$$ slip (31.0 pct) and then pyramidal I $$\langle c + a\rangle$$ slip (21.1 pct). After the peak-aged treatment, the frequency of basal $$\langle a\rangle$$ slip increased to ~ 70 pct, and the pyramidal I/II slips significantly decreased to ~ 20 pct, which indicates the precipitate strengthening on pyramidal $$\langle c + a\rangle$$ slips was significantly over basal $$\langle a\rangle$$ slip. Most activated slip systems (68.2 pct) exhibited large normalized Schmid factors ( $${m}_{\mathrm{nor}}$$ > 0.3), but substantial (18.2 pct) hard-oriented slip systems ( $${m}_{\mathrm{nor}}$$ < 0.1) were also activated, suggesting local stress deviation. The magnitude/distribution of intragranular misorientation angle and geometrically necessary dislocation (GND) density inside a grain cannot be correlated with the visibility of slip trace from a statistical viewpoint. The extremely high GND density near grain boundary (GB) was closely related to (i) significant disparity of max Schmid factors for a particular slip mode and/or (ii) high GB misorientation between adjacent grains.

In this work, the microstructural evolution, micro-crack formation, and mechanical anisotropy of the selective laser melted (SLM) carbon-free Mar-M509 Co-based superalloy were systematically studied under different linear energy densities (LED). Observation shows that the SLM Mar-M509 superalloy possesses a fully dense structure, whereas some micro-cracks exist along the building direction. The electron backscatter diffraction results reveal that dominant columnar grains tend to elongate along the building direction parallel to the XZ plane. Meanwhile, both a near fiber texture and a {100} near sheet texture are observed in different specimens. For the specimen with fiber texture, a high misorientation angle exists among different columnar grains, which aggravated the generation of micro-cracks under thermal stress. Higher LED results in higher micro-crack density in the SLM specimen due to higher thermal stress. Mar-M509 specimen fabricated under lower LED exhibits higher tensile strength due to more significant grain refinement. More prominent anisotropy of tensile performance was found in the high LED specimen, which can be attributed to the higher density of micro-cracks and crystallographic texture. Furthermore, the SLM Mar-M509 superalloy exhibits better mechanical properties than the traditional cast technique. In summary, this work can contribute to the development and the future application of SLM-fabricated Co-based superalloy.

In the present study, arrayed nano-precipitated TiC in a ferrite matrix was obtained through thermal treatment. The size and shape of the arrayed interphase nano-precipitates were unaffected by fatigue deformation in this Ti-microalloyed steel. In addition, arrayed arrangement of the interphase nano-precipitates was not disrupted by fatigue and still remained only at low cycle numbers, which corresponded to the shortest fatigue life. The interphase nano-precipitated steel was strengthened through a bowing mechanism through which unpinning occurred, dislocation loops were formed, and the microhardness of ferrite was increased. The development of an incipient cell structure in the ferrite matrix was caused by wavy dislocation. After the onset of fatigue, the grain was preferentially rotated toward the {101}α orientation. Higher strain amplitude or lower strain rate led to a more favorable degree of misorientation in the low-angle grain boundaries.

The important but highly complex α/β Burgers orientation relationship and slip behavior of a Ti–5.5Mo–7.2Al–4.5Zr–2.6Sn–2.1Cr titanium alloy plate were obtained and elaborated, which was subjected to hot rolling with 20%, 40%, and 60% reductions in thickness. The electron backscatter diffraction statistical results showed that the Burgers orientation relationship was strictly maintained in the initial microstructure and exhibited a slight deviation of ∼10° at 20% reduction. With the thickness reduction increasing to 40% and 60%, this classical relation between α- and β-Ti will be gradually broken. Furthermore, the low-angle grain boundaries fractions of the β phase were 94.95% and 92.77% at 20% and 40% reductions, respectively, indicating that the β phase had a significant contribution to the overall plastic deformation. For the α phase, the relative frequencies of the 2 ¯ 0>{0001}α and 2 ¯ 0>{10 1 ¯ 0}α slip systems were 32.81% and 44.43% at 20% reduction, respectively. Noticeably, under the applied loading of normal direction, the 2 ¯ 0>{0001}α slip system became more pronounced at 60% reduction (i.e., 59.01%) and, hence promoted a considerable strain partitioning in the α phase. In terms of typical α grains, an obvious intragranular misorientation diversity at 60% reduction was further traced, thereby reasonably leading to the Schmid factor gradient within grain interior and the breakdown of Burgers orientation relationship.

Variant selection under specific applied stresses during precipitation of α plates from prior-β matrix in Ti–6Al–4 V was investigated by 3D phase field simulations. The model incorporates the Burgers transformation path from β to α phase, with consideration of interfacial energy anisotropy, externally applied stresses and elastic interactions among α variants and β matrix. The Gibbs free energy and atomic mobility data are taken from available thermodynamic and kinetic databases. It was found that external stresses have a profound influence on variant selection, and the selection has a sensitive dependence, as evidenced by both interaction energy calculations and phase field simulations. Compared with normal stresses, shear stresses applied in certain directions were found more effective in accelerating the transformation, with a stronger preference to fewer variants. The volume fractions of various α variants and the final microstructure were determined by both the external stress and the elastic interaction among different variants. The α clusters formed by variants with Type2 misorientation ([1 1 -2 0]/60°) relation were found more favored than those with Type4 ([-10 5 5 -3]/63.26°) under certain applied tensile stress such as along β. The mechanical properties of different microstructures from our phase field simulation under different conditions were calculated for different loading conditions, utilizing crystal plastic finite element simulation. The mechanical behavior of the various microstructures from phase field simulation can be evaluated well before the alloys are fabricated, and therefore it is possible to select microstructure for optimizing the mechanical properties of the alloy through thermomechanical processing based on the two types of simulations.

The interaction between twins and grain boundaries (GB) has an important influence on the deformation and fracture behavior of materials. In the present work, {332} twinning transfer (TT) behavior and its effect on the twin shape in a deformed β-type Ti-23.1Nb-2.0Zr-1.0O Ti alloy were investigated experimentally and with molecular dynamics simulation. The crystallographic alignment factor of the two twinning systems in the neighboring grains and the misorientation angle of the grain pairs were found to influence the occurrence of TT. This further determines the twin shape: twins present a ruler shape when TT occurs but are in a lenticular shape otherwise. Such different twin shapes are attributed to the local stress states related to TT occurring or not. Both ruler-shaped paired twinning and lenticular twinning would provide effective mechanisms to release or reduce the stress concentration in front of the twin tips in different grain pairs.

The microstructural evolution law and the α variant selection relationship, as well as the deformation mechanism of the HIPed Ti-6Al-4V alloy, were investigated under the conditions of thermal compression and subsequent heat treatment. The results showed that lamellar α phase bending/kinking and fragmentation were the main spheroidizing mechanisms in the α+β phase region (850°C and 920°C), DDRX occurred as the restoration mechanism in the near-β region (940°C), and the heterogeneous microstructure originated from the temperature gradient distribution. The strain rate clearly affected the dynamically recrystallized grain fraction and diameter, e.g... both the fraction and diameter increased at a lower strain rate. The acicular α precipitated from β phase at 940°C obeyed the Burgers relationship with β, and their misorientation angle intensified at approximately 60°. GBα formed by reducing the adjacent lamellar α misorientation angle; therefore, the GBα nucleation energy was lowest. The microhardness variation was relatively stable along the X direction at α+β phase region deformation, while oscillation appeared at near-β deformation, which can be explained by microstructure heterogeneity after thermal compression. For heat treatment, the trimodal microstructure appeared at 940°C/0.001 s-1/60% thermal compression and subsequent 950°C/1 h/WQ heat treatment, and the result might guide practical production to optimize mechanical properties.

In order to investigate the grain growth behavior of a FGH96 superalloy during thermomechanical treatment, isothermal compression experiments of the superalloy were carried out on a Gleeble thermal simulator at the temperatures from 1020 to 1110 °C with strain rates from 10-3 to 1 s-1. Uniform heat treatment was performed on the deformed samples with typical Zener-Hollomon (Z) parameters after hot compression. Optical microscope (OM), electron backscatter diffraction (EBSD), transmission electron microscope (TEM) and finite element (FE) simulation were employed to explore the relationship between deformation conditions and microstructure evolution during thermomechanical treatment of the superalloy. The results show that with the decrease of Z parameter, the deformed microstructure in the center of the cross-section of the specimen transforms from a mixed state to a fully dynamic recrystallization (DRX) state. Under the conditions of high and medium Z parameters, obvious abnormal grain growth (AGG) emerges in the cross-section of the heat-treated samples, and inclines to form at higher strains with the decreasing Z parameter. Combined with the results of FE simulation, deformation conditions (Z parameter and strain) are suggested to be the main factors that control the normal grain growth (NGG) and AGG behaviors during thermomechanical treatment of the alloy, by influencing the deformation energy storage, the degree of DRX and γ′ precipitates. Stored energy in the special range of 1.25-1.38 J/mol, incomplete DRX and partial dissolution of γ′ precipitates can stimulate the occurrence of AGG. Under the stored energy conditions to ensure the occurrence of AGG, less DRX grains will favor individual formation of abnormally large grains (ALGs) with larger size after heat treatment. The microstructure with local misorientation (LM) between 0.25°-0.8° plays an important role in the later stage of ALGs growth. A variable β described as β = e·lnZ was proposed to define the formation condition of ALGs during thermomechanical treatment of the superalloy, and its corresponding mechanisms were also elucidated.

Laser processing results in modified mechanical properties and microstructural evolution due to high temperatures and fast cooling rates. Different laser surface treatment techniques are under investigation for their potential to alter local microstructure and properties while maintaining properties of the bulk material. Fatigue life of laser-engraved powder metallurgy steel is shown to be significantly reduced compared to as-sintered material, suggesting a degree of microstructural modification with engraving. The misorientation, dislocation density, and phase of samples engraved with a 2D matrix pattern using one laser pass and five laser passes are characterized using optical microscopy and SEM-EBSD, and a CFD simulation of the laser process quantifies the temperature profile of each laser engraving. Deep-engraved samples are seen to result in a possible martensitic transformation at the surface of the engraved region because of increased time at elevated temperature and extreme cooling rates. These findings reinforce the importance of understanding microstructural evolution during precision tailoring via laser surface modification.

Microstructure of the fusion zone of steel/nickel-alloy dissimilar metal welds (DMWs) for nozzle buttering was investigated by optical microscopy (OM), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and electron back-scattered microscopy (EBSD). The results showed that the dissimilar joint was complete, without welding defects. The structures of the fusion zone included the beach structure along the fusion boundary, the peninsula structures connected with the fusion boundary, and the island structures in the weld. The distribution of these three types of structures near the fusion boundary was uneven. The beach structure was formed because of the insufficient mixing and solidification of the molten liquid base material and the filler metal, with the width ranging between 0 and 150 μm. The peninsula and island structures were formed by the undercooling of the insufficiently mixed liquid base material and filler metal that entered the weld because of the convection and scouring of the weld pool. The composition of the three structures depended on the degree of mixing of the liquid base material and the filler metal, with a dilution ratio between 40 and 60%. The degree of dilution for the beach, peninsula, and island structures decreased in turn. With an increase in the dilution ratio, the initial solidification temperature of the corresponding composition increased significantly. When the dilution ratio exceeded 94.5%, the initial solidification phase transformed from the face-centered cubic γ-austenite into a body-centered cubic ferrite, with island structures solidified in the form of ferrites in the weld near the fusion boundary. The austenite grain orientations at weld side are dispersed with 75% large (> 15°) misorientation in frequency and the overall texture orientation distributes dispersedly with deviating from the direction.

Each 2D material has a distinct structure for its grain boundary and dislocation cores, which is dictated by both the crystal lattice geometry and the elements that participate in bonding. For the class of noble metal dichalcogenides, this has yet to be thoroughly investigated at the atomic scale. Here, we examine the atomic structure of the dislocations and grain boundaries (GBs) in two-dimensional PtSe2, using atomic-resolution annular dark field scanning transmission electron microscopy, combined with density functional theory and empirical force field calculations. The PtSe2 we study adopts the 1T phase in large-area polycrystalline films with numerous planar tilt GB distinct dislocations, including 5|7+Se and 4|4|8+Se polygons, in tilt-angle monolayer GBs, with features sharply distinguished from those in 2H-phase TMDs. On the basis of dislocation cores, the GB structures are investigated in terms of pathways of dislocation chain arrangement, dislocation core distributions in different misorientation angles, and 2D strain fields induced. Based on the Frank-Bilby equation, the deduced Burgers vector magnitude is close to the lattice constant of 1T-PtSe2, building the quantitative relationship of dislocation spacings and small GB angles. The 30° GBs are most frequently formed as a stitched interface between the armchair and zigzag lattices, constructed by a string of 5|7+Se dislocations asymmetrically with a small deviation angle. Another special angle GB, mirror twin 60° GB, is also mapped linearly by metal-condensed asymmetric or Se-rich symmetric dislocations. This report gives atomic-level insights into the GBs and dislocations in 1T-phase noble metal TMD PtSe2, which is a promising material to underpin extending properties of 2D materials by local structure engineering.

The Alnico 8 alloy has been printed using the selective laser melting additive manufacturing approach, resulting in material with magnetic properties in the as-printed state comparable to properties produced by conventional casting or powder metallurgy routes. Microstructural characterization in 3D, via electron backscattered diffraction (EBSD) in a TriBeam microscope, simultaneously reveals a fine-scale grain structure, grain orientations and sub-grain misorientation gradients as a function of proximity to spherical pores that form during the print process. The nanostructure of the 3D printed part has the same highly coherent spinodal α 1 / / α 2 structure observed in conventionally fabricated Alnico 8, which gives rise to a coercivity ( H c ) of 51.2 kA m - 1 . Further investigation of the phase constituents by TEM analysis provides an understanding of the microstructure evolution during the additive manufacturing process. Modified processing pathways for improved microstructure and properties are discussed.

The microstructure evolution of 7A85 aluminum alloy at the conditions of strain rate (0.001 − 1 s−1) and deformation temperature (250–450 °C) was studied by optical microscopy (OM) and electron back scattering diffraction (EBSD). Based on the K-M dislocation density model, a two-stage K-M dislocation density model of 7A85 aluminum alloy was established. The results reveal that dynamic recovery (DRV) and dynamic recrystallization (DRX) are the main mechanisms of microstructure evolution during thermal deformation of 7A85 aluminum alloy. 350–400 °C is the transformation zone from dynamic recovery to dynamic recrystallization. At low temperature (≼350 °C), DRV is the main mechanism, while DRX mostly occurs at high temperature (≽400 °C). At this point, the sensitivity of microstructure evolution to temperature is relatively high. As the temperature increased, the average misorientation angle ( $${\bar \theta _{\rm{c}}}$$ ) increased significantly, ranging from 0.93° to 7.13°. Meanwhile, the fLAGBs decreased with the highest decrease of 24%.

Quasicrystals exhibit long-range order but lack translational symmetry. When grown as single crystals, they possess distinctive and unusual properties owing to the absence of grain boundaries. Unfortunately, conventional methods such as bulk crystal growth or thin film deposition only allow us to synthesize either polycrystalline quasicrystals or quasicrystals that are at most a few centimeters in size. Here, we reveal through real-time and 3D imaging the formation of a single decagonal quasicrystal arising from a hard collision between multiple growing quasicrystals in an Al-Co-Ni liquid. Through corresponding molecular dynamics simulations, we examine the underlying kinetics of quasicrystal coalescence and investigate the effects of initial misorientation between the growing quasicrystalline grains on the formation of grain boundaries. At small misorientation, coalescence occurs following rigid rotation that is facilitated by phasons. Our joint experimental-computational discovery paves the way toward fabrication of single, large-scale quasicrystals for novel applications., Quasicrystals exhibit long-range order without periodicity. The authors report an approach for quasicrystal fabrication and show through in situ imaging and corresponding simulations the formation of a single decagonal quasicrystal arising from coalescence of multiple quasicrystals in a liquid.

In electron backscatter diffraction (EBSD), kernel average misorientation (KAM), grain average misorientation (GAM), and grain orientation spread (GOS) are considered as the reflection of the extent of recrystallization. This work presents a comparative study of KAM, GAM, and GOS to bring out the best-suited parameter to determine the extent of recrystallization in pure copper. The pure ETP (electrolytic tough pitch) copper samples were characterized through EBSD at three different states: (i) deformed (ii) partially recrystallized and (iii) fully recrystallized. The result shows that the GOS found to be dominating over KAM and GAM in distinguishing the strain-free and deformed grains for pure ETP copper. The cut-off point for delineating the deformed and the strain-free grains has also been determined and applied to low percentage deformation study where higher mechanical strength and electrical conductivity is achieved than the as-received sample.

In this study, texture development during the accumulative roll bonding (ARB) of Al–Cu multilayered composite was investigated using X-ray diffraction. Microstructural investigations were also conducted using optical and transmission electron microscopy. The results of textural investigation of the rolled specimens indicated that a strong β-fiber was developed and dominated mainly by the Brass and Copper components in both the Al and Cu layers during the early stages of the ARB process. Moreover, the intensity of the most textural components in both of the metallic layers decreased in the last two ARB cycles. No component other than a weak Rotated Cube was found in the Al layer after the last ARB cycle. In the Cu layer, on the other hand, a Cube component, known as the "recrystallization texture ", was developed which was accompanied by a "rolling texture" represented by the β fiber. Furthermore, the increased misorientation between the grains at high ARB cycles confirmed the formation of high angle grain boundaries in both of the metallic layers. Microstructural investigations showed that the average grain size of the final specimens (after 7 ARB cycles) was less than 500 nm in both Al and Cu layers.

The constitutive relationships of Al-Mg-Si alloy deformed at various strain rates, temperatures and strains were studied. The microstructure evolution was quantitatively characterized and analyzed, including recrystallization fraction, grain sizes, local misorientation, geometrically necessary dislocation and stored strain energy during hot deformation and subsequent heat treatment. The results show that the dislocation density and energy storage are linear with lnZ during hot deformation and subsequent heat treatment, indicating continuous recrystallization occurring in both processes. With higher lnZ, the dislocation density declines more sharply during subsequent heat treatment. When lnZ is less than 28, dislocation density becomes more stable with less reduction during subsequent heat treatment after hot deformation. As these dislocations distribute along low angle grain boundaries, the subgrain has good stability during subsequent heat treatment. The main recrystallization mechanism during hot deformation is continuous dynamic recrystallization, accompanied by geometric dynamic recrystallization at higher lnZ.

The UnitCell Tools package was developed to determine unit-cell parameters of a crystal from a single electron diffraction pattern with high-order Laue zone reflections acquired in the conventional transmission electron microscope., Electron diffraction techniques in transmission electron microscopy (TEM) have been successfully employed for determining the unit-cell parameters of crystal phases, albeit they exhibit a limited accuracy compared with X-ray or neutron diffraction, and they often involve a tedious measurement procedure. Here, a new package for determining unit-cell parameters from a single electron diffraction pattern has been developed. The essence of the package is to reconstruct a 3D reciprocal primitive cell from a single electron diffraction pattern containing both zero-order Laue zone and high-order Laue zone reflections. Subsequently, the primitive cell can be reduced to the Niggli cell which, in turn, can be converted into the unit cell. Using both simulated and experimental patterns, we detail the working procedure and address some effects of experimental conditions (diffraction distortions, misorientation of the zone axis and the use of high-index zone axis) on the robustness and accuracy of the software developed. The feasibility of unit-cell determination of the TiO2 nanorod using this package is also demonstrated. Should the parallel-beam, nano-beam and convergent-beam modes of the TEM be used flexibly, the software can determine unit-cell parameters of unknown-structure crystallites (typically >50 nm).

Stray grains are the most severe of the solidification defects that occur in the industrial single-crystal blade preparation process. In this study, a single-crystal dummy blade cluster with different crystal orientations controlled by the seeding method was prepared, and the influence of the position of the circular platform (relative to the sample and furnace body) on stray grain nucleation was investigated. Results show that the microstructure of the circular platforms could be divided into the center, expansion, and stray grain regions. The inside of the circular platform facing the center of the cluster is more prone to stray grain formation than the outside of the circular platform facing the furnace body. With an increase in the distance between the circular platform and the bottom of the dummy blade cluster, the stray grain region expands, whereas the expansion region narrows. The stray grain is slightly aggravated with increase of the misorientation. Finally, the mechanism underlying the influence of platform position on the formation of stray grains in single-crystal dummy blade clusters is discussed based on the temperature evolution during directional solidification.

Surface mechanical treatments are known to introduce deformation heterogeneity, thus entailing a combination of excellent strength and ductility in metallic metals. Accumulative skin pass rolling (ASPR) was employed to introduce heterogeneous structure in pure copper, which significantly improved yield strength and maintained high ductility. The experimental observations of the ASPR processed copper showed that surface grains possessed a much larger magnitude of misorientations and geometrically necessary dislocations (GNDs) than the centre grains. Crystal plasticity finite element modelling was utilised to provide an in-depth understanding of microstructure evolution during ASPR. It was found that the surface grains accommodated higher shear strain and had higher slip resistance than the centre grains. The multiple active slip systems in the surface grains induce the lattice rotations and then the formation of intragranular misorientations accompanied by a high density of GNDs, while the single active slip system in the centre grains can accommodate the applied material rotation without the lattice rotation.

The influence of cold rolling deformation on the electrochemical and corrosion behavior of 654SMO super-stainless steel in a high-temperature 3.5% NaCl solution was investigated by potentiodynamic curves, EIS, Mott–Schottky plots and XPS. Results of the electrochemical experiments and surface analyses showed that 654SMO under 33.3% reduction had a maximum deterioration in corrosion properties. After heavy deformation (55.6% and 66.7%), the corrosion resistance of 654SMO improved. XRD and EBSD were performed to illustrate the potential mechanism for the improvement in corrosion resistance. Results showed that there was no strain-induced martensite transformation for steels even under 66.7% deformation, and the dislocation density increased monotonically with an increasing deformation. The cold rolling texture of steels could be described by high Goss, S, brass and copper textures with a low brass-R component. Misorientation analysis and grain boundary characterization obtained from EBSD showed that a large number of mechanical twins formed in steels under 55.6% and 66.7% reductions. A hypothesis was proposed that the combined effect of the strong rolling texture and ∑3 twin boundaries ameliorated the corrosion resistance of 654SMO under large deformations.

In the present work, the behavior of recovery and recrystallization have been investigated in -oriented Mo-3Nb single crystals cold deformed by uniaxial compression. The macroscopic deformation characteristics and subsequent annealed microstructure evolution of the compressed Mo-3Nb single crystals were carried out by stereomicroscope and electron backscatter diffraction, respectively. Annealed grain boundary misorientation analysis shows Mo-3Nb single crystals no longer keep a monocrystal structure when the compressive strain exceeds 30%. The proportion of high-angle grain boundaries after annealing for Mo-3Nb single crystal with cold compression at high strain rate is larger than that at low strain rate, suggesting that increasing the strain rate can promote the recovery and recrystallization behavior. To elucidate the evolution process of substructure in the recovery and recrystallization, TEM analyses were performed. The annealed dislocation density is reduced and rearranged compared to the cold-compressed state. With the increase of compressive strain, the annealing sub-structure changes from recovery to recrystallization. The recovery process is primarily polygonization, and the mechanism of recrystallization nucleation is through the coalescence of sub-grains.

The recent development of electron-sensitive and pixelated detectors has attracted the use of four-dimensional scanning transmission electron microscopy (4D-STEM). Here, we present a precession electron diffraction-assisted 4D-STEM technique for automated orientation mapping using diffraction spot patterns directly captured by an in-column scintillator-based complementary metal-oxide-semiconductor (CMOS) detector. We compare the results to a conventional approach, which utilizes a fluorescent screen filmed by an external charge charge-coupled device camera. The high-dynamic range and signal-to-noise characteristics of the detector greatly improve the image quality of the diffraction patterns, especially the visibility of diffraction spots at high scattering angles. In the orientation maps reconstructed via the template matching process, the CMOS data yield a significant reduction of false indexing and higher reliability compared to the conventional approach. The angular resolution of misorientation measurement could also be improved by masking reflections close to the direct beam. This is because the orientation sensitive, weak, and small diffraction spots at high scattering angles are more significant. The results show that fine details, such as nanograins, nanotwins, and sub-grain boundaries, can be resolved with a sub-degree angular resolution which is comparable to orientation mapping using Kikuchi diffraction patterns. © 2021 Cambridge University Press. All rights reserved.

The influence of MoS2–Al2O3 nanofluid as a functional lubricant on the microstructure and corrosion resistance of hot-rolled steel surface was studied. Because of the excellent lubrication performance of the nanofluid, the rolled surface quality improved with a 18.2% and 69.5% reduction in surface roughness and oxide scale thickness, respectively, when compared with the base-fluid without nanoparticles. The further microstructure characterization determined that the grain size, local misorientation and deformed grain fraction of the steel decreased significantly. A diffusion layer of Al2O3, FeS and FeMo4S6 was found in the outer oxide layer of rolled surface. Closely arranged Al2O3 grains inhibited the oxidation of steel strips that the oxidation activation energy was increased by about 14.5%. Through density functional theory (DFT) calculation, the formation of FeS and FeMo4S6 was attributed to the migration of Mo and S atoms from MoS2 into the Fe lattice through substitutional and interstitial diffusion, respectively, with the energy barrier of 0.84 eV and 0.54 eV. Finally, the protection of diffusion layer, reduction in surface defects, and alleviation of residual stress and deformation resulted in the enhancement of corrosion resistance. This study provides a possible route to achieve surface enhancement during the hot rolling process.

The Fe49Co49V2 alloy is a soft magnetic material commonly used in high-performance electrical machines in form of a laminate made of stacked thin sheets. Laminate preparation inevitably induces defects along the cut edge, which will deteriorate the magnetic properties of the alloy. Three laminate cutting methods, namely, punching, electrical discharge machining (EDM), and laser cutting, have been assessed for their impact on the magnetic properties of the laminates. The effect of annealing treatment before and after the cutting process was also studied. The magnetic properties of the ring laminate samples were measured under a frequency of 400 Hz at room temperature. The grain size and local misorientation were evaluated by electron backscattering diffraction (EBSD). Our study indicates that grain boundary and local misorientation within the grains are key considerations when assessing the deterioration of the soft magnetic properties. The mean grain size along the edge of laser-cut laminates with a post-annealing treatment was about $29.3~\mu \text{m}$ , larger than that in the center area of about $24~\mu \text{m}$ . This process route also exhibited the lowest fraction of local misorientation of greater than 0.5° along the edge area. As a result, laminates produced by laser cutting followed by a post-annealing treatment displayed the best magnetic performance among all investigated manufacturing routes.

Microstructural evolution of a refractory tantalum-tungsten alloy (Ta-4% W) after cold rolling from small to large von-Mises strains (0.12–2.7) was quantitatively studied using transmission electron microscopy. Grain subdivision was observed to take place at two levels. Geometrically necessary boundaries nearly paralleling to slip planes enclosed volumes further divided by diffuse cells and by remnants of Taylor lattices. With increasing strain, the diffuse cells evolved into clear incidental dislocation boundaries enclosing cells, while the Taylor lattices disappeared. Grain subdivision was thus intermediate between those observed in cell forming and in non-cell forming alloys. Meanwhile, the average misorientation angle across all boundaries increased while the average boundary spacing decreased. Distributions of the microstructural parameters at each strain level were found to exhibit universal scaling laws. The microstructural evolution was found closely linking to the observed high strength and strain hardening of this alloy. Based on measured microstructural parameters, the flow stress was calculated utilizing linearly addition of the strengthening by solutes, incidental dislocation boundaries (Taylor strengthening) and geometrically necessary boundaries (Hall-Petch equation). The relative contribution of each strength mechanism evolved with increasing strain and with microstructural evolution: solutes and friction stress dominated at small strains while boundaries dominated at larger strains. Calculated strengths were in close agreement with experimental tension tests and demonstrated an unexpectedly high and continuous parabolic hardening without transition across this large strain range.

This study aims to understand the features of 11 2 ¯ 1 twin boundaries in a high strain rate compressed Mg-10Gd-3Y-0.4Zr using electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). Based on the Schmid factor calculations, the basal dislocations are easily activated within the 11 2 ¯ 1 twin and suppressed in the surrounding matrix. The consequent basal dislocation-twin interaction during deformation can lead to the misorentiation deviation of 11 2 ¯ 1 twin boundaries, accompanying with the formation of a step at the twin boundary. Such a 11 2 ¯ 1 twin boundary evolution mechanism provides a new vision of twinning behavior in Mg alloys.

The contrast of dislocations in 4H-SiC crystals shows distinctive features on grazing-incidence X-ray topographs for diffraction at different positions on the operative rocking curve. Ray-tracing simulations have previously been successfully applied to describe the dislocation contrast at the peak of a rocking curve.The present work shows that the dislocation images observed under weak diffraction conditions can also be simulated using the ray-tracing method. These simulations indicate that the contrast of the dislocations is dominated by orientation contrast. Analysis of the effective misorientation reveals that the dislocation contrast in weak-beam topography is more sensitive to the local lattice distortion, consequently enabling information to be obtained on the dislocation sense which cannot be obtained from the peak.

This study investigates the fatigue performance of wire arc additive manufactured (WAAM) SS 347 in different orientations. WAAM processed SS 347 plate features with grains mostly oriented in and crystallographic texture along the building direction (BD). Microstructure was mainly austenitic with a smaller fraction of ferrite. Tensile properties of the as-built SS 347 specimens were evaluated to understand the effect of orientation in regard to BD. Stress controlled fatigue tests were conducted at different stress amplitudes for samples in the horizontal direction (HD) and vertical direction (VD). The fatigue strength of as-built samples after sustaining 2×106 cycles were 135 MPa and 128 MPa for VD and HD specimens, respectively. Fatigue strength was less for both the samples in different orientation than the wrought counterpart (~40%). The increase in tensile strength and decrease in fatigue strength is attributed to the presence of austenitic columnar grains with a smaller ferrite fraction less than 5% and noticed phase transformation along with local recrystallization as a result of remelting the former layers along the BD during deposition. The higher kernel average misorientation values confirm the degree of grain misorientation along the BD. The fatigue failure mode was ductile for HD and VD specimens with striations in the crack propagation region and micro-voids coalescence in the final fracture region.

Forming limit diagrams (FLDs) are widely used in sheet metal industries to assess formability. These are graphical representations of major and minor strains on a 2-D plot separating safe and unsafe regions. Limiting strains were measured by digital image correlation (DIC) technique. In the present work, microstructure evolution and forming behavior of family of interstitial free steels: interstitial free (IF) and interstitial free-high strength (IF-HS) grades have been investigated. Both experimental and finite element (FE) simulated FLDs indicated higher formability for IF steel. Microstructural developments affect forming limits and influence forming limit diagrams. Evolving microstructure during forming was studied by texture developments using x-ray diffraction (XRD) and in grain average misorientation developments using electron backscattered diffraction (EBSD) techniques as a function of strain and strain paths. Estimated microstructural parameters revealed that the enhanced formability of IF steel was due to the presence of strong γ-fiber (ND// ) recrystallization texture and corresponding absence of θ-fiber (ND// ). On the contrary, IF-HS steel showed the abundant θ-fiber component and hence decreased formability.

Substructures of LiF crystal samples grown by the Kyropoulos and Bridgman–Stockbarger methods were studied. Measurements were made using the double-crystal x-ray diffractometry technique. The angular full width at half maximum (FWHM) of peaks was calculated for each diffraction pattern. Statistical processing of the measured FWHM indicated that samples grown by the Bridgman–Stockbarger method had smaller angular misorientation of the substructure and included areas suitable for manufacturing crystalline x-ray analyzer blanks of the required size.

In the present work, the laser-induction hybrid cladding technology with induction post-heating (post-LIHC) was utilized to deposit coatings on the full-scale rail surface, and the effects of different induction post-heating temperature on the morphology, microstructure and mechanical performance of the heat affected zone (HAZ) were first in-depth analyzed. Results indicate that with the increase of the average induction post-heating temperature (Ta) in post-LIHC, the microstructure of the HAZ first transforms from the fine acicular martensite structure to the composite structure of martensite and pearlite, then changes to the pure pearlite structure, and finally retransforms to the coarse martensite structure. Especially, the morphology of the “Martensite Zone” (MZ) in HAZ undergoes three remarkable change with Ta increasing: “flat-U-shaped” → “flat-W-shaped” → “vanished” → “flat-V-shaped”. Under the induction post-heating window of Ta = 508 °C ~ 565 °C, not only the MZ in HAZ can be inhibited absolutely, but also fine pearlite with much lower interlamellar spacing, smaller grain size and higher grain misorientation forms instead, making the strength and toughness are both enhanced significantly than the other three type HAZs and the rail substrate. In addition, increasing the induction post-heating temperature within the window of Ta = 508 °C ~ 565 °C can increase the interlamellar spacing and reduce the ferrite grain misorientation of the pearlite structure in HAZ, but has no obvious effect on the grain size therein.

Semi-solid metal forming processes cover a wide variety of technologies in manufacturing, generally leading to non-dendritic microstructures typified by rosette-like or spherical grains. With the contemporary experimental methods, researchers still cannot completely understand the formation of such microstructures. However, as a process coupled with dendritic growth, deformation and flow, the microstructural evolution during the semi-solid deformation has been scarcely simulated. With the vector-valued phase-field method, two-phase flow model and an innovative design of boundary conditions, the current research numerically compressed a single dendrite into a less dendritic polycrystalline structure. The resulting microstructure was consistent with the metallographic analysis and the simulation enables a clear observation of the whole process: the ripening transformed the highly branched shape into a less dendritic one; the subsequent deformation crushed the dendrite into a stubby structure; eventually, the deformation caused the boundaries inside this structure, dividing the solid into multiple grains. The analysis on the boundaries inside the deformed solid offered further insight into the formation of non-dendritic structures. These boundaries showed a tendency towards melting with increasing misorientation, demonstrating the possibility of the grain boundary wetting, which was considered as the source of the fragmentation when the dendrite undergoes deformation, but is hard to validate in situ even with the cutting-edge X-ray imaging technique.

Microstructure and microtexture of a dual-phase (DP) steel was investigated using the electron backscattered diffraction (EBSD) technique. A DP600 steel was produced by 60% cold-rolling a low carbon steel with an initial ferrite pearlite microstructure followed by intercritical annealing at 720°C for 1 h. Kernel average misorientation map of the DP600 steel showed that the density of geometrically necessary dislocations as well as the local misorientation is higher in the vicinity of ferrite–martensite interfaces compared to the middle of the ferrite grains. Microtexture analysis of the cold-rolled steel by EBSD revealed that a strong α fiber and weaker γ fiber texture forms after cold-rolling. After intercritical annealing, the intensity of the α fiber texture is significantly reduced, whereas that of the more desirable γ fiber texture is slightly increased. The maximum texture intensity in the DP600 steel was observed for (112)[110] component in the α fiber, and (111)[123] and (111)[112] components in the γ fiber.

Aluminum metal matrix composites of the varying percentage of SiC reinforcement were welded using the tungsten inert gas welding technique. For all the conditions of the specimen, the welding parameters were kept identical. The welded composites were thermally aged to peak age-hardening conditions. Significant differences in microstructure exist between aged and non-age hardened composites in terms of misorientation, grain boundary fractions and stored energy. These differences in microstructure were seen through identical changes in the mechanical behavior of the welded composites. After aging, microstructure showed refinement in grain size and preferential orientation. Hardness and tensile strength increased at different rates with increase in SiC content indicating that hardness was a clear function of stored energy and strength had a dependence on the misorientation. EBSD measured suggests that due to age hardening, a rearrangement in dislocation substructures occurred with precipitation of Mg2Si or increasing SiC content followed by dynamic recovery of the weld metal region which leads to enhancement of hardness. The increase in tensile strength with decreased misorien�tation was a clear indication that the effect of annihilation of dislocations as a result of recovery was less pronounced and precipitation strengthening was dominant. The present study aims to address the role of SiC addition in aluminum metal matrix composites on the welded microstructure and finally relating the microstructural changes to the observed mechanical behavior of the welded joints. The study reveals that strength not only de�pends on the average value of misorientation but also on the distribution of misorientation in the microstructure

Most biomedical implants are predominantly Mg-based because of their degradable properties. The effect of recrystallization and local misorientation induced by various rolling parameters on the biodegradation of pure Mg has been systematically studied. The results reveal that an increase in recrystallization fraction and a reduction in local misorientation of grains as the rolling temperature increased was beneficial to the degradation rate of pure Mg. There is basal texture variation arising from the occurrence of high twinning activity at a lower rolling temperature which suppresses the maximum texture intensity and also increases the degradation rate. This result also reveals that grain growth was beneficial to the degradation rate of Mg, as larger grain size give a lower degradation rate. The degradation rate generally increased with decreasing rolling temperature (i.e., 350°C

Mooring chain steel has been widely used for stabilizing offshore platforms and suffers from stress corrosion cracking. Herein, the microstructure difference, its relation to strength and susceptibility of stress corrosion cracking after tempered at different temperatures have been studied. Result shows increasing tempering temperature increases the proportion of low value CSL boundaries, decreases the local misorientation angle and promotes the precipitation of carbides. These factors induced the decrease of SCC susceptibility at higher tempering temperature. The resistance to SCC at 640 °C tempering temperature is about 20% higher than that of 580 °C at − 1000 mVSCE. The main strengthening mechanism of the ultra-high-strength steel is ultra-fine grain strengthening mechanism, precipitation strengthening mechanism, and dislocation strengthening mechanism. Increasing tempering temperature from 580 to 640 °C decreases the yield strength by 85 MPa, which is mainly attributed to larger carbides size.

As the manufacturing sectors are leaning toward additive manufacturing, leaving the traditional methods behind. Wire arc additive manufacturing (WAAM) technique is the growing technique to fabricate the aerospace, defense, and automotive sector components. The major problem associated with the WAAM technique is establishing the process parameters to acquire the defect-free components. In this research work, an attempt has been carried out to establish a wire arc additively manufactured component using Inconel 625 filler. A successful attempt has been made to build the thick slab wall component using Inconel 625. The microstructure analysis was studied in both longitudinal and transverse direction to check the homogeneity. The transverse microstructure at the near substrate region has a cellular structure. The columnar structure is observed in the layer bands between the layers, and the topmost layer revealed equiaxed with a dendritic structure. The longitudinal microstructure varies from a columnar structure in the inter-pass boundaries to fine equiaxed structures between the passes, and at the end, it is an equiaxed structure. Microsegregation in the dendritic core and interdendritic regions was evaluated along with microhardness measurement. The microhardness values along the different layers were increased when taken from bottom to top. Similarly, it increases across the passes due to the formation of an equiaxed dendritic structure. The EBSD investigation was performed to evaluate the manufactured component’s grain size (25.48 ± 61.02 μm), and misorientation angle, low boundary rotation angle (2–5°) and high boundary rotation angle (15–180°). Further, the local dislocation sites were observed through KAM mapping.

Bainite transformation kinetics, microstructure, and mechanical properties were comparably investigated by X-ray diffraction, scanning electron microscopy, electron backscatter diffraction, transmission electron microscopy observation, and tensile and impact tests for two treatments: with and without quenching before isothermal bainite transformation at 300 °C. Both the incubation time and growth stage of bainite transformation are accelerated by the introduction of prior martensite, especially the former. In addition, the bainite microstructure around the prior martensite is refined and shows a similar orientation with the martensite due to the strain field caused by the existence of prior martensite. The finer bainite microstructure and prior martensite improve the strength and hardness of the high-carbon nano-bainitic steel. Although the presence of prior martensite and low misorientation relationship between the martensite and the adjacent bainite microstructure are prejudicial to impact toughness, the nanoscale bainite microstructure can inhibit the crack propagation and then improve the impact toughness of the high-carbon nano-bainitic steel.