Search

For decades, Moore's Law has neared its limits, posing significant challenges to further scaling it down. A promising avenue for extending Moore's Law lies in three-dimensional integrated circuits (3D ICs), wherein multiple interconnected device layers are vertically bonded using Cu–Cu bonding. The primary bonding mechanism involves Cu solid diffusion bonding. However, the atomic diffusion rate is notably low at temperatures below 300 °C, maintaining a clear and distinct weak bonding interface, which, in turn, gives rise to reliability issues. In this study, a new method of surface modification using epoxy resin to form fine grains on a nanotwinned Cu film was proposed. When bonded at 250 °C, the interfacial grains grew significantly into both sides of the Cu film. When bonded at 300 °C, the interfacial grains extended extensively, eventually eliminating the original bonding interface. [ABSTRACT FROM AUTHOR]

Microstructures of tetragonal tungsten bronze-structured ferroelectric ceramics vary owing to abnormal grain growth. Control of the grain microstructure stability is a critical aspect in the electrical properties. In this study, the grain growth behavior was meticulously explored through a combination of experiments and numerical simulations. Effects of the liquid phase and initial particle-size distribution on the microstructural evolution were investigated under different grain boundary energy anisotropy conditions. The grain area and edge number were calculated to investigate the grain growth kinetics and shape variation. The results revealed that the presence of a large amount of the liquid phase contributed to rapid grain growth and a duplex structure formation. The grain-size inhomogeneity can be eliminated by using initial particles with a bimodal particle-size distribution. The grain shape was mainly determined by the degree of anisotropy of the grain boundary energy and was nearly unaffected by the process parameters. The findings of this study afford theoretical guidance for microstructure regulation and stable preparation of high-performance ferroelectric ceramics. [ABSTRACT FROM AUTHOR]

The abnormal grain growth behaviour and preferential orientation of AZ31 Mg alloy were systematically examined. Abnormal grain growth was observed after annealing at 500°C for 9 h, and the grain growth rate was 1.3 mm h−1. Due to the abnormal grain growth, the activation energy of grain growth was reduced from 172 to 104 KJ mol−1. The abnormal grains with <11 2 ¯ 0> orientation grew preferentially, which resulted in the increase of the <11 2 ¯ 0> type texture intensity and the decrease of the <0001>. The energy difference of the misorientation is the main driving force for the formation of abnormal grains with <11 2 ¯ 0> orientation. [ABSTRACT FROM AUTHOR]

If variety is the spice of life, then abnormal grain growth (AGG) may be the materials processing equivalent of sriracha sauce. Abnormally growing grains can be prismatic, dendritic, or practically any shape in between. When they grow at least an order of magnitude larger than their neighbors in the matrix—a state we call extreme AGG—we can examine the abnormal/matrix interface for clues to the underlying mechanism. Simulating AGG for various formulations of the grain boundary (GB) equation of motion, we show that anisotropies in GB mobility and energy leave a characteristic fingerprint in the abnormal/matrix boundary. Except in the case of prismatic growth, the morphological signature of most reported instances of AGG is consistent with a certain degree of GB mobility variability. Open questions remain, however, concerning the mechanism by which the corresponding growth advantage is established and maintained as the GBs of abnormal grains advance through the matrix. [ABSTRACT FROM AUTHOR]

The paper presents the results of modeling and testing of a heavy weight part made of Cr-Mo, which was V-modified ultrahigh strength steel grade AISI 4140, processed through a novel open-die forging program and two alternative routes of twostage heat treatment cycles designed to meet requirements of high-duty components for energy sector. By using unconventional forging conditions based on the assumption of large feed and reduction ratio and modifying the chemical composition, better control of the austenite grain was achieved to minimize abnormal grain growth and/or strain uniformity problems. Using the Finite Element Modeling, the multi-stage sequence of upsetting and the cogging strain distribution were optimized to minimize the strain variation along the length to a range 2.2÷2.7, and correlated with the microstructure generated at each main stage on the large cross-sections of the shaft. Mechanical and thermal processing cycles designed using the finite element method were fully verified physical modeling using a 16 ton forging block, including two alternative quenching strategies: oil vs. water spray and air. The material was studied in the as-forged, normalized and heat-treated states to observe the behavior of the hot-formed material and the effects of cooling conditions on the microstructure during the final heat treatment. It was found that the use of large feed ratios on cogging and varied cooling allowed to suppress the adverse effects of the inevitable abnormal grain growth, resulting in 1-2 ASTM in forged condition and reaching 6 ASTM and 8/9 ASTM after quenching in oil and water spray, respectively, which allowed a corresponding notched impact strength of 44÷48 and 85÷122 J/cm2 in the critical region of the forged shaft after tempering. [ABSTRACT FROM AUTHOR]

In order to fabricate homogeneous large-scale Ti-5Al-5V-5Mo-3Cr (Ti-5553) alloy bulk with fine and equiaxial β grain, we performed a series of multi-axial α + β field forging with 62 forging cycles on the large-scale Ti-5553 billet by using 12.5 MN high-speed hydraulic press. The β-annealed microstructure was the starting microstructure of the billet. After the 6th forging cycle, β grain deformed dramatically, and the grain-boundary network developed within the irregular β grain. As the forging cycle increased to 44, the volume fraction of the fine and equiaxial β grain that is less than 20 μm, which is caused by dynamic recrystallization, increased gradually. However, the incomplete dynamic recrystallization region within the original β grain could not be eliminated. As the forging cycle further increased, the volume fraction of the fine and equiaxial β grain did not increase. In contrast, the abnormal grain growth of the β phase occurred during 50th~62nd forging cycle. Here, we attribute the formation of the incomplete dynamic recrystallization region and the abnormal grain growth of the β phase to the high deformation rate of the α + β forging. The refining behavior of β grain and the abnormal coursing β grain, which is found during the multi-cycle multi-axial forging of large-scale Ti-5553 alloy billet, are seldom reported in the isothermal compression of small-scale Ti-5553 alloy specimen. The findings of the paper are instructive for improving the sub-transus forging strategy that is used to fabricate the large-scale homogeneity Ti-5553 alloy billet with fine and equiaxial β grain. [ABSTRACT FROM AUTHOR]

The effect of the bimodal grain size distribution in the range of several tens of micrometers is studied to investigate the mechanical properties of metallic materials with single‐phase ferritic microstructure. The previous studies on the bimodal distribution of grain size have been performed on materials with nanocrystalline, ultrafine, or multiphase microstructures, and have generally reported that the mixed structure of fine and coarse grains improves the ductility of the material, because the coarser grains preferentially accommodate deformation. However, herein, the coarse grains do not accept the deformation well during plastic deformation and cause nonuniform deformation, which lowers the work hardening coefficient and accelerates necking of sheet. The influence of the bimodal grain size distribution on the mechanical properties is evaluated using tensile and various formability tests. Microstructural changes before and after deformation are tracked by electron backscatter diffraction. [ABSTRACT FROM AUTHOR]

A phase-field model was revised to study the abnormal growth of Goss grains during the annealing process in Fe-3%Si steels, in which the interaction between the second-phase particles and Goss grain boundaries (GBs) was considered. The results indicate that the abnormal growth of Goss grains occurs due to the different dissolvability of the particles at Goss GBs compared with the other GBs. Moreover, the degree of abnormal growth increases first and then decreases with an increasing particle content. Meanwhile, the size advantage of Goss grain can further promote the degree of abnormal growth. Two types of island grains were found according to the simulated results, which is consistent with the experimental observations. A proper GB dissolvability of particles is the key factor for the formation of isolated island grains, and a higher local particle density at GBs is the main reason for the appearance of serial island grains. These findings can provide guidance for the desired texture control in silicon steels. [ABSTRACT FROM AUTHOR]

The effects of manufacturing conditions on the microstructure evolution of Ni-based superalloys are poorly understood, and the interchangeable terminology to describe some microstructure phenomena is inconsistent. This critical review aimed to address these issues through the discussion of seven microstructure phenomena that occur during thermomechanical processing of safety-critical components used in jet engines. Each phenomenon is outlined with reference to grain nucleation and growth mechanisms, as well as processing conditions under which they are observed. The processing conditions where each phenomenon dominates are visualised through a series of contour plots. Through this graphical representation, gaps of understanding in microstructure evolution were identified and accompanied by recommendations for areas of further study. [ABSTRACT FROM AUTHOR]

The abnormal grain growth (AGG) behaviour was reported during the solid-state sintering of a nano-sized BaTiO 3 powder using the spark plasma sintering technique. Microstructural observations revealed that coarse crystals containing large amounts of faceted pores burst into formation within minutes. The results challenged the traditional views that sintering was predominated by the atom-diffusion related processes. Instead, the phenomena were explained to be resulted from the oriented attachment of smaller BaTiO 3 grains. A modified two-sphere model for nanoceramic sintering was also proposed. [ABSTRACT FROM AUTHOR]

The origin of nonuniform microstructure and abnormal grain growth (AGG) was investigated in flash sintered 3 mol% yttria‐stabilized zirconia (3YSZ) ceramics. The microstructural homogeneity decreased with increasing direct current (DC) density and with dwell time in a flash state, eventually resulting in AGG in the specimen core, the first observation of AGG in 3YSZ. Abnormal grains up to 100 μm in size emerged when the DC density was ≥160 mA/mm2, and the specimen's density exceeded 99% of theoretical, starting from the cathode and propagating toward the anode. The results are discussed by comparison with established mechanisms and previous experimental evidence concerning AGG in oxides, focusing on the possible effects of the electrochemical reduction at the cathode end of the specimen. [ABSTRACT FROM AUTHOR]

0.9KNbO3-0.1BaTiO3 ceramics, with a bimodal grain size distribution and typical tetragonal perovskite structure at room temperature, were prepared by using an induced abnormal grain growth (IAGG) method at a relatively low sintering temperature. In this bimodal grain size distribution structure, the extra-large grains (~10–50 μm) were evolved from the micron-sized filler powders, and the fine grains (~0.05–0.35 μm) were derived from the sol precursor matrix. The 0.9KNbO3-0.1BaTiO3 ceramics exhibit relaxor-like behavior with a diffused phase transition near room temperature, as confirmed by the presence of the polar nanodomain regions revealed through high resolution transmission electron microscope analyses. A large room-temperature electrocaloric effect (ECE) was observed, with an adiabatic temperature drop (ΔT) of 1.5 K, an isothermal entropy change (ΔS) of 2.48 J·kg−1·K−1, and high ECE strengths of |ΔT/ΔE| = 1.50 × 10−6 K·m·V−1 and ΔS/ΔE = 2.48 × 10−6 J·m·kg−1·K−1·V−1 (directly measured at E = 1.0 MV·m−1). These greatly enhanced ECEs demonstrate that our simple IAGG method is highly appreciated for synthesizing high-performance electrocaloric materials for efficient cooling devices. [ABSTRACT FROM AUTHOR]

The aluminum alloys produced by friction stir based AM were commonly characterized by fine-grains and coarsened precipitates. Abnormal grain growth (AGG) occurred often when the deposited fine-grained aluminum alloys were subjected to a T6 heat treatment, limiting the application of the friction stir based AM technologies and the produced components. In this study, friction surfacing deposition additive manufacturing (FSDAM) were developed to fabricate components of commercial 7075 high-strength aluminum alloys. The effect of post-processing heat treatment on the microstructure and mechanical properties of the fine-grained 7075 aluminum alloys produced by FSDAM were investigated systematically. The new post-processing heat treatment that was able to generate nano-sized precipitates without AGG was developed for the deposited 7075 aluminum alloys. The ultimate tensile strength, yield strength and ductility of the deposited 7075 aluminum alloys were comparable to those of the extruded 7075 aluminum alloys, offering a new solution for additive manufacturing high strength aluminum alloy components cost effectively. [ABSTRACT FROM AUTHOR]

This work demonstrates that large pores promote abnormal grain growth, a commonly observed but poorly understood behavior. To investigate this phenomenon, calcia doped aluminum oxide is used as a model ceramic because of its known propensity for abnormal grain growth. Controlled porous microstructures are fabricated using polymer microspheres with nominal diameters approximately an order of magnitude larger than the average grain diameters. Electron backscattered diffraction maps indicate that the introduction of large pores (∼3 vol.%) promotes abnormal grain growth, increasing the total abnormal grain area by more than 60 % when sintered at 1600 °C for 4 h in air. The differences between samples with and without large pores provide insight into the initiation of abnormal grain growth, which is needed to predict microstructure evolution in complex systems with such defects. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Nb has an impact on grain growth tendency during brazing of ferritic stainless steel. • Increasing Nb can refine the grain size but reduce the degree of recrystallization. • The decrease in temperature for abnormal grain growth is related to high Nb content. • The pinning force at grain boundary decreases due to the dissolution of precipitates. • Increasing Nb can rice the precipitation temperature of Laves and M(C,N) phases. The significant effect of Nb content on abnormal grain growth in 444-type ferritic stainless steel during simulated brazing (heat treated at 1100 °C and held for 15 min) was studied, which was used in automotive exhaust systems. By slightly increasing of Nb from 0.26 to 0.59 wt%, the starting temperature of abnormal grain growth will decrease from 1100 to 1050 °C, indicating a decrease in brazing performance. Finer ferrite grains can be obtained in the steel plate with high Nb content, but the tendency of retaining sub-grain boundaries will also strengthen. The deformation stored energy associated with high-density dislocations obtained in sub-grains should be the main reason for decrease of the starting temperature of abnormal grain growth. In addition, an increase in Nb content can also improve the dissolution rate of coarse (Nb,Mo)(C,N) particles within the grain, especially the dissolution of Nb-rich precipitates at grain boundaries, which can weaken the grain boundary pinning force and easily cause abnormal grain growth. It seems to be related to the raising of the precipitation temperature of Laves phase and (Nb,Mo)(C,N) precipitates induced by the increase in Nb content. [ABSTRACT FROM AUTHOR]

The microstructure evolution and grain growth kinetics of the fine-grained extruded Mg-Nd-Zn-Zr alloy were investigated by holding the extruded plate for a wide range of time in the temperature range of 470 °C to 530 °C. By observing the optical micrographs, it was found that the material showed abnormal grain growth at the experimental condition of 470 °C × 24 h, and the time point of abnormal grain growth appeared significantly earlier with the increase in the experimental temperature. The evaluation of the second phase content within the alloy indicates that the presence of the second phase contributes to the microstructural stability of the Mg-Nd-Zn-Zr alloy. However, the slow coarsening/dissolution of the second phase is an important cause of abnormal grain growth. Based on the experimental data, the isothermal grain growth kinetic models of the fine-grained extruded Mg-Nd-Zn-Zr alloy were developed based on the Sellars model. The grain growth exponent was in the range of 5.5–8 and decreased gradually with the increase in the experimental temperature. The grain growth activation energy is approximately 150.00 kJ/mol, which is close to the bulk diffusion activation energy of magnesium, indicating that the grain growth is controlled by lattice diffusion. By energy spectrometry (EDS), the compositional changes of the second phase within this alloy at 500 °C were investigated. [ABSTRACT FROM AUTHOR]

The causes of rapid growth of coarse grains under secondary recrystallization are analyzed. According to the available experimental data the rapidly migrating boundaries of such grains are retarded by disperse particles less than by other particles. Numerical simulation shows that such behavior of coarse grains is responsible for formation of a microstructure typical for secondary recrystallization. The results obtained are important for creation and advancement of the technology of metallic and ceramic materials, the properties of which are affected by appearance and development of secondary recrystallization. [ABSTRACT FROM AUTHOR]

This study investigated the causes of microstructural changes and the resultant electrical properties according to the sintering temperature of 0.96(K0.46−xNa0.54−x)Nb0.95Sb0.05O3-0.04Bi0.5(Na0.82K0.18)0.5ZrO3 lead-free ceramics by analyzing the correlation between vacancy concentrations and 2D nucleation. When sintered for 4 h, no grain growth occurred for the x = 0.000 composition over a wide temperature range, demonstrating that the existence of initial vacancies is essential for grain growth. As x increased, that is, as the vacancy concentration increased, the critical driving force (ΔGC) for 2D nucleation decreased, and abnormal grain growth was promoted. The number and size of these abnormal grains increased as the sintering temperature increased, but at sintering temperatures above 1100 °C, they decreased again owing to a large drop in ΔGC. The x = 0.005 specimen sintered at 1085 °C exhibited excellent piezoelectric properties of d33 = 498 pC/N and kp = 0.45 due to the large number of large abnormal grains with an 83% tetragonal phase fraction. The x = 0.000 specimen sintered at 1130 °C with suppressed grain growth exhibited good energy storage properties because of its very high relative density and small grain size of 300 to 400 nm. [ABSTRACT FROM AUTHOR]

Despite decades of research, there is no agreement on the mechanisms contributing to the abnormal growth of {110}〈001〉 oriented Goss grains in Fe-Si electrical steels. Recently, it was shown that preferential dissolution of second-phase particles on the grain boundaries (GBs) near Goss grains leads to depinning and consequent abnormal growth. Careful analysis of microstructures from experimental results in Fe-Si steels and other materials indicates the presence of curved GBs surrounding the abnormally growing grain. We use a higher order phase field model to study the role of selective particle dissolution and GB energy differences on abnormal grain growth and concomitant morphology. The simulation results indicate that low-energy GBs around abnormal grains are necessary to develop the curved GB morphology while AGG primarily occurs by preferential dissolution of the particles. The low energy GBs significantly enhance the kinetics of abnormal growth, consistent with experimental results reported in the literature. [ABSTRACT FROM AUTHOR]

Owing to hot cracking, printing aerospace grade AA7050 is challenging via fusion-based additive manufacturing. Using a deformation-based additive process, here we show that forging-like tensile properties are achieved in additively manufactured AA7050 without chemical modification for the first time (excluding lubricant on feed-rod surfaces) — YS: 430 MPa; UTS: 491 MPa; elongation: 11.2% with T74 temper. [ABSTRACT FROM AUTHOR]

Large-size grain is one of the effective parameters to determine the superelasticity of Cu-based alloys. In this study, the effects of Ni addition on abnormal grain growth (AGG) and microstructure evolution of CuAlMnCoNi alloys are systematically investigated. The activation energy and driving force of grain boundary (GB) migration during AGG are evaluated. The results reveal that Ni significantly promotes AGG. Average grain size reaches 6.0 cm after three cyclic heat treatments (CHTs) in a CuAlMnCoNi alloy containing 2 at.% Ni. A maximum superelastic strain of 11.8 % can be obtained at 15 % applied strain. The addition of 2 at.% Ni increases the solvus temperature of the α-phase to about 818 °C and raises α-phase volume fraction at phase equilibrium. The precipitation of α-phase with high volume fraction causes high number density of dislocations. The misorientation angle of subgrain is increased by the addition of Ni, contributing to the AGG in CuAlMnCoNi alloys. The addition of Ni reduces the activation energy of GB migration and increases the GB migration driving force. [ABSTRACT FROM AUTHOR]

In general, single crystal shape memory alloys exhibit superior shape memory effect and superelasticity when compared to their polycrystalline counterparts. However, it is challenging and costly to prepare a single crystal in traditional ways, such as the Czochralski method and directional solidification technique. Recently, cyclic heat treatment (CHT) has emerged as a facile and cost-effective method to fabricate single crystal by inducing abnormal grain growth. In the present work, we aimed to fabricate Fe-Mn-Al-Cu single crystals utilizing the CHT technique. Single crystal Fe-Mn-Al-Cu shape memory alloys were successfully prepared, and the effect of CHT parameters on abnormal grain growth was investigated. It was revealed that increasing the cooling rate resulted in a non-monotonic response in the maximum grain size, which initially increased and was followed by a subsequent decrease. This behavior was attributed to the subgrain refinement, increase in subgrain misorientation angles, and the narrowing of the low density zones (LDZs) of subgrains. Decreasing the lower temperature of CHT caused similar trends in maximum grain size, due to the increase in subgrain misorientation angle and the expansion of the LDZs. Extending the holding time at the lower temperature of CHT had minimal impact on grain size. Increasing the heating rate of CHT resulted in a reduction in the maximum grain size because of the narrowing of the LDZs. Moreover, the addition of 2 wt% Cu led to a reduction of the maximum grain size, attributing to the decreased solvus temperature of the γ phase as a result of Cu addition. Consequently, the γ phase and subgrains were refined, and the LDZs were narrowed. • Cyclic heat treatment promotes abnormal grain growth mainly controlled by misorientation angle and the low density zone. • The cooling rate and the lower temperature of cyclic heat treatment are key factors for abnormal grain growth; the heating rate is secondary. • Increasing Cu content in Fe-Mn-Al-Cu reduces the width of the low density zone and inhibits abnormal grain growth. [ABSTRACT FROM AUTHOR]

[Display omitted] • A phase field method was employed to study the growth behavior of the large grains. • The growth rate of large grains slowed down as the initial grain size distribution widened. • Growth rate of a large grain was proportional to the number of surrounding grains. • This will be an important guide to obtain the target grain microstructure for the ferroelectric ceramics. The uniform initial particle size distribution was considered to be an important condition for the preparation of dense ceramics. With the rapid development of templated grain growth method, it is necessary to add large template particles into small matrix to promote the epitaxial growth of grains. However, abnormal grain growth will inevitably occur in this process. In this work, a phase field method was employed to study the growth behavior of the large grains into the small matrix. The effect of initial particle size distribution on the grain growth kinetics was investigated. Our simulations revealed that the growth rate of large grains slowed down as the initial grain size distribution widened. Regulating the initial grain size distribution will be an effective way to control abnormal growth of grain. It was found that the growth rate of a large grain was proportional to the number of surrounding grains. These results have implications for the design of the functional ceramics with a target grain microstructure. [ABSTRACT FROM AUTHOR]

Understanding the role of sintering aids during microstructure evolution is critical to the manufacture of densified SiC fibers. A variety of TEM characterization techniques are combined to investigate grain growth behavior in iron-doped SiC fibers. Ultra-large SiC grains in micron size, as the self-assembly of nano sub-grains into a similar orientation, were consistently discovered at the surface and indicative of abnormal grain growth. The growth front consisted of polycrystalline nanograins wetted by iron-rich particles, where several sub-grains were found to unify their (111) planes with a misorientation angle less than 10°, indicating grain rotation at the growth front. It is proposed that iron-rich particles form a quasi-liquid interfacial phase during sintering, which facilitates coherent attachment of grains and results in fast grain growth using neighboring irregular-shaped nanograins as building blocks. The imperfect ordered coalescence of nanograins introduces structural heterogeneities, including low angle grain boundaries and porosities. [ABSTRACT FROM AUTHOR]

Recent progress in the kinetics of grain coarsening and abnormal grain growth (AGG) is presented in this overview article. The factors affecting the kinetics of grain growth is reviewed with the emphasis on the recent findings on the solute drag and Zener pinning effects as well as the special case of duplex alloys, where the latter is discussed for the behavior of dual-phase steels during intercritical annealing. The common isothermal kinetics models for grain growth are listed, which is followed by the critical discussion on the simplifications and the commonly used methods for the determination of grain growth exponent (n) and activation energy (Q). The obtained values of n and Q for several classes of important engineering alloys such as microalloyed steels, stainless steels, magnesium alloys, aluminum alloys, titanium alloys, and high-entropy alloys are summarized with the discussion on the obtained values of kinetics parameters and their deviation from the theoretical expectations. Finally, the factors leading to AGG (such as the coarsening and dissolution of pinning particles and the crystallographic texture), the proposed mechanisms (such as the solid-state wetting and the grain boundary faceting/defaceting phenomena), and the kinetics of AGG (based on the empirical power law and the similarity of AGG to primary recrystallization in the form of secondary recrystallization) are reviewed. This overview can shed light on the understanding of grain growth and its effects. [ABSTRACT FROM AUTHOR]

ZnO based varistors added with minor content of Bi 2 O 3 , Sb 2 O 3 , Co 2 O 3 , SiO 2 , MnO 2 et al. with high voltage gradient, excellent mechanical and thermal properties were fabricated by Ga 2 O 3 doping and using raw ZnO nanoparticles. The compositions and microstructure of the varistors, as well as their electrical, mechanical, and thermal properties were investigated via XRD, XPS, SEM, E-J, C–V, mechanical, and thermal expansion measurements. Also, the mechanism of Ga 2 O 3 addition on the electrical and mechanical properties of the varistors was discussed in detail. Results showed that the added Ga 2 O 3 preferentially occupied the lattice position of ZnO crystal through the formation of a substitutional solid solution (Donor doping), it then occupied the void position through the formation of an interstitial solid solution (Acceptor doping), in which the residual Ga 2 O 3 existed in the grain boundary and served as inversion boundaries. The formation of the substitutional and interstitial solid solutions helped to improve the electrical properties, when Ga 2 O 3 content was 0.40 mol%, values of E 1mA , α, and K were 1235.00 V mm−1, 46.0, and 1.37, respectively, being due to the small particle size and the related content of donor, acceptor and grain boundary in ZnO grain; The increased content of inversion boundaries stimulated the abnormal growth of ZnO grain, and the formed plate-like grain helped to improve the mechanical properties and thermal expansion coefficient of the varistors, values of σ f , E f , and K IC could reach 147.43 MPa, 213.61 GPa and 2.05 MPa m1/2, showing improvements of 25.29%, 47.67%, and 38.51%, respectively, compared with those of ZnO based varistors without Ga 2 O 3. [ABSTRACT FROM AUTHOR]

The grains at the longitudinal weld in porthole extrusion profiles are more prone to abnormal growth during solid solution treatment, leading to a decline in mechanical properties. To improve the microstructure and enhance the mechanical properties at the longitudinal weld in profile, the precipitation behavior of the dispersoid in 2195 Al-Li alloy with different homogenization heating rates was studied. The impact of dispersoid morphology and distribution on grain structure and mechanical properties at the longitudinal weld was elucidated. The results indicated that the ramp heating homogenization treatment significantly promoted the precipitation of fine Al 3 Zr dispersoids, which effectively hindered the abnormal growth of grains within the low plastic deformation zone at the longitudinal weld and reduced the width of the coarse grain zone. The tensile strength and elongation of the ramp heating homogenized (RH) profiles after water quenching and aging were higher than those of the fast heating homogenized (FH) profiles. It was also found that the incoherent Al 3 Zr dispersoid within the recrystallized grains of the profile was prone to induce the precipitation of quench-induced phases. Due to the reduction of recrystallization fraction at the longitudinal weld in RH profile, the precipitation of quench-induced phases was inhibited. The strength of the air-quenched and aged RH profile was higher than that of the FH profile. It can be concluded that the extrusion process using the RH billet can improve the microstructure and mechanical properties at the longitudinal weld in 2195 Al-Li alloy profile. • Ramp heating homogenization treatment can promote the precipitation of Al3Zr. • Al3Zr reduces the recrystallization fraction and the width of the coarse grain zone. • Al3Zr inhibits abnormal grain growth within low plastic deformation zone. • RH billet optimizes microstructure, mechanical properties and quenching sensitivity. [ABSTRACT FROM AUTHOR]

The longitudinal weld of extrusion profiles will form dramatic abnormal grain growth (AGG) during solution treatment, leading to performance deterioration. A modified heat treatment method, i.e., an intermediate annealing treatment (IAT) was inserted into standard T6 treatment was proposed in this paper to alleviate AGG of longitudinal weld. 2196 Al–Cu–Li profiles with longitudinal weld were subjected to IAT with different parameters, and the grain growth behavior and microstructure evolution of them were studied. The processing window of IAT was determined as 450 °C/0–60 h and 475 °C/0–6 h and some parameters in between, the reasonable IAT temperature is below solution treatment about 50 °C. IAT at 450 °C/24 h is the most noticeable parameter for the suppression of AGG, a narrow AGG area formed during this IAT, and the fine grains surrounded AGG area exhibited continuous uniform coarsening, leading to releasing of sub-grain boundary energy and decreasing of driving force for AGG by 50%. Besides, many secondary phases formed during IAT and work as pinning particles, hence the width of AGG area in this sample reduced 90% compared to that of T6 samples, and the tensile strength increased about 20 MPa and the elongation increased by 42%. • IAT as a useful suppression method for AGG at longtidunal weld in 2196 Al–Cu–Li profiles was proposed. • The process window of IAT was determined. • The influence of the grain size and sub-grain structures on driving force for AGG was clarified. • The mechanism of IAT can suppress the AGG at longtidunal weld was illustrated. [ABSTRACT FROM AUTHOR]

This study utilized the irregular Sm(Co 0.69 Fe 0.22 Cu 0.07 Zr 0.02) 8.1 alloy powder as the primary material, combining the solid/liquid interface de-wetting effect and abnormal grain growth method for preparing the 1:7-type SmCo spherical single crystal powder. Through aging heat treatment, the anisotropic 2:17-type SmCo alloy spherical permanent magnetic powder with size distribution of 30–130 μm was successfully obtained. The study explored the spheroidization mechanism and single crystal growth rule of Sm(Co 0.69 Fe 0.22 Cu 0.07 Zr 0.02) 8.1 alloy powder, as well as the impact of solution-aging magnetic hardening treatment on the permanent magnet properties. The optimized permanent magnetic properties of the resulting 2:17-type SmCo alloy spherical powder were coercivity H ic = 1244 kA/m, and maximum magnetic energy product (BH) max = 224.5 kJ/m3 at room temperature. The anisotropic 2:17-type SmCo alloy spherical magnetic powder prepared using this method exhibits significant potential applications in the production of bonded magnets. [Display omitted] [ABSTRACT FROM AUTHOR]

Cold rolled grain oriented steel is used in transformer cores due to its superior magnetic properties. Large Goss oriented grains develop after the final secondary recrystallization provide low hysteresis loss. The present study represents the development of Goss orientation after each processing stage of Fe-3.78 wt% Si steel with the help of electron backscatter diffraction and x-ray diffraction techniques. The Goss oriented grains developed during hot rolling and hot band annealing did not remain stable in cold rolling. On the other hand, shear bands developed inside {111}<112> component of γ-fiber texture during cold rolling. Partial recrystallization of the cold rolled sheet revealed that Goss oriented grains started evolving inside the shear bands of {111}<112> oriented grains. Intermediate annealing between cold rolling passes was found to be not essential to achieve Goss orientation in primary recrystallization. The optimum primary recrystallization temperature was in between 923 and 948 K where a significant amount of Goss oriented grains were present. Further, secondary recrystallization was attempted at different temperatures between 1173 and 1473 K. Grain boundary curvature of Goss oriented grains and all other grains after both primary and secondary recrystallization was studied. Despite the percentage of convex boundaries surrounding Goss oriented grains was found slightly higher than that around other grains, it was insufficient to cause abnormal grain growth. • Goss texture evolution was critically examined after each processing stage in 3.78wt.% Si cold rolled grain oriented steel. • Goss oriented grains formed during hot rolling and hot band annealing become unstable on subsequent cold rolling process. • Shear bands formed inside {111}<112> oriented grains during cold rolling were the new source of Goss orientation. • Intermediate annealing between cold rolling passes is not essential to achieve Goss grains in primary recrystallization. • The grain boundary character alone was insufficient to explain the non-occurrence of abnormal grain growth of Goss grains. [ABSTRACT FROM AUTHOR]

Copper thin films are frequently utilized as microelectronic interconnects. Inducing abnormal grain growth (AGG) may result in reduced electrical resistivity of copper thin films. However, an in-depth understanding of AGG mechanism and quantitative simulation of microstructure evolution during AGG in copper thin films are still missing, prohibiting the regulation and even design of AGG process. In this paper, a multi-order-parameter phase-field (MOP-PF) model coupled with elastic mechanics under a finite element framework was first developed and applied to study the AGG mechanism in copper thin films. It was found that both elastic and grain boundary anisotropies can induce AGG, but elastic anisotropy dominates the evolution of individual grains. Subsequently, a quantitative simulation of microstructure evolution/kinetics during AGG in copper thin films was achieved by inputting the accurate materials parameters from theoretical/experimental data. A further combination with the Mayadas-Shatzkes model led to a quantitative prediction of the evolution of electrical resistivities, from which several feasible strategies were proposed for preparing high-performance copper thin films with reduced electrical resistivities. Furthermore, it is anticipated that the presently developed framework should be generally applicable for quantitative phase-field simulation of grain growth in bulk materials/films. [Display omitted] [ABSTRACT FROM AUTHOR]

The internal ion source of the Advanced Molecular Image Technologies (AMIT) superconducting cyclotron uses cathodes made of pure tantalum to generate high energy H− ion beams for the production of isotopes for positron emission tomography. During service, the cathodes are impacted by high-energy ions from the plasma. The resulting erosion creates craters that reduce the current density of the extracted beam. The cathodes eventually need to be replaced when the ion source can no longer be activated. This research explores the possibility of repairing the tantalum cathodes used in the AMIT cyclotron through laser metal deposition additive manufacturing. The damaged parts were first characterised by 3D imaging, scanning electron microscopy, and Vickers microhardness to understand the damage mechanisms occurring during service and quantify the extent of the damage. Different repair strategies were then tested employing both high-purity tantalum wire and powder feedstocks and the properties of the reconditioned electrodes were determined. The ability of laser metal deposition to restore the damaged cathodes for use in the AMIT cyclotron has been demonstrated. [Display omitted] • Tantalum cathodes used in superconducting cyclotron are damaged by ion impact. • Damage involves crater formation, localised melting and abnormal grain growth. • Wire- and powder-based laser metal deposition repair strategies were developed. • Damaged cathodes were reconditioned for use in the superconducting cyclotron. [ABSTRACT FROM AUTHOR]

An anomalous feature in polycrystalline grain growth in metals and ceramics is the rapid abnormal growth of a few grains relative to the surrounding matrix grains. In certain systems, this phenomenon is reported to be associated with the presence of first order phase transitions in the grain boundaries often referred to as complexion transitions. The fundamental question of how the growth advantage of abnormally growing grains persists in this context is not yet well understood. We present a thermodynamically consistent mechanism by which abnormal grain growth may occur. The presence of two complexion transitioned boundaries at a triple junction provides a driving force for partial wetting at the triple junction leading to the formation of a quadruple junction. The subsequent dissociation of the quadruple junction into two partial wetting triple junctions favors the persistence of abnormal grain growth. We incorporate this dissociation process into a multi-order parameter phase field model and demonstrate the occurrence of abnormal grain growth without the need for mobility advantage or additional driving forces. The results from simulations of abnormal grain growth capture experimentally observed microstructural features such as peninsular and island grains. Through a systematic study we show that the initial fraction of complexion boundaries plays a significant role in abnormal grain growth and that maximum abnormal grain growth is observed when the fraction of complexion boundaries is less than about 2%. [Display omitted] [ABSTRACT FROM AUTHOR]

The physical mechanisms that lead to the abnormal growth of Goss-oriented grains in grain-oriented electrical steel (GOES) are still not well understood, despite almost a century of research. The present paper reviews the existing hypotheses on the formation of Goss-oriented grains by abnormal grain growth and provides more insights into the underlying mechanism for Goss texture formation by proposing a new hypothesis named "Dislocation-assisted particle dissolution". Abnormally grown Goss-oriented grains in fully-processed industrial GOES samples are shown to contain a fine network of internal subgrain boundaries with very low angle (0.03° - 0.18°) each consisting of regular arrays of dislocations. These subgrain boundaries form a branched ray-like pattern from the Goss grain center towards its perimeter, i.e. they seem to have evolved with the grain during its growth. Structural and compositional analysis of these dislocations by controlled electron channelling contrast imaging (cECCI) and atom probe tomography (APT) show that these dislocations are enriched with solutes such as Sn, Cu, C, and more importantly, with Al, N and Mn, which all build the composition of the inhibitor particles that assist the abnormal growth of Goss-oriented grains. Additionally, molecular statics (MS) calculations are employed to compare the segregation tendencies of Al atoms on dislocations and on Σ9 boundaries. It is found that Al prefers to segregate to dislocations rather than to the boundaries. The origin and the role of subgrain boundaries are discussed based on the experimental and simulation results. The results indicate that, after the dissolution of inhibitors along the grain boundaries, solutes are absorbed by the subgrain dislocations. As a result, grain boundaries surrounding Goss grains become less decorated by solutes and precipitates and more mobile compared to the boundaries of matrix grains. Schematic showing the proposed dislocation-assisted particle dissolution (DAPD) mechanism. The origin and survival of the subgrain dislocations, as well as their role on the abnormal growth of Goss grains are shown with the corresponding production route of Grain-oriented electrical steels. Note that none of the images and symbols is meant to be in the correct length scale. Square symbols indicated AlN precipitates, circle symbols individual atoms. [Display omitted] [ABSTRACT FROM AUTHOR]

The abnormal grain growth occurs in 2219 aluminum alloy friction stir welds during solution treatment, which results in the deteriorating mechanical properties of the weld. In this paper, a novel intermediate heat treatment process after friction-stir welding, including rapid heating and high-temperature treatment at 560 °C and annealing treatments, was proposed to suppress abnormal grain growth in the weld during subsequent solution treatment. The effect of the intermediate heat treatment process on the microstructure and mechanical properties of the weld was investigated and analyzed. The results show that the grains in the nugget zone grow continuously in a short time at a temperature higher than the eutectic line. There is no abnormal grain growth in most regions of the weld treated with the intermediate heat treatment after solution treatment. Compared with tailor-welded blanks directly with solution treatment, the elongation of the tailor-welded blanks treated with the intermediate heat treatment and solution treatment increases from 13.5% to 20% because of the improvement of weld strength. The increase in mechanical properties is more significant after artificial aging treatment. Because of the disappearance of the pinning effect of particles at high-temperature treatment, abnormal grain growth induced by particles cannot occur. The grains grow normally, improving their ability to resist abnormal grain growth during solution treatment. Fine grains result in a more uniform distribution of deformation in the solution-treated weld. Furthermore, it is more difficult for the particles at the grain boundary to cause crack propagation along the grain boundary after artificial aging treatment. This work helps guide how to suppress abnormal grain growth in the weld and further deepen the understanding of the phenomenon. [ABSTRACT FROM AUTHOR]

Orientation related grain growth stimuli during primary and secondary recrystallization of the metal matrix in laminated metal/non-metal composites demonstrate unique effect on orientation evolution but has rarely been investigated. In this work, the recrystallization and grain growth of Cu in a graphene nanosheets (GNSs) reinforced laminated Cu matrix composite during sintering was thoroughly investigated. The microstructure, texture and lattice strain evolution of the Cu/GNS composite was examined referenced to the Cu stack without GNSs by ex-situ and in-situ orientation characterization techniques (SEM-EBSD, neutron diffraction and synchrotron radiation) from mesoscale to macroscopic scale. The results evidenced that a strong Cube orientation was produced in the Cu/GNS composite instead of the individual non-Cube orientations in the pure Cu stack without GNSs. Detailed strain-state analysis of the Cu foils in the Cu/GNS composite revealed that the anisotropic expansion behavior of the GNS that is incompatible with that of the Cu foils imposed multiple elastic constraints to the foils during the sintering process, resulting in a biaxial isostrain state in the surface layers and a uniaxial compressive strain state in the central layer of each Cu foil. The elastic anisotropy of Cu favors the growth of the Cube oriented grains to minimize the total strain energy. This work clarified the thermal strain induced abnormal grain growth of selected orientations. The mechanism revealed can be useful for analysing abnormal grain growth in elastically strained materials and can also be applied to fabrication process for texturization or even monocrystallization. Image, graphical abstract [ABSTRACT FROM AUTHOR]

• A combined theoretical and experimental study was performed on Fe doped SrTiO3 to understand the effects of point defects to explain abnormal grain growth in ionic solids with an emphasis on the structural and electrochemical character of the grain boundaries. • Effects of electrochemical drag as imposed by the interfacially accumulated charged defects result in two moving grain boundary types, highly mobile and immobile interfaces generate an abnormal grain growth microstructure. • Three grain size populations are statistically identified: (i) the normal grain population; (ii) the abnormal, large grain population formed due to high mobile grain boundaries; and (iii) an electrochemically persistent small grain size population that is stabilized due to electrostatic repulsion of the facing charged interfaces. A combined theoretical and experimental analysis was performed to understand the effects of extrinsic ionic species and point defects on the microstructural evolution of ionic polycrystalline ceramics. The model naturally incorporates the effects of drag on grain boundary motion as imposed by the interfacially accumulated charged defects for Fe doped SrTiO 3. Two moving grain boundary types, i.e., highly mobile and immobile interfaces result in abnormal grain growth. Fast moving grain boundaries leave a residual charge network behind in the interior of the grains in the form of bands of Fe Ti ′ , which in turn electrostatically attract oxygen vacancies, thus enhancing the local ionic conductivity of the polycrystal. Three grain size populations are statistically identified: (a) a normal grain population, as one would expect would happen in classical systems; (b) an abnormal , large grain population, which corresponds to those grains whose spatial extent is statistically greater than the average; and (c) an electrochemically persistent small grain size population that is stabilized by the grain boundary electrical energy. The study herein sets the stage to assess the effects of externally applied fields such as temperature, electromagnetic fields, stresses, and chemical stimuli to develop textured, oriented microstructures as tailored for a wide range of applications. [ABSTRACT FROM AUTHOR]

The effect of Al content on the abnormal grain growth of Fe–Mn–Al–Ni shape memory alloy is investigated in comparison with the previously reported Fe–Mn–Al–Ni–Ti alloy. Microstructural observations revealed that compared with 1.5Ti, 17Al (adding 2 at.% Al to the conventional Fe–Mn–Al–Ni) showed the potential to grow into a large single crystal. The obtained results indicate that the size control of the second phase, which can be achieved not only by introducing Ti, but rather universally by stabilizing BCC phase, and the resultant subgrain structure are vital for abnormal grain growth. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Summary: A novel heat stage, recently developed for use within the Scanning Electron Microscope, has facilitated Secondary Electron imaging at temperatures up to 850°C. This paper demonstrates one of the applications of in‐situ elevated temperature Scanning Electron Microscope imaging: observation and quantification of grain growth within the austenitic region of carbon steels. The resulting Secondary Electron data have used the technique of thermal etching to capture possible 'abnormal grain growth' in the austenitic region. Previous ex‐situ and post‐heating results from carbon steels indicate normal, non‐linear grain growth. Therefore, this new dataset provides greater insight into the heat treatment of steels. From comparison of the in‐situ data with the overall grain growth, measured ex‐situ, it is further concluded that abnormal grain growth is representative of the growth at temperature. Thus, the heating and cooling parts of the heat treatment are likely to account for the non‐linearity previously documented in ex‐situ results and, hence, the range of powers recorded when fitting power law models for steel grain growth. The ability of data derived from in‐situ thermal etching to represent the microstructure of the entire surface and the bulk material is also considered. Lay Description: A novel heating stage has recently been developed for use within the Scanning Electron Microscope (SEM); an instrument that uses electrons to image specimen surfaces at very high magnifications. The development of the heating stage has facilitated imaging at temperatures up to 850°C of the structure and topographic features of metals using two different detectors. This study focusses on observation and quantification of grain growth in steels at temperatures of 800 C. In Materials Science, grains refer to crystals of varying, randomly distributed, small sizes that together make up a solid metal. The temperature of 800 C is used as it is the desired temperature to heat treat steels in order to produce more favourable physical properties. It is also the temperature above which the material undergoes a phase change; phase change is a transition where the atoms rearrange from one order within a grain to another. In the case of steel, at room temperature atoms will be in what is called a ferrite phase (one order) but at 800 C, they will be in a different order within the grains, known as the austenite phase. Hence, the uniqueness of this dataset as the grain growth captured is in the high temperature steel phase of austenite. The steel samples used are made up of 0.4% Carbon, 99% iron and some manganese and other trace elements. The resulting data have, for the first time, shown so called 'abnormal grain growth' which is represented by a linear relationship between grain size and time. Abnormal grain growth is also observed in the images where it can be seen how larger grains grow at a high rate at the expense of smaller ones. Previous data taken after cooling of steels indicate normal non‐linear grain growth. Therefore, it is reasonable to suggest, this new dataset provides greater insight into the heat treatment processing of steels, demonstrating that they are potentially more complex than previously thought. [ABSTRACT FROM AUTHOR]

Secondary-phase particles are routinely dispersed in metals and ceramics to prevent grain growth and take full advantage of the small grain size in the mechanical properties of polycrystals. Somewhat surprisingly, the preferential or abnormal growth of a few grains is observed in particle-containing systems at relatively high temperature, which will limit the lifetime of the material. The origins and mechanisms of particle-assisted abnormal grain growth are widely contested. Here, we employ integrated three-dimensional X-ray imaging to throw new light on the complex interactions between grain boundaries and particles in an Al–Cu alloy as a model system. We observe abnormal grain growth in the presence of a highly non-random distribution of particles. The incipient grain size is set by the local distribution of particles such that the larger grains come from particle-poor regions. Subsequently, grains with a size advantage may "run away" from the grain size distribution, in agreement with predictions from an analytical model that takes into account the competing capillary and particle pinning pressures. Image, graphical abstract [ABSTRACT FROM AUTHOR]

In this study, the low-cost production of Cu-Al-Mn-Fe shape memory alloy single crystals exceeding 46 mm by abnormal grain growth was realized only through annealing their cast alloys. The results show that the misorientation formed during annealing may be responsible for such abnormal grain growth process. It was confirmed that this misorientation resulted from the dissolution of bcc β(FeAl) nanoparticles during heat treatment at a sufficiently temperature of approximately 1173 K. The rate of migration of the abnormal grain boundary was experimentally measured to be approximately 9.3 × 10-5 m s-1 within 2 min of the commencement of abnormal grain growth. Additionally, the range of composition of the alloys that can lead to abnormal grain growth was determined. When the Cu-13.0Al-6.5Mn-3.2Fe single crystal close to the [100] direction was deformed to a pre-strain of 12%, full shape recovery happened without any residual strain. At that time, the superelastic strain was approximately 9%. Such a superelastic characteristic remained nearly constant over 50 cycles, showing excellent fatigue resistance. The superelastic properties of the present Cu-13.0Al-6.5Mn-3.2Fe single crystal are compared to those of commercial Ni-Ti-based shape memory alloys. Therefore, it can be considered as a new kind of superelastic material having practical applications. The obtained results should be of great significance in the development of Cu-based shape memory alloys. Furthermore, it is expected that a similar microstructure can be designed for the production of more metallic single crystals. Image 1 • Abnormal grain growth happens when annealing Cu-Al-Mn-Fe cast alloys. • Large shape memory single crystal up to 46 mm in length is obtained. • The dissolution of bcc β(FeAl) nanoparticles results in the misorientation. • Single crystal exhibits excellent superelasticity of 12% and fatigue resistance. [ABSTRACT FROM AUTHOR]

Herein, a liquid‐assisted grain growth (LGG) mechanism for a vacuum‐processed Cu2ZnSn(S1−xSex)4 (CZTSSe) absorber that is enabled by the presence of a liquid phase containing predominantly Cu, Sn, and Se (L‐CTSe) is suggested to explain the large grain size of up to ≈6 µm obtained at low temperatures, such as 480 °C. In this system, LGG plays a key role in achieving a large grain CZTSSe absorber, but the residual L‐CTSe, a key factor in LGG, deteriorates the device performance. L‐CTSe residue can possibly remain when using metal precursors for reasons such as local composition nonuniformity due to the agglomeration of Cu–Sn alloys, uncontrolled Zn volatilization. It is expected that CZTSSe cells with L‐CTSe residues have lower efficiency and fill factor than CZTSSe cells without L‐CTSe due to the role of L‐CTSe as a shunt path and compositional misfit. These tendencies are observed in the statistical results. Thus, when synthesizing CZTSSe using a metal precursor in a two‐step process, it is considered important to design the precursors to remove unwanted L‐CTSe residues and optimization of composition. [ABSTRACT FROM AUTHOR]

In this work, we present a physically-parameterized microstructure evolution model for the Yttria-doped alumina system. Yttria-doped alumina is a well-known ceramic system which undergoes first-order phase-like transitions at grain boundaries, which can radically alter interface properties. The change in interfacial properties in turn can radically change microstructure outcomes during processing, including the induction of abnormal grain growth modes. In this work, we develop a simulation that evolves alumina microstructure as a function of yttria concentration and temperature. In the window studied, we achieve strong agreement with reviewed experimental results in identifying the windows for large grains, small grains, abnormal grain growth, and complexion transition kinetics (as measured by JMAK analysis). We then apply the model to study and demonstrate how the possible inclusion of second-phase particles or uneven solute distribution profiles will impact microstructure evolution. It is found that particles do not significantly affect abnormal grain growth in the window studied (but do lead to reduced grain size through pinning effects). It is found that even modest amounts of solute inhomogeneity will result in substantial changes in microstructure outcomes, frequently leading to clusters of abnormal grains. This model largely corroborates the expectations and hypotheses made from recent experimental studies in oxide-doped alumina systems. Further, it is found that there exists a peak transition fraction for the system at which abnormal grain size tends to be maximized. Image, graphical abstract [ABSTRACT FROM AUTHOR]

A comparative study between the ultrasonic attenuation and the nonlinearity is presented for the characterisation of microstructure in large dimension forgings. Results are provided for two austenitic stainless steel forgings of AISI type 304L with a diameter 200 mm, where microscopic observations reveal abnormal grain growth near the surface of one of the forgings. Frequency dependence of the nonlinearity parameter is used to discern variations in grain size in these forgings more precisely than attenuation measurements. The distribution of grain size is shown to have a significant influence on the nonlinearity parameter. Relative changes in the nonlinearity parameter with applied frequency were correlative with the microstructural variations in both the forgings. [ABSTRACT FROM AUTHOR]

We demonstrate the sensitivity of complexion time-temperature-transformation (TTT)-diagrams to composition and grain size in Eu-doped MgAl 2 O 4. 100 ppm and 500 ppm Eu-doped MgAl 2 O 4 undergo the same complexion transition, which causes abnormal grain growth, but exhibit different nucleation and grain growth rates. The Eu content per grain boundary area (Eu/GBA) was calculated for various heat treatments using a simple model based on average grain size. Despite their differences, a common Eu/GBA is calculated at the onset of abnormal grain growth. This common grain boundary excess has important implications for complexion TTT-diagrams and provides a new metric for predicting abnormal grain growth. Image, graphical abstract [ABSTRACT FROM AUTHOR]

We investigate the effect of direct electric current (DC) on grain growth in 100 nm thick iron-carbon films with carbon concentrations between 0.7 to 4.4 at%. The application of DC-current during annealing at 550°C confirms the expected transport of carbon in the direction of the electric current and the unexpected formation of elongated, abnormally large carbide and ferrite grains along the current direction in the carbon-rich regions. The formation of elongated grains is explained by electromigration-induced carbon flux divergences that result from the carbide precipitates. This presents a possible scenario for controlling microstructure evolution in iron by using DC electric currents. Changes for alternating current (AC) pulses had been observed before. Image, graphical abstract [ABSTRACT FROM AUTHOR]

The first Si-Fe electrical steel was produced in 1905, and the grain-oriented steel was discovered in 1930 after Goss demonstrated how optimal combinations of heat treatment and cold rolling could produce a texture giving Si-Fe strip good magnetic properties when magnetised along its rolling direction. This technology has reduced the power loss in transformers greatly and remains the basis of the manufacturing process today. Since then many postulations reported on the mechanism on abnormal grain growth (AGG) which is the key for Si-Fe superior magnetic properties, however, none have provided a concrete understanding of this phenomenon. Here, we established and demonstrated a new theory that underlines the fundamental mechanistic approach of abnormal grain growth in 3% Si-Fe steel. It is demonstrated, that the external heat flux direction applied during annealing and Si atom positions in the solid solution disordered α-Fe cube unit cell that cause lattice distortions and BCC symmetry reduction are the most influential factors in the early stage of Goss AGG than what was previously thought to be dislocation related stored energy, grain boundary characteristics and grain size/orientation advantages. Image, graphical abstract [ABSTRACT FROM AUTHOR]

The sinter-bonding of Fe-36 wt.% Ni powder to WC-Co, compacted under a vacuum, was performed at 1300 °C, for 2, 8 and 16 h. Three different holding times were studied during sample preparation. The results indicated that the compacted Fe-36 wt.% Ni/WC-Co sinter-bonded powders yielded a consolidated interface comprised primarily of hexagonal α-WC, cubic Fe 0.64 Ni 0.36 and the presence of the Co 3 W 3 complex, whose content increased as a function of holding time. Prolonged holding times promote bonding of the WC-Co/Fe–Ni component. However, excessive holding times result in significant contractions and failure by cracking. Furthermore, with increased holding time, grain sizes increased from the original size of 80 nm–390, 460, and 480 nm, when subjected to sintering temperatures of 1300 °C, for 2, 8 and 16 h, respectively. Grain growth occurs through the WC/Co/WC interfaces, not only in the liquid phase, but also in the solid state, at lower temperatures. Actual sintering temperatures are significantly lower than the melting point temperatures of cobalt or tungsten carbide because of the formation of intergranular films (complexion) at the WC/Co interface. Additionally, two abnormal grain-types were formed, exhibiting tungsten-rich characteristics that were complexed at the WC/Co interface, in addition to extreme abnormal grain growth (AGG), in the absence of cobalt films, located between the WC/WC grain boundaries. At the WC/Co interface, nanosized grains contribute to the AGG owing to the extremely large surface areas and short diffusion distances. The concentration gradient, together with extreme stress imbalance, at the WC-Co/Fe–Ni interface, results in particles to rotate, repack, and rearrange, which leads to the observed abnormal grains. [ABSTRACT FROM AUTHOR]

Reheat treatments for two HSLA steels, a forged Al-Nb-containing steel (Steel-1) and an as-rolled Nb-containing steel (Steel-2), were carried out for one to three hours at temperatures between 1090 and 1250°C which were selected by the precipitates' dissolution temperatures predicted by Thermo-Calc and DICTRA. Steel-1 contains continuous segregation bands with segregation spacing of 65 ± 10 µm, whereas Steel-2 contains discontinuous segregation bands with spacing of 35 ± 10 µm. Uniform grain size distributions occurred in Steel-1 for all reheat temperatures whereas abnormally large grains were observed in Steel-2 when reheating at 1090°C. A mechanism for grain size development in materials with continuous and discontinuous segregation bands based on austenite nucleation and growth and precipitate pinning in the segregation band is proposed. [ABSTRACT FROM AUTHOR]

In this study, the microstructural evolution that occurred during hot forming of Ti-6Al-4V with an initial microstructure of elongated and equiaxed hcp α grains and a network of intergranular bcc β-phase was investigated. Isothermal compression tests were carried out at different deformation temperatures (800–950 °C) and strain rates (0.01, 1 and 10s−1) using Gleeble 3500 thermomechanical simulator. The microstructures of the deformed samples were examined using optical and scanning electron microscopy. The images were analysed using ImageJ 1.48V software. The analysis showed that hot forming of the alloy was generally influenced by dynamic globularisation and dynamic recovery which are known mechanisms that control the deformation behaviour of titanium alloys. However, unique phenomena such as deformation-induced phase transformation and abnormal grain growth that are rarely reported in Ti-6Al-4V alloy with conventional starting microstructures were observed under certain deformation conditions for the Ti-6Al-4V with complex initial microstructure. Abnormal grain growth occurred at lower deformation temperatures and the higher strain rates of 1 and 10 s−1. Deformation-induced phase transformation reduced the β transus temperature of the alloy by 45 °C at the low strain rate of 0.01 s−1. [ABSTRACT FROM AUTHOR]