Grain Boundary Concentration Research Articles

Concurrent dramatic enhancement of high-temperature strength and ductility in a high-entropy alloy via chain-like dual-carbides at grain boundaries

Grain boundaries (GBs) are often known as intergranular cracking sources in alloys at high temperatures, resulting in limited high-temperature strength and ductility. Here, we propose a GB-dual-carbide (denoted as GB-DC) strengthening strategy and have developed a high-performance (NiCoFeCr)99Nb0.5C0.5 high-entropy alloy (HEA) with exceptional strength-ductility synergy at 1073 K. Chain-like coherent M23C6 carbides have been successfully introduced at GBs and remain a cube parallel crystallographic orientation with the face-centered cubic (FCC) matrix during deformation. Nano-scale NbC particles are distributed alternatively between M23C6 carbides and inhibit their coarsening. Both strength and ductility of the GB-DC HEA increase dramatically at strain rates ranging from 10−4 to 10−2 s−1 at 1073 K, compared with those of the single-phase NiCoFeCr HEA. Specifically, yield strength of 142 MPa, ultimate tensile strength of 283 MPa, and elongation of 34 % were obtained, which are twice that of the reference NiCoFeCr HEA (82 MPa, 172 MPa, and 18 %, respectively). EBSD investigations demonstrated that chain-like carbides enhance the GB cohesion at high temperature, and TEM analysis revealed that dislocations can go through the coherent phase boundaries (CPBs) and activate dipoles inner M23C6 carbides, which weakened the stress concentration in GBs. This substantially reduces the critical stress for dislocation generation and transmission to a stress level lower than that required for intergranular fracture. Theoretical estimation suggests that carbides result in a much higher activation energy (∼510 kJ/mol) for GB sliding and a rather low interface energy (∼101 mJ/m2) compared with the GB energy (1000 mJ/m2), which rationalizes the enhanced GB cohesion by carbides.

Grain boundary segregation for the Fe-P system: Insights from atomistic modeling and Bayesian inference

In this work we re-assess experimental data for grain boundary (GB) segregation of P in bcc Fe with thermodynamic and statistical methods. The data are based on Auger-Electron-Spectroscopy (AES) measurements which have provided P GB concentrations for various bulk contents and temperatures for ferrite. While in the previous investigations of this system a single-site McLean equation was used to extract segregation enthalpy and entropy, we employ multi-site segregation models as suggested by atomistic simulations. We use a recently introduced methodology based on inter-atomic potentials to calculate the segregation energy spectrum, as well as vibrational entropy and solute-solute interactions of P in polycrystalline Fe, thereby obtaining a three-dimensional distribution of energy, entropy and interactions. Using this trivariate distribution we predict P GB concentrations and compare them to the experimental measurements. Furthermore, we calibrate the parameters of physical models of increasing complexity to the experimental data with an inverse modeling approach based on Bayesian inference. While it is not possible to seamlessly link the results from AES to atomistic modeling, our investigation provides significant new insights for thermodynamic modeling of GB segregation. The vibrational entropy deduced from experiment differs from physics based atomistic simulations even when taking the spectral nature of energy, entropy and interactions into account. However, the correlations of the quantities are in good agreement when considering the trivariate model. Our investigation highlights the need for new and more accurate experimental datasets of GB segregation.

Elimination of Low-Angle Grain Boundary Networks in FeCrAl Alloys with the Electron Wind Force at a Low Temperature

Low-angle grain boundaries (LAGBs) accommodate residual stress through the rearrangement and accumulation of dislocations during cold rolling. This study presents an electron wind force-based annealing approach to recover cold-rolling induced residual stress in FeCrAl alloy below 100 °C in 1 min. This is significantly lower than conventional thermal annealing, which typically requires temperatures around 750 °C for about 1.5 h. A key feature of our approach is the athermal electron wind force effect, which promotes dislocation movement and stress relief at significantly lower temperatures. The electron backscattered diffraction (EBSD) analysis reveals that the concentration of low-angle grain boundaries (LAGBs) is reduced from 82.4% in the cold-rolled state to a mere 47.5% following electropulsing. This level of defect recovery even surpasses the pristine material’s initial state, which exhibited 54.8% LAGBs. This reduction in LAGB concentration was complemented by kernel average misorientation (KAM) maps and X-ray diffraction (XRD) Full Width at Half Maximum (FWHM) measurements, which further validated the microstructural enhancements. Nanoindentation tests revealed a slight increase in hardness despite the reduction in dislocation density, suggesting a balance between grain boundary refinement and dislocation dynamics. This proposed low-temperature technique, driven by athermal electron wind forces, presents a promising avenue for residual stress mitigation while minimizing undesirable thermal effects, paving the way for advancements in various material processing applications.

A Route to High Thermoelectric Performance: Solution‐Based Control of Microstructure and Composition in Ag2Se

AbstractThermoelectric materials convert heat into electricity, with a broad range of applications near room temperature (RT). However, the library of RT high‐performance materials is limited. Traditional high‐temperature synthetic methods constrain the range of materials achievable, hindering the ability to surpass crystal structure limitations and engineer defects. Here, a solution‐based synthetic approach is introduced, enabling RT synthesis of powders and exploration of densification at lower temperatures to influence the material's microstructure. The approach is exemplified by Ag2Se, an n‐type alternative to bismuth telluride. It is demonstrated that the concentration of Ag interstitials, grain boundaries, and dislocations are directly correlated to the sintering temperature, and achieve a figure of merit of 1.1 from RT to 100 °C after optimization. Moreover, insights into and resolve Ag2Se's challenges are provided, including stoichiometry issues leading to irreproducible performances. This work highlights the potential of RT solution synthesis in expanding the repertoire of high‐performance thermoelectric materials for practical applications.

Mn Additive Improves Zr Grain Boundary Diffusion for Sintering of a Y-Doped BaZrO3 Proton Conductor.

Yttrium-doped barium zirconate (BZY) has garnered attention as a protonic conductor in intermediate-temperature electrolysis and fuel cells due to its high bulk proton conductivity and excellent chemical stability. However, the performance of BZY can be further enhanced by reducing the concentration and resistance of grain boundaries. In this study, we investigate the impact of manganese (Mn) additives on the sinterability and proton conductivity of Y-doped BaZrO3 (BZY). By employing a combinatorial pulsed laser deposition (PLD) technique, we synthesized BZY thin films with varying Mn concentrations and sintering temperatures. Our results revealed a significant enhancement in sinterability as Mn concentrations increased, leading to larger grain sizes and lower grain boundary concentrations. These improvements can be attributed to the elevated grain boundary diffusion of zirconium (Zr) cations, which enhances material densification. We also observed a reduction in Goldschmidt's tolerance factor with increased Mn substitution, which can improve proton transport. The high proton conduction of BZY with Mn additives in low-temperature and wet hydrogen environments makes it a promising candidate for protonic ceramic electrolysis cells and fuel cells. Our findings not only advance the understanding of Mn additives in BZY materials but also demonstrate a high-throughput combinatorial thin film approach to select additives for other perovskite materials with importance in mass and charge transport applications.

Planar defects and strain distributions in polycrystalline BaFe2As2 superconductors synthesized by mechanochemical methods

In this study, the microstructure of polycrystalline Co-doped BaFe2As2 superconducting bulks was comprehensively analyzed. The synthesis process involved ball milling and subsequent spark plasma sintering (SPS). A strong correlation between the microstructure and synthesis conditions was observed. Specifically, when mechanochemical synthesis of raw metal powders was carried out at a ball milling energy (EBM) of 100 MJ/kg, the resulting Co-BaFe2As2 bulk contained nanograins with a high density of planar defects and exhibited a high critical current density (Jc) under both magnetic and self-fields. The findings suggest that planar defects are one of the influential factors on the superconducting properties. Atomic-resolution microstructural characterization revealed that the planar defects are parallel to (001) and exhibit distinctive atomic arrangements. Atomic-resolution elemental mappings displayed a remarkable barium concentration in planar defects and grain boundaries compared to the BaFe2As2 matrix. Local strain fields were also observed around planar defects, especially near their edges. These nanoscale strain fields could be considered as volumetric pinning centers, and effectively pin flux vortices in the random crystal orientation, thereby increasing Jc in the Fe-based superconducting bulk. Additionally, an extended investigation was performed to include a K-doped BaFe2As2 bulk that exhibits similar planar defects. Based on the results of the microstructural analysis, speculations were mode on the evolution process of the microstructure during the preparation of BaFe2As2 bulks.

Specifics of the Surface Structure of Steel Products After Various Laser Alloying Methodics

In modern conditions, volumetric alloying of steels is becoming an increasingly less economically viable process. However, the level of performance properties of unalloyed steels cannot cover the current industry needs. One of the ways to solve this problem – usage of various surface alloying methods of steels, makes it possible to obtain the required properties of the working surface of the alloyed part with minimal consumption of expensive alloying elements. Over the course of the study, combined method of laser-plasma alloying of steel surfaces was analyzed, its technological capabilities were determined, and the structural-phase state of surface layers, formed during laser and hybrid laser-plasma processing was compared. During comparative studies of samples obtained by both methods of surface alloying, it was found that in the case of laser-plasma alloying, the observed structure and carbide phases are smaller in size, with a low density and uniform distribution of dislocations in the metal of the alloyed layer. After various analysis, it was established that during both laser and laser-plasma methods of surface alloying, the crack formation tendencies was mostly attributed to various structural and concentration changes associated with the redistribution of elements, leading to the formation of sharp grain-boundary concentration gradients. An increase in the number of cracks is observed in regimes with higher heating temperatures, increased duration of exposure to high temperatures and reduced cooling rates.

Grain boundaries boost the prelithiation capability of the Li2CO3 cathode additives for high-energy-density lithium-ion batteries

Due to high theoretical capacity, Si anodes have attracted tremendous attention. Nevertheless, huge volume change during cycling together with large lithium loss substantially hinders their large-scale application. Prelithiation has emerged as a highly attractive strategy to compensate for the loss of active lithium. Li2CO3, which is ambient stable and delivers more than 5 times the theoretical capacity of the existing cathode materials, serves as an excellent cathode prelithiation additive. However, the practical application of Li2CO3 is limited by its sluggish charge transport and high critical decomposition potential. Herein, we report a facile route to fabircating nanosized Li2CO3 (N-Li2CO3) materials enriched with grain boundaries (GBs). First-principles investigations reveal that the Li-ion transport behavior is dependent on the concentration of GBs. The Σ(001) GB model exhibits higher Li-ion and electronic conductivities compared to those of the bulk counterpart. As a result, the ∼ 100 % capacity utilization of N-Li2CO3 with a delithiation capacity of 724 mAh/g is obtained, which is much higher than that of commercial Li2CO3 (115 mAh/g), greatly enhancing the reversible capacity, energy density and lifetime of the LiNi0.5Co0.2Mn0.3O2//Si-graphite full cell. These findings provide valuable understanding of the role of GBs and the correlation between microstructure engineering and performance optimization.

Genetic algorithm assisted multiscale modeling of grain boundary segregation of Al in ZnO and its correlation with nominal dopant concentration

Grain boundary (GB) segregation of Al in ZnO plays an important role in lowering its thermal conductivity for thermoelectric applications. However, the effect of Al concentration on the GB complexions and their transition is not well understood. Herein, a genetic algorithm assisted multiscale modelling framework was used to study the role of GB concentration on the GB segregation of Al on five special twin GBs of ZnO. A critical concentration of 5–6 atoms/nm2 was determined for the complexion transition from single layer to multilayer. Calculated segregation energies were used in a phenomenological model to link GB concentration with the nominal concentration of dopants. The model was used to calculate the nominal solubility of Al in ZnO as a function of grain size, which was validated with the experimental data from the literature. The proposed framework provides a path for establishing GB-structure – property correlation and thereby, predictive dopant engineering of ceramics.

Enhancing the performance of ZnGa2O4 metal-semiconductor-metal ultraviolet solar-blind photodetectors by surface fluorine plasma sensitization

ZnGa2O4 has a wide direct bandgap and excellent optical properties and is an emerging material for use in solar-blind ultraviolet (UV) photodetectors (PDs). Recently, metal-semiconductor-metal (MSM) based devices have gained popularity because of their low production cost, minimal design, flexible integration, and tunable performance. However, such devices suffer from low sensitivity. Herein, we propose a sensitization engineering strategy that involves surface fluorine plasma (SFP) treatment to enhance the performance of a ZnGa2O4 MSM solar-blind UV PD. Through this strategy oxygen vacancy defects are simultaneously passivated and the ratio of adsorbed oxygen species on the surface of the ZnGa2O4 thin film is changed. These modifications optimize the current under both dark and light conditions. In particular, the dark current has a trade-off relationship between the reduction in the oxygen vacancy concentration and changes in the crystal grain boundaries. As a result, the photocurrent is enhanced because of the increased amount of adsorbed oxygen. The PD prepared using a ZnGa2O4 thin film treated by SFP for 15 min exhibited excellent performance, specifically, it showed a large responsivity (42.22 A/W) and good specific detectivity (5.72 × 1014 Jones). Notably, these values are superior to those of most reported MSM solar-blind PDs. Moreover, the excellent rejection ratio and durability during repeated use demonstrate the benefits of SFP treatment for enhancing operating stability. Our study provides an effective avenue for optimizing the optoelectronic performance of oxide semiconductors.

Nanotwinned Copper Foil for “Zero Excess” Lithium–Metal Batteries

The “zero excess” lithium–metal battery cell concept, in which the pristine negative electrode consists only of the current collector, while all lithium is present only in the positive electrode active material, promises substantial improvements in energy density. However, the achievement of stable cycling for more than just a few cycles requires a careful design and adjustment of all cell components─especially the current collector at the negative electrode. Herein, we provide a comparative investigation of commercial, polycrystalline copper foil, characterized by a rather random [111], [200], and [220] orientation and a high concentration of grain boundaries, and nanotwinned copper foil, which has a solely [111]-oriented grain structure. Remarkably, the plated lithium on the foil with [111] orientation reveals a much more homogeneous morphology independent of the current density applied, while several dendritic lithium deposits are observed on the polycrystalline copper foil. This also translates into higher Coulombic efficiency and stabilized cycling performance of Cu[111]||NMC811 cells, highlighting the important impact of the crystal orientation of the current collector.

Cross-scale microstructure design of precursor-derived SiC-AlN nanoceramic composites hybrid with ex-situ ZrB2

ZrB2/SiC–AlN nanoceramic composites were densified at 1950 ​°C by hot pressing using an organic-precursor-derived SiC and commercially available AlN and ZrB2. A cross-scale microstructure was constructed by distributing the ZrB2 secondary phase (∼421 ​nm) within the SiC–AlN solid solution matrix. The substructure of the SiC–AlN matrix was agglomerated by nanograins with an average size of only 62 ​nm. ZrB2 connected around the majority of pores within the SiC–AlN matrix and contributed to the formation of numerous weak interfacial bonding, resulting in improved strength and toughness. The highest flexural strength and fracture toughness of 579 ​± ​52 ​MPa and 6.7 ​± ​0.1 ​MPa ​m1/2 were obtained from a 10 ​wt%-ZrB2/SiC–AlN sample, respectively. The high concentration of grain boundaries of the ZrB2/SiC–AlN nanoceramic composites resulted in heat insulation characteristic. The thermal diffusivity and conductivity were 3.6 ​mm2⋅s−1 and 14.3 ​W·(m·K)−1 at 1400 ​°C, respectively, while the electrical resistivity was 3.9×103 ​Ω·cm for the 10 ​wt%-ZrB2/SiC–AlN sample.

Models of recrystallization activated by a diffusion flow of impurities from a thin-film coating with a convection term at the crystal surface: exact solutions

Two models of recrystallization are proposed taking into account the convective flux of impurity exchange between the polycrystalline and the thin-film coating. The special boundary modes of recrystallization described by the single-phase and two-phase Stefan problems with the boundary condition at coated surface containing the convective term. The exact solutions of the formulated problems corresponding to the grain-boundary concentration of impurities are obtained. The detail theoretical analysis focused on the third type problem shows that the concentration of impurities and the width of the recrystallized layer increase with an increase in the annealing time. An increase in intensity of impurity exchange between the polycrystalline and the coating promotes an increase in the width of the recrystallized layer. The recrystallization front position increases with an increase in the surface concentration of impurities and it decreases with an increase in the intensity of the impurity flux from the surface. The rate of recrystallization kinetics increases with an increase in the intensity of impurity exchange between the polycrystalline and the coating.

(Invited) Optical Characterization of Bulk GaN Substrates and Homoepitaxial Films

Low ON-resistance and high breakdown voltage, made possible by improved critical electric field and mobility, has promoted GaN from a potential to the most promising semiconductor material for use in the next-generation of medium- and high voltage-power converters. The commercial availability of large area substrates, produced by HVPE (Hydride Vapor Phase Epitaxial, a quasi-bulk deposition technique) and ammonothermal bulk growth method, provides wafers with reduce concentrations of extended defect, allows the deposition of electronic grade epitaxial films and the realization of high performance electronic devices. Despite that, many steps of substrate preparation, such as miss-cut orientation and surface finishing, must be improved and standardized to yield reproducible epitaxial film growth. To verify the importance of substrate characteristics on the intrinsic properties of homoepitaxial MOCVD films, we initially evaluated substrate provided by various commercial supplies. The substrate effects on epi morphology, uniformity, and impurity incorporation were substantiated by growing simultaneously on wafers from different vendors. The goal of this work is to detect and identify defects in GaN substrates with a series of quick, non-destructive, inexpensive techniques with capabilities of mapping whole wafers.All evaluated substrates had nominally similar as-received specifications (resistivity, thickness, off-cut angle, bow, surface finish). The substrates were evaluated with a variety of techniques including Raman spectroscopy, photoluminescence, white light interferometry, and Nomarski imaging, enabling the detection of different concentrations of grain boundaries, impurities, point defects, v-shaped pits, polishing defects, crystal stress damage, and non-uniform insulating and conductive regions. The substrates can be grouped in two different categories: those with uniform characteristics, including carrier concentration, and those without. Comparing these results to those from homoepitaxial growth on the same wafers, the effects are both subtle and overt. Macroscopic surface morphology, which has shown a direct correlation to leakage current, copies and exaggerates that of the underlying substrate. Photoluminescence of the homoepitaxial surface along with Raman spectroscopy show that non-uniformities in the substrate carrier concentration can continue into the epitaxy.If time permits, results from vertical Schottky diodes, fabricated to quickly evaluate device performance, will presented. While most of the films showed the ability to withstand high electric fields, more uniform electrical properties were observed for those grown on substrates having more uniform properties. These results show that improving bulk substrates is the path to high voltage vertical devices, and that such substrates have a significant influence on device performance. Acknowledgments: Work at NRL is supported by the Office of Naval Research

Investigating the optical response of titanium-nitride thin films after silver ion implantation and post-thermal annealing

The paper reports the study on dielectric functions of TiN films implanted with Ag ions and after annealing at 400 °C and 700 °C, employing spectroscopic ellipsometry technique. By using Drude-Lorentz modelling we have analysed and discussed in detail the evolution of screened and unscreened plasma frequency as well as Drude parameter. In comparison to as deposited film the real part of dielectric constant for Ag-implanted layers exhibits less negative values with increasing ion fluence implying the films possess less metallicity, whereas after annealing TiN becomes more metallic. Simultaneously, after implantation, the imaginary part is more than an order of magnitude lower than for the as deposited TiN and several times lower than that of Au and Ag. The magnitude of imaginary contribution of Ag-implanted TiN films decreases further after subsequent heat treatment at both 400 °C and 700 °C annealing temperatures. Although the differences in stoichiometry and microstructural changes, such as crystallite size, concentration of grain boundaries and defect density were assumed to be the major reason for the variation in optical properties of TiN, spectroscopic ellipsometry data exhibited much stronger effects than expected and indicated some other mechanisms could also be responsible for such behaviour.

Plasticity and brittleness of the ordered βo phase in a TNM-TiAl alloy

In order to identify the reasons for the brittleness of a TNM-TiAl alloy (Ti51.05Al43.9Nb4Mo0.95B0.1 in at.%), the plastic deformation behaviour of the ordered βo phase is investigated. The corresponding powder was densified by Spark Plasma Sintering to produce a near lamellar microstructure made of γ/α2 lamellar colonies surrounded by γ and βo grains. Then, the room temperature tensile behaviour is studied by carrying out tensile tests and additional in-situ straining experiments in a transmission electron microscope (TEM). The TNM alloy exhibits a limited ductility, with the fracture surface of test specimens showing cleavage facets along lamellar interfaces. In addition, the βo grains contain nano-precipitates of the ωo phase and deform plastically by <111> superdislocations dissociated into two superpartial dislocations separated by an antiphase boundary. These dislocations glide in {011} planes and are observed to be localized into pile-ups, which is related to the ωo strengthening precipitation within the βo grains. This localised hardening behaviour leads to stress concentration in grain boundaries which is assumed to be responsible for delamination along lamellar interfaces in neighbouring lamellar colonies.

In situ ion irradiation of amorphous TiO2 nanotubes

Understanding of structural and morphological evolution in nanomaterials is critical in tailoring their functionality for applications such as energy conversion and storage. Here, we examine irradiation effects on the morphology and structure of amorphous TiO2 nanotubes in comparison with their crystalline counterpart, anatase TiO2 nanotubes, using high-resolution transmission electron microscopy (TEM), in situ ion irradiation TEM, and molecular dynamics (MD) simulations. Anatase TiO2 nanotubes exhibit morphological and structural stability under irradiation due to their high concentration of grain boundaries and surfaces as defect sinks. On the other hand, amorphous TiO2 nanotubes undergo irradiation-induced crystallization, with some tubes remaining only partially crystallized. The partially crystalline tubes bend due to internal stresses associated with densification during crystallization as suggested by MD calculations. These results present a novel irradiation-based pathway for potentially tuning structure and morphology of energy storage materials.Graphical abstract

Study of Atomic Hydrogen Concentration in Grain Boundaries of Polycrystalline Diamond Thin Films

This paper describes research focused on investigating the effect of hydrogen (H) atom insertion into the grain boundaries of polycrystalline diamond (PCD) films. This is required in order to understand the key morphological, chemical, physical, and electronic properties of the films. The PCD films were grown using the hot filament chemical vapor deposition (HFCVD) process, with flowing Ar gas mixed with CH4 and H2 gases to control film growth into microcrystalline diamond (MCD, 0.5–3 µm grain sizes), nanocrystalline diamond (NCD, 10–500 nm grain sizes), and ultrananocrystalline diamond (UNCD, 2–5 nm grain sizes) films depending on the Ar/CH4/H2 flow ratios. This study focused on measuring the H atom concentration of the PCD films to determine the effect on the properties indicated above. A simple model is presented, including a hypothesis that the two dangling bonds per unit cell of C atoms serve as the site of hydrogen incorporation. This correlates well with the observed concentration of H atoms in the films. Dangling bonds which are not passivated by hydrogen are postulated to form surface structures which include C double bonds. The Raman peak from these surface structures are the same as observed for transpolyacetyline (TPA). The data reveal that the concentration of H atoms at the grain boundaries is around 1.5 × 1015 atoms/cm2 regardless of grain size. Electrical current measurements, using a conductive atomic force microscopy (CAFM) technique, were performed using an MCD film, showing that the current is concentrated at the grain boundaries. Ultraviolet photo electron spectroscopy (UPS) confirmed that all the PCD films exhibited a metallic behavior. This is to be expected if the nature of grain boundaries is the same regardless of grain size.

The influence of lithium sources on properties of perovskite-type lithium ion conductor

Perovskite-type lithium-ion conductor Li0.33La0.56TiO3 was prepared via microwave sintering. The influence of lithium sources on the properties of the samples prepared and the compensation of lithium loss were investigated. XRD patterns, exhibiting a mixture of tetragonal and cubic phase, were all similar for the samples made with different lithium sources. The total conductivity of the sample made with Li2CO3 achieved 0.51 × 10−4 S/cm, which was the highest among all the samples made with different sources. The highest total conductivity of the sample made with Li2CO3 was attributed to the largest grains, which would result in a smaller concentration of less-conductive grain boundaries. The total conductivity of the sample compensated with 5% Li2O was 38% higher than the sample made stoichiometrically. Given that grain sizes were similar for the samples compensated with a varied amount of Li2O and the relative density of the sample compensated with 5% Li2O was even the lowest among these samples, the highest total conductivity was rooted in the highest ratio of cubic phase. These results indicated that lithium sources could influence the properties of the LLTO samples greatly by resulting in a variation on crystalline phase, grain size, and relative density, which collectively determine the migration of lithium ions in polycrystalline Li0.33La0.56TiO3.

Influence of SiC microstructure on its corrosion behavior in molten FLiNaK salt

The influence of the microstructure on the corrosion rate of three monolithic SiC samples in FLiNaK salt at 900 °C for 250 h was studied. The SiC samples, labeled as SiC-1, SiC-2, and SiC-3, had corrosion rates of 0.137, 0.020, and 0.043 mg/cm2h, respectively. Compared with grain size and the presence of special grain boundaries (i.e., Σ3), the content of high-angle grain boundaries (HAGBs) appeared to have the strongest influence on the corrosion rate of SiC in FLiNaK salt, since the corrosion rate increased six times as the concentration of high-angle grain boundaries increased from 19 to 32% for SiC-2 and SiC-1, respectively. These results stress the importance of controlling the content of HAGBs during the production process of SiC.