The irradiation stability of Cr-based protective coatings on zirconium alloys is critical for the development of accident-tolerant fuel claddings. However, conventional surface irradiation often produces shallow, nonuniform damage, obscuring interfacial behavior. In this study, we perform cross-sectional He2+ irradiation to directly examine the interfacial response and He bubble evolution across Cr monolayer and Cr/CrAlSiN multilayer coatings on Zr substrates. Irradiation was carried out at 500 and 750 degrees C to doses of 2-3 displacements per atom (dpa), enabling a direct comparison of temperature-dependent microstructural evolution. In the Cr monolayer, He implantation produced a homogeneous distribution of nanoscale bubbles throughout the damaged region and large cavities at the Cr/Zr interface, indicating severe Kirkendall-type voiding and interfacial decohesion at elevated temperature. In contrast, the Cr/CrAlSiN multilayer exhibited a periodically modulated bubble distribution, with bubble fragmentation and transformation into nanoscale platelets at CrAlSiN interfaces. A N-enriched Zr(N) interlayer formed spontaneously at the CrAlSiN/Zr interface, effectively suppressing bubble accumulation and interdiffusion. The nanochannel interfaces acted as He sinks and diffusion barriers, enhancing interfacial bonding and mitigating swelling. This work demonstrates that cross-sectional ion irradiation is a powerful approach for probing interfacial stability in multilayer systems, offering new insights into He-defect interactions and radiation tolerance engineering at buried interfaces. The findings highlight the potential of Cr/CrAlSiN multilayers as advanced coating architectures for high-temperature nuclear environments. (c) 2026 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/)

We investigate the nanoscale friction behaviour of MX2 monolayers (M = Mo, W; X = S, Se) on Au(111) and Ag(111) substrates with a silicon tip using classical molecular dynamics simulations with machine-learning-based force fields. This approach enables an accurate description of tip-surface interactions and friction mechanisms at the atomic scale. We observe a pronounced non-monotonic dependence of the friction force on the applied normal load, indicating a breakdown of Amontons's law at the nanoscale. Analysis of lateral force' signals and their spatial Fourier transforms reveals the coexistence of multiple sliding modes, including longitudinal sliding, lateral slip, and zig-zag motions. We show that the overall friction response is governed by the relative contributions of these motions. While the qualitative features of friction are largely substrate-independent, both the magnitude of friction and the balance between sliding modes depend sensitively on the substrate-monolayer combination. In particular, Au/MoSe2/Si exhibits significantly reduced friction due to suppression of lateral slip motion. Our results indicate that the method is broadly applicable for probing nanoscale friction in related heterostructures.

Helium accumulation in structural ceramics used in nuclear, fusion, and aerospace systems causes swelling, cracking, and early failure, yet controlling this damage has remained elusive. Here, we introduce defect landscape engineering, the deliberate creation of vacancy clusters prior to helium exposure, as a general strategy to suppress helium-induced degradation. Using alpha-SiC as a model, we combine advanced microscopy, strain mapping, helium depth profiling, positron annihilation spectroscopy, and atomistic simulations to demonstrate that tailored pre-damage transforms helium defect evolution. Instead of forming extended platelets and nanocracks, helium is trapped in stable, uniformly dispersed nanobubbles. Simulations reveal that small vacancy clusters act as dual-function sinks for irradiation-induced interstitials and preferential traps for helium, fundamentally altering the dynamics of cascade recombination. This mechanism is composition-independent and scalable, offering a new design principle for radiation-tolerant ceramics across carbides, nitrides, and oxides. By viewing defect control as a tunable parameter instead of a fixed material property, this work outlines a possible design route toward enhanced radiation tolerance in ceramics used in extreme environments.

In working conditions, chalcogen vacancies spontaneously occur in two-dimensional transition metal dichalcogenides (TMDCs) monolayers, affecting their optoelectronic and photocatalytic properties. To study how chalcogen vacancies affect such properties, we use quantum mechanical calculations considering prototypical MX_2 (M = Mo, W, X = S and Se) TMDCs monolayers. Structural optimisations show that M-X bond lengths about a vacancy are different compared to the bond lengths in the pristine structure. Band structure calculations reveal that the introduction of vacancies produce electronic states about the Fermi level, hence resulting in the reduction of the band gap. Work function and electrostatic potential calculations show that the introduction of vacancies induce an asymmetry in the electrostatic potential facilitating the charge separation; such feature is absent in a pristine monolayer. All the considered defective structures are capable of performing hydrogen evolution reaction, while co-catalyst is required to perform oxygen evolution reaction when used for water splitting. WS_2 and WSe_2 defective monolayers can serve as an efficient photocatalytic material for reducing CO_2 into useful chemical products. The presented results show that vacancy-containing TMDCs monolayers own photocatalytic capabilities compared to the pristine counterparts, thus showing that defective TMD monolayers have prospective applications and should not be regarded as flawed products to be discarded. Finally, the results might constitute guidelines for the experimental synthesis of vacancy-engineered MX_2 monolayers for optoelectronic devices and photocatalytic applications.

This work investigates the oxidation behaviour, coating integrity and net material loss of tungsten (W) and tungsten-molybdenum (W/Mo) coatings deposited on graphite substrates for fusion plasma-facing components under air-ingress conditions. Graphite offers high thermal conductivity and thermal shock resistance but suffers from poor erosion resistance, while W provides superior thermal stability and erosion resistance. A Mo interlayer was introduced between the W coating and graphite substrate to improve adhesion and interface stability. Samples were exposed to a controlled argon-air atmosphere at temperatures ranging from 270 to 650 degrees C for 15 min to 21 h. Oxidation behaviour and coating integrity were evaluated by mass-change measurements and surface analyses. Pure W coatings remained stable below 300 degrees C, whereas W/Mo coatings exhibited accelerated oxidation and formation of porous oxide scales at higher temperatures due to volatile Mo oxides. These results highlight the thermal and oxidation stability of multilayer coatings and their relevance for fusion components exposed to moderate-temperature air conditions during severe Loss-of-Vacuum Accidents.

This work presents an integrated methodology combining analytical and finite element (FEM)-based viscoelastic modeling for characterizing the nanoindentation response of coatings. The proposed framework combines two complementary modeling approaches: an analytical model based on the Burgers formulation to analyze nanoindentation load–displacement data and extract rheological parameters, and a numerical FEM model implemented in ABAQUS using a 2D axisymmetric indenter–coating-substrate configuration with viscoelasticity represented through Prony series. An automated inverse optimization routine employing the Nelder–Mead simplex algorithm minimizes the discrepancy between experimental and simulated responses. The methodology is demonstrated and validated on WSe2 coatings, showing an agreement between the analytical predictions, FEM simulations, and experimental measurements. Despite the geometric simplifications, the FEM approach provides accurate predictions while maintaining high computational efficiency of time-dependent mechanical behavior. The proposed framework provides a robust tool for characterizing viscoelastic behavior from nanoindentation data while enabling access to internal stress and strain fields, thereby offering deeper insight into plastic deformation, crack initiation, and failure mechanism.

ABSTRACT The corrosion behavior of MAX phases in molten chloride salts remains a critical limitation for their deployment in advanced nuclear and high‐temperature energy systems. Here, the corrosion mechanisms of Ti 2 SC, Ti 2 AlC, Hf 2 SC, and Hf 2 SB were systematically investigated in molten MgCl 2 –NaCl–KCl at 700°C under vacuum by combining static corrosion experiments with density functional theory (DFT) calculations. Ti 2 SC exhibited the highest corrosion resistance, maintaining relatively good structural integrity through the formation of a compact oxide‐rich corrosion product scale, whereas Hf 2 SB suffered catastrophic fragmentation and Hf 2 SC showed severe localized cracking. Ti 2 AlC experienced extensive degradation associated with Al depletion and porous oxide formation. Experimental observations reveal that corrosion resistance is governed by both the morphology and continuity of the oxide‐rich corrosion product scale and the chemical inertness of the X element toward chlorination. DFT calculations demonstrate that Cl adsorption strength, interlayer bond weakness, and preferential reactivity of Al, Hf, and B critically control atomic migration and lattice destabilization, while stronger M–X bonding contributes to improved structural stability during corrosion. These results establish a direct atomic‐to‐macroscopic correlation between MAX phase chemistry and molten chloride corrosion behavior, providing mechanistic design guidelines for corrosion‐resistant coatings in extreme environments.

The irradiation response of electron-beam welded Fe–9Cr steel was investigated using 2.75 MeV Fe ion irradiation at temperatures of 300 °C, 400 °C, and 500 °C up to 10 dpa. The base zone (BZ), heat-affected zone (HAZ), and weld zone (WZ) were characterized using nanoindentation and transmission electron microscopy (TEM) to evaluate the influence of microstructural heterogeneity on irradiation-induced hardening. Nanoindentation results show that hardness increases with dose at 300 °C and 400 °C, with the most pronounced hardening observed at 400 °C. At 500 °C, the hardening response is reduced and tends toward saturation at higher dose. The WZ exhibits the highest absolute hardness, whereas the BZ shows the most significant increase in average relative hardness. Concurrently, the hardness increase in the HAZ is between that in the WZ and BZ. TEM observations reveal the formation of dislocation loops, with higher density and size at intermediate temperature. The observed hardening behavior is attributed to the combined effects of defect accumulation and thermally activated recovery processes, with defect growth dominating at intermediate temperature and recovery becoming significant at higher temperature. The results highlight the role of initial microstructure in governing irradiation response in welded ferritic–martensitic steels.

The frictional and wear performance of molybdenum disulfide (MoS2) is strongly governed by its crystallinity, yet this influence remains largely unexplored. In this study, we present the first integrated experimental and atomistic study that establishes how structural order governs the tribological performance of MoS2. A wide spectrum of crystallinity, from amorphous to highly crystalline states, is investigated to evaluate its influence on the coefficient of friction (COF) and wear resistance. Experiments reveal a strong dependence of COF and wear on crystallinity, with crystalline MoS2 achieving ultralow friction and enhanced wear resistance. In contrast, amorphous and polycrystalline films display significantly higher COF and pronounced tribo-polishing effect. Complementary reactive molecular dynamics simulations capture the same trend and uncover the underlying mechanics: crystalline MoS2 maintains smooth sliding interfaces and enables frictional anisotropy through interlayer shear. However, sliding of disordered structures increases surface roughness, energy dissipation, and material removal. Furthermore, we examine the wear mechanisms under high normal loads, demonstrating that crystallinity enhances wear resistance by mitigating material deformation. The strong agreement between experiments and simulations confirms crystallinity as a dominant factor governing the tribological response of MoS2. Our findings provide atomic-scale insights into the mechanisms of superlubricity in layered materials and offer a fundamental basis for designing advanced solid lubricants and wear-resistant coatings.

Semiconductor photocatalysis offers a sustainable route for converting solar energy into chemical energy, enabling the production of clean fuels and valuable chemical products. To this aim, we explore van der Waals heterostructures made up of Janus PtSSe and WXY (X, Y = S, Se, Te and X ≠ Y), in the context of photocatalytic applications. The redox capabilities of various heterostructure configurations (atom facing types and stacking orders) are evaluated by aligning the absolute band edge positions with respect to redox potentials of hydrogen and oxygen evolution reaction (HER and OER) and CO2 reduction reactions. The stability of photocatalyst candidates is checked by layer binding energy, elastic constant calculations and ab initio molecular dynamics simulations. The optical absorption spectra suggest good light absorption in the visible range. Further, strain engineering is applied as a way to tune band edges and evaluate the possible use of the heterostructures as photocatalysts. This study shows that van der Waals heterostructure bilayers composed of Janus PtSSe and WSeTe in specific geometric configurations can be potential materials as photocatalysts for HER, OER and CO2 reduction reactions. Finally, we suggest that, although systems made up of PtSSe and WSTe cannot be used for photocatalytic applications, they can be explored for applications in thermoelectric energy conversion or infrared photovoltaics.

Molybdenum disulfide (MoS2) is recognized for its mechanical robustness and exceptional lubricity under extreme conditions. However, its fracture behavior remains relatively unexplored, particularly across different crystalline configurations. We perform reactive molecular dynamics simulations to investigate the role of crystallinity on the fracture properties and behavior of MoS2. In a departure from prior studies focused on specific crystal orientations, we examine a spectrum of crystallinity, ranging from perfect crystal to polycrystalline to amorphous structures. Fracture properties are measured using the J-integral, ultimate strain, and brittleness index. Our results indicate that the presence of grain boundaries and amorphous regions within polycrystalline MoS2 enhances ductility and fracture toughness. However, at high degrees of crystallinity, grain boundaries dominate and act as a potential regions of defect, promoting crack propagation. Through an analysis of grain boundary interactions and atomic strain profiles, we elucidate critical insights into the mechanisms driving the observed variations in fracture properties. This study highlights the potential for tuning MoS2 crystallinity to optimize its fracture toughness, advancing its application in challenging engineering environments.

A detailed analysis of the friction data from laboratory tests was carried out with a focus on the identification of the wear mechanisms acting on the contacting surfaces. In the past work, dynamical system theory has been successfully applied to tribosystems involving rolling pairs. However, its applicability to sliding metallic pairs is still far from being straightforward. To address this problem, a dynamic analysis in time and frequency was applied to the coefficient of friction (COF) data obtained from pin-on-disc tests of self-mated AISI-SAE 1080 steel. The tests were performed in either air or N-2 atmosphere and under a series of normal loads and sliding speeds. The power spectral density (PSD) and time-frequency spectrograms were calculated from the friction data by applying a fast Fourier transform. The samples from the tests with N-2 atmosphere attenuated the frequencies in the bandwidth between 8 and 10 Hz for all angular velocities, and it was validated by statistical analysis. Using a 3D profilometer, the width and depth of the wear tracks were measured, and the corresponding wear-rates were estimated. The lower wear-rates in the test with air are associated with the formation of oxides acting as a tribolayer on the contact. This study demonstrates that the wear mechanisms acting on the contacting surfaces in pin-on-disc tests can be correlated with the COF response in the frequency domain.

Understanding the effects of high-temperature helium (He) irradiation on the damage behavior of sintered silicon carbide (SiC) is crucial for assessing the material's stability in advanced nuclear reactors. In this study, we investigate the impact of 230 key He ions on SiC at temperatures of 800 degrees C and 1000 degrees C, utilizing three different irradiation fluences: 2 x 1016/cm2, 4 x 1016/cm2, and 1.6 x 1017/cm2. Raman spectroscopy and transmission electron microscopy were employed to analyze various damage features, including irradiation-induced lattice strain, platelet formation, dislocation loops, and helium bubbles. Our findings indicate that over-pressurized platelets predominantly formed on the (0001) plane, with a limited number of dislocation loops detected nearby. In contrast, numerous black spot defects were observed near grain boundaries, where platelets were absent. This variation in defect distribution underscores the unique damage behavior associated with high-temperature He irradiation. The insights gained from this study are essential for understanding the structural changes and integrity of SiC materials under conditions relevant to nuclear reactor applications.

This study provides a compelling comparison of the structural and mechanical responses of single-crystal silicon carbide (sc-SiC), nanocrystalline silicon carbide (nc-SiC), and amorphous silicon carbide (am-SiC) to hydrogen ion implantation at 650 degrees C across varying fluences. While both sc-SiC and nc-SiC exhibit blistering, micro-cracking, and exfoliation, am-SiC remains free of blisters, demonstrating superior resilience. Notably, nc-SiC, with its high density of stacking faults (SFs), requires a higher fluence to initiate blistering compared to scSiC. In sc-SiC, blistering leads to increased hardness, whereas in nc-SiC, the degradation of the SF structure results in a reduction in hardness. In contrast, am-SiC undergoes structural relaxation during irradiation, resulting in a significant increase in hardness while maintaining its structural integrity, with only the formation of nano-sized spherical bubbles observed. These findings highlight the exceptional suitability of am-SiC for nuclear applications, where resistance to radiation-induced microcracking is critical.

Transition-metal dichalcogenides (TMDs) are commonly used as solid lubricants in various environments. Molybdenum disulfide is the most studied and applied TMD solid lubricant, but other members may have similar or even better sliding properties. Tungsten diselenide is one of the materials that has rarely been investigated in terms of tribological properties. This paper provides a comprehensive tribological characterization of substoichiometric tungsten diselenide and molybdenum disulfide coatings deposited by magnetron sputtering. We focused on tribological properties at a macroscopic scale, particularly friction and wear dependence on applied load; however, a nanoscale frictional assessment of worn surfaces was performed as well to identify the major wear mechanisms. Substoichiometric tungsten diselenide outperformed traditional molybdenum disulfide, exhibiting much lower friction in humid air, suggesting lower coating sensitivity to the humid atmosphere. Moreover, a combination of nanotribological experiments in the wear tracks with sliding under different environmental conditions suggests that the key factor causing frictional load-dependence (deviation from Amonton's law) is frictional heating of the surface.

Surface-enhanced Raman spectroscopy (SERS) is a highly sensitive and selective technique. It greatly enhances the signal of an analyte compared to classical Raman spectroscopy, due to analyte–substrate interactions. A promising substrate for SERS is boron-doped graphene (B-graphene). At low boron concentrations of ∼1.39 at.%, it has been shown to enhance the Raman signal of simple organic molecules such as pyridine. The potential use of high-concentration B-graphene materials for SERS remains unexplored. Therefore, in our study, we investigate the influence of dopant concentration and relative adsorbate/substrate geometry on the effectiveness of B-graphene as a SERS substrate, with glucose as the analyte. We perform Density Functional Theory simulations using the PBE functional and the DFT-D2 van der Waals correction. By combining analysis of interatomic force constants and phonon eigenvector composition, we conclude that higher doping concentrations provide a larger enhancement to the Raman signal of glucose, while the molecule’s orientation relative to the surface plays a fundamental role in the Raman response. We suggest that 12.5 at.% B-graphene represents a potential substrate for SERS-based detection of glucose. Additionally, the phonon-based analysis can be promptly applied in the search for promising substrate materials for enhanced Raman response.

Graphite tiles are used as heat shields to protect components exposed to high-temperature plasma due to their high thermal resistance, and low atomic number, which reduces the maintenance requirements and the effect of plasma contamination. However, sputtering and hydrogen affinity are the main limitations for graphite. Tungsten has high energy threshold for sputtering and resistance to chemical erosion. Application of tungsten layer on graphite substrate may overcome graphite's limitations. This study explores the HiPIMS technique for depositing tungsten coating and tungsten coating with molybdenum interlayers onto graphite substrates. The aim was to study the influence of surface roughness on the adhesion, mechanical properties, and microstructure of coatings to optimize coated graphite for plasma-facing materials.

Multi-material laser powder bed fusion (MM-LPBF) offers the possibility of components with material and compositional complexity, as well as the geometric complexity for which additive manufacturing is known. LPBF materials are susceptible to fatigue failures due to stress concentrating roughness and porosity defects. Understanding fatigue failure processes is therefore important to enable adoption of multi-material parts, and suitable combinations of materials may offer a strategy to enhance fatigue performance by resisting crack propagation. This study focused on fatigue crack propagation in 316L/15-5 precipitation hardened (PH) bi-material stainless steels (SS), and the effect of residual stress distribution and yield stress gradient on fatigue crack propagation through the interface. The expected yield stress gradient effect in bi-materials (soft to hard interface) was simulated using FE models, showing a slight shielding effect with a drop in J-integral value. Contour cutting measurements detected a residual stress distribution near the bi-material interface that was tensile in 316L layer and compressive in 15-5PH layer. Fatigue crack propagation rates in bi-materials deviated from those in the corresponding single-material specimens. A relatively small shielding effect due to the yield stress gradient was detected within a short distance of the crack tip from the interface. However, the effects of residual stress were more pronounced and inhibited the crack growth rate by up to 77.8 % in regions of 15-5PH SS under residual compression, which suggesting that MM-LPBF parts can be designed such that the compressive residual stress is positioned to intercept and suppress propagating cracks to improve damage tolerance.

The frictional and wear performance of molybdenum disulfide (MoS2) is significantly influenced by its intrinsic arrangement of crystals or crystallinity. In this study, we investigate the effect of crystallinty on coefficient of friction (COF) and wear in MoS2 using a suite of reactive molecular dynamics (MD) simulations. A range of configurations, from amorphous to crystalline, is modeled to capture the effect of structural order on the tribological behavior. To study friction and wear, we simulate the sliding of a spherical rigid carbon body over the MoS2 surface under varying crystallinity conditions. Our results reveal a pronounced reduction in COF with decreasing crystallinity, with crystalline MoS2 exhibiting superlubricity. This behavior is attributed to the preservation of a flat sliding surface and frictional anisotropy, which enables lateral movement along low-resistance paths. In contrast, amorphous and polycrystalline MoS2 with lower degrees of crystallinity displays a substantially higher COF, driven by increased surface roughness and atomic-scale energy dissipation. Furthermore, we examine the wear mechanisms under high normal loads, demonstrating that crystallinity enhances wear resistance by mitigating material deformation. These findings provide atomic-scale insights into the tribological performance of MoS2, emphasizing the critical role of structural order in achieving ultralow friction. Our work corroborates with previous studies on superlubricity in MoS2 and extends this understanding to rigid-body sliding conditions, offering valuable implications for designing low-friction and wear resistant solid lubricants.

Cr coatings, as protective coatings of Zr-alloy fuel claddings, inevitably suffer from irradiation damage before they would possibly run into the accident condition. This study evaluates the radiation and oxidation tolerance of three Cr-based coatings with different microstructures (Cr, CrAlSi, and CrAlSiN) through He2 + ion irradiation and 1200 degrees C steam oxidation. The Cr and CrAlSi coatings experienced significant structural degradation, characterized by He bubble aggregation and amplified Kirkendall effects at elevated temperatures. In contrast, the irradiated CrAlSiN coating maintained structural integrity without measurable irradiation hardening. Following annealing at 800 degrees C for 30 min, approximately 40 % of injected He atoms were released, indicating a "self-healing" mechanism. The mechanism is attributed to uniformly distributed, low-density channels that act as sinks and release paths for irradiation-induced defects. Density functional theory simulations suggest that N atoms promote significant rearrangement of ions surrounding the free volume, inhibiting the formation of sites capable of trapping He atoms. Moreover, the CrAlSiN coating exhibited superior oxidation resistance compared to the Cr and CrAlSi coatings, even under high-temperature steam conditions. Notably, the irradiated CrAlSiN sample displayed a significantly thinner oxide scale compared to the pristine one (almost half), owing to a more protective oxide scale and rapid outward diffusion of Cr, Al, and Si through nanochannel veins. These findings illuminate the effects of structure and composition on irradiation and oxidation behavior in Cr-based coatings, offering insights for developing new-generation accident-tolerance fuel coatings for Zr-alloy claddings. (c) 2024 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.