Silicon carbide fiber-reinforced composites (SiC/SiC) are leading candidates to replace zirconium-based alloys as cladding in light water reactors (LWR), owing to their exceptional oxidation resistance and mechanical performance under accident conditions.However, pressure-less joining methods compatible with the extreme chemical and thermal environment of LWRs remain a major technological hurdle.This work evaluates two promising joining materials—Mo-wrap (a MoSi₂/Si composite) and SAY (a silica–alumina–yttria glass-ceramic)—under simulated LWR conditions.Joining was performed using both conventional furnaces and laser-assisted techniques.Joint integrity and microstructure were assessed by SEM/EDS and X-ray computed tomography. Hydrothermal stability was evaluated in static and flowing-water (loop) autoclaves up to 30 days at 330 °C and 150–155 bar.Mo-wrap joints showed partial degradation due to silicon dissolution, while SAY joints retained good structural integrity in static tests but suffered phase-selective corrosion under flowing conditions, with keivite emerging as the most stable crystalline phase.Laser-processed amorphous SAY joints exhibited improved corrosion resistance, though still limited under prolonged exposure.These findings advance the understanding of joining performance in nuclear-relevant environments and support the development of accident-tolerant fuel cladding.

The MAX phases constitute a family of atomically layered ternary carbides/nitrides with hexagonal structure (space group P63/mmc) applauded for their compositional versatility, which is demonstrated by the easy formation of solid solutions with varying chemical complexity. Intentionally tailoring chemically complex MAX phase solid solutions enables the production of materials with tuneable properties vis-a`-vis the requirements of the targeted application(s). This work synthesised high-purity (Ti,V,Zr,Nb,Hf)2(Al,Sn)C and (Ti,Zr,Nb,Hf,Ta)2(Al, Sn)C MAX phase solid solutions by reactive hot pressing metal hydride-based powder feedstocks at 1450 degrees C, also elucidating their elemental-diffusion-limited, complex formation mechanism. The hydrogenated, milled, and sieved powder feedstocks facilitated the formation of damage-tolerant ceramics with homogeneous microstructures and minute impurities. Sterically balanced M- and A-site elemental occupancies alleviated lattice distortions, whilst increasing the configurational entropy of the produced MAX phase compounds further enhanced their thermodynamic stability.

Electron transparent thin foils of compositionally complex MAX phases in the (Ta0.2Ti0.2Zr0.2Nb0.2Hf0.2)2(Al0.5Sn0.5)1.1C0.95 (CC-MAX-Ta) and (V0.2Ti0.2Zr0.2Nb0.2Hf0.2)2(Al0.5Sn0.5)1.1C0.95 (CC-MAX-V) material system were in situ irradiated in a transmission electron microscope (TEM) up to a fluence of 5.4superior×1017 ions.cm-2 with 6 keV He+ at 350 °C, 600 °C and 800 °C. Homogeneous and heterogeneous nucleation of helium bubbles, growth of bubbles, black spot damage (BSD), grain boundary tear, thin foil blistering and some amorphization was observable in both material systems at 350 °C. A 2D arrangement of helium into platelets was prevalent at 600 °C. He accumulation and vacancy adsorption was identified as the mechanism of cavity size growth at 350 °C and helium platelets occurrence and evolution was observed and understood as the growth of a Griffith-like nanocrack through the expansion of a dislocation dipole. At 800 °C, no amorphization was observed in both ceramics and helium bubble sizes were suppressed as compared to those observed at 350 °C. The superior damage recovery potential of CC-MAX-V as compared to the CC-MAX-Ta at 800 °C might be explained based on the ease of motion of V-V, V-Ti interstitial species configurations in the crystal lattice and the chemical environment mediated by V. The effects of electron-phonon coupling induced ionization induced annealing (IIA) in both material systems were discussed.

A new family of nanostructured ternary intermetallic compounds - named the ZIP phases - is introduced in this work. The ZIP phases exhibit dualistic atomic ordering, i.e., they form two structural variants: one with the fcc diamond cubic structure (space group Fd 3 ¯ $\bar 3$ m) and one with the hexagonal structure (space group P63/mmc). They are also characterized by metallic behavior, ionic bonding, and atomic zigzagging. Powder metallurgical routes involving pressure-assisted densification are adopted to demonstrate ZIP phase synthesis in the Nb-Si-Ni, Nb-Si-Co, Ta-Si-Ni, V-Si-Ni, and Nb-Si-Fe ternary systems. Crucially, reactive hot pressing is capable of producing high-purity ZIP phase materials after the judicious, elemental system-specific optimization of the processing route. Synthesis of phase-pure materials - demonstrated in the Nb-Si-Ni ternary system by the synthesis of quasi phase-pure Nb3SiNi2 and Ni3SiNb2 ZIP phase-based materials - is a steppingstone to the prospective exploitation of the ZIP phases. Characterization of Nb3SiNi2 and Ni3SiNb2 involves crystal structure determination, spatially resolved chemical analysis, and determination of select thermal, electrical, magnetic, mechanical, and physical properties. Density functional theory is used to assess the stability of Nb3SiNi2 & Ni3SiNb2 and derivative binary compounds at different temperatures, also exploring the exfoliation of these two ZIP phases along specific surfaces to produce 2D derivatives.

The MAX phases constitute a family of nanolaminated ternary carbides and nitrides renowned for their compositional versatility, as reflected in the easy formation of solid solutions with variable chemical complexity. Synthesizing MAX phase solid solutions with intentionally tailored chemical complexity can produce materials that are able to meet the property requirements of the targeted application(s). This work presents an effective strategy specifically developed to design and fabricate highly phase-pure ceramics based on chemically complex MAX phase solid solutions by sterically stabilizing their unit cells. Steric unit cell stabilization is achieved via a judicious balance of dissimilar M- and A-elements, which targets the minimization of lattice distortions. This work produced high-purity (up to 88.7 wt %) (Zr0.8,Ti0.2)2(Al,Sn,Pb)C and (Zr0.8,Ti0.2)2(Al,Sn,Pb,Bi)C 211 MAX phase solid solutions by spark plasma sintering at 1350-1500 °C. Molten Zn- and/or Pb-/Bi-containing intermetallics facilitated the synthesis of soft (3-5 GPa), coarse-grained (length >20 μm, thickness >10 μm), and damage-tolerant ceramics. Intermetallics comprising Zn, Pb, and Bi improved (a) C/carbide dissolution, (b) Sn/C diffusion, and (c) carbide wetting, thus producing a 312 (Zr0.8,Ti0.2)3(Al,Sn,Pb,Bi)C2 MAX phase solid solution. Forming (Zr0.8,Ti0.2)3(Al,Sn,Pb,Bi)C2 contributed to the growth of very large platelets (length >100 μm) with a distinct (312-core)/(211-shell) morphology. Zn did not occupy the A-site, unlike Al, Sn, Pb, and Bi. Sterically balanced A-site elemental occupancies, albeit nonequimolar, alleviated lattice distortions and aided the steric stabilization of the crystal structure, whereas the chemical complexity on the A-site increased the configurational entropy of the synthesized MAX phase compounds, despite pre-existing M-site compositional restrictions, further enhancing their thermodynamic stability.

Silicon carbide (SiC) is a high-performance ceramic renowned for its excellent strength, thermal stability, and corrosion resistance, making it highly critical for advanced applications. Yet, achieving reliable joints remains challenging, especially given the need for localized heating rather than bulk heating of an entire SiC component. Laser-assisted joining has emerged as a promising alternative, offering the advantages of localized heating, rapid processing without the need for pressure, and precise energy control that significantly minimizes impact on adjacent materials. This study examines the feasibility of using two different infrared diode lasers for pressure-less, localized joining of SiC/SiC tubes to SiC/SiC end-plugs. The results are compared with those obtained using conventional furnaces. A silica-alumina-yttria-based glass is utilized as the joining material. The morphology, microstructure, and mechanical strength of the joints are analyzed, with strength evaluated through push tests designed to detach the end-plug from the tube.

Oxide-dispersion-strengthened FeCrAl (ODS-FeCrAl) alloys are candidate accident-tolerant fuel cladding materials for light water reactors because they demonstrate satisfactory resistance to materials degradation effects such as high-temperature oxidation, radiation-induced swelling, and creep. Their perspective deployment to market is challenged, however, by their inherent susceptibility to irradiation embrittlement caused by the precipitation of the brittle Cr-rich alpha' phase at relatively low temperatures (<= 475 degrees C). This work used in situ self-ion irradiation (150 key Fe+) in a transmission electron microscope to elucidate the early stages of Cr-rich alpha' phase precipitation in three candidate ODS-FeCrAl alloy fuel cladding materials with different Cr contents (10, 12, and 20 wt.%) and microstructures. The early stages of the process resulting in the precipitation of the Cr-rich alpha' phase in these three ODS-FeCrAl alloys under Fe+ irradiation were investigated at room temperature and 300 degrees C up to total fluences of 1.7 x 1015 ions center dot cm-2 (2 dpa) and 3.4 x 1015 ions center dot cm-2 (4 dpa), using three damage dose rates (5 x 10-5, 3.3 x 10-4, and 2 x 10-3 dpa center dot s-1). Post-irradiation examination via scanning transmission electron microscopy, energy-dispersive X-ray spectroscopy and electron energy loss spectroscopy suggested that the precipitation of the Cr-rich alpha' phase might be promoted by the phase separation of the alloy matrix into Cr-rich and Fe-rich regions. Interestingly, oxygen impurities segregated preferentially in the Cr-rich regions, possibly promoting the radiation-assisted formation of the Cr-rich alpha' phase. alpha' phase precipitation was more pronounced at room temperature when compared to 300 degrees C, and it was clearly promoted by the progressive increase in the Cr content of the ODS-FeCrAl alloy.

The synthesis of high-purity M n+1 AX n (MAX) phase ceramics in the Hf-Al-C ternary system from nearstoichiometric feedstock powder mixtures has been exceptionally challenging due to the rapid concurrent formation of persistent, ultrafine HfC impurities. This work synthesized ceramics containing the nanolaminated Hf5Al2C3 5 Al 2 C 3 'superstructure', showing that it comprises alternating Hf2AlC 2 AlC and Hf3AlC2 3 AlC 2 atomic stackings. For the first time, the Hf5Al2C3 5 Al 2 C 3 complex structure was associated with the topotactic transformation of Hf2AlC 2 AlC into Hf3AlC2, 3 AlC 2 , which is observed upon heating the powder compact to temperatures higher than 1500 degrees C; moreover, an inverse decomposition reaction of Hf3AlC2 3 AlC 2 into Hf2AlC 2 AlC was observed as result of further heating the powder compact to temperatures exceeding 1600 degrees C. The crystal structure and lattice parameters of the Hf5Al2C3 5 Al 2 C 3 'superstructure' were determined. MAX phase ceramics containing up to 40-45 wt% Hf3AlC2/Hf2AlC 3 AlC 2 /Hf 2 AlC were produced with HfC as the main competing phase. The hardness and damage tolerance of these MAX phase ceramics were also evaluated.

The synthesis of high-purity Mn+1AXn (MAX) phase ceramics in the Hf-Al-C ternary system from near-stoichiometric feedstock powder mixtures has been exceptionally challenging due to the rapid concurrent formation of persistent, ultrafine HfC impurities. This work synthesized ceramics containing the nanolaminated Hf5Al2C3 ‘superstructure’, showing that it comprises alternating Hf2AlC and Hf3AlC2 atomic stackings. For the first time, the Hf5Al2C3 complex structure was associated with the topotactic transformation of Hf2AlC into Hf3AlC2, which is observed upon heating the powder compact to temperatures higher than 1500 °C; moreover, an inverse decomposition reaction of Hf3AlC2 into Hf2AlC was observed as result of further heating the powder compact to temperatures exceeding 1600 °C. The crystal structure and lattice parameters of the Hf5Al2C3 ‘superstructure’ were determined. MAX phase ceramics containing up to 40–45 wt% Hf3AlC2/Hf2AlC were produced with HfC as the main competing phase. The hardness and damage tolerance of these MAX phase ceramics were also evaluated.

A new potential class of nanolaminated and structurally complex materials, herein conceived as the Zigzag IntermetAllic (ZIA) phases, is proposed. A study of the constituent phases of a specific Nb--Si--Ni intermetallic alloy revealed that its ternary H-phase, \textit{i.e.}, the Nb$_3$SiNi$_2$ intermetallic compound (IMC), is a crystalline solid with the close-packed \textit{fcc} Bravais lattice, the 312 MAX phase stoichiometry and a layered atomic arrangement that may define an entire class of nanolaminated IMCs analogous to the nanolaminated ceramic compounds known today as the MAX phases. The electron microscopy investigation of the Nb$_{3}$SiNi$_{2}$ compound -- the first candidate ZIA phase -- revealed a remarkable structural complexity, as its ordered unit cell is made of 96 atoms. The ZIA phases extend the concept of nanolaminated crystalline solids well beyond the MAX phases family of early transition metal carbides/nitrides, most likely broadening the spectrum of achievable material properties into domains typically not covered by the MAX phases. Furthermore, this work uncovers that both families of nanolaminated crystalline solids, \textit{i.e.}, the herein introduced \textit{fcc} ZIA phases and all known variants of the \textit{hcp} MAX phases, obey the same overarching stoichiometric rule $P_{x+y}A_xN_y$, where $x$ and $y$ are integers ranging from 1 to 6.

Materials subjected to irradiation damage often undergo local microstructural changes that can affect their expected performance. To investigate such changes, this work proposes a novel approach to detect strain localisation caused by irradiation-induced damage in nuclear materials on the microstructural level, considering a statistically relevant number of grains. This approach determines local strains using highresolution digital image correlation (HRDIC) and compares them with the underlying material microstructure. Sets of images captured before and after irradiation are compared to generate full-field displacement maps that can then be differentiated to yield high-resolution strain maps. These strain maps can subsequently be used to understand the effects of irradiation-induced dimensional change and cracking on the microscale. Here, the methodology and challenges involved in combining scanning electron microscopy (SEM) with HRDIC to generate strain maps associated with radiation-induced damage are presented. Furthermore, this work demonstrates the capabilities of this methodology by analysing three different materials subjected to proton irradiation: a zircaloy-4 (Zry-4) metal irradiated to 1 & 2 dpa, and two ceramics based on MAX phase compounds, i.e., the Nb4AlC3 ternary compound and a novel (Ta,Ti)(3) AlC2 solid solution, both irradiated to -0.1 dpa. These results demonstrated that all materials show measurable expansion, and the very high strains seen in the MAX phase ceramics can be easily attributed to their microstructure. Grain-to-grain variability was observed in Zry-4 with a macroscopic expansion along the rolling direction that increased with irradiation damage dose, the Nb4AlC3 ceramic showed significant expansion within individual grains, leading to intergranular cracking, while the less phase-pure (Ta,Ti)(3) AlC2 ceramic exhibited very high strains at phase boundaries, with limited expansion in the binary carbide phases. This ability to measure irradiation-induced dimensional changes at the microstructural scale is important for designing microstructures that are structurally resilient during irradiation. (c) 2023TheAuthors. Publishedby Elsevier B.V.

MXenes are electrically conductive 2D transition metal carbides/nitrides obtained by the etching of nanolaminated MAX phase compounds, followed by exfoliation to single- or few-layered nanosheets. The mainstream chemical etching processes have evolved from pure hydrofluoric acid (HF) etching into the innovative "minimally intensive layer delamination" (MILD) route. Despite their current popularity and remarkable application potential, the scalability of MILD-produced MXenes remains unproven, excluding MXenes from industrial applications. This work proposes a "next-generation MILD" (NGMILD) synthesis protocol for phase-pure, colloidally stable MXenes that withstand long periods of dry storage. NGMILD incorporates the synergistic effects of a secondary salt, a richer lithium (Li) environment, and iterative alcohol-based washing to achieve high-purity MXenes, while improving etching efficiency, intercalation, and shelf life. Moreover, NGMILD comprises a sulfuric acid (H2 SO4 ) post-treatment for the selective removal of the Li3 AlF6 impurity that commonly persists in MILD-produced MXenes. This work demonstrates the upscaled NGMILD synthesis of (50 g) phase-pure Ti3 C2 Tz MXene clays with high extraction yields (>22%) of supernatant dispersions. Finally, NGMILD-produced MXene clays dry-stored for six months under ambient conditions experience minimal degradation, while retaining excellent redispersibility. Overall, the NGMILD protocol is a leap forward toward the industrial production of MXenes and their subsequent market deployment.

Chemically complex MAX phase-based ceramics in the (Ti,Zr,Hf,V,Nb)-(Al,Sn)-C system were synthesised by reactive hot pressing for 30 min at 1250-1450 degrees C under a load of 30 MPa for the first time in this work. The dense bulk ceramics contained chemically complex double solid solution MAX phases, each comprising five M-elements and two A-elements. The predominant 211 (Ti-0.23,Zr-0.18,Hf-0.20,V-0.11,Nb-0.28)(2)(Al-0.42,Sn-0.58)C MAX phase characterised all ceramics, while the 312 (Ti-0.23,Zr-0.31,Hf-0.31,V-0.08,Nb-0.08)(3)(Al-0.36,Sn-0.64)C-2 and 211 (Ti-0.26,Zr-0.07,Hf-0.07,V-0.47,Nb-0.13)(2)(Al-0.66,Sn-0.34)C MAX phases were only present in the ceramics sintered at 1350-1450 degrees C. A limited amount (4-5 vol%) of parasitic phases (mainly, binary intermetallics) was found in the pseudo-binary carbide-free ceramics sintered at 1350-1450 degrees C. IMPACT STATEMENT Chemically complex 211 & 312 double solid solution MAX phase-based ceramics with a MAX phase content up to 96 vol% were synthesised in the (Ti,Zr,Hf,V,Nb)-(Al,Sn)-C system for the first time.

Liquid lead (Pb)- and lead–bismuth eutectic (LBE)-cooled fast neutron reactors (Gen-IV LFRs) are one of the most technologically mature fission reactor technologies, due to their inherent safety, high power density, and ability to burn nuclear waste. Accelerator-driven systems (ADS), in particular, promise to address the issues of long-lived radiotoxic nuclear waste, emerging uranium ore shortages, and the ever-increasing demand for energy. However, the conditional compatibility of conventional structural materials, such as steels, with liquid Pb and liquid LBE is still an important concern for the deployment of these advanced nuclear reactor systems, making the environmental degradation of candidate structural and fuel cladding steels the main impediment to the construction of Gen-IV LFRs, including ADS. This article presents a comprehensive review of the current understanding of environmental degradation of materials in contact with liquid Pb and liquid LBE, with a focus on the underlying mechanisms and the factors affecting liquid metal corrosion (LMC) and liquid metal embrittlement (LME), which are the two most important materials degradation effects. Moreover, this article addresses the most promising LMC and LME mitigation approaches, which aim to suppress their adverse influence on materials performance. An outlook of the needed future work in this field is also provided.

In the present work, we apply a high-throughput density functional theory (DFT) screening of interesting M2AX phase compounds for nuclear applications by assessing their mechanical stability. Evaluation of mechanical stability allows to assess thermodynamically unstable phases and does not require the assessment of competing MX and intermetallic phases. We consider all possible combinations with M = {Ti, Cr, Zr, Nb}, A = {Al, Si, Sn, Pb, Bi} and X = {C}, including “out-of-plane” ordering that is so far unobserved in M2AX phases. For all fifty possible combinations, we determine the elastic constants and verify their mechanical stability. In addition, for each combination, the free surface energy is computed and the fracture toughness, KIC, is determined. The results are discussed in terms of combinations with high mechanical stability and high KIC. Apart from suggestions of interesting new combinations, the results also form the basis for any plasticity or fracture mechanics model for these MAX phases.

MAX phase ceramics are typically prepared by the reactive sintering of elemental powders that are often coarse, expensive, and prone to oxidation. The temperature-driven dehydrogenation of metal hydride powders offers an alternative synthesis approach, as the hydrides decompose into phase-pure, dimensionally fine elemental powder particles. The increased reactivity of these in situ formed, fine powder particles drastically reduces the formation temperature of the antecedent intermetallic phases, without forming excess binary carbides or facilitating powder oxidation in the Ti-Al-C and Zr-Al-C systems. This work elucidates the effect of metal hydrides on the sequence of formation reactions in MAX phase ceramics. In the Zr-Al-C system, the use of coarse, oxidation-prone elemental Zr powders prevented MAX phase formation, whereas spark plasma sintering of ZrH2 powders at 1500 degrees C produced ceramics containing 60 wt% Zr3AlC2. Similarly, in the Ti-Al-C system, spark plasma sintering of TiH2 powders at 1200 degrees C produced phase-pure Ti3AlC2 ceramics.

Kinking is a deformation mechanism ubiquitous to layered systems, ranging from the nanometer scale in layered crystalline solids, to the kilometer scale in geological formations. Herein, we demonstrate its origins in the former through multiscale experiments and atomistic simulations. When compressively loaded parallel to their basal planes, layered crystalline solids first buckle elastically, then nucleate atomic-scale, highly stressed ripplocation boundaries – a process driven by redistributing strain from energetically expensive in-plane bonds to cheaper out-of-plane bonds. The consequences are far reaching as the unique mechanical properties of layered crystalline solids are highly dependent upon their ability to deform by kinking. Moreover, the compressive strength of numerous natural and engineered layered systems depends upon the ease of kinking or lack there of.

This work addresses the early stages (<= 1000 h) of the dissolution corrosion behavior of 316L and DIN 1.4970 austenitic stainless steels in contact with oxygen-poor (C-O < 10(-8) mass%), static liquid lead-bismuth eutectic (LBE) at 500 degrees C for 600-1000 h. The objective of this study was to determine the relative early-stage resistance of the uncoated steels to dissolution corrosion and to assess the protectiveness of select candidate coatings (Cr2AlC, Al2O3, V2AlxCy). The simultaneous exposure of steels with intended differences in microstructure and thermomechanical state showed the effects of steel grain size, density of annealing/deformation twins, and secondary precipitates on the steel dissolution corrosion behavior. The findings of this study provide recommendations on steel manufacturing with the aim of using the steels to construct Gen-IV lead-cooled fast reactors.

Mould casting and sacrificial templating techniques, common in bioceramic technology, were employed to process porous TaCx ultra-high temperature ceramics intended as novel target materials for isotope separation on-line (ISOL) facilities, aiming primarily at the production of medical radioisotopes. A feedstock of Ta4AlC3 MAX phase powder, polyamide spheres and wax was used to obtain different porous TaCx grades with bimodal pore size distributions. The 'green' bodies underwent de-binding and vacuum annealing to decompose the MAX phase, whereas a reference material was also produced from commercial TaC powders. The thermal stability of the porous TaCx ceramics was assessed at ISOL-relevant conditions by heating in high vacuum up to 2200 degrees C. The MAX phase-derived TaCx porous ceramics evolved from biphasic TaCx/alpha-Ta2C to single-phase TaCx at higher temperatures, due to carbon incorporation. The porous TaCx microstructure was stable at 2200 degrees C with a specific surface area stabilizing at similar to 0.25 m(2)/g and thermal conductivity of 1-4 W/m K.