Search Results (343)

The development of multilayer coatings based on titanium carbides and nitrides remains one of the most active areas in materials science, owing to their ability to markedly enhance wear resistance and extend the service life of machine components. Particular interest is currently focused on tailoring conventional TiN/TiCN architectures through alloying metal additions. In this study, the tribological and mechanical performance of aluminum- and zirconium-doped TiN/TiCN multilayer coatings deposited by direct-current magnetron sputtering onto 41Cr4 steel was investigated. The morphology, elemental distribution, and phase constitution of the multilayer coatings were examined. It is shown that increasing the number of bilayers from two to four in TiN/TiCN–based multilayer coatings leads to improved tribomechanical characteristics. It was determined that zirconium provides a more pronounced beneficial effect than aluminum. The four-bilayer TiZrN/TiZrCN coating simultaneously exhibited the lowest coefficient of friction (0.11) and wear rate (10⁻⁶ mm³ m⁻¹ N⁻¹) at a hardness of 16.4 GPa. Full article

Zr alloy-shaped charge liners (SCLs) offer broad application prospects due to their multiple post-penetration damage effects. However, research on these liners is still in its early stages. The mechanisms of jet formation and penetration for Zr alloys SCL remain unclear, and the specific contribution of different liner regions to the penetration process is not yet understood. This gap in knowledge has limited their structural design to a black-box correlation between global structural parameters and macroscopic penetration efficiency. To address this gap, a region-tracing Smoothed Particle Hydrodynamics (SPH) simulation was employed. Following a strategy of “wall thickness layering + axial segmentation,” the Zr alloy liner was partitioned into ten characteristic regions. This methodology facilitated the tracking of material transport from each region during jet formation and penetration into an AISI 1045 steel target. The contribution of each region to the penetration depth was then quantitatively assessed via post-processing. For the first time, the “critical region” contributing most to penetration depth was identified, and the influence of the liner’s cone angle and wall thickness on the contribution of each region was revealed. This study enhances the theoretical framework for understanding the damage effects of Zr alloy shaped charge liners. It not only advances the fundamental understanding of jet penetration mechanisms but also provides a theoretical basis for the refined design and performance optimization of these liners. Full article

Precise control and characterization of coating thickness are critical for the reliability and structural integrity of zirconium alloy claddings in nuclear reactors. However, conventional techniques such as scanning electron microscopy (SEM) and metallographic microscopy are often limited by low efficiency, complex sample preparation, and destructive testing. This study proposes a fundamental parameter method based on energy-dispersive X-ray fluorescence. It is designed for the rapid, accurate, and non-destructive determination of zirconium alloy coating thickness. X-ray fluorescence intensity is theoretically calculated from measurement conditions and fundamental parameters, with consideration of absorption-enhancement effects from primary and secondary fluorescence. Quantitative thickness is obtained through iterative calculations until the measured intensity agrees with the theoretical intensity. Using this method, a series of chromium coatings with different thicknesses deposited on zirconium substrates were analyzed. The relative error of the calculated thickness was within ±5% for most samples compared with cross-sectional SEM results, demonstrating the accuracy of the proposed method. Full article

Modern materials science is focused on the development of steels with a range of performance characteristics, including high strength, wear resistance, corrosion resistance, and long-term performance in various conditions. Special attention is paid to the control of the microstructure of steels at the crystallization stage, which allows for the improvement of metal properties without significantly increasing the cost of the manufacturing process. One of the promising methods of microstructural engineering is the modification of steels with dispersed particles of refractory compounds, such as titanium carbide (TiC), zirconium carbide (ZrC), and tungsten carbide (WC). However, the processes of dissolution, dissociation, and interaction of such ceramic particles with the metal melt, as well as their influence on the formation of the microstructure and properties under the conditions of non-equilibrium crystallization, which is typical for centrifugal casting, are not sufficiently studied for austenitic stainless steels. In this work, the influence of dispersed carbide particles of TiC, ZrC, and WC, which are introduced into the melt of austenitic stainless steel (Cr ≈ 18%, Ni ≈ 10%) during centrifugal casting, on the redistribution of alloying elements, the formation of the microstructure, and the mechanical properties of the material is investigated. Special attention is paid to the kinetic nature of the dissolution and interaction of the carbides with the melt, as well as the directional distribution of elements across the cross-section of the billets. The study includes the analysis of the distribution of Ti, W, and Zr across the cross-section of the centrifugally cast billets, the study of the microstructure and phase composition of the inclusions using SEM/EDS, and mechanical testing. It is found that the implementation of dispersion hardening leads to an increase in the tensile strength by up to ~22% compared to the initial alloy (from 496 to 612 MPa), while the impact strength decreases by 5–25% (from 110 to 82 J/cm²) depending on the type and quantity of the introduced particles. The analysis of microhardness shows the presence of a gradient of local properties across the cross-section of the centrifugally cast billets, with microhardness values ranging from ~110 to 195 HV0.5. For the modified samples, the relative difference between the inner and outer zones is ~5–20%, reflecting the combined effect of non-equilibrium solidification, redistribution of alloying elements, formation and spatial distribution of secondary phases, and local structural heterogeneity. These results confirm the possibility of controlling the distribution of properties within a single billet. Full article

The long-term performance of metallic biomaterials in the oral environment is strongly influenced by their interaction with saliva and its variable chemical conditions. In this study, the biomimetic behavior of a Zr-2.5Nb alloy was investigated during immersion in artificial saliva with acidic, neutral, and alkaline pH for a period of 28 days, aiming to simulate diverse physiological and pathological oral conditions. The evolution of saliva pH was continuously monitored throughout the immersion period to assess the dynamic material–environment interactions. Surface morphology, elemental composition, and chemical structure were analyzed using scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM/EDX) and Fourier-transform infrared spectroscopy (FTIR), while corrosion resistance was evaluated through electrochemical measurements. The results revealed distinct pH-dependent surface responses, with acidic saliva promoting localized surface modifications and increased corrosion susceptibility, whereas neutral conditions favored the formation of stable and protective passive layers, and alkaline environments promoted the development of chemically complex surface layers that exhibited initial stabilization but underwent progressive degradation during long-term exposure. Overall, the Zr-2.5Nb alloy demonstrated a high degree of corrosion resistance and chemical stability, particularly under neutral and alkaline conditions, supporting its suitability for dental and oral biomedical applications. These findings provide a biomimetic perspective on pH-driven surface adaptation and long-term corrosion behavior, highlighting how dynamic material–environment interactions govern the performance of zirconium-based biomaterials in complex oral environments. Full article

To enhance the protection of zirconium alloys during loss-of-coolant accident conditions, the water vapor corrosion resistance of Y³⁺-stabilized zirconia coatings fabricated by plasma electrolytic oxidation on zirconium alloy was remarkably improved in this study. The corrosion resistance mechanisms of the coating were disclosed by simulating water vapor reaction processes in cubic zirconia (c-ZrO₂) and tetragonal zirconia (t-ZrO₂). The results revealed that the mass fraction of c-ZrO₂ in the coatings was increased from 9% to 32% by adjusting the Y³⁺ concentration. The mass gain and corrosion rate of the enhanced coating were approximately 60% and 37% after 3600 s water vapor corrosion at 1000 °C separately compared to those of traditional zirconia coating. This enhancement is attributed to the slower reaction rates of c-ZrO₂ with water vapor than t-ZrO₂, which suppresses corrosion and reduces the formation of Zr(OH)₄. Thus, less cracks appeared in coatings with higher c-ZrO₂ fractions, as their corrosion layers contained fewer corrosion products that induced stress concentration, which, in turn, protects the subsurface coatings from further corrosion. This study provides a viable strategy for developing coatings to protect zirconium alloys against water vapor corrosion in nuclear energy applications. Full article

Titanium-based alloys are widely used in dental implantology; however, the mechanical limitations of commercially pure titanium (cpTi) and unresolved concerns regarding stress shielding remain. This study evaluated the structure–property–function relationship of a novel β-type titanium-niobium-zirconium (Ti-Nb-Zr; TNZ) alloy for dental implant applications. Laboratory testing assessed the elemental composition, tensile properties, and fatigue resistance of the cpTi, compared with modified Grade 4 cpTi (MG4T). In parallel, a randomized, single-blind, controlled clinical trial was conducted over 12 months to compare the clinical performance of TNZ and MG4T implants under functional loading. A total of 80 participants (mean age: 54.2 years; 43 females, 37 males) were enrolled, with 77 completing the 12-month follow-up (TNZ: n = 38; MG4T: n = 39). Clinical outcomes included implant success and survival, peri-implant soft tissue parameters, marginal bone levels, fractal dimension (FD) analysis of trabecular bone, and adverse events. TNZ implants demonstrated superior fatigue resistance without an increase in the elastic modulus relative to MG4T. Clinically, both groups achieved 100% implant success and survival, with no implant-related adverse events. FD analysis revealed time-dependent bone remodeling without evidence of pathological adaptation. These findings support the functional viability of TNZ as a mechanically robust, biocompatible implant material. Further long-term, multicenter trials are warranted to confirm sustained clinical benefits and broader applicability. Full article

The performance of Zr-2.5Nb alloy pressure tubes in nuclear reactors is critically dependent on the behavior of precipitated hydrides. In this study, a hydrogen-charged Zr-2.5Nb alloy pressure tube was subjected to in situ tensile testing combined with electron backscatter diffraction to elucidate microcrack evolution and microstructural adaptation. Initially, longitudinal hydride–hydride interface cracks nucleated at non-coherent interfaces of two types of hydrides due to the inherent brittleness. Subsequently, stress redistribution by a small proportion of hydride–hydride interface cracks resulted in the emergence of microcracks at the transverse hydride–matrix interfaces, accompanied by partial hydride phase transformation. Finally, under high strain conditions, increased dislocation movement in the matrix triggered a single slip system, leading to the formation of numerous low-angle grain boundaries. As strain further increased, multiple slip systems were activated, and longitudinal matrix–matrix interface cracks began to nucleate at certain grain boundary locations. Full article

Experimental results are compiled to show apparent hysteresis seen in hydride thermal precipitation–dissolution cycling in zirconium alloys using X-ray diffraction, dynamic elastic modulus techniques, and differential scanning calorimetry (DSC). Gibbs’ phase rule is used to justify a description of a stable hydride in the H-Zr system in terms of a control volume with a hydride at its core, surrounded by a stress gradient that produces a stabilizing gradient of hydrogen in the solution. The conditions for a stable hydride are derived when the flux of hydrogen in solid solution is zero. DSC heat flow curves are analyzed with a thermodynamic model that predicts concentrations of hydrogen in a solution during temperature cycling and a description of experimental results that show how concentrations evolve at a constant temperature to the same final state when cycling is paused, from which hysteresis is deemed an illusion. The control volume is supported by previous energy calculations, performed with density functional theory. Implications of replacing the order parameter for phase field methods with the gradient of the yield stress are discussed. A practical method for forming a stable hydride is presented. Full article

To enhance the wear and corrosion resistance of Zr alloy components in marine engineering, this study investigated the influence of the applied voltage (ranging from 470 to 620 V) on the morphology, structure, and properties of ceramic coatings formed on a Zr alloy substrate by Micro-arc Oxidation (MAO) in a silicate–phosphate composite electrolyte. The results showed that with increasing voltage, the coating thickness increased (from 15.12 to 52.80 μm) and the surface roughness increased (from 1.12 to 4.89 μm), while both the surface and cross-sectional porosity first increased and then reached their minimum values at 620 V (1.61% and 5.75%, respectively). Phase analyses indicated that the coatings consisted mainly of monoclinic ZrO₂ (m-ZrO₂), along with minor amounts of SiO₂, ZrSiO₄, and Zr₃(PO₄)₄. The coating prepared at 620 V exhibited optimal performance: its hardness was 1.98 times that of the substrate, the wear volume decreased by approximately 87%, the self-corrosion potential shifted positively by 539 mV, the corrosion current density decreased by nearly two orders of magnitude, and the polarization resistance increased by approximately two orders of magnitude. These results demonstrate a substantial improvement in the service performance of Zr alloys for marine applications. Full article

Zirconium and its alloys are widely used in nuclear power engineering due to their favorable physical and mechanical properties and their low thermal-neutron absorption cross-section. Their high corrosion resistance in aqueous and steam environments at elevated temperatures is essential for the reliable operation of fuel assemblies and is associated with the formation of a stable, compact ZrO₂ oxide layer. However, under reactor conditions, the presence of hydrogen, iodine and other fission products can reduce corrosion resistance, making detailed corrosion assessment necessary. Manufacturing technology, alongside alloy composition, also plays a decisive role in determining corrosion behavior. This study presents corrosion test results for a Zr-1%Nb alloy processed under thermomechanical conditions corresponding to rolling in a special type of three-roll skew rolling–Radial-Shear Rolling (RSR). The applied rolling technology ensured the formation of a pronounced ultrafine-grained (UFG) structure in the near-surface layers, with an average grain size below 0.6 µm. EBSD and TEM observations revealed a largely equiaxed microstructure with refined grains and increased grain boundary density. The corrosion testing was performed in high-temperature steam vessels at 400 °C and 10.3 MPa for 72, 336, 720 and 1440 h. The results demonstrate that RSR processing is an efficient alternative to conventional multi-pass normal bar rolling with vacuum heat treatments, allowing a significant reduction in processing steps and eliminating the need for expensive tooling and intermediate thermal or chemical treatments. Bars manufactured using this method meet the ASTM B351 requirements. The specific weight gain did not exceed 22 mg/dm² after 72 h and 34.5 mg/dm² after 336 h. After 1440 h, the samples exhibited a continuous, uniform dark-grey oxide layer with an average thickness below 5.3 µm. Full article

The effect of the multilayer structure of Cr/CrN coatings deposited by reactive magnetron sputtering on zirconium alloy E110 (Zr–1Nb) on their thermal stability and resistance to steam oxidation at 1100 °C was studied. Coatings with different numbers of alternating Cr and CrN sublayers (1, 2, 4, and 6) were fabricated using experimental methods of X-ray diffraction (XRD) and scanning electron microscopy with energy-dispersive analysis (SEM/EDS). It was shown that an increase in the number of alternating Cr and CrN sublayers leads to the preservation of the cubic phase of CrN, the formation of a dense structure, and a decrease in Cr–Zr interdiffusion. After testing, multilayer coatings retaining the internal structure and a sufficiently structurally dense Cr₂O₃ layer effectively ensured air penetration. The best thermal stability was demonstrated by a six-layer coating, ensuring minimal oxidation and preservation of the E110 substrate. Full article

Growing environmental awareness has renewed interest in thorium as a nuclear fuel, underscoring the need for further studies to evaluate how reactors perform when conventional fuels are replaced with thorium-based alternatives. In this study, thermal hydraulics and solid mechanics computations were simulated using COMSOL multiphysics to investigate the safe operating conditions of a heavy water reactor with thorium-based fuel. The thermo-mechanical analysis of the fuel rod under transient heating conditions provides critical insights into strain, displacement, stress, and coolant flow behavior at elevated volumetric heat sources. After 3 s of heating, the strain distribution in the fuel exhibits a high-strain core surrounded by a low-strain rim, with peak volumetric strain increasing nearly linearly from 0.006 to 0.014 as heat generation rises. Displacement profiles confirm that radial deformation is concentrated at the outer surface, while axial elongation remains uniform and scales systematically with power. The resulting von Mises stress fields show maxima at the outer surface, increasing from ~0.06 to 0.15 GPa at the centerline with higher heat input but remaining within structural safety margins. Cladding simulations demonstrate nearly uniform axial expansion, with displacements increasing from ~0.012 mm to 0.03 mm across the investigated power range, and average strain remains negligible (≈10⁻⁴), while mean stresses increase moderately yet stay well below the yield strength of zirconium alloys, confirming safe elastic behavior. Hydrodynamic analysis shows that coolant velocity decreases smoothly along the axial direction but maintains stability, with only minor reductions under increased heat sources. Overall, the coupled thermo-mechanical and fluid-dynamic results confirm that both the fuel and cladding remain structurally stable under the studied conditions. By using COMSOL’s multiphysics capabilities, and unlike most legacy codes optimized for uranium-based fuel, this work is designed to easily incorporate non-traditional fuels such as thorium-based systems, including user-defined material properties, temperature-dependent thermal polynomial formulas, and mechanical response. Full article

Aluminum alloys used in harsh environments often suffer from inadequate protection due to the limited compactness and stability of existing chromate-free conversion coatings. This study designs and optimizes a corrosion-resistant vanadium-based conversion coating on 6061 aluminum alloy and investigates the influence of additives on its structure and performance. The effects of solution pH (2–4), reaction temperature (35–75 °C), and immersion time (10–30 min) on coating corrosion resistance were examined. The optimal parameters were determined as pH = 3, 55 °C, and 25 min, yielding a compact coating with excellent corrosion resistance (i_corr = 0.335 μA·cm⁻², E_corr = −0.596 V, |Z| = 48.7 kΩ·cm²). To further enhance performance, polyvinyl alcohol (PVA), chitosan (CS), and a combination of sodium hexametaphosphate and cerium nitrate (SHMP + Ce(NO₃)₃) were introduced into the conversion solution. Characterization by SEM, AFM, and contact angle measurements showed that SHMP + Ce(NO₃)₃ significantly improved coating uniformity and compactness (Rq = 131 nm, Ra = 107 nm), resulting in superior corrosion resistance (i_corr = 0.055 μA·cm⁻², |Z| = 67.9 kΩ·cm²). The coating exhibited strong adhesion (grade 5B) and no visible corrosion after 72 h of neutral salt spray exposure, demonstrating excellent protective capability. In contrast, PVA produced porous coatings with reduced resistance, while CS provided only limited improvement. Full article

Multilayer Cr/CrN coatings with two-, four-, and six-layer architectures were deposited on E110 zirconium alloy substrates by reactive magnetron sputtering. The effect of layer number on structure, phase composition, and performance was systematically investigated. XRD revealed that the coatings consisted mainly of CrN and Cr phases, with an increase in the CrN fraction and texture intensity as the number of layers increased. Cross-sectional SEM and EDS analyses confirmed the formation of dense multilayer structures with clear Cr/CrN interfaces and strong adhesion to the substrate. Nanoindentation showed a progressive increase in hardness and Young’s modulus from 2.59 ± 0.09 GPa and 97 ± 2 GPa (two-layer) to 5.0 ± 0.27 GPa and 110 ± 4 GPa (six-layer), respectively. Tribological and scratch tests demonstrated that the 6-layer coating exhibited the lowest wear rate and highest adhesion strength (Lc ≈ 20.5 N). Full article