arXiv subjects

Nabil Daghbouj

Publications and source records attributed to Nabil Daghbouj.

5 recordsLinked to original sources

arXiv2026

An integrated viscoelastic modeling framework combining analytical and FEM approaches: Application to WSe2 coatings

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.

physics.app-ph↗

arXiv2026

Cross-sectional helium irradiation reveals interface-controlled bubble evolution in Cr/CrAlSiN multilayer coatings on zirconium alloys

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 He irradiation to directly examine the interfacial response and He bubble evolution across Cr monolayer and Cr and CrAlSiN multilayer coatings on Zr substrates. Irradiation was carried out at 500 C and 750 C to doses of 2 and 3 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 and 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 and 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 and CrAlSiN multilayers as advanced coating architectures for high-temperature nuclear environments.

cond-mat.mtrl-sci↗

arXiv2026

Defect Landscape Engineering Suppresses Helium Damage in Ceramics

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 helium traps, fundamentally altering cascade recombination dynamics. 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.

physics.app-ph↗

arXiv2025

Nanoscale Strain Evolution and Grain Boundary-Mediated Defect Sink Behavior in Irradiated SiC: Insights from N-PED and DFT

Understanding irradiation-induced strain in silicon carbide (SiC) is essential for designing radiation-tolerant ceramic materials. However, conventional methods often fail to resolve nanoscale strain gradients, especially in polycrystalline forms. In this study, we employ nano-beam precession electron diffraction (N-PED) to perform high-resolution, multi-directional strain mapping in both single-crystal 4H-SiC and polycrystalline {\alpha}-SiC subjected to helium and hydrogen ion irradiation. The high-resolution X-ray diffraction (HR-XRD) simulations of He + H irradiated single-crystal 4H-SiC closely match the strain profiles obtained from N-PED, demonstrating the reliability and accuracy of the N-PED method. In He-irradiated polycrystalline {\alpha}-SiC at high temperatures, a bubble-depleted zone (BDZ) near the grain boundary (GB) reveals that GBs act as active sinks for irradiation-induced defects. N-PED further shows strain amplification localized at the GBs, reaching up to 2.5%, along with strain relief within the BDZ. To explain this behavior, density functional theory (DFT) calculations of binding and migration energies indicate a strong tendency for Si, C, and He atoms to segregate toward the GB core. This segregation reduces the availability of vacancies to accommodate He atoms and leads to local strain relaxation near the GB. Furthermore, first-principles tensile simulations reveal that Si and C interstitials mitigate He-induced GB embrittlement. Charge density and DOS analyses link this effect to the bonding characteristics between point defects and neighboring atoms at GB. These insights underscore the importance of grain boundary engineering in enhancing radiation tolerance of SiC for nuclear and space applications.

cond-mat.mtrl-sci↗

arXiv2025

A comparative nanotribological investigation on amorphous and polycrystalline forms of MoS2

The wear behavior of two amorphous and polycrystalline forms of MoS2 prepared by magnetron sputtering has been characterized in a combined nanoindentation and atomic force microscopy study. From the analysis of the depth and width of wear tracks estimated after scratching the surfaces with a Berkovich indenter and a loading force up to 2 mN, we conclude that both forms follow the Archard wear equation, and the wear resistance is about four times higher on the amorphous MoS2. Moreover, a comparison of lateral force maps on pristine and worn areas shows a considerable reduction of friction on both forms, which is possibly due to the significant smoothing of the surfaces caused by scratching. With normal forces in the micro N range, the analysis is made difficult by the fact that the linear dimensions of the wear tracks are comparable to those of the granular structures forming the surfaces. Even if the Archard equation could not be tested in this case, the wear resistance is considerably larger on amorphous MoS2 also on the nanoscale. In this way, our results disclose information on the nanotribology of MoS2 thin films in forms different from the layered structures commonly discussed in the literature. The amorphous form outperforms the polycrystalline one.

cond-mat.mtrl-sci↗