Search Results (1,155)

To address surface defects and enhance the wear resistance of 316L stainless steel parts fabricated by Selective Laser Melting (SLM), this study applied shot peening (SP) surface treatment to the SLM-processed samples. Ball-on-disk tribological tests were systematically conducted under water-lubricated conditions to investigate the evolution of surface morphology, microstructure, microhardness, and tribological performance before and after SP. The results indicate that SP induced severe plastic deformation in the surface layer, effectively refining the coarse columnar crystals and melt pool structures characteristic of SLM, and forming a crystalline hardened layer with a depth of 70–80 μm. Consequently, the surface microhardness increased by 21.97% compared to the un-peened samples. Under loads of 20 N and 30 N, the coefficient of friction (COF) of the SP-treated samples decreased by 16.36% and 12.4%, while the wear rate was reduced by 17.09% and 14.9%, respectively. In this load range, the samples primarily exhibited uniform plowing and localized adhesive wear, demonstrating significantly improved resistance to plastic deformation and crack initiation. However, when the load increased to 40 N, intense stress and thermal effects diminished the strengthening benefits of SP, resulting in no significant difference in tribological performance between the SP-treated and untreated samples. At this stage, the dominant wear mechanism transitioned to severe plastic deformation, extensive delamination, and thermally induced adhesion. Full article

This study examines the mechanical response of medium-manganese TRIP steels under different stress states, focusing on deformation-induced austenite-to-martensite transformation and ageing phenomena. Two steels with distinctly different ferrite–austenite morphologies and retained austenite (RA) fractions were analysed: a globular microstructure with 18% RA and a lamellar microstructure with 14% RA, produced by single (SA) and double annealing (DA), respectively. Continuous and interrupted tests were performed under in-plane shear, uniaxial tension, and plane strain stress states. Strain fields were analysed using high-resolution digital image correlation, while RA fractions were quantified as a function of strain by ex situ X-ray diffraction. The results demonstrate a pronounced stress-state dependence. SA samples exhibit discontinuous yielding, with uniaxial tests showing clear Lüders band formation. Both steels exhibit dynamic strain ageing manifested by Portevin–Le Chatelier (PLC) serrations and associated strain bands, which are most pronounced under uniaxial tension, weaker in plane strain, and barely detectable in in-plane shear. Static strain ageing is also evidenced by a strengthened yield response upon unloading–reloading in all samples. The SA globular microstructure exhibits higher PLC band inclination angles than the lamellar DA microstructure, consistent with its more pronounced anisotropy. The propagation velocity in uniaxial tensile samples decreases with increasing strain following the work-hardening response. For both steels, the austenite-to-martensite transformation rate is highest in uniaxial tension, slightly reduced in plane strain, and strongly suppressed under in-plane shear. A Beese–Mohr/Johnson–Mehl–Avrami–Kolmogorov formulation incorporating stress triaxiality and Lode angle captures these trends for both steels. For the stress states considered, the DA condition exhibits a consistently higher transformation rate than the SA condition, accompanied by a higher work-hardening rate. These findings highlight the coupled role of stress state and microstructural morphology in governing localisation behaviour and strain-induced transformation in medium-manganese steels. Full article

This paper investigates the degradation characteristics of a DC/DC converter operating under cold redundancy conditions when subjected to total ionizing dose (TID) effects. An optimized RCC isolated auxiliary power supply circuit was evaluated through ⁶⁰Co γ-ray irradiation up to 100 krad(Si) at dose rates of 3.89, 8.89, and 13.89 rad (Si)/s, with electrical characterizations performed at both the system level and the device level, focusing on the critical VDMOS transistors. The results indicate that the main output voltage and conversion efficiency remain essentially stable after irradiation, whereas the auxiliary supply voltage and efficiency degrade significantly, leading to a pronounced reduction in the controller supply margin. Device-level measurements reveal a negative threshold voltage shift of approximately 0.5–1.0 V with clear dose-rate dependence, while the subthreshold swing shows no obvious variation, suggesting that the degradation is primarily dominated by oxide-trapped charge effects. In addition, a substantial increase in drain current at low gate voltages is observed, which may further exacerbate restart risks under cold redundancy conditions. These findings demonstrate that the auxiliary power supply and startup margin constitute critical vulnerability points of cold-redundant DC/DC converters under TID stress and should therefore be primary targets for radiation-hardened design. Full article

In recent years, the rapid development of commercial satellite projects, such as low-Earth orbit (LEO) communication and remote sensing constellations, has driven the satellite industry toward low-cost, rapid development, and large-scale deployment. Commercial off-the-shelf (COTS) components have been widely adopted across various commercial satellite platforms due to their advantages of low cost, high performance, and plug-and-play availability. However, the space environment is complex and hostile. COTS components were not originally designed for such conditions, and they often lack systematically flight-verified protective frameworks, making their reliability issues a core bottleneck limiting their extensive application in critical missions. This paper focuses on COTS solid-state drives (SSDs) onboard the Jilin-1 KF satellite and presents a full-lifecycle reliability practice covering component selection, system design, on-orbit operation, and failure feedback. The core contribution lies in proposing a full-lifecycle methodology that integrates proactive design—including multi-module redundancy architecture and targeted environmental stress screening—with on-orbit data monitoring and failure cause analysis. Through fault tree analysis, on-orbit data mining, and statistical analysis, it was found that SSD failures show a significant correlation with high-energy particle radiation in the South Atlantic Anomaly region. Building on this key spatial correlation, the on-orbit failure mode was successfully reproduced via proton irradiation experiments, confirming the mechanism of radiation-induced SSD damage and providing a basis for subsequent model development and management decisions. The study demonstrates that although individual COTS SSDs exhibit a certain failure rate, reasonable design, protection, and testing can enhance the on-orbit survivability of storage systems using COTS components. More broadly, by providing a validated closed-loop paradigm—encompassing design, flight verification and feedback, and iterative improvement—we enable the reliable use of COTS components in future cost-sensitive, high-performance satellite missions, adopting system-level solutions to balance cost and reliability without being confined to expensive radiation-hardened products. Full article

Acrylonitrile Styrene Acrylate (ASA) is widely used in outdoor structural applications due to its favorable mechanical stability and weather resistance; however, its temperature-dependent plastic behavior remains insufficiently characterized for accurate numerical simulation. This study presents a non-standard method of calibrating the temperature-dependent Johnson–Cook (J-C) plasticity model for ASA in the practical operating temperature range below the glass transition temperature. Uniaxial tensile tests at constant strain rate 0.01 s⁻¹ were performed at −10 °C, +23 °C, and +65 °C to characterize the effect of temperature on the material’s plastic response. The J-C parameters $A$, $B$, and $n$ were identified for each temperature separately and globally using least-squares optimization implemented in MATLAB R2024b, showing good agreement with the experimental stress–strain curves. The calibrated parameters were subsequently implemented in Abaqus 2024 and validated through finite element simulations of the tensile tests. Numerical predictions demonstrated a very high correlation with the experimental data across all temperatures, confirming that the J-C model accurately captures the hardening behavior of ASA. The presented parameter set and calibration methodology provide a reliable basis for future simulation-driven design, forming analysis, and structural assessment of ASA components subjected to variable thermal conditions. Full article

This study presents a systematic investigation of laser surface hardening of 9CrSi tool steel with the aim of establishing the relationships between processing parameters, microstructural evolution, and resulting mechanical and tribological properties under the applied laser conditions. The influence of laser power, modulation frequency, and scanning speed on the hardened layer depth, microstructure, and surface properties was analyzed. Laser treatment produced a martensitic surface layer with varying fractions of retained austenite, while the transition zone consisted of martensite, granular pearlite, and carbide particles. X-ray diffraction identified the presence of α′-Fe, γ-Fe, and Fe₃C phases, with peak broadening associated with increased lattice microstrain induced by rapid self-quenching. The surface microhardness increased from approximately 220 HV_0.1 in the untreated state to 950–1000 HV_0.1 after laser hardening, with hardened layer thicknesses ranging from about 500 to 750 µm depending on the processing regime. Instrumented indentation showed higher elastic modulus values for all hardened conditions. Tribological tests under dry sliding conditions revealed reduced coefficients of friction and more than an order-of-magnitude decrease in wear rate compared with untreated steel. The results provide a parameter–microstructure–performance map for laser-hardened 9CrSi steel, demonstrating how variations in laser processing conditions affect hardened layer characteristics and functional performance. Full article

As the work hardening rate increases during the cold drawing of non-heat-treated steel (NHT steel), a significant loss in ductility and toughness can occur, leading to reduced formability and part quality. In this study, a bidirectional drawing process consisting of alternating forward and reverse passes is proposed to mitigate these issues and enhance the mechanical performance of the steel. Mechanical property evaluations, including tensile testing and three-point bending tests, were conducted to assess the effects of bidirectional drawing compared to conventional unidirectional drawing. The results showed that the bidirectionally drawn wire maintained a similar tensile strength to that of the unidirectionally drawn wire at a 70% area reduction, while exhibiting a 12% improvement in elongation. Microstructural analysis revealed grain refinement and reduced texture anisotropy in the bidirectionally drawn specimens, contributing to the observed enhancement in ductility. These findings indicate that bidirectional drawing is a promising approach for improving the formability and overall quality of high-strength, NHT steel components. Full article

Local scour around suction caisson foundations has emerged as a significant geotechnical hazard for offshore wind turbines as developments extend into deeper waters. This study quantitatively evaluates the scour-induced degradation of the bearing capacity of suction buckets in sand using a three-dimensional finite element model incorporating the Hardening Soil (HS) constitutive model. The HS framework enables realistic representation of stress-dependent stiffness, dilatancy, and plastic hardening, which are essential for simulating stress redistribution caused by scour. Parametric analyses covering a broad range of relative scour depths show that scour depth is the primary factor governing capacity loss. Increasing scour leads to systematic reductions in horizontal and moment capacities, evident stiffness softening, and a downward migration of plastic zones. A critical threshold is identified at S_d/L = 0.3, beyond which the rate of capacity deterioration increases significantly. The H–M failure envelopes contract progressively and exhibit increasing flattening with scour depth while maintaining nearly constant eccentricity. Empirical relationships between scour depth and key envelope parameters are further proposed to support engineering prediction. The results highlight the necessity of integrating scour effects into design and assessment procedures for suction bucket foundations to ensure the long-term performance and safety of offshore wind turbines. Full article

AISI 1045 steel often undergoes premature failure under combined corrosive-wear conditions due to its insufficient surface durability. To address this, a hot-dip aluminum (HDA) coating was deposited on the steel substrate. The microstructure, corrosion behavior, and tribological properties of the coating were systematically characterized using scanning electron microscopy (SEM), electrochemical techniques, and tribometry. The results reveal that the coating exhibits a continuous triple-layer structure, consisting of the steel substrate, an intermediate Fe-Al intermetallic compound layer, and an outer aluminum-rich layer. In a 3.5 wt.% NaCl solution, the coating formed a protective Al₂O₃ film, demonstrating clear passivation behavior. It significantly enhanced the substrate’s performance, achieving an approximately 90% reduction in wear rate and a substantial increase in charge transfer resistance. The coated sample showed a lower friction coefficient (0.24) compared to the bare substrate (0.34). Herein, this work demonstrates that a straightforward and industrially viable hot-dip aluminizing process can effectively improve the corrosion and wear resistance of medium-carbon steel. The findings provide a practical surface-hardening strategy for such steels operating in aggressive environments. Full article

The production of heavy gauge quenched and tempered steel plates requires alloying strategies that ensure adequate hardenability and microstructural uniformity under limited cooling rates. Molybdenum (Mo) and nickel (Ni) are key elements in this context, as they influence both hot-working behavior and phase transformation kinetics. This study investigates the effect of Mo (0.25–0.50 wt%) and Ni (0–1.00 wt%) additions on static recrystallization and transformation behavior using laboratory thermomechanical simulations representative of thick plate rolling conditions. Multipass and double-hit torsion tests were performed to determine the non-recrystallization temperature (Tnr) and quantify softening kinetics, while dilatometry was employed to construct Continuous Cooling Transformation (CCT) diagrams and assess hardenability. Results indicate that Mo significantly increases Tnr and delays recrystallization through a solute drag mechanism, whereas Ni exerts a minor but measurable effect, likely associated with stacking fault energy rather than classical solute drag. Both elements reduce ferrite and bainite transformation temperatures, enhancing hardenability; however, Mo alone cannot suppress ferrite formation at practical cooling rates, requiring combined Mo–Ni additions to achieve fully martensitic microstructures. These findings provide insight into alloy design for thick plate applications and highlight the limitations of existing predictive models for Ni-containing steels. Full article

This research systematically investigates the influence of multi-microalloying with Sn, Mn, Er, and Zr on the homogenized microstructure, aging behavior, and mechanical properties of a 6082 Al-Mg-Si alloy. The optimization of the homogenization treatment for the alloy was based on isochronal aging curves and conductivity measurements. The results show that the addition of Mn, Er, and Zr can precipitate thermally stable Al(Fe,Mn)Si dispersoids and Al(Er,Zr) dispersoids. The three-stage homogenization treatment resulted in the precipitation of more heat-resistant dispersoids, thereby achieving the best thermal stability. During direct artificial aging, the initial hardening rate of the Mn-containing alloy was slightly delayed, but its peak hardness was significantly increased. This is due to the dispersoids offering additional heterogeneous nucleation sites for the strengthening precipitates. Meanwhile, the Sn atoms release their trapped vacancies at the aging temperature, thereby promoting atomic diffusion. However, short-term natural aging before artificial aging accelerated the early-stage aging response of the Sn-containing alloy but resulted in a reduced peak hardness. Notably, the co-microalloying with Mn and Sn led to a higher peak hardness during direct artificial aging, while it caused a more significant hardness loss when a natural aging preceded artificial aging, revealing a distinct synergistic negative effect. The reason for the negative synergy effect might be related to the weakened ability of Sn to release vacancies after natural aging. This study clarifies the process dependence of microalloying effects, providing a theoretical basis for optimizing aluminum alloy properties through the synergistic design of composition and processing routes. Full article

To investigate the in situ irradiation effects of gallium nitride at varying temperatures, we combined ion beam-induced luminescence spectroscopy with variable-temperature irradiation using a home-built IBIL system and a GIC4117 2 × 1.7 MV tandem accelerator. Unlike previous static studies—limited to post-irradiation or single-temperature luminescence—we in situ tracked dynamic luminescence changes throughout irradiation, directly capturing the real-time responses of luminescent centers to coupled temperature-dose variations—a rare capability in prior work. To clarify how irradiation and temperature affect the luminescent centers of GaN, we integrated density functional theory (DFT) calculations with literature analysis, then resolved the yellow luminescence band into three emission centers via Gaussian deconvolution: 1.78 eV associated with C/O impurities, 1.94 eV linked to VGa, and 2.2 eV corresponding to CN defects. Using a single-exponential decay model, we further quantified the temperature- and dose-dependent decay rates of these centers under dual-variable temperature and dose conditions. Experimental results show that low-temperature irradiation such as at 100 K suppresses the migration and recombination of V_Ga/C_N point defects, significantly enhancing the radiation tolerance of the 1.94 eV and 2.2 eV emission centers; meanwhile, it reduces non-radiative recombination center density, stabilizing free excitons and donor-bound excitons, thereby improving near-band-edge emission center resistance. Notably, the 1.94 eV emission center linked to gallium vacancies exhibits superior cryogenic radiation tolerance due to slower defect migration and more stable free exciton/donor-bound exciton states. Collectively, these findings reveal a synergistic regulation mechanism of temperature and radiation fluence on defect stability, addressing a key gap in static studies, providing a basis for understanding degradation mechanisms of gallium nitride-based devices under actual operating conditions (coexisting temperature fluctuations and continuous radiation), and offering theoretical/experimental support for optimizing radiation-hardened gallium nitride devices for extreme environments such as space or nuclear applications. Full article

Cr8 steel should be Steel containing ~8 wt.% of chromium is widely used in demanding die applications due to its excellent wear resistance; however, conventional shot peening, while enhancing strength, inevitably increases surface roughness, thereby compromising overall performance. To address this limitation, this study systematically investigates the influence of ultrasonic surface rolling (USR) step size—comparing 0.06 mm and 0.12 mm—on mitigating surface degradation and improving surface integrity. Friction wear and electrochemical corrosion tests demonstrate that USR effectively reduces surface roughness and enhances microhardness. The 0.06 mm step size achieves superior results, yielding the lowest surface roughness (0.8317 μm), highest microhardness (647.47 HV), lowest friction coefficient (0.655), and optimal corrosion resistance (minimum corrosion rate reduction: 3.472 µA·cm⁻², corresponding to an inhibition efficiency of 37.05%). These performance improvements are attributed to the synergistic effects of surface smoothing and work hardening, resulting from more uniform processing achieved under a smaller step size. Consequently, a 0.06 mm step size is determined to be optimal, establishing the integrated shot peening–USR process as a highly effective strategy for enhancing surface properties and extending the service life of critical Cr8 steel components in industrial applications. Full article

The pervasive deployment of large language models (LLMs) has given rise to mounting concerns regarding the safety and security of the content generated by these models. Nevertheless, the absence of comprehensive evaluation methods constitutes a substantial obstacle to the effective assessment and enhancement of the safety and security of LLMs. In this paper, we develop the Safety and Security (S&S) Benchmark, integrating multi-source data to ensure comprehensive evaluation. The benchmark comprises 44,872 questions covering ten major risk categories and 76 fine-grained risk points, including high-risk dimensions such as malicious content generation and jailbreak attacks. In addition, this paper introduces an automated evaluation framework based on multi-model judgment. Experimental results demonstrate that this mechanism significantly improves both accuracy and reliability: compared with single-model judgment (GPT-4o, 0.973 accuracy), the proposed multi-model framework achieves 0.986 accuracy while maintaining a similar evaluation time (~1 h) and exhibits strong consistency with expert annotations. Furthermore, adversarial robustness experiments show that our synthesized attack data effectively increases the attack success rate across multiple LLMs, such as from 14.76% to 27.60% on GPT-4o and from 18.24% to 30.35% on Qwen-2.5-7B-Instruct, indicating improved sensitivity to security risks. The proposed unified scoring metric system enables comprehensive model comparison; summarized ranking results show that GPT-4o achieves consistently high scores across ten safety and security dimensions (e.g., 96.26 in ELR, 97.63 in PSI), while competitive open-source models such as Qwen2.5-72B-Instruct and DeepSeek-V3 also achieve strong performance (e.g., 96.70 and 97.63 in PSI, respectively). Although all models demonstrate strong alignment in the safety dimension, they exhibit pronounced weaknesses in security—particularly against jailbreak and adversarial attacks—highlighting critical vulnerabilities and providing actionable direction for future model hardening. This work provides a comprehensive, scalable solution and high-quality data support for automated evaluation of LLMs. Full article

Inconel 718 is widely used in chloride-bearing environments where localized corrosion resistance is critical. This study assesses the effect of continuous low-temperature plasma nitriding (425 °C, 2 h) on the microstructure, hardness, and localized corrosion behavior of Inconel 718. The nitriding treatment produced a surface layer with hardness values up to three times higher than those of the untreated material, associated with a nitrided layer of thickness 6.1–6.7 µm. X-ray diffraction confirmed the precipitation of CrN without the formation of nitrogen-expanded phases. Cyclic polarization tests revealed non-significant changes in the corrosion parameters, except for a two-fold increase in the corrosion rate of nitrided samples. Also, the critical pitting temperature (CPT) decreased by more than 30 °C on average in the nitrided condition, falling below 10 °C. These findings indicate that, although continuous plasma nitriding enhances surface hardening, it significantly compromises the alloy’s resistance to localized corrosion in chloride-rich environments. Full article