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The microstructures and tensile properties of the Ni–Co-based superalloys made by additive manufacturing (AM) were investigated. The results revealed that both normal and inverse Portevin-Le Châtelier (PLC) effects were observed in AM Ni–Co-based superalloys. In addition, AM significantly inhibited the PLC effect, the average stress decrements for the cast and wrought (C&W) alloys with the same nominal compositions were more than ten times as large as those for the AM alloys when tested at 400 °C with a strain rate of 3 × 10−4 s−1. In the AM Ni–Co-based superalloys, type C serrations had connections with the inverse PLC effect. Transmission electron microscope (TEM) was performed to investigate the interactions of solute atoms, dislocations, stacking faults (SFs) and the γ′ phase for a deep insight into mechanisms of the PLC effects and clarifying the changes in serration types and the conversion from normal to inverse PLC effect.

Following publication, concerns were raised regarding the peer-review process related to the publication of this article [...]

Laser cladding provides advanced surface treatment capabilities for enhancing the properties of components. However, its effectiveness is often challenged by the formation of hot cracks during the cladding process. This study focuses on the formation mechanism and inhibition of hot cracks in a novel cobalt-based alloy (K688) coating applied to 304LN stainless steel via laser cladding. The results indicate that hot crack formation is influenced by liquid film stability, the stress concentration, and precipitation phases. Most hot cracks were found at 25°–45° high-angle grain boundaries (HAGBs) due to the high energy of these grain boundaries, which stabilize the liquid film. A flat-top beam, compared to a Gaussian beam, creates a melt pool with a lower temperature gradient and more mitigatory fluid flow, reducing thermal stresses within the coating and the fraction of crack-sensitive, high-angle grain boundaries (S-HAGBs). Finally, crack formation was significantly inhibited by utilizing a flat-top laser beam to optimize the process parameters. These findings provide a technical foundation for achieving high-quality laser cladding of dissimilar materials, offering insights into optimizing process parameters to prevent hot crack formation.

Comparable investigation of pore-induced defects during in-phase (IP) and out-of-phase (OP) thermo-mechanical fatigue (TMF) were conducted on fourth-generation single crystal superalloy. It was discovered that recrystallizations and deformation twins would take shape near micro-pores at IP and OP cycling, respectively. High-resolution observation uncovered that the increasing a/6〈112〉 twinning dislocations and more frequent activation of 〈112〉{111} viscous slipping during OP-TMF accounted for twinning nucleation. Atom-scale mapping additionally disclosed the dual effect of Re, Co, and Cr in facilitating twinning formation and impeding of partial dislocations movement. It was deemed that the accumulation of pore-induced twins caused the premature fracture of alloy during OP-TMF.

The mechanical properties of direct laser deposition (DLD) parts are crucial for engineering applications, which are determined by the microstructure and texture. To achieve fine microstructure and higher mechanical performance, pulsed laser deposition is used to generate less heat accumulation and a higher cooling rate. However, the relationship between microstructure and thermal history is difficult to investigate due to the transient temperature change. In this work, a three-dimensional numerical model is developed to study the thermal behavior of the molten pool in the continuous laser deposition (CLD), the continuous pulsed laser deposition (CPLD), and the interval pulsed laser deposition (IPLD) processes. The microstructure of the deposition samples is investigated by optical microscope and electron back-scattered diffraction. The mechanical response of the deposition samples is investigated by tensile test and microhardness test. Compared with the CLD, CPLD, and IPLD result in higher temperature gradient and cooling rate, long columnar grains, and a strong fiber texture. However, grains with larger sizes and a texture with a herringbone pattern due to the change of heat flow are obtained in CLD samples. The test values of IPLD samples show higher tensile strength, higher yield strength, lower ductility, and higher hardness values. This research brings about a perspective for studying the thermal effects of deposition layers and a novelty deposition process to obtain specific microstructures and better mechanical properties.

The isothermal oxidation behavior and the microstructure stability was studied at 900 °C, 1000 °C and 1100 °C of the two alloys with and without Ru. The curves of oxidation weight gain show that the oxidation resistance decreases sharply with the addition of Ru. A multi-layered scale formed on the alloy surface, and it generally consisted of an external layer of NiO, an intermediate layer of spinel and an Al2O3 inner layer. The oxidation rate at 1100 °C is significantly higher than that at the other two temperatures due to more serious cracking and peeling of oxide scale. Compared with Ru-free alloy, the oxide layer of Ru-containing alloy is thicker and the oxide layer spallation more seriously. The oxide of Ru was found in the spinel layer and the vaporization of the oxide makes the scale spallation. Surprisingly, a large number of TCP phases were found in alloy matrix, especially in 2Ru alloy. This indicates that poor oxidation resistance will lead to a decline in microstructure stability.

The NbTiAlZrHfTaMoW refractory high-entropy alloy (RHEA) system with the structure of the B2 matrix (antiphase domains) and antiphase domain boundaries was firstly developed. We conducted the mechanical properties of the RHEAs at 298 K, 1023 K, 1123 K, and 1223 K, as well as typical deformation characteristics. The RHEAs with low density (7.41~7.51 g/cm3) have excellent compressive-specific yield strength (σYS/ρ) at 1023 K (~131 MPa·cm3/g) and 1123 K (~104.2 MPa·cm3/g), respectively, which are far superior to most typical RHEAs. And, they still keep appropriate plastic deformability at room temperature (ε > 0.35). The superior specific yield strengths are mainly attributed to the solid solution strengthening induced by the Zr element. The formation of the dislocation slip bands with [111](101_) and [111](112_) directions and their interaction provide considerable plastic deformation capability. Meanwhile, dynamic recrystallization and dislocation annihilation accelerate the continuous softening after yielding at 1123 K.

Abstract This study investigates the effect of microstructure on short-term and long-term oxidation behaviours of GH3536 superalloy fabricated by laser powder bed fusion (LPBF), in which the superalloy is isothermally oxidised at 950 °C for 6 h and 500 h in air. The LPBF sample exhibits improved oxidation resistance compared with a wrought counterpart after long-term exposure. The effect of microstructure diversity between LPBF and wrought samples on oxidation behaviour is discussed. The cellular structure produced during the LPBF process acts as a rapid diffusion path to accelerate the formation of a protective film in the initial stage, leading to an enhancement in oxidation resistance for extended exposure.

Due to the excellent combination of strength and ductility, eutectic high entropy alloys (EHEAs) are of great interests to the researchers. Here, a cobalt free cost-effective eutectic high entropy alloy was designed by VEC criterion. The cobalt element in AlCoCrFeNi2.1 alloy is replaced by Fe and Ni in equal proportions to maintain VEC value unchanged. The designed AlCrFe1.5Ni2.6 alloy exhibited a eutectic microstructure composed of FCC (L12) phase and BCC (B2) phase. The room temperature mechanical properties of the designed alloy were comparable to those of AlCoCrFeNi2.1 EHEA and better than those of a majority of as-cast high entropy alloys. An excellent combination of strength and ductility originates from the hetero-interface strengthening and slip continuity across the Kurdjumov-Sachs (K–S) interface. The present work proves the VEC criterion could successfully be used to design the cost-effective eutectic high entropy alloy and the designed alloy has a great potential in engineering applications.

The impact of a Pt-Al bond coat on the high-cycle fatigue (HCF) behaviour of fourth-generation single crystal superalloys at 760℃ and 900℃ was investigated. The Pt-Al bond coat was found to be almost negligible under low stresses at 760℃; however, the bond coat effect was detrimental at 900℃ or under high stresses at 760℃. At 760 °C with increasing high-amplitude stress, the tip cracks preferentially nucleated from defects within coat and propagated inwards, accelerating the fracture. The fatigue life of the coated alloys was considerably decreased at 900 °C, which was attributed to the damage accumulated in the bond coating via oxidation, crack-induced oxide cracking and interfacial microstructure degradation. An Elevated temperature led to the crack-induced oxides shifting from a small fan-shape to a large umbrella-shape, increasing the density of slip bands and quantity of secondary cracks in the substrate. Furthermore, more Ru diffused outwards at 900℃ than that at 760℃, which caused the disappearance of L-C dislocation locks and tertiary γ′ phases and aggravated TCP phases precipitation in the substrate at 900℃. Ultimately, to assess the degradation of the HCF life, an empirical life prediction method was developed, and the calculations results well matched the test results.

Vehicular ad hoc networks (VANETs) are the communication foundation for future intelligent transportation systems and guarantee safe driving of intelligent networked vehicles. Moreover, VANETs face a series of security challenges related to the protection of vehicle privacy, authenticity of transmitted information, and bandwidth limitations. To resolve these contradictions, many certificateless aggregate signature (CLAS) schemes have been proposed. However, the majority of them can neither resist malicious-but-passive key generation center attacks, replay attacks, and link attacks, nor track the actual identities of malicious vehicles. Meanwhile, the security of previous CLAS schemes in VANETs is only formally provided in the random oracle model (ROM), which might be insecure in actual implementation. In addition, most CLAS schemes still have problems of large verification delays and high communication overhead. To address the above-mentioned problems, a new conditional privacy-preserving CLAS scheme in VANETs is proposed, which adopts full aggregation technology to reduce computation and bandwidth resources. According to the formal security proofs under the computational Diffie-Hellman problem (CDHP) given in the standard model (SM), the security level of this scheme is higher than that of other CLAS schemes under ROM in practical applications. Additionally, the use of pseudonym mechanism realizes conditional privacy protection in VANETs. The performance analysis shows that this scheme has a higher efficiency in terms of computation and communication overhead compared with several previous CLAS schemes.

A novel low-density nickel-based single-crystal superalloy was prepared and the effect of solution treatment on the creep deformation mechanism was systematically investigated. The results reveal that the creep life increases with the increase of solution treatment time, which can be ascribed to microstructural homogenization. However, when the solution treatment time exceeds a threshold limit, the relative proportion of undesirable defects significantly increases, which accelerates the failure and compromises the creep life. The homogenization of the composition leads to the precipitation of a more homogenized γ′ phase and, in turn, results in a more uniform and dense dislocation network, thus hindering the dislocation movement and improving the creep life. The undesirable defects may lead to the stress concentration and weaken the effect of the dislocation network, thus accelerating the creep process and the dislocation are more likely to shear into the γ′ phase. In general, the current study provides guidance for selecting a more reasonable solution treatment time to improve the creep strength.

Ceramic cores are applied in electronics, aerospace, medicine, military, automotive, and other fields. However, the effects of the build direction, along with the shrinkage of the green body and thermal stress, on the mechanical properties of 3D ceramic cores have not been elucidated. To reveal the optimum conditions for crack resistance in a high-solid-loading ceramic core, a silicon-based ceramic core with a solid content of 60 vol% was fabricated through stereolithography 3D printing and analyzed in terms of its microstructure-level crack initiation and propagation. The green bodies were initially 3D printed in different build directions (length-directed, width-directed, and height-directed) and then sintered at different temperatures (1100 °C-1250 °C). Higher sintering temperatures generally produced more cracks, and the synergistic effects of the sintering temperature and build direction induced crack initiation and propagation. The width-directed sample sintered at 1200 °C, in particular, exhibited effectively controlled crack growth without sacrificing strength.

Magnesium is abundant in the Earth’s crust and seawater [...]

A novel fourth-generation nickel-based single crystal superalloy was brazed with Co-based filler alloy. The effects of post-weld heat treatment (PWHT) on the microstructure and mechanical properties of brazed joints were investigated. The experimental and CALPHAD simulation results show that the non-isothermal solidification zone was composed of M3B2, MB-type boride and MC carbide, and the isothermal solidification zone was composed of γ and γ’ phases. After the PWHT, the distribution of borides and the morphology of the γ’ phase were changed. The change of the γ’ phase was mainly attributed to the effect of borides on the diffusion behavior of Al and Ta atoms. In the process of PWHT, stress concentration leads to the nucleation and growth of grains during recrystallization, thus forming high angle grain boundaries in the joint. The microhardness was slightly increased compared to the joint before PWHT. The relationship between microstructure and microhardness during the PWHT of the joint was discussed. In addition, the tensile strength and stress fracture life of the joints were significantly increased after the PWHT. The reasons for the improved mechanical properties of the joints were analyzed and the fracture mechanism of the joints was elucidated. These research results can provide important guidance for the brazing work of fourth-generation nickel-based single crystal superalloy.

In this work, the effect of the Ru element on the γ′-phase evolution and deformation mechanism in the fourth-generation Ni-based single-crystal superalloy was investigated. Results show that the Ru element alters the distribution coefficient of other elements in the alloy to produce reverse partitioning behavior, which leads to a difference in microstructure between 0Ru and 3Ru. The addition of Ru triggered the incubation period before the beginning of the primary creep stage, which depends on the creep temperature and stress during creep deformation. TEM results revealed that Ru addition inhibits the slip system {111} at medium-temperature (760–1050 °C) and high-stress (270–810 MPa) creep, which brings a considerably low creep rate and high creep life to the Ru-containing alloy.

Band topology of Weyl semimetals is usually predetermined by material parameters and can hardly be manipulated, and their transport properties appear at low temperature. Here, the authors modify the topology via a weak magnetic field and observe a giant anomalous Hall effect at room temperature.

To efficiently manage the cloud resources, improve the quality of service, and avoid the violations of Service-Level Agreement (SLA) agreements, it is very important to make accurate forecast for cloud workload. Prior works concerning cloud workload forecasting are mainly designed based on Recurrent Neural Networks (RNN). However, when it comes to a highly-dynamic cloud workload scenario where resource utilization changes faster and more frequently, these RNN-based methods are not effective in obtaining the linear and non-linear relationships and cannot give accurate forecast, because classic RNN has the problem of vanishing gradient. To address this issue, we propose an Ensemble Forecasting Approach (EFA) for highly-dynamic cloud workload by applying Variational Mode Decomposition (VMD) and R-Transformer. Specifically, to decrease the non-stationarity and high randomness of highly-dynamic cloud workload sequences, we decompose the workload into multiple Intrinsic Mode Functions (IMFs) by VMD. The IMFs are then imported into our ensemble forecasting module based on R-Transformer and Autoregressive model, in order to capture long-term dependencies and local non-linear relationship of workload sequences. The effectiveness and adaptability of proposed EFA is verified on real-world workload from Google and Alibaba cluster traces. Moreover, the performance evaluation results show that the EFA performs higher forecasting accuracy than prior related works over various forecasting time lengths for highly-dynamic cloud workload.

Abnormal traffic detection is an important network security technology to protect computer systems from malicious attacks. Existing detection methods are usually based on traditional machine learning, such as Support Vector Machine (SVM), Naive Bayes, etc. They rely heavily on manual design of traffic features and usually shallow feature learning, which get a low accuracy for high-dimensional traffic. Although the method based on Long Short-Term Memory (LSTM) has an excellent ability to detect abnormal traffic. The sequence-dependent structure of LSTM cannot realize parallel computation, which leads to slow model training and limits its applicability. To address the above problem, we propose an efficient Bidirectional Simple Recurrent Unit (BiSRU) combined with feature dimensionality reduction for abnormal traffic detection. Specifically, in order to perform feature dimensionality reduction on the original high-dimensional network traffic, we design a stack Sparse Autoencoder (sSAE) to extract the compressed high-level features. For the purpose of realizing efficient parallel computation and accurate feature extraction, a BiSRU is utilized to extract the bidirectional structural features of the traffic. Finally, the experimental results show that our proposed method significantly outperforms existing methods in terms of accuracy and training time. The method we propose can timely and accurately detect various abnormal traffic and achieve effective network security protection.

The relationship between pulsed laser processing parameters and epitaxial growth of alloy is essential to additive manufacturing technology in repairing and manufacturing nickel-based single crystal (SX) superalloys. In this paper, orthogonal experiments of Laser Direct Energy Deposition (DED-L) process have been designed to optimize the process for the epitaxial growth of the SX superalloy. The relationship between process parameters and epitaxial growth of SX superalloy is established in a radar map, which shows that low laser power, pulse width and powder feeding rate help epitaxial growth in the DED-L process. It is implied that increasing the powder feeding rate value in the process range decreases the epitaxial growth rate of the molten pool and increases manufacturing efficiency. The size of the cladding layer width is greatly influenced by laser power (reached 44%) and pulse width (reached 38%). The deposited heigh of the cladding layer is mainly influenced by pulse width (reached 45%) and powder feeding rate (reached 42%). The process parameters have a similar level (approximately 33%) of influence on the powder using efficiency.

The effect of the Mo contents of 1.0 wt.%, 1.5 wt.%, 2.0 wt.%, and 3.0 wt.% on the microstructures and mechanical properties of the polycrystalline superalloy with a high W content was studied. The typical dendrite morphology was observed in the high-W superalloy with different Mo contents, containing γ matrix, γ′ phase, eutectic, and MC carbide. After the heat treatment, the primary MC carbides were decomposed into M6C carbides, while a needle-like topologically close-packed (TCP) phase was formed in the alloy with high Mo content, in contrast to the other three alloys with low Mo content. The Mo addition increased the lattice parameter of the γ and γ′ phases and also changed the lattice misfits of the γ and γ′ phase lattice misfits towards a larger negative. The addition of Mo improved the yield strength at room temperature due to the solid solution strengthening and coherency strengthening. The improvement of the stress rupture lives at 975 °C/225 MPa was due to the combination of the suppressed propagation of the microcracks by the carbides and a more negative misfit. When the Mo content reached 3.0 wt.%, the TCP phases formed and decreased the ultimate tensile strength and the stress rupture lives as a result.

Nowadays, vulnerability attacks occur frequently. Due to the information asymmetry between attackers and defenders, vulnerabilities can be divided into known and unknown. Existing researches mainly focus on the risk assessment of known vulnerabilities. However, unknown vulnerabilities are more threatening and harder to detect. Therefore, unknown vulnerability risk assessment deserves the widespread attention. To model the exploit process, directed graph models are applied to vulnerability risk assessment. And security metrics are used to quantify the exploitability of vulnerabilities. In this paper, according to the data source of nodes, related works of unknown vulnerability risk assessment based on directed graph models are divided into two types. One is based on network-level data, the other is based on system-level data. The former is to visualize the network status, while the latter is to reflect the running process of the system. The concept and purpose of these directed graph models are given at first. Then, these models are analyzed from three aspects, including advantages, flaws and solutions. After that, challenges and solutions of unknown vulnerability risk assessment based on directed graph models are given. Meantime, security metrics for unknown vulnerability risk assessment based on directed graph models are summarized and classified. Finally, future work directions of unknown vulnerability risk assessment are discussed from the perspective of techniques and application trends. Consequently, this paper can fill in the lack of current survey on unknown vulnerability risk assessment based on directed graph models.

Direct laser deposition (DLD) is widely used in precision manufacturing, but the process parameters (e.g., laser power, scanning patterns) easily lead to changes in dimensional accuracy and structural properties. Many methods have been proposed to analyze the principle of distortion and residual stress generation, but it is difficult to evaluate the involvement of temperature and stress in the process of rapid melting and solidification. In this paper, a three-dimensional finite element model is established based on thermal–mechanical relationships in multilayer DLD. Differences in temperature and residual stress between continuous laser deposition (CLD) and pulsed laser deposition (PLD) are compared with the numerical model. To validate the relationship, the temperature and residual stress values obtained by numerical simulation are compared with the values obtained by the HIOKI-LR8431 temperature logger and the Pulstec μ-X360s X-ray diffraction (XRD) instrument. The results indicate that the temperature and residual stress of the deposition part can be evaluated by the proposed simulation model. The proposed PLD process, which includes continuous pulsed laser deposition (CPLD) and interval pulsed laser deposition (IPLD), were found more effective to improve the homogeneity of temperature and residual stress than the CLD process. This study is expected to be useful in the distortion control and microstructure consistency of multilayer deposited parts.

Oxidized HDL (ox-HDL), unlike native HDL that exerts antiatherogenic effects, plays a proatherogenic role. However, the underlying mechanisms are not completely understood. This study was designed to explore the inductive effect of ox-HDL on endoplasmic reticulum (ER) stress-CCAAT-enhancer-binding protein homologous protein (CHOP)-mediated macrophage apoptosis and its upstream mechanisms. Our results showed that ox-HDL could be ingested by macrophages, causing intracellular lipid accumulation. As with tunicamycin (an ER stress inducer), ox-HDL induced macrophage apoptosis with concomitant activation of ER stress pathway, including nuclear translocation of activating transcription factor 6, phosphorylation of protein kinase-like ER kinase and eukaryotic translation initiation factor 2α, and upregulation of glucose-regulated protein 78 and CHOP, which were inhibited by 4-phenylbutyric acid (PBA, an ER stress inhibitor) and CHOP gene silencing. Additionally, diphenyleneiodonium (DPI, an oxidative stress inhibitor), probucol (a reactive oxygen species scavenger), and toll-like receptor 4 (TLR4) silencing reduced ox-HDL-induced macrophage apoptosis, oxidative stress, and CHOP upregulation. Moreover, HDL isolated from patients with metabolic syndrome induced macrophage apoptosis, oxidative stress, and CHOP upregulation, which were blocked by PBA and DPI. These data indicate that ox-HDL may activate ER stress-CHOP-induced apoptotic pathway in macrophages via enhanced oxidative stress and that this pathway may be mediated by TLR4.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Groundwater chemistry data are normally scarce in remote inland areas. Effective statistical approaches are highly desired to extract important information about hydrochemical processes from the limited data. This study applied a clustering approach based on the Gaussian Mixture Model (GMM) to a hydrochemical dataset of groundwater collected in the middle Heihe River Basin (HRB) of northwestern China. Independent hydrological data were introduced to examine whether the clustering results led to an appropriate interpretation on the hydrochemical processes. The main findings include the following. First, in the middle HRB, although groundwater chemistry reflects primarily a natural salinization process, there are evidence for significant anthropogenic influence such as irrigation and fertilization. Second, the regional hydrological cycle, particularly surface water-groundwater interaction, has a profound and spatially variable impact on groundwater chemistry. Third, the interaction between the regional agricultural development and the groundwater quality is complicated. Overall, this study demonstrates that the GMM clustering can effectively analyze hydrochemical datasets and that these clustering results can provide insights into hydrochemical processes, even with a limited number of observations. The clustering approach introduced in this study represents a cost-effective way to investigate groundwater chemistry in remote inland areas where groundwater monitoring is difficult and costly.