Search

Generally, edge crack of rolled magnesium alloy sheets initiates in the RD (rolling direction)-ND (normal direction) plane and then propagate in the RD-TD (transverse direction) plane. Hence, the Mg-2Zn-1.5Mn (ZM21) alloy sheets with and without crack notch were designed to carry out in-situ tensile experiments under 150 °C (the same temperature of rolling), with the aim to understand their crack propagation mechanism. The scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD) techniques were utilized to reveal microstructural evolution in real time at designated displacements. The results show that the prismatic slip, basal slip, and extension twining play synergistic role in coordinating strain during the tensile process in ZM21 alloy sheet at 150 °C. In both tensile samples with and without crack notch, localized strain is mainly concentrated at relatively fine grain area and the grain boundaries or triple junctions of the grains with large basal Schmid factor (SF) difference, which eventually leads to severe surface roughening and subsequent crack initiation. Compared with the sample without crack notch, the pre-cracked sample exhibits severer deformation at the crack tip due to strain concentration. Strain gradient distribution is observed at the crack tip region in the pre-cracked sample. The crack propagation path of the sample with pre-crack is identified and the underlying mechanism is also discussed.

Highlights • Al-Zr alloys can be effectively refined by TiCNnp. • A numerical model was well consistent with the experimental results. • In situ X-radiography study on Al-Cu-Zr alloys were carried out., Ex situ and in situ synchrotron X-radiography study on Al-Cu-Zr alloys with addition of Al-5Ti-1B and TiCN nanoparticles (TiCNnp) were carried out at different cooling rates. Al-Zr alloy can be effectively refined by TiCNnp via Ultrasonic treatment as compared with Al-5Ti-1B which has Zr poisoning effect. The influence of cooling rate on the nucleation and growth of grains have been studied quantitatively. The results show that the grain size was decreased and the growth rate was increased with the increasing of cooling rate. At the same cooling rate, the grain size with addition of 0.5% TiCNnp was smaller than that with the same addition of Al-5Ti-1B. The blocking factor f of TiCNnp decreases with increasing cooling rate. Based on the free growth model, a new numerical model considering the growth restriction effect of nanoparticles was established. The growth of grain was inhibited by the combining effect of solute and nanoparticles. The growth rate of grain is reduced due to part of the solid/liquid interface coated by nanoparticles. The blocking factor f is linearly decreased with the coverage ratio ω which is proportional to the critical grain radius. The grain size decreases with increasing cooling rate and decreasing f . This study is especially beneficial for Al alloys that have poisoning phenomenon inoculated by traditional refiner.

Closely related to the economy, the analysis and management of electricity consumption has been widely studied. Conventional approaches mainly focus on the prediction and anomaly detection of electricity consumption, which fails to reveal the in-depth relationships between electricity consumption and various factors such as industry, weather etc.. In the meantime, the lack of analysis tools has increased the difficulty in analytical tasks such as correlation analysis and comparative analysis. In this paper, we introduce EcoVis, a visual analysis system that supports the industrial-level spatio-temporal correlation analysis in the electricity consumption data. We not only propose a novel approach to model spatio-temporal data into a graph structure for easier correlation analysis, but also introduce a novel visual representation to display the distributions of multiple instances in a single map. We implement the system with the cooperation with domain experts. Experiments are conducted to demonstrate the effectiveness of our method.

A Multistage Elliptical Parametric (MEP) method is developed in this research for damage size evaluation in anisotropic composite laminates. The Lamb waves are actuated and sensed using piezoelectric (lead zirconate titanate, PZT) transducers arranged as a network of square cells. The dynamic response signals are processed using a continuous wavelet transformation (CWT) based on the Gabor wavelet for accurate time of flight (ToF) measurements. A numerical method is developed for the construction of non-elliptic path loci for each actuator-sensor pair. The damage is localized first using the least squares method, and then the damage edge points are located on each non-elliptic path loci as points which have the minimum distance from the damage location. The MEP method based on the damage edge points is implemented in multiple stages for damage size evaluation in a cross-ply laminate. Each stage is designed on the basis on excitation of specific prearranged transducers inside the square cell. The results indicate that the MEP method can quantitatively estimate the size of an elliptical damage in cross-ply laminates.

In the process of constructing the knowledge graph in the domain of electric power metering, the knowledge often comes from several different data sources, and because of the differences in structure and content among the data sources, there are also problems of multiple meanings of words and unclear referents in the integration of the acquired knowledge. Therefore, knowledge fusion processing is needed to eliminate the ambiguity of entities and attributes in terms of denotation. This paper proposes a knowledge fusion method based on text matching technology. The method includes three core steps. Firstly it use a crawler system to obtain corpus data. Secondly it use the BERT-based knowledge extraction model to extract knowledge and build the entity information knowledge base. Finally the entities are matched at the semantic level to complete the knowledge fusion process. The experimental results prove that the knowledge fusion effect of the method in this paper is good and the entity matching rate is high.

Glass microspheres are considered to be suitable fillers in syntactic foams due to their high specific strength, however, it's evidently easy to react with Al-Mg alloy or Mg alloy. A surface protection coating MgO were successfully prepared on microspheres using sol-gel method. The crystallization process and coating effect of MgO with different molar ratio acetic acid complexant in sol compositions were studied. The dried gels were dehydrated and polycondensed to form magnesium acetate and finally turned to be stable MgO after annealing at 400 °C. The MgO coatings, with small particles after annealing, successfully modified the surface of microspheres when the sol composition (molar) magnesium acetate hydrate/acetic acid/dry ethanol was 1:6:29. The MgO coating has inhibited the excessive interfacial reaction between the glass microspheres and the Al-Mg alloy matrix in syntactic foam which the reasons have been discussed.

Multivariate electricity consumption series clustering can reflect trends of power consumption changes in the past time period, which can provide reliable guidance for electricity production. However, there are some abnormal series in the past multivariate electricity consumption series data, while outliers will affect the discovery of electricity consumption trends in different time periods. To address this problem, we propose a robust graph factorization model for multivariate electricity consumption clustering (RGF-MEC), which performs graph factorization and outlier discovery simultaneously. RGF-MEC first obtains a similarity graph by calculating distance among multivariate electricity consumption series data and then performs robust matrix factorization on the similarity graph. Meanwhile, the similarity graph is decomposed into a class-related embedding and a spectral embedding, where the class-related embedding directly reveals the final clustering results. Experimental results on realistic multivariate time-series datasets and multivariate electricity consumption series datasets demonstrate effectiveness of the proposed RGF-MEC model.

Under compressive testing at 400C and a strain rate range of 0.05-5 s-1, the hot deformation behavior and microstructure evolution of an as-cast (AC), as-extruded (with a bimodal grain structure (named as Ex-1) or a relatively uniform fine grain structure (Ex-2)) WE43 alloy have been investigated and compared. The results indicate that the AC sample exhibits the highest peak stress, while the Ex-2 sample has the lowest value. Within the AC material, fine grains were firstly formed along the pancake-like deformed grains (as a necklace structure). The necklace structure was also formed within the Ex-1 and Ex-2 materials at high strain rates of 0.5 and 5 s-1. However, a lamellar structure that the coarse elongated grains divided by parallel boundaries was formed within the Ex-1 material. A relatively more homogeneous fine grain structure is achieved after a true strain of 1.0 within the Ex-2 material at a low strain rate of 0.05 s-1. In addition, a discontinuous dynamic recrystallization mechanism by grain boundary bulging is found to occur. After a true strain of 1.2, a (0001) fiber texture, a typical rare earth (RE) texture, and a relatively random texture are formed within the AC, Ex-1, and Ex-2 WE43 alloy material, respectively.

The microstructural evolution and high-temperature oxidation resistance performance of Zr-containing steel were investigated via isothermal oxidation at 1000 °C for up to 150 h. In the oxide formation stage (stage Ⅰ), Zr can promote the preferential growth of certain oxides. When oxidation proceeds to the oxide growth stage (stage Ⅱ), Zr has a more significant effect on improving the high-temperature oxidation resistance of the experimental steel. Furthermore, Zr does not directly participate in the formation of the oxide layer, but improves the composition and structure of the oxide film and promotes the formation of FeCr2O4, MnCr2O4, and Cr2O3 in the oxides.

The first principles method was utilized to study the interfacial properties of the TiB2 reinforced copper matrix materials. The interfacial stabilities were studied initially via the works of adhesion and interfacial energies. According to the results, TT-OT (Ti-terminated TiB2/Cu “OT” stacking) and BT-HCP (B-terminated TiB2/Cu “HCP” stacking) were confirmed to be the most stable interfaces. The charge density distribution, charge density difference, electronic localization function and partial density of state were analyzed for TiB2/Cu interfaces. The results indicate that Ti-terminated TiB2(0001)/Cu(111) interfaces were more inclined to form the metallic bond, while the B-terminated TiB2(0001)/Cu(111) interfaces were likely to form the ionic bond. Moreover, the interfacial elastic energy, interfacial fracture toughness and ultimate tensile tress were carried out to make clear of fracture mechanism of the TiB2(0001)/Cu(111) interfaces. The TT-OT and BT-HCP were confirmed to be the two most stable interfaces due to their largest interfacial elastic energies. The computational ultimate tensile tress for Ti-terminated TiB2(0001)/Cu(111) and B-terminated TiB2(0001)/Cu(111) interfacial models were 23 GPa and 25 GPa, respectively.

The effects of sintering temperature on the Ti/W–C phase evolution, microstructural change and wear properties of Fe-based composites were studied. The results show that Ti and W will generate unstable TixW1-x mesophase during the ball milling process, and the lattice constant of W increase from 3.1648 A to 3.5523 A. Furthermore, the in situ TiC and WC appear diffraction double peaks near the diffraction angle of 36° with the change of the sintering temperature. At the same time, as the sintering temperature approaches the Ti–Fe liquidus, the appearance of a large-sized reinforcing phase and the aggregation of Fe around it, synergistically improve the wear resistance of the material.

The corrosion and cavitation erosion-corrosion behaviour of two newly developed Fe-10Cr martensitic steels were investigated in 3.5 % NaCl solution compared with 304 stainless steel. It is found that the passivation ability of the martensitic steel was improved and the corrosion rate was decreased by the addition of Zr. The mass loss test showed that the martensitic steels, especially the steel microalloyed with Zr had better cavitation erosion-corrosion resistance than 304 stainless steel. Further characterisation of the white layer on the damaged surface indicated that the addition of Zr changed the cavitation erosion-corrosion mechanism of the martensitic steel.

As-cast irons and aluminum alloys are used in various industrial fields and their phase and microstructure properties are strongly affected by the undercooling degree. However, existing studies regarding the undercooling degree are mostly limited to qualitative analyses. In this paper, a quantitative analysis of the undercooling degree is performed by collecting experimental data and employing machine learning. Nine machining learning models including Random Forest (RF), eXtreme Gradient Boosting (XGBOOST), Ridge Regression (RIDGE) and Gradient Boosting Regressor (GBDT) methods are used to predict the undercooling degree via six features, which include the cooling rate (CR), mean atomic covalence radius (MAR) and mismatch (MM). Four additional effective models of machine learning algorithms are then selected for a further analysis and cross-validation. Finally, the optimal machine learning model is selected for the dataset and the best combination of features is found by comparing the prediction accuracy of all possible feature combinations. It is found that RF model with CR and MAR features has the optimal performance results for predicting the undercooling degree.

In this work, the presence of second-phase particles was found can significantly improve the oxidation and spallation resistances of a high-manganese austenitic heat-resistant steel. We show this unexpected improvement is originated from three correlated phenomena caused by the second-phase particles. First, the stratified growth of scale is avoided due to the chemical inhomogeneity of the novel steel. Further, the selective oxidation of second-phase particles provides a pinning effect for the scale. Last but not least, the accelerated outward diffusion of Mn reduces the critical Cr concentration for the formation of a stable protective Cr2O3 layer.

The TiB2/Al particle reinforced composites were prepared successfully through metal-salt reaction with different process conditions (mechanical stirring, one-stage and two-stages of ultrasonic vibration). It was usually taken more than 60 min to complete metal-salt reaction under mechanical stirring condition, lots of reinforcement agglomerations and residual intermediate such as Al3Ti was in the matrix. The reaction time was greatly shortened from 60 min to 5 min and particle agglomerations were eliminated successfully by the introduction of ultrasonic vibration at 850 °C. Through the introduction of ultrasonic vibration at 730 °C, not only most of the residual Al3Ti phase was broken or dissolved, but also the size of TiB2 was refined. The composite prepared by two-stage ultrasonic vibration has the optimal improvements of yield strength and ultimate tensile strength, which increased by are 108% and 98% respectively, hardness increased 61.5%. When only introducing the first stage of UVT, the elongation decreased from 34% to 20% owning to lots of rod-like Al3Ti in the matrix, after the second stage of UVT, the elongation restored to 33%. The effects of ultrasonic vibration on phase transformation, microstructure, and mechanical properties were studied by x-ray diffraction (XRD), optical microscope (OM), scanning electron microscope (SEM) and Electron Backscattered Diffraction (EBSD). Moreover, the effects of Orowan strengthening, thermal expansion mismatch strengthening, and grain refinement strengthening on mechanical properties were also discussed.

Al2O3 ceramics were successfully brazed under high vacuum conditions using the active Ni50Ti50 master alloy at 1320 °C with different holding time. The interfacial microstructure of the joint was characterized using SEM, EDS and TEM. The effects of holding time on the microstructure evolution and mechanical properties of the joints were investigated. The results revealed that the typical structure of the Al2O3/Ni–Ti joint brazed at 1320 °C for 45 min was Al2O3/AlNi2Ti + Ni2Ti4O/Ni2Ti4O/TiNi. Ni2Ti4O was continuously distributed as a layer adjacent to the Al2O3 substrate, whereas columnar AlNi2Ti phase existed in the Ni2Ti4O layer near the Al2O3 side. With the prolongation of holding time, the thickness of Ni2Ti4O layer increased obviously, and AlNi2Ti became longer and coarser. The maximum shear strength of 109 MPa was obtained when the joint was brazed at 1320 °C for 45 min. The hardness, Young's modulus and elastic recovery of the phases across the joints became a gradient property. The interfacial reaction layer with appropriate thickness was found beneficial for enhancing the Al2O3/Ni–Ti/Al2O3 joint strength.

A damage estimation method based on continuous wavelet transformation (CWT) of the normalized Lamb wave signals is proposed here. Lamb waves are actuated and sensed using piezoelectric (lead zirconate titanate, PZT) transducers arranged in the form of square detection cells on a plate-like structure. Excitation sequences based on pitch&ndash, catch and pulse&ndash, echo configurations are tested for the same arrangement of the transducers. The possibilities of the existence of damage for each actuator&ndash, senor pair are formed by using the normalized coefficient of CWT. The size of the possible damage region is directly controlled through envelopes defined by the coefficients of CWT, and no additional parameter is required to define its size. The aggregate damage image is constructed by the fusion of damage possibilities from all actuator&ndash, sensor pairs using damage indices based on conjunctive and compromised fusion schemes. The results indicate that the proposed method can estimate the location and severity of multiple damage with signals directly from the damaged plate, without the need of baseline signals from the undamaged plate, and the time-compensated signals provide better damage imaging than the raw signals. The most accurate and computationally inexpensive combination is the pulse&ndash, echo configuration with damage index based on conjunctive image fusion scheme. The method is computationally inexpensive and can be applied for multiple damage estimations in large structures to reduce the evaluation cost and inspection time during on-line structural health monitoring.

Diffusion bonding of titanium (Ti) to 17-4 PH high strength stainless steel is challenging owing to the formation of brittle Ti-Fe intermetallic compounds (IMCs) at joint interface. In the current study, it was demonstrated that such detrimental Ti-Fe IMCs can be effectively eradicated by using a silver (Ag) interlayer. The diffusion bonded Ti/Ag/17-4 PH stainless steel is characterized by Ti-Ag solid solution, TiAg, remnant Ag interlayer and Ag-(Fe, Cr, Ni) interdiffusion layer. The interfacial reaction phase TiAg exhibited no detrimental effect on bonding strength. During tensile test, ductile fracture took place in the remaining Ag interlayer of resultant joint. Bonding strength up to ∼420 MPa was obtained over bonding durations in the range of 15 ∼ 25 min. It is thus concluded that using an Ag interlayer is highly appealing in improving bonding strength of diffusion bonded Ti/17-4 PH stainless steel dissimilar joint.

Mg/Al composite plates containing two different architectures were successfully fabricated by co-extrusion directly from the as-cast alloys, with the aim to disclose the influence of multilayer architecture and interface characteristic on microstructure, texture and mechanical properties of Mg/Al plates. Our results show that texture components of Mg and Al layers in Mg/Al plates hardly change before and after annealing. The Mg layer has a strong basal texture (basal poles parallel to normal direction (ND)) with the basal poles slightly tilting from ND toward extrusion direction (ED). The Al layer exhibits high fraction of Brass, Copper and S components. The extruded Mg/Al-1 plate has yield strength of 131 MPa, but a high elongation of 17%. The extruded Mg/Al-2 plate exhibits similar yield strength (127 MPa) and a much lower elongation (4.0%) than the Mg/Al-1. After annealing at 350 °C for 3 h, both the yield strengths and elongations of Mg/Al-1 and Mg/Al-2 plates significantly decrease.

In this study, Mg/Al composite rod with a thin 6082 aluminum alloy coated AZ31 magnesium alloy was successfully prepared by co-extrusion. Microstructure and texture of the extruded Mg/Al rod were systemically studied. A comparative study about electrochemical behavior of the Mg core and the Al sleeve was also addressed. Our results show that, co-extrusion can greatly refine grains of Mg alloy, but does not change the texture component. The 6082 sleeve exhibits a much better corrosion resistance than the AZ31 core. This study provided a novel approach to improve corrosion resistance of Mg alloy. The Al sleeve served as a barrier to protect the Mg alloy from corrosion.

The effect of Ce on the oxidation behaviour and microstructure evolution of nickel-saving austenitic heat-resistant cast steel in air at 900 °C was investigated by performing the isothermal oxidation tests. After 200 h of oxidation, the oxidation resistance of Ce-containing steel was about 20 % higher than that of Ce-free steel. In addition to its role as a reactive element, alloyed Ce slowed the rate of manganese depletion from the substrate and subsurface ferrite formation, leading to the improvement of the oxidation resistance of Ce-containing steel.

Fe-Cr alloys with different chromium contents have been designed in the current study for the ball mill liner working in weakly alkaline slurry. The structure, mechanical properties, corrosion behavior and erosion-corrosion behavior of the alloys were investigated. The result shows that with the increasing Cr content, the hardness and corrosion resistance of the alloy are improved. However, the impact toughness of the alloy shows a decreasing trend with the increase of Cr content. The alloy with the Cr content of 6.978 wt% exhibits the best erosion-corrosion resistance among all alloys in the weakly alkaline slurry. Further analysis shows that the erosion-corrosion mass loss of these alloys in weakly alkaline slurry mainly results from pure mechanical erosion and the interaction between corrosion and erosion. The damage process has also been discussed by interaction models of corrosion and erosion. The result is beneficial to provide reference for selection and development of erosion-corrosion resistant material for ball mill liner working in weakly alkaline medium.

The oxidation behaviour of K-52 austenitic steel with rare earth elements investigated at 1000 °C for up to 150 h. The oxidation kinetics indicated that the addition of the rare earth elements Y or Ce improved the oxidation resistance of steel. However, the simultaneous addition of Y and Ce decreased the oxidation resistance. The oxidation films forming at different stages were evaluated in detail using surface analysis methods. The improved oxidation resistance primarily resulted from the formation of a complete spinel structure, the inner oxidation of silicon and the existence of MnO2 in the Mn-rich zone.

This study examined the oxidation properties of rare earth steel at high temperatures (600 °C–900 °C) in the air atmosphere by using Scanning Electronic Microscope (SEM) with an energy dispersive spectroscopy (EDS), x-ray diffraction analyzer (XRD) and atomic force microscopy (AFM) analysis method. High temperature oxidation experiment showed that rare earth element Ce played a very good antioxidant effect with the increasing oxidation temperature. After continuous oxidation at 600 °C, 700 °C, 800 °C and 900 °C for 150 h, the mass gain of the rare earth steel were 1.25 mg cm−2, 2.41 mg cm−2, 12.34 mg cm−2, and 13.37 mg cm−2, respectively. In comparison, the matrix steel under the same conditions were 1.31 mg cm−2, 2.94 mg cm−2, 13.98 mg cm−2, and 15.63 mg cm−2, respectively. AFM features of the oxidized surface confirmed that the rare earth element Ce could inhibit the growth rate of the oxide in the early stage of oxidation, and preferentially promote the formation of the spinel oxide. The surface-dense spinel oxide (Fe, Cr, Ni, Mn)3O4, the enrichment of Cr-containing layer in the middle, and the formation of the Si-rich oxide in the inner layer all affected the high-temperature oxidation resistance of the rare earth steel.

In order to study the effect of minor Zr on the oxidation resistance and the mechanical properties of nickel-saving austenitic heat-resistant cast steel, the oxidation resistance at 900 °C and the tensile properties at room temperature and at 900 °C of Zr-containing and Zr-free steels were carried out. The results showed that the addition of 0.011% Zr could slightly reduce the oxidation rate and improve the oxidation resistance of Zr-containing steel. In addition, the tensile properties of Zr-containing steel at room temperature and at 900 °C were significantly improved. Brittle fracture occurred in two experimental steels at both temperatures, and brittle characteristics appeared in the fractures.

Interfaces in heterostructures of crystalline materials could strongly affect the slip of dislocations. Such interfaces have become one of the most popular methods to tailor material strength and ductility. This review focuses on the interaction of dislocations and interfaces in heterostructures, in which at least one component is metallic, as investigated by molecular dynamics, in order to systematically summarize our understanding about how dislocations interact with the interfaces. All the possible heterostructures of metallic materials are covered, such as twin boundaries, grain boundaries, bi-metal interfaces and metal/non-metal interfaces. Dislocations may either penetrate the interfaces by inducing steps into the interfaces or dissociate within the interfaces, depending on the type and orientation of the interface as well as the applied strain. Related dislocation interactions at the interface are also presented. In addition, we also discuss the effect of dislocation types, of applied strain and of the deformation method on the interaction of dislocations and interfaces.

Single-crystalline rutile TiO2 nano-flower hierarchical structures were synthesized via a one-pot solvent-thermal method, and they are demonstrated to be ordered three dimensional (3D) hierarchical structures with single-crystalline rutile TiO2 nanorods as building blocks. They exhibited enhanced photocatalytic activity for the selective oxidation from benzylamine to N-benzylidenebenzylamine (N-BIBL) with high yield under visible light irradiation. Such a remarkable performance could be attributed to the rapid photocharge separation and inhibition of charge recombination due to the unique hierarchical structures of this single-crystalline rutile TiO2 nano-flower. The facilely prepared single-crystalline rutile TiO2 nano-flowers are promising materials in the field of photocatalytic fine chemical conversions and other photocatalytic applications.

Using cast tungsten carbide particles (CTCP) and reduced iron powders as raw materials, the porous ceramic preforms with honeycomb, strip, and layer structure, respectively, were prepared by loose sintering process; then, the CTCP/Cr26 ferrous matrix composites were fabricated by casting infiltration process. The microstructure of the composites was analyzed by SEM, XRD, and EDS. The results show that a sintered shell forms as a result of the reaction of Fe and W2C in the CTCP during loose sintering process; the inner part of the shell around the CTCp consists of WC and Fe3W3C phases, while the outer part between the particles is dominated by Fe3W3C. Therefore, the strength of preforms is enhanced because the particles are connected with each other by sintered shell. During casting infiltration process, a transition layer constituted by WC and Fe3W3C formed at the interface of CTCp and the matrix due to the dissolution and precipitation of the sintered shell in the high-temperature liquid iron. The three-body abrasive wear behavior of the composites was investigated. The result shows the wear resistance of honeycomb structure composite is comparable to that of whole layer (WL) structure composite, which is three times of heat-treated Cr26. However, the honeycomb structure composite has higher performance/cost ratio owing to the lower CTCp volume fraction and higher strength and toughness compared with the WL structure composite.