Abstract: ZnO is a typical direct wide band-gap semiconductor material. It has great development potential and application value, and with the rapid development of patterning technology, the precise and controllable fabrication of ZnO nanorod array is gradually being realized. This paper reviews the fabrication of patterned ZnO nanorod arrays using the laser interference lithography technique and describes in detail the applications of patterned ZnO nanorod arrays in energy devices, such as solar cells and photoelectrochemical cells. It is found that ZnO nanorod arrays prepared by laser interferometry have an enhanced light-harvesting ability and enlarged surface area, which is widely used to promote light absorption and carrier transport. It is thus considered that patterned ZnO nanorod arrays with controllable three-dimensional space structures have great research and application value.
Abstract: Because of the lack of coal-rock methods, a novel coal-rock recognition method was proposed based on max-pooling sparse coding in order to explore new coal-rock image recognition methods and efficiently handle high-dimensional coal-rock image data. This method adds the pooling operation when extracting coal-rock image features and adopts the integrated classifier, which consists of multiple weak classifiers when classifying coal-rock images. The experimental results show that this feature-extraction method based on max-pooling sparse coding can simply and effectively express the characteristic information of coal-rock images, greatly enhance the distinguishability of coal-rock images, and achieve a high recognition rate. This method also has good recognition stability. The results obtained herein could provide a new idea and method for automatic coal-rock interface recognition.
Abstract: This study tested the current vs. voltage curves of coals with angles of 0°, 30°, 45°, 60°, and 90° between the bedding plane and the axial direction at temperatures from 0 to 95℃ using a CHI660E electrochemical workstation. The concept of the series-parallel dominant degree was put forward. Moreover, the influence mechanism and the rule of the bedding structure of anthracite coal on coal resistivity under different temperatures were analyzed and investigated using the principle of minimum potential energy and polarization charge. The results show that the resistivity of the anthracite coal exhibits a strong regularity with temperature rise. A turning point appears at 55℃ for θ of the 0° samples, whereas the other samples have a turning point at 35℃. The series-parallel dominant degree reflects the impact mechanism of the bedding structure on coal resistivity and depends on the number of key bedding surface and the start time of the current going through. The resistivity increases with the increasing θ. In addition, the anisotropy coefficient of the anthracite coal increases with the temperature rise and elevates nearly twice in the scope of 35 to 65℃.
Abstract: This study established a two-dimensional mathematical model of solidification and heat transfer for a bloom with a 310 mm×360 mm cross-section using ANSYS software, which was verified by nail-shooting experiments in the narrow side of the bloom and surface temperature testing. The effect of the casting process parameters, such as superheat, casting speed, and secondary cooling intensity, on the solid fraction in the strand centerline and the solidified shell was investigated. Moreover, the optimum casting speed and the optimum solid fraction in the core of the partially solidified strand throughthe soft reduction zone were determined by the model considering the hot ductility of the high-carbon wear-resistant ball steel BU. Plant trials of BU with different casting speeds were performed to validate the theoretical model and analyze the effect of the casting speed on the segregation and shrinkage cavity of BU on a 310 mm×360 mm bloom caster equipped with final electromagnetic stirring (F-EMS) combined with mechanical soft reduction (reduction amount with 17 mm). The results show that the inner defects (e. g., center segregation, V-segregation, and shrinkage cavity) significantly improve when the casting speed is adjusted to meet the required soft reduction zone as a matter of priority; otherwise, the casting speed is only adjusted to preferentially satisfy the required F-EMS stirring region. The inner quality does not show any obvious improvement. Except for the internal cracks and the negative center segregation caused by the improper distribution of the reduction amount, the inner defects (e. g., macro segregation and shrinkage cavity) significantly improve with a casting speed of 0.52 m·min-1 and a solid fraction in the strand centerline ranging from 0.30 and 0.75 in the soft reduction zone.
Abstract: The morphology, composition, and number of inclusions in Fe-Mn-C(-Al) twining-induced plasticity (TWIP) steels were investigated by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and an automated program called "INCAFeature". The characteristics of the inclusions in four TWIP steels with different Al contents (0.002% -1.590%) as well as the influence of Al content on the precipitation of AlN inclusions were investigated. In addition, systematic thermodynamics calculations of AlN formed in TWIP steel were carried out using the appropriate thermodynamic data for high-Mn-Al TWIP steel. The results show that AlN would begin to precipitate and locally precipitate around the MnS(Se) -Al2O3 inclusions when the Al content in the steel reaches 0.75%. The thermodynamics calculations show that AlN could already form in the liquid TWIP steel at an Al content of 1.07%. Then, AlN would locally precipitate around the MnS(Se) inclusions, thus forming MnS(Se) -AlN aggregates. When the Al content increases to 1.59%, the precipitation temperature of AlN is 42℃ higher than the liquidus temperature of the TWIP steel. Furthermore, precipitated AlN inclusions in the liquid TWIP steel could act as heterogeneous nuclei for MnS(Se) inclusions, thus forming MnS(Se) -AlN inclusions. Moreover, according to the thermodynamics calculation, the lowest N content for AlN formation in the liquid Fe-18.21% Mn-0.64% C-1.59% Al steel is just 0.0043%. Therefore, the N content should be kept as low as possible to avoid the formation of excessive AlN inclusions during melting of Fe-Mn-C(-Al) TWIP steel.
Abstract: This study investigated the microstructures and the mechanical properties of the A380 alloy solidified at different squeeze pressures by polarizing microscopy, scanning electron microscopy, image analysis, and tensile test. The obtained results show that the microstructures of the squeeze casting specimens are much finer than those of gravity casting specimens. Moreover, the porosity and the mechanical properties of the squeeze casting specimens are remarkably improved compared with those of the gravity casting specimens. The size of the dendrite arm and the porosity decrease when the squeeze pressure is increased from 0 MPa to 75 MPa in the squeeze casting process. The eutectic volume fraction of the specimen increases, while the secondary dendrite spacing decreases. The size of the needle-like β-Al5 FeSi phase significantly decreases. In addition, a few α-Al8 (Fe,Mn)3Si2 phases with Chinese characters are observed in the grain boundary. The influence of the pressure on the microstructures, second-phase morphology, and mechanical properties of the squeeze casting specimens does not significantly improve with the increasing squeeze pressure when the squeeze pressure is larger than 75 MPa. The tensile strength and the elongation of the A380 alloy when the squeeze pressure is 75 MPa increase by 19% and 65%, respectively, compared with those of the gravity casting specimens.
Abstract: The influence of non-metallic inclusion on the performance of steels is closely related to the characteristic parameters. The in-situ scanning electron microscope (SEM) observation results of the crack initiation induced by TiN inclusion under tensile and fatigue loads in the ultra-high strength steel were analyzed. The stress fields of the inclusions and nearby matrix were then calculated using the MSC Marc finite element analysis software. Subsequently, the stress and strain fields of the TiN inclusions with different characteristic parameters and the nearby matrix were simulated. The results show that the mechanical behavior of the inclusions and the nearby matrix can be explained and predicted by finite element method. The maximum stress concentration is located around the sharp angle of a triangle inclusion. The position of the high-stress region in a rectangle inclusion is affected by the angle between the inclusion and the load direction. The position of the maximum stress in the matrix changes from the outer-inclusion region to the inter-inclusion region with the increase of the inter-inclusion distance. The high-stress region near the free surface results from the sub-surface inclusions, and the position of the maximum stress is affected by the distance from the inclusion to the free surface and the inclusion size.
Abstract: Hot isostatic pressing (HIP) was used to join two dissimilar aerospace alloys, namely Al12A12 and Ti6Al4V, for the first time. The microstructure and compositional evolutions were evaluated in the joint interface by scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffraction. The microhardness and shear strength tests were applied to study the mechanical properties of the joints. As a result, different intermetallic compounds (e. g., Al3 Ti, TiAl2, and TiAl) form in the reaction layer of Ti/Al. The findings show that the microhardness value of the joint region is 163 HV. The highest strength in the bonding zone is 23 MPa, which exhibites a 17.9% improvement compared to that only with Cu coating, but is lower than the bonding strength with the interlayer. The fracture mode is brittle fracture due to overburden and void formation. The elements of dissimilar materials diffuse into each other during the HIP. Furthermore, various intermetallic compounds form at the interface, which affects the mechanical properties of the joints.
Abstract: This study investigated the spiral line sample of A357 prepared by the squeeze casting (liquid die forging) process and the influence of the fluidity length on the composition segregation and microstructure segregation through chemical composition and metallographic analyses. The results show that the Si and Mg mass fractions of the start and the end of the spiral line sample along the flow length are greater than that in the middle of the spiral line sample. The initial grain size of α first increases, then decreases with the increase of the fluidity length. Meanwhile, the phase rate of the primary solid shows a fluctuating change with the increase of the fluidity length. The composition segregation and the microstructure change are caused by the forced flow of the filling liquid in the squeeze casting process.
Abstract: This study analyzed the effects of the oxide film of 14Cr12Ni2WMoVNb steel with QPQ (quench-polish-quench) treatment on tribological properties at room temperature and corrosion resistance of the layers. The microstructure and properties of specimens with and without oxide film were studied by metallographic analysis, X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), a scratch tester, friction and wear tester, and at an electrochemical workstation. Results show that the effects of the oxide film on tribological properties of the layers are related to load. When the friction time is 4 min and the load is low (50 N), the friction coefficient of the oxide film and the volume wear rate are effectively decreased. However, with a friction time of 4 min and a high load (100 N), the oxide film is destroyed, there is thus no reduction in the volume wear rate. The study also shows that the oxide film obviously improves the corrosion resistance of the layers. The Tafel polarization curve of the specimen with oxide film has an obvious passivation region, and the pitting potential is-13 mV. The surface of the specimen with the oxide film removed has a wide area of corrosion after salt spray corrosion for 12 h, whereas a large area of corrosion only occurs after 48 h of salt spray for the specimen with the oxide film.
Abstract: Nickel aluminum bronze is the main material used to cast large ship propellers. However, marine biofouling on the surface of the propeller alters the pH value, thereby accelerating tribocorrosion and threatening ship safety. In this study, a compact nickel aluminum bronze coating with a thickness of approximately 300 μm was deposited by cold spraying. The microstructure of the coating was observed by scanning electron microscopy and optical microscopy. The electrochemical corrosion properties and tribocorrosion behavior of the coating was determined using 3.5% NaCl solution in different pH environments of 3, 7, and 11. Results show that in a pH 3 environment, optional corrosion occurs on the nickel aluminum bronze substrate, cracks mainly containing Cu are mostly distributed on α phases, deep cannelure is observed on the wear trace of the coating, and abrasive wear occurs on the coating. In a pH 7 environment, adhesive wear occurs on the substrate, slice abrasive dust is distributed on the surface of wear trace of the substrate (because porosities on the coating absorb most of the abrasive dust and avoid three body friction), cannelure on the coating is relative shallow. In pH 11 environment, surface fatigue occurs on the surface of the substrate and deep cannelure is observed on the wear trace of coating, which contains cracks. Generally speaking, tribocorrosion resistance of coating enhances during cold spray process in different pH environments, resulting from cold working hardening and abrasive dust entering the coating pores.
Abstract: The corrosion behavior of the new 2Cr1Mo2Ni steel in the oil field formation water containing CO2 at 80℃ and 0.8 MPa was studied herein to clarify the role of Ni and Mo in the corrosion resistance of low-Cr steel. The surface morphology and the chemical composition of the corrosion scales were analyzed by scanning electron microscopy and energy dispersive spectroscopy (EDS). The polarization curves and the electrochemical impedance spectroscopy spectra were also obtained to explore the growth process of the corrosion scale. The results indicate that Mo and Ni are not as efficient as Cr in enhancing the corrosion resistance of the low-Cr steel. The low-frequency inductance loop disappears after 164 h immersion. Moreover, the corrosion scale completely covers the substrate surface. In addition, the protective corrosion scale forms after 240 h immersion.
Abstract: Under high-strain-rate conditions, Ti and steel in Ti-steel clad plate deformed, with the deformation compatibility mechanism playing a key role at the bonding interface. The interfacial microstructure and deformation mechanism of Ti-steel clad plate under high strain were investigated in this paper. The results show that, for the steel side, with increasing strain rate, the number of small-angle (3°-10°) grain boundaries increases and texture component {112} 〈241〉gradually evolves into textures {665} 〈386〉 and {111} 〈110〉. For the Ti side, with increasing strain rate, deformation twins appear. Different deformation twins such as tensile twin {1121} 〈1100〉, compression twin {1122} 〈1123〉, and tensile twin {1012} 〈1011〉are produced. The deformation mechanism of the Ti side at high strain rate transforms from a conventional"twin deformation"mode to the compound deformation mode"coexistence of dislocation slip and twin deformation. "With the increase of strain rate, the bonding interface would coordinate the different deformation resistances of both sides, to achieve a continuous deformation without any materials damage. The main coordination mechanism relies on the bonding interface and the slip of adjacent grains.
Abstract: This study presented a new bulging-pressing compound-forming process to solve the manufacturing problem of a thinwall specimen with a small round corner radius. Its key process parameters were the pre-forming depth, pre-forming concave round corner, and matching relation between the liquid bulging pressure and the backpressure punch velocity in the final forming process. The pre-forming depth determines the material reserves of the small round corner area in final forming. The best pre-forming concave round corner is the minimum punch corner in hydro-mechanical deep drawing. The calculating methods for the pre-forming depth and the pre-forming concave round corner were provided by a theoretical analysis. The mechanical model of the bulging-pressing compound forming process was built. Moreover, the deformation situation in the round corner area with different matching relations between the liquid bulging pressure and the backpressure punch velocity was provided by the stress state analysis. Meanwhile, the influences of the pre-forming depth and the matching relation between the liquid bulging pressure and the backpressure in final forming on the quality of the part were researched based on the finite element simulations and experiments. The accuracy of the theoretical analysis was verified. In addition, the applicability of the new process was proven.
Abstract: To improve the efficiency of frequency response function (FRF) model updating, the Kriging model is introduced into its optimization procedure, thus replacing the finite element model for iteration. The objective function is established based on the error of FRF curve at each corresponding frequency point, and a design of experiment (DOE) of the primary design parameters is performed. The sensitivity of each design is then assessed based on DOE results, and the parameters involved in model updating are selected. The Kriging model is constructed based on these selected parameters, and after confirming its response it participates in the model updating process. The GARTEUR aircraft model is used as an example, and it is found that based on acceleration FRF data, the FRF curve reappears at the checking point after model updating. The FRF curve is also predicted successfully when the structure is changed locally, and therefore the effectiveness of the Kriging method applied to FRF model updating is demonstrated.
Abstract: Maintenance of rotating machinery has significant practical implications for preserving the service condition and quality of products. Moreover, it directly affects the economic efficiency of enterprises. Although frequent maintenance can preserve the condition and quality of products, it can increase the cost of enterprises. Conversely, long intervals in maintenance can prove to be economical but would not ensure the desired condition and quality. This study presented a real-time maintenance strategy which was based on condition assessment using the fuzzy C-means method and the kurtosis index. Changes in the kurtosis index can be monitored to successfully capture the features of early faults. The performance condition was assessed using the fuzzy C-means method, and the result was considered as the reliability of the equipment. Enterprise-efficiency optimization was regarded as a proposed criterion to make a real-time maintenance recommendation. The result of analyzing data from a steel enterprise shows that this real-time maintenance strategy is more suitable for the management of on-site equipments. Moreover, it reduces the monitoring cost, thereby obtaining increased enterprise benefit.
Abstract: In order to improve the accuracy of switched current circuit fault diagnosis, a feature extraction and recognition method of switched current circuit based on wavelet packet optimization and optimization of BP neural network was proposed. Firstly, the wavelet packet decomposition of the original response signal of the switched current circuit was carried out. Then, the normalized energy value after the decomposition of the N layer was calculated, and the optimal wavelet packet basis was selected by using the characteristic deviation as the evaluation. Finally, the optimal fault feature vector was constructed. The extracted optimal fault characteristics were classified by BP neural network optimized by genetic algorithm. The results of this method were verified by the example circuit. The results show that all the soft faults are effectively classified, and the superiority of the method in the fault diagnosis of the switched current circuit is illustrated.
Abstract: For addressing the difficulties in the registration of multimodal images in image-matching guidance, a new visualinfrared image-registration approach based on ellipse symmetrical orientation moment was proposed. Scale and affine invariant maximally stable external regions features were extracted to fit the ellipse area in multimodal images. Cluster segmentation was used to automatically select the homogeneous regional features that were invariant between multimodal images. The ellipse symmetrical orientation moment was used to describe the similarity of the regional feature edges in different orientations. Based on the mutual-correlation criterion, the matching feature pairs of the visual and infrared images were obtained. The matching correction strategy was used to reduce the probability of mismatching. The experiments demonstrate that the matching success rate of the corresponding feature pairs between the visual and infrared image is improved to more than 95%, and the computation time is reduced by nearly half as compared with that required by traditional algorithms. The proposed algorithm can meet the image-registration algorithm requirements of a higher success rate and rapid speed as well as strong anti-jamming and stabilization for image-matching guidance.
Abstract: Traditional data mining methods are difficult to deal with the high dimensionality and dynamics characteristic of the time series. Therefore, in this study, a similarity dynamical clustering algorithm based on multidimensional shape features for time series (SDCTS) was proposed. First, the feature points of multidimensional time series are extracted to realize dimensionality reduction. Second, a new similarity measure criterion is defined with the shape features (slope, length, and amplitude) of the obtained multidimensional time series, and thus a dynamical clustering algorithm of multidimensional time series is proposed without predefining clustering numbers. The experimental results demonstrate that the SDCTS algorithm improves the clustering accuracy for time series compared with other algorithms.
Abstract: It was studied that the aquatic plant Acorus calamus and reed affected the enrichment ability of compound heavy metals (i. e. V, Cr and Cd) and physiological response and the two plants repair effects of polluted water were investigated by heavy metals. Results show that the tolerance index of two plants decreases with heavy metals concentration increasing in water body, whereas the growth of the Acorus calamus is better than that of reed. Under different concentrations of heavy metals, both Acorus calamus and reed show the strongest enrichment ability of Cd, followed by Cr, while the enrichment ability of V is relatively weak. Under same heavy metal concentration, Acorus calamus on the total enrichment quantities of three kinds of heavy metals are better than those of reed. When the mass concentration of heavy metal is 15 mg·L-1, the enrichment of three heavy metals by Acorus calamus is 1065.02, 1754.80 and 4372.40 mg·kg-1 for V, Cr and Cd, respectively. The enrichment index of Acorus calamus underground part of V, Cr and Cd is 2.1, 1.5 and 1.8 times better than that of reed. It is concluded that Acorus calamus is more suitable for the remediation of heavy metal pollution by V, Cr and Cd.
Monthly, started in 1955 Supervising institution：Ministry of Education Sponsoring Institution：University of Science and Technology Beijing Editorial office：Editorial Department of Chinese Journal of Engineering Publisher：Science Press Chairperson：Ren-shu Yang Editor-in-Chief：Ai-xiang Wu ISSN 2095-9389CN 2095-9389
