Micro-crack Defects Research Articles

Integrated hierarchical lanthanum niobium oxide surface coating to stabilize high-voltage performance and suppress Ni2+/Li+ cationic disorder in nickel-rich layered cathodes

High‑nickel ternary materials are the most promising lithium battery cathodes in terms of application and development potential. These materials face significant problems at elevated voltage, including cation mixing, interfacial reactions, microcracks, and lattice oxygen loss, which undermine their cyclic stability and safety. Metal oxide coating is the most direct and effective solution to alleviate this material degradation. Herein, we present an integrated LaNbO4 (LN) surface coating strategy for improving LiNi0.88Mn0.02Co0.10O2's (NMC-88) electrochemical performance and structural stability. The coating materials penetrate the bulk-layered structure and enhance structural integrity. Additionally, it protects the cathode surface against undesirable parasitic side reactions and achieves excellent electrochemical properties, optimal rate performance, and cyclic stability by improving lithium diffusion. The modified cathode maintains a specific capacity of 42 %, while the pristine NMC-88 cathode holds 25.69 % after 150 cycles at 2.8–4.5 V under 2C. The surface modification method reduces the H2-H3 phase and the overgrowth of the solid electrolyte interface, leading to enhanced cyclic performance. In comparison to NMC-88, the improved electrochemical performance and structural integrity of LN-coated NMC-88 are linked to the decrease in microcrack defects during cycling.

Extraction of asymptotic edges of microcracks in silicon nitride bearings based on adaptive nonlocal mean filtering and iterative tracking algorithm

The gradual change edge of the Si3N4 bearing roller microcracks with decreasing gray gradients are difficult to be extracted by threshold segmentation. The method for extracting the gradual change edge of Si3N4 bearing roller microcracks using adaptive non-local mean filtering and an iterative tracking algorithm is proposed. Widely distributed, large-span, dense noise is eliminated from the gradual change edges of microcracks in Si3N4 bearing roller microcrack images. In the iterative expansion process of microcrack defect shape, the gradual change edge pixel of microcrack is accurately tracked. The Si3N4 bearing roller microcrack image is enhanced by adaptive non-local mean filtering. The following are the experimental findings: The PSNR and SNR reach 38.12 dB and 40.94 dB, respectively. The microcrack gradual change edge pixels can be extracted with an edge coverage rate of 92.5 % and an accuracy of 93.8 % using the iterative tracking algorithm for Si3N4 bearing roller microcrack images.

The thermal deformation behavior and processing map of TC9 titanium alloy

This investigation delves into the thermal deformation behavior of TC9 titanium alloy. Compression tests at isothermal conditions were performed on a Gleeble thermal simulator under conditions spanning 700–1200 °C and strain rates of 0.001–1 s−1. The true stress-true strain curves indicated that stress increases with rising strain rate and decreasing temperatures. The softening mechanisms in the biphasic and monophasic regions were discussed. By correcting errors caused by friction, the strain-compensated Arrhenius-type constitutive equation, which accurately describes the flow behavior of TC9 titanium alloy, has been established. A processing map at a strain of 0.7 was constructed based on the power dissipation factor, revealing an unstable region at 700–800 °C/0.01–1 s−1 and 800–900 °C/0.1–1 s−1, where microcrack defects were observed, suggesting that processing should be avoided in this region. Efficiency values as high as 60–70 % indicate superplasticity deformation, with corresponding m values within this efficiency range of approximately 0.4–0.5, reaching the strain rate sensitivity index range of superplasticity titanium alloys. Tensile tests conducted at 900 °C and a deformation rate of 0.001 s−1 showed elongation exceeding 100 %. The sample compressed at 900 °C and 0.001 s−1 exhibits small grain size, uniform orientation, the lowest dislocation density, and a uniform two-phase mixture. These microstructural features indicate the material's good machinability.

Microstructures and Corrosion Behaviors of Non-Equiatomic Al0.32CrFeTi0.73(Ni1.50−xMox)(x = 0, 0.23) High-Entropy Alloy Coatings Prepared by the High-Velocity Oxygen Fuel Method

The non-equiatomic Al0.32CrFeTi0.73(Ni1.50−xMox) (x = 0, 0.23) high-entropy alloy (HEA) coatings were prepared by the high-velocity oxygen fuel (HVOF) method. The microstructures and corrosion behaviors of the HVOF-prepared coatings were investigated. The corrosion behaviors were characterized by polarization, EIS and Mott-Schottky tests under a 3.5 wt.% sodium chloride aqueous solution open to air at room temperature. The Al0.32CrFeTi0.73Ni1.50 coating is a simple BCC single-phase solid solution structure compared with the corresponding poly-phase composite bulk. The structure of the Al0.32CrFeTi0.73Ni1.27Mo0.23 coating, combined with the introduction of the Mo element, means that the (Cr,Mo)-rich sigma phase precipitates out of the BCC solid solution matrix phase, thus forming Cr-depleted regions around the sigma phases. The solid solution of large atomic-size Mo element causes the lattice expansion of the BCC solid solution matrix phase. Micro-hole and micro-crack defects are formed on the surface of both coatings. The growth of both coatings’ passivation films is spontaneous. Both passivation films are stable and Cr2O3-rich, P-type, single-layer structures. The Al0.32CrFeTi0.73Ni1.50 coating has better corrosion resistance and much less pitting susceptibility than the corresponding bulk. The corrosion type of the Mo-free coating is mainly pitting, occurring in the coating’s surface defects. The Al0.32CrFeTi0.73Ni1.27Mo0.23 coating with the introduction of Mo element increases pitting susceptibility and deteriorates corrosion resistance compared with the Mo-free Al0.32CrFeTi0.73Ni1.50 coating. The corrosion type of the Mo-bearing coating is mainly pitting, occurring in the coating’s surface defects and Cr-depleted regions.

Lightweight TiC based cermet fabricated by a pre-solid phase sintering-assisted pressureless infiltration process

This paper introduces a novel process, known as pre-solid phase sintering-assisted pressureless infiltration (PSPS-PI), aimed at addressing issues related to the segregation of hard particles and excessive porosity in the manufacturing of lightweight cermet based on TiC. The PSPS-PI process involves compressing a green TiC powder compact with a minor Ni powder addition, followed by vacuum-based solid-phase sintering to create a fully consolidated TiC preform. This study explores the influence of TiC particle size and Ni content on the microstructure and properties of TiC–Cu composites, conducting a comparison with direct pressureless infiltration (D-PI). The results indicate that the high-melting-point Ni element promotes the formation of sintering necks between TiC and Ni, aiding in the consolidation of TiC particles. The stable skeleton ensures that TiC particles remain in their initial positions during subsequent pressureless infiltration, effectively preventing TiC powder segregation. TiC and Ni create a dissolutive wetting system during pressureless infiltration. The formation of the Ni2SnTi intermetallic compound significantly enhances the wettability with Cu alloy, leading to a reduction in porosity and the occurrence of crack defects within the composite. As particle size decreases, the preform's porosity decreases, resulting in a reduced proportion of soft metal binder and lower residual stress. Consequently, finer TiC powder leads to improved cermet hardness and a reduction in the number of micro-crack defects. In general, PSPS-PI allows for the attainment of low porosity, a uniform microstructure, enhanced hardness, and outstanding wear resistance in the lightweight cermet based on TiC with the appropriate TiC particle size (D50 = 10.2 μm), achieving a remarkable hardness of 642.9 (Hv30) and excellent toughness.

A study of laser machining combined with dynamic chemical etching in micro‐hole drilling of 2.5D SiCf/SiC composites

AbstractIn this study, we used a novel method of laser machining combined with dynamic chemical liquid etching (LMDCE) to drill holes in 2.5D SiCf/SiC ceramic matrix composites (CMC‐SiC). A chemical solution that could quickly remove the recast layer without damaging the substrate was selected. Severe recast layer and microcrack defects were observed when laser machining was performed in the air. The surface of the material was highly carbonized due to the thermal effect of the laser. The effect of different defocus amounts and scanning speeds on the hole taper was studied. A lower scanning speed can ensure that a smaller taper is obtained by the microhole. The bore diameter of the holes processed with a defocusing amount of 0 or −1 mm is more uniform. The results show that with the assistance of a dynamic chemical solution, the fibers break neatly into needle‐like shapes, the thermal effect of the laser on the ceramic substrate is significantly weakened, the microhole shows good roundness, and there are no recast layers and oxides on the sample surface. In addition, microcracks are significantly reduced, and high‐quality microholes without a heat‐affected zone (HAZ) are machined. The method provides a new idea on how to eliminate machining defects and achieve higher‐quality micromachining for ceramic matrix composites.

MicroCrack-Net: A Deep Neural Network With Outline Profile-Guided Feature Augmentation and Attention-Based Multiscale Fusion for MicroCrack Detection of Tantalum Capacitors

The microcrack defect in the terminal electrode of the tantalum capacitor seriously affects the service life of the capacitor. However, the microcrack displays low contrast and large noises in the image. Meanwhile, the width of the microcrack is small, and the area in the image is tiny, which brings additional challenges to the detection of microcracks on the terminal electrodes. To improve the performance of detecting microcracks, this article proposes a detection model with outline profile-guided feature augmentation and attention-based multiscale fusion, titled with MicroCrack-Net. In this method, the microcrack outline is utilized to guide the lossless feature extraction to strengthen unobvious microcrack features without pooling operation to avoid information loss of tiny defects during the layer-by-layer processing in the convolutional neural network. A gradual attention mechanism is proposed to attract the attention of the detection model to local defect areas in the image with noises. Multiscale feature extraction and fusion are designed to process the data in tensors of the same size. The experimental results demonstrated that the proposed model is effective and has superior performance over VGG16, resNet50, resNext50, DenseNet, Racki-Net, and SegDecNet in detecting microcracks.

Influence of defects on high-temperature oxidation performance of GH3536 superalloys fabricated by laser powder bed fusion

• Microstructure and oxidation behaviour of an LPBF fabricated GH3536 superalloy was investigated. • Oxidation resistance is closely related to defect density while micro-cracks significantly impair the oxidation resistance. • Oxidation resistance can be improved by optimising processing parameters and powder composition. This study investigates the formation of defects and their impact on oxidation behaviour of GH3536 superalloys fabricated by laser powder bed fusion (LPBF). Defects of six series of samples manufactured by different parameters is dominated by pores, micro-cracks, and lack of fusion, respectively. The superalloy is isothermally oxidised in 950 °C dry air for 500 h. The oxidation resistance of LPBF GH3536 depends on the types and quantity of processing defects, wherein the sample with micro-cracks as the main defect exhibit the worst oxidation resistance. Electron probe microanalysis of the superalloy revealed the impact of micro-cracks on diffusion process. Defects seriously deteriorate the oxidation resistance, especially micro-crack defects. Reducing manufacturing defects in the samples can improve the corrosion resistance.

Welding defect detection in nuclear power plant spent fuel pool panels based on alternating current field measurement: experimental and finite element analysis

The overlay panels of spent fuel pools of nuclear power plants can easily become corroded and produce micro-crack defects. Surface crack defects tend to expand vertically, horizontally and obliquely, causing damage and fracture to the overlay panels and welds of spent fuel pools. Traditional non-destructive testing (NDT) cannot complete underwater testing in real time. In order to improve the timeliness of crack detection and shorten the inspection period, research on accurate inspection technology for surface cracks in the overlay panels of spent fuel pools is carried out in this paper based on alternating current field measurement (ACFM) and the weld defect detection process for the cladding panels of spent pools is optimised. In this work, different types of artificial defect are assumed and the distortion of the magnetic field characteristic signal caused by the defects is studied. The characteristics of magnetic field signals generated in different defect regions are studied by establishing a defect electromagnetic detection model for numerical calculation. Finally, experimental and numerical results are compared and analysed. The results show that ACFM can be used to quickly and effectively inspect for cracks in the base material, weld and interface of spent fuel pool overlay panels and it has the characteristics of accuracy, high resolution, high sensitivity and low delay. The research results, which have good application value, provide technical support for electromagnetic inspection of latent cracks in field spent fuel pools and early crack warning of underwater structural defects.

Design of EL defect detection system for photovoltaic power station modules

In recent years, the photovoltaic power generation industry has been vigorously promoted and developed, while the solar cell as its core component may have micro-crack defects, which directly affect the power generation efficiency and stability of the photovoltaic system. Therefore, it is necessary to adopt a low-cost, efficient and flexible method to detect defects in solar cells. At present, most of the existing micro-cracks detection is carried out in the laboratory, and there is no EL micro-cracks detection in the actual photovoltaic power station. The main purpose of this paper is to design a set of EL defect detection system that can be used for actual photovoltaic power station modules, which is different from the traditional laboratory-level or module-level defect detection, and to carry the designed detection algorithm to the integrated device to operate. Experiments have shown that the system can perform real-time detection of photovoltaic module defects based on the string level, which improves the detection efficiency while saving time and cost, and shows good performance.

Optimization design of process parameters for cold and hot composite roll forming of the AHSS square tube using response surface methodology

Advanced high-strength steel (AHSS) is a highly competitive material for the automobile industry to resolve the challenge of weight reduction and passenger safety. Cold and hot composite roll forming is a newly developed manufacturing technology, which aims to overcome the defects such as microcrack, severe work hardening, thickness reduction, and large corner radius in the traditional cold roll forming process of AHSS. In this paper, the mathematical models that represent the effect of line velocity, heating power, and deformation amount on the yield strength, outer corner radius, and microcrack length in the corner section of cold and hot composite roll-formed AHSS square tube are investigated by the response surface methodology with Box-Behnken design. The analysis of variance shows that the linear velocity has the greatest influence on the three responses, followed by the heating power and deformation amount. Furthermore, the experimental verification is carried out under the optimal combination of process parameters to manufacture the AHSS square tube with the desired performance. Compared to the cold roll-formed AHSS square tube, the product of strength and elongation in the corner section is increased by 53%, the corner thickness is increased by 60%, the outer corner radius is decreased by 94%, and the microcrack defect is not generated. The average magnitude of errors between the predicted and actual values is about 5%, which implies that the optimization design is accurate and reliable.

Corrosion Properties of Ni60/WC Coating with Abrasion‐Resistant Microdimples Ablated by Nanosecond Laser

Herein, the influence of laser‐ablated cracks in microdimples on the corrosion properties of Ni60/tungsten carbide (WC) coating is investigated. It is based on the dimension parameters of circular microdimples, which is optimized by unit and full‐size friction‐wear experiments for a textured plunger and sealed‐disk assembly element. The Poisson distribution is used to perform the statistical and characterization analyses of the microcrack defects on the surface of Ni60/WC coating with the circular microdimples ablated by the nanosecond laser. The key process parameters of laser machining in groups with a high and a low ratio of apparent microcrack are selected, and are compared with the nontextured group on the coating surface through immersion–corrosion and electrochemical–corrosion tests. It finds the high and low apparent‐microcrack groups under the action of static corrosion, and the coating has the similar corrosion behavior with the nontextured group. When apparent microcrack does not extend to the substrate, the nanosecond‐laser ablation of microdimples does not change the coating corrosion properties. Moreover, the corrosion properties of the coating are improved by laser ablation recrystallization. The experimental support is provided in the results for the application of microdimples on the surface of fracturing‐pump plunger coating in acidic environments.

Microcrack Defect Quantification Using a Focusing High-Order SH Guided Wave EMAT: The Physics-Informed Deep Neural Network GuwNet

It is challenging to apply deep learning in professional fields that lack big data support, especially in industrial structure health assessments using ultrasonic guided wave nondestructive testing (NDT) method. To solve this problem, one feasible solution is to introduce the concept of NDT physics into a deep neural network to compensate for the network's poor predictive abilities when trained on small datasets. Therefore, we propose a physics-informed deep neural network, named GuwNet, based on a unidirectional oblique-focusing (UOF) high-frequency, high-order shear horizontal guided wave electromagnetic acoustic transducer (EMAT) to quantify microcrack defects more accurately. First, the designed focused-transmission omnidirectional-reception UOF-EMAT can produce pure high-frequency, high-order guided waves. Through a circumferential arrangement of multiple receiving transducers, the maximum amount of information can be obtained regarding the reflected waves of the defect. This method solves the inherent problems of an EMAT (i.e., low energy conversion efficiency) and achieves effective detection of microcrack defects. Second, we study the quantification principle of microcrack defects suitable for UOF-EMAT, and propose a deep neural network using physical knowledge regarding this theory. We rationally design the network structure based on the quantitative principles and logic obtained from this article. In addition, feedback and feedforward loss functions suitable for evaluating different forms of variables are proposed to integrate the physical concepts of ultrasonic guided wave testing into the neural network training. Finally, we verify the performance of the proposed GuwNet based on the UOF-EMAT. Compared with traditional nonphysics-informed methods, the length, depth, and direction of the quantification errors are reduced to 0.127 mm, 0.279% <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d_t</i> , and 1.843°, respectively, and the average quantification error is reduced by more than 80%.

Micro-crack defects detection of semiconductor Si-wafers based on Barker code laser infrared thermography

Micro-crack defects are easy to form in the semiconductor Si-wafer surface during the production process, which finally effect the quality of silicon based microelectronic products. In order to ensure the quality and performance of products, it is important and necessary to carry out nondestructive testing (NDT) for Si-wafers. This paper experimentally investigates the performance of the Barker code laser infrared thermography (BCLIT) technique for the semiconductor Si-wafer defect detection, using an optical infrared thermography set-up in transmission method. The thermal wave signal response of the laser to the Barker code modulation waveform is collected by an infrared camera, which was stored as image sequences. Then the detectability was studied according to processed results via the Total Harmonic Distortion (THD) algorithm from obtained image sequence. In addition, linear frequency modulation thermal wave imaging (LFMTWI) technique was used to compare and analyze the performance of BCLIT. Experiments performed on the Si-wafer under the low power density condition indicate that the higher of the excitation power and the wider of the crack width, the better the detection effect. Furthermore, the performance of BCLIT is better than the traditional LFMTWI with all cases in evaluation index result of signal-to-noise ratio (SNR). The research results show that the BCLIT technique significantly improve SNR and defect detectability, and it can be used for the semiconductor Si-wafers micro-crack defects detection even under low power density excitation.

Comprehensive evaluation of damages in ferromagnetic materials based on integrated magnetic detection

In order to quickly and comprehensively detect residual stress, microcracks and other damages in ferromagnetic materials, this study developed an integrated magnetic non-destructive testing system with changeable magnetic field excitation based on anisotropic magnetoresistive (AMR) sensors. The system integrated magnetic memory detection, magnetic flux leakage (MFL) detection and magnetic Barkhausen noise (MBN) detection and was used to perform detection experiments on a 45# steel test-piece with precast residual stress zones and cracks in different directions. The experimental results showed that the proposed system can detect residual stress in a ferromagnetic test-piece, identify microcrack defects of different angles and quantitatively evaluate the residual stress. This paper provided a useful reference for the comprehensive evaluation of damages in ferromagnetic materials.

Composition-induced microcrack defect formation in the twin-wire plasma arc additive manufacturing of binary TiAl alloy: An X-ray computed tomography-based investigation

Composition-induced microcrack defect formation in the twin-wire plasma arc additive manufacturing of binary TiAl alloy: An X-ray computed tomography-based investigation

Research on Image Defect Detection of Silicon Panel Based on Prewitt and Canny Operator

The silicon panel is the core component of photovoltaic power generation, whose surface quality is related to its service life and power generation efficiency. However, microcracks, fragments, incomplete welding, broken grids, and other defects often occur in industrial production. The edge detection algorithm is usually used to detect defects in silicon panels, but the common edge detection algorithm has an impact on defect detection because of the grid shadow of the panel. The current mainstream defect detection algorithm based on convolutional neural network requires a large number of positive and negative samples of image data sets for pretraining the model, which consumes a lot of time and GPU computing power, and the steps are cumbersome. To solve the problem, a defect detection method based on Prewitt and Canny operators is proposed in this article. In this method, Prewitt and Canny operators are combined to eliminate the effect of grids on the detection. The microcrack defects and their specific positions can be detected efficiently and intuitively, therefore improving the detection accuracy. The experimental results indicate that the purity and integrity of the defect profile of the image processed by the algorithm are greatly improved. The foreground edge is clear, and the defect recognition accuracy is higher, which effectively prevent the impact of grid shadow on weld testing.

A Defect Detection Method for the Surface of Metal Materials Based on an Adaptive Ultrasound Pulse Excitation Device and Infrared Thermal Imaging Technology

Ultrasonic excitation has been widely used in the detection of microcracks on metal surfaces, but there are problems such as poor excitation effect of ultrasonic pulse, long time to reach the best excitation, and difficult to find microcracks. In this paper, an adaptive ultrasonic pulse excitation device and infrared thermal imaging technology have been combined, as well as their control method, to solve the problem. The adaptive ultrasonic pulse excitation device adds intelligent modules to realize automatic adjustment of detection parameters, which can quickly obtain reliable excitation; the multidegree-of-freedom base realizes the three-dimensional direction change of the ultrasonic gun to adapt to different excitation occasions. When the appropriate ultrasonic excitation makes microcracks in the resonance state, the microcracks can be frictionated, which produce heat rise with the temperature. Then, the microcrack defect can be detected by the infrared thermal instrument through the different surface temperatures with imaging recognition method. Our detection experiments of the titanium alloy plates and the aluminum alloy profiles of marine engineering show that the method can get reliable detection parameters in a short time and measure the crack length effectively. It can be used in many aspects such as crack detection in mechanical structures or complex equipment operating conditions and industrial production processes.

Using glass defect engineering to obtain order–disorder transformation in cathode for high specific capacity lithium ion battery

Vanadium-based glass shows high electronic conductivity without grain boundaries. It easily undergoes structural microcrack defects during fabrication using the melt-quenching method resulting in voids that affect its properties. This paper demonstrates that the cathode material obtained by nanocrystals precipitated by long-cycle electric fields are identical with those obtained by the heat treatment method. V2O5-Li3PO4 (VP) glass precipitates nanocrystals of Li3P and Li0.3V2O5 under heat treatment at 340 °C. It showed a prominent specific capacity of 269.4 mAh.g−1 in the first cycle at a current density of 50 mA.g−1, and 227.4 mAh.g−1 after 50 cycles with a retention rate of 86.3%, as the cathode of a lithium ion battery. Thermal field-controlled VP glass allows selective crystallization of nanocrystal of Li3P and Li0.3V2O5, which promote conductivity and charge transfer and significantly enhance the electrode reaction kinetics. Through ex-situ TEM, DSC, XRD and XPS, it was observed that discharge/charge caused disordered transitions in the amorphous VP, leading to the formation of nanocrystals of Li3P and Li0.3V2O5 after 100 cycles. Amorphous glass electrode material as a high-energy unstable state, has same tendency of precipitation of crystals to become stable under different treatment methods with long electric field cycles and thermal field induction.

Investigation of sensitivity of the ultra‐high frequency partial‐discharge detection technology for micro‐crack in epoxy insulator in GIS

The ultra-high frequency (UHF) method has been widely used in a gas-insulated system (GIS) for partial-discharge detection, and many achievements have been realised. In addition, many studies based on artificial defects have been made to confirm its validity. Therefore, the UHF method is generally believed to be sufficiently effective for GIS monitoring. However, in practical application, the authors find that for some micro-crack discharge in GIS insulator, the UHF method has low sensitivity. To fully study the characteristics of the micro-crack discharge in the GIS insulator, an experiment is conducted in this study using an actual post insulator with a micro-crack defect. The current signal based on IEC 60270 standard and the radio-frequency electromagnetic signal is simultaneously measured for thorough analysis. The results show that some submillimetre crack defects may occur in the GIS insulator. Its discharge is mainly presented as glow discharge, and the discharge signal frequency usually cannot reach the UHF band; thus, it cannot be effectively detected by the UHF method. This study provides complementary information to the applicability of the UHF method and inspires further study of the GIS insulator and its monitoring technology.