Search Results (10)

The solidified state after the melting of the forming layer in the laser powder bed fusion (LPBF) directly reflects the final forming quality. Compared with the powder layer and the melt pool, it is easier to recognize and remove the defects of contour parts in time by monitoring and processing the solidified region after the melting of the forming layer. To explore the application of a solidified region image in defect contour detection of the forming layer, an improved image segmentation model based on TranUNet is designed to extract the image features of the solidified region as process data, on which basis this paper analyzes the similarities and differences between forming process data and CT scanning results data. Addressing the characteristics of large data volume and significant feature scale variation in the solidified region image obtained during the LPBF process, an SA-TransUNet semantic segmentation model integrating SE attention mechanism and ASPP multi-scale feature extraction module is developed to achieve high-precision solidified region image segmentation, with an $IoU$ and a dice coefficient index up to 94.24% and 97.02%, respectively. By extracting the solidified region image of the LPBF forming layer through this model and calculating the geometric feature values of its contour, a comparative analysis is conducted with the corresponding contour geometric feature values of the formed part CT scan image, which verifies the feasibility of the solidified region image extraction method proposed in this paper for contour defect detection. Full article

Fe-Ni-based nanocrystalline coatings with unique magnetic properties are widely used as soft magnetic materials and usually act as the core component in electronic devices. Nanocrystallized particles and thin films have become a popular contemporary research direction. Electrical explosion, characterized by an ultrafast atomization and quenching rate (dT/dt ~ 10⁹–10¹¹ K/s) for the material, is a unique approach for the rapid “single-step” synthesis of nanomaterials and coatings. In this study, experiments were carried out with intertwined wire under a directional spraying device in atmospheric Ar ambience. Two load systems of Fe-Ni and Fe-Ni-Co were considered in this work. Electrical parameters and high-speed camera images were obtained to reveal the physical mechanism and dynamic process of explosive spraying. The morphologic and crystallographic results were characterized by SEM and XRD. The magnetic properties were measured via VSM equipment, and the parameters of saturation magnetization M_s, residual magnetization M_r, and coercivity H_c were emphasized in the hysteresis loop pattern. The experimental results indicate that a dense coating was prepared with extremely low porosity, and the morphology of the coating surface shows different regions characterized by solidified chunks and loose particles. XRD patterns showed that crystalline structures were discrepant under two load systems with different Ni weight proportions. Magnetic measurements gave a thin and narrow hysteresis loop, which represents loops with good soft magnetic properties. Quantitatively, coercivity H_c decreased from 59.3 to 52.6 and from 121.0 to 49.9 for the coatings not containing and containing Co under parallel and perpendicular fields, respectively. Full article

Glacier surges have been increasingly reported from the mountain and high-latitude cryosphere. They represent active glaciological processes that affect the evolution of natural landscapes, and they possibly lead to catastrophic consequences, such as ice collapse, which threatens the downstream communities. Identifying and monitoring surge-type glaciers has been challenging due to the irregularity of the behavior and limitations on the spatiotemporal coverage of remote-sensing observations. With a focus on the Karakoram region, with concentrated surge-type glaciers, we present a new method to efficiently detect glacier-surging activities by integrating the high temporal resolution of MODIS imagery and the long-term archived medium spatial resolution of Landsat imagery. This method first detects the location and initial time of glacier surges by trend analysis (trend and breakpoint) from MODIS data, which is implemented by the Breaks for Additive Seasonal and Trend (BFAST) tool. The initial location and time information is then validated with the detailed surging features, such as the terminus-position changes from Landsat, and the thickness-change patterns from surface-elevation-change maps. Our method identified 74 surging events during 2000–2020 in the Karakoram, including three tributary-glacier surges, and seven newly detected surge-type glaciers. The surge-type glaciers tend to have longer lengths and smaller mean slopes compared with nonsurge-type glaciers. A comparison with previous studies demonstrated the method efficiency for detecting the surging of large-scale and mesoscale glaciers, with limitations on small and narrow glaciers due to the spatial-resolution limitation of MODIS images. For the 38 surge-type nondebris-covered glaciers, we provide details of the surging, which depict the high variability (heavy-tailed distribution) in the surging parameters in the region, and the concentration of the surge initiation during 2008–2010 and 2013–2015. The updated glacier-surging information solidifies the basis for a further investigation of the surging processes at polythermal glaciers, and for an improved assessment of the glacier-mass balance and monitoring of glacier hazards. Full article

Increasing welding speed can promote the productivity of laser welding. However, humping defects often occur, which limits the application of this strategy. The existing explanations for the humping formation remain vague, and mitigation and suppression methods are limited. In this research, high-speed imaging experiments and numerical simulation of the high-speed laser welding process are performed. Through careful examination, the humping phenomenon is explained. At high welding speed, the high-speed melt flow caused by recoil pressure is hindered by the solidified region in the melt pool, leading to the occurrence of a swelling. The swelling then grows, forming a valley in front of the swelling under the effect of surface tension. The solidification of the valley results in the occurrence of a second swelling. This process repeats and humping defect forms. Marangoni force and viscous force also have influence on this process. In addition, it is found that adding a Tungsten Inert Gas arc behind the laser beam can effectively suppress the humping. Full article

Novel β-solidifying TiAl alloys have great potential for engineering applications in the aerospace and automotive industries. The introduction of the β₀ phase will inevitably affect crack propagation. However, the related mechanism is unclear. In this study, the crack propagation behavior of different β₀-containing microstructures was systematically investigated by three-point bending tests. The results show that the coarse γ/α₂ lamellar microstructure exhibits better fracture toughness than the fine-grain microstructure because large numbers of γ/α₂ lamellar boundaries can effectively hinder crack propagation. The propagation direction depends largely on the orientation of the γ/α₂ lamellae. When the angle between the crack propagation direction and the γ/α₂ lamellar boundary is small, the crack tends to propagate along γ/α₂ lamellae. When the angle is close to 90°, the crack generally propagates by the trans-lamellar mode. Moreover, the crack tends to traverse across the fine β₀/γ duplex region due to the low resistance of fine grains in the crack propagation. The transgranular and intergranular modes are the main fracture mechanisms in the microstructure of the fine β₀/γ grains. Some shear ligaments can also be identified in the lamellar microstructure and these can consume propagation energy. The enlarged image shows that the crack propagation direction can be changed by the β₀ phase, owing to its high hardness. The crack tends to stop at the β₀ phase region. Full article

Laser metal deposition (LMD) has demonstrated its ability to produce complex parts and to adjust material composition within a single workpiece. It is also a suitable additive manufacturing (AM) technology for building up dissimilar metals directly. However, brittle intermetallic compounds (IMCs) are formed at the interface of the dissimilar metals fabricated by LMD. Such brittle phases often lead to material failure due to thermal expansion coefficient mismatch, thermal stress, etc. In this work, we studied a Fe-Ti system with two brittle phases, such as FeTi and Fe₂Ti, as a model system. Fe was grown on top of Ti at various process parameters. The morphologies and microstructures were characterized by optical microscopy (OM) and scanning electron microscopy (SEM). No cracks along the interface between pure Ti and bottom of the solidified melt pool were observed in the cross-sectional images. Chemical composition in the fabricated parts was measured by Energy-dispersive X-ray spectroscopy (EDS). Electron backscatter diffraction (EBSD) was performed in addition to EDS to identify the crystalline phases. The Vickers hardness test was conducted in areas with different phases. The chemical composition in the melt pool region was found to be a determining factor for the occurrence of major cracks. Full article

Volcanic-aeolian interactions and processes have played a vital role in landscape evolution on Mars. Martian lava fields and associated caves have extensive geomorphological, astrobiological, and in-situ resource utilization (ISRU) implications for future Mars missions which might be focused on subsurface exploration. Although several possible cave “skylights” of tens to >100 m diameter have been spotted in lava fields of Mars, there is a possibility of prevalence of meter-scale features which are an order of magnitude smaller and difficult to identify but could have vital significance from the scientific and future exploration perspectives. The Icelandic volcanic-aeolian environment and fissure volcanoes can serve as analogs to study lava flow-related small caves such as surface tubes, inflationary caves, liftup caves, and conduits. In the present work, we have tried to explore the usability of unmanned aerial vehicle (UAV)-derived images for characterizing a solidified lava flow and designing a sequential methodology to identify small caves in the lava flow. In the mapped area of ~0.33 km², we were able to identify 81 small cave openings, five lava flow morphologies, and five small cave types using 2 cm/pixel high-resolution images. The results display the usefulness of UAV imaging for such analogous research, and also highlight the possibility of the widespread presence of similar small cave openings in Martian lava fields. Such small openings can facilitate optimal air circulation within the caves while sheltering the insides from physical weathering and harmful radiations. Using the available best resolution remote sensing images, we extend the analogy through the contextual and geomorphological analysis of several possible pit craters in the Tharsis region of Mars, in a region of extremely vesicular and fragile lava crust with pahoehoe-type morphology. We report two possible pit craters in this region, with diameters as small as ~20 m. The possibility that such small cave openings can lead to vast subterranean hollow spaces on Mars cannot be ruled out considering its low gravity. Full article

Quantitative understanding of the interactions of ultrasonic waves with liquid and solidifying metals is essential for developing optimal processing strategies for ultrasound processing of metal alloys in the solidification processes. In this research, we used the synchrotron X-ray high-speed imaging facility at Beamline I12 of the Diamond Light Source, UK to study the dynamics of ultrasonic bubbles in a liquid Sn-30wt%Cu alloy. A new method based on the X-ray attenuation for a white X-ray beam was developed to extract quantitative information about the bubble clouds in the chaotic and quasi-static cavitation regions. Statistical analyses were made on the bubble size distribution, and velocity distribution. Such rich statistical data provide more quantitative information about the characteristics of ultrasonic bubble clouds and cavitation in opaque, high-temperature liquid metals. Full article

Understanding the liquid phases and solidification behaviors of multicomponent alloy systems becomes difficult as modern engineering alloys grow more complex, especially with the discovery of high-entropy alloys (HEAs) in 2004. Information about their liquid state behavior is scarce, and potentially quite complex due to the presence of perhaps five or more elements in equimolar ratios. These alloys are showing promise as high strength materials, many composed of solid-solution phases containing equiatomic CoCrCu, which itself does not form a ternary solid solution. Instead, this compound solidifies into highly phase separated regions, and the liquid phase separation that occurs in the alloy also leads to phase separation in systems in which Co, Cr, and Cu are present. The present study demonstrates that in-situ neutron imaging of the liquid phase separation in CoCrCu can be observed. The neutron imaging of the solidification process may resolve questions about phase separation that occurs in these alloys and those that contain Cu. These results show that neutron imaging can be utilized as a characterization technique for solidification research with the potential for imaging the liquid phases of more complex alloys, such as the HEAs which have very little published data about their liquid phases. This imaging technique could potentially allow for observation of immiscible liquid phases becoming miscible at specific temperatures, which cannot be observed with ex-situ analysis of solidified structures. Full article

Sintering is a complex industrial process that applies heat to fine particles of iron ore and other materials to produce sinter, a solidified porous material used in blast furnaces. The sintering process needs to be carefully adjusted, so that the combustion zone reaches the bottom of the material just before the discharge end. This is known as the burnthrough point. Many different parameters need to be finely tuned, including the speed and the quantities of the materials mixed. However, in order to achieve good results, sintering control requires precise feedback to adjust these parameters. This work presents a sensor to monitor the sintering burn-through point based on infrared thermography. The proposed procedure is based on the acquisition of infrared images at the end of the sintering process. At this position, infrared images contain the cross-section temperatures of the mixture. The objective of this work is to process this information to extract relevant features about the sintering process. The proposed procedure is based on four steps: key frame detection, region of interest detection, segmentation and feature extraction. The results indicate that the proposed procedure is very robust and reliable, providing features that can be used effectively to control the sintering process. Full article