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ABSTRACT Nickel aluminum bronze (NAB) is a complex alloy used extensively in the marine environment. Fatigue strength of NAB is reduced by welding and prior seawater corrosion. This study investigated the combined effect of corrosion and plasma welding on the fatigue behavior of NAB. Natural seawater corroded samples were used in tension‐tension cyclic loading tests to observe fatigue crack initiation, propagation, and failure. Fatigue cracks initiated from corrosion pits at the weld toe. Stress corrosion and fatigue cracks propagated along the path of β′ and κIII phases. A short crack growth model (SCGM) predicted fatigue strength using experimentally obtained material properties and corrosion pit dimensions. Model predictions were used to develop S‐N curves and were within 30% of experimental results. The SCGM produced accurate and reliable fatigue life results that could be applied by industry to aid in revalidation decision making and inspection scheduling. [ABSTRACT FROM AUTHOR]

The inherent instability of laser welding, particularly keyhole instability, poses significant challenges in industrial applications, leading to defects such as porosities that compromise weld quality. Various forces act on the keyhole and molten pool during laser welding, influencing process stability. These forces are categorized into those promoting keyhole opening and penetration (e.g., recoil pressure) and those promoting keyhole collapse (e.g., surface tension, Darcy's damping forces), increasing instability and defect likelihood. This paper provides a comprehensive instability analysis to uncover key factors affecting keyhole and process instability, presenting future avenues for improving laser welding stability. Using a novel numerical method for simulating laser spot welding on aluminum with COMSOL Multiphysics 5.6, we investigated the effect of laser pulse shaping on keyhole and process instability. Our analysis focused on keyhole morphology, fluid flow behaviour, and force analysis. The results indicated that the curvature effect, Marangoni effect, and Darcy's damping force are primary contributors to instability, with the curvature effect and Darcy's damping force being the most dominant. Additionally, erratic and high-velocity magnitudes induce intense fluid flow behaviour, exacerbating keyhole instability. Moreover, single/quadruple peak triangular and variant rectangular ramp-down pulse shapes produced the least instability, while multi-pulse rectangular shapes exhibited intense instability. It was found that combining triangular/rectangular pulse shapes can reduce force and keyhole instability by smoothing spontaneous force spikes, resulting in a more stabilized welding process. Controlling fluid flow and abrupt force changes with appropriate pulse shaping is key to defect-free welded products. [ABSTRACT FROM AUTHOR]

The thin-walled part of ER2209 duplex stainless steel was prepared by plasma arc welding on the surface of Q235 substrate. The microstructure, mechanical properties, and corrosion resistance of the thin-walled part in different layers were investigated. The results show that the microstructure consisted of ferrite and various morphologies of austenite, including grain boundary austenite, Widmanstätten austenite, and partially transformed austenite. The austenite content gradually increased from 42% in the 05th layer to 58.5% in the 30th layer. The microhardness decreased from 293 HV in the 05th layer to 248 HV in the 30th layer and ultimate tensile strength decreased from 887 MPa in the 05th layer to 720 MPa in the 30th layer, while the elongation increased from 32.9% in the 05th layer to 40.7% in the 30th layer. The tensile samples in different layers showed ductile fracture. The corrosion resistance was enhanced with an increasing number of layers. [ABSTRACT FROM AUTHOR]

The Plasma Electrolytic Oxidation (PEO) process was investigated to enhance the adhesion of AA2024-O aluminum alloy with a polyetherimide (PEI) matrix composite, using oxy-fuel welding (OFW). A Central Composite Design (CCD) statistical model was used to optimize three independent parameters in PEO: immersion time (s), duty cycle (%), and electrolyte concentration (Na2B4O7·10H2O), aiming to achieve a maximum value of shear strength of the hybrid joint (in MPa). The hybrid joint without PEO treatment presented a resistance of 2.2 MPa while the best condition presented a resistance of 9.5 MPa, resulting in a value 4× higher than the untreated material, due to the characteristics of the coating, which presented a more hydrophilic surface, allowing better mechanical interlocking with the polymer matrix and resulting in mixed-mode failure (adhesive, cohesive, and light fiber). In addition to improving adhesion, the PEO treatment provided better corrosion resistance to the alloy, forming an inert aluminum oxide (Al2O3) coating, with an improvement of approximately 99.84% compared to the untreated alloy. The statistical design covers about 77.15% of the total variability of the PEO + welding process, with independent factors influencing around 48.4% of the variability. [ABSTRACT FROM AUTHOR]

Titanium alloys are widely applied in the aerospace field owing to their exceptional properties, but coarse grains can easily form during the welding process, seriously diminishing the mechanical properties of the welded joint. To address this problem, a pulsed current was introduced to refine the grain structure of titanium alloy welds. In this study, we investigated the effect of varying the pulsed current frequency on grain refinement in titanium alloy welds and explored the mechanism of grain refinement using the "overlap welding" method. The results showed that the grain refinement improved with increasing pulse current frequency, particularly at the original β and α grain boundaries. Compared to non-pulsed welding, the original β grain boundary decreased from 305 to 158 μm, and the maximum α grain size decreased from 93.236 to 46.693 μm when the pulse frequency was 100 Hz. Moreover, dendrite fragmentation was identified as the primary mechanism of grain refinement in pulsed plasma arc welding of the Ti6Al4V alloy. The repeated heating of the molten pool by application of the pulsed current caused the dendrite tip to remelt in the pasting region, promoting dendrite fragmentation. [ABSTRACT FROM AUTHOR]

Weld surfacing is the process of applying a layer of metal to the surface of metal objects by simultaneously melting the substrate. As a result of this process, the metal content of the padding weld can be as high as several tens of percents. It is a method used to regenerate machine parts and improve the properties of the surface layer, increasing its resistance to abrasion, corrosion, erosion, and cavitation. It also supports the repair and creation of permanent protective coatings in the engineering, automotive, energy, and aerospace industries. This makes it possible to repair damaged parts instead of completely replacing them, saving time and production costs. Plasma surfacing technology is used for components that require high hardness and corrosion resistance under various environmental conditions. Plasma wire surfacing is not sufficiently presented and described in the current literature, which creates problems in determining the appropriate process parameters. The influence of variable plasma surfacing parameters on steel C45 significantly affects surfacing weld geometry, the dilution factor, and microhardness. Higher currents can increase the dilution factor, integrating more base metal into the weld pool, which may alter the chemical composition and mechanical properties of the weld. Variations in surfacing speed and heat input also affect the microhardness of the surfaced joint, with higher heat inputs potentially leading to softer welds due to slower cooling rates. Optimizing these parameters is essential to achieving desired surfacing weld characteristics and ensuring the structural integrity of C45 steel joints. This paper presents the influence of varying plasma surfacing parameters on the surfacing geometry, the dilution factor, and microhardness. The tests were carried out on a Panasonic TM-1400 GIII automated surfacing machine with CastoMag 45554S solid wire as the filler material. Flat bars of C45 steel were prepared, and then the variable parameters of the surfacing process were developed. Tests were carried out to determine the dilution factor, followed by microhardness measurements. The results showed a significant dependence of the effect of the parameters on the surfacing geometry and the dilution factor. [ABSTRACT FROM AUTHOR]

Keyhole tungsten inert gas (keyhole TIG) welding is renowned for its advanced efficiency, necessitating a real-time defect detection method that integrates deep learning and enhanced vision techniques. This study employs a multi-layer deep neural network trained on an extensive welding image dataset. Neural networks can capture complex nonlinear relationships through multi-layer transformations without manual feature selection. Conversely, the nonlinear modeling ability of support vector machines (SVM) is limited by manually selected kernel functions and parameters, resulting in poor performance for recognizing burn-through and good welds images. SVMs handle only lower-level features such as porosity and excel only in detecting simple edges and shapes. However, neural networks excel in processing deep feature maps of "molten pools" and can encode deep defects that are often confused in keyhole TIG. Applying a four-class classification task to weld pool images, the neural network adeptly distinguishes various weld states, including good welds, burn-through, partial penetration, and undercut. Experimental results demonstrate high accuracy and real-time performance. A comprehensive dataset, prepared through meticulous preprocessing and augmentation, ensures reliable results. This method provides an effective solution for quality control and defect prevention in keyhole TIG welding process. [ABSTRACT FROM AUTHOR]

This study investigates the effects of post-weld heat treatment (PWHT) on the microstructures and mechanical properties of plasma arc-welded 316 stainless steel. The experimental parameters included the solid solution temperatures of 650 °C and 1050 °C, solid solution durations of 1 h and 4 h, and quenching media of water and air. The mechanical properties were evaluated using Vickers hardness testing, tensile testing, scanning electron microscopy (SEM), and optical microscopy (OM). The highest ultimate tensile strength (UTS) of 693.93 MPa and Vickers hardness of 196.4 in the welded zone were achieved by heat-treating at 650 °C for one hour, quenching in water, and aging at 500 °C for 24 h. Heat-treating at 650 °C for one hour, followed by quenching in water and aging at 500 °C for 24 h results in larger dendritic δ grains and contains more σ phase compared to the other conditions, resulting in increased strength and hardness. Additionally, it shows wider and shallower dimple structures, which account for its reduced impact toughness. [ABSTRACT FROM AUTHOR]

This study aimed to determine the nucleation mechanism, particle shape, and strengthening behavior of (Ti, Nb) (C, N) particles in Fe-based composite coatings. In this study, an in-situ technique combined with a plasma spray welding process was proposed to obtain a coating with in-situ (Ti, Nb) (C, N) particles. Composite coatings were successfully prepared on low-alloy steel by plasma spray welding using a mixture of Fe-based, Ti and Nb powders. N gas was used to provide the N atoms. The microstructural analysis results indicated that the reinforced particles transformed from irregular dendritic into massive and spherical particles, and then into spherical and lath particles, as the atomic ratio of Ti/Nb decreased. During solidification, TiN nucleated preferentially and Ti (C, N) particles were formed sequentially. Subsequently, NbC nucleated and grew with Ti (C, N) as its core, and (Ti, Nb) (C, N) particles were formed at the end. The microhardness values of these composite coatings were 680–970 HV, whereas that of low-alloy steel was 174 HV. The wear resistance of the composite coatings increased as the Ti/Nb atomic ratio decreased. The composite coating had the highest average microhardness and the best wear resistance when Ti/Nb = 1:3. Its average microhardness was five times more than that of the low-alloy steel. In addition, the mass loss of the composite coating was 0.4 mg, which is only one-sixth that of the low-alloy steel (2.4 mg). The main reason for this was the in-situ formation of (Ti, Nb) (C, N) particles, which were evenly distributed in the composite coatings. • The nucleation mechanism, particle shape, and strengthening behavior of the (Ti, Nb) (C, N) particles were investigated. • The problem of the uneven distribution of TiC or TiN in coatings was solved. • A reliable coating preparation method with a stable effect is provided. [ABSTRACT FROM AUTHOR]

Combining a preheating source with conventional arc welding is a promising method to study the weld quality and improvement of strength for high-strength super-alloy materials. The present research used an induction preheating source with plasma arc welding (PAW) to weld Inconel 625 thick plates. The investigation was performed at a constant induction current of 600 A, welding speed of 100 mm/min and a plasma welding current of 135 A. The induction-assisted plasma arc welding (IAPAW) demonstrated that a weld joint was possible with static induction preheating and a high plasma welding current at low welding speed. The microstructural observation showed various dendritic structures in the fusion zone (FZ). The FESEM and EDX analysis confirmed the formation of Laves phase in the interdendritic structure of the FZ. The ultimate tensile strength of the IAPAW joint reached to 658 MPa. The tensile fracture surface of the welded sample revealed a lower number of dimples, indicating the reduction of ductility. The XRD analysis was carried out at various zones and it confirmed the peak shifting towards the higher 2-theta value of the FZ.

In this paper, plasma arc welding (PAW) and plasma arc welding combined with gas tungsten arc welding (PAW + GTAW) were used to weld TC4 titanium alloy plate (thickness of 8 mm). The relationship between mechanical properties, corrosion resistance, phase composition, and microstructure of PAW welded joint (P) and PAW + GTAW welded joint (P + G) was compared. Tensile test and microhardness results show that P + G welded joints exhibit superior mechanical properties compared to P welded joints. The polarization curves and EIS results of both P and P + G samples were compared. The surface morphology of the samples was evaluated, and the potential corrosion mechanism of P and P + G samples was provided. The research results reveal that the PAW + GTAW welding has positively affected the corrosion performance of TC4 alloy welded joints. The improved corrosion resistance of welded joints is associated with a low β/α phase volume ratio, small grain size, and HAGB content. [ABSTRACT FROM AUTHOR]

Functionally graded materials (FGMs) are a new type of composite materials capable of facilitating the dependable bonding of dissimilar materials. A double‐wire plasma welding process is used to manufacture Stainless steel 316 L (SS316L)/Inconel 625 FGM. Subsequently, two thin‐walled structures with 5% gradient and non‐gradient are fabricated to investigate the morphology, microstructure, and properties in different gradients, focusing on the 67% SS316L region. In the findings, it is indicated that two depositions exhibit well‐formed structures with varying gradients and no macroscopic defects. The composition experiences an abrupt transition at the interface between depositions with a non‐gradient, whereas deposition with a 5% gradient does not exhibit this issue and demonstrates a higher effective deposition rate. The analysis of the energy dispersive spectrum indicates the presence of Nb elements at the grain boundary in the 67% SS316L region, with no observed cracks. This suggests resistance to cracking and impediment to the segregation of Nb. Additionally, the hardness and tensile strength in various regions exhibit a gradual increase with a 5% gradient of Inconel 625 content, while the tensile anisotropy is not noticeable. Consequently, the 5% gradient transition demonstrates a more favorable performance in comparison to the non‐gradient sample, resulting in the avoidance of the 75% SS316L region due to its poor performance. [ABSTRACT FROM AUTHOR]

The detection of keyhole-induced pore positions is a critical procedure for assessing laser welding quality. Considering the detection error due to pore migration and noise interference, this research proposes a regional prediction model based on the time–frequency-domain features of the laser plume. The original plume signal was separated into several signal segments to construct the morphological sequences. To suppress the mode mixing caused by environmental noise, variational modal decomposition (VMD) was utilized to process the signals. The time–frequency features extracted from the decomposed signals were acquired as the input of a backpropagation (BP) neural network to predict the pore locations. To reduce the prediction error caused by pore migration, the effect of the length of the signal segments on the prediction accuracy was investigated. The results show that the optimal signal segment length was 0.4 mm, with an accuracy of 97.77%. The 0.2 mm signal segments failed to eliminate the negative effects of pore migration. The signal segments over 0.4 mm resulted in prediction errors of small and dense pores. This work provides more guidance for optimizing the feature extraction of welding signals to improve the accuracy of welding defect identification. [ABSTRACT FROM AUTHOR]

The residual stress creates deleterious effects on joint properties of dissimilar welding due to differential thermophysical properties and mechanical constraints of dissimilar thickness. Accounting of solid-state phase transformation (SSPT) through the understanding of solidification behavior enhances the prediction accuracy of residual stress. The characterization of microstructural features improves the fundamental understanding of the residual stress evaluation. An attempt is made to comprehend the dependence of heat input on phase transformation and its effect on the generation of compressive residual stress in dissimilar welding. Three distinct heat inputs of 52, 63, and 77 J/mm are considered in micro-plasma arc welding (µ-PAW) of SS316L and SS310 with thicknesses of 800 µm and 600 µm, respectively. The measurement of residual stress is performed using the X-ray diffraction (XRD) method. The variation of δferrite from 11.2 to 7.9% is analogous to the variation of average δferrite lath size from 412 to 1040 nm, where inter-dendritic spacing varies from ~ 10 µm to ~ 20 µm. The solidification mode is identified as ferritic-austenitic (FA), which results in the formation of skeletal and lathy δferrite structures. Electron Backscatter Diffraction (EBSD) results show an increase in heat input leads to an increase in low-angle grain boundaries that results in a rise in the residual stress value. The phase fraction and residual stresses are computed employing a finite element (FE) based thermal-metallurgical-mechanical (TMM) model including the effect of SSPT. The reasonable agreement between the computed and experimental measurements with a maximum error of ~ 8.5% in weld size, ~ 7.5% in peak temperature, ~ 16% in retained δferrite, ~ 17% in residual stress, and ~ 5% in distortion demonstrates the reliability of the developed model. A lower level of heat input (52 J/mm) allows the formation of a high amount of δferrite, which generates comparatively more compressive stress as a disparity in thermal expansion coefficient α Ni ∼ 1.6 α Cr aids in the reduction of residual stress. [ABSTRACT FROM AUTHOR]

Based upon calculated data compositions of experimental aluminum alloys, which are characterized by the lowest tendency towards hot brittleness during casting, are selected. Sheets 2.5 mm thick are obtained from ingots of experimental alloys by hot rolling. It is shown that weldability of the Al–1Ca–5.5Zn–1.5Mg–0.5Mn alloy is at the level of that for serial alloy 1915. Analysis of the obtained data shows that cracking characteristics of the Al–2Ca–2.5Mg–0.4Mn alloy (alloy 2) (specimen cracking coefficient and critical deformation rate) are at a level corresponding to AMg3 alloy. The alloys studied with appropriate surface preparation are not prone to pore formation during fusion welding. Mechanical properties of joints of the alloys studied during argon-arc and plasma welding are determined. [ABSTRACT FROM AUTHOR]

Two major drawbacks of 4D-MR angiography based on superselective pseudo-continuous arterial spin labeling combined with CENTRA-keyhole and view-sharing (4D-S-PACK) are the low temporal resolution and long scanning time. We investigated the feasibility of increasing the temporal resolution and accelerating the scanning time on 4D-S-PACK by using CS-SENSE and PhyZiodynamics, a novel image-processing program that interpolates images between phases to generate new phases and reduces image noise. Seven healthy volunteers were scanned with a 3.0 T MR scanner to visualize the internal carotid artery (ICA) system. PhyZiodynamics is a novel image-processing that interpolates images between phases to generate new phases and reduces image noise, and by increasing temporal resolution using PhyZiodynamics, inflow dynamic data (reference) were acquired by changing the labeling durations (100–2000 msec, 31 phases) in 4D-S-PACK. From this set of data, we selected seven time intervals to calculate interpolated time points with up to 61 intervals using ×10 for the generation of interpolated phases with PhyZiodynamics. In the denoising process of PhyZiodynamics, we processed the none, low, medium, high noise reduction dataset images. The time intensity curve (TIC), the contrast-to-noise ratio (CNR) were evaluated. In accelerating with CS-SENSE for 4D-S-PACK, 4D-S-PACK were scanned different SENSE or CS-SENSE acceleration factors: SENSE3, CS3–6. Signal intensity (SI), CNR, were evaluated for accelerating the 4D-S-PACK. With regard to arterial vascular visualization, we evaluated the middle cerebral artery (MCA: M1–4 segments). In increasing temporal resolution, the TIC showed a similar trend between the reference dataset and the interpolated dataset. As the noise reduction weight increased, the CNR of the interpolated dataset were increased compared to that of the reference dataset. In accelerating 4D-S-PACK, the SI values of the SENSE3 dataset and CS dataset with CS3–6 were no significant differences. The image noise increased with the increase of acceleration factor, and the CNR decreased with the increase of acceleration factor. Significant differences in CNR were observed between acceleration factor of SENSE3 and CS6 for the M1–4 (P < 0.05). Visualization of small arteries (M4) became less reliable in CS5 or CS6 images. Significant differences were found for the scores of M2, M3 and M4 segments between SENSE3 and CS6. With PhyZiodynamics and CS-SENSE in 4D-S-PACK, we were able to shorten the scan time while improving the temporal resolution. • PhyZiodynamics improves temporal resolution maintaining TIC and high CNR. • By using CS-SENSES, scan time of 4D-S-PACK can be reduced by 1 min. • 4D-S-PACK with PhyZiodynamics and CS-SENSE may rival the 4D-DSA of diagnostic power. [ABSTRACT FROM AUTHOR]

The objective of this study is to investigate the formation of the structure and stress–strain state in the joints of AISI 304 stainless steel with a thickness of 2 mm and produced by welding with laser and plasma energy sources. It is established that the microhardness and parameters of the grain and subgrain structures of the welded joint material differ with respect to the dimensions of crystallites, grains, and subgrains according to the welding process. It is shown that, in terms of structure formation, including substructural features, the most favorable structures of 2 mm AISI 304 welded joints are formed by laser–plasma welding. It is predicted that the residual stressed state is less localized with the application of laser–plasma welding than laser welding, and it is characterized by a lower level of residual stresses compared to plasma welding. In all the cases, the maximal stress values are concentrated in the HAZ, and the value obtained using laser–plasma welding is in an intermediate position (431.7 MPa) between those of the laser (443 MPa) and plasma (413.7 MPa) processes. With laser–plasma and laser welding, displacements (deformations) are minimal and close to 0.2 mm. The method of electron speckle interferometry was used, and the results reveal that the error between the calculated and experimental values of equivalent stresses is no more than 6%, which is acceptable. The results of mechanical testing show that, under uniaxial tension, the strength of the welded joints made of AISI 304 steel using laser–plasma and laser welding is the highest and equal to 97% of that of the base metal. [ABSTRACT FROM AUTHOR]

The descaling roller is a significant component in steel rolling production. Under harsh service conditions, the descaling roller is subjected to the dynamic impact caused by high-pressure water erosion and a high-temperature billet descaling process for a long time. Under the harsh conditions of high temperature, strong wear, multi-cycle heat, force, flow, and multi-field strong coupling, the roller surface is prone to wear and corrosion failure, which affects the production cost and efficiency. Through plasma surfacing technology, a high-performance coating can be applied on the conventional metal surface to effectively improve its surface properties. It is important to carry out experimental research on the surface plasma surfacing of the descaling roller to prolong product life, improve product quality, and save cost. At present, the research on the 42CrMo scaler matrix plasma surfacing of nickel-based alloys with different WC contents is still lacking. In this paper, 70%NiCrBSi+30%WC powder and 40%NiCrBSi+60%WC powder were used as surfacing materials; plasma surfacing experiments were carried out on the 42CrMo matrix; and SEM, XRD, microhardness, friction and wear, and corrosion tests were carried out on the surfacing layer to evaluate the feasibility of preparing an ultra-high-hardness WC-particle-reinforced nickel-based alloy plasma surfacing layer on the descaling roller surface and to explore the WC hard phase dissolution behavior and complex secondary phase formation mechanism. The results show that γ(Fe/Ni), Fe-Ni, FeSi, Fe3C, and M7C3 are the main phases in the Ni/WC plasma surfacing layer. The diffusion and precipitation of elements occur in the molten pool, and complex secondary phases are formed in the surfacing layer. Compared with the 70%NiCrBSi+30%WC surfacing layer, the WC deposition phenomenon of the 40%NiCrBSi+60%WC surfacing layer has been significantly improved and has better hardness, wear resistance, and corrosion resistance. Based on the welding test, the correlation law between powder formulation, welding structure, and surfacing layer properties was revealed in this study, which lays a theoretical foundation for the preparation of high-performance coating on the descaling roller surface and has significant engineering application value and practical significance. [ABSTRACT FROM AUTHOR]

Numerical modelling techniques are usually employed in keyhole plasma arc welding (KPAW) process to comprehend the thermal analysis, effect of welding parameters, weld geometry and weld quality without physical experiments. The simulated results provide insights into various aspects of the process, thus reducing consumable costs and process time. Quality in KPAW mainly relies on thermal distribution during the progress of keyhole and weld pool. This review paper focuses on different heat source models and heat transfer models associated with the KPAW process, thus emphasizing the importance of compliance with keyhole generation and volumetric heat intensity distribution along the thickness of the base metal. The paper also covers the fundamental principles of heat transfer and thermo-physics involved in KPAW. [ABSTRACT FROM AUTHOR]

Austenitic stainless steels are very popular due to their high strength properties, ductility, excellent corrosion resistance and work hardening. This paper presents the test results for joining AISI 316Ti austenitic steel. The technologies used for joining were the most popular welding techniques such as TIG (welding with a non-consumable electrode in the shield of inert gases), MIG (welding with a consumable electrode in the shield of inert gases) as well as high-energy EBW welding (Electron Beam Welding) and plasma PAW (plasma welding). Microstructural examinations in the face, center and root areas of the weld revealed different contents of delta ferrite with skeletal or lathy ferrite morphology. Additionally, the presence of columnar grains at the fusion line and equiaxed grains in the center of the welds was found. Microstructural, X-ray and ferroscope tests showed the presence of different delta ferrite contents depending on the technology used. The highest content of delta ferrite was found in the TIG and PAW connectors, approximately 5%, and the lowest in the EBW connector, approximately 2%. Based on the tests carried out on the mechanical properties, it was found that the highest properties were achieved by the MIG joint (Rm, 616, Rp0.2 = 335 MPa), while the lowest were achieved by the PAW joint (Rm = 576, Rp0.2 = 315 MPa). [ABSTRACT FROM AUTHOR]

This document is a summary of a special issue of the journal "Materials" focused on the topic of surface engineering for wear, corrosion, and erosion prevention in metallic and ceramic materials. The special issue includes twelve scientific papers covering various aspects of the operational performance and properties of metallic and ceramic materials. The papers discuss topics such as the effects of peening treatments, corrosion resistance, tribological behavior, and wear improvement through microstructural modification and the deposition of wear-resistant coatings. The special issue received significant interest from authors and readers, leading to the announcement of a second volume on the same topic. The summary acknowledges the need for experimental data in surface engineering to understand the wear and performance of engineering materials. [Extracted from the article]

As an important barrier for high‐level radioactive waste transportation and deep burial disposal, the welding quality of nuclear waste container is particularly important. At present, nuclear waste container is usually manufactured by plasma arc welding. Therefore, in order to manufacture nuclear waste container parts with high quality, based on the finite element simulation software simufact welding, this paper uses a combination of numerical simulation and experimental verification to simulate the temperature field, stress field and deformation of the longitudinal weld of 316L nuclear waste container cylinder body by selecting different welding groove angles. The test results show that the groove angle of the V‐groove increases, the residual stress distribution and size increase, and the deformation increases. The stress value of the I‐shaped groove is between the V‐shaped groove angle of 30° and 45°, but the deformation is the smallest. In practical engineering applications, residual stress and deformation need to be considered comprehensive. Reasonable groove angle plays an important role in controlling residual stress and deformation after welding. [ABSTRACT FROM AUTHOR]

Combining a preheating source with conventional arc welding is a promising method to study the weld quality and improvement of strength for high-strength super-alloy materials. The present research used an induction preheating source with plasma arc welding (PAW) to weld Inconel 625 thick plates. The investigation was performed at a constant induction current of 600 A, welding speed of 100 mm/min and a plasma welding current of 135 A. The induction-assisted plasma arc welding (IAPAW) demonstrated that a weld joint was possible with static induction preheating and a high plasma welding current at low welding speed. The microstructural observation showed various dendritic structures in the fusion zone (FZ). The FESEM and EDX analysis confirmed the formation of Laves phase in the interdendritic structure of the FZ. The ultimate tensile strength of the IAPAW joint reached to 658 MPa. The tensile fracture surface of the welded sample revealed a lower number of dimples, indicating the reduction of ductility. The XRD analysis was carried out at various zones and it confirmed the peak shifting towards the higher 2-theta value of the FZ. [ABSTRACT FROM AUTHOR]

The mechanism of the pulsed hollow cathode arc welding (HCAW) process was revealed using a fully coupled model with a hollow cathode. We solved the governing equations with the Marangoni effect to study the dynamic behaviors of a molten pool with a square pulsing current (200~400 A, 900 Hz) and varying O2 content; the dynamics of the arc plasma and the weld pool in the HCAW process were investigated quantitatively. The results show that the intensity of the arc plasma was more significantly weakened by the design of the hollow cathode in HCAW than that in GTAW with a solid hollow cathode. We could obtain a stable molten pool even with a large pulsing current section (200 A–400 A) at higher frequencies. The flow dynamics of the molten pool were mainly dominated by the Marangoni effect with varying oxygen content, and we could promote penetration by increasing O2 content in HCAW. [ABSTRACT FROM AUTHOR]

The Keyhole Plasma Arc Welding (KPAW) process utilizes arc plasma highly constricted by a water-cooled cupper nozzle to produce great arc pressure for opening a keyhole in the weld pool, achieving full penetration to the thick plate. However, advanced control of welding is known to still be difficult due to the complexity of the process mechanism, in which thermal and dynamic interactions among the arc, keyhole, and weld pool are critically important. In KPAW, two large eddies are generally formed in the weld pool behind the keyhole by plasma shear force as the dominant driving force. These govern the heat transport process in the weld pool and have a strong influence on the weld pool formation process. The weld pool flow velocity is much faster than those of other welding processes such as Tungsten Inert Gas (TIG) welding and Gas Metal Arc (GMA) welding, enhancing the heat transport to lower the weld pool surface temperature. Since the strength and direction of this shear force strongly depend on the keyhole shape, it is possible to control the weld pool formation process by changing the keyhole shape by adjusting the torch design and operating parameters. If the lower eddy is relatively stronger, the heat transport to the bottom side increases and the penetration increases. However, burn-through is more likely to occur, and heat transport to the top side decreases, causing undercut. In order to realize further sophistication of KPAW, a deep theoretical understanding of the process mechanism is essential. In this article, the recent progress in studies regarding the interaction mechanism of arc, keyhole, and weld pool in KPAW is reviewed. [ABSTRACT FROM AUTHOR]

Hybrid plasma-arc welding with a consumable electrode (PAW-MIG) of sheet aluminum alloy blanks exposed to a fast-moving heat source is involved in the formation of residual stresses and strains that can lead to changes in size and shape, buckling distortion, fatigue strength reduction, and deterioration of other operational properties of the welded product. This necessitates to introduce additional arrangements for reducing welding strains, stresses, and displacements, such as rigid outfits. Finite-element analysis of residual stress-strain state parameters of PAW-MIG welded 1561 aluminum alloy butt joints 5 mm thick with two different process modes: in the free state and in the outfit followed by its removal after cooling, was performed. The PAW-MIG welding after the second alternative compared to the first one was established to reduce the total displacements by 15 times and equivalent stresses by more than 30%, it also provides a decrease in displacements on the weld axis: longitudinal by 1.5 times and buckling distortion by 16.7 times. [ABSTRACT FROM AUTHOR]

The effect of powder feed rate (PFR) on the structure, phase composition, and mechanical properties of Stellite 6 coating deposited on SS316L steel substrate by plasma welding is studied. It is shown that a high powder feed rate leads to delamination of the coating, and a low PFR leads to an extreme melting depth of the substrate due to the high thermal energy. It is shown that a cobalt-rich fcc phase is formed at low PFR, while the M23C6, M6C, MC, and M7C3 phases (M is W, Cr, Co, and Mo) are metastable. At high PFRs, a cobalt-rich hcp phase is formed in the coating structure. The cobalt-based hcp phase is more resistant to sliding wear than the other phases. The coatings deposited at higher PFRs increase the hardness and the wear resistance due to formation of an hcp cobalt phase in the structure, but the bond between the substrate and the coating is worse than when using low PFRs. Therefore, for critical components used in the petrochemical industry, Stellite 6 coatings deposited on stainless steel at lower powder feed rates are recommended. [ABSTRACT FROM AUTHOR]

The distributions of the arc pressure at the anode surface along the directions of the tungsten electrode alignment (x-axis) and that perpendicular to the x-axis (y-axis) in two-TIG welding were measured and analyzed with the aid of the numerical results. The influences of the electrode spacing, the proportion of the current through the electrodes with the same total current, the total current and the arc length on the arc pressure were investigated. The results showed that the two-TIG arc pressure is significantly lower than the single-TIG arc under the same conditions, and the distribution range is noticeably reduced. As the tungsten electrode spacing increases, the arc pressure decreases, and the direction in which the arc pressure distribution extends changes from the x-axis to the y-axis. When the currents through the two tungsten electrodes are different, the arc pressure distribution in the x-axis is not symmetrical but symmetrical in the y-axis. As the current ratio or the total current increases, the maximum arc pressure increases and the deviation of the maximum arc pressure from the central point becomes more pronounced. The arc pressure decreases as the arc length increases, and its distribution range extends more along the y-axis. [ABSTRACT FROM AUTHOR]

The effect of defects and microstructure on the mechanical properties of Ti-6Al-4V welds produced by tungsten inert gas welding; plasma arc welding; electron beam welding; and laser beam welding was studied in the present work. The mechanical properties of different weld types were evaluated with respect to micro hardness; yield strength; ultimate tensile strength; ductility; and fatigue at room temperature and at elevated temperatures (200 °C and 250 °C). Metallographic investigation was carried out to characterize the microstructures of different weld types, and fractographic investigation was conducted to relate the effect of defects on fatigue performance. Electron and laser beam welding produced welds with finer microstructure, higher tensile ductility, and better fatigue performance than tungsten inert gas welding and plasma arc welding. Large pores, and pores located close to the specimen surface, were found to be most detrimental to fatigue life. [ABSTRACT FROM AUTHOR]

Strain-hardened austenitic stainless steel (γ-SS) is extensively used in high-pressure hydrogen systems after welding. The weld may experience varying degrees of hydrogen embrittlement (HE) with different levels of pre-strain, which seriously threatens the reliability of hydrogen systems. Therefore, it is vital to research the effect of pre-strain on hydrogen-induced cracking of γ-SS welds. In this research, the impact of hydrogen on the mechanical properties of type 304 γ-SS plasma arc welding (PAW) welds with different levels of pre-strain are studied through slow strain rate tensile (SSRT) test. The pre-strain of the weld after hydrogen charging is optimized, then the causes of hydrogen-induced cracking are illustrated by microstructure analysis. The weld metal zone (WMZ) has a greater HE susceptibility than the base metal zone (BMZ). The HE susceptibility of the weld can decrease after solution-treated. The fracture of the weld with pre-strain of 5% is mainly due to dislocation and ferrite increasing the HE susceptibility. When the pre-strain is above 10%, the weld metal and the base metal have undergone a severe transformation from austenite to α′ martensite. The content of α′ martensite rises with the rising pre-strain. The HE susceptibility of the weld is greater than the base metal due to the influence of dislocations and ferrite. The brittle fracture is initiated primarily at the phase boundary. The strength of welds can be improved while keeping good HE resistance with pre-strain of 5%. [Display omitted] • The mechanical properties of the welds can be improved while keeping good resistance to hydrogen embrittlement with pre-strain of 5%. • The existence of ferrite reduces the relative elongation and relative reduction of area of the welds. • The brittle fracture of the weld is initiated primarily at the phase boundary between austenite and α′ martensite. [ABSTRACT FROM AUTHOR]

Plasma arc welding of super duplex stainless steel SAF 2507 and austenitic stainless steel 316L was carried out by using V‐grooves with different groove angles. In order to predict the temperature distribution during the welding process, the Simufact Welding finite element software was used to establish an equivalent heat source to simulate the plasma arc welding process. The equivalent heat source consists of Goldak heat source and conical heat source. In mechanical simulation, the elastoplastic behavior with isotropic hardening is realized. The numerical results are in good agreement with the experimental results. The results show that with the increase of groove angle, the equivalent stress, transverse residual stress, longitudinal residual stress and overall deformation of SAF 2507/316L dissimilar steel welded joint decrease gradually, and the overall deformation of the joint increases gradually. The groove angle has little influence on the equivalent stress, transverse residual stress and overall deformation, but has great influence on the longitudinal residual stress and Z‐direction deformation. Comprehensive analysis of the stress and deformation results under four groove angles shows that the groove angle is too large or too small, which has a great influence on the stress and deformation of the weldment. The groove angle of 60° is better for SAF 2507/316L dissimilar steel welding. [ABSTRACT FROM AUTHOR]

In the keyhole variable polarity plasma arc weldng (VPPAW) process at horizontal position, the metal driven by gravity gathered on one side of the molten pool, and the weld formation is difficult, especially for thick workpiece welding. A specially designed experiment to analyze the influence of gravity on weld formation and a novel nozzle structure with side holes was proposed to generate a novel non-axisymmetric side-compressed plasma arc and redistribute arc pressure. The arc shape and pressure distribution were studied, and the ratio of difference for arc pressure in different directions Rp was introduced to evaluate the effects of non-axisymmetric side compression for the plasma arc. The results indicate that the non-axisymmetric distributed side holes reshape the plasma arc both in the EN and EP phases. The pressure of the non-axisymmetric side-compressed plasma arc decreases relatively strongly in one direction (direction b) and relatively weakly in the other direction (direction a). Rp is significant at 1 mm to 5 mm from the arc center, with a relatively large Rp within this range. The compression effect is enhanced with an increase in welding current or plasma gas flow rate, and Rp increases from 24% to 49% as the plasma gas flow rate increases from 2 L/min to 4.5 L/min. Specially designed validation experiments confirm that the new plasma arc significantly affects the weld formation in keyhole VPPAW process. An aluminum alloy workpiece with 8 mm thickness and no groove preparation was welded by the novel plasma arc in a horizontal welding position, and the weld is well formed. [ABSTRACT FROM AUTHOR]

In this study, 6061 aluminum alloy was proposed for welding using bypass coupling double-sided arc welding (BCO-DASW) to further improve its welding quality and efficiency. To gain insight into the thermal and force regulation mechanism of the BCO-DASW of 6061 aluminum alloy, the dynamic effects of the high-temperature plasma inside the arc with various parameters were fully compared and investigated through the combined method of the physical experiment and the numerical simulation. The thermal flow field of the hybrid arc was analyzed numerically. Furthermore, its working adaptability and mechanical behaviors were studied experimentally. The results show that a single penetration of the 6 mm sheets can be achieved without visible defects when the center offset of the arcs is within 3 mm on both sides of the base metal during BCO-DASW. Through the thermal analysis, it was found that, compared with the MIG process, the introduction of the bypass arc lead to a temperature decrease at the bottom of the hybrid arc due to energy redistribution. Furthermore, through the kinetic analysis, it was found that not only could the level of arc pressure be reduced, but also the action range of the arc pressure could be regulated up to 4.6 mm. The thermal force regulation mechanism worked together to enhance the stability of the molten pool and achieves good joint strength during the BCO-DASW of 6061 aluminum alloy. This research not only has great significance in further improving the welding quality and efficiency of aluminum alloy, but also deeper understanding of the energy regulation mechanism during aluminum alloy welding. [ABSTRACT FROM AUTHOR]

An advanced plasma-MIG hybrid welding was employed for the butt-joint of titanium (Ti) alloy and aluminum (Al) alloy sheets in this study. First, the weld bead appearance and geometry of 3 mm thick Ti/Al butt-joint specimens under different hybrid welding parameters were investigated. Then, the effects of hybrid welding parameters on the mechanical properties, fracture surface, and weld bead microstructure of the specimen were researched. In addition, the fracture mechanism between weld bead geometry and failure load of specimen was further discussed. This study selected the plasma arc current, MIG welding current, and the central gas flow rate of plasma arc as the hybrid welding parameters. The results demonstrate that Ti/Al butt-joints produced at a higher MIG welding current of 110 A or a higher central gas flow rate of 0.3 L/min increase both the height of reinforcement and porosity of fusion zone. When the MIG welding current is set to 100 A and the central gas flow rate is set to 0.2 L/min, increasing the plasma arc current to 60 A improves both weld bead geometry and tensile strength. [ABSTRACT FROM AUTHOR]

Plasma arc deposition as an additive manufacturing technology has unique advantages for producing parts with complex shapes through layer-by-layer deposition. It is critical to predict and control the temperature field during the production process due to the temperature distribution and gradients determining the properties and performance of the part. Numerical simulation approaches, such as the finite element method, which provides a large amount of data for machine learning modeling, thus reducing the overhead of experimental measurements, are widely used in machine learning. In this paper, we propose a neural network combined finite element method and process prediction workflow. A one-dimensional convolutional neural network model for predicting 2D temperature distribution is developed by training the collected data on the planar temperature field of titanium–aluminum twin-wire plasma arc additive manufacturing and the finite element method. The results show that the predicted temperature mean square error is only 0.5, with less than a 20 °C error in peak temperature and a relative error below 1%. The proposed transfer learning method achieves the same training loss and is 500 iterations faster than basic training, which improves the training speed by 25%. The current study confirms the accurate performance of the ML model and the effectiveness of the optimization method. [ABSTRACT FROM AUTHOR]

This document provides a comprehensive review of advancements in material joining processes, including traditional techniques like welding and brazing, as well as modern innovations such as friction stir welding and laser welding. It discusses the challenges and limitations of each method, such as weight constraints and heat-affected zones, and suggests areas for improvement, such as optimizing process parameters and developing advanced materials. The document also emphasizes the importance of environmental sustainability in material joining processes. Additionally, there is a list of references from scientific articles covering topics such as adhesive bonding optimization, composite joint performance, and the use of artificial intelligence in predicting joint fatigue. This resource can be valuable for library patrons conducting research on adhesive bonding and welding. [Extracted from the article]

Pore is one kind of the typical defects in aluminum alloys laser welding. Porosity is an important indicator for evaluating welding quality, and porosity assessment has attracted increasing attention. This paper presents a multi-fidelity deep learning framework (MFDLF) that enables online porosity prediction without post-weld destructive inspection or radioactive detection. In the proposed approach, the maximum temperature on the bottom wall of the keyhole acquired by numerical simulation is used as the data of fidelity 1 (F1), and the coherent optical measurement technology is used to acquire the keyhole depth as the data of fidelity 2 (F2). After extracting the respective four fluctuation characteristics of the multi-fidelity data separately, a sparse auto-encoder (SAE) is used to fuse the four characteristics into an overall feature. Based on the obvious correspondence between porosity and multi-fidelity fusion features, the MFDLF is constructed with tandem two deep belief network (DBN) models, where the former DBN utilizes process parameters to predict the overall feature of F1 data (Feature 1) that is difficult to obtain in real time. Feature 1 is combined with the overall feature of F2 data (Feature 2) that can be obtained online to predict porosity through the latter DBN. The results show that the MFDLF can predict porosity with significantly higher accuracy than the models constructed using only single-fidelity data. [ABSTRACT FROM AUTHOR]

The control of phase balance has always been a tough challenge for the welding of duplex stainless steel, which heavily restricts its optimal serving performance in engineering. The microstructure development and mechanical characteristics of SAF2205 plasma arc welded joints were thoroughly examined in this paper. It was proven that the phase balance can be well controlled by plasma arc welding, and the austenite content of the welded joints was about 60%. Despite successful phase control, there was still grain coarsening and distortion; i.e., at the center of the welded zone, the gain size was about eight times that of the base metal, and the austenite was mainly in the form of grain boundary austenite and intragranular austenite, while more Widmanstatten austenites were found in the heat-affected zone. In addition, a transition region between the heat affected zone and the center exhibited columnar ferritic grains. Furthermore, the plasticity and toughness of the welded joints were significantly decreased, especially the elongation in the longitudinal direction, which is about 10% lower than that of the base metal, and transversal tensile strength remained comparable to the base metal, with only a slight reduction in longitudinal tensile strength. Lastly, the formation mechanism of microstructure and its correlation with mechanical properties were revealed. This investigation offers valuable insights into the structural integrity of duplex stainless steel welded joints in engineering applications. [ABSTRACT FROM AUTHOR]

This article discusses a study on the mechanical assessment of metal structures in dental prostheses that were repaired using laser welding and plasma welding. The study found that both methods can be used for repairs, but laser welding offers higher mechanical strength compared to plasma welding. Factors such as surface preparation, wire diameter, and the mechanical properties of the alloy used also influence the success of the repairs. The article concludes that laser welding is a viable option for repairing metal frameworks in dental prostheses, despite the samples fracturing under high mechanical loads. [Extracted from the article]

The paper introduces an innovative aerospace component production approach employing Wire Arc Additive Manufacturing (WAAM) technology to fabricate near-finished preforms from Ti6Al4V titanium. Tensile tests on WAAM Ti6Al4V workpieces demonstrated reliable mechanical properties, albeit with identified anisotropic behavior in horizontal samples, underscoring the need for optimization. This alternative manufacturing strategy addresses the challenges associated with machining forged preforms, marked by a high Buy To Fly (BTF) ratio (>10), leading to material wastage, prolonged machining durations, elevated tool expenses, and heightened waste and energy consumption. Additionally, logistical and storage costs are increased due to extended delivery timelines, exacerbated by supply issues related to the current unstable situation. The utilization of WAAM significantly mitigates initial BTF, preform costs, waste production, machining durations, and associated expenditures, while notably reducing lead times from months to mere hours. The novelty in this study lies in the application of Wire Arc Additive Manufacturing (WAAM) technology for the fabrication of titanium aircraft components. This approach includes a unique height compensation strategy and the implementation of various deposition strategies, such as single-seam, overlapping, and oscillating. [ABSTRACT FROM AUTHOR]

Additive Manufacturing (AM) is modernizing the manufacturing industry by enabling the layer-by-layer deposition process to manufacture objects in nearly any form with minimum material waste. However, components developed utilizing the AM process have dimensional constraints. To address this issue, AM-produced metal materials can be coupled with various welding processes. This article focuses on the foundations, highlighting the distinguishing features, capabilities, and challenges of welding-based AM processes by categorizing them into two major groups; arc welding-based AM like Cold Metal Transfer (CMT), Gas Metal Arc Welding (GMAW), Gas Tungsten Arc Welding (GTAW), Plasma Arc Welding (PAW), and high-energy density welding based AM like Laser Beam Welding (LBW) and Electron Beam Welding (EBW). The prior study findings of welding-based AM metal components on mechanical characteristics and microstructural characterization have been addressed. This work will aid researchers, academicians, and professional welders since it gathers vital information on welding-based AM processes. Furthermore, current research in the arena of welding-based AM and its future opportunities has been discussed. [ABSTRACT FROM AUTHOR]

The weld morphology of aluminum alloy oscillating laser welding has an important influence on the quality of welded joints. To understand the formation process of the weld morphology, the three-dimensional numerical simulation model and energy distribution model for circular shaped oscillating laser welding of 6061 aluminum alloy are developed in this paper to analyze the characteristics of weld morphology and the effect of the energy distribution on the weld width. The cross section of the weld and the energy distribution on the processing surface are obtained under the conditions of different oscillation frequencies. It is found that the left width of the weld is larger than the right width of the weld and the energy density on the left side of the weld is more concentrated than that on the right side of the weld. With the oscillation frequency increases, the weld width and peak of energy density decrease. Furthermore, the formation mechanism of the difference in weld width is revealed based on the energy distribution law of the oscillating laser welding process, which is of great significance for improving the quality of aluminum alloy oscillating laser welding. [ABSTRACT FROM AUTHOR]

Plasma arc cutting (PAC) has emerged as a versatile and efficient method for the precision cutting of various materials, including commercial-grade aluminium plates. The optimization of process parameters is crucial for achieving high-quality cuts, minimizing material wastage, and enhancing overall productivity. This study aims to systematically investigate and optimize the key process parameters in PAC of commercial-grade aluminium plates. The experimental design involves the manipulation of parameters such as arc current, gas pressure, and workpiece thickness. A Design of Experiments approach, specifically Taguchi’s orthogonal array, is employed to efficiently explore the parameter space and identify the optimal combination of settings. The response variables considered for optimization include minimum surface roughness, minimum burr height, and maximum material removal rate (MRR). Analysis of variance is performed to get the percentage influence of each process parameter on the performance characteristic. The results obtained from the optimization process are expected to provide valuable insights into enhancing the efficiency and precision of PAC for commercial-grade aluminium plates. Arc current is found to be the most significant parameter in altering the surface roughness. The thickness of the material is the most significant parameter in altering burr height. None of the parameters is found to be significant in altering the MRR from Analysis of Variance analysis. From signal-to-noise ratio analysis and average performance graph, the optimum combination of processes in altering the bur height and MRR are found as arc current at 50 amp, the gas pressure at 5.4 bar, and the thickness of the workpiece at 6 mm.