Search Results (425)

During operation, several parts of the thermal reactor burners sustain heavy damage and need to be replaced. Different solutions for parts manufacturing are investigated: thermal spraying, Selective Laser Melting (SLM), and hardfacing by Directed Energy Deposition plasma arc (DED-arc). Based on the comparison to original material and the duration of usage, application of those three methods for replacement is studied in order to determine the most suitable one, with Additive Manufacturing (AM) being proposed for targeting the problem. Thermal-sprayed items have a zirconium-oxide-based outer layer. SLM produces a monolithic item, while with the help of DED-arc, a composite structure with a sound metallurgical bond between the base and the added material is produced. The microstructures with the interface zones are observed. Samples are machined and ground, and their friction characteristics are taken with the help of acoustic emission (AE) and Electrical Contact Resistances (ECR) sensors during scratching. As a result, overlaying of the base stainless steel by DED-arc is proposed due to the better metallurgical stability of the added mixture in a hot environment above 800 °C and its hardness characteristics. Full article

With contemporary advancements in additive manufacturing (AM), it has become possible to obtain hull structures for spacecraft made of relatively cheap materials. The possibility of substituting super-austenitic stainless steel Avesta SMO 254 X1NiCrMoCuN20-18-7 (EN 10088) for that already used in the Starship SpaceX 304 L-Modified is focused on achieving better thermal stability and durability in extreme conditions. The Directed Energy Deposition Arc (DED-Arc) method for AM has enabled the production of high-strength-to-weight ratios. The aim is to engage low-cost material with treatment optimization to provide greater corrosion resistance and high yield and tensile strength. For the DED-Arc, a filler wire was selected for the welding source, Fronius TPS 400i. A simulation via the RoboDK Robot Development Kit for the FANUC ARC Mate 100ID10L is provided. Additional shot pining/vibration treatment is proposed for the finished structure, which can be a substitute for the cold-worked initial metal. A comparison is made for stainless steel that has already been tested for space travel. Regimes for the manufacturing process are proposed, with representative samples of Avesta SMO 254 obtained and tested using microhardness measurements, microcracking detection, porosity measurements, interface zone assessment, and microstructural analysis. The DED-Arc process can be applied to large-space shell manufacturing. A comparison is made with a focus on the mechanical and corrosion advantages. For Avesta SMO 254, microhardness measurements ranged from 235 to 246 HV1 and increased after treatment. The controlled parameters provided a maximum heat input of 0.7 KJ/mm, no defects, and a fine microstructure. The successful use of stainless steel with AM increases the potential for multiple space missions. The advanced method shows high quality, allows cost savings and provides extended service life. Full article

This study addresses a critical challenge in surface engineering: developing robust nanocomposite layers on high-performance thermoplastics without inducing macroscopic thermal degradation. While cold gas dynamic spraying (CGDS) of polymers is often described in the literature as a deposition process based on purely mechanical anchoring of particles into polymer surface, our work establishes a multi-scale, hybrid physical–chemical adhesion framework. Using a coupled 3D thermoplasticity finite element model with a Mie–Grüneisen equation of state and Johnson–Cook criteria, we evaluate the supersonic impact dynamics ($V_0=1000 \mathrm{m}/\mathrm{s}$) of single-walled (5,0) CNTs impacting a PEEK substrate at oblique angles (0–20°). The core scientific lies in bridging continuum mechanics with quantum-chemical statistics. By applying Weibull weakest-link theory to a 37-bond monomer model, we demonstrate that compliant $C_{arom}-O$ ether bonds selectively absorb impact energy, covering 8.37% of their dissociation barrier. This non-uniform energy sharing yields a 0.23% monomer activation probability, generating a high free-radical density of ~1100 ${\mathrm{\mu }\mathrm{m}}^{-2}$ beneath the particle plume. This localized “chemical nano-welding” network provides exceptional chemical adhesion, while the remaining 99.77% of intact chains ensure structural rigidity, reinforced by a mechanical “self-locking” field (residual compressive stresses up to 0.9 GPa). This study provides a scientific foundation for designing functional coatings tailored for engineering, aerospace, and biomedical applications. Full article

High-temperature corrosion severely impairs the service life of boiler heating tubes and threatens the safe and economical operation of thermal power units. With diversified fuels (coal, biomass and refuse-derived fuels) and continuously elevated operating parameters (steam temperature exceeding 620 °C for ultra-supercritical units), boiler heating surfaces are exposed to increasingly complex corrosive environments. High-temperature oxidation, sulfidation, chlorination, molten salt hot corrosion and deposit-induced multi-factor coupled corrosion coexist and exacerbate each other. This paper adopts a four-dimensional analytical framework of “mechanisms–technologies–materials–evaluation” to systematically summarize relevant research progress. From the perspective of corrosion mechanisms, the evolution of understandings from single high-temperature oxidation to multi-factor coupled corrosion is reviewed. In terms of surface coating technologies, seven mainstream processes including HVOF/HVAF spraying, plasma spraying, cold spraying, laser cladding and weld overlay are compared in terms of preparation characteristics and engineering applicability. For coating materials, twelve material systems such as NiCr alloys, MCrAlY, cermets, Fe-based amorphous/nanocrystalline alloys and high-entropy alloys are evaluated for their corrosion resistance under diverse service conditions. As for monitoring and evaluation, this work introduces full-range corrosion management technologies covering electrochemical monitoring, non-destructive testing, numerical simulation and life assessment. Finally, the paper discusses the application prospects of gradient coating design, AI-assisted material screening and digital twin technology, and points out key research gaps including long-term service reliability verification of coatings and quantitative prediction models for multi-factor coupled corrosion. Full article

In this study, manual welding electrodes with varying niobium (Nb) contents (0, 0.05, and 0.1 wt%) were developed for 960 MPa grade low-alloy high-strength steel, and deposited metals were produced through multilayer multipass welding. Microstructural characterization and mechanical testing were performed using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), electron backscatter diffraction (EBSD), and a universal testing machine to investigate the influence of Nb content and elucidate the strengthening mechanisms. The results demonstrate that under identical welding conditions, multipass thermal cycles induced a primary microstructural transformation from martensite to tempered martensite in all deposited metals, which predominantly comprised tempered martensite with minor fractions of bainite and second-phase particles. Increasing Nb content led to significant grain refinement. The second-phase particles exhibited sizes of 0.158 μm, 0.176 μm, and 0.168 μm, respectively, with volume fractions of 5.69%, 5.82%, and 5.90%. Nb addition substantially enhanced hardness and strength while causing a noticeable reduction in low-temperature impact toughness, though the values remained within acceptable limits. The deposited metal containing 0.05 wt% Nb exhibited optimal comprehensive mechanical properties, with a hardness of 386.7 HV, tensile strength of 1060 MPa, yield strength of 962 MPa, and Charpy impact energies of 41.95 J and 33.17 J at −40 °C and −60 °C, respectively. Theoretical calculations revealed that the dislocation strengthening contribution in martensite increased from 526 MPa to 600 MPa with increasing Nb content, representing the dominant strengthening mechanism, while grain refinement strengthening increased from 135.5 MPa to 157.6 MPa. Full article

Wire-arc directed energy deposition (arc-DED) of maraging 250 (M250) steel is of growing interest for aerospace, tooling, and defense applications, yet systematic process characterization data remain limited. This study presents a mixed quantitative–qualitative factorial comparison of three Fronius synergic transfer modes, GMAW-CMT-Mix, GMAW-CMT-Universal, and GMAW-Pulsed-Arc, for single-bead M250 deposition across wire feed speeds of 4.45 to 8.26 m/min and travel speeds of 0.3 to 1.5 m/min. Bead geometry and process behavior are characterized using non-contact optical profilometry and destructive methods (i.e., metallographic sectioning, optical microscopy, and Vickers microhardness). The material feed rate ratio, R_wt, is introduced as a unifying process descriptor; heat input and cross-sectional area scale linearly with R_wt, while travel speed primarily governs bead height and wire feed speed primarily governs bead width. At the highest travel speed tested, GMAW-CMT-Mix and GMAW-Pulsed-Arc exhibit bead humping, rendering those conditions unsuitable, while GMAW-CMT-Universal maintains stable deposition with consistent dilution and the lowest heat input at equivalent R_wt. GMAW-CMT-Mix yielded the highest dilution and hardness. Linear regression of process responses against R_wt gives $R^2$ exceeding 0.83 for both height and width across all modes. These results establish a characterization baseline supporting future multi-layer studies. Full article

This study investigates the influence of an austenitic buffer layer on the microstructure, hardness, and abrasive wear resistance of Fe–Cr–C hardfacing applied to high-chromium white cast iron (HCWCI) hammer tips used in sugarcane shredders. Hardfacing was performed by shielded metal arc welding with two Fe–Cr–C layers deposited directly on the HCWCI substrate and with an austenitic buffer layer followed by an Fe–Cr–C hardfacing layer. Microstructural characterization was carried out using optical microscopy, scanning electron microscopy with energy-dispersive X-ray spectroscopy, while hardness profiles were determined by micro-Vickers testing. Abrasive wear behavior was evaluated using a dry sand–rubber wheel test according to ASTM G65. The non-buffered hardfacing layer exhibited a hypereutectic Fe–Cr–C microstructure consisting of coarse primary chromium carbides, resulting in high hardness values of approximately 840 HV. In contrast, the buffered sample showed an austenite-rich matrix with finer eutectic carbides and reduced hardness of around 600 HV. Abrasive wear tests of the non-buffered sample showed a lower mass loss, whereas the buffered sample exhibited a substantially higher mass loss. These results demonstrate that Fe–Cr–C hardfacing without a buffer layer provides superior wear resistance. Full article

The Charpy impact resistance of monolithic high-strength and dissimilar structured steel was studied. A gas metal arc welding process was used to fabricate the structured steel by depositing a layer of austenitic stainless steel, followed by a layer of hardfacing material over the high-strength steel plate. ANSYS LS-DYNA^TM was used to simulate pendulum–striker impacts on steel Charpy samples. A Cowper–Symonds constitutive model was employed to capture the strain rate behavior. The corresponding material constitutive model parameters were obtained from the literature for the monolithic materials; an iterative numerical optimization method was used to couple the parameters of the structured steel simulation and experimental results. Numerical simulation results showed close agreement with experimental ones. Simulation is a valuable tool for explaining the fracture mechanism in the Charpy impact test and can be used to efficiently design parts made of structured steel that will be subjected to impacts or high-speed deformations. Full article

To address the performance degradation associated with retained high-temperature δ-ferrite in welded joints of high-silicon 20Cr11W2VTaSi steel—a candidate structural material for spallation targets in Accelerator Driven Subcritical Systems—this study systematically investigates the microstructural evolution and mechanical behavior of 20 mm-thick forged joints produced via automated tungsten inert gas (TIG) welding using a 7° U-groove narrow-gap configuration. Results demonstrate that the narrow-gap process—featuring reduced filler metal deposition and low heat input—is believed to suppress macrosegregation of ferrite-stabilizing elements (e.g., Cr, Si, Mo). As a result, the δ-ferrite content in the weld metal is constrained, exhibiting a fine, dispersed, worm-like morphology embedded within a uniform matrix of tempered martensite. Microhardness mapping confirms homogeneous hardness distribution across the joint, closely matching that of the base metal, with no statistically significant localized softening zones identified. Mechanical characterization reveals an optimal balance of strength and toughness: the joint achieves a room-temperature tensile strength of 820 MPa and retains 436 MPa at 550 °C; moreover, the Charpy impact energy at the weld center reaches 171.2 J. Full article

Wire arc additive manufacturing (WAAM) has emerged as a promising technology for producing large-scale metal components due to its high deposition efficiency, low material cost, and design flexibility. However, the widespread industrial adoption of WAAM is hindered by challenges in geometric accuracy, process stability, and defect control, which are closely related to two critical aspects: trajectory planning and real-time weld seam tracking. This review provides a comprehensive and critical analysis of recent advances in both fields, with an emphasis on their interconnection rather than treating them as separate research streams. Unlike existing reviews that primarily summarize path planning algorithms or image processing techniques in isolation, this paper explicitly examines the integration challenges and synergistic potential between offline trajectory optimization and online vision-based monitoring. Key topics include adaptive path strategies for sharp corners and intersections, interlayer filling methods to mitigate heat accumulation and residual stress, as well as passive and active visual sensing technologies for molten pool characterization and defect detection. The review further identifies a persistent gap in closed-loop systems that combine real-time image feedback with dynamic path replanning. Based on the analysis of representative studies, current limitations are discussed and future research directions are proposed, including the development of digital twins, multi-modal data fusion, and reinforcement learning-based adaptive control. This review offers a distinct perspective aimed at advancing intelligent, high-precision WAAM systems for complex metal components. Full article

This study proposes a novel dynamic composite heat source combining discrete tracking and vapor heating, which can precisely capture the transient energy deposition at the keyhole wall, and further discusses the formation mechanism of weld defects by investigating keyhole evolution and melt pool flow behavior. The weld morphology and dimensions predicted by the simulation are in good agreement with the experimental data, revealing the coupled mechanism between keyhole instability and porosity formation, as well as the generation mechanism of process-type porosity mainly influenced by the keyhole dynamic characteristics and the melt pool flow field together; specifically, keyhole instability forms a vapor cavity that will generate bubbles to participate in melt pool flow if it cannot be re-fused with the keyhole, and the bubble trajectory is related to buoyancy, gravity and liquid flow in the melt pool, with larger bubbles less likely to escape due to greater liquid viscous force. In addition, this study finds that increasing weld power and weld speed helps improve keyhole stability, weaken melt pool circulation intensity and shorten bubble escape path, thereby fundamentally revealing the formation mechanism of porosity defects during electron beam welding (EBW) of aluminum alloy, providing an effective numerical tool for optimizing EBW process parameters, and proposing corresponding inhibition measures to improve weld quality. Full article

Hot extrusion tools operate under severe thermal and mechanical conditions, which significantly limit their service life. During operation, the punch and die absorb large amounts of heat from the hot billet while being subjected to high pressures and intense friction, leading to severe abrasive wear and progressive hardness reduction. In practice, the punch generally exhibits a shorter service life than the die. The present study proposes a technological solution for reconditioning worn extrusion punches using vibration-assisted welding (VAW). A wear-resistant layer was deposited by MIG welding using DUR 600 filler material, while mechanical vibrations were introduced through a vibrating welding table. The applied vibration regime consisted of a frequency of 50 Hz–108 Hz and acceleration components of a_x = 30–60 m/s² and a_z = 35–70 m/s². The experimental investigations included macroscopic analysis, hardness and microhardness measurements, microstructural observations, and SEM-EDS line scanning analysis of the dilution zone between the cladding material and the base metal. The results suggest that vibration-assisted welding may influence the microstructural characteristics, hardness distribution, and dilution behavior of the cladded layer. The vibrated specimens exhibited higher hardness values in the range of 702 to 908 HV5–10. Under the investigated conditions, the process did not require additional hardening treatment, and only a stress-relief annealing stage was applied. The proposed VAW approach appears to be a promising option for the reconditioning of hot extrusion tools; however, further investigations are required to validate its performance under industrial conditions. Full article

Duplex stainless steel (DSS) blends impressive mechanical and chemical characteristics to withstand aggressive environments. Its fabrication by Gas Metal Arc Welding-Additive Manufacturing is an emerging research topic. However, its sensitive grain structure and alloy composition are prone to deterioration by repeated thermal shocks. Whether optimal weld parameters can resolve these challenges without additional costs from special fillers, gases, or mechanisms is a valid question. In this study, how different wire feed speeds, travel speeds, and weld voltages, chosen from a set of preliminary beads, translate into wall dimensions, phase formation and distribution, morphological transformation, and elemental segregation is investigated. The unique DSS microstructures were characterised using scanning electron microscopy and energy-dispersive spectroscopy to reveal differences in microstructural evolution and ferrite-austenite (α-γ) structure. The deposited walls exhibited satisfactory geometric quality with negligible distortions. However, the height suppression was noticeable at the deposition energy (DE) of 755 J/mm. Metallographic analysis revealed low γ phase formation (<30%) at low DE (230 J/mm) and excessive γ formation (>70%) in the high DE wall (755 J/mm). The parameters WFS:TS = 15, TS = 35 cm/min, WFS = 525 cm/min, and V = 20.804 volts suppressed the elemental segregation while maintaining a suitable phase balance without post-processing. Full article

Wire arc additive manufacturing (WAAM) is an efficient, low-cost technique for fabricating large-scale metallic components and, in particular, functionally graded materials (FGMs). This review focuses on the fabrication of 316L stainless steel–Inconel 625 FGMs by arc-based WAAM processes, examining Gas Metal Arc Welding (GMAW), Gas Tungsten Arc Welding (GTAW) and Plasma Arc Welding (PAW) in terms of their microstructural outcomes, compositional control strategies, residual stress development and mechanical performance. A critical finding emerging from the reviewed literature is that direct compositional interfaces between 316L and Inconel 625 can yield superior tensile strength and ductility and lower residual stresses compared to smooth gradient strategies, owing to the formation of detrimental secondary phases such as δ-phase, Laves phase and MC carbides at intermediate iron–nickel compositions encountered only during graded builds. The potential of Submerged Arc Additive Manufacturing (SAAM) as a future high-deposition-rate alternative for large-scale FGM fabrication is also discussed. Key challenges, including dilution control, Laves phase formation, residual stress management and the corrosion characterization of the graded region, are identified, together with priority research directions for advancing the industrial adoption of arc-based FGM components. Full article

This study evaluates the mechanical performance of FDM-printed poly(lactic acid) (PLA) structures joined using a portable Friction Stir Welding (FSW) device. A non-destructive optical band method was employed to assess weld homogeneity and material flow consistency. The influence of substrate infill density (15% and 100%) and tool pin geometry (cylindrical and truncated conical) was systematically analyzed. Results indicate that substrate density is the primary determinant of joint integrity; 100% infill specimens demonstrated superior structural homogeneity and consistent intensity profiles, whereas 15% infill specimens exhibited significant intensity fluctuations and poor consolidation, even with the addition of filler material. The mechanical evaluation revealed that the use of a tool pin is essential for effective load transfer, as specimens welded without internal agitation achieved only baseline tensile strengths of approximately 4 MPa. Among the pin-driven configurations, the cylindrical geometry outperformed the truncated conical design, reaching a peak tensile stress of 8.02 ± 1.42 MPa, corresponding to a joint efficiency of 27% relative to the 100% infill base material, compared to 6.25 ± 1.43 MPa. This performance gap is attributed to the cylindrical pin’s ability to maintain higher shear rates and more uniform pressure distribution at the weld root. These findings demonstrate the feasibility of portable FSW for structural joining of additively manufactured polymers and establish critical processing parameters for the optimization of portable FSW in engineering applications. Full article