Search Results (119)

Traditionally, repairing coated substrates requires completely removing damaged, wear-resistant layers before recoating. This process leads to high costs, extended downtime, and material waste. Flexible brazing tapes, which are composed of alloy powder and an organic binder, offer an alternative to full coating removal for targeted repairs. Despite this, the process of vacuum brazing these tapes may lead to the formation of defects, including pores caused by trapped gases or residual binder, which compromise coating durability and corrosion resistance. This study focuses on the utilization of laser remelting as a method for post-processing nickel- and iron-based mixed alloy brazing tapes, with the aim of improving the integrity of the coating. Surface quality was assessed via microscopy and microhardness testing by systematically varying laser power, scanning speed, and hatch distance. Among the parameters studied, the most suitable laser parameter combination was found to be 350 W laser power, 250 mm/s scanning speed, and a hatch distance of 0.02 mm. These parameters yielded crack- and pore-free coatings with a remelting depth of 160.3 ± 17.2 µm and a microhardness of 701 ± 23 HV1, which is an 85% increase over as-brazed samples. Wear testing revealed a reduced coefficient of friction, and electrochemical corrosion tests showed lower corrosion current density and enhanced repassivation behavior in remelted coatings. These improvements demonstrate that laser remelting significantly enhances the microstructure, hardness, wear resistance, and corrosion performance of brazed coatings, providing an effective method for localized repair while minimizing material consumption and processing duration. Full article

Four compositions of rapidly quenched ribbon brazing alloys based on Ag–Cu–Ti (Ag–26.5Cu–1.5Ti, Ag–25Cu–5Ti) and Ag–Cu–Zr (Ag–26.5Cu–1.5Zr, Ag–25Cu–5Zr) systems were produced. Initial ingots were synthesized by arc melting. Rapidly solidified ribbons, 50–100 μm thick, were then fabricated from homogenized ingots using a “Crystall-702” facility. A comparative analysis of the microstructure and phase composition of both the ingots and ribbons was conducted using scanning electron microscopy and X-ray diffraction. The analysis revealed the presence of Cu₄Ti and CuTi intermetallic compounds in the Ag–Cu–Ti alloys, and AgCu₄Zr and Zr₂Cu in the Ag–Cu–Zr alloys. Rapid quenching was found to produce metastable structures and significantly refine the intermetallic phases. Microhardness measurements of the ingot and ribbon states demonstrated a substantial influence of the processing route on the mechanical properties. The tensile strength of the ingots was also evaluated. The wetting angles of the rapidly quenched alloy melts on 99% Al₂O₃ (alumina) ceramic substrates under vacuum were determined. All produced ribbons, except for the Ag–26.5Cu–1.5Zr composition, demonstrated adequate wettability. Thus, these materials are considered promising for further research into heat-resistant metal–ceramic joints. Full article

The liquid oxygen subcooler is a key unit for the deep cooling, storage, and transportation of liquid oxygen. Its frequent start–stop operation under liquid nitrogen bath conditions introduces potential risks to service reliability. This study employs a thermo-structural sequential coupling approach to evaluate the stress behavior of ABS components in a flat plate-fin heat exchanger during the pre-cooling, heat-exchange, and recovery stages. Based on the maximum shear stress (Tresca) criterion, the evolution of principal stresses in the brazed layer under liquid nitrogen bath conditions was analyzed, and a conservative assessment of the material’s fatigue behavior was conducted. The results indicate that the equivalent stress is governed by the third principal stress, originating from the thermal compression effect induced by low-temperature constraint shrinkage. During the heat exchange phase (2700 s), the inlet equivalent stress reached 93.49 MPa, which is below the 258 MPa limit, falling within Region 1. Local stress concentration is primarily driven by thermal loading, with brazing layer thickness, curvature radius, and liquid oxygen pressure serving as key control variables. Under a safety factor of 1.15 (107 MPa), fatigue testing exceeding 1.5 million cycles has confirmed the static safety and operational reliability of the ABS. Full article

This study employed data-driven machine learning models to analyze the effects of filler material composition and other process parameters on mechanical properties during the crack repair of nickel-based superalloys such as K417G using wide-gap brazing technology. First, a linear regression model was used to analyze the influence of independent variables (filler material composition and other process parameters) on the dependent variables (tensile strength and elongation). The regression results indicated that temperature and filler composition significantly affected tensile strength and elongation. Subsequently, a TabNet machine learning model was applied to simulate the relationship between parameters such as composition and mechanical properties. The experimental results showed that when four parameters, namely, the filler composition, temperature, holding time, and pressure, were used as input features, the deviation between the actual and predicted values of elongation was minimal, with a value of only 1.5650. Full article

Aluminum–based brazing alloys have been developed for joining 7072 high–strength aluminum alloys. However, challenges related to their high melting points and joint softening still require further exploration. This study employs a combination of first–principles calculations and experimental techniques to examine the microstructure and mechanical properties of 7072 aluminum alloy joints brazed with (Ni, Y)–modified Al–Si–Cu–Zn filler alloys. Through the virtual crystal approximation (VCA) method, it was observed that the Al–10Si–10Cu–5Zn–xNi–yY (x = 0, 1.0, 2.0, 3.0, y = 0.2, 0.4, 0.6) filler alloy exhibits excellent mechanical stability, combining both high strength and reasonable ductility. Seven brazed joint samples with varying Ni and Y contents were fabricated using melting brazing and analyzed. The findings showed that Ni reduces the liquidus temperature of the filler, narrowing the melting range. This facilitates the conversion of the brittle Al₂Cu phase into a more ductile Al₂(Cu,Ni) phase, thus enhancing joint strength. Y acts as a heterogeneous nucleation site, promoting local undercooling, increasing the nucleation rate, and refining the microstructure. When the Ni content was 2.0 wt.% and the Y content was 0.4 wt.%, the tensile strength of the brazed joint reached a peak value of 295.1 MPa. Computational predictions align with the experimental results, confirming that first–principles calculations are a reliable method for predicting the properties of aluminum alloy brazing materials. Full article

This work investigates the creep damage behavior and life prediction of Bi-based brazing alloys and their corresponding joints under intermittent over-temperature conditions, and proposes an integrated real-time monitoring and analytical framework. Temperature–time histories of structural components are acquired using both fixed and mobile infrared thermography systems to quantify thermal fluctuations. These data are subsequently coupled with a materials database and an enhanced Kachanov–Rabotnov creep damage constitutive model to simulate the evolution of thermally induced stresses and the accumulation of damage. Structural parameters, including weld seam thickness and porosity, are incorporated to perform sensitivity analyses. Experimental findings reveal a pronounced decline in the yield strength of the Bi-based brazing alloy with increasing temperature, identifying this degradation as the principal driver of creep failure. Fractographic observations show intergranular rupture characteristics during creep, in distinct contrast to the transgranular fracture mechanisms observed under tensile loading. Model predictions exhibit excellent concordance with experimental data and faithfully capture the life evolution across varying thermal–mechanical conditions. The results demonstrate that the proposed system enables real-time assessment of the health state, residual life, and failure risk of critical components. Moreover, it provides a robust theoretical foundation and practical guidance for operational safety management and maintenance decision-making in large enclosed containment structures, including those employed in nuclear power systems. Full article

In this study, the joining of Cu/Al tubes was achieved using the magnetic pulse-assisted semi-solid brazing (MPASSB) technique. A coupled finite element method–smoothed particle hydrodynamics (FEM-SPH) model was established to analyze the influence mechanism of solid–liquid interface interaction on pore formation during the brazing forming process. The results indicate that the MPASSB technique can produce Cu/Al tube joints with excellent metallurgical bonding and performance at 390 °C, and no brittle Cu/Al intermetallic compounds (IMCs) are formed in the joints. Additionally, a stronger solid–liquid interface interaction and a higher surface roughness of the tubes lead to easier peeling of the copper matrix from the interface, thereby promoting pore formation. Mechanical property tests show that the shear strength of the joints prepared by this method can reach 63.3 MPa, and the fracture occurs in the brazing seam area adjacent to the copper–side interface. The MPASSB technique is expected to provide a feasible technical approach for the high-quality joining of dissimilar Cu/Al materials. Full article

Glass, as an amorphous material with excellent optical transparency and chemical stability, plays an irreplaceable role in modern engineering and technology fields such as semiconductor manufacturing and micro-electro-mechanical systems (MEMS). For example, borosilicate glass, with a coefficient of thermal expansion (CTE) that is close to having good thermal shock resistance and chemical stability, can be applied to MEMS packaging and aerospace fields. SiO₂ glass exhibits excellent thermal stability, extremely low optical absorption, and high light transmittance, while also possessing strong chemical stability and extremely low dielectric loss. It is widely used in semiconductors, photolithography, and micro-optical devices. However, the stress sensitivity of traditional mechanical joints and the poor weather resistance of adhesive bonding make conventional methods unsuitable for glass joining. Welding technology, with its advantages of high joint strength, structural integrity, and scalability for mass production, has emerged as a key approach for precision glass joining. In the field of glass welding, technologies such as glass brazing, ultrasonic welding, anodic bonding, and laser welding are being widely studied and applied. With the advancement of laser technology, laser welding has emerged as a key solution to overcoming the bottlenecks of conventional processes. This paper, along with the application cases for these technologies, includes an in-depth study of common issues in glass welding, such as residual stress management and interface compatibility design, as well as prospects for the future development of glass welding technology. Full article

In order to enhance the heat dissipation of a chip, this work investigates the enhancement of the thermal homogenization effect of a ceramic substrate with a high-thermal-conductivity graphene material to improve the interfacial heat transfer performance. AgCuTi-activated brazing material is used to connect the graphene film/AlN. The mechanism of the influence of brazing temperatures on the microstructure and thermal conductivity of joints is discussed. The thermal conductivity of the graphene/AlN double layer composite brazed at 890 °C for 10 min holding time was the highest at 482.3 W m⁻¹ K⁻¹. This study provides a new solution for the application of AlN ceramics in high-heat-flow scenarios. Full article

This paper presents a study on optimising self-brazing powder mixtures for powder metallurgy diamond tools, specifically focusing on wire saws used in cutting natural stone. The research aimed to understand the relationship between the chemical composition of powder mixtures and the hardness of the sintered matrix. The experimental process involved the use of various commercially available powders, including carbonyl iron, carbonyl nickel, atomised bronze, atomised copper, and ferrophosphorus. The samples made of different powder mixtures were compacted and sintered and then characterised by dimensional change, density, porosity, and hardness. The obtained results were statistically analysed using an analysis of variance (ANOVA) tool to create linear regression models that relate the material properties to their chemical composition. The investigated materials exhibited excellent sintering behaviour and very low porosity, which are beneficial for diamond retention. Very good sinterability of powder mixtures can be achieved by tin bronze addition, which provides a sufficient content of the liquid phase and promotes the shrinkage during sintering. Statistical analysis revealed that hardness was primarily affected by phosphorous content, with nickel having a lesser but still significant impact. The statistical model can predict the hardness of the matrix based on its chemical composition. This model, with a determination coefficient of approximately 80%, can be valuable for developing new metal matrices for diamond-impregnated tools, particularly for wire saw beads production. Full article

K417G superalloy is widely applied in gas turbine components such as blades, vanes, and nozzles. In this work, the oxidation behavior and mechanism of K417G alloy prepared by wide-gap brazing were investigated in air at 800, 900, 1000, and 1100 °C. Microstructures of the bonded joints differ in the wide-gap braze region (WGBR) and base metal (BM). The surface and cross-sectional morphology, composition, and structure of specimens were analyzed by XRD, SEM, and EDS after oxidation tests. The experimental data demonstrate that the WGBR (wide-gap brazed region) exhibits markedly superior oxidation resistance compared to the BM (base material) under elevated-temperature conditions exceeding 1000 °C. This performance disparity is quantitatively validated by oxidation kinetics analysis, where the weight gain curve of the WGBR demonstrates parabolic oxidation kinetics, as evidenced by its significantly lower parabolic rate constant relative to the BM. The oxide layers of the BM and WGBR are similar after oxidation at high temperatures of 800–900 °C, and they consist of an outermost layer of NiO, a middle mixed layer of Cr₂O₃, and an innermost layer of dendritic Al₂O₃. However, when the temperature is between 1000 and 1100 °C, the NiO on the surface of the BM spalls of due to thermal expansion coefficient mismatch in coarse-grained regions, resulting in oxidation mainly divided into outer layer Cr₂O₃ and inner layer Al₂O₃ and TiO₂. Under high-temperature oxidation conditions (1000–1100 °C), a structural transition occurs in the oxide scale of the BM, with the underlying mechanism attributable to grain-coarsening-induced oxide scale destabilization. Specifically, the coarse-grained structure of the BM (characteristic grain size exceeding 50 μm) is exhibited. Therefore, the WGBR demonstrates outstanding oxidation resistance, as evidenced by the formation of a continuous Al₂O₃ scale with parabolic rate constants of about 1.38 × 10⁻³ mg²·cm⁻⁴·min⁻¹ at 1100 °C. Full article

SiC matrix composites are widely used in high-temperature structural components of aircraft engines and nuclear reactor materials because of their excellent properties such as their high modulus, high strength, corrosion resistance, and high-temperature resistance. However, the bonding of SiCf/SiC composites poses significant challenges in practical engineering applications, primarily due to residual stresses, anisotropy in composite properties, and the demanding conditions required for high-performance joints. This work reviews various bonding technologies for SiC ceramics and SiC matrix composites. These include solid-state diffusion bonding, NITE phase bonding, direct bonding without filling materials, MAX phase bonding, glass ceramic bonding, polymer precursor bonding, metal brazing bonding, and Si-C reaction bonding. Key results, such as the highest bending strength of 439 MPa achieved with Si-C reaction bonding, are compared alongside the microstructural characteristics of different joints. Additionally, critical factors for successful bonding, such as physical mismatch and metallurgical incompatibility, are discussed in detail. Future research directions are proposed, emphasizing the optimization of bonding techniques and evaluation of joint performance in harsh environments. This review provides valuable insights into advancing bonding technologies for SiC composites in aerospace and nuclear applications. Full article

This study attempts to use fly ash as the brazing filler additive to increase the sustainable use of coal-fired power plant by-product materials. The experimental results show that adding 5 wt% fly ash into the Ag paste filler contributes to the interfacial reactions in heterogeneous reactive air brazing (RAB) of the ZrO₂ and Crofer alloy. The Ag-rich phase dominates the brazed zone. The interfacial reaction layers contain oxidation of the Cu-Ti coating layer, Crofer alloy, and the Si/Al-rich oxides from the fly ash particles. The 5% fly ash RAB joint maintained airtightness for 280 h under 2 psig helium at room temperature. When the test temperature was raised to 600 °C for 24 h, the pressure of the joint assembly still did not drop. When the fly ash addition was increased to 10 wt%, the joint assembly was no longer leak-free at room temperature. Many visible voids and cracks exist in the brazed zone and at the ZrO₂/braze and braze/Crofer interfaces. A high volume fraction of the fly ash particles results in many brittle Si/Al-rich oxides in the joint after RAB, and the fracture of these oxides significantly deteriorates the airtightness of the joint. This study shows the feasibility and potential of introducing 5 wt% fly ash particles to the Ag-rich paste filler during the RAB of ZrO₂ and Crofer for airtight applications. Full article

Metal inert gas (MIG) brazing was used to join galvanized thin sheets with thicknesses in the range of 0.8 to 2 mm in a lap joint configuration using CuAl₈ wire as filler. The process was used to manufacture built-up cold-formed steel beams composed of corrugated steel webs and flanges made from thin-walled cold-formed steel lipped channel profiles. The effect of heat input and sheet thickness on joint properties, such as macro- and microstructure, wettability, and mechanical characteristics such as microhardness and tensile strength were investigated. The bead geometry was assessed by studying the wettability of the filler material. The microstructure was investigated by digital and scanning electron microscopy, and the composition in the heat-affected zone (HAZ), interface, and bead was determined by energy dispersive spectroscopy. Formation of Fe–Al intermetallics was observed in the bead at the bead–base material interface. Some pores were noticed that formed due to the evaporation of the zinc coating. The bead shape and mechanical properties were found to be the best when 1.2 and 2 mm sheets were brazed using a heat input of 121.4 J/mm. This suggests that not only the heat input but also the thickness of the sheet metal play a crucial role in the production of MIG brazed joints. Full article

This paper focuses on the mechanical performance of an aluminum alloy with uneven microstructure formed after stamping and brazing. The mechanical behavior of the stamping area is studied through the crystal plasticity finite element method (CPFEM). Firstly, the crystal plastic parameters of the material are obtained by fitting the experimental and simulated results of nanoindentation. Then, a polycrystalline tensile model is established using a Step-by-Step Packing method, with orientation distribution assigned based on EBSD results, followed by polycrystalline tensile simulations using CPFEM. The results demonstrate that CPFEM can effectively simulate the mechanical behavior of the studied aluminum alloy. Additionally, the study reveals significant orientation-dependent mechanical responses. Full article