Search Results (60)

To enhance the grinding performance and service life of rail grinding wheels, a novel brazed–resin composite wheel was developed by embedding brazed CBN (cubic boron nitride) segments into a resin working layer. The brazed CBN segments were fabricated using a Cu–Sn–Ti + WC (tungsten carbide) composite filler via a cold-press forming–vacuum brazing process. Microstructural and phase analyses revealed the formation of Ti–B and Ti–N compounds at the CBN–filler interface, indicating metallurgical bonding, while the incorporation of WC reduced excessive wetting, enabling precise shape retention of the segments. Comparative laboratory and field grinding tests were conducted against conventional resin-bonded wheels. Under all tested pressures, the composite wheel exhibited lower grinding temperatures, generated predominantly strip-shaped chips with lower oxygen content, and produced fewer spherical oxide-rich chips than the resin-bonded wheel, confirming reduced thermal load. Field tests demonstrated that the composite wheel matched the resin-bonded wheel in grinding efficiency, extended service life by approximately 28.8%, and achieved smoother rail surfaces free from burn-induced blue marks. These results indicate that the brazed–resin composite grinding wheel effectively leverages the superior hardness and thermal conductivity of CBN abrasives, offering improved thermal control, wear resistance, and surface quality in rail grinding applications. Full article

Al-xSi-35Ge (x = 4, 6, 8, 10, 12, wt.%) filler metals were prepared to vacuum braze 6061 aluminum alloy. The wettability of filler metals was studied. A thermodynamics model of the Al-Si-Ge ternary alloy was established to analyze the mechanism and impact of Si in the microstructure of the brazed joint. The findings indicated that Si addition had a slight effect on the melting point of Al-xSi-35Ge filler metals. Great molten temperature region of fillers was responsible for the loss of Ge during the wetting process, making residual filler metal difficult to melt. The microstructure of the joint was characterized by a multilayer structure that was primarily composed of three zones: two transition regions (Zone I) and a filler residual region (Zone II). There was liquidation of filler metal for Al-Si-35Ge filler metals during brazing, resulting in holes and cracks in joints. Increasing the Si content in fillers could alleviate the liquidation of filler metal, owing to diminishing difference of chemical potential of Ge (μ_Ge) in fillers and 6061 substrates, hindering the diffusion of Ge from filler metal to substrates. Full article

A TC4 alloy was joined with Ti-Zr-Cu-Ni amorphous filler by vacuum brazing. The paper further explored how different brazing temperatures with a 20 min holding time, or varying holding times at a brazing temperature of 900 °C, impact the interface width, microstructure, composition distribution, microhardness, shear strength, and fracture surface of the brazed joints. The findings indicated that as the brazing temperature increased, the interface width became wider. Moreover, as the brazing temperature continued to rise, both the size of the Widmanstätten structure and the amount of the (Ti, Zr)₂(Cu, Ni) brittle phase increased continuously, leading to the joint exhibiting harder and more brittle properties. As the temperature rose from 860 °C to 900 °C, the microhardness went up from 462.8 HV_0.1 to 482.6 HV_0.1. But when the temperature continued to increase (920 °C, 940 °C), the microhardness started to decrease, until it reached 392.6 HV_0.1 at a holding time of 20 min. As the brazing temperature increased, the width of the joint interface expanded, and the shear strength continued to rise. When the brazing temperature rose to 940 °C, the shear strength increased to 223.9 MPa under a holding time of 20 min. With the prolongation of the holding time (from 10 min to 30 min), the Widmanstätten structure at the joint interface continuously grew towards the center. Additionally, the (Ti, Zr)₂(Cu, Ni) phase and eutectic structure were separated by the Widmanstätten structure. The microhardness and shear strength reached their maximum values at 900 °C, and the shear strength was measured at 137.6 MPa. Full article

Melting point depressants (MPDs) are required to lower the melting point of filler for brazing. In this study, Zr was used as the MPD, and powder filler was prepared by adjusting the Zr and Mo content referring to Thermo-Calc calculations. The prepared filler was used to braze a high-Mo Ni₃Al-based single crystal superalloy, IC21, for 1200 °C/30 min. The effects of adjusting the Zr and Mo content on the microstructure and tensile properties of the joint were investigated. The increase in Zr content promotes the formation of Ni₇Zr₂ in the joint, leading to a decrease in the tensile strength of the joint. The increase in Mo content forms diffusion barriers between the BM and filler, resulting in an enhancement in the tensile strength of the joint. However, continued increases in Mo content leads to an increase in the P-topologically close packed phase, causing a decline in the tensile strength of the joint. When the Zr content was (11.8–12.2) wt.% and the Mo content was (7.3–7.7) wt.%, the tensile strength of the joint at 980 °C reached a maximum of 550 MPa. This study provides a potential direction for the design of brazing filler composition for high-Mo Ni₃Al-based superalloys. Full article

Herein, we fabricated a low-melting-point Zr-16Ti-6Cu-8Ni-6Co eutectic filler based on a Zr-Ti-Cu-Ni filler to achieve effective joining of a Ti6Al4V (TC4) titanium alloy. The temperature at which the brittle intermetallic compound (IMC) layer in the seam completely disappeared was reduced from 920 °C to 900 °C, which broadened the temperature range of the Zr-based filler, brazing the TC4 without a brittle IMC layer. The shear strength of the Zr-16Ti-6Cu-8Ni-6Co brazed joint increased by 113% more than that of the Zr-16Ti-9Cu-11Ni brazed joint at 900 °C. The proportion of β-Ti in the seam of the Zr-16Ti-6Cu-8Ni-6Co brazed joint increased by 21.31% compared with that of the Zr-16Ti-9Cu-11Ni brazed joint. The nano-indentation results show that the elastic modulus of the β-Ti (143 GPa) in the interface is lower than that of the α-Ti (169 GPa) and (Ti,Zr)₂(Ni,Cu,Co) (203 GPa). As a result, the β-Ti is subjected to a greater strain under the same stress state compared with the α-Ti and (Ti,Zr)₂(Ni,Cu,Co), and the Zr-16Ti-6Cu-8Ni-6Co brazed joint can maintain a higher strength than the Zr-16Ti-9Cu-11Ni brazed joint under a middle–low erosion area of the TC4 base metal. This provides valuable insights into the use of high-strength, fatigue-resistant TC4 brazed joints in engineering applications. Full article

This study proposes a method to enhance the airtightness of the joint between the ZrO₂ and Crofer alloy using coating technology. With the aid of vacuum sputtering technology, a titanium–copper alloy layer with a thickness between 1.5 μm and 6 μm was first deposited on the surface of ZrO₂ and Crofer, respectively. The chemical composition of the deposited reaction layer was 70.2 Cu and 29.8 Ti in at%. Then, using silver as the base material in the reactive air brazing (RAB) process, we explore the use of this material design to improve the microstructure and reaction mechanism of the joint surface between ceramics and metal, compare the effects of different pretreatment thicknesses on the microstructure, and evaluate its effectiveness through air tightness tests. The results show that a coating of Cu-Ti alloy on the ZrO₂ substrate can significantly improve bonding between the Ag filler and ZrO₂. The Cu-Ti metallization layer on the ZrO₂ substrate is beneficial to the RAB. After the brazing process, the coated Cu-Ti layers form suitable reaction interfaces between the filler, the metal, the filler, and the ceramic. In terms of coating layer thickness, the optimized 3 μm coated Cu-Ti alloy layer is achieved from the experiment. Melting and dissolving the Cu-Ti coated layer into the ZrO₂ substrate results in a defect-free interface between the Ag-rich braze and the ZrO₂. The air tightness test result shows no leakage under 2 psig at room temperature for 28 h. The pressure condition can still be maintained even under high-temperature conditions of 600 °C for 24 h. Full article

A novel AgCuTi brazing foil with a unique microstructure was developed, which could achieve strong vacuum brazing of Ti6Al4V (TC4) and sapphire. The brazing foil was composed of Ag solid solution (Ag(s,s)), Cu solid solution (Cu(s,s)), and layered Ti-rich phases, and had a low liquidus temperature of 790 °C and a narrow melting range of 16 °C, facilitating the defect-free joining of TC4 and sapphire. The sapphire/TC4 joint fabricated by using this novel AgCuTi brazing foil exhibited an outstanding average shear strength of up to 132.2 MPa, which was the highest value ever reported. The sapphire/TC4 joint had a characteristic structure, featuring a brazing seam reinforced by TiCu particles and a thin Ti₃(Cu,Al)₃O reaction layer of about 1.3 μm. The fracture mechanism of the sapphire/TC4 joint was revealed. The crack originated at the brazing seam with TiCu particles, then propagated through the Ti₃(Cu,Al)₃O reaction layer, detached the reaction layer from the sapphire, and finally penetrated into the sapphire. This study offers valuable insights into the design of active brazing alloys and reliable metal–ceramic bonding. Full article

In order to address the issues of excessive brittle intermetallic compounds (IMC) formation in the TC4 brazed joints, two types of novel Ti-Zr-Cu-Ni-Sn amorphous braze fillers were designed. The microstructure and shear strength of the TC4/Ti-Zr-Ni-Cu-Sn/TC4 brazed joints were studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffractometer (XRD) and electronic universal materials testing machine. The results show that the optimized Ti₃₅Zr₂₅Ni₁₅Cu₂₀Sn₅ braze filler whose chemical composition is closer to the eutectic point possesses a lower melting point compared with the equiatomic Ti_23.75Zr_23.75Ni_23.75Cu_23.75Sn₅. This was beneficial to the sufficient diffusion of Cu and Ni elements with the base metal during brazing and reduces the residual (Ti,Zr)₂(Ni,Cu) content in the joint, which helps to improve the joint performance. The room-temperature and high-temperature shear strength of the TC4 brazed joints using the near eutectic component Ti₃₅Zr₂₅Ni₁₅Cu₂₀Sn₅ filler reached a maximum of 472 MPa and 389 MPa at 970 °C/10 min, which was 66% and 48% higher than that of the TC4 joints brazed with the equiatomic Ti_23.75Zr_23.75Ni_23.75Cu_23.75Sn₅ braze filler. Microstructural evolution and the corresponding mechanical response were in-depth discussed. Full article

Brazing is a joining process that involves melting a filler metal and flowing it into the joint between two closely fitting parts. While brazing is primarily used for joining metals, it can also be adapted for certain coating deposition applications. The present study investigates the microstructure and corrosion behavior and sliding wear resistance of WC (Tungsten Carbide)-CoCr-Ni reinforced Co-based composite coatings deposited onto the surface of AISI 904L stainless steel using a vacuum brazing method. The primary objective of this experimental work was to evaluate the influence of WC-based particles added to the microstructure and the properties of the brazed Co composite coating. The focus was on enhancing the sliding wear resistance of the coatings while ensuring that their corrosion resistance in chloride media was not adversely affected. The morphology and microstructure of the composite coatings were investigated using scanning electron microscopy (SEM) and phase identification by X-ray diffraction (XRD). The SEM analysis revealed in the coating the presence of intermetallic compounds and carbides, which increase the hardness of the material. The sliding wear resistance was assessed using the pin-on-disk method, and the corrosion properties were determined using electrochemical measurements. The results obtained showed that as the WC particle ratio in the Co-based composite coating increased, the mechanical properties improved, the alloy became harder, and the tribological properties were improved. The evaluation of the electrochemical tests revealed no significant alterations of the manufactured composite in comparison with the Co-based alloys. In all cases, the corrosion behavior was better compared with that of the stainless-steel substrate. Full article

To address the issues of high cost, low welding efficiency, and complex processes in vacuum brazing, we proposed a method of electromagnetic ultrasonic (EU)-assisted brazing with Al-12Si solder to join SiC ceramic and TC4 alloy. The results showed that the maximum magnetic induction strength (MIS) on the surface of the liquid solder was 0.629 T when subjected to a static and alternating magnetic field (MF). Additionally, the combined action of MF and eddy current generated a downward Lorentz force (LF) in the liquid solder, with the maximum LF in the horizontal and vertical directions being 48.91 kN m⁻³ and 60.93 kN m⁻³, respectively. Under the influence of an EU wave, the liquid solder exhibited capillary filling (CF) behavior. At 26 ms, the maximum length of CF was 12.21 mm. Full article

Sandwich structures and porous materials have been applied widely in various fields due to their excellent mechanical performance, and multifunctional composites will have a significant engineering demand in the future. Studying damped composites’ mechanical properties and failure forms has significant engineering value and significance. However, the current connecting processes for sandwich panels and porous materials must be improved. Therefore, to explore the ambiguity of the connection interface between the core material and panel in sandwich panels, as well as the mechanical properties of such structures, a sandwich panel with a metal rubber core material was prepared using vacuum brazing and cementing processes. Microscopic examinations using scanning electron microscopy and energy-dispersive spectroscopy were conducted to observe the physical bonding mechanism at the interface of the sandwich panel. The results indicate that the brazed sandwich panels exhibited a more uniform and continuous interface than the cemented sandwich panels. This work designs three-point bending compression experiments to investigate the effects of core material thickness, density, and preparation process on the bending mechanical properties of the sandwich panel. Failure modes of the sandwich panel during the experiments are analyzed. The experimental results show that the failures of the brazed sandwich panels are attributable to the bending deformation of the panel and the shear failure of the metal wire core material. The cemented sandwich panels exhibit separation failures in the area below the indenter and at both ends of the panel. The core material’s thickness and density significantly influence the bending performance of the sandwich panels. An increase in the core material’s thickness and density effectively enhances the sandwich panels’ peak load and energy absorption capacity. Full article

The manufacturing of active RF devices like klystrons is dominated by expensive and time-consuming cycles of machining and brazing. In this article, we characterize the RF properties of X-band klystron cavities and an integrated circuit manufactured with a novel additive manufacturing process. Parts are 3D printed in 316 L stainless steel with direct metal laser sintering, electroplated in copper, and brazed in one simple braze cycle. Stand-alone test cavities and integrated circuit cavities were measured throughout the manufacturing process. The un-tuned cavity frequency varies by less than 5% of the intended frequency, and Q factors reach above 1200. A tuning study was performed, and unoptimized tuning pins achieved a tuning range of 138 MHz without compromising Q. Klystron system performance was simulated with as-built cavity parameters and realistic tuning. Together, these results show promise that this process can be used to cheaply and quickly manufacture a new generation of highly integrated high power vacuum devices. Full article

Reactive Air Brazing (RAB) enables the joining of vacuum-sensitive oxide ceramics, such as Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ (BSCF), to metals in a one-step process. However, damage may form in ceramic or joint during RAB. In this work, experimental microstructure characterization, measurement, and prediction of local material properties using finite element analysis were combined to enlighten these damage mechanisms, which are currently not well understood. Micromechanical simulations were performed using representative volume elements. Cooling simulations indicate that small-sized CuO precipitations are most likely to cause crack initiation in BSCF during cooling. The ball-on-three-balls experiment with porous BSCF samples was analyzed numerically to determine the values of temperature-dependent BSCF fracture stresses. The inversely calibrated fracture stresses in the bulk BSCF phase are underestimated, and true values should be quite high, according to an extreme value analysis of pore diameters. Full article

The assessment of fatigue is a crucial concern in welded components and structures. This study investigates the fatigue properties and models for predicting fatigue crack growth in Ti-6Al-4V titanium alloy when processed by vacuum brazing with TiCuNi filler. Fatigue properties and the impact of the stress ratio were determined through constant amplitude fatigue tests. By utilizing the results obtained from variable amplitude fatigue tests, various prediction models for fatigue crack growth were examined: modifications for load interaction, residual stress, and crack closure. The results indicate that the microstructures in the brazed zone consist of numerous fine, elongated needle-like Widmanstätten structures. In terms of cycle counting methods, the rainflow method outperforms the simple-range method. In the stable crack growth rate region, fatigue crack growth rate increases with the rise in stress ratio in a manner similar to high-strength steels. The Paris model without any modification obtains good predictions. For models modified with crack closure, the Elber model yields slightly better prediction results than the Schijve model. Among fatigue crack growth prediction models, the Willenborg model with residual stress modification produces the best results. Fracture surfaces within fatigued specimens’ brazed zones exhibit ductile failure characteristics, where fatigue striations and secondary cracks were observed. Full article

In this paper, a novel 95Ag-2.5Ge-2.5Si (in wt %) filler is utilized for brazing yttria-stabilized zirconia (YSZ) electrolytes and commercial Crofer 22H interconnects for solid-oxide fuel cells’ (SOFCs) sealing application. Before brazing, surface metallization is applied on YSZ and Crofer 22H substrates to improve the wetting performance of the filler on YSZ and Crofer 22H substrates. The brazing procedure is performed at 900 °C for 10 min under a high vacuum (~10⁻⁶ torr) to prepare sandwiched YSZ/Crofer 22H brazed coupons. The metallization mentioned above can achieve reactive wetting toward YSZ ceramics. A Si/Ti-rich oxide layer and an Fe-Cr-Si alloying phase are formed at the brazed joints’ YSZ/filler and filler/Crofer 22H interfaces. After exposure to air at 750 °C for 100 h, Cu and Si contents suffer from oxidation and form CuO and SiO₂, respectively, in the brazed zone and the YSZ/filler interface of the joints. The Fe-Cr-Si alloying phase at the filler/Crofer 22H interface is preserved without apparent oxidation. The pressure-drop test results show that the brazed joints’ gas tightness does not deteriorate significantly after thermal aging, which is attributed to the good interfacial integrity of thermal-aged joints. Full article