Brazing Interface Research Articles

Analysis of High and Low Temperature Performance of Titanium Zirconium Molybdenum Alloy and High Temperature Alloy Brazed Joint

Abstract Using niobium as the intermediate layer and gold nickel (Au82-Ni) filler metal, TZM alloy and high-temperature alloy GH3128 were brazed. The brazed specimens were subjected to 400 cycles of high and low temperature cycling tests at temperatures ranging from 650 °C ∼ 680 °C (high temperature) to -196 °C (low temperature) for 10 minutes seperately. Then the microstructure variation before and after the experiment were observed and the shear strength of the specimens were tested at room temperature for 50 cycles of 400 high and low temperature testing.. The results show that the microstructure of the transition zone at the brazing interface after brazing is uniform and dense, with good wettability with the substrate and no defects such as cracks. The solder and substrate undergo diffusion reactions, and the molybdenum alloy, niobium, and niobium, high-temperature alloy had each form diffusion layers, formed intermetallic compounds on the brazing surface. After high and low temperature cycling, cracks exist in the braze seam between molybdenum alloy and niobium alloy. The cracking mode should be thermal fatigue based on the fracture morphology and phase analysis. The reasons of interface cracking are that due to different thermal expansion coefficients, low mutual solid solubility, and the formation of a large number of different types of intermetallic compounds, Mo and Nb materials have poor brazing compatibility and lower interface strength. Under cold and hot cycling conditions, brittle intermetallic compounds are prone to form crack source areas. As the number of cycles increases, the cracks gradually expand, ultimately leading to product leakage. In addition, the shear strength of brazed joints shows a decreasing trend with the increase of high and low temperature cycles in 400 high and low temperature tests.

Design method of immiscible dissimilar welding (Mg/Fe) based on CALPHAD and thermodynamic modelling

Joining dissimilar metals is a major challenge in joining technology; the weldability of immiscible systems is especially challenging. In this study, a design methodology for dissimilar welding is suggested. The Miedema model and Toop model are developed to calculate the thermodynamics of quaternary alloy systems (Mg-Fe-Al-Cu). Finite element modelling (FEM) of temperature fields and the calculation of phase diagrams (CALPHAD) are combined to provide prerequisite information for modelling. As a test subject, laser welded lap configuration joints of AZ31B magnesium alloy and DP590 steel with a copper coating were put into the design scheme. The interfacial elemental diffusion and formation of intermetallics (IMCs) along the interface during the welding process are predicted. This simulation design scheme predicts the interfacial reaction kinetics and identifies whether the intermediate element works or not. The effects of the Cu coating thickness on the weld constitution, interfacial microstructures and mechanical properties were studied. Cu coating promotes the weld formation fostering the metallurgical reaction of the fusion zone (FZ) with the steel brazing interface. The mechanism of interfacial reactions during the welding-brazing process has been clarified. The Vickers hardness distribution across the interface shows that the Cu-IMCs are ductile.

Multi-scale modeling for prediction of mechanical performance in brazed GH99 thin-walled structure

Superalloy thin-walled structures are achieved mainly by brazing, but the deformation process of brazed joints is non-uniform, making it a challenging research task. This paper records a thorough investigation of the effect of brazing parameters on the microstructure of joints and its mechanical properties, which mainly inquires into the deformation and fracture mechanisms in the shearing process of GH99/BNi-5a/GH99 joints. The macroscopic-microscopic deformation mechanism of the brazing interface during shearing was studied by Crystal Plasticity (CP) and Molecular Dynamics (MD) on the basis of the optimal brazing parameters. The experimental results show that the brazing interface is mainly formed by (Ni, Cr, Co) (s, s) and possesses a shear strength of approximately 546 MPa. The shearing fracture of the brazed joint occurs along the brazing seam, displaying the characteristics of intergranular fracture. MD simulations show that dislocations disassociate and transform into fine twinning with increased strain. CP simulated the shear deformation process of the brazed joint. The multiscale simulation results are consistent with the experimental results. The mechanical properties of thin-walled materials for brazing are predicted using MD and CP methods.

Comparative study on induction brazing of diamond with rare earth Nd-doped crystalline and amorphous Ni-based filler alloy

This essay aims to comparatively study the microscopic morphology and grinding properties of brazed diamonds with amorphous and crystalline filler alloy in the case of rare-earth Nd-doped modified Ni-based filler alloy. The results show that at the same content of Nd, Cr7C3 is mainly generated at the brazing interface of crystalline samples. In contrast, Cr27C6 is mainly generated at the brazing interface of amorphous samples. Amorphous solder material achieves a robust chemical metallurgical union, producing a dense and homogeneous carbide layer. The bonding strength between amorphous solder material and diamond is further enhanced. The addition of rare earth element Nd contributes greatly to the forming ability of amorphous filler alloy. Nd atoms in the amorphous solder material readily bond with Ni atoms, reducing the chemical corrosion of Ni atoms on diamonds and resulting in a lower degree of graphitization. When the amount of Nd added is 1.0 wt%, the morphology of amorphous filler alloy brazing diamond is more complete than the effect of the crystalline state, the degree of thermal damage is lower, and the surface of amorphous filler alloy brazing is smoother. Frictional wear experiments show that the amorphous filler alloy holds diamond better than the crystalline filler alloy, and the diamond specimens prepared with the amorphous filler alloy demonstrate a significantly superior grinding performance in comparison to the diamond specimens prepared with the crystalline filler alloy.

Numerical simulation of arc-droplet-weld pool behaviors during the external magnetic field-assisted MIG welding-brazing of aluminum to steel

The alternative longitudinal external magnetic field (LEMF) was verified to be effective to enhance the spreading and wetting capacity of the molten aluminum metal in metal inert gas (MIG) welding-brazing of aluminum to steel. This study proposed a three-dimensional arc plasma-molten aluminum-solid steel coupled model of LEMF-assisted MIG welding-brazing of aluminum to steel. The effect of LEMF on the arc plasma, metal transfer, weld pool behavior and temperature evolution at the brazing interface was analyzed. It was found that the alternative LEMF caused the periodical swinging of the arc plasma along the weld width direction and increased the velocity of the arc plasma under the undetached filler metal. The droplet velocity was decreased due to the deflection of the arc plasma force and the additional electromagnetic force. The periodical inclination of the droplet and arc plasma increased the lateral flow velocity of the molten aluminum metal so the spreading ability of the liquid aluminum on the surface of steel was improved. The heating area at the brazing interface between the molten aluminum and solid steel was expanded to improve the wetting of the molten metal. Besides, the peak temperature at the brazing interface decreased, which may suppress the growth of the intermetallic compound.

Dissimilar CMT joining of aluminum to Ti–Ni–Hf shape memory alloy with Al–Si filler

The joining of aluminum alloy and Ti–Ni–Hf shape memory dissimilar metals was realized by cold metal transfer (CMT) welding-brazing with an Al-based filler for the first time. The relationship between heat input, microstructures, and joint strength was studied. The joint consisted of three regions: the Al/SMA brazing interface, weld metal zone and Al-weld metal zone. The interfacial intermetallic compound (IMC) with thin strip or needle-like morphology was identified to be TiAl3. An inhomogeneous morphology of the IMC was observed from top to bottom along the brazing interface. The Ti–Ni–Hf SMA adjacent to the interface still presented reversible martensitic transformation. Moreover, the phase transition temperature increased slightly with the increasing of distance from the interface due to the variation in the Ti + Hf/Ni ratio. This meant that the functional properties of Ti–Ni–Hf SMA were not significantly affected by welding. With increasing heat input, the thickness of the IMC increased, and the joint strength decreased. The maximum tensile strength reached 122 MPa when the heat input was 553.6 J/mm. The fracture originated from the interface between the IMC and Ti–Ni–Hf and then propagated along the interface.

Quality Evaluation System of Monolayer Brazed Diamond Tools: A Brief Review

In this article, the studies undertaken on brazed diamond tools were reviewed. The influences of the brazing alloys with different active elements on the brazing quality of brazed diamond tools are emphatically discussed. The differences in the micromorphology, friction and wear properties, and mechanical properties of brazed diamonds caused by three different brazing alloys are described in detail. The quality evaluation of brazed diamond tools is discussed from several aspects, such as the difference in microstructure of the diamond/brazing alloy interface, the friction and wear of brazed diamond tools, and the strength and residual stress of the brazing interface. Finally, relevant open questions related to the brazed diamond tools’ performance are outlined, and the future has been prospected.

Interface strength investigations of 304 stainless steel/T2 red copper T-type brazed joint based on cohesive zone model

Gas wave refrigerators are a type of refrigeration equipment with broad application prospects. The oscillating tube, its core component, was manufactured by brazing to improve production efficiency. To study the brazing interface strength, a small 304 stainless steel/T2 red copper T-type brazed joint specimen was designed. The tensile process of the brazed joint was simulated using ABAQUS software based on the bilinear cohesive zone model (CZM), and the results were compared with the experimental tensile results. Damage critical stress and critical fracture energy of = 40MPa and = 35 mJ mm−2, respectively, were obtained. A VUMAT subroutine was used to obtain the fatigue life of the specimen, and the errors with the experiment were 1.8% and 5.6%, respectively. It was proved that the CZM can simulate the tensile and fatigue loading processes of T-type brazed joints. The microstructure of the fatigue fracture of the specimen was analyzed using scanning electron microscopy. In addition, the effects of cyclic displacement and base metal thickness on the interface fatigue damage process were simulated and analyzed. The results showed that with an increase in cyclic displacement, the crack initiation life decreased and the crack growth rate increased; the interface damage, the crack length, and the fatigue load increased with the increase in base metal thickness.

Microstructures and Mechanical Properties of V-Modified Ti-Zr-Cu-Ni Filler Metals

TA2 titanium alloy was brazed with Ti-Zr-Cu-Ni-V filler metals developed in a laboratory. The melting properties, the microstructures, phase compositions of filler metals and wettability, erosion properties, tensile properties of the brazed joint were studied in detail. The results show that with the increase of V content, the solidus-liquidus temperature of Ti-Zr-Cu-Ni-V filler metals increased, but the temperature difference basically remained unchanged, trace V element had a limited influence on the melting temperature range of Ti-Zr-Cu-Ni filler metals. The microstructure of Ti-Zr-Cu-Ni-1.5V filler metal was composed of Ti, Zr matrix, (Zr, Cu) solid solution and crystal phase. With the addition of V content, these phases containing V such as Ni3VZr2, NiV3, Ni2V in the molten filler metals increased. V was more inclined to combine with Ni to slow down the diffusion of Ni to titanium matrix. The wettability of filler metal with trace (≤0.5 wt.%) V to TA2 titanium alloy became worse, the wettability improved significantly with continuous increase of V content. The thickness of embrittlement layer and intergranular infiltration region decreased significantly by adding V. With the increase of V content, V could regulate the brazing interface reaction, more strengthened phases generated, which resulted the significant increase of the strength (302.72 MPa) and plasticity index (16.3%) of the brazed joint with Ti-Zr-Cu-Ni-1.5V filler metal.

Improvements in Brazed-Joint Properties of Silicon Nitride and Titanium Alloys Using Laser-Induced Microscale Rice Leaf Structures.

Si3N4 ceramics with a microscale rice leaf structure (MRLS) and titanium alloy were connected via brazing, and the influence of the surface microstructure on the ceramic connection was analyzed. MRLS fabrication is an efficient and high-degree-of-freedom method that can be used to change a material’s surface morphology and wettability. The MRLS was obtained at a laser power of 110 W, with line spacings of 100 and 50 μm. The laser-treated surface included nanoparticles and micro particles, exhibiting a coral-like structure after agglomeration. When the MRLS was used to braze the titanium alloy, no defects were observed at the brazing interface, and the formation was excellent. Throughout the brazed joint, the MRLS remained intact and formed a strong metallurgical bond with the brazing filler metal. A finite element analysis was performed to study the cross-sectional morphology after joint fracture; from the load-time curve, it was found that the MRLS on the surface not only helped improve the mechanical occlusion and brazing area at the interface, but also helped generate compressive stress on the Si3N4 side. Crack propagation was hindered, thereby increasing the joint strength.

Bonding Performance of Ag-Cu Brazing Solders and Half-Heusler Alloys for High-Performance Thermoelectric Generators.

Due to the uncertainty of the brazing solder composition and its unknown effect on the long-term stability of the interface, the brazing interface connection process for half-Heusler (hH) thermoelectric (TE) devices is still partially concealed and incomplete. In this work, we selected different types of Ag-Cu-based brazing solders with different Ag and Cu contents to assemble hH TE devices, observed the microstructure of the interface contact, and analyzed its formation mechanism. It is found that when the Cu element in the brazing solder is high, it tends to form an intermetallic compound (IMC) layer at the interface, which threatens the life of the device. On the contrary, when the content of the Ag element is high, the formation of the IMC layer will be avoided. Then, the long-term stability of the interface brazed by Ag72Cu28 with high Ag content was verified: the interface connection showed good contact resistivity stability and mechanical reliability; the fabricated uni-couple TE module achieved a maximum output power of 0.28 W and a maximum conversion efficiency of 7.34% at a temperature difference of 538 K. This work summarizes the selection principle of Cu-Ag-based brazing solder when assembling hH TE modules and verifies the long-term stability of the brazed connection interface. The experiment results can provide a reference for the actual fabrication of hH TE devices.

Energy absorption and deformation behavior of multilayer aluminum foam structures

In this study, the energy absorption properties as well as the macroscopic and microscopic deformation behaviors of aluminum foam multilayer structures during quasi-static compression were investigated. The compression data of four types of aluminum foam structures were compared. The comparison revealed that, under quasi-static compression, the uniform-density core layer and the addition of interlayer plates were beneficial for improving the buffer and energy absorption capacity of the structures. The digital image correlation detection method was used to simulate the macroscopic deformation process of the four types of structures, and the strain field changes of the aluminum foam structure at special points of the stress–strain curve were accurately and intuitively determined. In the cell unit, the core layer deformation mainly included bending, rotation, shear, and tension. In addition, several cracks appeared in the brazing interface between the solder and the aluminum plate. An analysis revealed that the cracks were mainly caused by Al2O3 during brazing and stress concentration.

Interfacial behaviors and joint properties of the dual beam laser fusion brazing Ti6Al4V/AA7075 dissimilar metals

The AA7075 aluminum alloy with Ti6Al4V titanium alloy in lap configuration was successfully joined with laser fusion brazing method without filler wire. The effects of laser fusion brazing parameters, including defocus distance and laser power, on the joint appearance, interfacial microstructure and mechanical properties of the joints were explored. The results indicated that a good joint appearance could be obtained with variation of defocus distances. The adjustable range of laser power was expanded with the increase of defocus distance, from the range of 1600-1800 W with the laser spot diameter of 1.0 mm (defocus distance of +10 mm) to 2600 W–3400 W with the laser spot diameter of 2.7 mm (defocus distance of +20 mm). It was observed that the wettability of molten aluminum alloy on titanium alloy was improved with the increase of laser power, the wetting length was increased from 1.76 mm to 3.62 mm and the contact angle was decreased from 32.8° to 21.6° upon increasing the total laser power from 2400 W to 3000 W with the defocus distance of +15 mm. There was a continuous 0.7 ± 0.2 μm thick TiAl3 IMC (intermetallic compound) layer at the brazing interface with the defocus distance of +15 mm and laser power of 3000 W. The tensile strength and fracture location of the joints were mainly dependent on the spreadability and IMC thickness along the interface. Poor spreadability and too thick IMC thickness at the inner part of interface will result in fracture along the Al/Ti interface and lower strength. The best mechanical properties of the joints with the fracture load of 3621 N on average could be obtained with the defocus distance of +20 mm and laser power of 3400 W.

Microstructure and Performance of Graphite/Copper Joints by Brazing with Different Interfacial Structures

Graphite/copper joints are prepared by brazing with Cu‐50TiH2 filler. The influence of the interfacial structure on the microstructure and mechanical properties of graphite/copper joints is investigated. Straight and zigzag interfacial configurations are designed. The microstructure and compositions on the brazing interface are observed and analyzed, and the shear strength of the joints is evaluated. The interfacial morphologies show a good metallurgical combination with no apparent defects. The interfacial transition layer mainly consists of a Cu‐based solid solution, Ti‐Cu intermetallic compound, and small amounts of TiC near the graphite substrate. The widths of the transition layer are ≈25–50 and 490 μm, respectively, for straight and zigzag interfacial configurations. There is a high hardness region that corresponds to the transition layer close to the graphite matrix. The shear strength of the joint with a zigzag structure interface can reach 17.9 MPa, which increases by 2.75 times compared to that of the straight interface. The zigzag structure between the graphite and the transition layer effectively improves the joint strength due to the increases in the bonding area and deflection of the fracture path.

Fabrication technology and shear failure behaviours of elastic–porous sandwich structure with entangled metallic wire mesh

Elastic–porous sandwich structure with entangled metallic wire mesh (EMWM) is of particular interest, and is a complex and novel rigid–flexible heterogeneous material. This study introduced the fabrication technology and explored the shear failure behaviours of elastic–porous sandwich structures. The elastic–porous sandwich structure with different configurations such as the side structures, the core relative density and the thickness ratio of core/face-sheet on the failure behaviours were analysed by experimental shear tests. The experimental results demonstrated that the failure mode of the elastic–porous sandwich structure could be divided into four stages, that is linear, gradual-soft deformation, damage deformation, and stable damage failure. The different side structures were presented in two non-forming directions of the EMWM, which had the similar failure behaviours but different shear resistance deformations in the shear experiment. With the increase in relative density of EMWM, the capability of resisting shear deformation of the elastic–porous sandwich structure improved. However, the effect of increase in the core/face-sheet thickness ratio on the shear resistance deformation of elastic–porous sandwich structures showed opposite change compared with the increase of the core in relative density. The microstructures and morphologies revealed that the metallurgical bond of the brazing interface was formed, and vacuum brazing could greatly improve the interfacial bonding strength between the core and face sheet.

Dissimilar joining of stainless steel and aluminum using twin-wire CMT

The twin-wire CMT with Al-Si filler was used as weld/brazing process for dissimilar joining of stainless steel and aluminum. It is shown that this approach can ensure a satisfactory performance of the joint and the dissimilar joint exhibits typical characteristics of common known steel/aluminum weld brazing joints. Intermetallic compounds (IMCs) were detected next to the steel as a layer of Fe2Al5, as a layer of Fe3Al2Si4 adjacent to the aluminum side and as a scattered phase of Fe4Al13 in between. The total thickness of the IMCs was determined with 2–4 μm. The maximum tensile strength of the weld joints without reinforcement was up to 96 MPa and cross tensile test specimens fractured at the brazing interface at about 35% of the strength of the aluminum. An increase of the wire feeding rate and decrease of the welding speed thereby outperform beneficial in respect to wetting characteristics. However, excessive heat input (e.g., wire feeding rate larger than 7.5 m/min) causes a reduction of the mechanical properties. A groove gap about 1 mm ensures furthermore a good back appearance.

Study on laser/DP-MIG hybrid welding-brazing of aluminum to Al-Si coated boron steel

The aluminum-steel hybrid assemblies would simultaneously reach the engineering aim to reduce weight and improve fuel efficiency. However, it is of great challenge to join aluminum to steel due to the great difference in thermal properties and the formation of IMC. In this work, a better joint between aluminum and Al-Si coated boron steel was successfully achieved using laser/DP-MIG hybrid welding-brazing. The examinations of welding appearance, macrostructure, interface microstructure, and tensile tests were carried out. The laser/DP-MIG hybrid welding-brazing could simultaneously strengthen metallurgic bonding and wettability compared to conventional MIG joint. The plasma characteristics of laser/DP-MIG hybrid source contributes to suppress the formation and growth of IMC. Three phases and its formation mechanism were demonstrated in detail: τ 5 -Fe 2 Al 8 Si, θ-Fe(Al,Si) 3 , and η-Fe 2 (Al,Si) 5 . The average joint strength of laser/DP-MIG was 271.8 N/mm whereas that of conventional MIG was 138.4 N/mm. The substantial adhesion area at the brazing interface and the brittle IMC is the two main factors in determining the tensile strength.

Influence of laser power on interface characteristics and cracking behavior during laser remanufacturing of nodular cast iron

Nodular cast iron shows poor weldability due to obvious crack tendency caused by chilled structure in interface region during welding and cladding process. However, chilled structure could be eliminated by controlling interface heat input during laser cladding process. In this paper, brazing interface characteristic with no chilled structure could be obtained by controlling the heat input of the interface, and the results showed that the brazing interface illustrated higher strength compared with the chilled structure interface. The results illustrated that the tensile strength of specimens with brazing and intermittent chilled structure characteristic could reach 564 MPa. However, tensile strength of specimens with continuous chilled structure characteristic was lower than 353 MPa. Cracks formed in the interface zone and extended to the ledeburite region. FEM method with the help of ANSYS software was adopted to determine the thermal cycles of the interface region during the cladding process, and the mechanism of the interface behavior was studied.

Promoting the bonding strength and abrasion resistance of brazed diamond using Cu–Sn–Ti composite alloys reinforced with tungsten carbide

Abstract Diamond brazing is widely used in manufacturing wear–resistant tools. However, designing Cu–based filler metals with good welding characteristics and excellent mechanical properties remains a challenging task. In this work, diamond particles were connected to Q460 steel by using Cu–Sn–Ti composite fillers reinforced with different contents of micron–scale tungsten carbide (WC) particles. The microstructure of the brazing interface was analyzed via scanning electron microscopy and energy dispersive spectroscopy. The phase constitution of the brazed seam was characterized via X–ray diffraction. The effects of adding reinforcement on the mechanical properties of the vacuum brazed diamond samples were comprehensively analyzed and discussed. Results showed that the connection between diamond particles was effectively promoted by the addition of 15 wt% WC particles to the Cu–Sn–Ti fillers. The diamond and steel matrix were closely connected because of the formation of TiC and Cu Ti compounds. Samples with 15 wt% WC had a higher shearing strength and a lower abrasion loss than samples with different WC contents. Morphological examination of the wear surface showed that the interface reaction between WC and Cu–based filler alloys was tightly connected. Reinforcement with WC effectively improved the bonding strength and wear resistance of the samples. • The WC reinforced particles were added into Cu-Sn-Ti filler alloys to promote the strength and hardness. • The excessive wetting reaction was inhibited, and the exposure height of diamond particles was increased. • The effective grinding area was increased with the WC particles adding into fillers. • The shearing strength of the samples was significantly increased due to the WC reinforced Cu-Sn-Ti filler metals. • The coefficient of friction and grinding obstacle were lower, and the grinding performance was significantly improved.

Effects of a post-weld heat treatment on the microstructure and mechanical properties of dual-spot laser welded-brazed Ti/Al butt joints

Abstract The influence of a post-weld heat treatment (PWHT), which included a solution treatment and an artificial aging treatment, on the microstructure and mechanical properties of laser welded-brazed Ti/Al joints with Al-12Si filler was investigated. The thickness of the intermetallic compound (IMC) layer at the brazing interface increased with increasing solution treatment time at 530 °C. Si atoms diffused from the weld to the IMC layer during solution treatment, forming a Si-poor region adjacent to the brazing interface. The phases in the IMC changed from Ti(Al,Si)3, nanograined Ti7Al5Si12, and Ti5Si3 in the welded-brazed sample to Ti7Al5Si12 with a high stacking fault density in the solution-treated sample. The net-shaped Al-Si eutectic microstructure in the fusion zone was affected by the PWHT. The size of the Si particles in the fusion zone increased with increasing solution treatment time, and the artificial aging treatment further coarsened the Si particles. The softening of the heat-affected zone (HAZ) in the Al base metal was eliminated by the PWHT. The tensile strength of the Ti/Al joint increased from 177 to 260 MPa. This result of this study indicate that the mechanical properties of Ti/Al welded-brazed joints can be improved by a PWHT.