Brittle Intermetallic Compounds Research Articles

Evaluation of Microstructure and Mechanical Properties of TiAl/HI-TEMP 820/ SCM440H Materials Manufactured through Vacuum Brazing according to Process Temperature

The TiAl alloy is attracting attention as a lightweight and heat-resistant material, because of its high specific strength, excellent high-temperature formability, and fatigue strength. However, its applications are limited by its high unit price and low room temperature ductility. To overcome this issue, dissimilarly bonded materials have been extensively employed. This involves joining a brittle metal to a low-cost metal that possesses excellent plasticity, using various dissimilar bonding techniques. In this study, TiAl/HI-TEMP 820/SCM440H materials were fabricated using a vacuum brazing process under different temperature conditions. After the brazing process, the microstructure of the interfacial area revealed seven distinct layers resulting from chemical reactions between the base metals and the filler metal. These reaction layers consisted of a Ni solid solution, intermetallic compounds (Ti<sub>3</sub>Al, TiNi<sub>2</sub>Al, Ti<sub>2</sub>Ni, FeNi), and borides (CrB, TiB<sub>2</sub>, FeB). To analyze the effect of brazing temperature on the relationship between the microstructure and mechanical properties at the interface of TiAl/HI-TEMP 820/SCM440H materials, conventional uniaxial tests and nanoindentation tests were performed. The measured nanohardness exhibited a significantly large distribution for each reaction layer, with the highest hardness values observed in the intermetallic compounds and borides layers. Additionally, room temperature tensile tests confirmed that fractures initiated in the highhardness and brittle intermetallic compounds and borides layers.

Laser metal deposition of titanium on stainless steel with high powder flowrate for high interfacial strength

Direct joining of titanium and stainless steel 316 L with a strong interface is very challenging due to the formation of the brittle intermetallic compounds FeTi and Fe2Ti in the intermixing zones and to the high residual stress induced by the mismatch of the thermal expansion coefficients. In this bimetallic directed energy deposition study, firstly, deposition of Ti on stainless steel was carried out using conventional process parameter regime to understand the interfacial cracking susceptibility and then a novel high powder flowrate approach is proposed for controlling the dilution and constraining the intermetallic phases forming at the interface. The influence of high temperature substrate preheating (520 °C) on the cracking susceptibility and interface strength was also investigated. The deposited Ti samples and their interfaces with the 316 L substrate were characterized with optical microscopy, scanning electron microscopy and energy dispersive X-ray spectroscopy to investigate the geometry, microstructures and chemical compositions in relation to the cracks. The high powder flowrate deposition of Ti on stainless steel 316 L results in an extremely thin dilution region (~ 10 μm melt pool depth in the substrate) restricting the formation of the intermetallic phases and cracks. The ultimate shear strength of the interfaces of the crack free sample was measured from cuboid deposits and the highest measured strength is 381 ± 24 MPa, exceeding the weaker base material pure Ti. The high interfacial strength for high powder flowrate deposition is due to the substantial attenuation and shadowing of the laser beam by the in-flight powder stream as demonstrated by the high-speed imaging resulting in an extremely small dilution region.

Enhanced tensile strength of TiAl/Ti2AlNb diffusion bonding joint by a novel post-bonded hot deformation

Dissimilar TiAl-based alloys weld by solid-state bonding, also known as diffusion bonding (DB), usually show brittle intermetallic compounds, high interfacial stress, and poor properties. A novel post-bonded process strategy, slight deformation in the direction of stress parallel to the bonding interface, was developed in the post-bonded treatment of the TiAl/Ti2AlNb joint. The effect of post-bonded processes on the interfacial microstructure, element diffusion, fracture characteristics and mechanical properties were systematically investigated. The results showed that the post-bonded hot deformation (PBHD), compared to the traditional post-bonded heat treatment (PBHT), can effectively increase the major elements diffuse and the growth of the reaction layer, as well as promote the precipitates which distribute uniformly in the reaction layer, finally resulting in superior tensile strength. Compared with the DB samples, the ultimate tensile strength of the PBHD joint increased by 45.58%. In addition, the fracture behavior was further analyzed based on the microfracture morphology and crack propagation path. These findings will facilitate the development of advanced manufacturing processes of blisk for high-temperature light alloys.

Research on microstructure and mechanical properties of TC4/304 clad plates by asymmetric rolling with local strong stress

In order to solve the problems of complex traditional preparation process and low bonding strength of titanium/steel clad plates, TC4/304 clad plates were prepared by asymmetric rolling with local strong stress (ARLSS), the effect of rolling temperature on the interface bonding of clad plates was studied. The two-dimensional simulation model of TC4/304 clad plates rolling was established by finite element method, and its accuracy was verified by experiments. The experimental results show that the interfacial bonding strength of the clad plates increased with the increasing temperature, but when the temperature reached 950 °C, the brittle intermetallic compounds (IMCs) formed extremely fast, which greatly weakens the bonding strength. The clad plates showed the best bonding strength at 900 °C. After corrugated roll bonding (CRB) (33 % reduction ratio), the bonding strength at the peak was lower than that at the trough. After FRB (46 % reduction ratio), the interface bonding strength was slightly improved. The final peak bonding strength reached 519 MPa, and the trough bonding strength was 527 MPa. The improvement of bonding strength mainly came from the improvement of TC4 matrix strength. The finite element simulation results showed that multiple cross shear zone in the deformation zone of the CRB stage were beneficial to the bonding of dissimilar metals. While the deformation of the clad plates material in the FRB stage was consistent, which effectively avoided the cracking of the bonded area and further improved the bonding strength. Therefore, the strong non-uniform plastic deformation of ARLSS process had a significant effect on the deformation coordination of dissimilar metals and the quality improvement of clad plates.

Ultrastrong and ductile NiFeCrAlV complex-concentrated alloy via dual-morphology brittle intermetallic compound

Complex-concentrated alloys (CCAs) have received a lot of attention recently due to their exceptional balance between strength and ductility. In this work, a brittle intermetallic compound strengthening Ni46.3Fe21Cr18.5Al10V4.2 (at%) CCA has fabricated via carefully two-step thermomechanical treatment. The microstructure, phase composition, and mechanical properties of this alloy were investigated systematically. The microstructure characterization that brittle dual-morphology B2 particles are major second phases for the alloy under the two-step heat treatment. The microstructure characterization reveals that the coarse spherical B2 intermetallic compounds pinned grain boundaries and the dispersed dual-morphology B2 intermetallic compounds in the FCC matrix are key factors contributing to excellent mechanical properties. The yield strength and ultimate strength of the CCA enhanced substantially from 920 MPa and 1230 MPa in the annealed state, respectively, to 1400 MPa and 1660 MPa after aging treatment, while the uniform elongation remains above 18.5%. This work reveals the mechanical properties of the CCA can be enhanced by controlling B2 particles morphology and dispersion via suitable thermomechanical processing to meet the requirements of engineering applications.

Enhancing performance and microstructure analysis in laser welded of R60702 zirconium alloy and 304 stainless steel with TA2/ Q235 composite interlayer

Zirconium (Zr) alloy and stainless steel (SS) will form brittle intermetallic compounds (IMCs) during the welding process, which will reduce the performance and reliability of the joint. To solve this problem, the TA2/Q235 composite interlayer was added between the Zr alloy and the SS. The microstructure and mechanical properties of the joint were evaluated. The experimental results show that the formation of IMCs in Zr alloy and SS joints can be completely inhibited by laser welded with the addition of interlayer. The final mechanical properties of the joint were determined by the weld of TA2-Zr alloy, when the joint strength reaches 161.64 MPa. The fracture surface of the joint presents a brittle fracture mode. The main product of the fracture surface is α-Zr and a small amount of α-Ti and (Ti, Zr) solid solution.

Microstructure Evaluation of Magnetic Field–Assisted Dissimilar Laser Welding of NiTi to Stainless Steel

Abstract Significant attention has been directed to the need for a strong and lightweight welding technology for joining the NiTi shape memory alloys (SMAs) to stainless steel (SS). Dissimilar NiTi/SS joints suffer from the brittle and inevitable intermetallic compounds (IMCs) like TiFe, TiFe2, and FeNi that are formed during the welding process. To tackle this challenge, this study explores the use of an engineered magnetic field during the dissimilar laser welding of NiTi to SS. The presence of a magnetic field delivered a remarkable improvement in the tensile strength (over 452 MPa) of the joint, with a notable difference in the microstructure. The effect of the magnetic field on microstructure was investigated; material characterizations showed brittle IMC-free microstructure and a change in grain growth mechanism from columnar to cellular growth during the solidification. Further, fractography analysis proved a ductile failure mode at the joint.

Interfacial microstructure evolution and mechanical properties in laser welded Invar alloy/TC4 dissimilar joints

The present study examined the evolution of interfacial microstructure and its effect on the mechanical properties of Invar/TC4 dissimilar joints by laser welding. The results indicated that various intermetallic compounds (IMCs) were formed in the interface layer of the TC4 side, such as Ti2Cu, TiCu and TiNi phases, while the columnar dendrites grown epitaxially perpendicular to the fusion line were observed on the weld seam (WS). Moreover, the boundary between dendrites growing in different directions within the WS was attribute to the high thermal conductivity of the filler metal and the non-equilibrium rapid cooling facilitated by the composition gradient. Besides, excessive heat input intensified the migration of elements and phase transition behavior, leading to the formation of brittle Ti-Fe phases in the interface layer, which significantly weakened the mechanical properties of the dissimilar joints and resulted in brittle fracture characteristics. The strength of the joint exhibits a parabolic distribution with heat input. When the heat input was below 600 J/cm, the joint fractured in the interface layer of the TC4 side, with a maximum tensile strength of 298.4 MPa at 600 J/cm. However, when the heat input exceeded 600 J/cm, the formation of brittle Ti-Fe IMCs contributed to a decrease in joint strength. The investigation provides an efficient and stable method for achieving high-strength Invar/TC4 dissimilar alloy welding.

Understanding the interplay of Zn vapours and formation of intermetallic compounds during remote laser welding of Zn-coated steel to aluminium in a zero-gap lap joint configuration

Remote laser welding (RLW) of Zn-coated steel to aluminium is challenged by: (1) Zn vaporisation causing spatters and poor seam surface when welding in a zero-gap lap joint configuration; and (2) brittle intermetallic compounds (IMCs) at the weld interface, leading to cracks and poor weld integrity. This paper aims to study the impact of Zn coating during the RLW of Zn-coated steel to aluminium in a nominal zero part-to-part gap lap configuration. The combination of metallurgical and mechanical analysis with an in-process monitoring approach, using a high-speed camera, allowed the study of the interplay between Zn formation/out-gassing, molten pool dynamics and formation of IMCs. Findings revealed that the presence of a Zn coating results in an un-even connection area between steel and aluminium, with localised lack of fusion. A significant 72% joint efficiency compared to parent aluminium was achieved when Zn is removed, opposed to 65% when Zn is present.

Investigating parametric effects during TIG welding of dissimilar metals

This paper explores the optimization of Tungsten-Inert-Gas (TIG) welding process parameters for creating a hybrid structure of Aluminium 6061 and Stainless Steel 304 using a copper filler rod (ER-Cu). The Welding of these two materials has industrial relevance owing to its weight reduction capabilities and environmental benefits. However, Aluminium and Stainless-Steel have different melting points and thermal properties. Aluminium has twice coefficient of thermal expansion and six times coefficient of thermal conductance as compared to Stainless-Steel. This difference often results in residual stresses and brittle intermetallic compounds in the weld region. We have chosen the Welding Current, Welding Speed, and Gas Flow Rate as input parameters, and Ultimate Tensile Strength (UTS) and Micro-hardness as response parameters. We have employed the Response Surface Methodology (RSM) using a Box-Behnken design to evaluate the influence of input parameters on UTS and Micro-hardness. Furthermore, an Analysis of Variance (ANOVA) is conducted to determine the input parameters' significance on the response parameters. Our surface plots demonstrate that UTS improves with increased Welding Current and reduced Welding Speed. Simultaneously, Micro-hardness increases with elevated Welding Speed and decreased current, up to a specific limit. The peak value of UTS (79 MPa) was observed with a Current range of 85-90 A, Speed range of 95-100 mm/min, and Gas Flow Rate of 14.5-15 l/min. On the other hand, maximum Micro-hardness (260HV) was obtained with a Current range of 80-85 A, Speed range of 105-110 mm/min, and Gas Flow Rate of 14.5-15 l/min. This research contributes to improving the manufacturing process of hybrid structures, specifically by optimizing the advantages of both Aluminium and Stainless Steel while addressing the challenges that arise during their combination. The study's conclusions have major consequences for sectors looking to take advantage on the mutually beneficial characteristics of different metals in welding applications.

The Effect of Homogenization Heat Treatment on 316L Stainless Steel Cast Billet.

This investigation aims to analyze the effect of homogenization heat treatment at 1240 °C for 2 and 6 h on the hardness, distribution, morphology, and chemical composition of the δ-ferrite and sigma phases in 316L stainless steel cast billet. A field emission scanning electron microscope, combined with electron back-scattered diffraction, a field emission electron probe microanalyzer with a wavelength dispersive spectrometer, and a Vickers microhardness tester are applied to identify various phase evolutions in the cast billet. The morphology of the δ-ferrite and sigma phases in the austenite matrix of the 316L cast billet are strongly related to the subsequent hot and cold wire drawings. The homogenization heat treatment is expected to provide a driving force to form spheroid interdendritic δ-ferrite and to minimize the amount of the brittle sigma intermetallic compound in the austenite matrix. The homogenization heat treatment at 1240 °C effectively spheroidized all δ-ferrites into blunt ones in the cast billet. The transformation of δ-ferrite into sigma is dominated by temperature and cooling rate. The fast air cooling after homogenization between 1240 and 850 °C retards the precipitation of the sigma in the δ-ferrite. There are two δ-ferrite transformation mechanisms in this experiment. The direct transformation of the δ-ferrite into sigma is observed in the as-cast 316L stainless steel billet. In contrast, the eutectoid transformation of the δ-ferrite into the sigma and austenite dominates the 316L cast billet homogenized at 1240 °C, with a slow furnace cooling rate.

Analysis of microstructures and fractures in Ag–In transient liquid phase bonded joints

Silver (Ag) and indium (In) are increasingly investigated as transient liquid phase (TLP) bonding materials for die attachment in next generation power modules. In this study, we systemically investigated the relationship between the microstructural evolution, shear strength, and fracture behavior of Ag–In TLP bonded joints. During bonding, Ag9In4 was the primary phase formed between the solid Ag and liquid In. The Ag9In4 joints exhibited brittle fractures with an intergranular fracture mechanism. The shear strength increased as bonding time and temperature increased (from 26.9 MPa to 53.0 MPa), attributed to the improved cohesiveness of grain boundaries. As the bonding process progressed, ζ (Ag3In) formed and developed between Ag and Ag9In4 owing to the solid–solid interdiffusion. The ζ (Ag3In) joints, obtained from the conditions of 250 °C and 40 min, exhibited the highest shear strength of 82.87 MPa. Here, the ductile fracture was characterized with an intergranular fracture mechanism. This ductility was partially attributed to the relatively low hardness of ζ (Ag3In) (2.1 GPa). The high strength and ductility of ζ (Ag3In) found in this study present differ from the conventional understanding of the inherently brittle intermetallic compounds. Therefore, the study findings form the basis for enhancing the reliability of power modules.

Behaviour of aluminium/steel hybrid RSW joints under high cycle fatigue loading

The lightweight construction of automotive car bodies is the more important to reduce the fuel consumption and costs. High-strength steels and aluminium alloys are suitable for achieving these aims. Recent car bodies contain both materials, therefore necessary to make reliable joints between them. The resistance spot welding (RSW) can be used for joining of car bodies and it is applicable for aluminium/steel hybrid joints, too. High cycle fatigue (HCF) test results can be rarely found in the literature while HCF loading basically determines the lifetime of hybrid joints. 5754-H22, 6082-T6, and DP600 base materials were used for similar and hybrid RSW joints and HCF tests were performed. Number of cycles to failure values, failure modes, furthermore brittle intermetallic compound (IMC) layers were studied and analysed. In both aluminium/steel hybrid joints, the HCF test results showed better endurance limit like concerning aluminium/aluminium similar joints, but worse than steel/steel joints. For 5754-H22 alloy the endurance limit values are 648 N, 939 N, and 1285.5 N, for similar aluminium, hybrid, and similar steel joints, respectively. For 6082-T6 alloy these values are 513 N, 625.5 N, and 1285.5 N, respectively. In case of similar joints only base material fracture happens, but hybrid joint specimens show different failure modes. Base material fracture and shearing after partial base material fracture were typical failure modes in case of 5754-H22/DP600 and 6082-T6/DP600 hybrid joints, respectively. The full and partial plugging as a failure modes appeared for hybrid joints, too. The IMC layer characteristics showed opposite results in cases of hybrid joints, both the layer thicknesses of the shared and plugged joints and the thickness differences between the inner and outer parts of the joints were different.

Enhancing NaBH4 regeneration using an Al-rich alloy

Onsite hydrogen generation by sodium borohydride hydrolysis resolves hydrogen energy supply system challenges. However, the spent-NaBH4 regeneration is still a problem in the closed loop of this irreversible reaction. As the by-product is the key to the problem, NaB(OH)4 is regarded as not the boron source but the hydrogen source of NaBH4 regeneration. Therefore, in this study, inexpensive Al metal and NaB(OH)4 are ball milled under argon to regenerate NaBH4 without additional hydrogen input. However, the ball-milling reaction is hindered by the flexible Al and impact oxide layer, and the NaBH4 yield is only approximately 22 %. Therefore, a brittle intermetallic compound Mg2Al3 is reacted with NaB(OH)4 by ball milling, achieving a NaBH4 yield of over 42 %. The mechanism study shows that the brittleness of the raw material plays an important role in promoting the ball-milling reaction. This study achieves NaBH4 regeneration using only Al as the reducing agent and provides a promising method to promote the mechanochemical regeneration of NaBH4.

Microstructure evolution and mechanical properties of brazing joint for ultra-thin-walled Inconel 718 considering grain size effect and brazing temperature

The systematic investigation of the mechanical properties and microstructure evolution process of ultra-thin-walled Inconel 718 capillary brazing joints is of great significance because of the exceptionally high demands on its application. To achieve this objective, this study investigates the impact of three distinct brazing temperatures and five typical grain sizes on the brazed joints’mechanical properties and microstructure evolution process. Microstructural evolution analysis was conducted based on Electron Back Scatter Diffraction (EBSD), Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD), High-Resolution Transmission Electron Microscopy (HRTEM), and Focused Ion Beam (FIB). Besides, the mechanical properties and fracture behavior were studied based on the uniaxial tension tests and in-situ tension tests. The findings reveal that the brazing joint’s strength is higher for the fine-grain capillary than the coarse-grain one, primarily due to the formation of a dense branch structure composed of G-phase in the brazing seam. The effects of grain size, such as pinning and splitting, are amplified at higher brazing temperatures. Additionally, micro-cracks initiate around brittle intermetallic compounds and propagate through the eutectic zone, leading to a cleavage fracture mode. The fracture stress of fine-grain specimens is higher than that of coarse-grain due to the complex micro-crack path. Therefore, this study contributes significantly to the literature by highlighting the crucial impact of grain size on the brazing properties of ultra-thin-walled Inconel 718 structures.

Fabrication of TA2–304 SS laminated metal composite using directed energy deposition-arc: Microstructure, mechanical property, and corrosion resistance

Conventional fabricating methods of TA2–304 SS laminated metal composite (LMC) (e.g., hot rolling, hot stamping, and explosive welding) have difficulty in removing brittle TiFe intermetallic compounds (IMCs) and are not suitable for the preparation of the small size structure components or transition joints. Additive manufacturing of LMCs has the potential to achieve the desired microstructure, properties, and structure. In this study, TA2–304 SS LMC, which has been extensively employed in pipe flanges of nuclear plants and bows of sonar dome, was well fabricated by utilizing directed energy deposition-arc (DED-arc) and copper‑nickel alloy transition interlayers, and the formation of brittle TiFe IMCs was suppressed. The results of this study indicated that the standard deviation of the height of the surface morphology reconstructed by adopting Python VTK technique was evaluated as 0.67. Furthermore, copper‑nickel transition interlayers possessed the capability of isolating Ti from Fe atoms through the formation of laminar-distributed microstructure. Specifically, the Interlayer1 was comprised of (Fe, Cr) grains with different shapes and small-size (Cu) equiaxial grains, Interlayer2 covered large-size (Cu, Ni) dendritic grains and intergranular (Cu), and the TA2 layer comprised α-Ti and Ti2Cu. The result also showed that thermal cycle-induced recovery and recrystallization and diffusion-induced elemental interaction accounted for the different microstructures. Moreover, the interface between the TA2 and Interlayer2 layers contained TiCu4 + (Cu), Ti3Cu4 + TiCu4, Ti2Cu + TiCu, and TiCu + Ti2Cu eutectoid microstructures, which resulted in the highest hardness of 450Hv as well as crack initiation and extension. Furthermore, due to the uniform-distribution of microstructure in the absence of brittle IMCs, the average shear strength was 234.0 MPa, which reached the strength of the conventional method and conformed to the standard requirements. Multiple groups of galvanic reactions between different transition materials can result in reduced corrosion resistance, and the oxidation-reduction reactions can lead to the formation of massive oxides.

Improving bonding strength and reliability of brazed titanium/copper dissimilar joint using vanadium interlayer

Conventional practice of brazing titanium (Ti) to copper (Cu) using Ag-28Cu eutectic filler alloy is of limited success because of the generation of brittle Ti-Cu intermetallic compounds (IMCs). The bonding strength is unsatisfactory owing to embrittlement of IMCs, and it is difficult to reproduce the bonding strength as the joint microstructure is highly sensitive to brazing parameters. In the current study, it was demonstrated that the formation of such undesirable IMCs can be suppressed and strong Ti/Cu joint can be obtained by brazing at 850 °C using a refractory vanadium (V) interlayer 15 μm in thickness deposited on Ti substrate, in combination with an Ag-Cu-Ti active filler alloy. The V interlayer successfully blocked the interaction between Ti and filler alloy. Bonding mechanisms of the resultant joint can be deduced to be a synergy of active brazing in the V/Ag-Cu-Ti/Cu half and solid-state diffusion bonding at the Ti/V interface. The thus developed joint was comprised of continuous Ti-V solid solution, unconsumed V interlayer and remaining filler alloy. Attributed to elimination of brittle IMCs at joint interface, excellent bonding strength of ∼220 MPa which is comparable with strength of Cu base metal was achieved. Moreover, since the joint evolution was dominated by sluggish solid-state diffusion at the Ti/V interface and very limited erosion of V interlayer by the Ag-Cu-Ti filler, desirable IMC free joint can be obtained over a wide range of brazing time (2 ∼ 5 min), enabling outstanding reliability of the high bonding strength.

A Novel Strategy for Realizing Reliable Welding of Aluminum-Steel

This study proposed a novel welding strategy called active-expulsion-assisted resistance spot welding (RSW), which was used to address the limitations of RSW of aluminum to steel. The method primarily comprised an intentionally set expulsion stage and a locking stage. In the expulsion stage, a short-duration expulsion pulse with a relatively large welding current was applied to melt the aluminum and induce liquid aluminum expulsion. Then, in the locking stage, a welding current pulse was used to join the locking sheet and the steel workpiece. A combination of quenched and partitioned 1180 steel and AA6016 aluminum alloy with and without adhesive was used for welding. Experimental results showed that the expulsion pulse efficiently removed the aluminum alloy in the weld, creating the conditions for fundamentally avoiding the formation of brittle intermetallic compounds in the nugget during the subsequent welding stage. After the welding pulse, a strong joint was generated between the locking sheet and the steel, thus realizing a firm connection for the combination of welding and riveting between an aluminum alloy and steel substrate.

Effect of laser power, speed and offset on the welding performance of 304 SS/Al2O3 ceramics

In this study, 304 SS/Al2O3 ceramic structural parts were successfully prepared by laser heat source biasing using AgCuTi as filler. The method removes residual thermal stresses by retaining unfused 304 SS (stainless steels), provides protection to the Al2O3 ceramics, and connects the two sides of the substrate using the wettability of the AgCuTi filler. Based on the 304 SS/Al2O3 connectivity, the Gibbs free energy changes of Ti–Fe and Ti–Cu compounds at the weld were calculated from the thermodynamics perspective to determine the possible phases. The temperature field of the joint was also investigated using finite element simulation to analyze the temperature changes in the fusion zone, the interface I (304 SS/AgCuTi), and the interface II (AgCuTi/Al2O3) under different welding parameters, and predict the welding parameters that can achieve an effective connection without destroying the Al2O3 ceramics, which were experimentally verified. The maximum tensile strength of the joints was 94.9 MPa when the laser power was increased from 372 W to 432 W. The maximum tensile strength of the joints was 90.5 MPa when the laser speed was increased from 440 mm/min to 630 mm/min. The maximum tensile strength of the joints was 89 MPa when the laser offset was increased from 1.4 mm to 1.9 mm. By analyzing the microstructure, it was found that brittle intermetallic compounds (IMCs) such as FeTi and Cu2Ti were generated at interface I, which was the main factor affecting the strength of the joint. Many Ag(s,s) and Cu(s,s) solid solutions were found at AgCuTi and interface II. By analyzing the microstructure, the interface organization of the joint is composed of 304 SS + α-Fe/γ-Fe + FeTi/Cu2Ti + Ag(s,s)/Cu(s,s) + Ti2Cu + Al2O3. Finally, the Arrhenius function calculates the diffusion coefficients and diffusion concentrations of Ti and Fe elements.

Effects of In and Ga on Spreading Performance of Ag10CuZnSn Brazing Filler Metal and Mechanical Properties of the Brazed Joints

Ag-based brazing filler metals are preferred in many industries, but the high price of Ag restricts their wider application. Therefore, developing novel low-Ag brazing filler metals has aroused extensive interest. In this study, the effects of the In and Ga elements on the melting behavior and spreading property of Ag10CuZnSn filler metal and the microstructure and strength of the brazed joints were investigated. The results show that both In and Ga can significantly decrease the solidus and liquidus temperatures of the filler metal. The In element can dissolve into the liquid filler metal and the Ga element can decrease the surface tension of the melted filler metal, which, in turn, improves the spreading area. The In element prefers to dissolve into the Ag-rich phase, and the Ga element prefers to dissolve into the Cu-rich phase; both improve the strength of the filler metal through solid-solution strengthening. The shear strength of the 304 stainless-steel brazed joint reached a peak value of 396 MPa when the Ag10CuZnSn-1.5In-2Ga (wt%) filler metal was used. However, the excessive addition of In and Ga forms brittle intermetallic compounds (IMCs) in the brazing seam, which decreases the strength of the brazed joint.