Brittle Intermetallic Compounds Research Articles

Experimental and numerical research on formation mechanism of intermetallic compounds in laser brazing welding for Ti/Al dissimilar alloy

Laser brazing is an esteemed technique for Ti/Al dissimilar alloy welding, yet the emergence of brittle intermetallic compounds (IMCs) restricts its broader application. In-depth knowledge of IMCs formation provides critical insights for process optimization targeting IMCs structural improvement, pivotal to high-performance of Ti/Al joint. Herein, we establish macroscopic heat transfer-fluid flow coupled model for laser brazing welding of Ti/Al dissimilar alloys firstly, followed by a comprehensive characterization of the types, distribution, and crystallographic features of IMCs, thereby elucidating the impact mechanism of laser offset on IMCs growth. Incremented laser offset prompts a conversion from transverse to tangential flow at the Ti/Al interface, attenuates peak temperatures and liquid phase duration, and significantly revises solidification parameters, thereby reducing the IMCs layer to 5 μm, augmenting solid-state transformation characteristic, and diversifying crystallographic orientations of IMCs. Ultimately, enhanced tensile strength in the Ti/Al joint is attributed to the presence of thinner IMCs with finer grains, produced by larger laser offset. This article constitutes a pivotal progression in modeling heat transfer-flow behaviors for Ti/Al laser brazing welding, revealing IMCs genesis with unparalleled granularity guided by crystal selective growth principles. It also lays a theoretical foundation for IMCs micro-structure improvement strategy via temperature-flow regulation.

Fabrication and evaluation of Ti6Al4V /NiCrBSi bimetallic structure with Nb/Cu bilayer by laser melting deposition

The fabrication of high-quality bimetallic structures using titanium and nickel alloys is a desirable integration for fully leveraging their remarkable properties. This study is dedicated to the surface modification of titanium brake discs, using laser melting deposition to produce the Ti6Al4V/NiCrBSi bimetallic structure and inhibition of brittle phase formation by Nb/Cu bilayer. The results showed the generation of brittle intermetallic compound phases was effectively resisted using Nb/Cu bilayer, thus preventing cracking and peeling of the Ti6Al4V substrate and NiCrBSi coatings. Moreover, the bimetallic structure fractured at the weakest position, i.e. at the Nb/Cu interface, with a maximum strength of 243.20 ± 55.16 MPa during the tensile testing, exhibiting brittle-like failure behaviour. Additionally, the friction and wear properties of the Ti6Al4V substrate and NiCrBSi coatings were evaluated at both room temperature and elevated temperature (600 °C). The results reveal that the NiCrBSi coatings effectively improved the friction and wear properties of the Ti6Al4V.

Development of Hot-Wire Laser Additive Manufacturing for Dissimilar Materials of Stainless Steel/Aluminum Alloys

The formation of brittle intermetallic compounds (IMCs) at the interface between dissimilar materials causes considerable problems. In this study, a multi-material additive manufacturing technique that employs a diode laser and the hot-wire method was developed for stainless steel/aluminum alloys. An Al-Mg aluminum alloy filler wire (JIS 5183-WY) was fed on an austenitic stainless-steel plate (JIS SUS304) while varying the laser power and process speed and using paste-type flux and flux-cored wire. The effects of laser power and process speed on phenomena during manufacturing and IMC formation were investigated. Finally, the wall-type multilayer specimens were fabricated under optimized conditions. The suppression of IMC formation to a thickness of less than 2 μm was achieved in the specimens, along with a high interfacial strength of over 120 MPa on average.

Direct spot joining of thin gauge aluminum alloy to stainless steel and joint performance in a corrosion environment

Direct joining of aluminum alloy and steel sheets offers a great potential for achieving effective structural lightweighting for transportation systems. The major challenge is how to avoid the formation of brittle intermetallic compounds (IMCs), which can be detrimental to joint load capacity and corrosion resistance. This paper presents a friction-based direct solid-state joining method for welding thin aluminum alloy (AA6061-T6) to stainless steel (316). Using a flat head friction heating tool, high quality interfacial bonding was achieved under a spot time of 20s and 1000 rpm without detrimental IMCs. The effects of an automotive-relevant corrosion environment condition on joint strengths were then examined through mechanical testing. The test results show that aluminum and stainless-steel spot joints produced by the proposed method exhibit no corrosion-induced damage or cracking nor any noticeable reduction in strengths, resulting in dominantly ductile failure mode.

Fabrication of tungsten inert gas-welded dissimilar aluminium joints using different friction stir processing tools through response surface method

ABSTRACT AA6061-T6 and AA7075-T6 materials find wide application in manufacturing industries due to their excellent engineering properties. Fusion welding generates solidification cracks, high residual stresses, and brittle intermetallic compounds that degrade joint qualities. To solve these difficulties, friction stir processing (FSP) is frequently employed, which improves joint properties through local microstructural refinement. In this study, the combined effect of FSP parameters, namely tool pin profile (TPF), tool rotation speed (TRS), and travel speed (TS), on tungsten inert gas (TIG) weld properties was investigated. Response surface methodology (RSM)-based mathematical models were developed to predict responses, namely ultimate tensile strength (UTS), impact toughness (IT), microhardness (MH), and residual stress (RS). The optimal FSP parameters were determined through the desirability function technique. Post-FSP increased the UTS, IT, and MH of TIG welds by 71.51%, 95.40%, and 72.46%, respectively, and decreased the RS by 58.46%. ANOVA findings exhibited that TPF was the most influential parameter, followed by TRS and TS. The dissimilar aluminium TIG+FSP joints showed an optimal UTS of 282.08 MPa, an IT of 17.32 J, a MH of 121.48 HV, and an RS of 22.09 MPa when using a TRS of 1108.49 rpm and a TS of 37.74 mm/min with a THF pin.

Metallurgical characteristics of aluminum-steel joints manufactured by rotary friction welding: A review and statistical analysis

Rotary friction welding (RFW) is a solid-state joining process that can be used to join different alloy systems such as aluminum-steel alloys. Rotary friction welding has become increasingly appealing for various industries due to the sustainable advantages that it offers, including overall cost reduction, weight minimization, and unique properties. However, the formation of brittle intermetallic compounds (IMCs) at the interface can be a challenge in the welding process of aluminum-steel alloys. This paper reviews the metallurgical characteristics of aluminum-steel alloy joints manufactured by rotary friction welding. The different types of intermetallic compounds that can form at the interface, as well as the factors that affect their formation, are discussed. The effects of rotary friction welding parameters on the microstructure and mechanical properties of the joints are also presented. Specifically, minimizing interfacial reaction layers via post-weld heat treatment and controlling the heat input during the process is crucial to suppressing the formation of intermetallic compounds. This study employed artificial intelligence modeling, specifically the artificial neural network - multilayer perceptron, to investigate the effect of various parameters on the ultimate properties of the parts welded together. Overall, this paper provides an excellent resource for industries looking to embrace rotary friction welding to tackle the challenge of dissimilar Al-steel joining.

Integrating interfacial bonding and coordinated deformation in steel/Al bilayers via a pin-less friction stir-assisted synchronous joining-forming approach

The potentials of steel/Al alloy laminated structures for lightweighting in the automotive industry are increasingly recognized, particularly for reducing energy consumption. However, optimal formability and high-temperature stability in these hybrid structures remain a persistent challenge during the current manufacturing process. This challenge arises from the intricate control required over the Fe-Al intermetallic compounds (IMCs) layer at the dissimilar interface. In this work, steel/Al alloy bilayer laminated structures were fabricated by a thermomechanical joining-forming approach involving pin-less friction stir-assisted incremental sheet forming with synchronous bonding technology. These structures exhibit desirable shear bonding strength of 129 MPa (equivalent to 93.5 % of the shear strength of the AA5052-H32 base material). Mechanisms of local plastic flow, viscoplastic flow, and fast inter-atomic diffusion are evaluated using quasi-static elements. A phenomenological bond fraction model is proposed to describe the collapse of interfacial ellipsoidal microvoids. Cohesive numerical simulation reveals that the interfacial plastic strain is dispersedly distributed with slight cohesive damage due to stable heat-force conditions. Experimental results with confirmed models demonstrate the stability of the programmable process for mechanical-metallurgical bonding and coordinated deformation. Furthermore, a cyclic thermomechanical loading mode is proven effective in tuning interfacial diffusion and inhibiting the growth of the IMC layer. This integrated joining-forming strategy is also applicable to other challenging metallic pairs that are prone to brittle IMCs.

Effect of Ag interlayer on the microstructural properties and nanocreep behavior of Ti6Al4V/AA7075 dissimilar laser weldments

Creep failure poses a potential risk in dissimilar welded joints between aluminum and titanium alloys, potentially compromising the joint's integrity. This study utilizes laser beam welding (LBW) to achieve dissimilar joining of AA7075 and Ti6Al4V by incorporating an Ag interlayer. The role of Ag interlayer for dissimilar joining of AA7075 and Ti6Al4V alloys and its impact on the microstructure and nanocreep behavior of joints is examined. The findings showed that the use of Ag decreased the interaction of Ti/Al considerably with each other which led to a reduction in the formation of brittle intermetallic compounds. The nanohardness and atomic force microscopy (AFM) results indicated that the Ti6Al4V HAZ exhibited the highest hardness and least plastic deformation, owing to the formation of α′ martensite. The nanoindentation creep analysis revealed the highest stress exponent value in Ti6Al4V HAZ, pointing to a dislocation climb creep mechanism. Additionally, the results also suggested that the observed creep mechanism might be attributed to both diffusional creep and dislocation climb for other zones.

Investigation on Friction Stir Welding Parameters: Mechanical Properties, Correlations and Corrosion Behaviors of Aluminum/Titanium Dissimilar Welds

In industrial applications, welding of dissimilar metals such as aluminum (Al) and titanium (Ti) is a prerequisite for the development of hybrid components with improved mechanical and corrosion properties. However, dissimilar welding of the Al/Ti system is highly challenging due to differences in the physical and thermal properties of the two materials. In the present investigation, an attempt has been made to fabricate a dissimilar friction stir weld (FSW) of commercially pure Al and Ti and to elucidate the mechanism associated with superior joint formation. The process parameters, such as tool rotation speed, traverse speed and tool offset position have been optimized using Taguchi’s optimization technique. A detailed investigation of the weld with optimum process parameters has been carried out to reveal the mechanism of joint formation. The superior mechanical properties (24% higher ultimate tensile strength and 10% higher ductility than that of base Al) of the weld are attributed to the fabrication of a defect-free joint, formation of intercalated particles and an Al/Ti interlocking interface, homogeneous distribution of fine second-phase (Ti and/or intermetallics) particles in the weld nugget, reduction in the evolution of brittle Al3Ti intermetallic compounds (IMCs) and recrystallization and grain refinement of Al in the weld nugget. The potentio-dynamic polarization test indicated that the optimized Al/Ti weld has ~47% higher corrosion resistance than Al; it had a very mild corrosion attack due to the homogeneous dispersion of fine particles. The method and mechanism could have an immense influence on any dissimilar weld and metal matrix composites, improving their mechanical properties and corrosion resistance.

Tailoring interfacial structure and achieving excellent strength-ductility synergy of Al/Mg/Al composite via porthole die co-extrusion and post-annealing

Porthole die co-extrusion (PDCE) is an effective strategy for fabricating high-performance laminated bimetal composites. In this study, PDCE and post-annealing treatment were employed to tailor the interfacial structure and matrix microstructure of Al/Mg/Al composite, and the ensuing evolution in the fracture behaviors and mechanical properties were systematically investigated. A mechanical bond without the formation of intermetallic compounds (IMCs) at Al/Mg interface, strip-like substructure in Al layer, and bimodal structure composed of fine recrystallized grains coexisting with coarse deformed grains in Mg layer were achieved by PDCE and maintained after annealing at 200 °C. Increasing the annealing temperature or time caused the formation and growth of IMCs (γ-Mg17Al12 and β-Al3Mg2) layers, with the growth mode transforming from a combination of grain boundary and lattice diffusion at 300 °C to the predominant lattice diffusion at 400 °C. For Al layer, the static recrystallization (SRX), normal, and abnormal grain growth could not be triggered until the temperature higher than 400 °C. However, the SRX and grain growth in Mg layer were extremely boosted as the temperature increased to 300 °C. The differences in the plasticity and strength between Al and Mg layers resulted in the multi-step fracture of Al/Mg/Al composite without IMCs. With increasing of annealing temperature, early-stage delamination of Al and Mg layers took place due to the rupture of brittle IMCs, followed by independently deformation of each constituent layers. Al/Mg/Al composite annealed at 200 °C for 1 h show superior tensile strength of 191 MPa and maximal ductility of 22.7%.

Laser-directed energy deposition of Ti6Al4V/AA2024 alloy component based on interweaving structure

The presence of brittle intermetallic compounds (IMCs) can easily lead to cracks at the interface of titanium/aluminum alloy components. A novel interweaving structure was proposed and a Ti6Al4V/AA2024 dissimilar alloy component was prepared. The interlocking between Ti6Al4V and AA2024 mitigates the adverse effects of brittle IMCs on the Ti/Al interface, while the interweaving of Ti6Al4V and AA2024 avoids the generation of continuous IMCs. The average compressive shear strength of the Ti6Al4V/AA2024 alloy component is 86.1 MPa, which is 79 % of that of as-deposited AA2024. The fracture occurred in the interweaving layer in shear tests.

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.

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.