Brittle Intermetallic Compounds Research Articles

Brazing of TC4 Alloy Using Ti-Zr-Ni-Cu-Sn Amorphous Braze Fillers.

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 Ti23.75Zr23.75Ni23.75Cu23.75Sn5. 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 Ti23.75Zr23.75Ni23.75Cu23.75Sn5 braze filler. Microstructural evolution and the corresponding mechanical response were in-depth discussed.

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.

High bonding strength of Ti /steel clad plates prepared by a developed electromagnetic induction heating followed by rolling

Titanium/steel clad plates exhibit significant potential for industrial applications, such as petrochemical and aerospace, due to their combined advantages of two components. In the conventional hot rolling process, the formation of brittle intermetallic compounds (IMCs) had a detrimental effect on the mechanical properties of Ti/steel clad plates. Therefore, the present study proposed an electromagnetic induction heating rolling (EIHR) technique for efficiently fabricating Ti/steel clad plates with high bonding strength at a relatively low temperature, while avoiding the formation of brittle IMCs. Additionally, a pure iron DT4 interlayer with good fluidity was introduced between Ti and steel, which can further enhance both the interface bonding strength and elongation of the clad plates. Based on the electron backscattered diffraction characterization results of the interface, it was found that the addition a DT4 interlayer facilitated dynamic recrystallization of steel side and led to a reduction in dislocation density. Moreover, a pronounced {100}〈011〉 rotational cube texture was evident on the (100) pole figures as a result of substantial plastic deformation during the rolling process. Finally, the relationship between interface microstructure and mechanical performance was established.

Homogenization treatment-induced reduction of brittle intermetallic compounds in Ti2AlNb/Ti60 brazed joints: Effect on microstructure and mechanical properties

The microstructure evolution and mechanical properties of Ti2AlNb/Ti-36.5Zr–10Ni–15Cu-0.5Co-0.5Nb/Ti60 brazed joints before and after homogenization treatment were comprehensively evaluated. Initially, the joints brazed at 900 °C for 15 min exhibited a continuous coarse strip network of Ti2Cu, Ti2Ni, Zr2Cu and Zr2Ni brittle intermetallic compounds in the central region of the braze seam, which detrimentally affecting the mechanical properties. Subsequent homogenization at 600 °C for 1 h, the amount of continuous brittle intermetallic compounds significantly decreased through sufficient atomic diffusion. Concurrently, the inadequately transformed eutectic β-Ti within the intermetallic compounds underwent an active eutectoid reaction. This structural transformation established a coherent interface with elastic distortion between the α-Ti and intermetallic compounds, effectively minimizing the lattice mismatch. Thus, a widmanstatten structure (i.e., acicular intermetallic compounds within a eutectoid microstructure matrix) with improved mechanical properties was formed. Consequently, a mean shear strength of 350.3 MPa was attained after treatment at 600 °C for 1 h, marking a substantial 206 % increase compared to that before homogenization treatment. This finding underlines the pivotal role of homogenization treatment in optimizing the performance of aeroengine components.

Dissimilar linear friction welding of AZ31 magnesium alloy and AA5052-H34 aluminum alloy

The intermetallic compound (IMC) layer, tensile properties, and fracture behavior of dissimilar Mg/Al joints and their relationship during linear friction welding (LFW) are investigated to develop a strategy to obtain high-strength Mg/Al dissimilar materials. The thickness of the Mg/Al-based IMC layer decreases as the applied pressure increases and the frequency decreases. The IMC layer is mainly composed of Mg17Al12 and Mg2Al3 at the weld interface. The tensile strength of the joints fabricated at an appropriate frequency of 50 Hz and a high pressure of 200 MPa during LFW is 235 MPa, which is 94 % the tensile strength of AZ31 and is attributed to the effective suppression of the Mg2Al3 IMC layer growth. At a lower frequency, large defects and pores are formed near the weld interface edge on the Mg side owing to the low welding temperature. The joint fabricated at a higher frequency exhibits a thick and brittle Mg2Al3 IMC layer at the weld interface because of the high growth rate; thus, the dissimilar joints fractured primarily at the Mg2Al3 IMC layer. The inhibition of the Mg2Al3 IMC layer growth yields superior tensile properties in Mg/Al dissimilar materials.

Ti/Mg dissimilar joining by eutectic-melting-induced liquid metal dealloying

Ti and Mg alloys, which have thermodynamically immiscible main components, have been chemically joined in previous work using a third element with high affinity for both elements. However, this strategy is challenging in precisely controlling brittle intermetallic compounds formed at a joint interface. In this study, we mechanically joined pure Ti and pure Mg without brittle layers by forming bicontinuous microstructure, 3D entanglement of immiscible phases, at the joint interface. We butt-joined pure Mg and Ti–Cu alloy interlayer, which we pre-diffusion bonded to the pure Ti and heated at 813 K and 20 MPa for 5 min. At the joint interface, Cu and Mg eutectic melted, which induced liquid metal dealloying of the interlayer. The entire Ti–Cu interlayer is dealloyed, and a byproduct (Mg–Cu phase) is removed by pressurization during melting. These brittle layer removal processes left only α-Ti/Mg–Cu phase bicontinuous microstructure at the joint interface, improving the joint strength. Ti/Mg joints fractured at the Mg base metal at ca. 90 MPa by tensile tests. The findings of this study provide the basis for achieving immiscible alloy joining, for which effective joining methods have not yet been established.

Corrosion behavior of AA2024/pure copper bimetal manufactured by friction stir welding with a hybrid zinc-graphite interlayer

The effect of utilization of zinc (Zn) and graphite (Gr) as a hybrid interlayer for dissimilar lap joint of AA2024 and pure copper, employing friction stir welding (FSW), was investigated in this study. The microstructure of the samples was examined using a scanning electron microscope (SEM), and the composition of the present phases was evaluated with energy-dispersive spectroscopy (EDS) and X-ray diffraction (XRD). Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) tests were performed to analyze the corrosion behavior. Subsequently, the post-corrosion morphology was examined using SEM and EDS. The results show that applying two passes of FSW in the presence of hybrid Zn-Gr interlayer, led to the modification of detrimental brittle intermetallic compounds (IMCs). The corrosion investigations demonstrated that the corrosion current density (icorr) in the AA2024/(Zn-Gr)/Cu sample after 1- pass FSW was reduced by about 80% in comparison to the Al/Zn/Cu sample. This behavior can be attributed to the presence of a large number of diffusion channels and the inhibitory effect of graphite particles. The 2-pass FSWed AA2024/(Zn-Gr)/Cu sample exhibited the highest level of corrosion resistance, owing to the better dispersion of graphite particles, which led to improved passivation on the aluminum side. As a result, the inherent issue of intergranular corrosion in the Al–Cu alloy was effectively resolved at the joint interface. This ultimately led to an enhanced corrosion resistance of the Al–Cu bimetals produced by FSW.

The impact of ring-shaped laser beam on dissimilar welding of Al-Cu thin sheets for battery tab-to-busbar connection: Microstructural, mechanical and electrical characteristics

Al-Cu dissimilar laser welding has gained substantial attention in the electric vehicle battery manufacturing, while challenged by the formation of brittle Al-Cu intermetallic compounds (IMCs). This study investigated the impact of beam shaping technology on the characteristics of Al-Cu dissimilar laser welds by using a coaxial core and ring dual beam laser system. The investigation assessed multi-level weld characteristics including weld geometry, IMC formation, mechanical and electrical properties. Results showed that the dual laser beam can effectively avoid imperfections observed with single beam, such as full penetration related to core-only beam and surface discontinuity defects associated with ring-only beam, respectively. For the core-only weld, extensive upward migration of Cu promoted the formation of brittle CuAl2 and Cu9Al4/Cu3Al2, leading to a considerable reduction in joint strength and a sharp increase in the electrical resistance. For the ring-only weld, the insufficient bonding area between Al and Cu sheet, leads to a significant degradation of joint strength, although a minimal electrical resistance was identified. An optimized power splitting was determined at 40% for the core beam and 60% for the ring beam, which allows the minimal formation of Al-Cu IMCs and consequently, the improved mechanical strength and reduced electrical resistance.

Effect of Ti content on weld formation and mechanical properties of welded joints of TA2/Q235 bimetallic sheets

Due to the issue of brittle Ti-Fe intermetallic compounds, a challenge for the welding of Ti/steel bimetallic sheets is presented. In this study, four types of multi-principal powders of Fe25-xCo25Ni25Cu25Tix were designed based on eutectic high-entropy alloys (HEAs), which were used as filler materials for laser welding of TA2/Q235 bimetallic sheets. The impact of Ti content in the filler powders on weld formation and mechanical properties was investigated. It is found that with an increase in the Ti content, the hardness values of the weld zones generally increased, whereas the tensile strengths decreased. The maximum tensile strength of ∼298.4 MPa was achieved in the joint using Fe20Co25Ni25Cu25Ti5 filler powders, in which the weld metal met the definition of an HEA.

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.

Interfacial coherence regulation and stabilization of molybdenum/Kovar alloy welded joint by CoCrCuFeNi high entropy alloy

The crux of molybdenum/Fe-base alloy welded joint is embrittlement and consequently deteriorated strength. The current researches just attribute it to brittle intermetallic compound inside the weld. However, no brittle phase continuously precipitates at the fracture location of the molybdenum/Kovar alloy electron beam welded joint, meaning that the unstable phase interface is the real fundamental reason for the brittleness of joint, instead of the phases themselves. Noncoherent interfaces are formed between α-Mo and eutectoid α-Fe + μ(Fe3Mo2) deriving from solid-state phase transition. To optimize interfacial coherence and stabilize the interface, CoCrCuFeNi high entropy alloy is added into the weld. The new interfaces between α-Mo and eutectic face-centered cubic (fcc) + laves are transformed into coherent interfaces. σ(FeCr) nanoparticles precipitate at α-Mo/fcc interface, indicating the decreased interfacial energy and more stable interface. The tensile strength of the joint is increased from 262 to 366 MPa. The present work provides guidance for optimizing welding quality between molybdenum and Fe-base alloy.

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.