Intermetallic Formation Research Articles

Temperature-Dependent Products in Gallium Flux Reactions of Cerium and Transition Metals.

Reactions of cerium and transition metals in excess molten gallium were carried out, exploring the formation of different cerium intermetallics as the flux reaction is cooled. Ce/T/Ga reactions with T = Ni, Cu, Pd, Ag, and Zn produce a high-temperature product, which converts into a low-temperature product in the flux. The phases present in the flux mixture were determined by quenching identical reactions at 750 and 300 °C and identifying the isolated products using elemental analysis and X-ray diffraction. The compounds CeGa2, CeCu0.37Ga3.63, CePd0.32Ga3.68, Ce5Ag1.76Ga17.29, and Ce5Zn1.37Ga17.73 were isolated by quenching at 750 °C. Upon cooling to 300 °C, the corresponding reactions instead yielded CeGa6, Ce2CuGa12, Ce2PdGa12, Ce2Ag0.7Ga9.1, and CeZnxGa7-x. All of these structures contain cerium in the ThCr2Si2-related layers. Large crystals of high-temperature products CeCu0.37Ga3.63, CePd0.32Ga3.68, Ce5Ag1.76Ga17.29, and Ce5Zn1.37Ga17.73 were used for magnetic susceptibility measurements. All of these materials show highly anisotropic ferromagnetic ordering of Ce3+ moments below 8 K, which is in contrast to the antiferromagnetism seen for the compounds that were isolated at 300 °C.

Effect of Fe-Al intermetallics on fatigue properties of aluminum to steel dissimilar spot welds

Lightweight structures made of aluminum alloys and high strength steels are increasingly used for improving vehicle fuel efficiency. One barrier for joining aluminum and steel is the formation of brittle Fe-Al intermetallics that can have deleterious effects on joint ductility and strength under static loading conditions. However, it is unclear how the intermetallics affect the joint fatigue properties. In this study, the effect of intermetallics on fatigue properties of dissimilar metal joints between a 6xxx aluminum alloy and a high-strength steel is investigated on welds created by ultrasonic interlayered resistance spot welding (Ulti-RSW). Joint efficiency calculations are used to normalize the peak load so the fatigue properties of Ulti-RSW are compared with a wide range of joining processes in the literature. During fatigue testing the failure mode transitions from interfacial or button pull-out failure during low cycle fatigue loading (below 100,000 cycles) to through-thickness failure during high cycle (above 100,000 cycles). Based on the stress intensity factors calculated using a simple 2D fracture mechanics model, the transition in failure mode is attributed to the plastic deformation near the notch tip. Overall, this study shows that the intermetallics have little effect on the high-cycle fatigue properties of dissimilar spot joints.

Convolutional neural network based methodology for flexible phase prediction of high entropy alloys

ABSTRACT The advent of high entropy alloys has created a design space that is unfeasible to explore solely through experimentation, thus necessitating the use of computational methods, such as artificial neural networks. This study proposes a new architecture utilizing a convolutional layer to extract relevant elemental features from the alloy composition without limiting the model to specific elements by treating the elemental composition of the high entropy alloy in a similar manner to a row of pixels, using relevant elemental properties in lieu of color values. This convolutional model was able to predict the crystal structure of solid solutions in a high entropy alloy composition with an accuracy of 89.3% in a six-way classification and the formation of intermetallics with an accuracy of 91.4% during holdout validation, while being capable of accurately predicting the primary crystal structure of high entropy alloys containing elements the model was not trained on. Significant space still exists for further experimentation and improvement with this methodology, including augmenting the available datasets and implementation of additional convolutional layers. Due to the limited interpretability of the model architecture, care should be taken when inferring trends from the model prior to validation through experimental, or well-established computational methods.

The shape recovery behavior of compressively deformed Fe–Mn–Si–Cr–Ni alloys

Cylindrical alloys fabricated from shape memory Fe–xMn–5Si–5Ni–yCr were produced by utilizing diverse solid volume fractions through the use of the powder metallurgy and sintering technique. The shape recovery due to compressive force was analyzed and correlated with the volume fractions. A higher concentration of manganese (Mn) will result in a decrease in shape recovery as a result of the formation of oxides, precipitates and unintended intermetallics during the furnace cooling process. The dislocation occurring within and around the grain boundary is another significant factor contributing to the reduction in shape recovery. The increase in chromium (Cr) content reduces the likelihood of dislocation around the grain boundary. The effectiveness of compressive deformation was examined and correlated.

Interface enhancement mechanism of rolled Mg/Al clad plate with particle interface control

In this study, the cold-spraying process was utilized to deposit Al particles onto an Al slab, an Mg slab, and both Al and Mg slabs to form an ultra-thin interlayer, and then the clad slabs were rolled at 400 °C, developing three roll-bonding processes: the roll-bonding process with cold-sprayed Al powder on the Al slab (CS-Al), the roll-bonding process with cold-sprayed Al powder on the Mg slab (CS-Mg), and the roll-bonding process with cold-sprayed Al powder on both the Al slab and the Mg slab (CS-Both). The effects of three different cold-sprayed Al particle interlayer processes on the mechanical properties of rolled Mg/Al clad plates were investigated to improve the mechanical properties. The microstructure, texture evolution, intermetallic compound formation, mechanical properties, and mechanisms involved in the Mg/Al clad plate rolling were systematically investigated. The results showed that the pre-bonding between the particles and the substrates through cold-spraying had a significant impact on the bonding strength of the Mg/Al clad plates, and the CS-Both process can increase the average shear strength of the Mg/Al clad plates to 49.24 MPa at a medium reduction rate of 37.5 %, 2.5 times that of the conventional rolling process. The CS-Both process constructed more evident dual microscopic three-dimensional interfaces and promoted more thorough atomic diffusion at the interface through the double-sided cold-spraying process. Meanwhile, the dual cold-sprayed Al coatings on both the Mg slab and Al slab underwent dynamic recrystallization during rolling to form a homogeneous unit with no additional coating interfaces. Fine grain strengthening and dislocation strengthening were judged to be important mechanisms for improving the mechanical performance of the interfacial layer.

EXPERIMENTAL INVESTIGATION OF MECHANICAL AND METALLURGICAL PROPERTIES IN FRICTION STIR SPOT WELDING OF DISSIMILAR AA6061-T6 TO COPPER

In this study, the effects of important parameters of the FSSW process, rotational speed and dwell time, have been investigated on mechanical and metallurgical properties of dissimilar AA6061-T6 to the pure copper welded joint. In addition, the results were compared with the similar Al-Al and Cu-Cu welded joints. The results indicate that an increase in the rotational speed from 1250 to 1600 rpm and dwell time from 5 to 10 seconds improves the tensile and flexural strength of all the welded samples. Furthermore, at rotational speeds lower than 1250 rpm, due to reduced frictional heat generation, and above 1600 rpm, due to excessive heat production, the quality of the joints decreases. In this welding process, the amount of frictional heat generated directly affects the metallurgical structure, hardness of different welding zones, and intermetallic formations formed. The microstructure and the microhardness studies reveal that different welding parameters lead to the formation of fine grains and recrystallization in the stir zone and other regions with an increase in rotational speed and dwell time. This phenomenon is a result of the heat generated by friction and severe material deformation during welding. The refinement of grains contributes to increasing the hardness and strength. Moreover, the hardness analysis of the welded regions shows that the dissolution and growth of precipitates in the weld metal and its vicinity create a weaker region compared to the base metal, resulting in a decrease in hardness relative to the base metal.

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.

Characterizing of a unique Al/Cu FGMMC fabricated via the ARB-CRB process followed by annealing

This study investigates the influence of different annealing temperatures on the microstructure and growth of the intermetallic phase in an Al/Cu functionally graded metal matrix composite (FGMMC ( produced by the accumulative roll bonding (ARB)-cold roll bonding (CRB) process. SEM images show the evolving distribution of Cu content in the composite, with the finest and thinnest Cu layer observed in the Al/20Cu region. The annealing at 400°C and 450°C for 2, 4, and 6 hours results in the formation of intermetallic layers (Al2Cu, Al4Cu9, and AlCu) with a clear progression from the Al side to the Cu side, as confirmed by SEM-EDS and TEM analysis. Increasing the annealing conditions increases the thickness of the intermetallic layers. In addition, the intermetallic layers are thicker in the FGMMC sample than in the ARB sample under the same conditions due to the additional strain during the process. The findings demonstrate that a diffusion-controlled mechanism governs the growth of the Al2Cu, Al4Cu9, and AlCu layers. The tensile test results indicate that as the Cu content increases from 20 wt% to 80 wt%, the ultimate tensile strength of the layers increases from 288.24 MPa to 373.66 MPa, while the elongation decreases from 8.2 % to 5.3 %. After annealing, however, these values decreased due to the restoration phenomenon and intermetallic formation. The fracture surface predominantly exhibits a brittle mode, especially with increasing Cu content and annealing conditions.

Silicon effect on retardation of Fe-Zn alloying behavior: Towards an explanation of liquid zinc embrittlement susceptibility of third generation advanced high strength steels

Silicon (Si) aggravates liquid metal embrittlement (LME) susceptibility of Zn-coated advanced high strength steels (AHSS) by inhibiting intermetallic formation between liquid Zn and the AHSS substrate at elevated temperatures. This study performed detailed microstructural and elemental characterization of an LME-susceptible Si-bearing AHSS to reveal the fundamental mechanism by which Si inhibits Fe-Zn intermetallic reactions. Notably, the interaction between Si-alloyed AHSS and liquid Zn at elevated temperatures results in pronounced Si enrichment in a thin region of the substrate in contact with the liquid. This Si enrichment behavior is at the core of the retarded Fe-Zn reactions, and is explained from a fundamental standpoint by analyses of the phase equilibria in the Fe-Zn-Si ternary system and diffusion kinetics using DICTRA®. Specifically, the liquid dissolves the surface layers of the AHSS substrate upon initial contact at elevated temperatures. The liquid phase, however, has no appreciable solubility for Si; hence, almost all of the Si atoms from the dissolved substrate layers are “back diffused” into the substrate leading to Si enrichment. The Si-enrichment of the substrate reduces the thermodynamic driving force for nucleating intermetallic phases at the steel/coating interface, making it difficult to form a “protective” interfacial layer barrier between the liquid and the substrate. Further, Si enrichment results in an increase in the chemical potential of Zn and reduction in the chemical potential of Fe in the substrate; both these factors slow the kinetics of substrate dissolution and Fe-Zn alloying, leading to an increased liquid fraction in the coating available to activate LME.

Sintering behaviour of liquid phase sintered 90Mo-10(Ni–Cu) alloys

Molybdenum (Mo), a refractory material, boasts an elevated melting point of 2610 °C and is predominantly synthesised through powder metallurgy at high temperatures reaching 2000 °C, necessitating the use of liquid phase sintering (LPS) technique. This study investigates the LPS of Mo with varying proportions of Ni–Cu binders, aiming to understand the mechanism of intermetallic formation and to manufacture low-cost, dense, intermetallic-free and near-net-shape Mo-base alloys. Employing the manufacturing design paradigm for 90W-10(Ni–Cu) tungsten heavy alloys (WHAs) and utilising conventional powder metallurgy techniques, Mo-based 90Mo10(Ni–Cu) alloys were synthesised. Initial findings indicate that the densification of Mo-compacts increases with increasing the Ni–Cu ratio in the binder phase. However, an excess of Ni results in the loss of structural rigidity and geometric distortion during sintering. In Ni-rich alloys, two distinct liquid phases, Ni-rich and Cu-rich, emerge at sintering temperatures. These phases exhibit different solubilities for Mo and solidify into a dual-phase matrix. Intriguingly, in contrast to WHAs, 90Mo-10(Ni–Cu) alloys with a Ni-rich composition manifested irregular Mo particles, a dual-phase matrix, and δ-MoNi intermetallic compound formation. The formation of the intermetallic compound can be avoided by reducing the solubility of Mo in the Ni-rich liquid during sintering. Microstructural evolution and distortion are analysed using stereological quantification of various microstructural parameters. It reveals that alloys with low Mo solubility, high connectivity and high dihedral angle maintain their structural rigidity and resist distortion. Both micro-hardness and bulk hardness increased with increasing Ni–Cu ratios in the binder phase. Based on the present results, a mechanism for liquid phase sintering in the 90Mo-10(Ni–Cu) system in the presence of two liquid phases is postulated.

Friction Stir Welding between Marine Grade Aa 5083 and HSLA Steel

The revolutionary method of solid-state joining technique has already attracted significant attention of advance welding and joining research community. The technique has been continuously developing for many alloy systems for similar and dissimilar joints. Recent research in these areas aiming to join complex dissimilar alloy pairs, composite, polymers, ceramics etc. This paper presents a study of friction stir welding between marine-grade aluminum alloy AA 5083 and HSLA steel, configured in a butt arrangement. The study investigates the evolution of Fe-Al series of intermetallic layer formation at the joint interface and its effective management to yield best joint efficiency. The FSW in the said alloy pairs yielded an 83.25% welding efficiency based on the aluminum alloy side strength. XRD analysis along with SEM examination revealed the formation of Al13Fe4 and Al5Fe2 as intermetallic compounds which was confirmed by the EBSD analysis. The obtained results are discussed in the paper considering the effect of the weld joint performance.

Microstructure and properties of Cu/Si composites for electronic packaging: Effect of tungsten layer on silicon particles

Cu/Si composite are ideal electronic packaging materials, but the intense formation of Cu-Si intermetallics during preparation leads to a significant decrease in their plasticity and thermal conductivity. In this paper, a W layer was formed on Si particles using the sol-gel method, and Cu/Si composites were prepared by hot pressing. The results show that the maximum thickness of the W layer is 1.64 μm, and the minimum thickness is only 809 nm. The W layer acts as a diffusion barrier, effectively inhibiting the Cu-Si interfacial reaction and intermetallics formation, thus preventing the deterioration of matrix and reinforcement properties. Compared with the Cu/Si composite, the elongation of the Cu/Si@W composite improves from 0.2 % to 1.7 %, and the thermal conductivity increases by 7 times to 233.9 W/(m·K). Additionally, among the four samples, the Cu/Si@W composite has the lowest coefficient of thermal expansion (CTE). The W layer enhances the mechanical properties and thermal conductivity while reducing the CTE of Cu/Si composite for improved electronic packaging application.

Optimization of process parameters of cold metal transfer arc welding of AA 6061 aluminium Alloy-AZ31B magnesium alloy dissimilar joints using response surface methodology

The fabrication of dissimilar metal joints, particularly between AA 6061 aluminum alloy (Al) and AZ31B magnesium alloy (Mg), poses significant technical challenges due to their distinct metallurgical characteristics and the inherent difficulties associated with welding such materials. These challenges include the propensity for intermetallic compound formation, thermal cracking, and differences in thermal and mechanical properties between the two alloys. Cold Metal Transfer (CMT) welding, known for its low heat input and controlled metal transfer, offers a potential solution to these issues. However, optimizing the process parameters to ensure strong, defect-free joints requires a systematic approach. This study aims to optimize CMT welding parameters using parametric mathematical modeling (PMM) to produce high-strength Al and Mg dissimilar joints and to study the effects of CMT parameters on tensile strength (TS) and weld metal hardness (WMH), as well as the microstructural features of AA 6061 aluminum alloy/AZ31B magnesium alloy (Al/Mg) dissimilar joints. Al/Mg dissimilar butt joints were produced by the CMT process using ER4043 as filler wire. CMT, a low-heat input welding technique, was used to mitigate issues such as intermetallic compounds (IMCs), wider heat-affected zone (HAZ), and distortion. The CMT parameters, particularly wire feed speed (WFS), welding speed (WS), and arc length correction (ALC), were optimized using response surface methodology (RSM) to maximize the TS and WMH of the Al/Mg dissimilar joints. Polynomial regression was employed to create PMMs that integrated these CMT parameters to forecast the TS and WMH of the joints. An analysis of variance (ANOVA) was applied to assess the feasibility of the PMMs. The results indicated that the Al/Mg dissimilar joints, produced using a WFS of 4700 mm/min, a WS of 280 mm/min, and an ALC of 10%, exhibited higher TS and WMH values of 33 MPa and 95.8 HV, respectively. The PMMs provided precise forecasts for the TS and WMH of the Al/Mg joints with an error rate of less than 1% and a confidence level of 97%.

Increased thermal conductivity and decreased electron–phonon coupling factor of the aluminum scandium intermetallic phase (Al3Sc) compared to solid solutions

Aluminum scandium alloys and their intermetallic phases have arisen as potential candidates for the next generation of electrical interconnects. In this work, we measure the in-plane thermal conductivity and electron–phonon coupling factor of aluminum scandium alloy thin films deposited at different temperatures, where the temperature is used to control the grain size and volume fraction of the Al3Sc intermetallic phase. As the Al3Sc intermetallic formation increases with higher deposition temperature, we measure increasing in-plane thermal conductivity and a decrease in the electron–phonon coupling factor, which corresponds to an increase in grain size. Our findings demonstrate the role that chemical ordering from the formation of the intermetallic phase has on thermal transport.

Nanoindentation and isothermal compression behaviour of Al–4Cu–Ni composites

The present investigation explores the nanoindentation and isothermal compression behaviour of Al–4Cu-xNi (x = 2, 4, 6, 8 and 10 wt%) Aluminium matrix composites produced by pressureless sintering technique. The scanning electron microscope (SEM) and X-ray diffraction (XRD) analyses of sintered samples reveal the presence of core-shell type Al3Ni and Al3Ni2 intermetallic formation at the interface between Ni particulates and the Al–Cu matrix. Nanoindentation study shows hardness of 1.55 ± 0.15, 4.65 ± 0.44, 21.02 ± 0.42, 13.17 ± 0.13, 5.53 ± 0.89, 6.28 ± 0.19, 8.39 ± 0.14 GPa corresponding to α-Al matrix, Ni, Al3Ni2, Ni and Al3Ni2 interface, Al3Ni, and their respective interface. The composite containing 10 wt % Ni possesses the highest yield strength at room temperature. At 200 °C it could retain 54 % of its room temperature strength (91 MPa). The HR-TEM analysis shows that particulate and precipitation hardening was the predominant mechanisms during the initial stage of an isothermal compression. However, as the compression progressed, the pinning effect, dynamic recovery (DRV), and work hardening mechanisms became active. According to the current study findings, interface qualities substantially impact composite performance at both room temperature and elevated temperatures. The creation of strong intermetallic compounds (Al3Ni2 and Al3Ni) due to an intensive endothermic interaction between the Al and Ni particles is linked to this effect.

Inhibition of intermetallic compounds using pure Ni or Ni–Al2O3 nanocomposite coating during the ultrasonic-assisted soldering of Mg/Al dissimilar metals

The widespread utilization of lightweight Mg and Al alloys underscores the importance of establishing reliable connections between them. However, joining dissimilar Mg/Al alloys presents challenges, primarily due to uncontrolled formation of intermetallic compounds during the process, leading to weakened joint performance. To inhibit its formation, a Ni or Ni–Al2O3 nanocomposite coating served as a barrier layer during ultrasonic-assisted soldering AZ31 Mg/6061 Al using Sn–3.0Ag–0.5Cu solder. By investigating the impacts of Ni/Ni–Al2O3 composite coating on microstructure, intermetallic compounds formation, and joint performance, we found that the Ni coating partially inhibited Mg diffusion into the solder at 260 °C for 20 min, thus limiting excessive Mg2Sn compound formation and increasing shear strength by approximately 110% compared to uncoated joints. However, with an extension of the holding time to 30 min, block-shaped Mg2Sn compound reemerged as the primary cause of joint failure. Using Ni–Al2O3 composite coating further broadened the process window of Mg/Al soldering, eliminating block-shaped Mg2Sn compound in the joint at 260 °C for 40 min. The incorporation of Al2O3 further enhanced joint properties, with the maximum shear strength of the Mg(Ni–Al2O3)/SAC/Al joint reaching approximately 66.6 MPa, an improvement of 18.3% compared to the joint with Ni coating. This enhancement shifted the fracture position from the Ni/SAC interface to the SAC solder. Additionally, due to grain refinement in the Ni matrix, the microhardness of the Ni–Al2O3 composite coating surpassed that of the Ni coating. A model of Ni/Ni–Al2O3 composite coating preventing intermetallic compounds formation of was proposed. This nanocomposite coating-ultrasonic assisted soldering method effectively avoids the issue of excessive intermetallic compounds formation when joining dissimilar metals.

Microstructure Evolution and Deformation Behavior of High Strength Titanium Clad Steel Plate in the Thermal Compression

This research involves conducting unidirectional axial thermal compression experiments on high‐strength titanium‐clad steel plates (TCSPs) at different temperatures and strain rates. Thermally compressed samples are evaluated for macromorphology, microstructure, macroscopic texture, and dislocation density. Deformation consistency is observed in α‐titanium under certain conditions, but not in β‐titanium. Pearlite is the main deformation microstructure near the steel interface, expanding with temperature. Striped grain clusters are observed in the α‐titanium near the interface, enhancing deformation uniformity; furthermore, the prevalence of striped grains increases with higher strain rates. However, dynamic recrystallization in β‐titanium hinderes deformation consistency. The fiber presence of texture <111>//ND ensures consistent deformation consistency, whereas the plate texture {0001} <100> in the α‐titanium encourages it. During the deformation process at a consistent rate of strain, it is observed that both matrices initially exhibit a rise, followed by a decline in dislocation density as the temperature increases, peaking at 850 °C. Dislocation density rises as strain rate increases, while temperature remaines constant. At temperatures exceeding 850 °C, bonding strengths decrease with deformation rate and remain comparable. Bonding strengths decreases at 800 °C due to intermetallic compound formation.

Optimization of chemistry and process parameters for control of intermetallic formation in Mg sludges

Intermetallic formation in sludge during magnesium (Mg) melting, holding and high pressure die casting practices is a very important issue. But, very often it is overlooked by academia, original equipment manufacturers (OEM), metal ingot producers and even die casters. The aim of this study was to minimize the intermetallic formation in Mg sludge via the optimization of the chemistry and process parameters. The Al8Mn5 intermetallic particles were identified by the microstructure analysis based on the Al and Mn ratio. The design of experiment (DOE) technique, Taguchi method, was employed to minimize the intermetallic formation in the sludge of Mg alloys with various chemical compositions of Al, Mn, Fe, and different process parameters, holding temperature and holding time. The sludge yield (SY) and intermetallic size (IS) was selected as two responses. The optimum combination of the levels in terms of minimizing the intermetallic formation were 9 wt.% Al, 0.15 wt.%Mn, 0.001 wt.% (10 ppm) Fe, 690 °C for the holding temperature and holding at 30 mins for the holding time, respectively. The best combination for smallest intermetallic size were 9 wt.% Al, 0.15 wt.%Mn, 0.001 wt.% (10 ppm) Fe, 630 °C for the holding temperature and holding at 60 mins for the holding time, respectively. Three groups of sludge factors, Chemical Sludge (CSF), Physical Sludge (PSF) and Comprehensive Sludge Factors (and CPSF) were established for prediction of sludge yields and intermetallic sizes in Al-containing Mg alloys. The CPSF with five independent variables including both chemical elements and process parameters gave high accuracy in prediction, as the prediction of the PSF with only the two processing parameters of the melt holding temperature and time showed a relatively large deviation from the experimental data. The Chemical Sludge Factor was primarily designed for small ingot producers and die casters with a limited melting and holding capacity, of which process parameters could be fixed easily. The Physical Sludge Factor could be used for mass production with a single type of Mg alloy, in which the chemistry fluctuation might be negligible. In large Mg casting suppliers with multiple melting and holding furnaces and a number of Mg alloys in production, the Comprehensive Sludge Factor should be implemented to diminish the sludge formation.

The phases formed in Sn/Co thin bilayer upon heating

The structure and phases formed in Sn/Co thin films are interesting both from the solid-state chemistry point of view and due to applications of such a metallic bilayer. The phases forming in thin films Sn/Co obtained by thermal vacuum evaporation on two different substrates SiO2 and MgO(100) at different annealing temperatures have been studied. Annealing above 110°С results in intermetallics formation in the films. The hcp-cobalt is grown in the films on SiO2 substrate, and the fcc-Co is observed on MgO(100) substrate. It is found that the stable α-Co3Sn2 intermetallic is formed at higher annealing temperature in film on MgO(100) substrate. We show that transformations related to mass transfer in the Sn/Co bilayers were up to 500°С and were finished upon reaching the thermodynamically equilibrium phase composition at this temperature.

Al-Cu intermetallic phase growth in hybrid metal extrusion & bonding welds exposed to isothermal annealing or direct current cycling

Joining of aluminium (Al) to copper (Cu) is of great interest to power generation, transportation and electronic industry. However, dissimilar metal joining often promotes intermetallic phase formation at the joined interface, which in redundancy can cause mechanical degradation and increased electrical resistance. The welding technique hybrid metal extrusion & bonding (HYB) is proven capable of joining dissimilar metals with a total intermetallic phase layer thickness <▪. To test how Al-Cu HYB joints perform as electrical conductors, a 6101 Al alloy HYB-welded to Cu is exposed to heat treatment at ▪ or cycling of direct current density up to ▪. In-depth micro- and nanostructure characterisation by (scanning) transmission electron microscopy and atom probe tomography are used to describe the structure and chemistry of the formed intermetallic phases.The Al-Cu HYB joints exhibited resilience against intermetallic phase growth during isothermal heat treatment or exposure to electric current. However, a non-symmetry is observed dependent on the current direction, creating voids in Cu near, and in the intermetallic layers when the current goes from Al to Cu. Detailed microstructure characterisation unveils Si and Mg in the intermetallic phase layers. Their origin and role in intermetallic phase growth are discussed.