Evolution Of Intermetallic Compounds Research Articles

Modeling of temperature- and strain-driven intermetallic compound evolution in an Al–Mg system via a multiphase-field approach with application to refill friction stir spot welding

The prospect of joining dissimilar materials via solid-state processes presents an opportunity to obtain multi-material structures having a synergy of desirable properties of the joined materials. However, the issue of the formation of intermetallic compounds at the weld interface of dissimilar materials arises with that, depending upon the temperature and pressure conditions as per phase diagram. As the thickness of the intermetallic compounds may determine the mechanical properties of the joint, understanding the driving mechanisms and evolution of these intermetallic compounds in solid-state joining processes, such as refill friction stir spot welding (refill FSSW), is crucial. In this contribution, we account for the effect of different driving forces in a multiphase-field approach and investigate the evolution of the intermetallic compounds driven by chemical and mechanical forces. A finite-element simulation of the refill FSSW is pursued to obtain the peak temperature and strain at different locations of the weld interface. The microstructure simulations obtained via the multiphase-field model give insight into the morphology and kinetics evolution of the intermetallic compounds for both, the absence of strain (purely chemically-driven model) as well as presence of strain (chemo-mechanically-driven model). The consideration of strain proves to result in thicker intermetallic compound layer. Furthermore, the impact of interface energy and initial grain configuration is found to be significant on the overall intermetallic compounds evolution.

Investigation of phase equilibria of the Au–Ni–Sn ternary system and interfacial reactions in the Au/Sn/Ni/Cu multilayer couple

Au and Ni are widely used in the under-bump metallization, whereas Sn and Cu serve as common bonding materials and substrates, respectively. Solder joints consisting of an Au/Sn/Ni/Cu multilayer structure are widely found in the electronic packaging. Both phase equilibria of the Au–Ni–Sn ternary alloys and interfacial reactions of the Au/Sn/Ni/Cu multilayer structure were applied to the solid/solid-state reaction couple technique. The results showed that the Ni3Sn2 and AuSn4 phases respectively had a great solubility of the third element and the ternary AuNi2Sn4 phase existing in the Au–Ni–Sn ternary alloys was formed at 180 and 240 °C. The Sn/Ni/Cu multilayer structure was prepared by electroplating Sn/Ni layers on the Cu substrate. Afterward, the Sn/Ni/Cu multilayer and Au foil were screwed together to obtain the Au/Sn/Ni/Cu multilayer structure, followed by reactions at 150, 180 and 200 °C for different durations. The thickness of the intermetallic compounds (IMCs) increased with the increase in the reaction time and temperature. The IMC evolution in the couple remained unchanged at different temperatures. An increase in the reaction time converted the AuSn4 and AuSn2 phases to the AuSn phase. The voids formed in the couple were attributed to the volume shrinkage effect, which decreased with an increase in the reaction temperature. The (Ni, Au)3Sn2 phase was formed at the Ni side; the Ni layer functioned as an effective diffusion barrier to prevent the formation of the Cu–Sn IMCs.

Interfacial structures and mechanical properties of Cu/Sn/Cu containing SiC nanowires under transient liquid phase bonding

In order to achieve low-temperature bonding and high-temperature service, Cu/Sn/Cu and Cu/Sn-0.6SiC/Cu structure were fabricated by transient liquid phase (TLP) bonding, and the microstructure evolution of intermetallic compound (IMC) and mechanical performance of TLP bonding solder joints were investigated. The results demonstrated that the scalloped Cu6Sn5 IMC and lamellar Cu3Sn IMC formed at Sn/Cu interface gradually grew up in both solder joints as the bonding time increased. The asymmetrical growth of IMC was formed on both sides at TLP solder joints interface, whereas the interfacial IMC growth rate of Cu/Sn-0.6SiC/Cu was smaller than that of Cu/Sn/Cu solder. After TLP bonding for 120 min, Cu/Sn/Cu structure was composed of total Cu6Sn5 and Cu3Sn IMC and Cu/Sn-0.6SiC/Cu structure still contained remaining Sn phase. SiC nanowires (SiC NWs) dispersed in the solder matrix could impede the growth path between Sn and Cu, so SiC NWs doped to Sn solder could slow down the IMC growth. Moreover, introducing SiC NWs could promote the shear strength of composite solder compared with Sn solder joints during TLP bonding.

Microstructural evolution of intermetallic compounds between crystalline/amorphous Cobalt-Phosphorous coatings and lead-free solders

In the advanced microelectronic packaging, Cu/Sn joints require high-quality diffusion barriers to inhibit Cu–Sn intermetallic compounds (IMCs) growth and improve the interface brittleness. Cobalt-Phosphorous (Co–P) alloy coatings are ideal candidates due to their good wettability, promising diffusion resistance and low interfacial brittleness. In this work, the microstructural evolution of IMCs between crystalline/amorphous Co–P coatings and lead-free solders during the solid-state diffusion were systemically investigated. The microstructure, phase distribution, and grain characteristics of coatings and IMCs were carefully characterized by SEM, EPMA, EBSD, and TEM. It was found that the consumption rate of crystalline Co–P, 21.2 nm/h, was significantly slower than that of amorphous Co–P, 96.4 nm/h, and exhibited an excellent diffusion resistance, which was attributed to the nanocrystalline structure and the P-rich layer which performed the diffusion barriers for Sn and Cu atoms. Compared with Ni, amorphous Co–P coatings could better improve the interfacial brittleness with soft and ductile Co–Sn compounds (hardness of 3.0 GPa) growing with the rapid diffusion of Co, and the toughened Co–Sn–P attributing to the diffusion of Sn. Kinetic analysis showed that the growth rate-controlling process of Co–Sn IMCs was jointly controlled by interfacial reaction and volume diffusion, and the effect of the interfacial reaction is more pronounced in the amorphous system, which leads to coarse Co–Sn grains that are beneficial to the softness and ductility of IMCs. Crystalline and amorphous Co–P coatings can be applied to the surface treatment for die pads and print-circuit-board pads according to their own characteristics, respectively.

Effect of Holding Time on Bonding Strength and Joint Interface Microstructure of Vacuum Diffusion Bonded Dissimilar Austenitic Stainless Steel - Titanium Alloy Joints

In this investigation, the effect of holding time on the microstructure of joint interface and bonding strength of vacuum diffusion bonded dissimilar austenitic stainless (ASS) – titanium (Ti) alloy joints were investigated. The dissimilar joints of ASS - Ti alloy were developed using the holding time of 30, 45, 60, 75 and 90 minutes in a vacuum chamber at a temperature of 900⁰C and pressure of 14 MPa. The bonding strength of ASS – Ti alloy joints was evaluated using the ram tensile test. The microhardness survey was done perpendicular to the joint interface. The microstructure of the joint interface was analyzed using optical microscopy (OM). The evolution of intermetallic compounds at the joint interface was analyzed using X-ray diffraction (XRD). The microstructure of the joint interface was correlated to the bonding strength of joints.

Effects of temperature and strain rate on tensile properties of (Ag,Cu)-Sn intermetallic compounds: A molecular dynamics study

With the advent of environment friendly microelectronic packaging technologies, the demand of lead-free solders alloy has escalated. Leadfree solder material is an alloy of Tin (Sn), Silver (Ag) and Copper (Cu) and is widely known as SAC solder. Intermetallic compounds (IMC) like Ag3Sn, Cu3Sn and Cu6Sn5 are proven to adversely affect the mechanical properties of lead-free solder joints. This study presents the effects of temperature and strain rate on mechanical performances of these IMCs found in SAC solders. In addition, weakest and most sensitive IMC among these is detected. Modified embedded atom method potential parameters are used in LAMMPS to simulate the stress-strain behavior with deformation evolution of intermetallic compounds in different temperature and strain rates. The simulation was performed at 298 K–498 K with 50 K regular increment and at the strain rates of 108 s−1, 109 s−1, and 1010 s−1. Insight from this study suggest that the tensile properties of these IMCs increased with the increased in strain rates and decrease in temperature. Furthermore, the effect of temperature on tensile strength is observed to be higher at low strain rate whereas strain rate influence is lower at low temperatures. Among all the intermetallic, Ag3Sn exhibits lowest tensile properties with lowest stability, conversely Cu3Sn exhibits highest tensile properties with highest stability.

Microstructural evolution and mechanical properties of the Al–Cu dissimilar joint enhanced by stationary-dynamic shoulder friction stir welding

Material mixing and intermetallic compounds (IMCs) are the key factors that affect the mechanical properties of dissimilar metal joints. In this paper, a feasible method of stationary-dynamic shoulder friction stir welding has been developed, which reduces the mixing of materials and inhibit the growth of IMCs during the Al-Cu welding process. The stationary-dynamic shoulder was composed of a stationary shoulder with a larger diameter and a rotational shoulder with a smaller diameter. While the stationary shoulder provided the upsetting force to guarantee the weld formation, the rotational shoulder served for material stirring and heat input. Compared with conventional friction stir welding, the mechanical properties of joints obtained by the new method were significantly improved. The maximum tensile strength was 243 MPa, which was equivalent to 90 % of Cu base metal and 54 % of Al base metal. Furthermore, the evolution of IMCs across the transition layer was analyzed in depth. The results indicated that, with an increase in the rotation speed, the IMCs layer gradually became thicker. However, when the thickness reached a certain level, it promoted the generation of micro-cracks on IMCs and reduced the strength of the joint. According to thermodynamic and kinetic analysis, IMCs were formed with respect to Al2Cu-Al4Cu9 sequence, which was consistent with transmission electron microscopy results.

Evolution of interfacial IMCs and mechanical performance of joints of Mg/Al dissimilar metals soldered by using Ga-coating protection

The soldering of Al/Mg dissimilar metals by using Sn–9Zn solder at a low temperature of 230 °C was investigated. A liquid gallium layer was coated on the faying surface of the base metals to avoid secondary oxidation and contact between Mg and Sn-based filler metal before soldering. The growth and distribution of intermetallic compounds (IMCs) at the interface of Mg/solder was focused on. The interface was composed of scattered large and dense small blocky IMC layers. The discontinuous Mg2Sn layer was found to be the key factor dominating the mechanical performance of the joints. The highest shear strength of 38 MPa was reached at a reasonable holding time of ∼10 min. An over long holding time would cause the segregation of gallium which would deteriorate the water resistance of the joints.

Effects of interlayer metal on microstructures and mechanical properties of friction stir lap welded dissimilar joints of magnesium and aluminum alloys

The content of intermetallic compounds (IMCs) in friction stir lap welded (FSLW) dissimilar joints of Mg and Al alloys could be reduced by the addition of interlayer metal to improve the mechanical properties of the joints, while the underlying mechanism is still unclear. In this study, Cu and Ni powders are added as the interlayer materials into the FSLW joints of AZ31 Mg alloy and Al–Zn–Cu–Mg alloy, respectively. The types, sizes, and distributions of IMCs have been characterized, and the shear properties of the joints have been evaluated. Moreover, the mechanism underlying the influence of the interlayer metals on the evolution of IMCs in the joints and the effect of IMCs on the shear properties of the joints have been studied. The results showed that the order of phase formation in the joint without interlayer was Al12Mg17, Al3Mg2, MgZn2, CuMg2, Al2Cu, while the order of phase formation in the joint with added Cu interlayer was Al2Cu, CuMg2, AlCu, Al12Mg17, Al3Mg2, Cu5Zn8, and that in the joint with added Ni interlayer was Mg2Ni, Al3Ni, Al3Ni2, MgNi2, AlNi, Al12Mg17, Al3Mg2, MgZn2, Ni3Zn22, NiZn, Al2Cu. Due to the formed physical barrier and the mechanism of phase formation, the addition of interlayer metal effectively inhibited the formation of a Mg–Al phase. The bonding strengths between Mg–Cu, Al–Cu, Al–Ni, and Mg–Ni phases and matrix were higher than that between Mg–Al phase and matrix, which improved the shear properties of the joints with Cu and Ni interlayers.

Modeling of Temperature- and Strain-Driven Intermetallic Compound Evolution in an Al-Mg System Via a Multiphase-Field Approach with Application to Refill Friction Stir Spot Welding

Modeling of Temperature- and Strain-Driven Intermetallic Compound Evolution in an Al-Mg System Via a Multiphase-Field Approach with Application to Refill Friction Stir Spot Welding

The Evolution of Intermetallic Compounds in High-Entropy Alloys: From the Secondary Phase to the Main Phase

High-performance structural materials are critical to the development of transportation, energy, and aerospace. In recent years, newly developed high-entropy alloys with a single-phase solid-solution structure have attracted wide attention from researchers due to their excellent properties. However, this new material also has inevitable shortcomings, such as brittleness at ambient temperature and thermodynamic instability at high temperature. Efforts have been made to introduce a small number of intermetallic compounds into single-phase solid-solution high-entropy alloys as a secondary phase to their enhance properties. Various studies have suggested that the performance of high-entropy alloys can be improved by introducing more intermetallic compounds. At that point, researchers designed an intermetallic compound-strengthened high-entropy alloy, which introduced a massive intermetallic compound as a coherent strengthening phase to further strengthen the matrix of the high-entropy alloy. Inspired from this, Fantao obtained a new alloy—high-entropy intermetallics—by introducing different alloying elements to multi-principalize the material in a previous study. This new alloy treats the intermetallic compound as the main phase and has advantages of both structural and functional materials. It is expected to become a new generation of high-performance amphibious high-entropy materials across the field of structure and function. In this review, we first demonstrate the inevitability of intermetallic compounds in high-entropy alloys and explain the importance of intermetallic compounds in improving the properties of high-entropy alloys. Secondly, we introduce two new high-entropy alloys mainly from the aspects of composition design, structure, underlying mechanism, and performance. Lastly, the high-entropy materials containing intermetallic compound phases are summarized, which lays a theoretical foundation for the development of new advanced materials.

Microstructures evolution and growth kinetics of intermetallic compounds in Cu/Sn/Cu system during ultrasonic soldering process

PurposeThis study aims to investigate the effect of ultrasound on interfacial microstructures and growth kinetics of intermetallic compounds (IMCs) at different temperatures.Design/methodology/approachTo investigate the effect of ultrasound on IMCs growth quantitatively, the cross-sectional area of IMCs layers over a confirmed length was obtained for calculating the thickness of the IMCs layer.FindingsThe generation of dimensional difference in normal direction between Cu6Sn5 and its adjacent Cu6Sn5, formation of bossed Cu6Sn5 and non-interfacial Cu6Sn5 in ultrasonic solder joints made the interfacial Cu6Sn5 layer present a non-scallop-like morphology different from that of traditional solder joints. At 260°C and 290°C, the Cu3Sn layer presented a wave-like shape. In contrast, at 320°C, the Cu3Sn in ultrasonic solder joints consisted of non-interfacial Cu3Sn and interfacial Cu3Sn with a branch-like shape. The Cu6Sn5/Cu3Sn boundary and Cu3Sn/Cu interface presented a sawtooth-like shape under the effect of ultrasound. The predominant mechanism of ultrasonic-assisted growth of Cu6Sn5 growth at 260°C, 290°C and 320°C involved the grain boundary diffusion accompanied by grain coarsening. The Cu3Sn growth was controlled by volume diffusion during the ultrasonic soldering process at 260°C and 290°C. The diffusion mechanism of Cu3Sn growth transformed to grain boundary diffusion accompanied by grain coarsening when the ultrasonic soldering temperature was increased to 320°C.Originality/valueThe microstructural evolution and growth kinetics of IMCs in ultrasonically prepared ultrasonic solder joints at different temperatures have rarely been reported in previous studies. In this study, the effect of ultrasound on microstructural evolution and growth kinetics of IMCs was systematically investigated.

Interfacial microstructural characterization and mechanical properties of inertia friction welding of 2219 aluminum alloy to 304 stainless steel

Aluminum alloy/steel hybrid components are receiving more and more attention in recent years due to their great potential in reducing weight while maintaining the mechanical properties of the structure. Inertia friction welding was performed to join 2219 aluminum alloy (Al alloy) bar to 304 stainless steel bar. The effects of welding parameters on the evolution of intermetallic compounds (IMCs) and tensile strength of the joints were investigated. High-quality welded joints can be obtained at the parameters combination of the medium friction pressure (120 MPa) and low rotational speed (1100 rpm) from the experimental study. Microstructural analyses indicated that the enrichment of Cu element at the friction interface formed Al2Cu IMCs instead of Fe-Al IMCs, which was usually reported to exist at the Al alloy/steel friction welded interface. The formation of the Al2Cu IMCs layer was mainly attributed to the accumulation of Al2Cu (precipitate in 2219 Al alloy base metal) at the wavy surface of the steel, significantly promoting the growth of Al2Cu by the subsequent precipitation process. However, cracks could easily occur in a thicker Al2Cu IMCs layer at a high heat input, which seriously deteriorated the mechanical properties of joints. Therefore, the massive formation of the Al2Cu IMCs layer should be suppressed by controlling the welding parameters to avoid any internal cracks at the weld interface.

Interfacial IMC evolution and shear strength of MWCNTs-reinforced Sn–5Sb composite solder joints: Experimental characterization and artificial neural network modelling

Abstract The continuous miniaturization of electronic products and the constantly rising functionality demand by final users necessitate major challenges for the academia and the industry to produce reliable lead-free solders for long-term service. In the present study, an analysis on the influence of MWCNTs (multi-walled carbon nanotubes) on the interfacial IMC (intermetallic compound) evolution and shear strength of Sn–5Sb solder joint was performed. The composite solder joint samples were developed through the reflow soldering process and thereafter subjected to isothermal aging at different temperatures (120 °C, 150 °C and 170 °C). Given the promising properties of MWCNTs, empirical findings showed that inhibited interfacial IMC evolution and enhanced shear strength were markedly achieved due to the presence of MWNCTs in the Sn–5Sb solder alloy. Artificial neural network (ANN) model was developed by making use of the experimental data to characterize the composite solder joints. Various influential parameters that affect the thickness of the IMC layer and the shear strength performance of the composite solder joints including the MWCNTs content, aging temperature and aging time were considered as the input parameters for the ANN model. Having used the statistical parameters such as the coefficient of determination (R2) and root mean square error (RMSE) to evaluate the model, the ANN model developed in this study adequately predicted the IMC layer thickness (R2 = 0.9913; RMSE = 0.0234) and shear strength (R2 = 0.9798; RMSE = 0.0314) of the composite solder joints.

Stabilized Interfacial Intermetallic Compound Evolution in Ni-Coated Carbon Fiber Reinforced Sn-3.5Ag Composite Solder Joint

Stabilized Interfacial Intermetallic Compound Evolution in Ni-Coated Carbon Fiber Reinforced Sn-3.5Ag Composite Solder Joint

Multiphase-field modeling of temperature-driven intermetallic compound evolution in an Al–Mg system for application to solid-state joining processes

Solid-state joining of dissimilar materials results typically in the formation of intermetallic compounds at the weld interface, which strongly determines the resulting mechanical properties. To tailor the joint strength, understanding of the formation of the intermetallic compound and their driving mechanisms is crucial. In this study, the evolution of temperature-driven Al3Mg2 and Al12Mg17 intermetallic compounds in an Al–Mg system for application to solid-state joining processes via a multiphase-field approach is numerically investigated. To this end, the CALPHAD approach to obtain the thermodynamic parameters of the relevant phases is used in conjunction with the multiphase-field model. The simulation results are qualitatively compared with experimental results in the literature in terms of thickness and morphology of intermetallic grains, exhibiting a reasonable agreement. The influence of grain boundary diffusion and interface energy on the morphology and kinetics of the intermetallic compound grains is investigated in detail with the established multiphase-field model.

Investigation of Interfacial Layer for Friction Stir Welded AA7075-T6 Aluminum to DP1180 Steel Joints

Abstract Interfacial layers greatly influence the performance of steel–aluminum friction stir welding (FSW) joints, and understanding the formation and evolution of intermetallic compounds (IMC) can help improve the mechanical properties of the welds. In this study, FSW was used to join DP 1180 high-strength steel to 7075 Al at different welding speeds. The effect of the galvanized layer on the IMC formation and evolution, and the mechanical performance of the steel–Al FSW joints were investigated. It was found that the galvanized steel–Al joints were formed only by metallurgical bonding, a continuous IMC layer composed of FeAl, Fe3Al, and Al–Zn eutectic developed at the joint interfaces. Joints were mechanically and metallurgically bonded in the non-galvanized steel, and a 3 µm thick IMC layer consisting of FeAl existed only in the stir zone (SZ). IMC layer formation was predicted according to thermodynamic principles, which is consistent with the interfacial microstructure evolution identified by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Shear tensile test results showed that the galvanized layer can effectively improve the metallurgical bonding strength of the steel–Al joints, and the optimum tensile properties were found in galvanized steel–Al joints.

Four dimensional (4D) microstructural evolution of Cu6Sn5 intermetallic and voids under electromigration in bi-crystal pure Sn solder joints

Electromigration (EM) causes intermetallic and void growth that decreases the reliability and lifetime of solder joints. As a diffusion-controlled process, EM is highly dependent on the fastest diffusion pathways in a structure. In anisotropic β-tetragonal Sn those pathways are along high angle grain boundaries and along the c-axis of the Sn grains. A bicrystal sample with two major grain orientations and two major grain boundary types was EM tested for 100 h. EM was interrupted at intervals for x-ray microtomography to reveal the 3D evolution of intermetallic compounds (IMCs) and voids within the joint. Quantitative IMC growth along high angle grain boundaries and twins was captured for the first time and related to the effective Cu diffusivity of multiple grains. Using a correlative approach that combined scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) mapping, IMC growth and morphology were linked to the evolution of the Sn grain structure. Unusual void shrinkage and void splitting behavior were connected to uneven cathode interface consumption and thermal compression.

Microstructure evolution and mechanical properties of ultrasonically TLP bonded Mg joint

AZ31B Mg alloys were joined with a pure Zn interlayer via ultrasonic-assisted transient liquid phase bonding. The formation and evolution of intermetallic compounds (IMCs) and the mechanical properties of the bonded joints were investigated. Results showed that joints could form within an extra short time of 0.1 s via eutectic reaction, eutectoid reaction and diffusion bonding. Mg-Zn eutectoid structures, IMCs of MgZn and MgZn2 formed inside the bonded joint. The width of the MgZn2 phase decreased with prolonged ultrasonication time, high ultrasonication power, and sonotrode pressure. The entire joint was characterized by eutectoid structures without MgZn2 at a high sonotrode pressure of 0.4 MPa. MgZn2 had a higher hardness and modulus than MgZn, Mg-Zn eutectoid structure, and Mg substrate. Joints fractured through the MgZn2 phase and eutectoid structure had shear strength values of 30 and 40 MPa, respectively.

Effect of Annealing on the Interface and Mechanical Properties of Cu-Al-Cu Laminated Composite Prepared with Cold Rolling.

Cu-Al-Cu laminated composite was prepared with cold roll bonding process and annealing was carried out to study the phase evolution during the annealing process and its effect on the mechanical properties of the composite. The experimental results showed that after annealing the brittle intermetallics in the interface mainly includes Al4Cu9, AlCu and Al2Cu. With the increase of annealing temperature, the tensile strength of the composite decreases and the elongation shows a different variation which increases at the beginning and then decreases after a critical point. This phenomenon is related to the evolution of intermetallic compounds in the interface of the composite. It was also found that the crack source of the tensile sample is in the interface and delamination appeared at high annealing temperature (450 °C).