Intermetallic Compound Phase Research Articles

Enhancement of the Al/Mg Dissimilar Friction Stir Welding Joint Strength with the Assistance of Ultrasonic Vibration

The assistance of ultrasonic vibration during the friction stir welding (FSW) process has been verified as an effective approach for the improvement of joint strength. In the present study, experimentation on Al/Mg dissimilar alloys in butt joint configuration is implemented by employing FSW with and without the assistance of ultrasonic vibration. An optimized tool shoulder diameter of 12 mm is utilized, and the ultrasonic vibration is applied perpendicularly onto the tool along the welding direction, which is named UVaFSW. The results of joint appearance and macrostructure, characteristics of the intermetallic compounds (IMCs), as well as joint strength and fracture appearance are compared between Al/Mg FSW joints with and without ultrasonic vibration. It is demonstrated that the material intermixing between Al and Mg alloys is substantially strengthened in the UVaFSW joint compared with that in the FSW joint. Additionally, the ultrasonic vibration can be beneficial for the reduction of IMC thickness, as well as the formation of intermittently distributed IMC phases at the Al–Mg bonding interface. Consequently, the mechanical properties of Al/Mg FSW joints are significantly improved with the assistance of ultrasonic vibration. The maximum ultimate tensile strength is 206 MPa at tool rotation speed of 800 rpm and welding speed of 50 mm/min for the Al/Mg UVaFSW joint.

Microstructure evolution and mechanical properties in an ultralight Mg-2.76Li–3Al-2.6Zn-0.39Y alloy

A novel Mg-2.76Li–3Al-2.6Zn-0.39Y alloy was prepared by multidirectional forging (MDF) and rolling (R) to improve strength and ductility, and its microstructural evolution and mechanical properties were investigated by an optical microscope, X-ray diffraction (XRD), transmission electron microscope (TEM), and tensile tester. After MDFR, the ultimate tensile strength was 275 ± 8 MPa, the yield strength was 207 ± 7 MPa, and the elongation was 29% at a grain size of 6.8 ± 1.1 μm. The specific modulus of this alloy was 30.04 MN m kg−1, and the specific strength was 183.58 kN m kg−1. Microstructural examination of decreased-temperature MDF revealed the presence of a bimodal microstructure, which is favorable for the enhancement of both strength and ductility. The deformation mechanisms of MDF are intense mechanically shearing fragmentation and incomplete dynamic recrystallization. XRD analysis revealed that the present alloy consists of α(Mg) phase, and Al2Y, Mg17(Al,Zn)12, Mg2Y, and AlLi intermetallic compounds. TEM analysis confirmed the existence of Mg17(Al,Zn)12 compound and dislocation wall and pile-up. Portevin–Le Chatelier (PLC) effect or serrated flow was discovered in this alloy. The relationship between the break-away stress and the experimental stress was proposed as a criterion for judging the occurrence of the PLC effect. The estimated stress is consistent with the experimental stress. The contributions of different strengthening mechanisms to tensile yield strength were estimated. The estimated tensile yield strength is in good agreement with the experimental tensile yield strength.

Residual stress induced failure of Ti-6Al-4V/Si3N4 joints brazed with Ag-Cu-Ti filler: The effects of brazing zone’s elasto-plasticity and ceramics' intrinsic properties

The residual-stress induced failure of Ti-6Al-4V/Si3N4 joints brazed with two different Si3N4 ceramics possessing different intrinsic properties was elucidated through experimental and finite-element (FE) thermo-mechanical simulations incorporating the local elasto-plastic properties of the as-received Ag-Cu-Ti filler and the brazing zone characterized by nano-indentation. All tested joints fractured mainly from the ceramics due to residual stress, and their bending strengths increased when using Si3N4 ceramics of higher intrinsic strength. FE-analysis based on the as-received filler’s properties overestimated the nominal bending strengths by approximately 100 MPa in both joints; nano-indentation revealed that the depletion of ductile Ag-Cu phase and growth of hard Cu-Ti intermetallic compounds reduced the plastically deformable thickness after being brazed, whereby they resulted in higher residual stress in the ceramics. Finally, the validity of FE-estimated bending strengths was enhanced when considering the effective plastically deformable thickness of filler (30 μm) instead of the as-received state (50 μm).

Continuous hot corrosion behaviour of an FeCrAlSi coating prepared by laser cladding

FeCrAlSi coatings were prepared using laser cladding technology and subjected to a continuous hot corrosion test in a eutectic 75 wt% Na2SO4 + 25 wt% K2SO4 salt at 800 °C in air. The FeCrAlSi coating consists of mainly the FeCr solid solution, AlFe intermetallic compound and little FeAl2 phase, and the microhardness and tribological properties improved over those of the untreated substrate. In the earliest stage of hot corrosion, a protective Al2O3 film is formed. During the subsequent hot corrosion process, the O2− concentration gradually increases. The alkalinity of the molten salt/coating interface then increases to the level at which it reacts with Al2O3, and the newly formed porous Al2O3 film is less protective. In the mid-stage of hot corrosion, Cr continues to diffuse upward through the porous Al2O3 film, and petal-like Cr2O3 forms on the pores, gradually forming a continuous Cr2O3 film. In the subsequent hot corrosion process, the internal oxidation of the Al intensifies, and the phenomenon of Al2O3 phase diffusing into the interior is more obvious. In the last stage of hot corrosion, the SiO2 film exists in the internal corrosion layer, which is passivated in the molten sulphate. Additionally, Al2O3 no longer penetrates the coating, thus forming a protective oxidation film with the (Cr, Fe)2O3 + Al2O3 in the external corrosion layer, which effectively slows oxidation and sulphuration reactions.

Experimental investigation and thermodynamic assessment of phase equilibria in the Cr-Re-Ru ternary system

The phase equilibria of the Cr-Re-Ru ternary system at 1100 °C and 1200 °C have been experimentally investigated using electron probe microanalyzer and X-ray diffraction. The σ1-Cr2Re3 and σ2-Cr2Ru phases with the same D8b crystal structure do not form a continuous intermetallic compound phase at 1100 °C and 1200 °C in the Cr-Re-Ru ternary system confirmed by experimental results. According to the experimental results in this work, the Cr-Re-Ru ternary system has been assessed by means of the CALPHAD (CALculation of PHAse Diagrams) method. The calculated isothermal section at 1400 °C shows that the two independent phases σ1-Cr2Re3 and σ2-Cr2Ru are replaced by the continuous intermetallic compound σ. The current established thermodynamic database of the Cr-Re-Ru ternary system may provide the essential information, and support for the thermodynamic assessment of multicomponent system and the development of Ni-based superalloys.

Investigation on Laser Welding of Al Ribbon to Cu Sheet: Weldability, Microstructure, and Mechanical and Electrical Properties

The pulsed laser welding of Al ribbon to Cu sheet was investigated for the electrical interconnections in power electronic modules. The various experimental conditions with the different laser powers, scan speeds, and heat inputs were employed for obtaining the defect-free Al/Cu joints. During the Al/Cu laser welding, the intermetallic compounds were formed in the welding zone. An electron probe microanalyzer and transmission electron microscopy confirmed the phases of intermetallic compounds, which were found to be Al4Cu9, Al2Cu, AlCu, etc. The computational fluid dynamics simulation revealed that the Marangoni effect induced the circulation of the molten pool, resulting in the mixture of Al and Cu and the formation of swirl-like structures at the Al/Cu joints. The tensile shear strengths and electrical resistances of the Al/Cu joints were measured, and they showed a strong correlation with the welding area. A decrease in mechanical strength and an increase in electrical resistance were measured with increasing the welding area of Al/Cu joints. Moreover, the process window for the defect-free Al/Cu joints was developed, and the experimental conditions for Al/Cu laser braze-welding were examined to minimize the intermetallic compounds formation at the Al/Cu joints.

Investigation on peritectic solidification in Sn-Ni peritectic alloys through in-situ observation

The solidification of Sn-Ni peritectic alloys in which both the primary Ni3Sn2 and peritectic Ni3Sn4 phases were intermetallic compound phases (IMCs) with narrow solubility ranges was investigated through confocal laser scanning microscope. Analysis on the interface migration at different cooling rates shows that the rate of peritectic reaction is much smaller than previous reports, and the growth of peritectic phase is mainly attributed to direct precipitation from the melt in Sn-Ni alloy after peritectic reaction. In addition, different from other peritectic alloys where the solidified phases are solid solution phases, the "step" growth of both Ni3Sn2 and Ni3Sn4 phases was observed. The dependences of the step thickness on both the cooling rate and solidification time were measured, which shows that the step thicknesses of both phases gradually decrease as solidification proceeds. This was confirmed to be attributed to the difference between the actual and equilibrium melt concentrations during solidification. In addition, the increase of the normal growth velocity of Ni3Sn4 phase with increasing cooling rate was also proved through both the experimental observation and quantitative prediction.

Designing AlCoCrFeNiTi high-entropy alloy with the directional array TiN by magnetic field-assisted laser cladding

The directional array TiN-reinforced AlCoCrFeNiTi high-entropy alloy (HEA) coatings were successfully synthesized by magnetic field-assisted laser cladding on Ti-6Al-4V (TC4) alloy. The effect of magnetic induction intensity of AlCoCrFeNiTi HEA coatings was investigated methodically on thermodynamic calculation, microstructure characterization and corrosion resistance. The results show HEA coatings are mainly composed of body-centered cubic (BCC) solid solution phase, (Ni, Co)Ti2 intermetallic compound and TiN ceramic phase. With 1 T magnetic induction intensity assisted laser cladding, the microstructures of in situ TiN display a "cross" shape of the directional array. In 3.5 wt.% NaCl solution, the 1 T HEA coating could significantly decrease the corrosion rate compared with TC4 alloy.

Thermal expansion and thermal conductivity of RT 2 (R: Gd, Dy, Er; T: Al, Ni) intermetallic compounds for magnetic refrigerator

Highly efficient hydrogen liquefaction is required for upcoming hydrogen energy society. Magnetic refrigeration is expected as a method to realize efficient hydrogen liquefaction, and the performance depends on properties of magnetic materials. RT 2 (R: rare-earth; T: Al, Ni) Laves phase intermetallic compounds with a second-order magnetic phase transition are one of the promising magnetocaloric materials. Thermal expansion, magnetostriction, and thermal conductivity of ErAl2, DyNi2, DyAl2 and GdNi2 were measured in magnetic fields using polycrystalline samples because of the important properties for practical use in a magnetic refrigerator. Thermal expansions showed anomalies at the magnetic transition temperature. However, those in 0 T were nearly the same as copper. Magnetostriction were not as large as magnetocaloric materials with a first-order magnetic phase transition such as TbMn2. Thermal conductivities in 0 T were almost in agreement with the literature data, and magnetic field dependence was small. These results indicate that RT 2 compounds are suitable as magnetic refrigerants for hydrogen liquefaction in practical use.

Growth velocity and microhardness dependences of intermetallic compound phases on solubility range during peritectic solidification

It is well known that the growth of solid phases are determined by both the external solidification growth conditions and the solidification characteristics of themselves. The growth of intermetallic compound phases (IMCs) has been analyzed in two peritectic systems containing IMCs: Sn-Ni and Sn-Mn through secondary dendrite, indicating that the solidification characteristics of them are closely related to the growth of IMCs in these alloys. However, the relationship between the solidification characteristics of IMCs and the growth of secondary branch has not been discussed yet. The IMCs can be classified to be different types according to whether their solubility ranges are nil. Thus, the solubility ranges of IMCs are chosen as the representative solidification characteristics. In this work, through a morphology parameter φ characterizing the morphology of secondary branch, the quantitative relationship between the growth behaviors of secondary dendrite arm of IMCs and their solubility ranges has been established. Comparison in both the theoretical prediction of this work and the experimental measurement between these two peritectic systems demonstrated that the solid phases whose solubility range are larger should have a larger growth velocity vtip of secondary branch in the same growth conditions. In addition, the growth-dependent microhardness of the intermetallic compound phases were investigated, which also shows that the microhardness of intermetallic compound phases are also dependent on the growth velocity, thus the solubility range of themselves. It is commonly assumed that the microhardness of the solidified phase is nearly constant in steady state directional solidification. However, the microhardness of the IMCs at the tips of secondary branches gradually decrease during directional solidification, which is consistent with the gradual reduction in vtip. In addition, the variation of the microhardness is more obvious in IMC with larger solubility range.

Transient solid-liquid interfacial reaction between Al wire and Au/Cu pad during parallel gap micro-resistance welding

Reliable bonding of thick Al wires and plated Au pad is important for the packaging of power modules. The interfacial phases of the Al/Au/Cu joint after parallel gap micro-resistance welding were observed by transmission electron microscopy (TEM). Obvious Al, Au and Cu elemental interdiffusion can be observed by energy dispersive spectrometer (EDS) mapping, indicating the occurring of sufficient interfacial reaction. Under the effect of current and heat, the core temperature is higher than the melting point of Al. Liquid Al will react with Au and (Au, Cu) Al2 intermetallic compound (IMC) phase was formed rapidly within 20 ms. Besides, excessive Al atoms rapidly diffuse through the Cu-based solid solution, and react with Cu forming (Cu, Au) Al4 IMC phase.

Influence of porous Cu interlayer on the intermetallic compound layer and shear strength of MWCNT-reinforced SAC 305 composite solder joints

In this study, the synergetic effect of multi-walled carbon nanotubes (MWCNTs) and porous Cu interlayer (PCI) on the intermetallic compound (IMC) formation and shear strength of Sn–3.0Ag–0.5Cu (SAC 305) solder system was investigated. The solder joints were prepared by subjecting two different series of MWCNTs-reinforced SAC 305 solder systems (i.e., SAC–0.01CNT and SAC–0.04CNT) sandwiched with porous Cu interlayer having pores per inch (PPI) of 15, 25 and 50 to reflow soldering on Cu substrate. Electron microscopy and spectroscopy techniques were used to view and detect the intermetallic compound phases, respectively. The scallop-shaped Cu6Sn5 IMC phase was observed at the solder/PCI interface, while on the other hand, an additional layer-type Cu3Sn IMC phase formed alongside the Cu6Sn5 IMC at the solder/Cu interface. Given the promising properties of PCI material, empirical findings showed that the presence of PCI in the solder joint inhibited the formation of interfacial IMC layer at the solder/Cu substrate with the SAC–0.01CNT–25PCI exhibiting the least IMC thickness. More so, the PCI material effectively enhanced the shear strength of the MWCNTs-reinforced composite solder joints. Generally, the strengthening capacity of the PCI material was greatly underscored in the SAC–0.01CNT–xPCI series with the sample prepared with PCI of 15 PPI demonstrating the superior shear strength of 21.1 MPa.

First principles study on interface optimization mechanism of Cu-Al composite plate and strip by vibration cast-rolling technology

ABSTRACT Cu-Al composites have an important industrial prospect due to their excellent properties. The interface layer of Cu-Al composites has always been a key factor affecting its performance. Vibration cast-rolling process was independently developed to improve the interface properties of Cu-Al laminated composites. A pilot-scale experiment of solid-liquid composite of Cu-Al was carried out on a self-made vibration cast-rolling pilot test platform. The interface was observed by scanning electron microscope (SEM), and the phase of the interface was analyzed by X-ray diffraction (XRD). Based on the experimental results, a cell model of intermetallic compounds was established, and the mechanical and electronic properties of intermetallic compounds were calculated by first principles to explore the optimization mechanism. The results show that vibration can improve the comprehensive properties of Cu-Al composite plate interface, which can be attributed to the change of intermetallic compound phase and proportion.

Study on corrosion behavior of β-Sn and intermetallic compounds phases in SAC305 alloy by in-situ EC-AFM and first-principles calculation

This work studies the corrosion behavior of β-Sn and intermetallic compounds (IMCs) in Sn96.5Ag3.0Cu0.5 (SAC305) alloy through micro-structure observation, in-situ electrochemical technique and first-principles calculation. The results show that corrosion behavior of SAC305 is affected by galvanic corrosion, electronic structure and material microstructure. The Volta potential difference between Cu6Sn5, Ag3Sn and Sn is up to 234 and 174 mV. The length percentage of high angle grain boundaries (HAGBs) for β-Sn and eutectic phase is 11.61 % and 35.18 %. The calculated electronic density of state explains the corrosion behavior of SAC305 from corrosion kinetics perspective. The corresponding corrosion failure mechanism is proposed.

Study of electromigration in Sn-Ag-Cu micro solder joint with Ni interfacial layer

This paper reports the extreme sensitivity of the microstructure evolution in Sn-Ag-Cu (SAC) micro-solder joint, consisting of 15–20 µm thick solder alloy and electrolytic Ni plated Cu electrodes, to electromigration (EM) conditions resulting from a kinetic competition between the growth of Ni3Sn4 intermetallic compound (IMC) and EM of Sn in solder matrix. Microstructural analysis of samples tested at various conditions reveals that the voiding in the solder joint develops to the full extent only when the EM rate of Sn in the solder alloy is sufficiently greater than the growth rate of Ni3Sn4 IMC because the IMC phase is EM-inactive. The decisive evidence for such behavior is found from the samples tested at 160 and 170 °C under 35 kA/cm2. The samples tested at 170 °C show the classic solder joint microstructure that typically develops under the influence of EM, that is the exaggerated growth of Ni3Sn4 at the anode as a result of Ni-EM and voids at the cathode interface of the joint as a result of Sn-EM. Contrarily, such characteristic features are not found in samples tested at 160 °C, instead, the joint is fully converted to Ni3Sn4 without sign of its biased growth and voiding activities. The near absence of biased EM microstructure at 160 °C is believed to result from the stress-gradient developed by Sn EM counteracting the EM force on Ni. No such effect is at work at higher temperatures due to the significantly higher initial Sn EM rate which leads to voids and reduces the stress gradient.

Microstructural Assessment of a Multiple-Intermetallic-Strengthened Aluminum Alloy Produced from Gas-Atomized Powder by Hot Extrusion and Friction Extrusion.

An aluminum (Al) matrix with various transition metal (TM) additions is an effective alloying approach for developing high-specific-strength materials for use at elevated temperatures. Conventional fabrication processes such as casting or fusion-related methods are not capable of producing Al–TM alloys in bulk form. Solid phase processing techniques, such as extrusion, have been shown to maintain the microstructure of Al–TM alloys. In this study, extrusions are fabricated from gas-atomized aluminum powders (≈100–400 µm) that contain 12.4 wt % TM additives and an Al-based matrix reinforced by various Al–Fe–Cr–Ti intermetallic compounds (IMCs). Two different extrusion techniques, conventional hot extrusion and friction extrusion, are compared using fabricating rods. During extrusion, the strengthening IMC phases were extensively refined as a result of severe plastic deformation. Furthermore, the quasicrystal approximant IMC phase (70.4 wt % Al, 20.4 wt % Fe, 8.7 wt % Cr, 0.6 wt % Ti) observed in the powder precursor is replaced by new IMC phases such as Al3.2Fe and Al45Cr7-type IMCs. The Al3Ti-type IMC phase is partially dissolved into the Al matrix during extrusion. The combination of linear and rotational shear in the friction extrusion process caused severe deformation in the powders, which allowed for a higher extrusion ratio, eliminated linear voids, and resulted in higher ductility while maintaining strength comparable to that resulting from hot extrusion. Results from equilibrium thermodynamic calculations show that the strengthening IMC phases are stable at elevated temperatures (up to ≈ 600 °C), thus enhancing the high-temperature strength of the extrudates.

Effect of laser remelting on microstructure and properties of two Ni-base coatings by supersonic particles deposition

Remelting treatment of In718 and In625 coatings deposited by supersonic particles were conducted by using laser technology. The microstructure, phase composition, microhardness, wear resistance and corrosion of the coating before and after remelting were studied. The results showed that defects such as voids and cracks of the deposited coating were eliminated by laser remelting treatment, the microstructure of the coating became compact and uniform and the bonding mode changed from mechanical bonding to metallurgical bonding. The deposited coating consisted of γ-Ni solid solution and Fe3Ni2 intermetallic compound phase, remelting to form a new phase Ni3(Al,Ti) and high hard phase carbide (Nb,Mo) C. The average microhardness of the remelted coating was 6.96 GPa, which was 1.72 times than that of the deposited coating. The wear resistance of remelting coating was significantly better than that of deposited coating and substrate, and its wear form was mainly abrasive wear. The corrosion resistance of the coating was significantly improved after remelting treatment.

Tensile resistance, microstructures of intermetallic compounds, and fracture modes of welded steel/aluminum joints produced using laser lap welding

Abstract The joining of DP780 steel to Al5052 was conducted by laser lap welding, in which the metal vapor and spatters were monitored by a high-speed camera. A universal testing machine was used to test the mechanical properties of the welded joints, and the changing law of lap tensile resistance with the laser welding parameters was analyzed. Optical microscope and scanning electron microscope were used to observe the macro-structure and micro-structure, respectively. Three different intermetallic compounds (IMCs) phases, i.e. banded Fe2Al5, FeAl2 and needle-like FeAl3 were generated at the steel/Al interface on microscopic observation. The aim of this research is to investigate the relationship among the lap tensile resistance, the welding parameters and the failure mode under different energy densities. Experimental results showed that the steel/Al joints have two different fracture modes at low heat input and high heat input. The failures happened along the heat-affected zone of the weld and along the steel/Al joint interface, respectively. And both of the two failure modes are brittle fractures. Additionally, cracks appeared at the fracture interface, and needle-like particle clusters were found in the fracture microstructure.

Experimental determination of phase diagram at 450 °C in the Zn–Fe–Al ternary system

Phase equilibria in multi-phase Zn–Fe–Al alloys were experimentally measured using a field-emission electron probe micro-analyzer for alloy samples, and a precise iso-thermal phase diagram at 450 °C in the entire composition range of the Zn–Fe–Al ternary system, except for the Fe-rich corner, was determined. The ternary solubility ranges of the Γ-Fe4Zn9, Γ1-Fe21.2Zn80.8, δ1k-FeZn7, and ζ-FeZn13 on the Fe–Zn side and of the ζ-FeAl2, η-Fe2Al5, and θ-Fe4Al13 on the Fe–Al side were consistent with the latest corresponding binary data, whereas no δ1p-Fe13Zn126 phase was detected. The single-phase region of the Γ2-Fe8Zn87Al4 ternary intermetallic compound phase is significantly narrower than that reported in the previous studies. The solubility of Fe in the liquid phase increased consistently and continuously from the value in the Zn–Fe binary system (0.6 at.%) up to 1.2 at.% at 31 at.% Al with increasing Al content. In the Al-rich portion of the phase diagram at 450 °C, the Fe(Al, Zn)6 intermetallic compound phase was newly discovered, and confirmed to be an isomorph extended from the FeAl6 phase which is metastable in the Fe–Al binary system.

Intermetallic Diminution During Friction Stir Welding of Dissimilar Al/Mg Alloys in Lap Configuration Via Ultrasonic Assistance

This study shows the influence of ultrasonic vibrations on the nature and thickness of intermetallic compounds (IMCs) and the correlation with the weld shear load. An ultrasonic vibration assembly comprised of novel horn attachments and a special welding tool has been developed to impart a thermomechanical-acoustic effect on the stirred zone (SZ). The IMC analysis is made at the SZ and interfaces to portray a complete scenario of their formation mechanism. The outcomes depict a complete elimination of harmful IMC phase Al3Mg2 (β) and the shrinkage of Al12Mg17 (γ) at acoustically treated regions under the optimum parameters. The aforesaid evidence is further supported by elemental mapping, energy-dispersive X-ray spectrometry, and diffraction pattern analysis. With ultrasonic assistance, a maximum reduction in IMC layer thickness up to 56.5 pct has been achieved. The weld shear load and joint efficiency are increased by 26.1 and 26.1 pct, respectively, during the ultrasonic addition. The acoustic assistance helps diminish the IMC thickness, while the morphology and mechanism of their formation remain the same.