Ag-Cu Eutectic Alloy Research Articles

Oxygen adsorption of molten Ag[sbnd]Cu eutectic alloy and its associated surface modification

The surface tension of liquid AgCu eutectic alloy has been measured in a wide range of oxygen partial pressures using two different methods: the constrained drop method and the electromagnetic levitation method. In order to investigate the influence of oxygen potential on the surface tension of the Ag40Cu (at.%) eutectic alloy, the oxygen partial pressure was varied between 8.62 × 10−15 and 2.42 Pa. At low oxygen partial pressure, the surface tension of the AgCu eutectic alloy measured in the temperature range of 1223–1476 K, shows temperature dependence in a good agreement with previously reported results. At higher oxygen partial pressures, the decrease in surface tension is more pronounced and the oxygen adsorption on the surface accordingly increases. Moreover, at high oxygen partial pressure, the oxygen adsorption on the AgCu eutectic alloy was found to be far greater than the expected saturation limit taking into account the theoretically calculated surface concentration of Cu in the AgCu eutectic alloy and the surface excess of oxygen on the molten Cu at saturation. This phenomenon can be explained with a model where the surface of the AgCu eutectic alloy undergoes Cu-substitution at the Ag sites during the oxygen adsorption process.

Vacuum brazing ZSCf composite ceramics to TC4 alloy with Ag-Cu filler

In this study, the carbon fiber reinforced ZrB2-SiC composite ceramic was joined to Ti6Al4V alloy with Ag-Cu eutectic alloy filler at varied holding time and a fixed temperature of 800℃. Interface microstructure and shear strength of brazing joints were studied. The brazed ZSCf ceramics/AgCu/TC4 alloy is endowed with good metallurgical bondings. A typical interfacial structure of joints brazed for 10min was found as ZSCf/TiC/Ti5Si3/Ag(s,s)/Cu(s,s)+TiC/TiCu/Ti2Cu/(TiC+TiCu)/TC4 alloy. Increase of holding time did not vary the precipitated phase of the joints but decreased thickness of the Ag(s, s) and Cu(s, s) reaction layer and gradually thickened the Ti-Cu reaction layer near the TC4 side. The formation process of reaction products was discussed in detail. The holding time substantially influenced shear strength of the joints. A maximum shear strength of 39MPa was reached at a brazing time of 20min.

Effect of Heterophase Interfaces on Microstructure and Crystallographic Texture Evolution During Rolling of Directionally Solidified Ag-Cu Eutectic Alloy

A directionally solidified Ag-Cu eutectic alloy was deformed by rolling to understand the role of heterophase interfaces on the deformation behavior of ultrafine and nanocrystalline face-centred cubic metals. During rolling, the initial 〈220〉 fibre texture was gradually shifted to a Brass type texture for both Ag and Cu phases. More interestingly, a similar path of texture evolution was observed for both the phases at all strain levels. The in-depth transmission electron microscopy analysis revealed that the Ag lamellae deformed primarily by twinning, while the Cu lamellae deformed by twinning and dislocation slip. Furthermore, the special cube-on-cube and twin heterophase interfaces facilitated co-deformation and co-rotation of the adjacent Ag and Cu lamella due to a strong latent hardening effect, which stimulated a similar texture evolution for both phases.

Investigation of the origin of anomalous eutectic formation by remelting thin-gauge samples of an Ag-Cu eutectic alloy

Sandwiched between two fused silica blocks, thin-gauge samples of Ag-39.9 at.%Cu eutectic alloy were solidified over a range of undercoolings. Subsequently, the samples that consisted consistently of fully lamellar eutectic were rapidly heated to a target temperature below the eutectic temperature. Increasing the initial undercooling prior to solidification or the target temperature of heating led to more anomalous eutectic and worse orientation of phases in the final microstructure. It is conclusively indicated that the formation of anomalous eutectic in bulk samples results from remelting of the primary lamellar eutectic.

Laser‐induced metallization of porous Si3N4 ceramic and its brazing to TiAl alloy

AbstractThe poor wettability of traditional brazing filler alloys on the surface of ceramics always lead to the formation of defects in the joints and weaken the bonding strength eventually, especially the porous ceramics. Metallization on ceramics is an effective way to improve the wettability. In this work, laser‐induced cladding process was applied to metalize the surface of porous Si3N4 ceramic, and the traditional AgCu eutectic filler alloy can wet on the metalized surface completely. The metalized porous Si3N4 ceramic brazed to TiAl alloy successfully using AgCu filler alloy. The interfacial microstructure and mechanical property of the porous Si3N4/TiAl alloy brazed joint was significantly improved by the novel laser‐induced metallization process.

Interfacial microstructures formation mechanism between SiO2 substrate and AgCuTi braze alloys

The wetting characteristics of braze alloys (AgCu eutectic and AgCu eutectic −2 wt% Ti) on SiO2 substrate are observed and the results show that small percentage additions of Ti into the AgCu eutectic alloy leads to a dramatic decrease in the steady contact angle. The interfacial microstructures are responsible for the steady contact angle decreasing of different braze alloys on the SiO2 substrate. The aim of this work is to investigate the interfacial microstructures formation mechanism between SiO2 substrate and AgCuTi braze alloys. Scanning electron microscopy (SEM) equipped with an energy dispersive X-ray spectroscopy (EDS) and high-resolution transmission electron microscopy (HRTEM) were employed to analyze the interfacial microstructures. The results show that the molten AgCuTi alloy infiltrates into the SiO2 side, resulting in the formation of SiO2/Ti2O/(Ti4Cu2O+AgCu)/AgCu/(AgCu+Ti5Si3) structures. The Ti atoms in the molten braze alloy firstly accumulated along the surface of SiO2 and then reacted with SiO2 to form the Ti2O layer, at the same time, Si liberated from thermal degradation of SiO2 dissolved into the molten AgCuTi solution and reacted with Ti to form Ti5Si3 compounds. Ti-Cu rich in the molten AgCuTi would react with Ti2O at the interface to form the Ti4Cu2O M6X compounds. Both the experiment results and the theoretical thermodynamics analysis support the proposed viewpoint of interfacial microstructures formation mechanism between the SiO2 substrate and AgCuTi braze alloys.

Microstructural evolution in the braze joint of sapphire to Kovar alloy by Ti-Cu metallization layer

Sapphire was metallized by magnetron sputtering Ti-Cu bilayer films on the surface and was brazed to Kovar alloy (Fe-Ni-Co) using Ag-Cu eutectic alloy. The microstructures of these joints were investigated. The correlation between the Al2O3/Kovar joining strength and the microstructures of the braze joints was discussed. The results show that Ni atoms in Kovar alloy diffused towards the Ti-Cu metallizaton layer and remained as (Ni, Cu) solution during the solidification process. The metallization layer became thicker and evolved into a reaction layer which consisted of (Ni, Cu) solution, Cu-Ti-O and TiO. This reaction layer in the joint played an important role in relieving residual stress. Thus the maximal tensile strength of 72.6±4.4MPa was achieved. However, as the holding time was further prolonged, Ni atoms diffused through the (Ni, Cu) solid solution into the reaction layer resulting in formation of Ni3Ti intermetallic compounds and transformation of TiO to Ti2O3, which leads to the joint strength decreasing.

Interfacial reactions at the joints of CoSb3-based thermoelectric devices

CoSb3-based alloys are among the most promising thermoelectric materials. The Ag-Cu eutectic alloy, Ag-39.9 at%Cu, has a melting point at 779.1 °C and is a good braze candidate for thermoelectric modules used in mid-temperatures. Since the Ag-39.9 at%Cu alloy reacts significantly with the CoSb3 substrate, the introduction of a barrier layer is necessary, and Co, Ni and Ti are potential barrier layers. This study systematically examines the reactions at the joints, Ag-Cu/Co/CoSb3, Ag-Cu/Ni/CoSb3 and Ag-Cu/Ti/CoSb3. Interfacial reactions are observed between the CoSb3 substrate and barrier layers at 450 °C and 600 °C, although they are significantly reduced with the introduction of barrier layers. CoSb2 and CoSb phases are formed at the Co/CoSb3 contact, Ni5Sb2 and (Co,Ni)Sb phases at Ni/CoSb3, and TiSb, TiSb2 and TiCoSb phases at Ti/CoSb3. After reaction at 450 °C for one day, the reaction layer thick is 2 μm, 24 μm, and 0.4 μm in the Co/CoSb3, Ni/CoSb3 and Ti/CoSb3 couples, respectively. Co has both good adhesion and low interfacial reaction rates with CoSb3 and Ag-39.9 at%Cu alloy, and it is concluded that Co is a good barrier layer at 450 °C for the CoSb3-based modules when Ag-Cu eutectic braze is used.

Joining of SiO2f/SiO2 composite to Al2O3 ceramic using AgCu-Ti brazing filler metal

SiO2f/SiO2 composite was joined to Al2O3 ceramic using AgCu-Ti active filler at brazing temperature of 1153 K for 10 and 60 min, respectively, and sound joints were achieved. It was found that a thin reaction layer had been formed close to each of the joined materials, and the brazing seam matrix was composed of homogeneous Ag-Cu eutectic alloy. The joint interface was analyzed by SEM, EDS, and XRD. The typical interface structure of joint brazed at 1153 K for 10 min could be described as the following sequence: SiO2f/SiO2 → TiO2 + Ti5Si4 → TiO2 + Cu3Ti3O → Ag-Cu eutectic alloy → (Ti-O) + (Ti-Cu-O) → Al2O3. However, Cu2Ti4O but not Cu3Ti3O was detected in the joints brazed at 1153 K for 60 min. Besides, the reaction layers of joint brazed at 1153 K for 60 min were much thicker than those for 10 min. The SiO2f/SiO2-Al2O3 joints brazed at 1153 K for 10 min showed an average shear strength of 38.6 MPa, evidently higher than that (26.0MPa) brazed at 1153 K for 60 min.

Influence of Growth Rate and Magnetic Field on Microstructure and Properties of Directionally Solidified Ag-Cu Eutectic Alloy.

We report the influence of growth rate and external magnetic field on the eutectic lamellar spacing and properties of directionally-solidified Ag-Cu eutectic alloys. The results indicated that the relationship between the lamellar spacing of directionally-solidified Ag-Cu alloys and the growth rate matched the prediction of the Jackson-Hunt model, and the constant was 5.8 µm3/s. The increasing external magnetic field during solidification tilted the growth direction of the lamellar eutectics, and coarsened the eutectic lamellar spacing. These decreased the microhardness and strength of Ag-Cu alloys, but increased their electrical conductivity. The competitive strengthening contributions between the refinement of the eutectic lamellar spacing and the change in growth direction of the eutectics resulted in higher strength in the as-rolled sample with a 0.8 T magnetic field than with other samples, which was confirmed from higher relieved deformation energy using differential scanning calorimetry.

Microstructural evolution during the brazing of Al2O3 ceramic to kovar alloy by sputtering Ti/Mo films on the ceramic surface

Alumina (Al2O3) ceramics were metallized by magnetron sputtering Ti/Mo bilayer films on the surface with a subsequent high temperature sintering and were brazed to Kovar alloy (Fe-Ni-Co) using Ag-Cu eutectic alloy. The Ti/Mo metallization film and the brazing seam microstructures were investigated and the correlation between the Al2O3/Kovar joining strength and the microstructures of the brazing seam was discussed. The results show that the joining strength is related to the thickness of the Ti/Mo adhension layer which depends on the holding time during brazing. The mutual diffusion of the elements at the interface firstly increases the thickness of the adhension layer as the holding time increases and the Mo film acts as a barrier layer to block the diffusion of Ti atoms into the seam. The optimal brazing joining strength of 72.6±5.0MPa could be achieved at a brazing temperature of 810°C for 14min However, if the holding time is further prolonged, Mo atoms will diffuse into the (Ni, Cu) solid solution, resulting in the diffusion of Ti atoms and the adhension layer becoming indistinguishable. Therefore, the intermetallic Ni3Ti forms in the seam and the titanium oxide changes from TiO to Ti2O3 or Ti3O5, which leads to the joint strength decreasing.

Rapidly solidified Ag-Cu eutectics: A comparative study using drop-tube and melt fluxing techniques

A comparative study of rapid solidification of Ag-Cu eutectic alloy processed via melt fluxing and drop-tube techniques is presented. A computational model is used to estimate the cooling rate and undercooling of the free fall droplets as this cannot be determined directly. SEM micrographs show that both materials consist of lamellar and anomalous eutectic structures. However, below the critical undercooling the morphologies of each are different in respect of the distribution and volume of anomalous eutectic. The anomalous eutectic in flux- undercooled samples preferentially forms at cell boundaries around the lamellar eutectic in the cell body. In drop-tube processed samples it tends to distribute randomly inside the droplets and at much smaller volume fractions. That the formation of the anomalous eutectic can, at least in part, be suppressed in the drop-tube is strongly suggestive that the formation of anomalous eutectic occurs via remelting process, which is suppressed by rapid cooling during solidification.

Spasmodic growth during the rapid solidification of undercooled Ag-Cu eutectic melts

A melt fluxing technique has been used to undercool Ag-Cu eutectic alloy by 10–70 K and the subsequent recalescence has been studied using high speed imaging. Spasmodic growth of the solidification front was observed, in which the growth front would make a series of quasi-periodic jumps separated by extended periods during which time growth appeared to arrest. Evidence of this previously unreported mode of growth is presented. The high speed images and microstructural evidence support the theory that anomalous eutectics form by the growth and subsequent remelting of eutectic dendrites.

The Effects of Adding Elements of Zinc and Magnesium on Ag-Cu Eutectic Alloy for Warming Acupuncture

The warming acupuncture for hyperthermia therapy is made of STS304. However, its needle point cannot be reached to a desirable temperature due to heat loss caused by low thermal conductivity, and the quantification of stimulation condition and the effective standard establishment of warming acupuncture are required as a heat source. Accordingly, in this study, after Ag-Cu alloys with different composition ratios were casted and then mixed with additives to improve their physical and mechanical properties, the thermal conductivity and biocompatibility of the alloy specimens were evaluated for selecting suitable material. Ag-Cu binary alloys and ternary alloys added 5 wt% Zn or 2 wt% Mg were casted and then cold drawn to manufacture needles for acupuncture, and their physical properties, thermal conductivity, and biocompatibility were evaluated for their potential use in warming acupuncture. The results of this study showed that the physical and mechanical properties of the Ag-Cu alloys were improved by additives and that the thermal conductivity, machinability, and biocompatibility of the Ag-Cu alloys were improved by Mg addition.

Containerless solidification of Ag-Cu eutectic alloy under acoustic levitation condition

The containerless melting and solidification of Ag-Cu eutectic alloy were accomplished by acoustic levitation together with laser heating.The temperature field of levitated alloy droplet was investigated through CMOS image processing and numerical calculation.Due to the effect of acoustic radiation pressure,the alloy droplets deform from spherical to oblate or disklike shapes.Their surface temperature rises along the meridian line from the equator to the poles during cooling process.Surface ripples are observed on those samples with greater deformation(a/b2.1).And it is found that eutectic grains nucleate at the center of these ripples,and grow in the direction parallel to the propagation of ripples.The surface nucleation and the radial advance of solid-liquid interface are revealed to be the two key factors for the formation of surface ripples.The enhancement of sound pressure can induce the surface nucleation of levitated Ag-Cu eutectic alloy.

Progress of microgravity material research during the period of 2007—2009

Orbital experimental researches on crystal growth of Mn-doped GaSb and Bi2Se0.21Te2.79 are briefly summarized. The space experiments were completed in September of 2007 on broad the Foton-M3 satellite of Russia. Ground-based researches on the solidification behaviors of Al-Al3Ni, Al-Al2Cu, Ag-Cu eutectic, Al-Pb monotectic and Cu-Co peritectic alloys in a 50-meter-high drop tube were investigated. New experimental results on the ultrasonic field and the temperature recycling induced to chiral symmetry breaking of NaClO3 crystal also were reported in the present paper.

Low-Temperature Interface Reaction Between Titanium and the Eutectic Silver-Copper Brazing Alloy

Reaction zones formed at 790 °C between solid titanium and liquid Ag-Cu eutectic alloys (pure and Ti-saturated) have been characterized. When pure Ag-Cu eutectic alloy with 40 at.% Cu is used, the interface reaction layer sequence is: αTi/Ti2Cu/TiCu/Ti3Cu4/TiCu4/L. Because of the fast dissolution rate of Ti in the alloy, the reaction zone remains very thin (3-6 μm) whatever the reaction time. When the Ag-Cu eutectic alloy is saturated in titanium, dissolution no longer proceeds and a thicker reaction zone with a more complex layer sequence grows as the reaction time increases. Four elementary chemical interaction processes have been identified in addition to Ti dissolution in the liquid alloy. These are growth of reaction layers on Ti by solid state diffusion, nucleation and growth from the liquid of TiCu4, isothermal solidification of silver and, finally, chemical conversion of the Cu-Ti compounds by reaction-diffusion in the solid state. A mechanism combining these processes is proposed to account for the constitution of Ti/Ag-Cu/Ti joints brazed at 780-800 °C.

Titanium metallization of Si 3N 4 ceramics by molten salt reaction: coating microstructure and brazing property

Metallization of ceramic surface by molten salt reaction is a simple and inexpensive method for improving the brazing property of ceramics. In this paper, the microstructure of the coating on the metallized Si 3N 4 surface produced by molten salt reactions was investigated. The results show that titanium reacted with Si 3N 4 to form a multi-layer structure in the coating. Based on thermodynamics calculations and thermogravimetric analysis, the possible reaction between titanium and Si 3N 4 was discussed. Wetting experiment proved that the metallized Si 3N 4 could be completely wetted by AgCu eutectic alloy. The metallized Si 3N 4 was brazed to 45 steel with a maximum joint strength of 226 MPa.

Effects of Surface Roughness of Base Metals on the Residual Stress of Filler Metals at Brazed Joints

The purpose of this study is to make clear some effects of surface roughness of the base metals on the residual stress of the filler metals at brazed joints. Although brazing and soldering techniques have been used in the mechanical industry as the metallurgical joining process for a long time, both techniques are still extensively applied to assemble electric circuits, electronic instruments and other precision machine parts. This paper presents some experimental data of the relationship between the surface roughness of the base metals (mild steel, SUS410, pure Titanium and Ti-6A1-4V) and residual stress of the filler metals (Ag-Cu eutectic alloy, Pd-Ag alloy and Pd-Cu alloy) at brazed joints using 7kW resistance vacuum furnace. Through the study we arrived at the following conclusions: the residual stress at the brazed joints of the specimens with coarse surface of the base metals have a higher value than that of one with smooth surface of the base metals. In the process it's observed that the actual brazed area at the joint of the specimens with higher roughness has a higher stress value than that of one with smooth surface, that is, the shape factor value of the coarse roughness have the larger value than that of one with smooth surface of the brazed surface. And also, concerning the tensile strength of the brazed specimens, we have observed that the tensile strength of the brazed specimens with coarse surface have a higher value than that of one with smooth surface of the base metal. The above observation holds consistently for all the different materials used in this study.

Microstructure and bond strength of Ni-Cr steel/Si3 N4 joint brazed with Ag-Cu-Zr alloy

The interfacial microstructure and bond strength were examined for a Ni-Cr steel/Si3 N4 joint brazed using an Ag-Cu eutectic alloy containing 5 wt-%Zr. The reaction of Si3N4 with the brazing alloy formed a very thin ZrN layer with a cubic structure (a = 4.577 Å) at the interface. No Zr silicide (Zr5Si3) was present at the interface even though its formation is thermodynamically possible. The reaction product did not contain any of the dilute ceramic phases or intermetallics which are commonly seen in other active metal brazing systems. This strongly implies that the elements of the Ni-Cr steel and Ag or Cu in the brazing alloy, did not participate in the interfacial reaction. The shear strength of the joint was strongly dependent on the thickness of the reaction layer and the morphology of CuZr2 precipitates in the brazement. A joint with a reaction layer thickness of 0.5 μm, which was formed by brazing at 950°C for 30 min, showed the highest fracture shear strength (∼ 202 MPa).