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Purpose: This paper aims to conduct work to obtain high-quality brazed joint of YAG ceramic and kovar alloy. Design/methodology/approach: Wetting and spreading behavior of AgCuTi filler alloy on YAG ceramic and kovar alloy under vacuum (2∼3 × 10–4 Pa) and argon conditions was investigated and compared. Then, YAG ceramic was brazed to kovar alloy under a high vacuum of 2∼3 × 10–4 Pa; the influence of holding time on the interface structure of the joint was investigated. Findings: The wettability of AgCuTi on YAG is poor in the argon atmosphere, the high oxygen content in the reaction layer hinders the formation of the TiY2O5 reaction layer, thereby impeding the wetting of AgCuTi on YAG; in the vacuum, a contact angle (?=16.6°) is obtained by wetting AgCuTi filler alloy on the YAG substrate; the microstructure of the YAG/AgCuTi/kovar brazed joint is characterized to be YAG/Y2O3/(Fe, Ni)Ti/Ag(s, s) + Cu(s, s)/Fe2Ti + Ni3Ti/Fe2Ti/kovar; at 870 °C for the holding time of 10 min, a (Fe, Ni) Ti layer of approximately 1.8 µm is formed on the YAG side. Originality/value: Wetting and spreading behavior of the brazing filler alloy under different conditions and the influence of the holding time on the interface microstructure of the joint were studied to provide references for obtaining high-quality brazed joints. [ABSTRACT FROM AUTHOR]

This work studied the effect of Si/Zn ratio on the structure of B2O3–Al2O3–SiO2 (BAS) parent glass and the microstructure, properties of the resulting glass‐ceramics after heat treatment. Additionally, the effects of different pre‐oxidation temperature of Kovar alloys and sealing temperature on the shear strength of these sealed glass–ceramics‐to‐Kovar samples were studied. First, the parent glass precipitated three kinds of crystals Al0.52Zr0.48O1.74 (PDF#53‐0294), ZrO2 (PDF#37‐1484), and ZnAl2O4 (PDF#05‐0669) in BAS glass–ceramics. The coefficient of thermal expansion of glass–ceramics increased from 48.17 × 10−7 to 54.92 × 10−7°C−1 with the gradual increase of ZnO content. With an optimizing pre‐oxidized temperature of Kovar at 950°C, a champion sample with the highest sealing strength of 6.086 MPa was achieved when BAS glass–ceramics sealed to Kovar at 1000°C for 30 min. Moreover, the sealing interface was observed to consist of four distinct regions: the matrix alloy, the alloy iron‐deficiency area, the iron‐rich glass–ceramics, and the matrix glass–ceramics. [ABSTRACT FROM AUTHOR]

Copyright of Bulletin of the Chinese Ceramic Society is the property of Bulletin of the Chinese Ceramic Society Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A Kovar alloy composite wire inlaid with copper core was developed through hot isostatic pressing sintering and subsequent multi-pass drawing. The interface between the Kovar alloy and copper was revealed, and the physical properties of the composite wire were investigated. The results show that the Kovar alloy and copper diffuse mutually during the forming process, producing a stable metallurgical bond. When the diameter of the wire is 2.8 mm, a diffusion layer of about 16.5 μm was found at the interface. The concentration of the diffused element had a gradient distribution from the interface to both sides. Combining the excellent properties of Kovar alloy and copper, the composite wire has comprehensive physical properties. The electrical and thermal conductivities are 9.38 × 106 S·m−1 and 72.2 W·m−1·K−1, respectively. The composite wire has a low coefficient of thermal expansion, and the average coefficient of thermal expansion is lower than 6.36 × 10−6 ℃−1 in the temperature range of 25–450°C.

Fe–29Ni–17Co powder mixes were obtained by mixing nickels and cobalt powders, using the reduced iron powders and carbonyl iron powders as the raw materials, respectively, and the sintered Fe–29Ni–17Co Kovar alloy samples were prepared by pressing and sintering at the different temperatures. The effects of the raw iron powder type and sintering temperature on the microstructure and properties of the sintered body were investigated. The results show that the sintered samples prepared by the carbonyl iron powders have the higher relative density and the better comprehensive performance, the relative density of the sintered body sintered at 1250 ℃ is 97.51%, which is about 1.40% higher than that of the sintered body prepared by the reduced iron powders. The hardness and tensile strength of the samples prepared by the carbonyl iron powders reach HRB 84.6 and 533.8 MPa, respectively, and the thermal conductivity, average thermal expansion coefficient (20～400 ℃), and electrical resistivity are 16.45 W·m−1·K−1, 4.71×10−6 K−1, and 0.38 Ω·cm, respectively. The distribution of austenite in the sintered body obtained from the carbonyl iron powders is more uniform, the microstructure stability is better after the low temperature treatment, and the degree of martensitic transformation is lower.

This paper investigates the wettability of Kovar alloys with high-borosilicate glass and microscopically analyses the mechanism of wettability and diffusion between Kovar and borosilicate glass. First, Kovar was oxidised at 800 °C for 5, 15, 25, 35, and 60 min to observe the oxide morphology of the Kovar surface layer and to analyse the composition of the oxide layer. To investigate the wetting pattern formations of Kovar and high-borosilicate glass under different wetting temperatures, times, and preoxidation conditions, Kovar and high-borosilicate glass obtained from different oxidation treatments were held at 1060 °C for 20 min for wetting experiments, and the glass–metal wetting interface morphology and elemental distribution were observed using SEM and EDS. The elemental diffusion at the wetting interface between the borosilicate glass and the Kovar with different preoxidation and at the glass spreading boundary was investigated. The longitudinal diffusion of the liquid glass in the metal oxide layer formed a new tight chemical bond of Fe2SiO4, and the lateral diffusion of the liquid glass in the Kovar surface layer formed a black halo. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Central South University is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The brazed joining between Kovar alloy and sapphire was successfully achieved by using TiB whisker reinforcement and applying the surface micro-nano structure. We systematically studied the composition and mechanical properties of Kovar/Sapphire joint. The typical interfacial structure of the joint brazed at 825 °C for 10 min was determined as Sapphire/ γ-TiO/ Ti 3 (Cu,Al) 3 O/ Ag(s,s) + Cu(s,s) + TiB/ Ti 2 Cu + TiFe 2 + TiNi 3 / Kovar alloy. The addition of B forms tiny TiB whisker reinforcement phase in situ, which refines the interface structure. The presence of micro-nano structures improves the interface products on the sapphire side: reducing the generation of Ti 3 (Cu,Al) 3 O and replacing it with γ-TiO. This makes the phase transition on the sapphire side smoother and reduces thermal expansion coefficient mismatch, thereby enhancing joint strength. Under suitable brazing parameters, the maximum shear strength of the joint is 137 MPa. This study provides new insights for optimizing and improving connections between sapphire ceramics and metals, with potential applications in more ceramic/metal joining. • Kovar alloy and sapphire were brazed using TiB whisker reinforcement and micro-nano surface structure processing. • The addition of B reduces filler fluidity but doesn't affect interfacial reaction layer formation. • The dispersed TiB whiskers can refine the phases in the brazed joint and improve the shear strength of the joint. • Micro-nano structures help generate γ-TiO, reduce thermal expansion mismatch, and enhance the strength of the joint. [ABSTRACT FROM AUTHOR]

Electron beam welding with and without beam offset was conducted respectively to investigate the evolution of microstructure and mechanical properties of molybdenum/Kovar joint with beam offset variation. As electron beam was deflected from molybdenum to Kovar, the defects of pores and cracks were decreased due to due to the optimization of liquidity of molten pool and tenacity of the weld, respectively. Welds consisted of γ-Fe matrix, reticular α-Fe, and eutectoid α-Fe + μ (Fe 3 Mo 2). Both the α-Mo and eutectoid α-Fe + μ (Fe 3 Mo 2) were decreased when electron beam was deviated from molybdenum to Kovar. The tensile strength was increased with beam offset from molybdenum to Kovar at room temperature, indicating the increase from 118 MPa of the weld with beam offset to Mo to 191 MPa of that without beam offset and then to 201 MPa of that with beam offset to Kovar. As the temperature was increased to 400 °C and then to 800 °C, the tensile strengrh for the weld was firstly increased and then decreased due to the optimized tenacity of α-Mo and the change in vulnerable area of the weld from the fusion line at molybdenum side to that at Kovar side. • Microstructural evolution as beam was deviated from Mo to Kovar was analyzed. • The deformability and tenacity of all phases were investigated. • Mechanical property change with beam offset from Mo to Kovar was studied. • Tensile property change with the increase in temperature was analyzed. [ABSTRACT FROM AUTHOR]

Copyright of Rare Metal Materials & Engineering is the property of Northwest Institute for Nonferrous Metal Research and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

• A Co interlayer has been proposed to bond TC4 titanium alloy and 4J29 kovar alloy. • The use of Co interlayer can inhibit the formation of Fe-Ti intermetallic compounds. • The bonding mechanism of TC4/Co/4J29 bonded joints is investigated. • By decreasing the bonding temperature, the quality of TC4/Co/4J29 bonded joints can be improved. The diffusion bonding of TC4 titanium alloy and 4J29 kovar alloy was conducted using pure Co interlayer. The results showed that maximum tensile strength of 58.5 MPa was acquired for bonded joint made at 825 °C. At titanium alloy side, due to formation Ti-Co phases, such as TiCo 3 , TiCo 2 , TiCo and CoTi 2 , brittleness of bonded joints was enhanced. Furthermore, with increase in bonding temperature, tensile strength of bonded joints gradually decreased because of the production of Ti-Co intermetallic compounds with a thicker thickness. [ABSTRACT FROM AUTHOR]

In this study, the effects of isothermal aging on the interfacial reactions, shear strength and failure mode of Sn37Pb/electroplated Cu (EPC)/Kovar solder joints were investigated in detail. Various interfacial intermetallic compound (IMC) layers were formed in all as-reflowed solder joints. The as-reflowed solder joints were aged up to 360 h at 150 °C before single-lap shear tests. The microstructure of interfacial IMCs layers was affected by the isothermal aging, as well as deposited thickness of Cu film on Kovar substrate. Single-lap shear tests results revealed that the introduction of Cu film on Kovar significantly improved the shear strength of Sn37Pb/EPC/Kovar solder joints. This is because the Cu film could act as a sacrificial layer and react with molten solder to form a thin Cu-Sn IMCs layer, which was expected to protect Au/Ni films from further reaction with solder, rendering a enhanced bonding strength of joints. The shear strength of Sn37Pb/EPC/Kovar solder joints with same aging time increased first and then decreased with the increase of deposited Cu film thickness. The shear strength of aged solder joints decreased with increasing aging time, which could be ascribed to the thicker IMC layer generated at the joint interface. • The surface morphologies of deposited Cu films were analyzed by AFM tests. • Various interfacial IMCs layers were formed in all as-reflowed solder joints. • A novel method to improve the shear properties by introducing a Cu film is proposed. • The failure modes of aged solder joints changed during long-term aging treatment. [ABSTRACT FROM AUTHOR]

Al2O3 ceramic and Kovar alloy brazed joints were achieved using three types of Ag‐based interlayers: a AgCuTi foil, a AgCuTi/Cu foil/AgCuTi multi‐interlayer and a AgCuTi/Cu foam/AgCuTi multi‐interlayer. The effects of the addition of Cu interlayers on the interfacial microstructure and mechanical properties of Al2O3/AgCuTi/Kovar brazed joints were investigated. When Kovar alloy and Al2O3 ceramic were brazed with 50 μm Cu foil at 900°C for 10 minutes, the Cu foil was completely dissolved in the liquid filler. A nearly continuous Cu layer remained in the joint when the thickness of the Cu foil reached 100 μm under the same brazing conditions. With the increase in Cu foil thickness, the thickness of Ti–O compounds + Ti3Cu3O reaction layer formed nearby the Al2O3 ceramic first increased and then remained the same. The Al2O3/Kovar joints brazed with 100 μm Cu foil at 900°C for 10 minutes showed a maximum shear strength of 138 MPa. A low brazing temperature was beneficial to maintain the original structure of the Cu foam. Furthermore, when the joints were brazed at 880°C for 10 minutes, the average shear strength of the Al2O3/AgCuTi/Cu foam/AgCuTi/Kovar joints was 140 MPa, which was 30 MPa higher than that of a single AgCuTi interlayer. [ABSTRACT FROM AUTHOR]

The low temperature sealing of Kovar alloy to DM305 electronic glass was realized by using lead-free glass solder of the Bi2O3-ZnO-B2O3 system in atmospheric environment. The sealing process was optimized by pre-oxidation of Kovar alloy and low temperature founding of flake glass solder. The effects of sealing temperature and holding time on the properties of sealing joint were studied by means of X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS), etc. The results showed that the pre-oxidized Kovar alloy and DM305 electronic glass were successfully sealed with flake glass solder at the sealing temperature of 500 °C for 20 min. Meanwhile, the joint interface had no pores, cracks, and other defects, the shear strength was 12.24 MPa, and the leakage rate of air tightness was 8 × 10−9 Pa·m3/s. During the sealing process, element Bi in glass solder diffused into the oxide layer of Kovar alloy and DM305 electronic glass about 1 μm, respectively.

In order to realize reliable sealing and combination of constructional glass and Kovar alloy, the effects of temperature, holding time, roughness and oxide layers on their wetting property were studied. When the temperature increased from 800℃ to 900℃, the viscosity of liquid glass reduced, so the wetting angle decreased from 69.5° to 31.1°. When the holding time prolonged from 5 min to 40 min at 850℃, the liquid glass had enough time to diffuse under the condition of low viscosity, and the wetting angle increased by 30%. With an increase in roughness of steel sheet surfaces, the barrier increased which was needed to overcome by the liquid glass to spread around. When the roughness value Ra increased from 0.186 μm to 0.563 μm, the wetting angle increased from 46.9° to 69.5°. The oxide layer on the surface of Kovar alloy and the liquid glass had diffusion reaction that could form strong ionic bonds, which increased the wetting property considerably, and the wetting angle could decrease by 23.6%. Therefore, during the actual sealing process, increasing the temperature and holding time, decreasing the roughness of steel sheet surfaces, and steel sheet pretreatment could effectively improve the wetting property of the glass and Kovar alloy.

Joining single-crystal diamond with the Kovar alloy has great application potential in the field of optoelectronic devices. In this work, single-crystal diamond was brazed with a Kovar alloy by using an AgCuTi metal filler at a temperature of 830 °C with a dwell time of 5 min. The corresponding microstructures and interfacial products of the brazed joints were systematically studied. AgCuTi interacts with diamond, and a continuous TiC reaction layer with a thickness of 0.5–1 μm forms at the interface between diamond and the residual AgCuTi metal filler. In contrast, there is no obvious reaction layer at the interface between the Kovar alloy and the residual metal filler; however, it is observed that the metal filler penetrates the Kovar alloy along the grain boundary of the Kovar alloy. In addition, the compression shear strength of the brazed joint was tested, and the fracture morphologies were analysed. The maximum shear strength of the brazed joint is 102.73 MPa, and the fracture shows mixed ductile and brittle characteristics. [Display omitted] • Single crystal diamond and Kovar were brazed with AgCuTi filler metal. • Typical microstructure: single crystal diamond/TiC/(Fe, Ni) Ti/Ag (s, s), Cu (s, s)/Fe 2 Ti, Ni 3 Ti/Fe 2 Ti/Kovar. • The maximum shear strength of brazed joint is 102.73 MPa and the fracture shows ductile and brittle mixed characteristics. [ABSTRACT FROM AUTHOR]

This paper discusses the surface modification processing of kovar alloy (Fe-29.72wt%Ni-16.28wt%Co) by Na2SO4 electrolyzed oxidizing water (hereinafter referred to as EO water). First, the etching effect of Na2SO4 EO water on the surface of kovar alloy was clarified by comparative experiments of chemicals and NaCl EO water. The comparative study showed that as for the etching effect on the surface of kovar alloy, Na2SO4 EO water was superior to H2SO4 solution, but inferior to NaCl EO water. Next, by the observation using SEM image, the influence of Na2SO4 EO water on the surface shape of kovar alloy was clarified. The results indicated that when using Na2SO4 EO water, the surface of polished test pieces which had not been heat-treated becomes smooth, but in the test pieces surface which had been heat-treated, a lot of dimples had occurred. When using the supersonic together with one of Na2SO4 EO water or NaCl EO water, the surface shape became smooth. Lastly, as for the test pieces after heat treatment, the surface oxidation layer removal experiment by the immersion was carried out. The results showed that Na2SO4 EO water could remove the surface oxidation layer like H2SO4 solution approximately. However, thin surface oxidation layer might be formed when using Na2SO4 EO water. By this study, we received the suggestion that Na2SO4 EO water could be applied to the surface treatment such as the etching of kovar alloy.

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 Al 2 O 3 /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 ± 4.4 MPa 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 Ni 3 Ti intermetallic compounds and transformation of TiO to Ti 2 O 3 , which leads to the joint strength decreasing. [ABSTRACT FROM AUTHOR]

YAG ceramic was brazed to Kovar alloy under a high vacuum of 6–8 × 10−4 Pa. A good contact angle (θ eq = 10.7°) was obtained by wetting AgCuTi filler metal on the YAG ceramic substrate, and the associated interfacial microstructure was characterized. The microstructure of the achieved YAG/Kovar joints brazed by AgCuTi filler was characterized by SEM, TEM and XRD, which was found to be YAG/Y 2 O 3 /(Fe, Ni)Ti/Ag(s, s) + Cu(s, s)/Fe 2 Ti + Ni 3 Ti/Fe 2 Ti/Kovar. The effects of different brazing temperatures on the joint structure were investigated. The thickness of the (Fe, Ni)Ti reaction layer increases, and the banded structure formed by Fe 2 Ti and Ni 3 Ti intermetallic compounds (IMCs) widens with increasing brazing temperature. Nanoindentation and shear tests were used to characterized the mechanical properties of the joints. As the brazing temperature increased, the shear strength of the joints first increased and then decreased. A joint with an optimal shear strength of 51.3 MPa was obtained at 870 °C for 10 min. The nanoindentation test reveals the obvious differences in mechanical properties between phases: (Fe,Ni)Ti phase has higher Young's modulus and hardness than Fe 2 Ti–Ni 3 Ti phase and Ag–Cu eutectic. • YAG and Kovar was brazed with AgCuTi filler metal. • Typical microstructure: YAG/Y 2 O 3 /(Fe,Ni)Ti/Ag(s,s), Cu(s,s)/Fe 2 Ti, Ni 3 Ti/Fe 2 Ti/Kovar. • A contact angle of 10.7° was obtained by wetting AgCuTi filler metal on YAG. • Mechanical properites of the joint were confirmed by nanoindentation and shear strength. • The maximum shear strength of 57.3 MPa was achieved with the parameter of 870 °C/10 min. [ABSTRACT FROM AUTHOR]

This paper describes the elucidation about the influence of NaCl electrolyzed oxidizing water (It abbreviates as EO water) on the surface of kovar alloy (Fe-29.72wt%Ni-16.28wt%Co). First, the etching characteristic of NaCl EO water against the surface of kovar alloy was clarified using chemicals for comparative immersion experiments. The comparative study showed that as for the etching efficiency on the surface of kovar alloy, NaCl EO water was superior, and the selective etching tendency is weak to HCl solution. Next, by the observation using SEM image, the influence of NaCl EO water on the surface shape of kovar alloy was clarified. The results indicated that when using NaCl EO water, the test pieces surface of only polishing becomes smooth but in the test pieces surface of heating processing, the small pit occurs. Lastly, as for the test pieces after heating processing, it did the surface oxidation layer removal experiment by the immersion. The results show that NaCl EO water can remove the surface oxidation layer like HCl solution approximately. However, the surface oxidation layer which is thin newly is formed in the surface which was processed with NaCl EO water. By this study, we got the suggestion that NaCl EO water can be applied to the surface treatment such as the etching of kovar alloy.

Alumina (Al 2 O 3 ) 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 Al 2 O 3 /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±5.0 MPa could be achieved at a brazing temperature of 810 °C for 14 min 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 Ni 3 Ti forms in the seam and the titanium oxide changes from TiO to Ti 2 O 3 or Ti 3 O 5 , which leads to the joint strength decreasing. [ABSTRACT FROM AUTHOR]

Ti/Mo bilayer thin films were deposited onto Al 2 O 3 ceramic by magnetron sputtering with a subsequent high temperature sintering to ensure the robust brazing of Al 2 O 3 ceramic to Kovar (Fe–Ni–Co) alloy. The interface reaction process between Ti film and Al 2 O 3 ceramic as well as the joining strength between metallized Al 2 O 3 ceramic and Kovar alloy were investigated systematically using X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis, transmission electron microscopy, and electronic universal testing machine. The results show that the active Ti film can react with Al 2 O 3 ceramic to form Ti 3 Al and TiO during high-temperature sintering process, in which the amount, size and morphology of TiO crucially depend on the sintering temperature. As the sintering temperature reaches 1200 °C, a plenty of spherical TiO nanoparticles with ~ 150 nm in diameter and metallic nature can be created across the Ti/Al 2 O 3 interfaces, which can effectively act as ‘bridges’ to join Ti film to Al 2 O 3 substrate firmly. Hence, the optimal joining strength of 69.6±3.1 MPa between metallized Al 2 O 3 ceramic and Kovar alloy can be obtained, much better than those counterparts metallized at 900 °C and 1050 °C almost without the existence of observable TiO. [ABSTRACT FROM AUTHOR]

An AgCuTi/Cu/AgCuTi sandwich composite filler was employed to improve the bonding between Kovar alloy and AlN ceramic. The effect of Cu interlayer with various thicknesses and the brazing temperature on the microstructure and mechanical properties of the joints were investigated. The results showed that a complex structure with Fe 2 Ti layer/(Fe, Ni)Ti layer/Ag(s,s) + Cu(s,s) + CuTi 2 /TiN layer formed in the Kovar/AlN brazed joints when the sandwich composite interlayer was used. However, the excessive thickness of Cu interlayer would generate cracks along uninterrupted Cu layers, which is detrimental to the mechanical properties of joint. The shear tests showed the joints with Cu interlayer exhibited lower residual stress in comparison with the one without Cu interlayer. Maximum shear strength of 114 MPa was reached with the Cu interlayer thickness of 100 μm at 1153 K, which improved by about 100% to that of the joint obtained only with AgCuTi filler. Further SEM and TEM analysis revealed that the location/content control of Fe-Ti and Ni-Ti brittle intermetallic compounds and the existing state of Cu interlayer may be the key factors in improving the shear strength of Kovar/AlN joints. The brazing mechanism of AgCuTi/Cu/AgCuTi composite filler between AlN and Kovar joint was also discussed. • AlN ceramic is successfully brazed to Kovar alloy using AgCuTi/Cu/AgCuTi filler. • Fe-Ti and Ni-Ti compounds are only distributed near Kovar by adding Cu interlayer. • The joint strength increases from 57 MPa to 114 MPa due to the introduction of Cu interlayer. [ABSTRACT FROM AUTHOR]

During chemical vapour deposition of diamond coatings on transition metal (Fe, Co, Ni) substrates, porous graphitic carbon preferentially forms on the substrate surfaces and it induces a spontaneous spallation of the diamond films. In this study, an Al surface barrier film of 80nm thick has been used on a Kovar alloy substrate to enhance the interfacial adhesion of diamond films. Characterisation of the top deposit, interlayer and the underlying substrate was performed by Raman spectroscopy, energy dispersive X-ray analysis, scanning electron microscopy, synchrotron NEXAFS, and X-ray diffraction. The Al interlayer has effectively inhibited the formation of intermediate graphitic carbon and markedly enhanced the adhesion of diamond films. Continuous and adherent diamond films were achieved on the alloy substrate. This investigation also indicates the importance of the continuity of the Al interlayer in maintaining an integrity of the adherent diamond films. [ABSTRACT FROM AUTHOR]

Large magnet system is an essential component of most current or planned fusion devices. Axial insulation breaks are required in order to electrically isolate the cryogenic distribution system from the potential high voltage of the magnet system and bus bars. The epoxy resin based insulation break could be the weak link in magnet design, due to insulation sensitivity to high irradiation doses. The \Al2\O3 ceramic material instead of epoxy based material was used to manufacture the insulation break. Kovar alloy which has a similar mean coefficient of thermal expansion with \Al2\O3 ceramic in the temperature range of 300–1073 K was used as two ends of the insulation breaks. The ceramic tubes and Kovar alloy tubes were vacuum brazed together using silver-based filler at 1073 K. The helium tightness, the insulation resistances and dielectric breakdown were checked at room temperature and \LN2 temperature. Then 2 kN traction and compression were tested at room temperature and \LN2 temperature. The maximum tensile force of 8.62 kN and 8.18 kN were measured at room temperature and \LN2 temperature, respectively. The three point bending test was carried out. The test results of 4.5 kN and 3.6 kN were measured at room temperature and \LN2 temperature, respectively. The 50 thermal shock cycles were performed from 77 K to 300 K to ensure that the ceramic break could operate under rapid temperature change. [ABSTRACT FROM PUBLISHER]

High-entropic weld was acquired by adding high-entropy alloy interlayer into molybdenum/Kovar alloy electron beam welded joint to optimize the mechanical properties. The tensile strength of joint was up to 358 MPa when the high-entropy alloy interlayer was 1.0 mm thick, corresponding to the increase of 87% compared to the only 191 MPa of the joint without high-entropy alloy interlayer. The microstructure of the weld was transformed from γ-Fe matrix with reticular α-Fe into the combination of pro-eutectic fcc and eutectic fcc + laves, as is expected from the increase in the volume of high-entropy alloy into the weld. The brittle reaction interface along the fusion line of molybdenum side was predominately changed after adding high-entropy alloy interlayer. The original continuous σ(FeMo) at the edge of α-Mo in reaction interface, which was responsible for the inferior bearing capacity of the joint, was gradually decreased and replaced by intermittent fine σ(FeCr) as the high-entropy alloy interlayer was thicker. The optimization of tensile strength derived from the transformation from continuous σ(FeMo) to intermittent σ(FeCr). The superior affinity of Cr to Fe and Mo compared to the affinity between Fe and Mo itself was the underlying reason for the decrease and morphology change in brittle σ. • High-entropic weld was acquired by adding high-entropy alloy interlayer. • Tensile strength of Mo/Kovar joint was increased from 191 MPa to 358 MPa. • Strengthening mechanism was studied from microstructure evolution. • The affinity among Cr, Fe and Mo was analyzed. [ABSTRACT FROM AUTHOR]

The oxidation of Kovar alloy was investigated, the wetting and spreading behavior of hard and soft glasses on Kovar alloy were studed by using the sessile drop method, and the quality and the seal strength of glass-Kovar seals were tested. The experimental results indicated that the preoxidation of Kovar alloy for approximately 10 min at 700°C in air resulted in excellent adherence in glass-Kovar seals. The wetting and spreading behavior of glass on preoxidized Kovar alloy were superior to that on nonoxidized Kovar alloy. The wetting ability of ASF110 glass, at 950°C and 980°C in Ar and N atmospheres, was significantly superior to that of ASF200R and ASF700 glasses. The seal quality of the glass-preoxidized Kovar seal was superior to that of the glass-nonoxidized Kovar seal. The shear strength of the ASF110 glass-preoxidized Kovar seal, which was prepared at 980°C for 20 min in an Ar atmosphere, was approximately 3.9 MPa. [ABSTRACT FROM AUTHOR]

Abstract: The wetting and spreading behavior of borosilicate glass on Kovar with oxides of FeO+Fe3O4 was investigated as a function of wetting time by the sessile drop method. The contact angle and drop base diameter were measured by the VHX-100K digital microscopy. The top view of spreading and cross-sectional microstructure of glass/Kovar was investigated by SEM, and elements distribution of Fe, Co, Ni and Si in interfacial regions was characterized by EDS line scanning. The results showed two halos were formed at the fringe of glass base in the wetting process. By analyzing the change of contact angle and drop base diameter, wetting process could be divided into three stages: incubation period, reaction period and equilibrium period. Chemical reaction is occurred between glass and oxides, and the reaction product is Fe2SiO4. Chemical and mechanical bonding effects are all present in the wetting of glass to Kovar. [Copyright &y& Elsevier]

Abstract: The microstructural evolution and interfacial reactions of Au/Sn/Au/Au/Ni/Kovar joint were investigated during aging at 180 and 250°C for up to 1000h. The Au/Sn combination formed a rapid diffusion system. Even in non-annealed joint, three phases such as AuSn, AuSn2 and AuSn4 were formed. After initial aging at 180°C, the AuSn, AuSn2, AuSn4, Au and Sn phases, which were formed after plating, were fully transformed into ζ-phase and δ-phase, and (Ni,Au)3Sn2 intermetallic compound (IMC) layer was observed between the ζ-phase and Kovar. As a whole, the microstructure of the joint was stable during aging at 180°C. On the other hand, the solid-state interfacial reaction was much faster at 250°C than at 180°C. During aging at 250°C, the Ni layer on the Kovar reacted primarily with the δ-phase in the solder, resulting in the formation and growth of the (Au,Ni)Sn IMC layer at the interface. After aging for 48h, the Fe–Co–Ni–Au–Sn phase was formed underneath the (Au,Ni)Sn IMC layer. Furthermore, cracks were observed inside the interfacial layers after complete consumption of the Ni layer. The study results clearly demonstrate the need for either a thicker Ni layer or an alternative surface finish on Ni, in order to ensure the high temperature reliability of the Au/Sn/Au/Au/Ni/Kovar joint above 250°C. [Copyright &y& Elsevier]

Abstract: This study examines the wetting and sealing of Kovar alloy with 7056 Glass. First, the Kovar alloy underwent pre-oxidization treatment at three different temperatures (700, 800 and 900°C) and for seven different isothermal holding periods (0, 3, 5, 10, 15, 30 and 60min), producing oxide layers of different thickness on the surface of the alloy. Then the wetting experiment was conducted at 925°C for 15min to observe the wettability of 7056 Glass on the underlying Kovar alloy discs. Finally, Kovar alloy and 7056 Glass were joined at thermal treatment temperature of 825–1000°C with isothermal holding for 15min at every interval of 25°C. The wetting phenomenon and interface structure were observed under optical microscope and elemental analysis was also conducted on the glass-to-metal junction using an electron probe micro-analyzer. Experimental results reveal that Kovar alloy pre-oxidized at 700°C and held isothermally for 5–15min would have a denser and more compact oxide layer of 4–7μm thick showing good adherence. Kovar alloy pre-oxidized at 700°C and 10min isothermal holding and heated in furnace filled with nitrogen only would obtain good wettability. Finally, thermal treatment temperature of 900°C and 15min isothermal holding resulted in a bigger surface area of the reaction layer and high-quality glass-to-metal junction. [Copyright &y& Elsevier]

A voltage in the opposite direction to that of anodic bonding was applied to anodically bonded joints of Fe and Kovar alloys to borosilicate glass at a temperature at which thermal diffusion of the alkali ions in the glass was activated. Disjunction of the bond interfaces occurred in the Kovar/glass joints. On the other hand, the Fe/glass joints retained cohesion of their bond interface after a long application of the reverse voltage. In an as-bonded Kovar alloy/glass joint, a reaction layer of a crystalline Fe oxide was found at the bond interface. The content of Fe in Kovar alloy adjacent to the bond interface decreased. The oxide layer was formed by the reaction between Fe from the Kovar alloy and O from the alkali ion depletion layer in the glass. The reaction layer in an Fe/glass joint was of amorphous Fe–Si oxide. This layer was much thicker than the reaction layer in the Kovar/glass joint. After application of the reverse voltage, Fe in the amorphous oxide layer in Fe/glass was substituted by alkali ions. It was suggested that this process mitigated concentration of alkali ions at the bond interface and prevented disjunction of Fe/glass joints by the reverse voltage. [Copyright &y& Elsevier]

The low temperature sealing of Kovar alloy to DM305 electronic glass was realized by using lead-free glass solder of the Bi2O3-ZnO-B2O3 system in atmospheric environment. The sealing process was optimized by pre-oxidation of Kovar alloy and low temperature founding of flake glass solder. The effects of sealing temperature and holding time on the properties of sealing joint were studied by means of X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS), etc. The results showed that the pre-oxidized Kovar alloy and DM305 electronic glass were successfully sealed with flake glass solder at the sealing temperature of 500 °C for 20 min. Meanwhile, the joint interface had no pores, cracks, and other defects, the shear strength was 12.24 MPa, and the leakage rate of air tightness was 8 × 10−9 Pa·m3/s. During the sealing process, element Bi in glass solder diffused into the oxide layer of Kovar alloy and DM305 electronic glass about 1 μm, respectively. [ABSTRACT FROM AUTHOR]

The braze joints of Si 3 N 4 -Kovar using AgCuTi braze alloys are investigated systematically with the brazing temperatures between 860 °C and 950 °C for 2–30min. The correlation between the joint strength and the microstructures of the braze joints is discussed. These results show that the reaction layer plays an important role in interface bonding. Growth of the reaction layer is a reaction-diffusion process, which mainly depends on the diffusion of Ti. The diffusion activation energy (Q) is estimated as 170.9–248.7 kJ/mol in this system, which may provide data support for Si 3 N 4 /metal braze joints. As the holding time is further prolonged (in the range of 10–30min), intermetallic compounds (IMCs) forms in the braze seam, which will prevent Ag solid solution from alleviating interfacial thermal stress. With the increasing of the brazing temperature, the residual thermal stresses increases. As a results, larger residual thermal stress is produced in the braze joints at higher braze temperature, which result in a weaker bonding. • The braze joints of Si 3 N 4 -Kovar using AgCuTi are investigated systematically. • An interfacial reaction layer plays an important role in interface bonding of Si 3 N 4 -Kovar. • Growth of the reaction layer is a reaction-diffusion process. • Ag(s, s) plays an important role in relieving residual thermal stress. • The fracture mechanism of the joint is further explored. [ABSTRACT FROM AUTHOR]