The influence of brazing conditions on joint strength in Al2O3/Al2O3 bonding

The brazing of alumina ceramic to itself was performed using Ag₅₇Cu₃₈Ti₅ filler alloy. The bonding was carried out in a vacuum of 7 × 10^?3 Pa, and the joining conditions were at 1073, 1123, 1173, 1223, 1273 and 1323 K for 1.8ks under a pressure of 0.01 MPa, at 1123 K with a pressure of 0.01 MPa for 0, 0.3, 0.9, 1.8, 2.7 and 3.6 ks, and at 1123 K for 1.8 ks with pressures of 0, 0.01, 0.05, 0.10, 0.15, 0.20 and 0.30 MPa, to determine the effects of joining temperature, pressure and holding time on the joint strength. The joint strength was measured by shear tests. The interface microstructures and fractured surfaces after testing were observed by scanning electron microscopy (SEM). It was shown that the shear strength of Al₂O₃/Al₂O₃ joints was largely affected by the joining conditions; it first increased and then decreased with increasing joining temperature, pressure and holding time and depended mainly on the strength of interfacial reaction layer itself and the interface bonding strength between the reaction layer and the ceramic. The maximum joint strength was obtained when the reaction occurred under a suitable temperature, pressure and time, and the reaction layer thickness was about 2 μm. SEM observations revealed that there were four types of fracture and each kind corresponded to a different strength.     

Diffusion bonding between Ti‐6Al‐4V alloy and interstitial free steel

This work deals with diffusion bonded joints between Ti–6Al–4V alloy and interstitial free (IF) steel at different temperatures under a pressure of 5 MPa for 30 min. The effect of bonding temperature on the microstructure and mechanical properties of the joint interface was investigated using optic microscopy, a scanning electron microscope (SEM) equipped with X‐ray energy dispersive spectrometer (EDS) and shear strength measurements. The intermetallic phases such as FeTi and Fe₂Ti occurred at the interface of bonded specimens. In addition, it was seen that shear strength of bonded specimens decreased with increasing temperature due to growing intermetallics.     

Microstructure and mechanical properties of diffusion bonded Al/Mg2Si metal matrix in situ composite

In this research, Al/Mg₂Si composite produced by gravity casting, was joined by diffusion welding technique at 6 MPa pressure with various welding temperatures and durations. This metal matrix composite (MMC) containing 15% Mg₂Si particles was produced by in situ technique. Specific diffusion bonding process was introduced as a low vacuum technique. Microstructure and shear strength of the joined areas were determined. Scanning electron microscopy examination was carried out on the welded interfaces and shear tests were conducted to the samples interface to find out the effect of welding temperatures and durations on the weldability. It was found that high welding temperatures resulted in increase of shear strength. However, increase in welding duration did not make any detectable changes. The bonded interface could be developed as a wavy state depending on the amount of parent material deformation that was associated with bonding temperature. Results indicated that MMC can be joined by diffusion welding technique successfully with satisfactory shear strength.     

Technology and interface structure for diffusion bonding of Fe3Al/18-8 dissimilar materials

Abstract

The effects of technological parameters on the interface morphology and shear strength of Fe₃Al/18-8 diffusion bonded joints have been researched by means of a JXA-80 scanning electron microscope (SEM) and a digital tensile press test machine. Microstructural characteristics and fracture morphology near the Fe₃Al/18-8 diffusion interface, obtained under conditions of various technological parameters, have been analysed using the SEM. The test results indicate that a diffusion bonded joint with higher shear strength (σ_τ = 226 MPa) may be obtained with a heating temperature T = 1020 – 1040°C, holding time t = 45 – 60 min and pressure P = 12 – 15 MPa.     

Relationship between X-ray diffraction and unidirectional solidification at interface between diamond and brazing filler metal

Brazing single crystal diamonds by using silver-copper eutectic filler containing reactive metal: titanium has been carried out. Unidirectional solidification brazing method was tried to obtain stable brazed strength. The diamond specimen was cooled down by contact with copper cooling mass of which temperature was controlled at a room temperature, 470 K and 670 K, respectively. The brazing temperature was 1080 K. The brazing filler was solidified from diamond brazing surface and we called this method as unidirectional solidification brazing. The brazed specimen was examined in shear strength by an original apparatus. In the case of diamond (100), the average shear strength shows more than 120 MPa and maximum shear strength is 240 MPa. These specimens are stronger than that made by usual brazing method. After the strength test, interface orientation between the diamond and the brazing filler was investigated by X-ray diffractometer. In the case of brazing diamond (100), diamond (100) – TiC (111) – Ag (111) orientation can be detected. In the case of brazing diamond (111), diamond (111) – Cu (111) orientation can be detected. Misfits for those orientations were calculated. The value for TiC (111) // diamond (100) is 0.05016, on the other hand the value for TiC (111) // diamond (111) is 0.2125. The brazed interface of diamond (111) is more delicate for thermal stress than diamond (100).     

Effect of heat treatment on interface microstructure and bond strength in explosively welded Ti/304L stainless steel clad

Abstract

The effects of heat treatment on the microstructure and bond strength at the interface of explosively welded titanium/304L stainless steel clad have been investigated. The microstructure of the clad interface were examined using optical and scanning electron microscopy (SEM), energy dispersive X-ray (EDX) and X-ray diffraction (XRD) techniques. At 700°C, the formation of intermetallic phases σ and Fe₂Ti besides β-Ti were confirmed, while in samples, heat treated at 800°C and 900°C, other intermetallic phases such as λ and FeTi, NiTi, NiTi₂ phases were detected in addition to σ and Fe₂Ti phases. The shear test results show that the shear strengths of heat treated samples are overall significantly lower than that of stress relieved samples. This could be due to the formation of brittle intermetallic phases at the interface. Despite of formation of the intermetallic phase at 700°C, the shear strength of the sample is still more than the minimum standard amount of 137·9 MPa. It is also observed that the higher the heat treatment temperature, the lower the interface shear strength, which can be explained by the fact that the volume fraction of intermetallics increases with increasing temperature. The shear strength values of heat treated samples are lower than those of diffusion bonded clads. This could be attributed to the fact that the total widths of intermetallic layers achieved in heat treated samples are larger than those of for diffusion bonded ones.     

Structure and properties of diffusion bonded transition joints between commercially pure titanium and type 304 stainless steel using a nickel interlayer

The solid-state diffusion bonding was carried out between commercially pure titanium and Type 304 stainless steel using nickel as an interlayer in the temperature range of 800–900 °C for 9 ks under 3 MPa load in vacuum. The transition joints thus formed were characterized in the optical and scanning electron microscopes. The inter-diffusion of the chemical species across the diffusion interfaces were evaluated by electron probe microanalysis. TiNi₃, TiNi and Ti₂Ni are formed at the nickel–titanium (Ni–Ti) interface; however, the stainless steel–nickel (SS–Ni) diffusion interface is free from intermetallic compounds up to 850 °C temperature. At 900 °C, the Ni–Ti interface exhibits the presence of α-β Ti discrete islands in the matrix of Ti₂Ni and λ + χ + α-Fe, λ + FeTi and λ + FeTi + β-Ti phase mixtures occur at the SS–Ni interface. The occurrence of different intermetallics are confirmed by the x-ray diffraction technique. The maximum tensile strength of ∼276 MPa and shear strength of ∼209 MPa along with 7.3% elongation were obtained for the diffusion couple processed at 850 °C. At the 900 °C joining temperature, the formation of Fe–Ti base intermetallics reduces the bond strength. Evaluation of the fracture surfaces using scanning electron microscopy and energy dispersive spectroscopy demonstrates that failure takes place through Ni–Ti interface up to 850 °C and through the SS–Ni interface of the joint when processed at 900 °C.     

Joining of carbon/carbon composites for nuclear applications

Using hot pressing, carbon/carbon composites were joined using a Ti₃SiC₂/SiC interlayer which was in situ synthesized by the reaction of TiC and Si. Phase composition of the interlayer was characterized by X-ray diffraction. Morphologies of the joints before and after shear test were determined by scanning electron microscope and energy dispersive spectroscopy. The mechanical strength of the joints was assessed by shear strength test. Phase analysis reveals that the interlayer was mainly composed of ternary Ti₃SiC₂, SiC, and little TiC. The microstructure observation results show that the dense and uniform interlayer adheres firmly to the C/C composites. A composition gradient reaction layer was formed at the joining interface between C/C substrates and interlayer. The room temperature average shear strength of the joints is about 38.9 ± 3.6 MPa. The joining mechanism and failure behavior of the joints were also discussed.     

Optimization of bond strength between gold alloy and porcelain through a composite interlayer obtained by powder metallurgy

The purpose of this study was to evaluate the influence of a composite interlayer (at the metal-ceramic interface) on the shear bond strength of a metal-ceramic composite when compared with a conventional porcelain fused to metal (PFM).Several metal-ceramic composites specimens were produced by hot pressing. To identify which was the best composition for the interlayer several composites, with different relations of metal/ceramic volume fraction, were bonded to metal and to ceramic substrates. The bond strength of the composites to substrates was assessed by the means of a shear test performed in a universal test machine (crosshead speed: 0.5 mm/min) until fracture. Some interfaces of fractured specimens as well as undestroyed interface specimens were examined with optical microscope and scanning electron microscope (SEM/EDS).The shear bond strength results for all composites bonded to metal and to ceramic substrates were significantly higher (>150 MPa) than those registered in the upper range of conventional porcelain fused to metal (PFM) techniques (∼80 MPa). The use of a composite interlayer proved to enhance metal/ceramic adhesion in 160%.     

Vacuum diffusion bonding of TiB2 cermet to TiAl based alloys

Abstract

Vacuum diffusion bonding of TiB₂ cermet to TiAl based alloys was carried out at 1123 – 1323 K for 0.6 – 3.6 ks under 80 MPa. The microstructural analyses indicate that a compound Ti(Cu, Al)₂ is formed in the interface of the TiB₂ /TiAl joints, and the width and quantity of the Ti(Cu, Al)₂ compound increase with the increase of the bonding temperature and bonding time. The experimental results show that the shear strength of the diffusion bonded TiB₂ /TiAl joint is 103 MPa, when TiB₂ cermet is bonded to TiAl based alloy at 1223 K for 1.8 ks under 80 MPa.     

Diffusion bonding of Fe-28Al(Cr) alloy with low-carbon steel in vacuum

Fe-28Al(Cr) alloy and low-carbon steel were diffusion bonded in a vacuum of 10⁻⁴-10⁻⁵ Pa. The relationship of the bond parameters and shear strength at the interface was discussed. Microstructure characteristics and the reaction products at the interface were investigated by scanning electron microscopy (SEM) and X-ray diffractometry (XRD). The thickness of the diffusion reaction layer was measured with electron probe microanalysis (EPMA). The results indicated that controlling bonding temperature 1333 K for 3.6 ks, shear strength at the interface can be up to 112 MPa. Three kinds of reaction products were observed to have formed during the vacuum diffusion bonding, namely FeAl, Fe₃Al and α-Fe (Al) solid solution. The thickness (X) of the diffusion reaction layer increases with bonding time (t) according to a parabolic law X²=6.4×10³ exp(−104.1/RT)(t-t₀) (μm²).     

Interfacial Shear Strength Measurements of SiC Fiber-Reinforced Titanium Composites

A continuous loading push-out test technique was used to measure the interfacial shear strength of SiC fiber reinforced Ti matrix composites. The interracial shear strength of samples as-fabricated and after heat exposed at 700 and 800℃ for 50 h was successfully determined. It has been found that the interfacial shear strength of the specimen exposed at 700℃ was higher than that of as-prepared and exposed samples at 800℃. The shear strength of the as-prepared samples was about 112.45 MPa, and increased to about 153.77 MPa after heat-treating at 700℃ for 50 h, but decreased to 133.11 MPa after treating at 800℃ for 50 h. Scanning electron microscope (SEM) was used to investigate the interfacial morphology of the samples. The brittle phase was the main products of interface for samples exposed at 800℃, and the interface was easily peeled off.     

Open-cell copper foam joining: joint strength and interfacial behaviour

A copper (Cu) foam was brazed with Cu-4.0Sn-9.9Ni-7.8P filler foil for joint strength and interface analysis. Brazed 50 pores per inch (PPI) Cu foam yielded a maximum compressive strength of 14.4?MPa with a 127% increment compared to nonbrazed Cu foam. 15 PPI Cu foam produced a maximum shear strength of 2.7?MPa. Scanning electron microscopy showed that the thickness of the brazed seam decreased with increasing the Cu foam’s PPI. The formation of the Cu, Cu₃P (P: phosphorus) and Ni₃P (Ni: nickel) at the Cu/Cu foam interface was validated using energy-dispersive X-ray spectroscopy (EDX) and X-ray diffraction. EDX line scanning analysis revealed the diffusion of P and Ni into Cu foam, which took place via capillary force action.     

Microstructure and strength of high nitrogen steel joints brazed with Ni-Cr-B-Si filler

Brazing of high nitrogen austenitic stainless steels was carried out by using Ni-Cr-B-Si filler metal. The effects of brazing temperature (1020–1100°C) on the microstructure and shear strength of the joints were investigated. The results show that BN compounds with hexagonal structure are formed at the interface by the reaction of N from substrate and B from filler. The brittle Cr₅B₃ compounds with high microhardness are observed in the centre of brazing seam. The BN content increases and the Cr₅B₃ content decreases with the increase in brazing temperature. However, the content of BN compounds played a determinable role on the joint strength. The optimal shear strength of joints was 176.7?MPa when the joining temperature was 1020°C.     

SiCf/TC17复合材料界面剪切强度测试与有限元分析

界面强度对钛基复合材料的性能有重要影响。采用纤维顶出实验(push-outtest)对连续SiC纤维增强TC17复合材料的界面剪切强度进行了测试,采用SEM观察了样品的形貌。以纤维/基体完全分离后的摩擦力为出发点,采用有限元方法确定了复合材料成型过程中残余应力的产生温度,并计算了残余应力的分布,比较了顶出实验样品制备前后残余应力的变化情况及样品厚度、体积分数对残余应力分布的影响;采用内聚力模型(CZM)分析了界面的化学结合强度。结果表明:SiCf/TC17复合材料高温成型后的冷却过程中开始产生残余应力的温度为775℃;顶出实验样品制备后界面处生成了残余剪切应力,其大小和分布与样品的体积分数和厚度相关,界面处的残余剪切应力造成了界面剪切强度的测试结果与界面化学结合强度的差异;室温下SiCf/TC17复合材料的界面化学结合强度约为450MPa。     

电热作用对碳纤维/树脂复合材料界面应力的影响电热作用对碳纤维/树脂复合材料界面应力的影响

碳纤维/树脂复合材料广泛应用于民用航空器结构中,在服役期间会受到复杂环境（湿热、腐蚀、复杂应力和电热作用等）的作用,低强度电流对碳纤维/树脂复合材料的影响受到的关注较少。以碳纤维/树脂复合材料为研究对象,根据碳纤维的温敏效应和通电时的电阻变化规律,计算出碳纤维单丝/环氧树脂复合试样的界面温度范围,之后采用拉曼光谱测试和单丝断裂实验研究了低强度电流对单丝复合体系界面应力和界面剪切强度的影响。结果表明:随着电流强度的提高,单丝复合体系的界面温度随之升高,电流为8 mA时,界面温度高达约200℃。随着电流强度的增大,单丝复合体系的界面压缩应力表现为先增大后减小的趋势,电流高于7 mA后,界面处树脂出现烧蚀降解破坏;单丝断裂实验结果表明随着电流强度增大,单丝复合体系的界面剪切强度呈现先升后降的趋势,在6 mA时界面剪切强度达到最大值62.39 MPa,而8 mA时界面剪切强度仅为34.95 MPa。      

Microstructure and strength of brazed joints of Ti3Al-base alloy with different filler metals

The interfacial microstructure and properties of brazed joints of a Ti₃Al-based alloy were investigated in this paper to meet the requirements of the use of Ti₃Al-based alloy in the aeronautic and space industries. The effects of different brazing fillers on the interfacial microstructure and shear strength were studied. The relationship between brazing parameters and shear strength of the joints was discussed, and the optimum brazing parameters were obtained. The brazed joints were qualitatively and quantitatively analyzed by means of EPMA, SEM and XRD. The results showed that using a AgCuZn brazing filler, TiCu, Ti(Cu,Al)₂ and Ag[s,s] were formed, the shear strength of the joint was decreased because of the formation of TiCu and Ti(Cu,Al)₂; using a CuP brazing filler, Cu₃P, TiCu and Cu[s,s] were formed at the interface of the joint, the former two intermetallic compounds decreased the shear strength. The analysis also indicated that using the TiZrNiCu brazing filler, the optimum parameters were temperature T=1323 K, joining time t=5 min, and the maximum shear strength was 259.6 MPa. For the AgCuZn brazing filler, the optimum parameters were joining temperature T=1073 K, joining time t=5 min, and the maximum shear strength was 165.4 MPa. To the CuP brazing filler, the optimum parameters were joining temperature T=1223 K, joining time t=5 min, and the maximum shear strength is 98.6 MPa. Consulting the results of P. He, J.C. Feng and H. Zhou [Microstructure and strength of brazed joints of Ti₃Al-base alloy with NiCrSiB, Mater. Charact., 52(8) (2004) 309–318], relative to the other brazing fillers, TiZrNiCu is the optimum brazing filler for brazing Ti₃Al-based alloy.     

Microstructure and shear strength of Mo-Cu/Cr18-Ni8 brazing joint in vacuum

High density Mo-Cu composite and Cr18-Ni8 stainless steel were brazed with Ag-Cu filler metal in vacuum of 10⁻⁵ Pa. The microstructure characteristics of Mo-Cu/Cr18-Ni8 brazed joint were investigated by field-emission scanning electron microscope (FESEM) with energy dispersive spectrometer (EDS) and shear strength was measured by shearing test. The results indicated that a Mo-Cu/Cr18-Ni8 joint with shear strength of 125 MPa was obtained at 940 °C for 20 min. There were Ag-Cu eutectic and Cu-rich phase without brittle intermetallic compounds formed in the joint. The shear fracture exhibited plastic feature with shear dimple and fracture located at the interface between braze seam and Cr18-Ni8 stainless steel.     

Effects of temperature on interface microstructure and strength properties of titanium–niobium stainless steel diffusion bonded joints

Abstract

The effects of temperature on interface microstructure and strength properties of Ti/stainless diffusion bonded joint using Nb interlayer, processed in the temperature range 800–950°C for 1·5 h in vacuum were investigated. The stainless steel/Nb interface is free from intermetallic phase up to 900°C; however, Fe₂Nb+Fe₇Nb₆ phase mixture has been observed at 950°C processing temperature. The Nb/Ti interface is free from intermetallic for all processing temperatures. The maximum tensile strength of ～287 MPa (～90% of Ti) and shear strength ～222 MPa (～75% of Ti) along with 6·9% ductility have been achieved in the diffusion bonded joints, when processed at 900°C. The bonded samples failure takes place through the stainless steel/Nb interface for all processing temperatures during the loading.     

Structure and properties of solid state diffusion bonding of 17-4PH stainless steel and titanium

Abstract

Solid state diffusion bonded joint between titanium and 17-4 precipitation hardening stainless steel was carried out in the temperature range of 800–1050°C in steps of 50°C for 30 min and also at 950°C for 30–180 min in steps of 30 min under a uniaxial pressure of 3·5 MPa in vacuum. Bonded samples were characterised using light microscopy, field emission scanning electron microscopy and X-ray diffraction technique. Up to 850°C for 30 min, FeTi phase was formed at the diffusion interface; however, α-Fe+λ, χ, Fe₂Ti and FeTi phases and phase mixtures were formed above 850°C for 30 min and at 950°C for all bonding times. Maximum tensile strength of ～326 MPa, shear strength of ～254 MPa and impact toughness of ～24 J were obtained for the diffusion couple processed at 1000°C for 30 min and 30–180 min time interval at 950°C, and maximum tensile strength ～323 MPa, shear strength ～243 MPa and impact toughness of ～22 J were achieved when bonding was processed for 120 min. The residual stress of the bonded joints increases with the increase in bonding temperatures and times.