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Advances In Brazing Science Technology And Applications Pdf

advances in brazing science technology and applications pdf

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Advances in Brazing

The CeO 2 nanoparticles were reinforced in the eutectic Ag-Cu-Ti filler via mechanical mixing and melting route. The joint shear strength was improved with the addition of CeO 2 up to 0. Bonding of ceramic materials to metals is a recent hot topic in various engineering applications, including heat exchangers, connectors, capacitors, thermoelectrics, solar cells, and complex structural joints [ 1 , 2 ].

It is always a practical challenge to bond these ceramic materials directly due to a wide difference in physicochemical and mechanical properties of ceramics and metals that imposes a great challenge in microjoining operations [ 2 ]. For this purpose, various popular brazing fillers are already developed where the most popular ones are eutectic Ag-Cu or Ag-Cu-Ti alloys as reported in the past [ 3 , 4 ].

However, with regard to complex geometry, the thickness of IMCs, and cost, each filler is unique and has limitations of its own [ 5 ]. In such case, the selection of a superior filler metal is required for high reliability of brazed ceramic joints. If we inspect previous literatures, we see two major issues that are needed to be minimized in ceramic brazing, such as wetting of the contact surfaces and the stress development caused by the mismatch in mechanical and thermal properties of two contact materials that depend on the deformation characteristics of the filler used [ 1 — 5 ].

There are various strategies developed to resolve these mentioned issues. First is the use of active metal brazing techniques. Active metal brazing is a simple and cost-effective approach where active elements like Ti or Zr as wetting promoters are used between the contact surfaces for bonding [ 1 , 6 ].

Therefore, the popular Ag-Cu-Ti filler seems to be more reliable over the Ag-Cu filler due to its good wetting to most of the ceramics [ 7 ]. Second is the use of additive elements or reinforcement particles to refine the interfacial layer, redistribute the stress in the matrix, and relax the joint stress.

These secondary phases act as a wetting enhancer when used in optimum amounts [ 8 , 9 ]. It was reported that the use of reinforcements provides outstanding benefits in terms of joint strength and interfacial characteristics [ 10 , 11 ]. In the past, the use of nanomaterials has already been suggested as a potential technology for controlling the wetting, refining the grains, IMCs, as well as to tailor the joint microstructure [ 8 — 11 ]. In lead-free soldering, a variety of nanoparticles have found a wide scope in popular Sn-based alloys for tailoring the microstructure containing harmful Cu 6 Sn 5 and Cu 3 Sn IMCs across the Cu-Sn interface [ 12 — 14 ].

Analogous to brazing, nanoparticles have been tried in few studies related to the low-temperature Al-brazing filler and remarkably improved wetting and joint performance are obtained. There are various studies in the past where researchers have used metal or nonmetallic additives to control the brazing performance. Miao et al. Zhao et al. In another study, Miao et al. However, in ceramic brazing, limited studies exist on nanocomposite-based brazing fillers [ 24 — 26 ]. Among these nanoreinforcements, rare earth oxide, particularly, CeO 2 , has been used frequently for low temperature joining of electronic devices as well as in multiple applications such as photonics, energy storage devices, sensing, and power electronics.

In view of these merits, we have chosen CeO 2 nanoparticles produced via solution combustion method to reinforce the Ag-Cu-Ti matrix and apply for brazing of ZrO 2 and Ti-6Al-4V plates in the lap-joint configuration. The microstructural, mechanical, and thermal properties of the composite fillers were studied. Cerium oxide nanopowder was prepared by using the high-temperature solution combustion method using ceric ammonium nitrate, citric acid, and glycine [ 27 ]. Both the base materials were diced by using a diamond saw into slices with a size of Four different types of composite fillers with different CeO 2 contents were used in the experiment, as shown in Table 1.

The brazeability of the composite fillers was determined from the spreading ratios of filler melted before and after melting Figure 1. The solidified composite filler 0. The spreading ratio S was estimated from the difference in the spread ratios before and after experiment [ 28 ]. The composite filler was rolled down to a thickness of 0. The surface morphology of the developed composite fillers and joint cross section were examined in a field emission scanning electron microscope FE-SEM, Hitachi, Japan.

The microhardness was automatically calculated and displayed over the display panel of the machine. The shear strength of the joint was estimated according to the JIS Z standard [ 29 ].

The schematic of the set-up used for the shear test is shown in Figure 3. The peak broadening indicates the nanocrystallinity of the powder with an increased lattice strain.

The average crystallite size D of the powder particles is given by the Scherer equation [ 27 ]:. In general, the XRD peak broadening is governed by various factors such as the instrumental effects, crystallite size, and lattice strain. The contribution to lattice strain is given by a modified Scherer equation:. It is to be noted that as the particle size reduces, the number of surface atoms increases as compared to the bulk.

This increase in the surface atoms per unit volume raises the lattice strain which is associated with the structural distortion. This results in high reactivity of the particles at nanoscale level. The morphology of the CeO 2 powder particles Figure 4 b is like loose spongy type which is a typical morphology obtained for combustion synthesized powder [ 27 ].

This type of structure is already observed in the past by several researchers. The results indicated various peaks in the XRD spectrum. The X-ray patterns of other samples were almost similar. There was no indication of the formation of new phases related to CeO 2 which indicated that there is no reaction of the filler matrix with the reinforcement particles Figure 5 a.

The different morphology of the composite fillers is shown in Figures 5 b — 5 e. We can see that the addition of CeO 2 nanoparticles has a great effect on the filler morphology. The corresponding phases were analyzed by the EDS, as shown in Figures 5 b — 5 d and 5 f. The bright and dark phases are shown by spots 1 and 2, while Cu-Ti IMCs are distributed across the interface spot 3 , as shown in Figure 5 f. The EDS analysis results given in Table 2 also show the probable compositions of the phases of spots 1—3.

After the addition of CeO 2 nanoparticles, the Ag- and Cu-rich regions were found to be smaller up to the addition of 0. In other words, there is a refinement in the microstructure of the filler alloy. Generally, the morphology of the composite filler is refined by the addition of nanoparticles into the filler matrix. There are various theories proposed in the past that explain the effect of nanoparticles on composite morphology. According to the absorption theory of surface-active materials [ 8 — 11 ], addition of nanoparticles decreases the surface-free energy of the crystal plane where maximum adsorption of nanoparticle occurs.

The resultant surface energy is given from equation 5 : where A j represents the surface area of j th plane and is independent of concentration. Therefore, surface energy will be minimum when is maximized [ 8 — 13 ]. Thus, the growth velocity of a particular plane, j , will be decreased. As a result, the nanoparticles can be adsorbed easily to the IMC plane and restrict their growth. Another theory for the effect of nanoparticles on morphology says that nanoparticles act as nucleating agents, and, therefore they increase more nucleation sites in the matrix as well as on the IMCs during solidification [ 8 — 13 ].

Therefore, according to the aforementioned theories, the presence of an optimum amount of nanoparticles into the filler matrix will promote the grain and IMC refinement of the filler.

This may be due to the high amount of CeO 2 nanoparticles getting segregated in due course, and localized cracking was noticed [ 9 — 11 ]. It has been reported by many researchers that high surface-active nanoparticles have a tendency of agglomeration. This localized segregation results in buildup of porosity and cracks may form in the joint after solidification [ 11 — 13 ]. It was observed that the spreading ratio rises continuously with the increase in CeO 2 fraction in the filler.

When the content of CeO 2 was more than 0. This can be correlated with the presence of high surface energy ceria nanoparticles which depress the surface tension of the filler and enhance the wetting [ 20 ]. However, at a high amount of ceria nanoparticles in the matrix, the viscosity of the filler increases and therefore wetting decreases instead of the presence of the active Ti element [ 20 ]. It is also noted that, in spite of a higher spreading ratio on Ti-6Al-4V, it decreased up to some extent on zirconia substrates.

This is obvious due to the presence of strong covalent bonding in zirconia ceramics compared to the metallic ones in metal.

It can be concluded that the addition of an optimum amount of CeO 2 nanoparticles 0. Only one sharp melting peak is noticed. The melting point of Ag falls near The melting point of Ag-Cu-Ti- x CeO 2 fillers is slightly higher but falls within the normal working limits of brazing.

The various onset melting points and peak melting temperature of the composite fillers are shown in Table 3. In other words, the change in the melting point of Ag-Cu-Ti- x CeO 2 composites is not high enough to bring any change in service temperature conditions. The interface zone is composed of several black and white patches. The interfacial elements were identified by the EDS analysis Figure 8 e.

The spot 1 shows a fine layer near the Ti-6Al-4V side. The white and black phases spots 2 and 3 correspond to the Ag- and Cu-rich phases. The at. Also, Ag Ti was prominent near the interface as shown although it existed a little across the interface. The reason can be a very small amount which is not sufficient enough to minimize the IMCs considerably in the matrix. The thickness of this layer is different for each condition being minimum Also, the thickness of the interfacial layer is on a little higher side The mechanism of joint formation can be understood by the model presented in Figure 9.

The reaction proceeds in various steps. During brazing, when the temperature is above the solidus of the filler, various elements diffuse to each other across the interface Figures 9 a and 9 b. The filler melts, and then Ti is dissolved into the molten filler and interacts with Cu atoms.

Ag occupies the solid solution matrix of the filler. ZrO 2 is bonded under the influence of Ti which is absorbed in the surface pores through capillary action at the ZrO 2 surface Figures 9 c — 9 d. The CeO 2 nanoparticles are attached to the IMCs and prevent their further growth, as shown by thickness measured from the joint SEM in previous section.

It is seen that the microhardness increases from This shows a reasonable increase in hardness

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Ceramic to metal joining has its potential applications in microelectronics packaging, metal—ceramic seals, vacuum tubes, sapphire metal windows, etc. But there are many limitations in joining this duo of materials that range from their structures, nature of bonding, physical properties to a complex phenomenon like wetting, spreading and adhesion. The current review discusses these critical issues from the aspects of thermodynamics, the role, and type of active elements, Ag—Cu—Ti brazing filler system and the reliability factors like residual stress, coefficient of thermal expansion, material reliability, pores and unbonded regions on the surface which affect the mechanical reliability of the joint. Both ceramics and metals are widely used engineering materials. Ceramics are brittle in nature with its strength almost two-third of its theoretical strength. They are lightweight, hard, stable at high temperature, brittle and have low fracture toughness [ 1 ]. On the other hand, most metals are soft, ductile with better fracture toughness and have less strength compared to ceramics [ 2 ].

advances in brazing science technology and applications pdf

Advances in Joining and Welding Technologies for Automotive and Electronic Applications

The CeO 2 nanoparticles were reinforced in the eutectic Ag-Cu-Ti filler via mechanical mixing and melting route. The joint shear strength was improved with the addition of CeO 2 up to 0. Bonding of ceramic materials to metals is a recent hot topic in various engineering applications, including heat exchangers, connectors, capacitors, thermoelectrics, solar cells, and complex structural joints [ 1 , 2 ].

Chapter Brazing of nickel-based filler metals for pipes and other components in contact with drinking water. Brazing processes offer enhanced control, adaptability and cost-efficiency in the joining of materials. Unsurprisingly, this has lead to great interest and investment in the area.

Advances in Brazing: Science, Technology and Applications

Comprehensive and unique source integrates the material usually distributed among a half a dozen sources. Presents a unified approach to modeling of new designs and develops the skills for complex engineering analysis.

By Elsevier Science. Eustathopoulos, F. Hodaj and O.

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Не успел он набрать международный код, как в трубке раздался записанный на пленку голос: Todos los circuitos estan ocupados - Пожалуйста, положите трубку и перезвоните позднее.

Хейл засмеялся: - Можете пристраивать к ней черный ход - я слова не скажу.  - Потом в его голосе зазвучали зловещие нотки.  - Но как только я узнаю, что вы следите за мной, я немедленно расскажу всю эту историю журналистам. Я расскажу, что Цифровая крепость - это большая липа, и отправлю на дно все ваше мерзкое ведомство. Стратмор мысленно взвешивал это предложение.

Мы слухачи, стукачи, нарушители прав человека.  - Стратмор шумно вздохнул.  - Увы, в мире полно наивных людей, которые не могут представить себе ужасы, которые нас ждут, если мы будем сидеть сложа руки. Я искренне верю, что только мы можем спасти этих людей от их собственного невежества. Сьюзан не совсем понимала, к чему он клонит.

Recent Advances in Active Metal Brazing of Ceramics and Process

Беккер показал на бутылки, которые смахнул на пол. - Они же пустые.

Это девушка. Она стояла у второй входной двери, что была в некотором отдалении, прижимая сумку к груди. Она казалось напуганной еще сильнее, чем раньше.

Никому не показалось удивительным, что два дня спустя АНБ приняло Грега Хейла на работу. Стратмор решил, что лучше взять его к себе и заставить трудиться на благо АНБ, чем позволить противодействовать агентству извне. Стратмор мужественно перенес разразившийся скандал, горячо защищая свои действия перед конгрессом. Он утверждал, что стремление граждан к неприкосновенности частной переписки обернется для Америки большими неприятностями.

Advances in Brazing

Весь вечер оказался сплошной комедией ошибок. В его ушах звучали слова Стратмора: Не звони, пока не добудешь кольцо. Внезапно он почувствовал страшный упадок сил. Если Меган продала кольцо и улетела, нет никакой возможности узнать, где оно. Беккер закрыл глаза и попытался сосредоточиться.

 Понятия не имею. Я уже говорила, что мы ушли до их прибытия. - Вы хотите сказать - после того как стащили кольцо.


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