Temperature diffusion welding

Typically, coatings most often in use as intermediate layers are silver, nickel, copper, and gold however, silver is used by far the most often. This is so because of the low dissociation temperature of silver oxide, making it relatively easy to obtain clean surfaces. Also, the typical thickness range of electroplates used, in practice, for diffusion welding is about 15 to 40/rm, but thicknesses as great as 130 )um must sometimes be used. A considerable variety of steel types as well as aluminum and a host of other difficult-to-join metals and even beryllium have been and continue to be diffusion bonded with the use of electroplated intermediate layers. 

Takeda T, Kunitomi K, Horie T, Iwata K. Feasibility of the applicability of a diffusion-welded compact intermediate heat exchanger to next-generation high-temperature gas-cooled reactors. Nucl Eng Design, 1997 168 11-21. 

Takeda, T., Kunitomi, K., Horie, T., Iwata, K., Feasibility study on the applicability of a diffusion-welded compact intermediate heat exchanger to next-generation high temperature gas-cooled reactor, Nucl. Eng. Des. 1997, 168,11-21. Bier W., Keller W., Linder G., Seidel, D., Schubert, K., Martin, H., Gas-to-gas heat transfer in micro heat exchangers, Chem. Eng. Process. 1993, 32, 33-43. Schubert, K., Brandner J., Fichtner M., Linder G., Schygulla, U., Wenka, A., Microstructure devices for applications in thermal and chemical process engineering, Microscale Therm. Eng. 2001, 5,17-39. www.fzk.de, Forschungszentrum Karlsruhe, 17 July 2004. 

In our study, a new CHX can be used over 900°C condition is designed and manufactured. The CHX consists of only plates welded with diffusion. The tensile and creep strengths in the diffusion welding are superior to those in the brazing especially in high temperature condition. 

In our study, a contact pressure, ambient temperature and holding time, which significantly affect the diffusion welding, are selected as a parameter. Besides these parameters, the ambient pressure is determined as low as possible so that the impurity composites are not included between two plates. The ambient pressure is set to 6x10 Pa by vacuum pumps in this test. 

The CHX with the diffusion welding would also become feasible for the IHX because the strength of the diffusion welding in high temperature condition is apparently higher than that of brazing, and the thermal performance and cost are superior to the... 

The early tests prove that the ambient temperature of 1150°C, contact pressure of 49MPa and holding time of 30 minutes are selected as the best condition for the diffusion welding. The welding surfaces between plates are sound in this case. The tensile strength and creep strength of the welding will be tested this year. 

Diffusion welding is of particular importance for titanium materials because these materials are more amenable to a homogeneous band in the solid state state than other metals. After welding, the joint zone shows a higher temperature under high vacuum or, in an inert atmosphere, a microstructure very similar to that of the base metal. 

Diffusion welding is a technique used to join metals it consists of pressing at temperatures 50%-75% of the melting point of the metal parts to be joined [44,45]. Usually, the load applied provokes no macroscopic deformation of the material. At high temperature, the metal atoms diffuse through the lattice, thus joining the parts pressed together. 

Diffusion welding process is controlled by temperature and time through Pick s second law (13.14) described in Section 13.3.2 for the case of hydrogen diffusion in a metal lattice. 

Metals characterized by high diffusion coefficients allow the diffusion welding at relatively low temperatures for short times. Another important technological feature of adding silver to palladinm is given by the high diffusivity of silver that makes easier the diffusion welding. In fact, the diffnsion coefficient of silver is as follows ... 

Through Equation 13.30, the diffusion length of silver is calculated versus time for different temperatures, as presented in Figure 13.16. For instance, Pd-Ag foils of thickness 50 m can be joined through diffusion welding when the diffusion length is about 100 pm the thickness of two metal foils overlapped. For such a case, it is observed that less than 1 h at 1000°C is needed. 

Transition Joints. Use of explosion-clad transition joints avoids the limitations involved in joining two incompatible materials by bolting or riveting. Many transition joints can be cut from a single large-area flat-plate clad and deflvered to limit the temperature at the bond interface so as to avoid undesirable diffusion. Conventional welding practices may be used for both similar metal welds. 

Thermal imaging is sensitive to iafrared radiation that detects temperature changes over the surface of a part when heat has been appHed. Thermal diffusion ia a soHd is affected by variatioa ia composition or by the preseace of cracks, voids, delamiaatioas, etc the effects are detected by surface temperature changes. Defects cannot be detected if their depth below the surface is more than two to three times their diameter. Nondestmctive testing has been primarily used for composites and analysis of adhesive bonds or welds. Several studies are documented ia the Hterature (322—327). 

Air contains 1% of Ar that can dissolve and diffuse into glass at high temperatures. For a glass cylinder heated to high temperature for 2 h with only one surface in contact with air (all other surfaces are welded to a metal capsule). The glass cylinder initially does not contain any Ar and can be viewed as semi-infinite. Ar diffusivity is 10 m /s. Calculate the diffusion profile. 

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