Diffusion welding compositions

From a knowledge of plate and weld composition define a new range of possible diffusivity coefficients, D, within the limits shown in Fig. 5.17 at 20°C. 

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 diffusion welding and cold-rolling procedure previously described for the synthesis of the Ni-based membrane has been also applied to the production of a Pd-Ag/Nb/Pd-Ag composite membrane. In this application, two Pd-Ag foils with a thickness of 25 pm were used to cover a Nb plate with a thickness of 1 mm. This composite membrane was rolled down to a thickness of 128 pm (of which about 122 pm was Nb bulk, between two very thin Pd-Ag layers of 3 pm). The permeation tests carried out at 180°C... 

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). 

Another theoretical aspect of adhesion can be optimized with surface treatment. The interdiffusion theory described by Voyutski [6] involves the diffusion of macromolecular chains across a polymer interface. In this case the interface is transformed progressively to a wide interphase. Welding of composites is then the main technique that can enhance this particular aspect. This welding can be performed with ultrasonic, electric induction, or resistance techniques [7]. 

As production demands have led to increasingly higher operating temperatures and pressures, protection of carbon steel waterwah tubes has involved studding, application of weld overlay or thermal spray, or the use of composite (stainless-clad carbon steel) or chromized (diffusion-coated carbon steel) tubes to provide resistance to sulfidation and oxidation on the fireside. 

Besides diffusion problems, fractal analysis can be applied to such problems as lamination of composites, powder and pellet resin coalescence, latex paint structure, internal weld line shape, and tack of uncured elastomers. In this area, theory is ahead of experiment. 

Coatings for carbon and Cr-Mo steels are often overlaid, and of composition corresponding to the austenitic alloys listed in Table 5-1, although several steel products are diffusion aluminized, particularly for resistance to sulBdation attack (Sivakumar and Rao, 1982 Bayer, 1995). The weld overlay process, in which an arc-welding method is used to deposit a 2-3 mm coating (i.e., clad-... 

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