Diffusion-bonding

Takeda et al. [141] described the conditions applied for the diffusion bonding of nickel-based alloys (Hastelloy). A test piece of a plate and fin heat exchanger (dimensions 40 mm x 40 mm x 3 mm, channel dimensions 1000 pm x 1000 pm) was first cleaned with a 1% solution of nitric acid and hydrogen fluoride to remove the oxidation layer. A pressure as low as 6 mPa was necessary to run the process. For NiCrFe and other materials, other authors claim that an even lower pressure of 1 pPa is required. A welding temperature of 1 150 °C and a contact pressure of 

440 bar for a duration of 30 min were identified as optimized conditions. Significant deformation of the test piece was required according to the authors. However, other authors claim 3% deformation to be sufficient [44], Leak tightness was verified at ambient temperature up to 630 bar. 

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Defect Evaluation in Diffusion Bonding Interface of Dissimilar Metals Using Ultrasonic Testing Method. 

This study detects the defect of the void and the exfoliation in the solid phase diffusion bonding interface of ductile cast iron and stainless steel with a nickel insert metal using ultrrasonic testing method, and examine the influence of mutual interference of the reflectional wave both the defect and the interface. 

Evaluation of Bonding Process in Diffusion Bonding Joints of Dissimilar Metals using Ultrasonic Testing Method. 

This study was in real time measured that the reflective echo height of the bonding interface in the solid phase diffused bonding process of carbon steel and titanium using ultrasonic testing method. As a result, the following were made discernment. 

On the other hand, the reliability of the product improves, too, if each state of the plasticity deformation, the creep deformation, and the diffusion joint in the solid phase diffusion bonding as the bonding process, is accurately understood, and the bonding process is controlled properly. 

Fig. 4. Diffusion bonding process (a) apply metal foil and cut to shape, (b) lay up desired pHes, (c) vacuum encapsulate and heat to fabrication temperature, (d) apply pressure and hold for consoHdation cycle, and (e) cool, remove, and clean part.

Electronic-Grade MMCs. Metal-matrix composites can be tailored to have optimal thermal and physical properties to meet requirements of electronic packaging systems, eg, cotes, substrates, carriers, and housings. A controUed thermal expansion space tmss, ie, one having a high precision dimensional tolerance in space environment, was developed from a carbon fiber (pitch-based)/Al composite. Continuous boron fiber-reinforced aluminum composites made by diffusion bonding have been used as heat sinks in chip carrier multilayer boards. 

Fig 19 11 Joining methods for ceramics (a) glaze bonding, (b) diffusion bonding, (c) metallisation plus brazing. In addition, ceramics can be clamped, and can be joined with adhesives. 

Pt electrodeposits may also be produced from molten salt electrolytes. Such a high-temperature process has the advantage that the deposits are diffusion bonded to the titanium substrate and thus have good adhesion, and, if necessary, thick deposits can be produced. However, they have the disadvantage that because of the complexity of the process there is a limitation on the size and shape of the object to be plated, and the resultant deposits are softer and less wear resistant than those from aqueous solutions... 

Figure 11.12 Badly deformed bonded array of microchannels with poorly understood design and intermediate phase diffusion-bonding parameters.

The ShimTec reactor from Chart Industries [18, 19] is an example of a HEX reactor with diffusion-bonded plates (Figure 12.2). The reactor is composed of three plates one process plate sandwiched between two utility plates. All the units are made of 316 stainless steel, unless stated otherwise. Swagelok fittings are used for all the connections. 

Figure 1.26 Large-capacity heat exchanger, e g. for use on oil platforms, constructed from diffusion-bonded plate stacks comprising a vast number of millimeter-sized channels. This apparatus was manufactured by Heatric (Poole, UK).

As an alternative to seals, irreversible bonding can be applied, e.g. by laser welding the surface of a microstructured stack [29, 30] or by diffusion bonding via vacuum compression of a microstructured stack [18, 37-39], For better handling and fluid interconnection, diffusion-bonded stacks may be surrounded by a shell [18, 37-39], Diffusion-bonded stacks typically are more compact. In addition, this interconnection technique is principally amenable to small-series production. Accordingly, it is seen as a proper way to realize future commercial, off-the-shelf micro reactors,... 

Microfabrication of the parallel channels was performed by mechanical surface cutting of metal tapes [31]. In the case of aluminum alloys, ground-in monocrystalline diamonds were used [45]. In the case of iron alloys, ceramic micro tools have to be used owing to the incompatibility of diamonds with that material. Such a microstructured platelet stack is provided with top and cover plates, diffusion bonded and connected to suitable fittings for the inlet and withdrawal ducts by electron beam welding (Figure 3.9). 

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. 

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