Diffusion Bonding of Metals

Dear Colleagues,

Diffusion bonding is an amazing technology for producing holohedral joints, and also of internal structures. Although expensive equipment is required to maintain an inert atmosphere at high temperatures, and an external load has to be applied to the parts to be joined, diffusion bonding is used extensively in, e.g., aerospace industries and for internal cooling structures for molding tools.

The main process parameters are bonding temperature, dwell time, and bearing pressure. In addition, the aspect ratio and the number of layers to be bonded affect deformation during the diffusion bonding process.

Furthermore, additional issues must be considered to reach the goal, forming a monolithic part with vacuum tightness and resistance to high internal pressures by grain growth across bonding planes. For this, surface roughness must be leveled. Apart from the roughness values affecting vacuum tightness, the number of layers has an impact on the degree of deformation.

Materials science aspects resulting from the heat treatment, such as grain growth and its impact on mechanical or corrosive properties of the materials, must be considered.

To facilitate grain growth across bonding planes, the passivation layer must be soluble in the bulk material or must be removed by appropriate surface preparation, e.g. by brushing or pickling.

Interlayers like thin amorphous foils or additional metals deposited by PVD-processes may facilitate bonding by formation of a temporary liquid phase due to high interfacial energy or forming eutectic compositions. The occurrence of liquid phases at considerably lower temperature helps to limit grain growth of the matrix material, and the coefficient of diffusion in liquids is several orders of magnitude higher than in solids.

For this Special Issue in Metals, we welcome research articles and reviews addressing theoretical aspects, specific designs for diffusion bonding, diffusion bonding equipment, surface preparation, bonding experiments of all kinds of metallic materials, including use of different inter- and multilayers, preparation and characterization of diffusion-bonded parts, as well as examples of applications of diffusion bonding.

Dr. Thomas Gietzelt
Guest Editor

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