Modeling the interaction between surface condition and diffusion characteristics for diffusion bonding of nickel alloys

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Dissimilar and similar welds joined over the entire surface with or without interlayer materials are characteristics of diffusion bonding. This makes diffusion bonding particularly suitable for manufacturing of monolithic components, e.g. in microapparatus engineering, which are composed of a large number of layers or sheets. In such microapparatuses, processes such as cooling, chemical mixing or chemical reactions can be carried out at higher efficiencies than in conventional systems. Depending on the process-related operating conditions, high-performance materials such as nickel alloys are used for these components. An additional possibility to improve the efficiency of microapparatuses is to increase the reaction area per component volume. This requires a significant reduction in the size of the channel structures, so that the process energies during diffusion bonding (joining temperature, joining time and joining pressure) must be reduced in order to ensure the dimensional accuracy of the channel structures and the required material and joining properties. In this project, research is to be carried out into how the microstructure and surface properties of the joining surfaces must be shaped by turning and diamond smoothing processes in order to increase the diffusivity and thus reduce the process energies. The scientific objectives are to determine the mechanisms and interrelationships that lead to a change in the surface roughness, grain size and residual stress state during turning and diamond smoothing of nickel and Alloy 625. Furthermore, for these materials the determination of the relationships between the geometrical surface and the physical surface layer properties, the process regime of diffusion bonding, and the properties of the resulting joint is carried out. In addition, based on the results of the investigations, the contact angle measurement is to be qualified in such a way that a quick and easy evaluation of the joining surfaces can be made in order to enable a prediction of the required process energies. From this, a model is to be developed which, on the basis of the input variables contact angle and surface roughness of the joining surfaces, enables the derivation of suitable process conditions for diffusion bonding.