Modified nanopastes for pressureless nanojoining in the field of structural applications

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Joining with nanoparticles (nanojoining) is a promising alternative to conventional brazing and soldering processes. The lower sintering and melting temperature of the nanoparticles compared to corresponding bulk material enables reduced joining temperatures, so that nanojoining offers great advantages. However, new challenges also arise with this joining process. For example, high pressures must be applied to the surfaces to be joined during the process in order to achieve sufficient joint strengths, which limits the flexibility and applicability of nanojoining. In order to counteract the disadvantages of applying joining pressure, the aim of this project is to achieve the desired properties of a nanojoint entirely without or at least with significantly reduced joining pressure. This would allow greater flexibility in the design of the joining geometry, simplify system technology and process steps, and also enable mechanically sensitive component structures to be joined.The starting point of the investigations are Ni nanopastes, which can be used for joining in the field of structural applications. In the proposed project, a concept is presented in which the metal content of the nanopastes is expanded by a component which is present in the liquid phase at the joining temperature. The main aim of this is to reduce the porosity in the joint and to improve the bonding between the nanoparticles and the base material. With the help of the liquid phase, it is attempted to achieve a microstructure which leads to sufficiently high joining strengths without the need for joining pressure in the ideal case. By carefully selecting this component according to the mixing behavior with nickel, a high remelting temperature and thus a high operating temperature of the joined assembly can be guaranteed through in situ alloy formation. The basic feasibility of this concept is demonstrated on the basis of our own preliminary work. In addition, fundamental investigations are also planned to create a model that allows a better understanding of the influence of the joining pressure on the microstructure and the joint strength.