Influence of Brazing Process Parameters on the Mechanical Properties of Nickel Based Superalloy

A common nickel based superalloy Inconel625 was brazed with Ni- base braze filler material (AMS4777) contained depressants such as B and Si. Different braze gap, time of brazing and form of braze filler material were considered. It was determined that melting point depressant B, Si tend to form hard and brittle phases in the joint during the braze cycle. Brittle phases significantly reduce mechanical properties (e. g. tensile strength) of the joint. Therefore it’s important to define optimal process parameters to achieve high strength joints, free of brittle phases. High ultimate tensile strength values can be obtained, if the joint area is free of brittle phases which is equivalent to a complete isothermal solidification of the joint. Isothermal solidification takes place only, if the concentration of the melting point depressant element of the braze filler material in the joint is continuously reduced by diffusion into the base- material. For a given brazing-temperature, long brazing times and small braze-filler-material-volumes (small braze-gaps) are beneficial for isothermal solidification. On the base of obtained results it can be stated, that the braze-filler-material-form has an influence on the joint quality. Better properties can be achieved by the use of foil instead of paste because of reduced amount of voids or better bonding/wetting by using foil.