Wide gap brazing of stainless steel to nickel-based superalloy

Abstract

High temperature brazing with nickel-based filler metal was carried out to study the wide gap brazing of stainless steel to nickel-based superalloy. Both the filler metal and the additive metal were provided by a brazing preform that was produced from gas atomized powders by hot isostatic pressing. This brazing preform was inserted into the gap between the joining partners, and subsequently brazed by induction heating in a reducing atmosphere. During the brazing process, a pressure of about 1 MPa was applied across the joint thus deforming the preform and equalizing the production tolerances of the joining partners. The results show that during brazing the filler metal melts and reacts with both the solid base metal and the solid additive forming a new alloy with the desired mechanical properties. Tensile test specimens exhibited a strength of about 390 MPa indicating that isolated brittle phases which were stabilized in joints brazed at the lower end of the brazing temperature do not affect the strength of the wide gap joint. Consequently, the wide gap brazing technique discussed in this paper makes it possible to join large parts that cannot be joined by conventional high temperature brazing with capillary clearances. It can also replace conventional welding techniques because of the possibility to join dissimilar metals and the short process time required.