Novel joining of dissimilar materials in the graphite/Hastelloy N alloy system using pure Au doped with Si particles

The purpose of this investigation was to describe and discuss the fundamental issues involved in brazing of graphite to Hastelloy N alloy by using pure Au foil doped with Si particles. The introduced method was to bring the Si into the Au and enabled the Si concentration to be varied from 5 to 15 at.% in the braze. It was then possible to study the effect of this parameter on the joints' microstructure, as well as the mechanical performance. The detailed microstructure of the graphite/braze interface, braze, Hastelloy N beside the braze seam, was characterized by transmission electron microscopy (TEM) coupled with high-resolution transmission electron microscopy (HRTEM). The results show that Si with accurate control in quantity will produce a robust graphite/Hastelloy N alloy joint, due to its strong effect in modifying the microstructure. When incorporating 5 at.% Si, the obtained maximum joint shear strength is 32.5 MPa, equal to the strength of graphite substrates. The underlying factor that Si affects the microstructure and joint bond strength was unveiled. The performed investigation will be beneficial to deeply understand the fundamental issues involved in producing the graphite-metal combinations.