Graphite-to-304SS Braze Joining by Active Metal-Brazing Technique : Improvement of Mechanical Properties

In the present investigation, an attempt has been mad
to improve the mechanical strength of graphite-stainless steel-brazed joint. Due to high capillary action, the liquid filler alloy usually tends to percolate into the pores of graphite causing severe stress in the graphite near the joint interface resulting in poor joint strength of 10-15 MPa. In the present investigation, a thin coating of SiC was applied on graphite before the joining process to avoid the penetration of liquid filler alloy in to the pores of the graphite. Active filler alloy Ag-Cu-Ti was used to braze the substrates. The brazing was carried out at 850, 900, 950, and 1000oC. The characterization of the interfaces of the brazed joints was carried out using scanning electron microscopy attached with energy dispersive spectroscopy and x-ray diffraction analysis. From the correlation between the microstructural and mechanical properties, shear strength of approximately 35 MPa for graphite 304ss-brazed joint produced at 900o was demonstrated. After the shear tests, the fracture surfaces were analyzed by SEM-EDS.