Brazing of hot isostatically pressed-Al2O3 to stainless steel (AISI 304L) by Mo-Mn route using 72Ag-28Cu braze

Joining of stainless steel (AISI 304L) to hot isostatically pressed alumina (HIP-Al-2(3)2(4)2(3)2(3)O() using the brazing alloy 72Ag-28Cu was investigated. The microstructural characterization at various stages of joining, including metallization, annealing of overlaid Ni coating, and brazing, was comprehensively evaluated. The interface structure and the growth of phases were analyzed with optical microscope, scanning electron microscope, and electron probe microanalyzer (EPMA). Additionally, the leak tightness of these joints was assessed using a He-leak detector. Experimental results indicated the development of the manganese aluminate spinel (MnAl)O() layer at the metallizing stage, which penetrated into HIP-Al)O(. The Ni overlaid coating further resulted in the formation of the Ni(Mo) solid solution layer followed by the Mo-rich phase. During the solid-state reaction and subsequent brazing cycle, the growth of the spinel layer close to HIP-Al)O (was not adversely affected. The microstructure of the brazed joint was complex. It showed a eutectic structure within the brazed zone and a thin layer of Mo-rich, Ni-rich phases close to HIP-Al)(O)(2)(3), Increasing the brazing time resulted in the excessive growth of the thin layer that seriously affected the leak tightness of the joint.