Abstract
An aluminum oxide (Al oxide) intermediate layer was applied as an diffusion barrier to the brazing of a stainless steel using a filler of evaporated nickel-chromium-boron alloy (Ni-Cr-B) film. When the diffusion barrier was not applied, the tensile strength of the brazed joint of a Ni-Cr-B filler coated steel was increased as the filler thickness increased from 7μm to 10μm. On the other hand, a Ni-Cr-B filler of less than 7μm thickness was almost ineffective in increasing the tensile strength of joints without the diffusion barrier. It is presumed that Ni and B in the filler metal diffused into the substrate during the thermal cycle for brazing, and this raised the liquidus temperature of the filler metal to a temperature above the brazing temperature. An intermediate layer of Al oxide was effective in reducing the diffusion of Ni and B in the filler into the substrate. Hence it increased the tensile strength of the brazed joint. The brazed joint of the steel plated with Ni-Cr-B/Al oxide double layers showed sufficient tensile strength when used in an automobile metal honeycomb catalyser.
