Abstract
The reaction sequence between a sputtered nickel coating and surface-oxidized Al clad braze sheet was investigated using X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). XPS on the surface showed that both the nickel and alumina layers remained roughly intact with some interactions occurring locally, confirmed by optical and SEM characterizations. The predominant phase found upon nickel entering the Al-Si melt was Al3Ni, and it was proposed that this formation led to the disruption of the alumina layer mechanically, primarily due to mechanical disruption of the oxide by the intermetallic and its bonding with the alumina layer. These interactions of aluminum and nickel were proposed to occur at defects inherent in the alumina layer either during fabrication or as a result of fracture caused by thermal stresses while floating on the molten clad layer.
Published Version
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