Abstract
Bond formation of thin ferritic stainless steel foils containing 20Cr–5Al (wt-%) was observed under near vacuum pressure of ∼10-3 Pa. Debonded (peeled off) surfaces exhibited a white scaly morphology after bonding above 1400 K. No bond formation was observed below 1400 K, so the critical temperature for bond formation must exist around 1400 K. The critical temperature also depends on the surface roughness of the foil (the thickness of the gap between foils), which can be explained in terms of aluminium evaporation behaviour between foils. A theoretical model is proposed to estimate the effect of aluminium evaporation on the critical temperature. It is also suggested that aluminium evaporation between foils can protect the bonding surface from the residual oxygen gas.
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