Pressureless diffusion bonding of ferritic stainless steel foil controlledby metal evaporation

Bond formation of thin ferritic stainless steel foils containing 20Cr-5Al ( wt-%) was observed under near vacuum pressure of similar to 10(-3) Pa. Debo nded (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 temp erature also depends on the surface roughness of the foil (the thickness of the gap between foils), which can be explained in terms of aluminium evapo ration behaviour between foils. A theoretical model is proposed to estimate the effect of aluminium evaporation on the critical temperature. it is als o suggested that aluminium evaporation between foils can protect the bondin g surface from the residual oxygen gas.