THE HIGH-TEMPERATURE SULFIDATION BEHAVIOR OF NB-AL-SI COATINGS SPUTTER-DEPOSITED ON A STAINLESS-STEEL

The sulfidation behavior of amorphous 58 at.%Nb-38 at.%Al-4 at.%Si and 59 at.%Nb-35 at.%Al-6 at.%Si coatings sputter-deposited on a stainles s steel substrate of SUS 304 has been studied at 1 kPa sulfur vapor pr essure over the temperature range of 973-1173 K. The scales formed on the coating were bilayered, primarily consisting of an outer non-prote ctive layer of Al2S3 and an inner barrier layer of NbS2. Beneath the c oating the formation of (Fe, Cr, Ni) depleted, Al enriched zone was ob served, which resulted from the mutual diffusion between the coating a nd the substrate. The coating improved effectively the sulfidation res istance of the stainless steel, although elements in the substrate dif fused outwards in the coating and small amounts of their ions were con tained in the sulfide scales. The high sulfidation resistance of the c oated specimens seems attributable to the formation of a protective Nb S2 scale, instead of less protective FeNb2S4, even in the presence of iron, incorporated by outward diffusion from the substrate, in the coa ting. Copyright (C) 1996 Elsevier Science Ltd