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The influence of sulfur pressure on Sulfidation behaviour of NiCoCrAl(Y) alloys at high temperature
Author(s) -
Godlewska E.,
Roszczynialska E.,
Żurek Z.
Publication year - 1994
Publication title -
materials and corrosion
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.487
H-Index - 55
eISSN - 1521-4176
pISSN - 0947-5117
DOI - 10.1002/maco.19940450604
Subject(s) - sulfidation , yttrium , sulfide , sulfur , alloy , materials science , metallurgy , high temperature corrosion , partial pressure , vapor pressure , grain boundary , inorganic chemistry , analytical chemistry (journal) , microstructure , chemistry , oxide , oxygen , environmental chemistry , organic chemistry
Sulfidation of alloy having nominal composition Ni‐23Co‐19Cr‐12Al (wt%) with and without the addition of 0.6% yttrium was studied at temperatures 1073–1273 K in sulfur vapor at atmospheric pressure and in H 2 /H 2 S gas mixtures at sulfur pressure of 10 −3 and 10 −1.5 Pa. Sulfidation runs were followed thermogravimetrically. Phase and chemical composition of sulfide scales and scale morphologies were determined by means of XRD, EDX, EPM and SEM analyses. After certain initial period sulfidation of both materials followed approximately a parabolic rate law. The estimated sulfidation rates for each alloy increased with sulfur pressure and temperature. The sulfide scales on both materials showed complex microstructures and compositions, depending on sulfidation conditions, with several sulfide and sulfospinel phases present, such as (Ni,Co)S, (Ni,Co) 3 S 4 , (Ni,Co)Cr 2 S 4 , (Cr,Ni,Co)Al 2 S 4 or (Cr,Ni,Co)S and (Cr,Ni,Co) 3 S 4 . There was no evidence of yttrium segregation either to the grain boundary regions in the scale or to the alloy/scale interface. Yttrium dissolved in the sulfide phases and accelerated the sulfidation process. This behaviour was ascribed to the doping effect.