Sulfidation Behavior of a Nickel-base Superalloy in N2-H2-H2S Mixtures

摘要

Sulfidation behavior of a nickel-based superalloy,AISI 685, was investigated in N2-H2-H2S mixtures within atemperature range of 673 to 873 K. Pure Ni and Cr, which are twomain components of AISI 685, were also tested as references.Uniform internal sulfidation occurred on AISI 685 at a lowersulfur-partial-pressure than the dissolution pressure of Ni3S2whether stressed or not. On the other hand, grain boundarysulfidation occurred on AISI 685 at a higher sulfur-partial-pressure than the dissolution pressure of Ni3S2 at 873 K under astatic stress. Whereas no grain boundary sulfidation was observedat or below 773 K even under a stress of 588 MPa. The grainboundary penetrations were brought by sulfidation of Ti, Mo, Aland Cr near the alloy grain boundaries. The time dependence of thegrain boundary sulfidation length followed a parabolic rate law.