1999 Volume 48 Issue 5 Pages 299-306
Sulfidation behavior of a nickel-base superalloy, AISI 685, was investigated in N2-H2-H2S mixtures within a temperature range of 673 to 873K. Pure Ni and Cr, which are two main components of AISI 685, were also tested as references. Uniform internal sulfidation occurred on AISI 685 at a lower sulfur-partial-pressure than the dissolution pressure of Ni3S2 whether stressed or not. On the other hand, grain boundary sulfidation occurred on AISI 685 at a higher sulfur-partial-pressure than the dissolution pressure of Ni3S2 at 873K under a static stress. Whereas no grain boundary sulfidation was observed at or below 773K even under a stress of 588MPa. The grain boundary penetrations were brought by sulfidation of Ti, Mo, Al and Cr near the alloy grain boundaries. The time dependence of the grain boundary sulfidation length followed a parabolic rate law.
