Intergranular creep fracture in aggressive environments

Abstract Gaseous species can diffuse along a boundary and oxidize impurities or precipitates. In nickel alloys O 2 can attack C or carbides to produce CO at high virtual pressures. This provides a driving force for cavity nucleation and growth at particle interfaces, which acts in addition to the applied stress in forcing fracture. In this paper it is shown that the oxidation pressure can become comparable to, or even larger than, the stresses normally applied in stress-rupture tests. The dependence of this pressure on temperature and oxygen pressure is derived for various oxidation reactions. Since oxide-dispersion-strengthened alloys are known to be more susceptible to cavitation than precipitate strengthened alloys, it is also possible that internal oxidation enhances cavitation by producing oxide particles from elemental impurities, or by converting metal-carbide and metal-intermetallic interfaces to metal-oxide interfaces. The kinetic steps which may become rate limiting when cavity nucleation and growth is induced by oxidation, are discussed.

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