Stress Accelerated Grain Boundary Oxidation of Incoloy Alloy 908 in High Temperature Oxygenous Atmospheres

  • M. M. Morra
  • S. Nicol
  • L. Toma
  • I. S. Hwang
  • M. M. Steeves
  • R. G. Ballinger
Part of the An International Cryogenic Materials Conference Publication book series (ACRE, volume 40)

Abstract

Heat treatments of magnets utilizing INCOLOY® alloy 908* as a conduit have been successfully performed in vacuum. Similar experience with large scale heat treatment in an inert gas environment such as argon is lacking. Prior studies on other nickel-iron base superalloys that are susceptible to intergranular oxygen embrittlement and cracking emphasize the importance of establishing an allowable oxygen impurity level in argon for alloy 908. Initial screening using C-ring tests have shown that cracking can occur in an argon atmosphere if proper control over the oxygen impurity level is not maintained. Stress-rupture tests performed in air show that this material is susceptible to intergranular cracking in notched sections when subjected to stresses in excess of 300 MPa for a stress-concentration factor (Kt) of 4.1 at the notch. A series of stress-rupture tests are now underway on alloy 908 base metal in oxygen containing argon atmospheres. A double-edged notched test specimen design is used to determine the rupture time as functions of applied stress, temperature and oxygen concentration. The oxygen concentration at the specimen notches is continuously measured using an electrochemical sensor. Initial results suggest that an argon atmosphere does yield an improved stress-rupture life over air at low oxygen concentrations. Results are discussed to establish whether the possibility for heat treatments in argon exists and if so what guidelines must be used for successful heat treatment.

Keywords

Intergranular Crack Rupture Life International Thermonuclear Experimental Reactor Fatigue Crack Growth Behavior Inco Alloy 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© Springer Science+Business Media New York 1994

Authors and Affiliations

  • M. M. Morra
    • 1
  • S. Nicol
    • 1
  • L. Toma
    • 2
  • I. S. Hwang
    • 1
  • M. M. Steeves
    • 2
  • R. G. Ballinger
    • 3
  1. 1.Department of Materials Science and EngineeringMassachusetts Institute of TechnologyCambridgeUSA
  2. 2.Plasma Fusion CenterMassachusetts Institute of TechnologyCambridgeUSA
  3. 3.Departments of Nuclear Engineering and Materials Science and EngineeringMassachusetts Institute of TechnologyCambridgeUSA

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