Advertisement

Control of Stress-Accelerated Oxygen-Assisted Cracking of INCOLOY® Alloy 908 Sheath for Nb3Sn Cable-in-Conduit

  • J. S. Smith
  • J. H. Weber
  • H. W. Sizek
Part of the Advances in Cryogenic Engineering Materials book series (ACRE, volume 42)

Abstract

INCOLOY® alloy 908 is a controlled thermal expansion precipitation hardenable Ni-Fe superalloy having outstanding cryogenic properties to 4 K. The alloy was developed for Nb3Sn cable-in-conduit sheathing and other cryogenic applications and has been specified for the ITER model superconducting magnet coils. INCOLOY alloy 908, like other superalloys, exhibits intergranular cracking under certain combinations of environment, stress, and material heat treatment conditions. For example, cracking may occur while material is exposed in air at temperatures between about 500 and 800°C if the total tensile stress is greater than some threshold tensile stress. This mechanism, known as stress-accelerated grain boundary oxygen-assisted cracking (or SAGBO), is analogous to intergranular stress corrosion cracking. INCOLOY alloy 908 SAGBO behavior is discussed in the general context of other superalloys. Using a variety of test methods, we examine the SAGBO characteristics under varying environmental-stress conditions. Some practical methods are available to eliminate or minimize SAGBO cracking in Nb3Sn reaction heat treatments.

Keywords

Residual Stress Tensile Residual Stress Intergranular Crack Shot Peening Corner Radius 
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.

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

References

  1. 1.
    R.G. Ballinger, D.F. Smith, and B.L. Lake, U.S. Patent No. 4, 785, 142, November 15, 1986.Google Scholar
  2. 2.
    M.M. Morra, R.G. Ballinger, J.L. Martin, M.O. Hoenig, and M.M. Steeves, INCOLOY 9XA, a new low coefficient of thermal expansion sheathing alloy for use in ICCS magnets, “Advances in Cryogenic Engineering,” 34: 157–164 (1987).Google Scholar
  3. 3.
    M.M. Morra, R.G. Ballinger, and I.S. Hwang, INCOLOY 908, a low coefficient of expansion alloy for high strength cryogenic applications: part I. physical metallurgy, Metallurgical Transactions A, 23A: 317–3192 (December 1992).CrossRefGoogle Scholar
  4. 4.
    L.S. Toma, M.M. Steeves, and R.P. Reed, “INCOLOY alloy 908 Data Handbook,” Massachusetts Institute of Technology, PFCC/RR-94–2 (March 1994).CrossRefGoogle Scholar
  5. 5.
    R.L. Tobler, Cryogenic mechanical properties and fracture mechanics of alloy 908, Proceedings U.S. ITER INCOLOY alloy 908 Workshop, 17–1 to 17–29 (1994).Google Scholar
  6. 6.
    A. Nyilas, J. Zhang, B. Obst, and A. Ulbricht, Fatigue and fatigue crack growth properties of 316LN and INCOLOY 908 below 10 K, “Advances in Cryogenic Engineering,” 38: 133–140 (1992).Google Scholar
  7. 7.
    K. Sadananda and P. Shahinian, High-temperature time-dependent crack growth, Micro- and Macro-Mechanics of Crack Growth, Met. Soc. of AIME, 119–130 (1981).Google Scholar
  8. 8.
    K. Sadananda and P. Shahinian, Creep crack growth in alloy 718, Metallurgical Transactions A, Vol. 8A: 439–449 (March 1977).CrossRefGoogle Scholar
  9. 9.
    S. Floreen, The creep fracture of wrought nickel-base alloys by a fracture mechanics approach, Metallurgical Transactions A, 6A: 1741–1749 (September 1975).CrossRefGoogle Scholar
  10. 10.
    J.M. Larson and S. Floreen, Metallurgical factors affecting the crack growth resistance of a superalloy, Metallurgical Transactions A, 8A: 51–55 (January 1977).CrossRefGoogle Scholar
  11. 11.
    K.J. Hsia, A.S. Argon, and D.M. Parks, Dominant creep failure process in tensile components, Transactions of the ASME Journal of Engineering Materials and Technology, 114: 255–264 (July 1992).CrossRefGoogle Scholar
  12. 12.
    M.M. Morra, Stress Accelerated Grain Boundary Oxidation of INCOLOY alloy 908 in High Temperature Oxygenous Atmospheres, Doctoral thesis, Massachusetts Institute of Technology (1995).Google Scholar
  13. 13.
    G. Sachs and G. Espey, A new method for determination of stress distribution in thin-walled tubing, Trans. AIME, 147: 348–360 (1942).Google Scholar
  14. 14.
    J.S. Smith, Controlling elevated temperature oxygen-assisted embrittlement of INCOLOY alloy 908 for Nb3Sn C-I-C sheathing applications, Proceedings U.S. ITER INCOLOY alloy 908 Workshop, 11–3–1 to 11–3–16(1994).Google Scholar
  15. 15.
    J.H. Schultz, Deoxidation of internal conduit helium during heat treatment, TPX no. 1314–950418-MIT-J Schultz-01, presented at TPX Conduit Material Manufacturing Risk Assessment at PPPL (April 1995).Google Scholar
  16. 16.
    M.M. Steeves, T.A. Painter, M. Takayasu, R.N. Randall, J.E. Tracey, I.S. Hwang, and M.O. Hoenig, The US demonstration poloidal coil, IEEE Trans. Mag., 27: 2369–2372 (March 1991).Google Scholar
  17. 17.
    L.S. Toma, I.S. Hwang, M.M. Steeves, and R.N. Randall, Thermomechanical process effects on hardness and grain size in INCOLOY alloy 908, “Advances in Cryogenic Engineering,” 40B: 1307–1314 (1994).Google Scholar

Copyright information

© Springer Science+Business Media New York 1996

Authors and Affiliations

  • J. S. Smith
    • 1
  • J. H. Weber
    • 1
  • H. W. Sizek
    • 1
  1. 1.Inco Alloys International, Inc.HuntingtonUSA

Personalised recommendations