High-cycle fatigue-life of the cast nickel base-superalloys in 738 LC and IN 939

The high cycle fatigue (HCF) properties of two cast nickel base-superalloys, IN 738 LC and IN 939, were investigated using both fracture mechanics samples and smooth specimens. The crack propagation behavior was studied in terms of linear fracture mechanics at RT and at 850 °C. In addition to the influence of temperature, the influences of frequency, mean stress, and environment (vacuum, air, sulfidizing atmosphere) were studied. At 850 °C, the fatigue thresholds were found to be higher in air than in vacuum. This could be explained by crack branching. The high scatter of fatigue crack propagation rates could be related also to this phenomenon. The S/N curves at 850 °C can be predicted treating crack growth from casting pores as the predominant failure mechanism. At RT the same method is not as successful. The reason for this may be that crack growth laws measured on long, branched cracks are not applicable to short, unbranched cracks. At RT, no significant influence of frequency on S/N-curves and fatigue crack growth rates was observed for frequencies up to 20 kHz.

[1]  W Hoffelner,et al.  Fatigue crack growth at 20 kHz-a new technique , 1980 .

[2]  R. Stickler,et al.  Effects of aging treatments on the Microstructure of the Ni-base superalloy IN-738 , 1979 .

[3]  R. Pelloux,et al.  High temperature fatigue crack growth in a cobalt base superalloy , 1973 .

[4]  V. Kumar,et al.  An engineering approach for examining crack growth and stability in flawed structures , 1981 .

[5]  L. James.  Effect of thermal aging upon the fatigue-crack propagation of austenitic stainless steels , 1974, Metallurgical and Materials Transactions B.

[6]  Peter Gudmundson,et al.  A fracture mechanics analysis of ultrasonic fatigue , 1982 .

[7]  D. Jablonski,et al.  Fatigue crack propagation at elevated temperatures in solid solution strengthened superalloys , 1977 .

[8]  R. Skelton,et al.  Fatigue crack growth rates and thresholds in steels under oxidising conditions , 1978 .

[9]  B. N. Leis,et al.  Low-Cycle Fatigue and Life Prediction , 1982 .

[10]  W. Hoffelner,et al.  Gefügeuntersuchungen an Proben aus IN 939 nach Wechselverformung bei hohen Temperaturen , 1981 .

[11]  P. Flewitt,et al.  Microstructural changes which occur during isochronal heat treatment of the nickel-base superalloy IN-738 , 1978 .

[12]  D. Coutsouradis,et al.  High temperature alloys for gas turbines , 1978 .

[13]  J. Scully.  THE THEORY OF STRESS CORROSION CRACKING IN ALLOYS , 1972 .

[14]  F. M. Owner,et al.  High Temperature Alloys for Gas Turbines , 1948, The Journal of the Royal Aeronautical Society.

[15]  M. Merz,et al.  Corrosion and mechanical stress at high temperatures , 1981 .

[16]  Lee A. James,et al.  Some preliminary observations on the extension of cracks under static loadings at elevated temperatures , 1972 .

[17]  P. R. Sahm,et al.  High-Temperature Materials in Gas Turbines , 1975 .

[18]  G. G. Stokes.  "J." , 1890, The New Yale Book of Quotations.

[19]  K. Sadananda,et al.  A fracture mechanics approach to high temperature fatigue crack growth in Udimet 700 , 1979 .

[20]  R. N. Parkins.  The Theory of Stress Corrosion Cracking in Alloys , 1972 .

[21]  M. Müller.  Theoretical Considerations on Corrosion Fatigue Crack Initiation , 1982 .

[22]  J. R. Haigh,et al.  The growth of fatigue cracks at high temperatures under predominantly elastic loading , 1975 .