SEDL / STP / STP945-EB / STP23274S

Elevated Temperature Fatigue Crack Growth of Single Crystal René N4 Superalloy

Venkataraman, S
Resident NRC research associate and senior scientist, AFWAL MLLN, Wright-Patterson Air Force Base, OH

Nicolas, T
Resident NRC research associate and senior scientist, AFWAL MLLN, Wright-Patterson Air Force Base, OH

Khobaib, M
Research scientist, University of Dayton Research Institute, Dayton, OH

Pages: 8    Published: Jan 1988

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Abstract

Constant-load-amplitude fatigue crack growth tests were conducted at 0.33 Hz over a temperature range of 538 to 871°C for single crystal René N4 nickel base superalloy. Crack growth behavior was found to be similar in the Paris law regime for the entire temperature range tested except for a slight increase in growth rate at 871°C at higher levels of the stress intensity range. Mainly, two distinct modes of fatigue fracture were observed, namely, a flat, featureless, Stage II fracture morphology and a faceted, crystallographic, Stage I cracking mode. The Stage II fatigue fracture occurred over the entire range of ΔK at the three highest temperatures. At 538°C, however, a transition from Stage II to Stage I fatigue fracture occurred with increase in ΔK. The higher crack growth rates at higher temperatures in the high-stress-intensity range were attributed to casting defects present in the material.