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Factors influencing the analytical representation of creep crack development in Alloy 939

Factors influencing the analytical representation of creep crack development in Alloy 939 Creep crack growth rates originally gathered for the 𝛾′ strengthened cast nickel based superalloy Alloy-939 in terms of apparent stress intensity factor are re-evaluated as a function of the time dependent C* parameter, with crack propagation rates being insensitive to grain size at 750 and 850 °C. However, whereas a˙C(Ka) rates at 750 °C are significantly lower than those at 850 °C, equivalent a˙C(C*) rates are relatively insensitive to temperature, comparing well with the plane strain a˙C(C*) rates predicted using an approximate reference stress based C* model. While overall CT-specimen creep crack growth times for Alloy-939 can be predicted using uniaxial creep-rupture strength data when expressed in terms of reference stress at 850 °C, this appears not to be possible at 750 °C. The observation is explained with respect to evidence provided by a modified time dependent failure assessment diagram. The influence is examined of thermal transient durations at 850 °C (from 750 °C), or at 750 °C (from 850 °C) on a˙C(Ka) creep crack growth rates and tR(𝜎ref) overall lives. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Strength, Fracture and Complexity IOS Press

Factors influencing the analytical representation of creep crack development in Alloy 939

Strength, Fracture and Complexity , Volume 15 (1): 13 – Jun 14, 2022

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Publisher
IOS Press
Copyright
Copyright © 2022 © 2022 – IOS Press. All rights reserved
ISSN
1567-2069
eISSN
1875-9262
DOI
10.3233/sfc-228001
Publisher site
See Article on Publisher Site

Abstract

Creep crack growth rates originally gathered for the 𝛾′ strengthened cast nickel based superalloy Alloy-939 in terms of apparent stress intensity factor are re-evaluated as a function of the time dependent C* parameter, with crack propagation rates being insensitive to grain size at 750 and 850 °C. However, whereas a˙C(Ka) rates at 750 °C are significantly lower than those at 850 °C, equivalent a˙C(C*) rates are relatively insensitive to temperature, comparing well with the plane strain a˙C(C*) rates predicted using an approximate reference stress based C* model. While overall CT-specimen creep crack growth times for Alloy-939 can be predicted using uniaxial creep-rupture strength data when expressed in terms of reference stress at 850 °C, this appears not to be possible at 750 °C. The observation is explained with respect to evidence provided by a modified time dependent failure assessment diagram. The influence is examined of thermal transient durations at 850 °C (from 750 °C), or at 750 °C (from 850 °C) on a˙C(Ka) creep crack growth rates and tR(𝜎ref) overall lives.

Journal

Strength, Fracture and ComplexityIOS Press

Published: Jun 14, 2022

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