Mechanism-based life model for out-of-phase thermomechanical fatigue in single crystal Ni-base superalloys

ABSTRACT This paper describes an enhanced physics‐inspired model to predict the life of the second‐generation single crystal superalloy PWA 1484 experiencing out‐of‐phase (OP) thermomechanical fatigue (TMF). Degradation due to either pure fatigue or a coupling between fatigue and environmental attac...

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Bibliographic Details
Published in:Fatigue & fracture of engineering materials & structures 2012-07, Vol.35 (7), p.658-671
Main Authors: AMARO, R. L., ANTOLOVICH, S. D., NEU, R. W.
Format: Article
Language:English
Subjects:
Applied sciences
bithermal fatigue
crack initiation
Exact sciences and technology
Fatigue
life modelling
Load
Materials fatigue
Mechanical properties
Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology
Metals. Metallurgy
Ni-base superalloy
Single crystals
thermomechanical fatigue
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Summary:ABSTRACT This paper describes an enhanced physics‐inspired model to predict the life of the second‐generation single crystal superalloy PWA 1484 experiencing out‐of‐phase (OP) thermomechanical fatigue (TMF). Degradation due to either pure fatigue or a coupling between fatigue and environmental attack are the primary concerns under this loading. The life model incorporates the effects of material anisotropy by utilizing the inelastic shear strain on the slip system having the highest Schmid factor while accounting for the effects of temperature‐dependent slip spacing and stress‐assisted γ′ depletion. Both conventional TMF and special bithermal fatigue (BiF) experiments were conducted to isolate and therefore better understand the interactions between these degradation mechanisms. The influences of crystallographic orientation, applied mechanical strain range, cycle maximum temperature and high temperature hold times were assessed. The resulting physics‐inspired life estimation model for OP TMF and OP BiF predicts the number of cycles to crack initiation as a function of crystal orientation, applied strain amplitude and stresses, temperature, cycle time (including dwells), and surface roughness within a factor of 2.
ISSN:8756-758X
1460-2695
DOI:10.1111/j.1460-2695.2011.01660.x