Constitutive modelling of creep degradation due to rafting in single-crystalline Ni-base superalloys

Abstract. The objective of this paper is to critically analyse the effect of the γ' morphology evolution on the creep strain rate behaviour in the temperature range 900 -1100°C where rafts form in superalloys for single crystal turbine blade and vane applications. A close examination of the experimental results has shown different regimes of strain accumulation depending on the value of the applied stress and temperature. The experimental results have been rationalised in terms of the γ' shape evolution during creep. IntroductionThe long and large tertiary stage, that dominates the creep curve shape of γ' reinforced nickel base superalloys for temperatures/stresses relevant for high temperature components, has been often modeled supposing a single strain softening mechanism is operative. For example the accelerating tertiary creep has been often described by a linear dependence of strain rate on strain[1-4]:

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“…6, i.e. at 950°C under 220 and 155 MPa [11], confirming that this kind of effects is detected quite often. …”

Section: Cmsx-4 Superalloysupporting

confidence: 66%

Influence of Gamma Prime Evolution on the Creep Behaviour of SX Nickel Base Superalloys

Maldini

Lupínc

Angella

2011

AMR

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“…The high temperature material investigated by our group is the singlecrystal nickel-base superalloy CMSX-4 widely used in gas turbine industry. The present paper reports on the experimental results of our activities, the microstructurally-based mechanical model based on these results is presented in [7].…”

Section: Introductionmentioning

confidence: 99%

Microstructural Degradation of CMSX-4: Kinetics and Effect on Mechanical Properties

Epishin¹,

Link²,

Nazmy³

et al. 2008

Superalloys 2008 (Eleventh International Symposium)

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The γ/γ'-microstructure of nickel-base superalloys gradually degrades during high temperature loading which deteriorates the mechanical properties. In the work presented the kinetics of microstructural degradation of the superalloy CMSX-4 was investigated metallographically in a wide parameter field (T, σ, t).The effect of microstructural degradation on mechanical properties was determined by mechanical testing of specimens pre-annealed under load. The laboratory results were compared with the microstructure of ex-service blades of CMSX-4.

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“…Recently, Fedelich et al [20] measured the increase in the microstructural periodicity k and the c channel width x of CMSX-4 commercial superalloys as a function of service time, temperature, and applied stress. An analytical expression was proposed, which seems to capture the findings from detailed observations on the transition of c¢ morphology from cuboid to rafted shape.…”

Section: A Fedelich's Phenomenological Modelmentioning

confidence: 99%

“…Fan et al [22] follow the approach of Fedelich et al's work [20] in describing the channel width and rafting degree but attempt to bring in a more physical approach. They describe the isotropic coarsening of the microstructural periodicity, as follows:…”

Section: B Fan's Modelmentioning

confidence: 99%

The Compositional Dependence of the Microstructure and Properties of CMSX-4 Superalloys

Zwaag

2017

Metall Mater Trans A

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The degradation of creep resistance in Ni-based single-crystal superalloys is essentially ascribed to their microstructural evolution. Yet there is a lack of work that manages to predict (even qualitatively) the effect of alloying element concentrations on the rate of microstructural degradation. In this research, a computational model is presented to connect the rafting kinetics of Ni superalloys to their chemical composition by combining thermodynamics calculation and a modified microstructural model. To simulate the evolution of key microstructural parameters during creep, the isotropic coarsening rate and c/c¢ misfit stress are defined as composition-related parameters, and the effect of service temperature, time, and applied stress are taken into consideration. Two commercial superalloys, for which the kinetics of the rafting process are selected as the reference alloys, and the corresponding microstructural parameters are simulated and compared with experimental observations reported in the literature. The results confirm that our physical model not requiring any fitting parameters manages to predict (semiquantitatively) the microstructural parameters for different service conditions, as well as the effects of alloying element concentrations. The model can contribute to the computational design of new Ni-based superalloys.

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Constitutive modelling of creep degradation due to rafting in single-crystalline Ni-base superalloys

Cited by 71 publications

References 17 publications

Influence of Gamma Prime Evolution on the Creep Behaviour of SX Nickel Base Superalloys

Influence of Gamma Prime Evolution on the Creep Behaviour of SX Nickel Base Superalloys

Microstructural Degradation of CMSX-4: Kinetics and Effect on Mechanical Properties

The Compositional Dependence of the Microstructure and Properties of CMSX-4 Superalloys

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