Cyclic plastic response of nickel-based superalloy at room and at elevated temperatures

This work investigates the oxidation of a nickel based superalloy, namely Alloy X, in water at elevated temperatures: subcritical water at 261°C and 27 MPa, the transition between subcritical and supercritical water at 374°C and 27 MPa, and supercritical water at 380°C and 27 MPa for 100 hours. The morphology of the sample surfaces were studied using scanning electron microscopy coupled with focused ion beam milling, and the surface chemistry was investigated using X-ray diffraction, Raman spectroscopy, energy dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy before and after exposure studies. Surfaces of all samples were identified to comprise of a ferrite spinel containing aluminum.

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Creep rupture properties of bare and coated polycrystalline nickel-based superalloy Rene®80

Journal of Mining and Metallurgy Section B Metallurgy ◽

10.2298/jmmb201203036b ◽

2021 ◽

pp. 36-36

Author(s):

M.M. Barjesteh ◽

S.M. Abbasi ◽

K.Z. Madar ◽

K. Shirvani

Keyword(s):

Elevated Temperatures ◽

Life Time ◽

Creep Rupture ◽

Polycrystalline Nickel ◽

Creep Life ◽

Nickel Based Superalloy ◽

Platinum Aluminide ◽

Rupture Properties ◽

Low Activity ◽

Rupture Behavior

Creep deformation is one of the life time limiting reasons for gas turbine parts that are subjected to stresses at elevated temperatures. In this study, creep rupture behavior of uncoated and platinum-aluminide coated Rene?80 has been determined at 760?C/657 MPa, 871?C/343 MPa and 982?C/190 Mpa in air. For this purpose, an initial layer of platinum with a thickness of 6?m was applied on the creep specimens. Subsequently, the aluminizing were formed in the conventional pack cementation method via the Low Temperature-High Activity (LTHA) and High Temperature-Low Activity (HTLA) processes. Results of creep-rupture tests showed a decrease in resistance to creep rupture of coated specimen, compared to the uncoated ones. The reductions in rupture lives in LTHA and HTLA methods at 760?C/657 MPa, 871?C/343 MPa and 982?C/190 MPa were almost (26% and 41.8%), (27.6% and 38.5%) and (22.4% and 40.3%), respectively as compared to the uncoated ones. However, the HTLA aluminizing method showed an intense reduction in creep life. Results of fractographic studies on coated and uncoated specimens indicated a combination of ductile and brittle failure mechanisms for all samples. Although, the base failure mode in substrate was grain boundary voids, cracks initiated from coating at 760?C/657MPa and 871?C/343. No cracking in the coating was observed at 982?C/190MPa.

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A Concise Binomial Model for Nonlinear Creep-Fatigue Crack Growth Behavior at Elevated Temperatures

Materials ◽

10.3390/ma15020651 ◽

2022 ◽

Vol 15 (2) ◽

pp. 651

Author(s):

Jianxing Mao ◽

Zhixing Xiao ◽

Dianyin Hu ◽

Xiaojun Guo ◽

Rongqiao Wang

Keyword(s):

Fatigue Crack ◽

Fatigue Crack Growth ◽

Crack Growth ◽

Dwell Time ◽

Elevated Temperatures ◽

Nonlinear Creep ◽

Nickel Based Superalloy ◽

Proposed Model ◽

Creep Fatigue ◽

Creep Fatigue Crack

The creep-fatigue crack growth problem remains challenging since materials exhibit different linear and nonlinear behaviors depending on the environmental and loading conditions. In this paper, we systematically carried out a series of creep-fatigue crack growth experiments to evaluate the influence from temperature, stress ratio, and dwell time for the nickel-based superalloy GH4720Li. A transition from coupled fatigue-dominated fracture to creep-dominated fracture was observed with the increase of dwell time at 600 °C, while only the creep-dominated fracture existed at 700 °C, regardless of the dwell time. A concise binomial crack growth model was constructed on the basis of existing phenomenal models, where the linear terms are included to express the behavior under pure creep loading, and the nonlinear terms were introduced to represent the behavior near the fracture toughness and during the creep-fatigue interaction. Through the model implementation and validation of the proposed model, the correlation coefficient is higher than 0.9 on ten out of twelve sets of experimental data, revealing the accuracy of the proposed model. This work contributes to an enrichment of creep-fatigue crack growth data in the typical nickel-based superalloy at elevated temperatures and could be referable in the modeling for damage tolerance assessment of turbine disks.

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