Dwell Time Fatigue Crack Growth In Ni Base Superalloys
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Dwell Time Fatigue Crack Growth In Ni Base Superalloys
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Author :
language : en
Publisher:
Release Date : 2003
Dwell Time Fatigue Crack Growth In Ni Base Superalloys written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2003 with categories.
The state-of-the-art dwell-time fatigue crack growth models applicable to materials systems such as Waspaloy, Rene'95, Rene'88 and IN 100 were critically assessed. The review included models based on linear elastic fracture mechanics (LEFM) and those based on time dependent fracture mechanics (TDFM). The pertinent creep deformation and time and cycle dependent crack growth rate data on these materials were also collected to enable the evaluation of these models and for the establishment of their respective regimes of applicability and their limitations. The gaps in the available experimental and computational data for implementing the promising models were identified as part of the review. An experimental test plan and a plan for providing computational needs for addressing these shortcomings are proposed.
Effect Of Dwell Times On Crack Propagation In Superalloys
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Author : Jonas Saarimäki
language : en
Publisher: Linköping University Electronic Press
Release Date : 2015-12-10
Effect Of Dwell Times On Crack Propagation In Superalloys written by Jonas Saarimäki and has been published by Linköping University Electronic Press this book supported file pdf, txt, epub, kindle and other format this book has been release on 2015-12-10 with categories.
Gas turbines are widely used in industry for power generation and as a power source at "hard to reach" locations where other possibilities for electrical supply are insufficient. There is a strong need for greener energy, considering the effect that pollution has had on global warming, and we need to come up with ways of producing cleaner electricity. A way to achieve this is by increasing the combustion temperature in gas turbines. This increases the demand on the high temperature performance of the materials used e.g. superalloys in the turbine. These high combustion temperatures can lead to detrimental degradation of critical components. These components are commonly subjected to cyclic loading of different types e.g. combined with dwell-times and overloads at elevated temperatures, which influence the crack growth. Dwell-times have shown to accelerate crack growth and change the cracking behaviour in both Inconel 718 and Haynes 282. Overloads at the beginning of the dwell-time cycle have shown to retard the dwell time effect on crack growth in Inconel 718. To understand these effects more microstructural investigations are needed. The work presented in this licentiate thesis was conducted under the umbrella of the research program Turbo Power; "High temperature fatigue crack propagation in nickel-based superalloys", concentrating on fatigue crack growth mechanisms in superalloys during dwell-times, which have shown to have a devastating effect on the crack propagation behaviour. Mechanical testing was performed under operation-like conditions in order to achieve representative microstructures and material data for the subsequent microstructural work. The microstructures were microscopically investigated in a scanning electron microscope (SEM) using electron channeling contrast imaging (ECCI) as well as using light optical microscopy. The outcome of this work has shown that there is a significant increase in crack growth rate when dwell-times are introduced at the maximum load (0% overload) in the fatigue cycle. With the introduction of a dwell-time there is also a shift from transgranular to intergranular crack growth for both Inconel 718 and Haynes 282. When an overload is applied prior to the dwell-time, the crack growth rate decreases with increasing overload levels in Inconel 718. At high temperature crack growth in Inconel 718 took place as intergranular crack growth along grain boundaries due to oxidation and the creation of nanometric voids. Another observed growth mechanism was crack advance along phase boundaries with subsequent severe oxidation of the phase. This thesis comprises two parts. The first giving an introduction to the field of superalloys and the acting microstructural mechanisms that influence fatigue during dwell times. The second part consists of two appended papers, which report the work completed so far in the project.
Cracks In Superalloys
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Author : Jonas Saarimäki
language : en
Publisher: Linköping University Electronic Press
Release Date : 2018-01-18
Cracks In Superalloys written by Jonas Saarimäki and has been published by Linköping University Electronic Press this book supported file pdf, txt, epub, kindle and other format this book has been release on 2018-01-18 with categories.
Gas turbines are widely used in industry for power generation and as a power source at hard to reach locations where other possibilities for electrical power supplies are insufficient. New ways of producing greener energy is needed to reduce emission levels. This can be achieved by increasing the combustion temperature of gas turbines. High combustion temperatures can be detrimental and degrade critical components. This raises the demands on the high temperature performance of the superalloys used in gas turbine components. These components are frequently subjected to different cyclic loads combined with for example dwell-times and overloads at elevated temperatures, which can influence the crack growth. Dwell-times have been shown to accelerate crack growth and change cracking behaviour in both Inconel 718, Haynes 282 and Hastelloy X. On the other hand, overloads at the beginning of a dwell-time cycle have been shown to retard the dwell-time effect on crack growth in Inconel 718. More experiments and microstructural investigations are needed to better understand these effects. The work presented in this thesis was conducted under the umbrella of the research program Turbo Power; "High temperature fatigue crack propagation in nickel-based superalloys", where I have mainly looked at fatigue crack growth mechanisms in superalloys subjected to dwell-fatigue, which can have a devastating effect on crack propagation behaviour. Mechanical testing was performed under operation-like cycles in order to achieve representative microstructures and material data for the subsequent microstructural work. Microstructures were investigated using light optical microscopy and scanning electron microscopy (SEM) techniques such as electron channeling contrast imaging (ECCI) and electron backscatter diffraction (EBSD). The outcome of this work has shown that there is a significant increase in crack growth rate when dwell-times are introduced at maximum load (0 % overload) in the fatigue cycle. With the introduction of a dwell-time there is also a shift from transgranular to intergranular crack growth for both Inconel 718 and Haynes 282. The crack growth rate decreases with increasing overload levels in Inconel 718 when an overload is applied prior to the dwell-time. At high temperature, intergranular crack growth was observed in Inconel 718 as a result of oxidation and the creation of nanometric voids. Another observed growth mechanism was crack advance along ?-phase boundaries with subsequent oxidation of the ?-phase. This thesis comprises two parts. Part I gives an introduction to the field of superalloys and the acting microstructural mechanisms related to fatigue and crack propagation. Part II consists of five appended papers, which report the work completed as part of the project.
Dwell Fatigue Crack Growth At Elevated Temperatures In An Advanced Nickel Disc Superalloy
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Author : Suyang Yu
language : en
Publisher:
Release Date : 2016
Dwell Fatigue Crack Growth At Elevated Temperatures In An Advanced Nickel Disc Superalloy written by Suyang Yu and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2016 with categories.
Creep Fatigue Environment Crack Tip Kinetics Of Ni Base Superalloys
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Author : Jeffrey Evans
language : en
Publisher:
Release Date : 2014
Creep Fatigue Environment Crack Tip Kinetics Of Ni Base Superalloys written by Jeffrey Evans and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2014 with Crack tip categories.
Several time-dependent damage mechanisms can operate during creep-fatigue loading. In the crack tip region, creep deformation, stress relaxation, oxygen diffusion along grain boundaries, and grain boundary oxidation are all occurring during the hold period of a creep-fatigue cycle. These conditions can lead to grain boundary embrittlement; however, it depends on the rates of the different processes. A comparison of the kinetics can determine which mechanisms are operational and which mechanism is the rate limiting step in the time-dependent damage process during creep-fatigue crack growth. This paper presents results for intergranular embrittlement occurring within a 10 s hold period and compares the kinetics of the processes.
Near Threshold Fatigue Crack Growth Behavior Of Fine Grain Nickel Based Alloys
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Author : John A. Newman
language : en
Publisher:
Release Date : 2003
Near Threshold Fatigue Crack Growth Behavior Of Fine Grain Nickel Based Alloys written by John A. Newman and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2003 with Fracture mechanics categories.
Fatigue Crack Propagation Of Nickel Base Superalloys At 650 C
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Author : TP. Gabb
language : en
Publisher:
Release Date : 1988
Fatigue Crack Propagation Of Nickel Base Superalloys At 650 C written by TP. Gabb and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1988 with Creep categories.
The 650°C fatigue crack propagation behavior of two nickel-base superalloys, René 95 and Waspaloy, were studied with particular emphasis placed on understanding the roles of creep, environment, and two key grain boundary alloying additions, boron and zirconium. Comparison of air and vacuum data showed the air environment to be detrimental over a wide range of frequencies for both alloys. In-depth analysis of René 95 showed that at lower frequencies, such as 0.02 Hz, failure in air occurred by intergranular, environmentally assisted creep crack growth, while at higher frequencies, up to 5.0 Hz, environmental interactions were still evident but creep effects were minimized. The effect of boron and zirconium in Waspaloy was found to be important where environmental and/or creep interactions were present. In those instances, removal of boron and zirconium dramatically increased crack growth. It is therefore plausible that effective dilution of these elements may explain, in part, a previously observed trend in which crack growth rates increased with decreasing grain size.
The Fracture Morphology Of Nickel Base Superalloys Tested In Fatigue And Creep Fatigue At 650 C
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Author :
language : en
Publisher:
Release Date : 1981
The Fracture Morphology Of Nickel Base Superalloys Tested In Fatigue And Creep Fatigue At 650 C written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1981 with categories.
High Temperature Fatigue Crack Growth Behavior Of Alloy 10
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Author :
language : en
Publisher:
Release Date : 2001
High Temperature Fatigue Crack Growth Behavior Of Alloy 10 written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2001 with categories.
Near Threshold Crack Growth In Nickel Base Superalloys
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Author : HR. Van Stone
language : en
Publisher:
Release Date : 1988
Near Threshold Crack Growth In Nickel Base Superalloys written by HR. Van Stone and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1988 with Crack closure categories.
The influence of stress ratio on the elevated-temperature crack growth behavior of the nickel-base superalloys René 95 and Alloy 718 is discussed. The near-threshold and Region II crack growth behavior of a wide variety of microstructures for each alloy are explained using phenomenological descriptions of closure, that is, K-dependent or K-independent closure. K-dependent closure is the type of closure observed for nickel-base superalloys where increasing the R-ratio causes a uniform lateral shift of the entire fatigue crack growth curve. K-independent closure is the type commonly reported for steels and titanium alloys where increasing the R-ratio has a larger influence on near-threshold crack growth than on Region II crack growth. The existence of K-dependent closure in nickel-base superalloys results in microstructurally sensitive crack growth rates, even at high R-ratios. This permits the use of K-based crack growth prediction techniques and simplifies alloy and process development for applications having complex loading spectra.