Grain boundary microstructure and fatigue crack growth in Allvac 718Plus superalloy

Viskari, Leif; Cao, Yu; Norell, Mats; Sjöberg, Göran; Stiller, Krystyna Marta

doi:10.1016/j.msea.2010.11.080

Cited by 70 publications

(46 citation statements)

References 10 publications

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“…Some authors had reported the existence of a hexagonal closed pack (HCP) phase [27][28][29][30]. However, the vast majority of the available literature had referred to the grain boundary precipitates in ATI 718Plus as the δ phase.…”

Section: η Phasementioning

confidence: 99%

Grain boundary precipitation in Inconel 718 and ATI 718Plus

Hassan

Corney

2017

Materials Science and Technology

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Grain boundary precipitates in Inconel 718 and ATI 718Plus are important to control during hot working processes, since they can control the grain size. Precipitating excessive or insufficient amounts can be detrimental to the final component. Therefore, it is important for manufacturers to understand the formation and kinetics of grain boundary precipitation and the effect this has on mechanical properties. This review considers the background of grain boundary precipitation, including the effect of the thermal stability of γ and γ phases. In addition, the effect of stress on the grain boundary phases and their precipitation kinetics in different conditions are also included. Also, the impact of grain boundary precipitation on the mechanical properties is explored. ARTICLE HISTORY

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Section: η Phasementioning

confidence: 99%

Grain boundary precipitation in Inconel 718 and ATI 718Plus

Hassan

Corney

2017

Materials Science and Technology

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“…Such films, with penetration depths of around 1-10 µm ahead of the tip, have been observed in dedicated experiments in several Ni-based superalloys [67,93,94]. SAGBO as a crack propagation mechanism has been discussed and suggested as a possible crack propagation mechanism in several other papers [64,65,86,[95][96][97][98][99][100][101][102][103]. SAGBO is also supported by observations in Paper IV, Fig.…”

Section: Introductionsupporting

confidence: 70%

Cracks in superalloys

Saarimäki¹

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Linköping 2018Cover image: An orientation imaging map illustrating the general crack propagation behaviour of a 2160 s dwell-time tested Inconel 718 bar run at 550 ○ C, with a 15 % superimposed overload at the beginning of the dwell-time.During the course of research underlying this thesis, Jonas Saarimäki was enrolled in Agora Materiae, a multidiciplinary doctoral program at Linköping University, Sweden. Printed by LiU-Tryck 2018 © Jonas Saarimäki AbstractGas 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 iii iv 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 δ-phase boundaries with subsequent oxidation of the δ phase.This thesis comprises two parts. Part I gives an introducti...

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“…But, excessive levels of the coarse ¤ are detrimental to properties due to solute depletion of the £ AA phase in 718. 12,16,17) Although ¤ precipitation in 718Plus proved to actually be ©-Ni 3 Al 0.5 -Nb 0.5 , its morphology and chemical composition indicated that it should have an effect similar to the ¤ phase in 718. 10) Because of its morphology, the ¤-phase does not contribute significantly to the hardening of the alloy.…”

Section: Discussionmentioning

confidence: 98%

“…Using the chemical composition of alloy 718 as the base, the Al/Ti and Al+Ti content were modified and the Fe content was decreased from 18% to 10%, together with addition of 1% W and 9% Co to form alloy 718Plus. 16) It is interesting to note that the strength phase of the resulting alloy is converted from predominately £ AA to £ A after modifying the composition and the operating temperature improves to 977 K (704°C). These improvements are not realized at the expense of the attractive properties of the alloy which still retains the excellent mechanical properties, good fabricability of alloy 718.…”

Section: Introductionmentioning

confidence: 99%

The Effect of Aluminum on Microstructure and Mechanical Properties of ATI 718Plus Alloy

Wang

Deng

et al. 2015

Mater. Trans.

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In this reported study, the influence of aluminum concentration on the microstructure and mechanical properties of alloy ATI 718Plus was investigated. The experimental results revealed that the content of aluminum has a significant effect on the solvus temperature and the chemical compositions of the £ A and ¤ phases of ATI 718Plus. The experimental data showed that an increased concentration of aluminum in the alloy caused the tensile strength to increase, but had a negative impact on the metal's ductility. The distribution of aluminum in the matrix and phases of the alloy were systematically examined using the atom probe tomography (APT) technique. The precipitation of phases in the alloy resulting from heat treatment was predicted using the JMatPro 6.0 software application and the predicted results were verified experimentally using electrolytic phase separation followed by microchemical analysis. In addition, a more detailed analysis of the size distribution of the £ A and crystal structure of the ¤ phase in the alloy was performed using SEM and XRD analysis. A full discussion of the effects of aluminum content on the mechanism of the generation of the alloy microstructure and evolution of the tensile properties is included in this report.

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Grain boundary microstructure and fatigue crack growth in Allvac 718Plus superalloy

Cited by 70 publications

References 10 publications

Grain boundary precipitation in Inconel 718 and ATI 718Plus

Grain boundary precipitation in Inconel 718 and ATI 718Plus

Cracks in superalloys

The Effect of Aluminum on Microstructure and Mechanical Properties of ATI 718Plus Alloy

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