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Research Papers: Nuclear Power

Effect of Oxygen Potential on Crack Growth in Alloys for Advanced Energy Systems

[+] Author and Article Information
Julian K. Benz

Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139

Ji Hyun Kim

Division of Energy Engineering, Ulsan National Institute of Science and Technology (UNIST), Ulsan, Republic of Korea 681-800

Ronald G. Ballinger

Department of Nuclear Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139

J. Eng. Gas Turbines Power 132(10), 102901 (Jun 30, 2010) (7 pages) doi:10.1115/1.3155793 History: Received November 11, 2008; Revised November 14, 2008; Published June 30, 2010; Online June 30, 2010

The effect of oxygen partial pressure on crack growth rates in Alloy 617 has been studied using both static and fatigue loadings at 650°C over the oxygen partial pressure range 1019103atm. Tests were conducted at either the constant stress intensity factor K for static conditions or the constant ΔK in fatigue. Oxygen concentration was measured on both the inlet and outlet of the test retort as well as in situ with a probe located directly at the specimen surface. For fatigue loading the crack path was observed to be transgranular but crystallographic with a decreasing growth rate as the oxygen concentration decreased. However, for static loading the crack path shifted to intergranular at the same Kmax (fatigue) and exhibited what appears to be an increasing crack growth rate with decreasing oxygen concentration.

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Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic of the autoclave used for static and fatigue testing at high temperatures

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Figure 2

Crack length versus the number of cycles showing the transition in crack growth rates in a test sequence; R=0.1 and the atmosphere consists of 1000 ppm O2 in argon

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Figure 3

Fatigue crack growth da/dN versus the stress intensity factor range with R=0.1

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Figure 4

Fatigue crack growth da/dt versus the stress intensity factor range with R=0.1

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Figure 5

Fatigue crack growth da/dN versus the stress intensity factor range with R=0.5

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Figure 6

Fatigue crack growth da/dt versus the stress intensity factor range with R=0.5

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Figure 7

Scanning electron and optical micrographs of typical fracture surface and microstructure

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Figure 8

Static crack growth versus time as a function of oxygen partial pressure. K=49.5 MPa√m. Note that crack length approaches allowable maximum value of a/W for K.

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Figure 9

Scanning electron micrograph of specimen oriented edge-on to show transition between fatigue and static loading. Also shown is the crack tip region.

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Figure 10

Fatigue crack growth rate versus stress intensity range at R=0.1 compared with data from Hsu (10) at R=0.05

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Figure 11

Fatigue crack growth rate versus stress intensity range at R=0.5 compared with data from Hsu (10) at R=0.6

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