Research Papers

In Situ Imaging of High Cycle Fatigue Crack Growth in Single Crystal Nickel-Base Superalloys by Synchrotron X-Radiation

[+] Author and Article Information
Liu Liu, Christopher J. Torbet, Tresa M. Pollock

Department of Materials Science and Engineering, University of Michigan, Ann Arbor, MI 48109

Naji S. Husseini, Divine P. Kumah, Roy Clarke

Applied Physics Program, University of Michigan, Ann Arbor, MI 48109

J. Wayne Jones

Department of Materials Science and Engineering, University of Michigan, Ann Arbor, MI 48109jonesjwa@umich.edu

J. Eng. Mater. Technol 130(2), 021008 (Mar 12, 2008) (6 pages) doi:10.1115/1.2840966 History: Received August 09, 2007; Revised November 29, 2007; Published March 12, 2008

A novel X-ray synchrotron radiation approach is described for real-time imaging of the initiation and growth of fatigue cracks during ultrasonic fatigue (f=20kHz). We report here on new insights on single crystal nickel-base superalloys gained with this approach. A portable ultrasonic fatigue instrument has been designed that can be installed at a high-brilliance X-ray beamline. With a load line and fatigue specimen configuration, this instrument produces stable fatigue crack propagation for specimens as thin as 150μm. The in situ cyclic loading/imaging system has been used initially to image real-time crystallographic fatigue and crack growth under positive mean axial stress in the turbine blade alloy CMSX-4.

Copyright © 2008 by American Society of Mechanical Engineers
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Figure 1

(a) Microstructure features associated with nickel-base superalloy single crystals and (b) fatigue damage resulting from cyclic strain localization at carbides

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Figure 2

Overview and details of portable ultrasonic fatigue instrument: (a) load frame showing specimen location, (b) detail of “carrier” specimen showing center hole for X-ray beam transmission and attachment locations for the microspecimen, and (c) microspecimen installed on the carrier

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Figure 3

Details of finite element method (FEM) analysis of strain development in microspecimen during loading of the carrier specimen. The colored band contour represents the tensile stress S22 with unit MPa.

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Figure 4

Installation of the portable ultrasonic fatigue instrument at the beamline: (a) schematic showing the imaging configuration and (b) photograph of installation on the optical bench

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Figure 5

Images of a fatigue crack produced by ultrasonic fatigue: (a) merged optical images to show relative intersections of the crack with front and back specimen surface and (b) synchrotron X-ray image of the same fatigue crack

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Figure 6

Representative fatigue crack growth behavior observed in the microspecimen during ultrasonic fatigue: (a) crack length versus number of cycles and (b) crack growth rate versus stress intensity factor range

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Figure 7

In situ synchrotron X-ray images of fatigue crack growth during ultrasonic fatigue



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