Short crack initiation and growth at 600 °C in notched specimens of Inconel718


Connolley, T., Reed, P.A.S. and Starink, M.J. (2003) Short crack initiation and growth at 600 °C in notched specimens of Inconel718. Materials Science and Engineering A, 340, (1-2), 139-154. (doi:10.1016/S0921-5093(02)00169-7).

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Description/Abstract

The natural initiation and growth of short cracks in Inconel®718 U-notch specimens has been studied at 600 °C in air. U notches were introduced through broaching, and hardness traces and optical microscopy on cross-sections through the U notch broaching showed that the broaching process had introduced a deformed, work hardened layer. Fatigue tests were conducted under load control using a 1-1-1-1 trapezoidal waveform, on specimens with as-broached and polished U-notches. Multi-site crack initiation occurred in the notch root. Many of the cracks initiated at bulge-like features formed by volume expansion of oxidising (Nb,Ti)C particles. In unstressed samples, oxidation of (Nb,Ti)C particles occurred readily, producing characteristic surface eruptions. Scanning electron microscopy on metallographic sections revealed some sub-surface (Nb,Ti)C oxidation and localised matrix deformation around oxidised particles. A mechanism for crack initiation by carbide expansion during oxidation is discussed. Surface short crack growth rates in the notch root of polished specimens were measured using an acetate replica technique. Observed short-crack growth rates were approximately constant across a wide range of crack lengths. However, there was a transition to rapid, accelerating crack growth once cracks reached several hundred micrometers in length. This rapid propagation in the latter stages of the fatigue life was assisted by crack coalescence. Polishing the U-notch to remove broaching marks resulted in a pronounced increase in fatigue life.

Item Type: Article
ISSNs: 0921-5093 (print)
Related URLs:
Keywords: crack initiation, Ni superalloys, carbide, oxidation, IN718
Subjects: T Technology > TN Mining engineering. Metallurgy
Divisions: University Structure - Pre August 2011 > School of Engineering Sciences
ePrint ID: 22096
Date Deposited: 16 Mar 2006
Last Modified: 27 Mar 2014 18:11
Contact Email Address: m.j.starink@soton.ac.uk
URI: http://eprints.soton.ac.uk/id/eprint/22096

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