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Research Papers

Influence of Surface Anomalies Following Hole Making Operations on the Fatigue Performance for a Nickel-Based Superalloy

[+] Author and Article Information
C. Herbert

Rolls-Royce University Technology Centre
(UTC) in Manufacturing,
The University of Nottingham,
University Park, Nottingham, NG7 2RD, UK
e-mail: christopher.herbert@rolls-royce.com

D. A. Axinte

Professor
Rolls-Royce University Technology Centre
(UTC) in Manufacturing,
The University of Nottingham,
University Park, Nottingham, NG7 2RD, UK
e-mail: dragos.axinte@nottingham.ac.uk

M. Hardy

Corporate Specialist—Nickel Alloys,
Rolls-Royce Plc,
ELT-10, PO Box 31,
Derby, DE24 8BJ, UK
e-mail: mark.hardy@rolls-royce.com

P. Withers

Professor
School of Materials,
The University of Manchester,
Grosvenor Street,
Manchester M13 9PL, UK
e-mail: p.j.withers@manchester.ac.uk

1Corresponding author.

Contributed by the Manufacturing Engineering Division of ASME for publication in the JOURNAL OF MANUFACTURING SCIENCE AND ENGINEERING. Manuscript received February 3, 2014; final manuscript received May 4, 2014; published online August 6, 2014. Assoc. Editor: Y. B. Guo.

J. Manuf. Sci. Eng 136(5), 051016 (Aug 06, 2014) (9 pages) Paper No: MANU-14-1047; doi: 10.1115/1.4027619 History: Received February 03, 2014; Revised May 04, 2014

Aero-engine manufacturers are continuously striving to improve component performance and reliability while seeking to increase the efficiency of manufacturing to reduce costs. Efficiency gains by using higher rates of material removal, however, can be counter-productive if they give rise to surface anomalies that distort the material microstructure and reduce the resistance of the material to fatigue crack nucleation. This paper investigates the effect of hole making processes and parameters on surface integrity and the initiation of cracks from low-cycle fatigue (LCF). It reports the dependence of elevated temperature (600 °C) low-cycle fatigue performance of nickel alloy RR1000 from surfaces produced from hole making and subsequent surface conditioning. As-machined surfaces include a reference “damage-free” surface, and two distorted microstructures: (i) a white layer, produced to a depth of 5 and 10 μm and (ii) a distorted gamma prime (γ') structure, produced to a depth of 10 and 15 μm. The effect of shot peening damage-free and 10 μm deep white layer surfaces was also evaluated. It was found that the presence of white layer significantly reduced fatigue performance compared with that shown by the damage-free surface, regardless of whether the white layer was subsequently shot peened or not. In contrast, surfaces showing distorted γ' structures produced much less debit in fatigue life and only from a depth of 15 μm. These results have been rationalized from an examination of fracture surfaces and from measurement of residual stresses before and after fatigue testing. This research is of particular importance as it is among the few reports that quantify the effect of different levels of work piece surface integrity on the fatigue life of a nickel-based superalloy that has been developed for critical rotating components in aero-engine applications.

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Figures

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Fig. 1

Single hole fatigue specimen geometry (dimensions in mm)

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Fig. 2

Layout of the equipment used for LCF testing

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Fig. 3

SEM analysis in hoop direction: (a) damage-free; (b) white layer I; (c) white layer II; (d) material drag I; (e) material drag II; (f) shot-peened damage-free surface; and (g) shot-peened white layer I

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Fig. 4

Residual stresses on hole surfaces before fatigue testing in (a) axial and (b) hoop directions

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Fig. 5

Number of cycles to failure for specimens with different surface quality conditions

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Fig. 6

SEM inspection viewed normal to the fracture plane of (a) “damage-free,” (b) white layer I, (c) white layer II, (d) material drag I, (e) shot-peened “damage-free” surface, and (f) shot-peened white layer I surface. In each case, the bore of the hole is on the RHS.

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Fig. 7

Inclined (45 deg) SEM view of intersection of the hole with the fracture surface for (a) “damage-free,” (b) white layer I, (c) material drag I, (d) material drag II, (e) “damage-free” after shot peening, and (f) white layer I after shot peening

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Fig. 8

Residual stresses on hole surfaces after LCF testing in (a) axial and (b) hoop direction

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