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Research Papers

Mechanisms of Acute Angle Laser Drilling Induced Thermal Barrier Coating Delamination

[+] Author and Article Information
H. K. Sezer1

Laser Processing Research Centre, School of Mechanical, Aerospace and Civil Engineering, University of Manchester, Manchester M60 1QD, UKkursadsezer@yahoo.co.uk

L. Li

Laser Processing Research Centre, School of Mechanical, Aerospace and Civil Engineering, University of Manchester, Manchester M60 1QD, UK

1

Corresponding author.

J. Manuf. Sci. Eng 131(5), 051014 (Sep 24, 2009) (6 pages) doi:10.1115/1.4000102 History: Received October 07, 2008; Revised July 27, 2009; Published September 24, 2009

Laser fabrication of cooling holes in certain parts of the aero-engine components involves percussion or trepan drilling at acute angles (e.g., 16–30 deg) to the surface. These parts are often covered with plasma sprayed ceramic thermal barrier coatings (TBCs) to protect them from reaching excessive temperatures in hot engine environments. Delamination of the TBC is the main problem of laser drilling acute angled holes in the coated components. The present study investigates the mechanisms involved in the development of the delamination cracks. A significant role of melt ejection in the formation of cracks and the delamination at the coating/coating interface of the leading edge of a laser-drilled inclined hole was identified. It is shown that the delamination mechanisms at the TBC coating/bond coating and the bond coating/substrate interfaces are different. Melt ejection induced stresses were identified as the key mechanisms for the former type, while the thermal effects dominates the latter type.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

Images of laser-drilled inclining holes using 45 pulses of 1.5 ms duration, 10.5 J energy, and pulse repetition rates ranging from 0.1 Hz to 30 Hz; (A) surface pictures (B)–(G) cross sections of holes drilled with 0.1 Hz, 1 Hz, 3 Hz, 5 Hz, 10 Hz, and 30 Hz pulse repetition rates

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Figure 2

Schematic of a laser-drilled inclined hole

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Figure 3

Variation in hole angle with pulse repetition rate

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Figure 4

Variation in hole diameter and taper with pulse repetition rate

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Figure 5

Variation in BC/TBC and BC/substrate delamination crack lengths and TBC undercutting with laser pulse frequency

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Figure 8

Schematic representation of tension stress in leading edge TBC due to melt impact during acute angle laser drilling

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Figure 7

Schematic representation of pulse frequency effect on temperature at the laser-material interaction region without considering the latent heat, beam defocusing, multiple reflections, and absorption coefficient variations with hole depth

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Figure 6

Microstructures showing BC/substrate and BC/TBC interface delamination at the wall of a laser-drilled hole in TBC Nimonic 263 superalloy using 45 pulses at 1.5 ms duration, 10.5 J energy, and laser pulse repetition rates (a) 0.1 Hz, (b) 1 Hz, (c) 3 Hz, (d) 5 Hz, (e) 10 Hz, and (f) 30 Hz (drilling angle: 30 deg to surface)

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