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Effect of beam angle on HAZ, recast and oxide layer characteristics in laser drilling of TBC nickel superalloys

Sezer, H. K. and Li, L. and Schmidt, M. and Pinkerton, A. J. and Anderson, B. and Williams, P. (2006) Effect of beam angle on HAZ, recast and oxide layer characteristics in laser drilling of TBC nickel superalloys. International journal of machine tools & manufacture, 46 (15). pp. 1972-1982. ISSN 0890-6955

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Abstract

Industrial applications of laser drilling include the production of cooling holes at acute angles in certain parts of the aero-engine components. These parts are often covered with ceramic thermal barrier coatings (TBC) to protect them from reaching excessive temperatures in hot engine environments. Acute angle TBC drilling brings three major simultaneous complications to the process. These are: (i) multi-layer drilling, (ii) non-symmetrical geometry and melt ejection, and (iii) increased depth of drilling. In a previous investigation by the authors, delamination of TBC was found as a main problem of angled drilling and mechanisms involved were studied. In the present study, implications of these difficulties on the hole quality is investigated through a comparative study of vertical and acute angle drilled holes. Characteristics of recast layer, heat-affected zone (HAZ), oxide layer and TBC delamination are investigated. Variation of these metallurgical characteristics with the depth of the hole is evaluated. Results for vertical and inclined holes are compared. The extent of HAZ, recast layer and oxide layer is seen to vary significantly with location and is found increasing with decreasing drilling angle to surface. Numerical simulation of pulsed laser heating of TBC Nimonic 263 was carried out for acute angle drilling with assist gas considerations. Results from the simulation suggested that the total heat transfer rate is higher on the leading edge side than the trailing edge of the heated region. Experimentally observed larger HAZ on leading edge side and larger recast layer on trailing edge side are explained by the analysis of heat flow characteristics obtained with the model. (c) 2006 Elsevier Ltd. All rights reserved.

Item Type: Article
Journal or Publication Title: International journal of machine tools & manufacture
Uncontrolled Keywords: Laser drilling ; Thermal barrier coating ; Recast layer ; Heat affected zone
Subjects: T Technology > TA Engineering (General). Civil engineering (General)
Departments: Faculty of Science and Technology > Engineering
ID Code: 59522
Deposited By: ep_importer_pure
Deposited On: 04 Nov 2012 15:16
Refereed?: Yes
Published?: Published
Last Modified: 24 Jan 2014 05:34
Identification Number:
URI: http://eprints.lancs.ac.uk/id/eprint/59522

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