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Laser Repair of Superalloy Single Crystals with Varying Substrate Orientations

Mokadem, S. ; Bezençon, C. ; Hauert, A. ; Jacot, A. ; Kurz, W.

In: Metallurgical and Materials Transactions A, 2007, vol. 38, no. 7, p. 1500-1510

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    Title
    • Laser Repair of Superalloy Single Crystals with Varying Substrate Orientations
    Author
    • Mokadem, S.. Institute of Materials, Ecole Polytechnique Fédérale de Lausanne, 1015, Lausanne EPFL, Switzerland
    • Bezençon, C.. Institute of Materials, Ecole Polytechnique Fédérale de Lausanne, CH-3960, Sierre, Switzerland
    • Hauert, A.. Institute of Materials, Ecole Polytechnique Fédérale de Lausanne, CH-3960, Sierre, Switzerland
    • Jacot, A.. Institute of Materials, Ecole Polytechnique Fédérale de Lausanne, CH-3960, Sierre, Switzerland
    • Kurz, W.. Institute of Materials, Ecole Polytechnique Fédérale de Lausanne, CH-3960, Sierre, Switzerland
    Document Type
    • Postprint
    Language
    • English
    Published in
    • Metallurgical and Materials Transactions A, 2007, vol. 38, no. 7, p. 1500-1510. Kluwer Academic Publishers-Plenum Publishers; http://www.springer-ny.com
    Other Version
    Classification
    • Engineering
    OAI-PMH Identifier
    • oai:doc.rero.ch:311822
    Summary
    The casting and repair of single-crystal gas turbine blades require specific solidification conditions that prevent the formation of new grains, equiaxed or columnar, ahead of the epitaxial columnar dendrites. These conditions are best determined by microstructure modeling. Present day analytical models of the columnar-to-equiaxed transition (CET) relate the microstructure to local solidification conditions (temperature gradient and interface velocity) without taking into account the effects of (1) a preferred growth direction of the columnar dendrites and (2) a growth competition between columnar grains of different orientations. In this article, the infiuence of these effects on the grain structure of nickel-base superalloy single crystals, which have been resolidified after laser treatment or directionally cast, is determined by experiment and by analytical and numerical modeling. It is shown that two effects arise for the case of a nonzero angle between the local heat flux direction and the preferred dendrite growth axis: (1) the regime of equiaxed growth is extended and (2) a loss of the crystal orientation of the substrate often occurs by growth competition of columnar grains leading to an "oriented-to-misoriented transition” (OMT). The results are essential for the definition of the single-crystal processing window and are important for the service life extension of expensive components in land-based or aircraft gas turbines