Thermal-mechanical fatigue of MAR-M 509 with a thermal barrier coating

An experimental set-up utilizing indirect induction heating suitable for th ermal-mechanical fatigue (TMF) tests of high-temperature materials with the rmal barrier coatings (TBC) is described. This set-up employed for TMF test ing of the Co-based superalloy MAR-M 509 with a NiCoCrAlY bond coat and a Z rO2 topcoat was able to generate temperature gradients across the TBC simil ar to the in-service conditions inside a gas turbine. The tests show the de velopment of an extensive inelastic strain during the high temperature comp ressive part of each cycle usually counterbalanced during the tensile part, a fast saturation of the stress response within the first loading cycles, and an exponential decrease in lifetime with increasing applied mechanical strain range. Micro structural analysis demonstrates that life of the sampl es was not limited by TBC-related processes but by cracks initiated on oxid ized carbides on the uncoated surface of the samples. (C) 2001 Elsevier Sci ence B.V. All rights reserved.