Oxidation Resistance of Electroplated Pt-Ir Alloy Coatings on Ni-Based Single Crystal Superalloys Followed by Diffusion Annealing Treatment

Abstract

  Oxidation resistance of electroplated Pt and Pt-Ir alloy coatings followed by simple annealing heat treatments was investigated. The so-called 2nd generation Ni-based single crystal superalloy TMS-82+ and 4th generation TMS-138 were used as substrate materials. The cyclic oxidation tests and corresponding surface observations suggested the comparable oxidation resistance of Pt-coated TMS-82+ and Pt-Ir-coated TMS-138. However, cross-sectional microstructural analysis revealed that Pt-coated TMS-82+ exhibited the accelerated formation of voids, indicating the beneficial effect of Ir addition in terms of suppressed void formation. This study also revealed the importance of cross sectional analysis for thoroughly evaluating specimens subjected to the cyclic oxidation tests, and confirmed that oxidation resistance of the electroplated coatings was dependent on the quality of films deposited, which was drastically affected by the substrate surface finishing and substrate composition.