Formation and Evaluation of Oxidation Behavior of Zirconia- Aluminide Coating on Nickel- Based Alloy

Abstract

Practical applications of thermal barrier coatings with aluminide bond-coats are limited due to oxide scale spallation of the aluminide coating under applied thermal stresses. Considering the positive effects of oxygen-active elements or their oxides on the high temperature oxidation behavior, in this research zirconia was introduced into an aluminide coating. For this purpose, a Watts type bath was used to electroplate a layer of Ni-ZrO2 composite on a Ni-based substrate. Aluminizing was performed using the conventional two-step process at 760 and 1080 °C. Microstructural characterization of coatings in the as-coated conditions and after cyclic oxidation via 5-hour cycles at 1050 °C was performed using electron microscopy, energy dispersive spectroscopy and X-ray diffractometry. The results showed that the general three-zone microstructure of the simple high activity aluminide coatings develops below the pre-deposited nickel-zirconia layer and latter converts to a nearly un-alloyed porous NiAl. In spite of its porous surface layer, the zirconia modified coating has a higher oxidation resistance than the unmodified aluminide coating.

Keywords

• aluminide coating
• composite electroplating
• microstructure
• zirconia
• cyclic oxidation