Abstract
A commercial NiCoCrAlYHfSi coating deposited on a Ni-base superalloy substrate was characterized before and after high temperature oxidation. The combination of Y, Hf and Si additions are reported to improve coating performance. Advanced characterization techniques including scanning transmission electron microscopy were used to study the segregation behavior of Y and Hf ions to the alumina grain boundaries after 200h at 1050°C and 100 and 200h exposures at 1100°C. After both exposure times, two distinct oxide layers were observed. The outer transient layer included many Y- and Hf-rich oxide particles. The inner layer consisted of columnar α-Al2O3 grains normal to the surface of the coating. Segregation of Y and Hf ions was found on the alumina grain boundaries as has been observed in model alloys with similar compositions. Isothermal exposures for up to 200h at 1050° and 1100°C caused a minimal increase in surface roughness. However, 200 one-hour cycles at 1100°C resulted in a more significant increase in surface roughness.
