Affiliation:
1. Center for Engineering Research and Center of Research Excellence in Corrosion, Research Institute, King Fahd University of Petroleum and Minerals, P.O. Box 1639, Dhahran 31261, Saudi Arabia
Abstract
Titanium is a key element in nickel-base superalloys needed with aluminum to achieve the desired volume fraction of the strengthening γ′-phase. However, depending upon its concentration, titanium can degrade the adherence of aluminum oxide by forming TiO2 particles near the oxide-metal interface. This effect is extended to thermal barrier coating systems where in this case, the bond coat replaces the superalloy as the underlying substrate. Noting that the onset of failure of thermal barrier coating systems coincides with the first spall of the thermally grown oxide, titanium level in the superalloy can have an important effect on the useful life of the coating. Therefore, this study was undertaken to examine the effect of titanium on the performance of a thermal barrier coating system. Included in the study were two Ni-base superalloys with similar chemical composition except for the Ti content and a Pt-containing bond coat consisting of γ′+γ-phases all top coated with zirconia stabilized by 7 wt % yttria. Coating performance was evaluated from thermal exposure tests at 1150°C with a 24 h cycling period to room temperature. Various electron-optical techniques were used to characterize the microstructure. The coating system on the low-Ti alloy was found to outperform that on the high-Ti alloy. However, for both alloys, failure was observed to occur by loss of adhesion between the thermally grown oxide and underlying bond coat.
Subject
Mechanical Engineering,Energy Engineering and Power Technology,Aerospace Engineering,Fuel Technology,Nuclear Energy and Engineering
Cited by
17 articles.
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