Abstract
A novel aluminizing process based upon room temperature Al-electrodeposition from Ionic Liquids followed by diffusion heat treatment was applied on bare- and CoNiCrAlY-coated Inconel 738 (IN738). The aluminized samples were tested by isothermal oxidation at 1000 °C in air. The microstructural and chemical evolution of the samples were determined as function of oxidation time and compared with the currently applied coatings obtained via pack cementation. The newly proposed method is suitable for the CoNiCrAlY coating, but not for the bare IN738. In the latter, the formed Al-enriched layer is much thinner and the anticorrosion properties resulted in being reduced. This is probably due to the presence of precipitates, which slow down the aluminum inward diffusion impairing the formation of a well-developed interdiffusion zone (IDZ). Traces of the electrolyte, embedded during the Al-electrodeposition process, can be seen as the origin of these precipitates.
Highlights
Inconel 738 (IN738) is a nickel-based superalloy widely used as a high temperature material for gas turbine and aerospace applications
The formed Al-enriched layer is much thinner and the anticorrosion properties resulted in being reduced. This is probably due to the presence of precipitates, which slow down the aluminum inward diffusion impairing the formation of a well-developed interdiffusion zone (IDZ)
The results show comparable oxidation resistance for the over-aluminizing process while on bare IN738 the sample produced with the two-step process resulted less performing respect to the ones produced by pack cementation
Summary
Inconel 738 (IN738) is a nickel-based superalloy widely used as a high temperature material for gas turbine and aerospace applications. Its industrial success is based on the superior creep resistance with respect to other alloys at the high operating temperatures employed in gas turbine engines (up to 1300 ◦ C). It presents low resistance to hot corrosion and high temperature oxidation. For this reason, surface modifications are mandatory in order to improve the durability of IN738 parts in the hot sections of gas turbines. The oxidation and corrosion resistance of high-temperature alloys and coatings is dependent on the formation and retention of a thin, dense, continuous external oxide scale, which serves as a diffusion barrier preventing oxygen diffusion and the rapid oxidation of the metal beneath
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