Microstructure and oxidation behavior of Al + Si co-deposited coatings on nickel-based superalloys

Abstract

Diffusion coatings have been widely used to metallic protective coatings or bond coats in thermal barrier coatings (TBCs) to protect the aeronautical turbine blades from detrimental oxidation and hot corrosion. However, degradation of these coatings caused by oxidation or hot corrosion can be particularly severe and rapid in the operating environment of the turbine. We present an experiment to modify γ-Ni + γ′-Ni 3 Al coating by co-deposition of Al and Si in order to improve the performance of coatings. In this study, microstructure and oxidation behavior of Al and Si co-deposited diffusion coatings were investigated. These coatings were deposited by Pt electroplating followed by aluminization and siliconization using the pack cementation process. The composition (in wt.%) of the packs was 2Al-4NH 4 Cl-xSi-(94 − x)Al 2 O 3 with different Si contents (x = 4, 6, 8 and 10) and the corresponding microstructure of the coatings was δ-Ni 2 Si. The isothermal oxidation tests at 1000°C in air indicated that the coating formed using the packs containing 10 wt.% Si had optimal oxidation resistance. After oxidation, the microstructure of the coatings was that of Cr 2 NiO 4 + NiO or NiO + Al 2 O 3 . The mechanisms through which Sirich coating forms and protects against oxidation are discussed.

Microstructure and Oxidation Resistance of a Si Doped Platinum Modified Aluminide Coating Deposited on a Single Crystal Superalloy

“…According to the kinetic curves ( Figure 4) and cross-sectional morphologies (Figure 8) of the PtAl and PtSiAl coatings, the PtSiAl coating possesses a lower mass gain than the PtAl coating and the thickness of the alumina layer formed on the surface of the PtSiAl coating is thinner. It can be concluded that the addition of Si could reduce the oxidation rate of the Pt modified aluminide coating, since Si could cut down the transient oxidation stage and promote the formation of α-Al2O3 [25,26]. It has been reported that the growth rate of the meta-stable θ alumina is higher than that of the stable α-alumina [27,28].…”

Microstructure and Cyclic Oxidation Resistance of Ce-Si Modified Aluminide Coating Deposited by Pack Cementation on Inconel 738LC

“…It is noteworthy that the intensity of the Ni2Si phase is increased from Ce0Si3 to Ce1Si6 sample According to the following relation (equations 1-3). In other words, the addition of silicon up to 6% increases the amount of Ni2Si formation leading to more resistance of the coating against hot oxidation [36].…”

“…Conventional aluminide coatings have been modified by adding beneficial elements such as chromium, silicon, cobalt, and platinum [17,[22][23][24][25] or by doping reactive elements (REs), e.g., hafnium, zirconium, cerium, lanthanum, yttrium, and other REs by using numerous techniques such as pack cementation, chemical vapor deposition (CVD), slurry, or co-diffusion methods [26][27][28][29][30][31][32][33][34]. Nonetheless, the addition of silicon into conventional aluminide coatings enhances the resistance against carburization, hot corrosion, and high-temperature oxidation [16,35,36]. On the other hand, the high silicon content has negative side effects on the mechanical performance of the coating resulting in cracking and spallation.…”

Production and Characterization of Al-Si Coatings Fabricated by Mechanical Alloying Method on Inconel 625 Superalloy Substrates

“…Additionally, there are TBC systems containing a ceramic top layer, e.g., ZrO 2 , together with the coatings mentioned above [8,9]. Moreover, Al-Si coatings produced on these high-temperature alloys were reported to improve the high-temperature oxidation resistance of these alloys [10,11].…”

“…The formation of an additional oxide phase (SiO 2 ) further benefits the protection of the nickel-based superalloy substrate, by delaying the formation of harmful phases (NiO and γ -Ni 3 Al) [16]. In addition, Fu et al (2014) reported that both coating elements react with nickel and form Ni 2 Si and Ni 3 Al, and the addition of Si promotes the formation of higher Al content NiAl phase (which is favorable to form protective Al 2 O 3 ) from Ni 3 Al [11]. Zang et al also reported that adding silicon helps to form a dense Al 2 O 3 layer, and sets a barrier to oxygen diffusion [13].…”