The Si influence on the microstructure and oxidation resistance of Ti-Al slurry coatings on Ti-48Al-2Cr-2Nb alloy

Effect of Si Content on Deposition and High-Temperature Oxidation of Al-Si Coatings Obtained by Magnetron Sputtering PVD Method

“…The PVD coatings presented in this work had a lower mass gain than the comparable slurry Al-Si coatings produced by Moskal et al [27] on TiAl48-2-2: the lowest mass gain they observed was 0.9 mg/cm 2 , which showed the Al-12.5Si (in at.%) slurry coating after 500 h of oxidation at 900 • C. The lower mass gain of the magnetron-sputtered coatings in the present work could be a result of the different substrate alloy composition or the heat treatment of the coating. In [27], a diffusion treatment at 950 • C for 4 h in an argon atmosphere was performed, which led to a melting of Al-Si coatings due to the eutectic temperature of 577 • C [37]. As a result, the coatings of [27] exhibited a higher Si content at the coating/surface interface after diffusion treatment.…”

“…In [27], a diffusion treatment at 950 • C for 4 h in an argon atmosphere was performed, which led to a melting of Al-Si coatings due to the eutectic temperature of 577 • C [37]. As a result, the coatings of [27] exhibited a higher Si content at the coating/surface interface after diffusion treatment. Compared to that, the Si ≤ 12 at.% coatings produced in this work had a higher Si content below the surface of the coating, which could have positively influenced the oxidation behavior.…”

“…For γ-TiAl alloys, the formation of a titanium nitride layer would be detrimental due to the "nitrogen effect", which promotes the formation of a non-protective TiO 2 layer rather than protective Al 2 O 3 [5,26]. Therefore, the suppression of a nitride formation in Ti-Al-Si systems could also be one important effect arising from Si-based coatings on γ-TiAl alloys, as indicated by Moskal et al [27].…”

“…Thus, systematic studies are required to find the optimal range for the best oxidation protection of Al-Si-based coatings. Only a few of these studies have been published so far: a systematic study of Al-Si coatings on γ-TiAl with Si contents between 0 and 100% in the slurry was performed by Moskal et al [27]. They found that Si contents of 5 and 12.5 at.% Si in the slurry led to the most beneficial oxidation behavior after 500 h of oxidation at 900 • C. In the study by Swadźba et al [17], a low Si content had the lowest mass gain after 130 cycles of 23 h at 850 • C. These authors also compared a pure aluminide coating with "high-Si" and "low-Si" containing Si-aluminide coatings produced by pack cementation (90 and 80 wt.% Si in the pack) [17].…”

Effects of carbon addition on Ti–Al–Si coatings synthesized by self‐generated gradient hot‐dipping infiltration method

“…[19] Meanwhile, with the increase of the TiAl 3 coating thickness and silicon content, the oxidation resistance of the coating will be further improved. [20,21] However, it is difficult to form a TiAl 3 phase layer by directly adding silicon to Ti-6Al-4V alloy, because titanium, aluminum, and silicon tend to react to generate Ti-Si intermediate phase and Ti-Al-Si phase. [17] The self-generated gradient hot-dipping infiltration (SGHDI) method has been shown to form a continuous TiAl 3 phase layer in the early stage of coating preparation, in which the aluminum atoms in the TiAl 3 phase are partially substituted by the silicon atoms.…”