Effect of γ′ Phase Elements on Oxidation Behavior of Nanocrystalline Coatings at 1050 °C

Abstract

To study the effect of γ′ phase elements on the oxidation behavior of nanocrystalline coatings, two comparable nanocrystalline coating systems were established and prepared by magnetron sputtering. The oxidation experiments of the nanocrystalline coatings on the K38G and N5 superalloys were carried at 1050 °C for 100 h, respectively. The chemical composition of the above coatings is the same as the substrate alloy, including the γ′ elements, such as Al, Ta, and Ti. After serving at a high temperature for certain periods, their oxides participated and then affected the oxidation behavior of the coatings. The Al2O3 scale can be formed on the N5 coating, which cannot be formed on the K38G coating. Tantalum and titanium oxides can be detected on the oxide scale, which ruin its purity and integrity.

Corrosion Behaviors of Nitride Coatings on Titanium Alloy in NaCl-Induced Hot Corrosion

“…By contrast, the apparent internal oxidation and spallation occurred to the 4 μm thick TiAlN coating after hot corrosion at 600 °C for 100 h, leading to the complete protection failure in localized regions. Similar corrosion (10) AlN + 3∕4O 2 (g) → 1∕2Al 2 O 3 + 1∕2N 2 (g) ΔG = −474.91 kJ∕mol (11) AlN + 3∕2Cl 2 (g) → AlCl 3 (g) + 1∕2N 2 (g) ΔG = −315 kJ∕mol processes occurred to the 4 μm thick TiAlN coating. However, the kinetic curve and morphologies after hot corrosion indicate that the TiAlN coating with thickness of 4 μm is too thin to restrain the aggressive action of corrosion media running through the whole coating.…”

“…Similarly, at the early stage of corrosion TiAlN was fast oxidized to its oxides based on Eqs. ( 8) and (10). Afterward, sodium salt was generated by the reaction between NaCl and oxides of TiAlN.…”

“…One effective technique to shield the alloy substrates from hot corrosion is to apply protective coatings such as metallic coatings (e.g., Al-based coatings, Nanocrystalline and NiCrAlY coatings) [7][8][9][10][11][12], ceramic coatings [13][14][15][16][17], enamel [14,18,19], silicon and silicide coatings [20][21][22][23][24][25][26], silicone-based composite coatings [27], and thermal barrier coatings [28][29][30]. Owing to the chemical inertness, well thermal stability, remarkable mechanical properties and similarity of the coefficients of thermal expansion in accordance with titanium alloy, nitride ceramic coatings including TiN and TiAlN are the promising approaches to protect titanium alloys against hot corrosion [31].…”

Influence of the Co/Ni Ratio and Dendritic Segregations on the High-Temperature Oxidation Resistance of Multinary Co-Rich Superalloys at 850 °C and 1050 °C

“…With respect to thermodynamic stability, Ta 2 O 5 and Ta 2 WO 8 can be expected to grow below the dissociation pressure of Cr 2 O 3 . [58][59][60] No Ti enrichment, as it was described for the thick spots on dendrite cores, can be identified in the Ta-containing layer. Therefore, at least for the interdendritic regions, the formation of TaTiO 4 can be excluded in case of the ERBOCo system.…”