Magnetron Sputtered Silicon Coatings as Oxidation Protection for Mo‐Based Alloys

Abstract

Mo‐based alloys with solidus temperatures around and above 2000 °C are attractive high‐temperature structural materials for future applications in the hot section of gas turbines. However, their oxidation behavior is poor due to pesting starting at 600 °C and nonprotective oxide growth at temperatures above 1000 °C. To ensure a sufficient oxidation resistance over a wide temperature range, protective coatings become inevitable. Herein, silicon coatings have been applied by magnetron sputtering on Mo‐9Si‐8B and on titan–zirconium–molybdenum alloy (TZM). The coating architecture is designed to minimize the intercolumnar gaps and porosity, thereby increasing the density. Specimens are tested at 800 and 1200 °C in air isothermally for up to 300 h. The focus is put on the chemical reactions at the coating–substrate interface, the phase formation, and the evolution of the thermally grown oxide. An initially globular SiO2 evolves into a uniform SiO2 layer providing excellent oxidation protection. The investigations reveal a rather slow interdiffusion between the coating and the alloys when tested in air. At the coating–substrate interface exclusively, the Mo3Si phase develops. Finally, the phase formation at the coating–substrate interface is studied in detail for various heat treatments in air and vacuum.

Effect of Water Vapor on the Oxidation Behavior of the Eutectic High‐Temperature Alloy Mo‐20Si‐52.8Ti

“…The experimental results presented in this work clearly show that that water vapor accelerates oxidation processes and an appropriate environmental barrier coating (EBC) system is required for MoSiTi alloys if exposed to wet surroundings. The point is addressed in the companion article by Anton et al of the current issue …”

Reactive Sputtered Ytterbium Silicate Environmental Barrier Coatings for Protection of Mo-Si-Based Alloys

“…Thus, a crystallisation treatment was necessary and was carried out at 900 • C for one hour followed by one hour at 1200 • C in a box furnace under lab air conditions without interrupting the annealing. This crystallisation treatment was chosen due to the former studies on Mo-Si-based materials in order to compare the results after oxidation testing [23,24]. For the oxidation tests, the samples were further hold for 10 h to 100 h at 1200 • C and for 100 h at 800 • C right after the crystallisation treatment.…”

“…Therefore, adhesion and stresses, caused by a mismatch in CTEs, should not be a problem [21,22]. In previous papers, the development of a silica forming oxidation protective coating was shown firstly by depositing a pure Si layer on the Mo-Si-based alloy which showed promising oxidation potential [23]. Secondly, a coating system consisting of a graded Mo-Si interlayer and a Si top layer was deposited on Mo-Si-based alloys.…”

Oxidation Protection of High-Temperature Coatings on the Surface of Mo-Based Alloys—A Review

“…As an important physical vapor deposition technology, magnetron sputtering technology is also widely used in metal surface coating [28]. In addition, the molten salt and laser cladding technologies are also mentioned [29][30][31][32][33][34][35][36][37][38][39]. The composition, structure and oxidation characteristics of all kinds of coatings have been given in relevant figures and tables [40].…”