Effect of water vapor on the failure behavior of thermal barrier coating with Hf-doped NiCoCrAlY bond coating
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Effect of water vapor on the failure behavior of thermal barrier coating with Hf-doped NiCoCrAlY bond coating Wenhao Duan1, Peng Song1,a), Chao Li1, Taihong Huang1, Zhenhua Ge1, Jing Feng1, Jiansheng Lu1 1
Faculty of Materials Science and Engineering, Kunming University of Science and Technology, Kunming 650093, China Address all correspondence to this author. e-mail: [email protected], [email protected]
a)
Received: 13 November 2018; accepted: 28 January 2019
The cyclic oxidation experiment of yttria-stabilized zirconia coatings deposited on NiCoCrAlYHf alloys by air plasma spraying was investigated at 1050 °C in air and in air containing water vapor. The results revealed that water vapor has a great influence on the oxidation resistance of the thermal barrier coatings (TBCs). Compared with the samples oxidized in air atmosphere, TBCs oxidized in air containing water vapor had a longer lifetime. It was also found that different atmospheres could lead to different HfO2 formation positions, which could decrease the rumpling in the oxide layer. In particular, after the coatings on Hf-doped NiCoCrAlY were first pretreated in air containing water vapor for 24 h at 1050 °C, the lifetime of the pretreated coating was doubled compared to the coating in laboratory air only. The water vapor pretreatment of the coatings could be an important method for optimizing the lifetime of TBCs.
Introduction Thermal barrier coating (TBC) is a protection system that increases the efficiency of gas turbine engines and extends the life of metal parts [1, 2]. TBCs consist of different layers, such as a bond coat (BC). The BC is usually a nickel-based alloy used as Al reservoir to form thermally grown oxides (a-Al2O3, TGO), and the top coat (TC) is 7YSZ, which is usually 7–8 wt% Y2O3-doped ZrO2 [1, 2, 3, 4, 5]. MCrAlY is used more and more in moist air or high water vapor industrial gas. Interaction with MCrAlY-coated turbine blades leads to the formation of a spinel environment on the overlay [6]. Therefore, the investigation of oxidation behavior of MCrAlY-coated turbine blades in high-temperature water environment is of great significance [7]. Protection from oxidation and hot corrosion of alloys is based on a dense, continuous, slowly growing layer of relatively chemical inertia and adherent oxide scales [8, 9]. The thermal growth oxide (TGO) layer in TBC usually exists as alumina (a-Al2O3) on aircraft and industrial gas turbine engines at high temperatures [10, 11]. It has been proved that water vapor is one of the important factors that affect the growth of alumina layer. Huang et al. [12] found that in Ar 1 H2 1 H2O environment, the oxidation rate of the coating would be lower
ª Materials Research Society 2019
than that in Ar 1 O2. In addition, atmospheres had an important effect on the phase transition from h-to a-Al2O3: accelerated phase transition by a rapid diffusion process of oxygen. The oxidation process of NiAl alloys in different atmospheres (15% H2O 1 Ar, 20% O2 1 Ar, and 15% H2O 1 17% O2 1 Ar) at 1100 °C was invest
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