Microstructure and hot corrosion resistance of Si-Al-Y coated TiAl alloy
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Microstructure and hot corrosion resistance of Si-Al-Y coated TiAl alloy LI Yong-quan(李涌泉)1, 2, XIE Fa-qin(谢发勤)2, YANG Shao-lin(杨少林)1 1. School of Materials Science & Engineering, North Minzu University, Yinchuan 750021, China; 2. School of Aeronautics, Northwestern Polytechnical University, Xi’an 710072, China © Central South University Press and Springer-Verlag GmbH Germany, part of Springer Nature 2020 Abstract: In order to obtain a high-performance surface on TiAl alloy that can meet the requirements in hot corrosion environment, Si-Al-Y coatings were fabricated by pack cementation process at 1050℃ for 4 h. Corrosion behaviors of the TiAl alloy with and without Si-Al-Y coatings are compared to illustrate the factors and corresponding mechanism in molten salt environment of 25wt% K2SO4 and 75wt% Na2SO4 at 900 °C. The obtained Si-Al-Y coating was mainly composed of a TiSi2 outer layer, a (Ti, X )5Si4 and (Ti, X )5Si3 ( X represents Nb or Cr element) middle layer, a TiAl2 inner layer and a Al-rich inter-diffusion zone. The inter-phase selective corrosion containing corrosion pits extending along α2 phase from lamellar interfaces in hot corrosion tested TiAl alloy was observed. However, by being coated with Si-Al-Y coating, the hot corrosion performance of TiAl alloy was improved remarkably. Key words: TiAl alloy; Si-Al-Y coating; structure; hot corrosion Cite this article as: LI Yong-quan, XIE Fa-qin, YANG Shao-lin. Microstructure and hot corrosion resistance of Si-Al-Y coated TiAl alloy [J]. Journal of Central South University, 2020, 27(9): 2530−2537. DOI: https://doi.org/10.1007/ s11771-020-4478-8.
1 Introduction Possessing low density, high specific strength, excellent high temperature performance and other superior properties, TiAl alloys have been considered important high-temperature structural materials to be potentially used in industrial and aeroengine turbomachineries [1, 2]. For instance, TiAl alloys are being considered to replace Ni-based superalloy in the temperature range of 1073−1173 K in aero-engine, to achieve a component weight reduction over 50% [3, 4]. However, the low chemical activity of Al hinders the selective oxidation to form protective Al2O3 scale, and the resulted poor oxidation and corrosion
resistance of TiAl has been a major barrier to its practical applications and commercialization [5, 6]. In recent years, remarkable advancements have been made in solving the aforementioned problem through adding alloying elements such as B, Nb, Cr, Al and W [7−10]. Unfortunately, further alloying usually leads to mechanical properties deterioration of TiAl alloys [11]. Therefore, a protective coating is necessary to ensure the long-term mechanical and structure integrity of TiAl alloys in oxidation and corrosion environments. For instance, in ocean environment, the deposited sodium sulfate and sylvite can cause serious corrosion and accelerate the degradation of TiAl alloys [12]. Among various coating systems, Si-Al composite coatings are considered to be suitable for
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