硅酸镱环境障涂层抗熔盐腐蚀行为与机制研究

Molten Salt Corrosion Behaviors and Mechanisms of Ytterbium Silicate Environmental Barrier Coating

稀土硅酸盐环境障涂层(EBC)是应用于新一代高推重比航空发动机热端部件的重要材料,但其在高温熔盐环境的腐蚀行为与机制尚不明晰。本工作采用真空等离子喷涂技术(VPS)制备了Yb_(2)SiO_(5)/Yb_(2)Si_(2)O_(7)/Si环境障涂层,并研究了该涂层体系在900℃、Na_(2)SO_(4)+25%NaCl(质量分数)熔盐环境中的腐蚀行为与机制。研究发现,所制备的Yb_(2)SiO_(5)/Yb_(2)Si_(2)O_(7)/Si涂层体系结构致密,各层之间结合良好;涂层体系腐蚀240 h,熔盐组分渗透Yb_(2)SiO_(5)涂层,在Yb_(2)Si_(2)O_(7)中间层发生富集。涂层中Yb_(2)SiO_(5)相具有良好的稳定性,Yb_(2)O_(3)第二相与熔盐发生反应,且随腐蚀时间延长, Yb_(2)O_(3)含量减少。中间层Yb_(2)Si_(2)O_(7)相与熔盐反应生成磷灰石相NaYb_(9)Si_(6)O_(2)6和钠硅酸盐,并产生Cl_(2)和SO_(2)等挥发性物质,从而影响服役寿命。硅黏结层中未发现熔盐渗透现象,保持完整。该涂层体系具有良好的抗熔盐腐蚀性能。

Environmental barrier coating(EBC) is essential for protection of ceramic matrix composite hot-sections in future gas turbine engines with high thrust-to-weight ratio. Rare-earth silicates, such as Yb_(2)SiO_(5)and Yb_(2)Si_(2)O_(7), have been developed for potential application as EBC. However, the corrosion behaviors and mechanisms of EBC in molten salt environment such as Na_(2)SO_(4)at high temperature are not clear. In this work, the Yb_(2)SiO_(5)/Yb_(2)Si_(2)O_(7)/Si coating was prepared by vacuum plasma spraying(VPS). The molten salt(Na_(2)SO_(4)+25% NaCl, in mass) corrosion behaviors and mechanisms of the coating at 900 ℃ for 60-240 h were investigated. Results showed that the Yb_(2)SiO_(5)/Yb_(2)Si_(2)O_(7)/Si coating exhibited dense structure with good bonding between the triple ceramic layers. The molten salt of Na_(2)SO_(4)+25% NaCl penetrated the Yb_(2)SiO_(5)top layer and enriched in the Yb_(2)Si_(2)O_(7)interlayer, while the interfacial bonding between the coating and substrate still remained good after corrosion for 240 h. The Yb_(2)SiO_(5)phase in the top layer exhibited good stability, while the second phase of the Yb_(2)O_(3)reacted with molten salt. The content of the Yb_(2)O_(3)decreased with the increase of corrosion time. The Yb_(2)Si_(2)O_(7)phase in the interlayer reacted with molten salt to form apatite phase of NaYb_(9)Si_(6)O_(2)6and sodium silicate as well as volatile species such as Cl_(2)and SO_(2), which might shorten the service life of the coating. Moreover, there was almost no molten salt in the silicon bond layer, which remained intact. The Yb_(2)SiO_(5)/Yb_(2)Si_(2)O_(7)/Si coating exhibited good resistance to molten salt corrosion.