DD98M纳米晶AlSi渗层制备及抗高温腐蚀性能研究

Preparation and High Temperature Corrosion Behavior of Aluminized Nanocrystalline Coating on DD98M Alloy

采用磁控溅射技术在DD98M合金表面制备了同成份的纳米晶,采用多弧离子镀技术在DD98M纳米晶涂层表面沉积了AlSi涂层,对上述制备态纳米晶+AlSi复合涂层进行了真空扩散处理,得到了外层为β-NiAl层、内层为γ'-Ni_3Al层的双层结构复合涂层。研究了合金、DD98M纳米晶涂层及复合涂层在1050℃恒温氧化及900℃下Na_2SO_4+25%K_2SO_4混合熔盐体系中的热腐蚀行为。结果表明:1050℃恒温氧化时,DD98M合金表面生成NiO,α-Al_2O_3,Ta_(0.8)O_2,CrTaO_4及NiAl_2O_4等组成的混合氧化物膜,氧化膜开裂剥落严重。纳米晶涂层表面生成α-Al_2O_3和少量NiAl_2O_4组成的混合氧化物膜,复合涂层表面形成了均匀致密的单一α-Al_2O_3膜。纳米晶涂层和复合涂层大幅提高了合金的抗恒温氧化性能。在900℃下Na_2SO_4+25%K_2SO_4熔盐中,DD98M合金20 h后即发生了灾难性腐蚀,沉积态纳米晶及其预氧化涂层提高了合金的抗热腐蚀性能,复合涂层大幅提高了合金的抗热腐蚀性能。

A nanocrystalline coating of DD98M was firstly deposited on the surface of high temperature alloy DD98M via magnetron sputtering, then a thin layer of Al-5.2 Si(mass fraction, %) was next deposited via multi-arc ion plating on top of the nanocrystalline coating, which was further subjected to vacuum diffusion treatment at 870 ℃ for 3 h, finally a two-layered aluminide coating composed of an outerβ-NiAl layer and an inner γ’-Ni3Al layer was obtained on the DD98M alloy. The isothermal oxidation behavior at 1050 ℃ in air and hot corrosion performance in molten salts Na2SO4+25%K2SO4 at 900 ℃ of the plain DD98M alloy, the nanocrystalline coating or the two-layered aluminide coating coated DD98M alloy were comparatively investigated. Results revealed that after isothermal oxidation at 1050 ℃, mixed oxides of NiO, α-Al2O3, Ta0.8O2, CrTaO4 and NiAl2O4 formed on the surface of DD98M alloy, and the oxide scale cracked and spalled seriously. An oxide scale composed of α-Al2O3 with a small amount of NiAl2O4 formed on the surface of the nanocrystalline coating of DD98M alloy. A dense oxide scale of simplex α-Al2O3 formed on the surface of the two-layered aluminide coating. It seems that the bilayered aluminide coating prepared with tri-step process can significantly enhance the oxidation resistance of the DD98M alloy. In molten salts Na2SO4+25% K2SO4 at 900 ℃, catastrophic corrosion occurred for the plain DD98M alloy only after 20 h corrosion. The as-deposited and pre-oxidation nanocrystalline coating can improved the corrosion resistance of the alloy to certain extent. However, the two-layered aluminide coating can apparently improve the corrosion resistance of the DD98M alloy.