Pt+Hf改性的gamma-Ni+gamma prime-Ni3Al基金属材料在多组元氧化剂中的氧化行为

Materials used for high pressure turbine applications usually serve in the high-temperature high-pressure atmosphere, which is one of the most severe man-made environments. To meet such ever-demanding requirements, high-temperature materials are being developed from generation to generation ranging from superalloys to protective coatings. This is due to the fact that the alloy designers aiming at the high-temperature strength practically as the exclusive goal in developing new materials. By increasing the amount of refractory elements, such design inevitably sacrifices the high-temperature oxidation resistance of superalloys with decreasing amount of Al and/or Cr. Protective coatings are applied onto the superalloys substrate, therefore, to compensate their inferior oxidation resistance. The novel coating materials, Pt+Hf-modified gamma-Ni+gamma prime-Ni3Al-based alloys, have been developed in recent years in USA. Comparing to the traditional beta-NiAl, this new material not only possesses superior high-temperature oxidation resistance, but also accommodate the Ni-based superalloy substrate with the inherent phase compatibility...Most high-temperature oxidation studies regarding to this new material were conducted in atmospheres with oxygen as the only oxidant. Many engineering application environments, however, contain certain level of other type of oxidants, such as H2O and SO2. Although at a lower level, these oxidants may impose significant effects on alloys high-temperature oxidation resistance. Up to now, a considerable amount of studies have been carried out trying to understand the H2O effects on the oxidation resistance of Cr2O3-forming alloys. Nevertheless, it appears that the similar studies on Al2O3-forming alloys are scarce. Limited reports are sometimes even contradictory. The mechanism responsible for these findings thus remains unclear. Furthermore, atmospheres involving sulfur only with a ppm level could significantly deteriorate metals and alloys protectiveness by forming the fast-growing unstable sulphides. Each one of these topics has received insufficient attention in terms of research, yet each is of considerable practical important for current and future engineering applications...To further explore the high-temperature oxidation and sulfidation behavior of the Pt+Hf-modified gamma-Ni+gamma prime-Ni3Al-based alloy materials, it is proposed to conduct an investigation of the fundamentals of the effects of water vapor and sulfur dioxide on Al2O3, NiO and NiAl2O4. The project will address the problems in scaling behavior of selected model alloys in multi-oxidant gaseous atmospheres. The expected results could help in understanding the H2O and SO2 effects, which will provide the foundation to further modify alloys compositions.

金属防护涂层的抗高温氧化研究多集中在将空气中的氧气作为唯一的氧化剂，通过形成保护性热生成氧化物以达到对前者的保护。而实际工作气氛中通常含有各类其他氧化剂，如H2O和SO2。尽管其含量相对较低，却对氧化物的形成、生长及保护性有很大影响。目前有关这类气体对氧化铝的影响研究相当匮乏。我们的前期研究表明，Pt+Hf改性的gamma-Ni+gamma'-Ni3Al基金属材料在干燥空气中比传统的beta基材料具有更好的抗高温氧化性能。为了继续考察这种下一代高温涂层材料在多组元氧化剂气氛中的表现，本项目准备采用含H2O和SO2气氛，通过研究：1）H2O对活性元素影响的氧化铝、氧化镍和镍铝尖晶石氧化物的高温形成及生长机制；2）氧化-硫化气氛对保护性氧化铝膜的破坏机理，揭示多组元氧化剂对该材料高温服役性能的影响机制，为进一步优化改进材料成分，提高其在多组元氧化剂中的抗高温氧化腐蚀能力提供物理化学依据。

项目完成了在镍基高温合金基体表面制备Pt/Ir改性铝化物涂层，制备得到的铝化物涂层由外层富Pt-Ir-Ni-Al层和内层的β-NiAl层组成，阐明了制备工艺参数对Pt/Ir改性铝化物涂层的组织结构、元素分布和性能的影响规律，揭示了Pt/Ir改性铝化物涂层的形成机理。测试分析了Pt/Ir改性铝化物涂层的抗高温氧化及腐蚀性能，在1150℃下的循环氧化实验证明了Pt/Ir改性铝化物涂层具有优异的抗氧化性能。研究表明，涂层最外层的Pt对于涂层氧化性能的提高起着非常重要的作用，因此，Ir在最外层时涂层的抗氧化性能最差。此外，Pt和Ir的加入提高了涂层表面Al的浓度，使其可以生成稳定的保护性的氧化物层，并且抑制了合金元素的互扩散和TCP相形成。喷砂表面的Pt/Ir改性铝化物涂层均表现出良好的氧化性能。Pt/Ru改性铝化物涂层比Pt改性铝化物涂层有更好的抗腐蚀性能。在1050°C下 NaCl和水蒸气气氛下腐蚀以后，Pt/Ru改性铝化物涂层表面形成平整、连续且结合良好的氧化铝层，Pt的添加起到了促进氧化铝生成，改善涂层抗氧化性能的作用，Ru的添加增加了涂层的强度，抑制了起皱的发生。