采用电弧离子镀沉积Cr和粉末包埋法渗Al的联合工艺制备了Al-Cr涂层, 并利用粉末包埋法制备了渗Al涂层, 分析了2种涂层的组织结构和成分, 研究了镍基高温合金DSM11基体、渗Al涂层和Al-Cr涂层在1000和1100 ℃下的恒温氧化行为. 结果表明: 渗Al涂层和Al-Cr涂层组织致密, 与基体结合良好且成分分布均匀. 2种涂层都明显分为2个区域: 外层和互扩散区. 渗Al涂层外层由b-NiAl相和Ni₂Al₃相组成, Al-Cr涂层外层由b-NiAl相、Ni₂Al₃相、a-Cr相和AlCr₂相组成. Al-Cr涂层可以显著改善基体合金的抗氧化性能, 且明显优于渗Al涂层. Al-Cr涂层优良的抗氧化性能源于在氧化过程中出现了Cr(W)析出带, 能够一定程度阻碍涂层中的Al元素向基体扩散, 降低了涂层退化速度, 而Cr的存在可以促进Al的选择性氧化, 提高涂层的自修复能力.

Currently, Ni-based superalloys are widely applied to turbine blades or other components of gas turbines for their excellent high temperature mechanical properties. These components must exhibit a high level of resistance to the oxidation and corrosion conditions generated by the combustion environment. The general design philosophy is to select a high strength substrate alloy to withstand the stress and apply a surface coating to give maximum protection from the environment. In this work, a Cr-modified aluminide (Al-Cr) coating were prepared by combining arc ion plating and pack cementation aluminizing. As a contrast, a simple aluminide coating was developed by pack cementation aluminizing. The isothermal oxidation behaviors at 1000 and 1100 ℃ were investigated on the Ni-based superalloy DSM11 substrate, aluminide coating and Al-Cr coating. The results demonstrate that aluminide coating and Al-Cr coating are dense and adhere tightly to the substrate. The microstructures of aluminized coating and Al-Cr coating are divided in two distinguished areas: the outer layer and the interdiffusion zone. The outer layer of the aluminized coating is composed of b-NiAl and Ni₂Al₃ phases, while the Al-Cr coating consists of b-NiAl, Ni₂Al₃, a-Cr and AlCr₂ phases. The DSM11 substrate shows bad oxidation behavior at 1000 ℃ isothermal oxidation test. The aluminide coating and Al-Cr coating both possess good oxidation properties in this test. Compared with aluminide coating, Al-Cr coating exhibits much better oxidation behavior due to the formation of Cr(W) zones, which can delay the process of Al depletion by hindering the diffusion of Al from the coating to the substrate. As for 1100 ℃ isothermal oxidation test, a large amount of mixed oxides include NiCr₂O₄ spinel and a-Al₂O₃ form on the surface of DSM11 substrate. The oxide scale on the surface of aluminide coating is simplex a-Al₂O₃ at the initial stage, while prolonging the oxidation time it changes into less protective mixed structure composed of NiCr₂O₄ spinel and a-Al₂O₃ with massive internal oxidation, leading to great degradation and even failure of the coating. The surface of Al-Cr coating is covered with thick a-Al₂O₃ during the whole oxidation process. The localized scaling zones produced during oxidation are re-covered by newly formed a-Al₂O₃. It benefits from the third element effect of Cr, which implies that the Al-Cr coating degenerates primarily by consuming Al-reservoirs. Moreover, the presence of Cr can promote the selective oxidation of Al and the self-repair abilities of the coating.