采用电弧离子镀技术及后续热处理工艺在镍基高温合金上制备了均匀NiCrAlY涂层和梯度NiCrAlY涂层, 分析了2种涂层的组织结构, 对比研究了2种涂层静态空气下1000和1100 ℃恒温氧化行为以及1100 ℃的循环氧化行为. 结果表明: 均匀NiCrAlY涂层由γ'/γ相和少量β-NiAl相、α-Cr相组成, 成分分布均匀;梯度NiCrAlY涂层具有外层富Al和内层富Cr的结构, 其中外层由β-NiAl相和少量γ'/γ相、α-Cr相组成. 一方面, 梯度涂层的初始Al含量较高;另一方面, 氧化过程中其富Cr区两侧出现了对富Al区的Al向基体扩散起阻碍作用的Cr(W)析出带.这两方面使梯度涂层长时间维持更多的Al存储相, 提升了氧化膜的迅速生成及再生成能力,从而使涂层具有较好的抗氧化性能.
MCrAlY(M=Ni and/or Co) overlay coatings are wildly adopted on hot components in gas turbine engines to protect them from rapid oxidation. Various methods can be applied to prepare MCrAlY overlay coatings, which formed by the arc ion plating method possess outstanding properties in terms of interfacial strength, porosity and componential distribution, and thus excellent oxidation properties. To increase the Al content is deemed an economical and effective solution for enhancing the service performance and life for MCrAlY coatings at elevated temperature because the degradation process relies greatly on the ceaseless forming and spallation process of the protective α-Al2O3 scales during high-temperature oxidation. However, high content of Al will lower the melting point and decrease the ductility of the coating. This phenomenon can be partly resolved through a gradient coating design. In this paper, a conventional NiCrAlY coating and a gradient NiCrAlY coating have been prepared by the combined method of arc ion plating and subsequent diffusion treatment on Ni--base superalloy substrate. The microstructures, morphologies, isothermal oxidation behavior at 1000 and 1100 ℃ and cyclic oxidation behavior at 1100 ℃ have been investigated on the two kinds of the coatings. The results have revealed that the conventional NiCrAlY coating with uniform components is composed of γ'/γ phase, β-NiAl phase and some α-Cr precipitate phase. While the gradient NiCrAlY coating have showed layered microstructure, i.e., an Al-enriched outer layer and a Cr-enriched inner layer, primarily consists of β-NiAl phase, γ'/γ phase and some α-Cr precipitate phase in the outer layer. During the oxidation, it is evident that the vanishment of β-NiAl phase and the enlargement of γ'/γ phase for both the coatings. Nevertheless, the gradient coating has maintained higher Al content during long-term oxidation due to the massive β-NiAl phase obtained in the outer layer after vacuum annealing and the Cr(W) zones precipitated beside the Cr--enriched inner layer during the oxidation. Adequateβ-NiAl phase, as reservoir phase of Al, directly delay the process of Al depletion; Cr(W) zones, to a certain extent, slow down the degradation by hindering the diffusion of Al from the gradient coating to the substrate. As a result, the ability of forming and healing the protective α-Al2O3 scales in the gradient coating have been enhanced, which has eventually improved the high-temperature oxidation properties.
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