采用电弧离子镀技术在NiCrAlY涂层与O相Ti2AlNb合金之间沉积不同Al∶Al2O3比例的 Al--Al2O3薄膜作为扩散阻挡层. 研究了900 ℃下恒温氧化500 h后NiCrAlY/Al--Al2O3/Ti2AlNb 体系中Al--Al2O3层阻挡合金元素互扩散的行为, 以及对涂层氧化动力学曲线的影响. 结果表明, 没有添加扩散阻挡层的NiCrAlY/Ti2AlNb体系, 涂层和基体之间的元素互扩散十分严重, 涂层丧失抗氧化能力；而添加扩散阻挡层的材料体系, 涂层和基体之间的元素互扩散受到抑制, 涂层的长期抗高温氧化性能得到提高. 对于3Al--Al2O3, 1Al--Al2O3和0Al--Al2O3~3种扩散阻挡层, 综合比较材料体系的抗氧化性能、阻挡层阻挡涂层和基体元素互扩散能力、以及涂层和基体之间结合力, 当1Al--Al2O3薄膜作为扩散阻挡层时, 材料性能最优异. 同时, 本文利用扩散阻挡系数简洁定量地表示出不同Al∶Al2O3比例阻挡层的阻挡扩散能力.
The orthorhombic Ti2AlNb alloys have received significant attentions because of their good physical and mechanical properties. However, these orthorhombic alloys face problems of oxidation at high temperature, especially above 700 ℃. To solve these problems, the use of surface coatings is an efficient way. However, when single coating was applied on the orthorhombic Ti2AlNb alloys, problems of serious interdiffusion and interfacial reaction were encountered, which resulted in worse oxidation behavior and deteriorated mechanical properties. To obtain good oxidation protection of NiCrAlY coating on the orthorhombic Ti2AlNb alloy, an efficient diffusion barrier should be added. In this study, NiCrAlY/Al--Al2O3 double--coatings were deposited on the orthhombic--Ti2AlNb alloy by arc ion plating. NiCrAlY coating acted as oxidation resistance coating and Al--Al2O3 coating acted as diffusion barrier. By introducing metallic Al in the Al2O3 film, the problem of coefficient of thermal expansion (CTE) mismatch between film and alloy substrate might be mitigate. Also metallic Al in the Al2O3 film can act as diffusion path which permits proper interdiffusion to improve the interface adhesion. The oxidation and interdiffusion behavior of specimens with and without diffusion barriers were investigated by oxidation tests at 900 ℃. The results indicated that substantial interdiffusion and rapid oxidation degradation occurred in the coated specimens without diffusion barrier. With Al--Al2O3 diffusion barriers, deferred interdiffusion and improved oxidation resistance were observed. Different contents of metallic Al in the Al2O3 coatings had different efficiency of diffusion barrier, and also affected interfacial mechanical properties. Among these NiCrAlY/Al--Al2O3 coatings, double--coating containing 1Al--Al2O3 diffusion barrier exhibited best performance. Coefficient of diffusion hindering was used to compare and quantify the efficiency of the diffusion barriers.
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