HIGH TEMPERATURE OXIDATION RESISTANCE AND MECHANICAL PROPERTIES OF NiCrAlY/Al--Al2O3 COATINGS ON AN ORTHORHOMBIC Ti2AlNb ALLOY
LI Haiqing1,2, GONG Jun2, SUN Chao2
1. Aerospace Research Institute of Materials and Processing Technology, China Academy of Launch Vehicle Technology,Beijing 100076
2. State Key Laboratory for Corrosion and Protection, Institute of Metal Research, Chinese Academy of Sciences,
Cite this article:
. HIGH TEMPERATURE OXIDATION RESISTANCE AND MECHANICAL PROPERTIES OF NiCrAlY/Al--Al2O3 COATINGS ON AN ORTHORHOMBIC Ti2AlNb ALLOY. Acta Metall Sin, 2012, 48(5): 579-586.
Abstract 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.
