Formation Process of a Rhenium-Based Diffusion Barrier on a Nickel-Based Superalloy
- PDF / 1,095,745 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 81 Downloads / 236 Views
0980-II05-29
Formation Process of a Rhenium-Based Diffusion Barrier on a Nickel-Based Superalloy Yongming Wang, Somei Ohnuki, and Toshio Narita Materials Science Division, Graduate School of Engineering, N-13, W-8, Kita-Ku, Sapporo, 060-8628, Japan
ABSTRACT The formation process of a rhenium-based diffusion barrier coating on a nickel-based single-crystal superalloy has been investigated. The diffusion barrier can be formed by two steps, electroplating and Cr cementation. A tri-layer film structure consisting of Ni / Ni-63Re / Ni was prepared by electrolytic plating onto the substrate, and it was found that the Re-Ni plating film composed of amorphous alloy which is characterized by X-ray diffraction (XRD) analysis. The barrier films, which formed by followed Cr-Pack cementations at 1573 K for 20, 50, 240, 360 and 600 min, were investigated with scanning electron microscope (SEM) and electron probe micro analyzer (EPMA). The change in thickness of barrier film was likely anomalous, and the chemical composition of barrier film changed along the curve of solubility limit of Ni in Re-NiCr sigma phase. INTRODUCTION In achieving a further increase in efficiency for gas turbine, new and advanced materials have a major role to play. Nickel-based single-crystal superalloys have been used for turbine blades and vanes in aero and stationary gas turbines derive their good mechanical properties at elevated temperatures. On the other hand, the life time of the components of gas turbine can substantially increased by the use of thermal barrier coatings (TBCs), which result in decreases in metal surface temperatures. However, with more increasing the turbine operating temperature, the microstructural deterioration of the base alloys and the TBC that caused by interdiffusion of atoms has become serious problem [1]. Recently, a novel diffusion barrier bond coat, having a duplex structure of Al reservoir and Re-based alloy film, has successfully been developed and was demonstrated to be available to suppress the interdiffusion between the bond coat and substrate. Thus, it is deservedly expected to improve the life span of the components of gas turbine. The Re-based alloy film acting as the role of diffusion barrier is chosen for its high melting temperature and low diffusivity and good stability in high temperature as well as its very low solubility of Al [2]. This study is focusing on fundamental understanding of formation process of the diffusion barrier, such as changes in morphology and composition. EXPERIMENTAL Diffusion barrier layer can be formed by two steps: electroplating and Cr-pack cementation. Nickel-based single crystal superalloy TMS-82+ was used as substrates, and its
nominal composition is Ni - 7.8Co - 4.9Cr - 1.9Mo - 8.7W - 5.3Al - 0.5Ti - 6.0Ta - 0.1Hf - 2.4Re (mass %) [3]. The alloy was first cut into disk-shape pieces with about 1.2mm in thickness and 15mm in diameter, and then each piece was cut into four partitions. These specimens were plated in the same manner. The procedure of formation of the Rhenium-ba
Data Loading...
