Microstructural Instability of an Experimental Nickel-Based Single-Crystal Superalloy
- PDF / 4,214,447 Bytes
- 9 Pages / 595.276 x 790.866 pts Page_size
- 61 Downloads / 217 Views
Microstructural Instability of an Experimental Nickel‑Based Single‑Crystal Superalloy Bin Yin1,2 · Guang Xie1 · Xiangwei Jiang1 · Shaohua Zhang1 · Wei Zheng1 · Langhong Lou1 Received: 29 November 2019 / Revised: 6 January 2020 © The Chinese Society for Metals (CSM) and Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Microstructural instability with the precipitation of topologically close-packed (TCP) phases of an experimental nickel-based single-crystal superalloy has been investigated. A significant amount of σ phases are distinguished in the interdendritic region of the as-cast samples after thermal exposure at 900 °C for 1000 h. The σ phases are preferentially precipitated at the periphery of coarse γ/γ′ eutectic, and their morphological evolution from needles to granules is observed. Microstructural analysis suggests that the local segregation of Cr and Ti at the periphery of coarse γ/γ′ eutectic accounts for the formation of σ phases in the as-cast samples. After heat treatment with low solution temperature and short holding time, the dendritic segregation of alloying elements (i.e., W, Re, Ti and Ta) and the volume fraction of γ′ phase in the interdendritic region are similar to that of the as-cast samples. However, no TCP phases are present in the interdendritic region of the heat-treated samples after thermal exposure, which is primarily ascribed to the elimination of local segregation of Cr and Ti near the coarse γ/γ′ eutectic. Moreover, small quantities of μ phases are precipitated in the secondary dendrite arm near the interdendritic region after thermal exposure, due to the increased volume fraction of γ′ phase and the concomitant enrichment of W and Re in the γ matrix. Keywords Nickel-based single-crystal superalloy · Topologically close-packed (TCP) phases · Segregation · Eutectic
1 Introduction Ni-based single-crystal (SX) superalloys are widely applied in industrial gas turbines, aircrafts and jet engines due to their excellent mechanical properties at elevated temperature. In order to improve high-temperature strength and creep resistance, high levels of refractory elements, such as Mo, W and Re, are added in SX superalloys, which strongly promote the precipitation of topologically close-packed (TCP) phases [1–3]. TCP phases, such as σ and μ phases, are detrimental to the mechanical properties of SX superalloys since they promote the depletion of refractory elements
Available online at http://link.springer.com/journal/40195. * Guang Xie [email protected] 1
Superalloys Division, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China
School of Materials Science and Engineering, University of Science and Technology of China, Hefei 230026, China
2
in the γ matrix, and can initiate cracks or accelerate crack propagation [4–6]. Usually, TCP phases are preferentially distributed in the dendrite core due to the dendritic segregation of Re and W [7]. In order to avoid the formation of TCP phases, heat treatment with high solution temperature and l
Data Loading...
