ISSN: 1003-6326
CN: 43-1239/TG

Vol. 26    No. 8    August 2016

Microstructual evolution and stability of second generation single crystal nickel-based superalloy DD5
Ren-jie CUI, Zhao-hui HUANG
(Science and Technology on Advanced High Temperature Structural Materials Laboratory,
Beijing Institute of Aeronautical Materials, Beijing 100095, China
Abstract: The microstructual evolution and stability of a second generation single crystal (SC) nickel-based superalloy DD5 with minor grain boundary (GB) strengthening elements (C, B and Hf) were studied as a function of as-cast, heat treatment and thermal exposure. The microstructure and composition of the alloy were investigated by optical microscopy, scanning electron microanalysis (SEM), electron probe microanalysis (EPMA), energy dispersive spectrometry (EDS) and extraction analysis. In the as-cast condition, the microstructure observations and composition analysis showed that γ phase was the primary solidification phase and there were three microsegregations in the metal matrix. The morphology of these microsegregations depended on element segregations. After heat treatment, the dendrite cores contained fine and cuboidal-shaped γ′ particles with an average edge length of about 0.5 μm, while interdendritic regions contained irregularly-shaped γ′ particles and MC/M23C6 carbides. The mass fraction of γ′ phases was 61.685%. After exposure at 980 °C for 1000 h, no TCP phase was observed in both dendritic and interdendritic regions, indicating a good microstructual stability of the DD5 alloy at 980 °C.
Key words: single crystal superalloy; DD5 alloy; microstructural evolution; heat treatment; thermal exposure
Superintended by The China Association for Science and Technology (CAST)
Sponsored by The Nonferrous Metals Society of China (NFSOC)
Managed by Central South University (CSU)