Evolution of Micro-Pores in a Single-Crystal Nickel-Based Superalloy During Solution Heat Treatment
- PDF / 2,167,456 Bytes
- 5 Pages / 593.972 x 792 pts Page_size
- 14 Downloads / 214 Views
ngle-crystal (SX) nickel-based superalloys have been widely used in turbine blades for their high-temperature capabilities. However, defects, such as stray grains, freckles, and micro-pores, limit the performance of the SX superalloys.[1–5] Among these defects, micro-pores that are always found during directional solidification (DS)[6–9] and homogenization[10–12] have critical effects on fatigue and creep properties.[4,13–16] Two kinds of micro-pores have been observed in the interdendritic region in SX superalloys. One type of the micro-pores is the solidification pores (S-pores), which forms due to the contraction of liquid metal and the sharp decrease in gas solubility during the final stage of solidification.[6,7] The second kind of micro-pores is named as H-pores, which has been observed during solution heat treatment of the SX alloys.[10] The level of
XIANGWEI LI is with the Superalloys Division, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China and also with School of Materials Science and Engineering, University of Science and Technology of China, Hefei 230026, China. LI WANG and JIAN ZHANG are with the Superalloys Division, Institute of Metal Research and also with Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China. Contact e-mail: jianzhang@ imr.ac.cn JIASHENG DONG and LANGHONG LOU are with the Superalloys Division, Institute of Metal Research. Manuscript submitted December 22, 2016. Article published online March 13, 2017 2682—VOLUME 48A, JUNE 2017
H-pores is associated with solution temperature and time.[10,17,18] Several experimental reports are available in the literature on the growth of micro-pores at high temperatures.[10,17–19] However, the S-pore and H-pore in the previous studies have not been distinguished. In fact, it is difficult to separate them based on the 2-dimensional observation. It was found that the formation and growth of micro-pores during heat treatment may be resulted from imbalanced cross-diffusion fluxes.[10,20] For example, the measured porosity increase during homogenization has been rationalized using the model based on the Kirkendall-Frenkel effect.[20] Epishin et al.[21,22] also found that the rapid diffusion of certain elements in SX superalloys results in the new micro-pore formation. However, the detailed evolution kinetic of S-pore and H-pore has not yet been reported. In the present paper, X-ray computed tomography (XCT) is used to characterize the micro-pores in three dimension (3-D).[23] Moreover, the observation of micro-pores enables to distinguish S-pores and H-pores, providing an opportunity to quantitatively analyze growth and coarsening behavior of each pore. A third-generation nickel-based single-crystal (SX) superalloy DD33 was used in the present experiment. The master alloy was directionally solidified into / 16 9 200 mm SX bars by the high-rate solidification process. The experimental samples with 10 mm in length and 1 mm 9 1 mm in cross section were machine
Data Loading...
