Reaction of Ni-Based Superalloy with Liquid Sn During Liquid-Metal-Cooled Directional Solidification
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Reaction of Ni-Based Superalloy with Liquid Sn During Liquid-Metal-Cooled Directional Solidification J. SHEN, Z.G. XU, Y.Z. LU, W. ZHENG, L.H. LOU, and J. ZHANG The liquid metal cooling (LMC) process has attracted increasing attention in the investment casting industry in recent years. Liquid Sn is generally used as the cooling medium in state-of-the-art LMC processes even though Sn is known to be a detrimental element in Ni-based superalloys. Therefore, Sn contamination in superalloys has become one of the top concerns for the LMC process. In this work, the reaction between liquid Sn and a Ni-based superalloy was investigated. The detectable reaction between superalloy and liquid Sn began at approximately 500 C, and the reaction products became complex with increasing temperature. At high temperatures beyond 750 C, a very short contact period of less than 1 minute led to a severe surface reaction. The results were compared to the surface reaction zone of the large blade. The critical time when the superalloy casting contacted liquid Sn is obtained based on experimental observations and numerical simulations. The surface reaction will occur if the ceramic mold cracked at this point or previously. The surface contamination during LMC solidification is associated with the volume of the casting. The present results indicate that surface reaction would be avoided if the volume of the large blade is reduced to ~ 30 pct of the original size. https://doi.org/10.1007/s11661-018-4758-1 The Minerals, Metals & Materials Society and ASM International 2018
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INTRODUCTION
DIRECTIONAL solidification (DS) has been widely used in the manufacturing of advanced gas turbine blades to achieve high operation performance. The liquid metal cooling (LMC) process has been attracting more attention in the investment casting industry in recent years due to the high thermal gradient obtained during solidification. The improved gradient is highly significant for the increasing demand for large DS and single-crystal (SX) components for heavy duty industrial gas turbine (IGT) applications,[1–4] i.e., a stable and cost efficient production process must be employed by the foundries to ensure high production yields and excellent part-to-part consistency. Optimization of processing parameters, which control the microstructure and typical mechanical properties of DS and SX alloys cast by the LMC process, have been reported in previous studies.[5–11] Finer dendritic arm
J. SHEN, Z.G. XU, Y.Z. LU, W. ZHENG, L.H. LOU, and J. ZHANG are with the Superalloys Division, Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang 110016, China. Contact e-mail: [email protected] Manuscript submitted March 15, 2018.
METALLURGICAL AND MATERIALS TRANSACTIONS A
spacing and a more uniform microstructure is obtained compared to that obtained by the conventional high rate solidification process, especially for large castings. Improved and stable mechanical behaviors are also expected.[3–8] The reduced freckle tendency,[7] hot tearing sensi
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