Korean Journal of Materials Research (한국재료학회지)

Materials Research Society of Korea (한국재료학회)
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Segregation Phenomenon of As-Cast and Heat Treatment Microstructures in Investment Casting of IN738LC Superalloy

IN738LC 초내열합금 정밀 주조의 주조 및 열처리 미세조직에 구성되는 성분 편석 현상

  • Choe, Byung Hak (Dept. of Metal and Materials Engineering, Gangneung-Wonju National Univ.) ;
  • Han, Sung Hee (Dept. of Metal and Materials Engineering, Gangneung-Wonju National Univ.) ;
  • Kim, Dae Hyun (Dept. of Metal and Materials Engineering, Gangneung-Wonju National Univ.) ;
  • Ahn, Jong Kee (Hanwha Aerospace) ;
  • Lee, Jae Hyun (School of Materials Science and Engineering. Changwon National Univ.)
  • 최병학 (강릉원주대학교 신소재금속공학과) ;
  • 한성희 (강릉원주대학교 신소재금속공학과) ;
  • 김대현 (강릉원주대학교 신소재금속공학과) ;
  • 안종기 (한화에어로스페이스) ;
  • 이재현 (창원대학교 재료공학부)
  • Received : 2021.03.12
  • Accepted : 2021.07.01
  • Published : 2021.07.27
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Abstract

The effect of solidification rate on micro-segregation in investment casting of IN738LC superalloy was studied. In Ni-based superalloys, the micro-segregation of solute atoms is formed due to limited diffusion during cast and solidification. The microstructure of cast Ni-based superalloys is largely divided into dendrite core of initial solidification and interdendrite of final solidification. In particular, mosaic shaped eutectic γ/γ' and carbides are formed in the interdendrite of the final solidification region in some cases. The micro-segregation phenomena formed in regions of dendrite core and interdendrite including eutectic γ/γ' and carbides were analyzed using OM, SEM/EDS and micro Vickers hardness. As a result of analysis, the lack of (Cr, W) and the accumulation of Ti were measured in the eutectic γ/γ', and the accumulation of (Cr, Mo) and the lack of Ti were measured in the interdendrite between dendrite and eutectic. Carbides formed in interdendritic region were composed of (Ti, W, Mo, C). The segregation applied to each microstructure is mainly due to the formation of γ' with Ni3(Al,Ti) composition. The Ni accumulation accompanied by Cr depletion, and the Ti accumulated in the eutectic region as a γ' forming elements. The Mo tends to diffuse out from the dendrite core to the interdendrite, and the W diffuse out from the interdendrite to the dendrite core. Therefore, the accumulation of Mo in the interdendrite and the deficiency of W occur in the eutectic region located in the interdendrite. Heat treatment makes the degree of the micro-segregation decrease due to the diffusion during solid solution. This study could be applied to the heat treatment technology for the micro-segregation control in cast Ni-based superalloys.

Keywords

Acknowledgement

This work was supported by "Human Resources Program in Energy Technology (No. 20194030202450)" and "Power Generation & Electricity Delivery (No. 20181110100310 & 20193310100090)" of the Korea Institute of Energy Technology Evaluation and Planning from the Ministry of Trade, Industry and Energy, Republic of Korea.

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