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Effect of Critical Cooling Rate on the Formation of Intermetallic Phase During Rapid Solidification of FeNbHfBPC Alloy

  • Kim, Song-Yi (Advanced Process and Materials R&D Group, Korea Institute of Industrial Technology) ;
  • Oh, Hye-Ryeong (Electronic Convergence Materials & Device Research Center, Korea Electronics Technology Institute) ;
  • Lee, A-Young (Advanced Process and Materials R&D Group, Korea Institute of Industrial Technology) ;
  • Jang, Haneul (Advanced Process and Materials R&D Group, Korea Institute of Industrial Technology) ;
  • Lee, Seok-Jae (Division of Advanced Materials Engineering, Research Center for Advanced Materials Development, Chonbuk National University) ;
  • Kim, Hwi-Jun (Advanced Process and Materials R&D Group, Korea Institute of Industrial Technology) ;
  • Lee, Min-Ha (Advanced Process and Materials R&D Group, Korea Institute of Industrial Technology)
  • Received : 2020.12.18
  • Accepted : 2021.01.26
  • Published : 2021.06.30

Abstract

We present the effect of the critical cooling rate during rapid solidification on the nucleation of precipitates in an Fe75B13P5Nb2Hf1C4 (at.%) alloy. The thermophysical properties of the rapidly solidified Fe75B13P5Nb2Hf1C4 liquids, which were obtained at various cooling rates with various sizes of gas-atomized powder during a high-pressure inert gas-atomization process, were evaluated. The cooling rate of the small-particle powder (≤20 ㎛) was 8.4×105 K/s, which was 13.5 times faster than that of the large-particle powder (20 to 45 mm; 6.2×104 K/s) under an atomized temperature. A thermodynamic calculation model used to predict the nucleation of the precipitates was confirmed by the microstructural observation of MC-type carbide in the Fe75B13P5Nb2Hf1C4 alloy. The primary carbide phase was only formed in the large-particle gas-atomized powder obtained during solidification at a slow cooling rate compared to that of the small-particle powder.

진공 가스분사법으로 제조된 Fe75B13P5Nb2Hf1C4 합금의 응고중 액상의 크기와 이에 따른 냉각속도의 변화가 정출상의 형성에 미치는 영향에 대한 고찰을 하였다. 고온 액상에서 동일한 조건으로 응고된 서로 다른 크기의 액상이 구형의 분말형태로 응고될 때 크기에 따른 임계냉각속도의 차이를 계산하였으며, 액상의 평균 반지름이 3배정도 크기 차이가 날 경우 고상으로 변태할 때 임계냉각속도가 13.5배까지 차이가 나는 것을 알 수 있었다. 이러한 임계냉각 속도의 차이에 따른 정출상의 형성과 정출상의 형태와 크기에 따른 탄화물의 형성 거동을 조사하여 열역학 계산으로 예측된 결과와 비교 분석하였으며, 분말입자의 크기가 20~45 마이크론일 경우 Hf과 Nb이 포함된 MC타입의 탄화물이 초정으로 형성 되는 것을 알 수 있었으며 이때 Hf과 Nb의 비율은 합금의 조성 및 냉각속도에 따라 변화됨을 관찰 할 수 있었다.

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