Journal of the Korean Crystal Growth and Crystal Technology (한국결정성장학회지)

The Korea Association of Crystal Growth (한국결정성장학회)
권호 표지
DOI QR코드

DOI QR Code

Fabrication of TiAl alloy by centrifugal casting and its microstructure

원심주조법에 의한 TiAl 합금의 제조 및 미세구조 분석

  • Ryu, Jeong Ho (Department of Materials Science and Engineering, Korea National University of Transportation) ;
  • Lee, Ho Jun (Department of Materials Science and Engineering, Korea National University of Transportation) ;
  • Cho, Hyun Su (Department of Materials Science and Engineering, Korea National University of Transportation) ;
  • Paeng, Jong Min (Department of Materials Science and Engineering, Korea National University of Transportation) ;
  • Park, Jong Bum (Department of Materials Science and Engineering, Korea National University of Transportation) ;
  • Lee, Jung-Il (Department of Materials Science and Engineering, Korea National University of Transportation)
  • 류정호 (한국교통대학교 신소재공학과) ;
  • 이호준 (한국교통대학교 신소재공학과) ;
  • 조현수 (한국교통대학교 신소재공학과) ;
  • 팽종민 (한국교통대학교 신소재공학과) ;
  • 박종범 (한국교통대학교 신소재공학과) ;
  • 이정일 (한국교통대학교 신소재공학과)
  • Received : 2017.09.08
  • Accepted : 2017.10.18
  • Published : 2017.10.31
Download PDF
⟨ Previous Next ⟩

Abstract

In this study, TiAl alloy was fabricated by a centrifugal casting method for turbo charge of automotive. Optimum conditions for defectless morphology using various ceramic mold were investigated. The crystal structure, microstructure, and chemical composition of the TiAl prepared by centrifugal casting were studied by X-ray diffractometer (XRD), optical microscopy (OM), field emission scanning electron microscopy (FE-SEM) and energy dispersive spectroscopy (EDS), microvickers hardness analyzer (HV). Two kinds of dendrite structures were observed with 4-fold and 6-fold symmetries. The FE-SEM, EDS and HV examinations of the as-cast TiAl showed that the thickness of the oxide layer (${\alpha}$-case) was typically less than $50{\mu}m$.

본 연구에서는 자동차 터보차저(turbo charger)용 터빈휠을 제조하기 위하여 고속원심주조법을 이용하여 TiAl 합금을 주조하였다. 여러 가지 조성의 주형을 사용하여 주조결함이 최소화 되는 최적의 몰드 조건을 찾고자 하였으며, 주조된 TiAl 합금의 결정구조와 미세조직을 고찰하였다. TiAl 샘플의 XRD 분석 결과 ${\gamma}$-TiAl 상과 ${\alpha}_2-Ti_3Al$ 상으로 구성되어 있음을 확인하였으며, 광학현미경과 FE-SEM 분석을 통하여 TiAl 샘플은 6-fold 및 4-fold 대칭성으로 이루어진 두 개의 수지상(dendrite) 형태로 이루어져 있음을 확인할 수 있었다. 또한 샘플의 단면에서 표면과 가까운 지점과 내부에서 측정한 원소함량의 차이를 확인할 수 있었으며, 마이크로비커스 경도계를 이용하여 표면에서 $50{\mu}m$ 미만의 영역에서 경도상승 영역 alpha-case 층이 형성되었음을 확인하였다.

Keywords

References

  1. S.G. Pyo, J.K. Oh, N.J. Kim and M. Yamaguchi, "Al compositional dependence on the deformation behavior and mechanical properties in ultra high purity TiAl alloys", J. Kor. Inst. Met. & Mater. 38 (2000) 629.
  2. I.-S. Jung, M.-C. Kim, J.-H. Lee, M.-H. Oh and D.-M. Wee, "Phase equilibria of TiAl alloy by directional solidification", J. Kor. Inst. Met. & Mater. 37 (1999) 448.
  3. Y.H. Lee, J.T. Yeom, N.K. Park, S.S. Hong, I.O. Shim, S.M. Hwang and C.S. Lee, "Prediction of microstructure durign high temperature forming of Ti-6Al-4V alloy", J. Kor. Inst. Met. & Mater. 43 (2005) 847.
  4. D.-G. Lee, Y.H. Lee, C.S. Lee and S. Lee, "Effect of volume fraction of tempered martensite on dynamic deformation properties of Ti-6Al-4V alloy having bimodal microstructure", J. Kor. Inst. Met. & Mater. 42 (2004) 455.
  5. X. Wu, "Review of alloy and process development of TiAl alloys", Intermetallics 14 (2006) 1114. https://doi.org/10.1016/j.intermet.2005.10.019
  6. J.Y. Jung, J.K. Park and C.H. Chun, "Influence of Al content on cast microstructures of Ti-Al intermetallic compounds", Intermetallics 7 (1999) 1033. https://doi.org/10.1016/S0966-9795(99)00011-4
  7. T. Tetsui, K. Shindo, S. Kobayashi and M. Takeyama, "A newly developed hot worked TiAl alloy for blades and structural components", Scripta Mater. 47 (2002) 399. https://doi.org/10.1016/S1359-6462(02)00158-6
  8. S. Djanarthany, J.-C. Viala and J. Bouix, "An overview of monolithic titanium aluminides based on $Ti_3Al$ and TiAl", Mater. Chem. Phys. 72 (2001) 301. https://doi.org/10.1016/S0254-0584(01)00328-5
  9. H. Clemens and H. Kestler, "Processing and application of intermetallic ${\gamma}$-TiAl-based alloys", Adv. Eng. Mater. 2 (2000) 551. https://doi.org/10.1002/1527-2648(200009)2:9<551::AID-ADEM551>3.0.CO;2-U
  10. T. Tetsui, "Application of TiAl in a turbocharger for passenger vehicles", Adv. Eng. Mater. 3 (2001) 307. https://doi.org/10.1002/1527-2648(200105)3:5<307::AID-ADEM307>3.0.CO;2-3
  11. K. Liu, Y.C. Ma, M. Gao, G.B. Rao, Y.Y. Li, K. Wei, X. Wu and M.H. Loretto, "Single step centrifugal casting TiAl automotive valves", Intermetallics 13 (2005) 925. https://doi.org/10.1016/j.intermet.2004.12.004
  12. S.-Y. Sung and Y.-J. Kim, "Modeling of titanium aluminides turbo-charger casting", Intermetallics 15 (2007) 468. https://doi.org/10.1016/j.intermet.2006.07.009
  13. P.X. Fu, X.H. Kang, Y.C. Ma, K. Liu, D.Z. Li and Y.Y. Li, "Centrifugal casting of TiAl exhaust valves", Intermetallics 16 (2008) 130. https://doi.org/10.1016/j.intermet.2007.08.007
  14. J. Fan, X. Li, Y. Su, J. Guo and H. Fu, "Effect of growth rate on microstructure parameters and microhardness in directionally solidified Ti-49Al alloy", Mater. Des. 34 (2012) 552. https://doi.org/10.1016/j.matdes.2011.05.007
  15. H.-S. Jang, I.-S. Jung, M.-H. Oh and D.-M. Wee, "Characterization of TiAl alloy including ${\beta}$-stabilizer I. Phase transformation at elevated temperatrure", J. Kor. Inst. Met & Mater. 38 (2000) 1042.
  16. I.-S. Jung, H.-S. Jang, M.-H. Oh and D.-M. Wee, "Characterization of TiAl alloy including ${\beta}$-stabilizer II. Directional solidification and mechanical properties", J. Kor. Inst. Met & Mater. 38 (2000) 1047.
  17. S.Y. Sung and Y.J. Kim, "Alpha-case formation mechanism on titanium investment casting", Mater. Sci. Eng. A 405 (2005) 173.