Korean Journal of Metals and Materials (대한금속재료학회지)

The Korean Institute of Metals and Materials (대한금속재료학회)
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Effect of Microstructural Factors on Fatigue and Fatigue Crack Propagation Behaviors of Mill-Annealed Ti-6Al-4V Alloy

미세조직적 인자가 밀소둔된 Ti-6Al-4V 합금의 피로 및 피로균열전파 거동에 미치는 영향

  • Park, Sanghoo (Dept. of Materials Engineering and Convergence Technology, ReCAPT, Gyeongsang National University) ;
  • Kim, Sumin (Dept. of Materials Engineering and Convergence Technology, ReCAPT, Gyeongsang National University) ;
  • Lee, Daeun (Dept. of Materials Engineering and Convergence Technology, ReCAPT, Gyeongsang National University) ;
  • Ahn, Soojin (Dept. of Materials Engineering and Convergence Technology, ReCAPT, Gyeongsang National University) ;
  • Kim, Sangshik (Dept. of Materials Engineering and Convergence Technology, ReCAPT, Gyeongsang National University)
  • 박상후 (경상대학교나노신소재융합공학과) ;
  • 김수민 (경상대학교나노신소재융합공학과) ;
  • 이다은 (경상대학교나노신소재융합공학과) ;
  • 안수진 (경상대학교나노신소재융합공학과) ;
  • 김상식 (경상대학교나노신소재융합공학과)
  • Received : 2018.08.24
  • Accepted : 2018.10.08
  • Published : 2018.12.05
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Abstract

To understand the effect of microstructural factors (i.e., the size of ${\alpha}$ phase, equiaxed vs bimodal structure) on high cycle fatigue (HCF) and fatigue crack propagation (FCP) behaviors of mill-annealed Ti-6Al-4V (Ti64) alloy, three specimens of EQ (equiaxed)-8 (8 indicates the size of ${\alpha}$ grain), BM (bimodal)-8, and BM-16 were studied. The uniaxial HCF and FCP tests were conducted at an R ratio of 0.1 under sinusoidal fatigue loading. The microstructural influence (i.e., EQ vs BM) was not significant on the tensile properties of mill-annealed Ti64 alloy, and showed an increase in tensile strength and elongation with decreasing gauge thickness from 50 mm to 1.3 mm. The microstructure, on the other hand, affected the resistance to HCF substantially. It was found that the EQ structure in mill-annealed Ti64 has better resistance to HCF than the BM structure, as a result of different crack initiation mechanism. Unlike HCF behavior, the effect of microstructural features on the FCP behavior of mill-annealed Ti64 was not significant. Among the three specimens, BM-16 specimen showed the highest near-threshold ΔK value, probably because it had the greatest slip reversibility with large ${\alpha}$ grains. The effect of microstructural factors on the HCF and FCP behaviors of mill-annealed Ti64 alloy are discussed based on fractographic and micrographic observations.

Keywords

Acknowledgement

Grant : 항공용 Ti-6AI-4V 판재 및 대형 열간 성형 부품 제조 기술 개발

Supported by : 산업 통상 자원부, 과학 기술부

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