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Vol.56, No.12, 845 ~ 854, 2018
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| Title |
| Effect of Microstructural Factors on Fatigue and Fatigue Crack Propagation Behaviors of Mill-Annealed Ti-6Al-4V Alloy |
| 박상후 Sanghoo Park , 김수민 Sumin Kim , 이다은 Daeun Lee , 안수진 Soojin Ahn , 김상식 Sangshik Kim |
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| Abstract |
| To understand the effect of microstructural factors (i.e., the size of α 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 α 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 millannealed 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 α 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.
(Received August 24, 2018; Accepted October 8, 2018) |
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| Key Words |
| Ti-6Al-4V, microstructure, fatigue, fatigue crack propagation, mill-annealing |
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