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Korean Journal of Metals and Materials > Volume 55(9); 2017 > Article
Korean Journal of Metals and Materials 2017;55(9): 615-623. doi: https://doi.org/10.3365/KJMM.2017.55.9.615
Hydrogen-Affected Tensile and Fatigue Properties of Ti-6Al-4V Sheets by Superplastic Forming
Jinil Son1, Junhyuk Park2, Daeho Jeong2, Yongnam Kwon3, Masahiro Goto4, Sangshik Kim2
1MTDI Inc., Durability and Damage Tolerance Testing Lab., Jinju 52845, Republic of Korea
2Gyeongsang National University, Dept. of Materials Engineering and Convergence Technology, ReCAPT, Jinju 52828, Republic of Korea
3Korea Institute of Materials Science, Dept. of Materials Processing, Changwon 51508, Republic of Korea
4Oita University, Dept. of Mechanical Engineering, Oita 870-1192, Japan
Correspondence  Sangshik Kim ,Tel: +82-55-772-1667, Email: sang@gnu.ac.kr
Received: 8 May 2017;  Accepted: 19 May 2017.  Published online: 30 August 2017.
Mill-annealed Ti-6Al-4V (Ti64) sheets were formed into rectangular shaped pans with two square recesses by the superplastic forming (SPF) technique under high pressure using commercial grade argon gas. The SPF process induced a significant decrease in the tensile ductility and high cycle fatigue (HCF) resistance of the Ti64 alloy. The fractographic analysis of as-fabricated Ti64 sheets showed a hydrogen-affected layer on the surface, possibly incurred by a small amount of water vapor in the commercial grade argon gas. This hydrogen-affected layer with a depth of approximately 60 μm tended to decrease tensile ductility and the resistance to HCF, by encouraging easy crack initiation on the surface. The effect of hydrogen on the mechanical properties of the SPF processed Ti64 sheets was discussed based on fractographic and micrographic observations.
Keywords: alloys, hot working, hydrogen, fatigue, titanium alloy, superplastic forming
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