Quantitative relationship between microstructural factors and fatigue life of Ti-5Al-2Sn-2Zr-4Cr-4 Mo (Ti-17) fabricated using a 1500-ton forging simulator

¹ Department of Science and Technology, Meijo University, Nagoya 468-8502, Japan
² Institute for Materials Research, Tohoku University, Sendai 980-5377, Japan
³ Department of Materials and Manufacturing Science, Graduate School of Engineering, Osaka University, Osaka 565-0871, Japan
⁴ Institute of Materials and Systems for Sustainability, Nagoya University, Nagoya 464-8601, Japan
⁵ Faculty of Chemistry, Materials and Bioengineering, Kansai University, Osaka 564-860, Japan
⁶ Department of Mechanical Engineering, School of Science and Engineering, Kindai University, Osaka 577-8502, Japan
⁷ Faculty of Engineering, Fukui University of Technology, Fukui 910-8505, Japan
⁸ National Institute for Materials Science (NIMS), Tsukuba 305-0047, Japan
⁹ Kobe Steel, LTD., Kobe 675-0023, Japan

Abstract

The microstructures, tensile properties, and fatigue lives of the forged Ti-17 using a 1500-ton forging simulator subjected to different solution treatments and a common aging treatment under both load- and strain-controlled conditions to evaluate high cycle fatigue and low cycle fatigue lives, respectively were examined. Then, the tensile properties, microstructures, and relationships between fatigue lives and the microstructural factors were discussed.

The fatigue limit under load-controlled conditions increases with increasing solution treatment temperature up to 1143 K, which is in the (α + β) region. However, it decreases with further increase in the solution treatment temperature to 1203 K in the b region. The fatigue ratio at fatigue limit is increasing with decreasing solution treatment temperature, namely increasing the volume fraction of the primary α phase, and it relates well qualitatively with the volume fraction of the primary α phase when the solution treatment temperature is less than the b transus temperature. The fatigue life under strain-controlled conditions to evaluate the low cycle fatigue life increases with decreasing solution treatment temperature, namely increasing the volume fraction of the primary α phase. The fatigue life under strain-controlled conditions to evaluate the low cycle fatigue life relates well quantitatively with the tensile true strain at breaking of the specimen and the volume fraction of the primary α phase for each total strain range.