Strength-Ductility Relationship in Solution Treated and Aged α+β Type Ti-4.5%Al-3%V-2%Fe-2%Mo Titanium Alloy

• Published in: ISIJ International Vol. 44; no. 11; pp. 1911 - 1917
• Main Authors: Fukai, Hideaki, Minakawa, Kuni-nori, Ouchi, Chiaki
• Format: Journal Article
• Language: English
• Published: Tokyo The Iron and Steel Institute of Japan 2004; Iron and Steel Institute of Japan
• Subjects: Applied sciences; ductility; elongation; Exact sciences and technology; Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology; Metals. Metallurgy; notch tensile strength; primary α; solution treating and aging; tensile strength; titanium alloy; transformed β; void formation; Mechanical properties; Ductility; Strength
• ISSN: 0915-1559; 1347-5460
• DOI: 10.2355/isijinternational.44.1911

The microstructural variation with solution treating or aging conditions in SP-700 alloy with Ti-4.5%Al-3%V-2%Fe-2%Mo was investigated, and the effect of the microstructure on strength-ductility balance of this alloy was studied by tensile testing using both the smooth and notched specimens. Solution treating in the α+β region formed a two-phase microstructure consisting of the primary α and transformed β phases, and the microstructure and hardness of the latter were widely varied by the cooling rate. The microstructures of the transformed β obtained by water quenching were α″, athermal ω and retained β phases, while air cooling formed acicular α in β matrix and its width became thicker with reduction of cooling rate. Water-quenched and aged alloy exhibited better strength-ductility balance compared with air-cooled and aged one, which appeared to be due to retardation of void formation during straining. Strength after aging in this alloy could be analyzed by a law of mixture, and micro-hardness and the volume fraction of the transformed β phase were found primarily to control strength. Reduction of hardness difference between the primary α and transformed β phases by the increase of the oxygen content of this alloy improved strength-ductility balance. Notch tensile strength increased with strengthening due to age-hardening and also the increase of cooling rate after solution treating, and showed a peak value at tensile strength of around 1300 MPa.