An investigation of the effect of fatigue deformation on the residual mechanical properties of Ti-6Al-4V ELI

• Published in: Metallurgical and materials transactions. A, Physical metallurgy and materials science Vol. 31; no. 8; pp. 1937 - 1948
• Main Authors: AKAHORI, Toshikazu, NIINOMI, Mitsuo, FUKUNAGA, Kei-Ichi
• Format: Journal Article
• Language: English
• Published: New York, NY Springer 01.08.2000; Springer Nature B.V
• Subjects: Applied sciences; Condensed matter: structure, mechanical and thermal properties; Crack initiation; Crack propagation; Deformation effects; Dislocation density; Elongation; Equiaxed structure; Exact sciences and technology; Fatigue cracks; Fatigue failure; Fatigue, brittleness, fracture, and cracks; Fracture mechanics; Hardening; Hardness; Heat treating; Impact strength; Investigations; Low cycle fatigue; Mechanical and acoustical properties of condensed matter; Mechanical properties; Mechanical properties of solids; Metals. Metallurgy; Microcracks; Multiplication; Physics; Proof stress; Stress cycles; Tensile properties; Tensile strength; Titanium base alloys; Plastic fatigue; Charpy test; Fatigue testing; Crack formation; Vanadium alloys; Ternary alloys; Mechanical properties; Widmanstaetten structure; Plastic deformation; Hardness; Experimental study; Test bar; Titanium base alloys; Aluminium alloys; Tenacity; Fatigue cracks; Tensile properties
• ISSN: 1073-5623; 1543-1940
• DOI: 10.1007/s11661-000-0221-0

Tensile properties, hardness, and Charpy impact toughness of Ti-6Al-4V extralow interstitial (ELI) with equiaxed α and Widmanstätten α structures at various stages of fatigue were investigated. Fatigue crack initiation characteristics of the same alloy were also investigated in this study. In the equiaxed α structure, fatigue cracks initiated mainly at the interface between primary-α grains, while in the Widmanstätten α structure, they initiated across α plates at an angle of around 45 deg to the stress axis. Specimens with the Widmanstätten α structure fractured before adequate fatigue hardening was achieved because a multitude of microcracks readily formed. Specimens with the equiaxed α structure fractured after adequate fatigue hardening developed. Tensile strength, 0.2 pct proof stress, and hardness increased clearly with increasing stress cycles and fatigue steps, particulary in the low-cycle fatigue (LCF) region, while impact toughness and elongation showed a reverse trend. It is suggested, therefore, that the dislocation density multiplies more rapidly near the specimen surface during the early stages of fatigue, while during the later stages of fatigue, dislocation density increases near the center of the specimen. Also, the dislocation multiplication will continue until saturation of the entire specimen has occurred.