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Title: The impact of basal plane texture on the mechanical behaviour of Ti 6Al 4V
Author: Lardner, M. I.
Awarding Body: University of Wales Swansea
Current Institution: Swansea University
Date of Award: 2000
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The hexagonal α phase of Ti 6/4 can develop strong crystallographic textures that result in anisotropic plate properties. Ti 6/4 is used extensively in the aerospace industry due to a high strength to weight ratio with good fatigue and creep resistance. The benefits of using this alloy are restricted by scatter in fatigue behaviour, forcing the designer to use greater safety margins, thus the aim of this project is to provide a better understanding of the relationship between microstructure, texture and mechanical properties. Properties including strain controlled fatigue life, Young's Modulus and crack propagation rates have been experimentally determined for strongly textured material. The high textural intensity results in high stiffness values, especially for the transverse direction. Strain control fatigue levels are shorter in the transverse direction due to cycling between much higher stresses. However loading parallel and perpendicular to basal planes reveals no difference in crack growth rates. Fatigue strength is higher than for less textured material. Crack tip plasticity induced closure is indicated by fractographic observations of striation spacing. Crack growth is up to ~ 25% faster through the bulk of specimens than near free surfaces, which are under plane stress conditions. Striation data imply that crack path deflection accelerates growth near free surfaces, but increases crack resistance through the bulk of a specimen. Texture data were acquired using the electron backscatter diffraction (EBSD) technique enabling the determination of crystal orientation from individual grains on a bulk sample. This technique was used to investigate the orientations of lamellar α regions in a bimodal microstructure. Within such a region parallel α lamellae share a common orientation. These regions can develop strong textures that are qualitatively the same as for primary α grains in the same locality. Additional texture data were supplied by Rolls Royce.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available