Mechanical behaviour due to texture and microstructure in advanced titanium alloys

• Main Author: Whittaker, M. T.
• Published: Swansea University 2003
• Subjects: 669
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.636593

Since their emergence in the 1950's, titanium alloys have been widely used in high performance engineering, particularly the aero industry. Considerable advances have been made in this time and the rate of development of the industry has been excellent. However, most of these advances have been made through alloying, and the same rate of development cannot be continued by this method alone. It is likely that, for the development to continue, a major revision of the way in which these alloys are processed and used is necessary. An attribute that has not being fully explored is the role of texture on mechanical and environmental properties. Improved control of microstructure and texture may yet lead to significant advances. In the past, most studies of texture effects have been limited to the alloy Ti6-4. In this programme of work, a large range of mechanical testing was undertaken on both Ti6-4 and Ti550, which showed considerable variations from the Ti6-4 in primary a grain size, primary a volume fraction and chemical composition. Tests included monotonic tensile tests, uniaxial strain control LCF and load control HCF tests, crack propagation tests, threshold tests and load controlled testing on various notch geometries. All tests were performed under tensile loading. Although the effects of texture and microstructure have been characterized separately for certain mechanical properties, little is known about their combined effect and their interaction under specific loading conditions. An attempt has been made to isolate the effects of grain size, grain shape, primary a volume fraction, texture intensity and texture type. The thesis also explores the role of texture and R ratio effects in notched specimens with various geometries, an area which has received little attention. It has been shown that trends in notched specimens can be predicted from strain control data in textured materials. Notch geometries have also been shown to be poorly described by use of only the stress intensity factor, K_t, without consideration of plastic zone and geometry effects. The relationship between texture and microstructure has been found to be closely interwoven, with texture effects being very dependent on microstructural conditions.