Materials fundamental study of the properties and deformation of titanium alloys at room temperature

Nelson, Kayleigh (2020) Materials fundamental study of the properties and deformation of titanium alloys at room temperature. PhD thesis, University of Glasgow.

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Abstract

The titanium alloy, Ti-6Al-4V is investigated to increase the current understanding of deformation in this significant alloy at a variety of length-scales. The strain rate sensitivity of titanium alloys is generally consid- ered negligible, however, parallels observed in the rate dependant behaviour have led to a renewed interest in the room temperature deformation. The results of a strain rate jump (SRJ) have been examined using combined high energy x-ray diffraction and microscopy techniques. This deformation is compared to that of constant strain rates where the SRJ is observed to cause texture strengthening and good alignment post jump with the higher constant strain rate for billet Ti-6Al-4V. Microstructural changes have been tracked during deformation via in situ high energy x-ray diffraction in the form of lattice strain evolution.
Rolled plate Ti-6Al-4V products (UDR and CR) have been compared with the cross rolled material exhibit- ing the highest strength in the direction of loading. Crystallographic texture has been examined using EBSD analysis. Lattice strain evolution is captured, again using synchrotron high energy XRD. Good macroscopic alignment is observed in the stress-strain response between SRJ and constant strain rate conditions where the timing of the jump does not appear to influence this phenomenon. The strain rate sensitivity can- not be adequately captured macroscopically by a single parameter as lattice strain evolution is dependant on crystallography. An effective moduli dependant on material texture is suggested for Ti-6Al-4V product forms.Computational, CPFE modelling has been performed on various instantiated microstructures to enable the prediction of lattice strain evolution for each of the product forms analysed. The impact of macrozones and texture elements is observed to influence this evolution.
The β phase in Ti-6Al-4V is often neglected in analysis due to its low volume fraction, the in situ examination of both Ti-6Al-4V and Ti-6.5Al, an alloy designed to replicate the α phase, question the validity of this sim- plification where the omission of the β phase is observed to dampen the strain hardening response compared to Ti-6Al-4V. α-phase Ti-Al alloys of varying aluminium contents have also been examined showing differing hardening responses, strain rate sensitivity and increasing strength with increased aluminium content.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Subjects: T Technology > T Technology (General)
Colleges/Schools: College of Science and Engineering > School of Engineering
Supervisor's Name: McBride, Dr. Andrew
Date of Award: 2020
Depositing User: Dr Kayleigh Nelson
Unique ID: glathesis:2020-75180
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 19 Mar 2020 14:34
Last Modified: 19 Mar 2020 14:36
URI: http://theses.gla.ac.uk/id/eprint/75180

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