Texture evolution in Ti-6AI-4V
File(s)
Author(s)
Wyatt, Simon James
Type
Thesis
Abstract
Crystallographic orientation and microstructural morphology control properties in engineering materials.
Titanium alloys are used extensively in commercial turbofan aircraft engines, due to their high strength
and excellent corrosion resistance. The formation of preferred crystallite orientations during
manufacturing must be understood in order to maximise component lifespan and avoid failure. In this
thesis, I present a methodology which generates virtual 3D microstructures representing a material,
conforming to an approximation of a 2D reference surface characterised by electron backscatter
diffraction (EBSD). The subsurface grains of this microstructure are instanced using statistical
information taken from the map, controlling grain size and texture. The subsurface texture is controlled
through optimisations of an orientation distribution function (ODF) and misorientation distribution
function (MDF). The influence of this control is shown through simulating deformation within the
DAMASK crystal plasticity fast Fourier transform (CP-FFT) solver, to demonstrate the effect of
subsurface texture on the stress and strain partitioning on the reference surface. The textures of Ti-6Al
4V formed through hot-rolling at temperatures between 750 and 950 °C are characterised by EBSD. As
this method measures spatial and orientation information describing a 2D surface the material, I
investigate the mechanisms through which lattice orientations of crystallites evolve during processing.
EBSD maps are segmented by preferred orientation to demonstrate the spatial distribution of texture
fibres. By measuring phase composition through direct backscatter spectroscopy (DBS) and elemental
composition through energy dispersive x-ray spectroscopy (EDS), I demonstrate the influence of the β
phase on the formation of texture fibres during rolling, with weak evolution of all existing texture fibres
as the Ti-6Al-4V bar plastically deforms through slip. Through CP-FFT simulations of synthetic textured
polycrystals in DAMASK, using the orientations of the texture fibres observed by EBSD, I simulate the
texture evolution during deformation by hot rolling. Through examination of lattice rotation, slip shear
rates and twinning shear rates, I demonstrate that the texture evolution resulting from plastic deformation
at high temperatures is conducted entirely by crystal slip, resulting in only small lattice rotations and weak
texture evolution. This is in agreement with the textures obtained through EBSD of hot-rolled Ti-6Al-4V.
Titanium alloys are used extensively in commercial turbofan aircraft engines, due to their high strength
and excellent corrosion resistance. The formation of preferred crystallite orientations during
manufacturing must be understood in order to maximise component lifespan and avoid failure. In this
thesis, I present a methodology which generates virtual 3D microstructures representing a material,
conforming to an approximation of a 2D reference surface characterised by electron backscatter
diffraction (EBSD). The subsurface grains of this microstructure are instanced using statistical
information taken from the map, controlling grain size and texture. The subsurface texture is controlled
through optimisations of an orientation distribution function (ODF) and misorientation distribution
function (MDF). The influence of this control is shown through simulating deformation within the
DAMASK crystal plasticity fast Fourier transform (CP-FFT) solver, to demonstrate the effect of
subsurface texture on the stress and strain partitioning on the reference surface. The textures of Ti-6Al
4V formed through hot-rolling at temperatures between 750 and 950 °C are characterised by EBSD. As
this method measures spatial and orientation information describing a 2D surface the material, I
investigate the mechanisms through which lattice orientations of crystallites evolve during processing.
EBSD maps are segmented by preferred orientation to demonstrate the spatial distribution of texture
fibres. By measuring phase composition through direct backscatter spectroscopy (DBS) and elemental
composition through energy dispersive x-ray spectroscopy (EDS), I demonstrate the influence of the β
phase on the formation of texture fibres during rolling, with weak evolution of all existing texture fibres
as the Ti-6Al-4V bar plastically deforms through slip. Through CP-FFT simulations of synthetic textured
polycrystals in DAMASK, using the orientations of the texture fibres observed by EBSD, I simulate the
texture evolution during deformation by hot rolling. Through examination of lattice rotation, slip shear
rates and twinning shear rates, I demonstrate that the texture evolution resulting from plastic deformation
at high temperatures is conducted entirely by crystal slip, resulting in only small lattice rotations and weak
texture evolution. This is in agreement with the textures obtained through EBSD of hot-rolled Ti-6Al-4V.
Version
Open Access
Date Issued
2019-11
Date Awarded
2020-03
Copyright Statement
Creative Commons Attribution NonCommercial ShareAlike Licence
Advisor
Britton, Thomas
Dunne, Fionn
Sponsor
Engineering and Physical Sciences Research Council (EPSRC)
Rolls-Royce plc
Publisher Department
Materials
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)