effects of alloying elements on twinning in alpha-titanium alloys

295 Pages·2001·47.19 MB·English

by  Arnas Fitzner

E A E
FFECTS OF LLOYING LEMENTS ON TWINNING
-
IN !LPHA TITANIUM ALLOYS
A thesis submitted to the University of Manchester for the degree of
Doctor of Philosophy
in the Faculty of Engineering & Physical Science

2014

Arnas Gerald Fitzner

School of Materials
Table of Contents
Table of tables ........................................................................................................................... 10!
Table of figures ......................................................................................................................... 11!
1.! Introduction ........................................................................................................................ 31!
2.! Aim and Objectives ........................................................................................................... 34!
3.! Literature review ................................................................................................................ 35!
3.1.! Crystal structure and microstructure .......................................................... 35!
3.2.! Deformation mechanisms of the " phase ................................................... 37!
3.2.1.! Slip ............................................................................................................ 38!
3.2.2.! Twinning ................................................................................................... 43!
3.2.3.! Interaction between slip, twinning and grain boundaries .......................... 46!
3.2.4.! Detection of slip and twinning: .................................................................. 47!
3.2.5.! Influence of deformation systems on hardening behaviour ...................... 48!
3.3.! Effects of alloying .......................................................................................... 50!
3.3.1.! Solubility and phase formation ................................................................. 50!
3.3.2.! Impact of alloying on lattice and c/a ratio development ............................ 54!
3.3.3.! Diffusion rates and electric resistivity ....................................................... 56!
3.3.4.! Solid solution strengthening ..................................................................... 57!
3.3.5.! Precipitation Strengthening ...................................................................... 59!
3.3.6.! Ordering in Ti-Al and effects on mechanical behaviour ............................ 60!
3.3.7.! CRSS dependencies ................................................................................ 64!
3.3.8.! Stacking faults .......................................................................................... 66!
3.3.9.! Stacking sequences and faults ................................................................. 67!
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3.3.10.! Stacking fault probability evolution when alloying Ti .............................. 67!
3.3.11.! Calculation and application to dislocation motion ................................... 70!
3.3.12.! Effect of alloying on twinning .................................................................. 71!
3.4.! Textures in Titanium alloys .......................................................................... 72!
3.4.1.! Cold rolling texture .................................................................................... 72!
3.4.2.! Texture changes during deformation and the role of alloying ................... 73!
4.! Experimental materials and methods .............................................................................. 76!
4.1.! Compositional choices of binary model alloys .......................................... 76!
4.2.! Practical aspects of model alloy manufacturing ........................................ 78!
4.2.1.! Casting, "-forge of model buttons ............................................................ 81!
#$%$%$! !-cross roll of model buttons ..................................................................... 81!
4.2.3.! Heat treatments ........................................................................................ 83!
4.2.4.! Chemical Analysis .................................................................................... 85!
4.3.! Metallographic preparation .......................................................................... 86!
4.4.! Optical microscopy ....................................................................................... 87!
4.5.! Mechanical properties .................................................................................. 89!
4.5.1.! Macro hardness indentation ..................................................................... 89!
4.5.2.! Nanoindentation ....................................................................................... 90!
4.5.3.! Compression tests .................................................................................... 92!
4.5.4.! Tension tests ............................................................................................ 94!
4.6.! Scanning electron microscopy .................................................................... 98!
4.6.1.! Imaging with SEM ..................................................................................... 98!
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4.6.2.! Texture determination with EBSD (Electron Backscatter Diffraction) ....... 98!
4.6.3.! Element analysis .................................................................................... 103!
4.7.! Digital image correlation ............................................................................. 103!
4.7.1.! Principle of DIC in submicron resolution ................................................. 104!
4.7.2.! Gold pattern application .......................................................................... 104!
4.7.3.! Imaging and image processing ............................................................... 104!
4.7.4.! Slip trace analysis ................................................................................... 105!
4.8.! TEM ............................................................................................................... 108!
4.8.1.! TEM foil preparation ............................................................................... 108!
4.8.2.! TEM diffraction and DF imaging ............................................................. 108!
4.8.3.! DITABIS image plates ............................................................................ 111!
4.9.! Diffraction spectra on WISH, ISIS .............................................................. 113!
4.9.1.! Setup and data manipulation .................................................................. 114!
4.9.2.! Practical aspects for result interpretation ............................................... 116!
4.10.! In-situ compression tests at Engin-X ...................................................... 117!
4.10.1.! Measurement strategies ....................................................................... 117!
4.10.2.! Engin-X setup ....................................................................................... 119!
4.10.3.! Observation of twinning on Engin-X while loading in RD ..................... 122!
4.10.4.! Twin observation in different loading directions at Engin-X .................. 130!
5.! Baseline characterisation ............................................................................................... 133!
5.1.! Chemistry of alloys ..................................................................................... 133!
5.2.! Homogeneity of received material ............................................................. 135!
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5.2.1.! Mechanical homogeneity ........................................................................ 135!
5.2.2.! Microstructural homogeneity .................................................................. 138!
5.2.3.! Textural homogeneity ............................................................................. 139!
5.3.! Crystal structure .......................................................................................... 143!
5.4.! Microstructural similarities and differences of investigated alloy range
145!
6.! The effect of Aluminium on deformation by twinning in " titanium ........................... 146!
6.1.! Introduction .................................................................................................. 146!
6.2.! Materials and Methods ................................................................................ 149!
6.2.1.! Material preparation ................................................................................ 149!
6.2.2.! Microstructure analysis ........................................................................... 150!
6.2.3.! Mechanical testing .................................................................................. 152!
6.2.4.! In-situ loading using neutron diffraction .................................................. 152!
6.3.! Results .......................................................................................................... 153!
6.3.1.! Starting material ..................................................................................... 153!
6.3.2.! Flow curves ............................................................................................ 156!
6.3.3.! Deformation microstructures and textures .............................................. 158!
6.3.4.! Diffraction peak evolution ....................................................................... 159!
6.3.5.! Summary of results ................................................................................. 161!
6.4.! Discussion ................................................................................................... 161!
6.4.1.! Ordering in Ti-Al ..................................................................................... 162!
6.4.2.! Twinning in Ti-Al ..................................................................................... 162!
6.5.! Conclusion ................................................................................................... 164!
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7.! The Effect of Al on slip and slip-twin interactions in Ti using DIC ............................. 167!
7.1.! Introduction .................................................................................................. 167!
7.2.! Experimental methods ................................................................................ 169!
7.2.1.! Sample preparation and experimental procedure .................................. 169!
7.2.2.! Imaging and image processing ............................................................... 170!
7.2.3.! Slip trace analysis ................................................................................... 171!
7.3.! Results .......................................................................................................... 172!
7.3.1.! Observations of slip traces ..................................................................... 173!
7.3.2.! Slip-twin interaction ................................................................................ 176!
7.4.! Discussion ................................................................................................... 181!
7.4.1.! Slip .......................................................................................................... 181!
7.4.2.! Twinning ................................................................................................. 182!
7.5.! Summary ...................................................................................................... 183!
8.! The relationship between nanohardness and the flow stress of Ti alloys: Effect of
straining and solute content .................................................................................................. 185!
8.1.! Introduction .................................................................................................. 185!
8.2.! Experimental methods ................................................................................ 187!
8.2.1.! Materials ................................................................................................. 187!
8.2.2.! Characterisation of micro and macro textures ........................................ 188!
8.2.3.! Mechanical testing and macroscopic anisotropy .................................... 188!
8.2.4.! Nanoindentation ..................................................................................... 188!
8.3.! Results .......................................................................................................... 189!
8.3.1.! Yield stress and stress-strain behaviour ................................................. 189!
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8.3.2.! Texture and Microstructural evolution .................................................... 190!
8.3.3.! Nanohardness ........................................................................................ 193!
8.3.4.! Effect of Al content ................................................................................. 193!
8.3.5.! Effect of strain hardening ........................................................................ 195!
8.4.! Discussion ................................................................................................... 197!
8.4.1.! Orientation dependence of hardness ..................................................... 197!
8.4.2.! The effect of Al addition .......................................................................... 197!
8.4.3.! Strain hardening ..................................................................................... 199!
8.4.4.! Implications for work hardening behaviour ............................................. 201!
8.5.! Conclusion ................................................................................................... 203!
9.! The effect of Tin on deformation by twinning in " titanium ........................................ 205!
9.1.! Introduction .................................................................................................. 205!
9.2.! Materials and Methods ................................................................................ 207!
9.2.1.! Material preparation ................................................................................ 207!
9.2.2.! Microstructure analysis ........................................................................... 208!
9.2.3.! Mechanical testing .................................................................................. 208!
9.2.4.! In-situ loading using neutron diffraction .................................................. 209!
9.3.! Results .......................................................................................................... 209!
9.3.1.! Starting Material ..................................................................................... 209!
9.3.2.! Flow curves ............................................................................................ 212!
9.3.3.! Diffraction analysis from in-situ experiment ............................................ 213!
9.3.4.! Deformation microstructures and textures .............................................. 214!
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9.4.! Discussion ................................................................................................... 215!
9.5.! Conclusion ................................................................................................... 218!
10.! The effect of Zirconium and grain size on deformation by twinning in " titanium . 219!
10.1.! Introduction ................................................................................................ 219!
10.2.! Materials and Methods .............................................................................. 221!
10.2.1.! Material preparation .............................................................................. 221!
10.2.2.! Microstructure analysis ......................................................................... 221!
10.2.3.! Mechanical testing ................................................................................ 222!
10.2.4.! In-situ loading using neutron diffraction ................................................ 223!
10.3.! Results ........................................................................................................ 224!
10.3.1.! Starting Material ................................................................................... 224!
10.3.2.! Macro and micromechanical behaviour ................................................ 226!
10.3.3.! Diffraction peak evolution ..................................................................... 227!
10.3.4.! Deformation microstructures and textures ............................................ 229!
10.4.! Discussion ................................................................................................. 231!
10.5.! Conclusion ................................................................................................. 235!
11.! The Effect of Oxygen on twinning in Ti-10Al .............................................................. 236!
11.1.! Introduction ................................................................................................ 236!
11.2.! Materials and Methods .............................................................................. 238!
11.2.1.! Material preparation .............................................................................. 238!
11.2.2.! Microstructure analysis ......................................................................... 238!
11.2.3.! Mechanical testing ................................................................................ 239!
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11.2.4.! In-situ loading using neutron diffraction ................................................ 239!
11.3.! Results ........................................................................................................ 240!
11.3.1.! Starting Material ................................................................................... 240!
11.3.2.! Flow curves .......................................................................................... 242!
11.3.3.! Diffraction peak evolution ..................................................................... 243!
11.3.4.! Deformation microstructures and textures ............................................ 244!
11.4.! Discussion ................................................................................................. 245!
11.5.! Conclusion ................................................................................................. 247!
12.! Communications ............................................................................................................ 248!
12.1.! The effect of ageing on twinning in Ti6Al4V ........................................... 248!
12.1.1.! Starting material ................................................................................... 248!
12.1.2.! Mechanical behaviour ........................................................................... 252!
12.1.3.! Deformation textures and microstructures ............................................ 253!
12.1.4.! Summary and Conclusion .................................................................... 254!
12.2.! The effect of ageing on twinning in Ti5Al2.5Sn ...................................... 255!
12.3.! The effect of ageing on twinning in the Ti-Sn system ........................... 257!
12.4.! Effect of alloying on ductility ................................................................... 258!
12.4.1.! Introduction ........................................................................................... 258!
12.4.2.! Results of tensile tests .......................................................................... 259!
12.5.! Fe segregation in Ti-Zr system ................................................................ 272!
13.! Summary ........................................................................................................................ 273!
14.! Future work .................................................................................................................... 276!
15.! References ..................................................................................................................... 278!
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Table of tables
Tab. 3-1: Commonly observed slip and twin systems in Ti [Hasija 2003, Chun 2005, Zaefferer
2003, Bozzolo 2010, Padilla 2007, Yang 2011, Yoo 1981, Li 2013], ................................. 37!
Tab. 3-2: Values for Vegards law and further details for the elements [Merck 2011] ................. 55!
Tab. 4-1: Atomic measures of used elements [Merck 2011] ....................................................... 79!
Tab. 4-2: Overview of alloys and heat treatments ...................................................................... 84!
Tab. 4-3: Parameters and thresholds for nanoindentation method “Modulus at a depth” on MTS
Nanoindenter XP ................................................................................................................ 91!
Tab. 4-4: Evaluation of theoretical Schmid factors and trace angles for various slip systems and
the {10!2}<10!1> tension twin for the examples of grain 5 and 6 in Ti-10Al shown in Fig.
4-25. ................................................................................................................................. 107!
Tab. 4-5: ISIS, Wish HRPD: Run numbers and associated sample details .............................. 115!
Tab. 4-6: Neutron scattering properties for important alloying elements of Ti [Dianoux 2002] . 117!
Tab. 4-7: Length and angular values for the major lattice planes in hcp lattice for CP-Ti. ........ 122!
Tab. 5-1: Chemical composition of observed Ti-alloys during this project in ppm unless stated
as wt%. Aged samples marked by superscriped a. .......................................................... 133!
Tab. 5-2: Chemistry of model alloys in atomic percentage indicated by % and impurities in ppm
......................................................................................................................................... 134!
Tab. 6-1: Heat treatments of the model alloys in this study and resulting grain size ................ 150!
Tab. 6-2: Chemical composition of the model alloys in this study and lattice parameters from
neutron diffraction at Engin-X, ISIS .................................................................................. 153!
Tab. 7-1: Chemical composition of the model alloys in this study ............................................ 169!
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