Sha W., Malinov S. Titanium Alloys: Modelling of Microstructure, Properties and Applications
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Author contact details
Professor Wei Sha
School of Planning, Architecture and Civil Engineering
The Queen’s University of Belfast
David Keir Building
Stranmillis Road
Belfast
BT9 5AG
Northern Ireland
UK
Email: w.sha@qub.ac.uk
Dr Savko Malinov
School of Mechanical and Aerospace Engineering
The Queen’s University of Belfast
Ashby Building
Stranmillis Road
Belfast
BT9 5AH
Northern Ireland
UK
Email: s.malinov@qub.ac.uk
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This book is a research monograph, cumulating the experience and results of
over ten years’ research by the authors. It covers both conventional titanium
alloys and titanium aluminides.
Since 1999, the authors have been funded by the UK Engineering and
Physical Sciences Research Council (EPSRC), for carrying out the following
projects:
(i) Modelling of the evolution of microstructure during processing of
titanium alloys.
(ii) Computer-based modelling of the evolution of microstructure during
processing of gamma Ti–Al alloys.
(iii) Collaborative research in modelling the evolution of material
microstructures.
(iv) Atomistic simulation of γ/α
2
interfaces and dislocations relevant to
lamellar titanium aluminides.
Funding has also been provided by the Queen’s University of Belfast, the
Royal Society, Royal Academy of Engineering, and Invest Northern Ireland
for many smaller projects, most of them jointly with international collaborators.
These projects have led to about 100 publications, reflecting research effort
in modelling of many correlations in the path of processing parameters to
microstructure to properties in titanium alloys. The authors have developed
a number of models and computer program packages that are based on
experimental results, physical metallurgy theories and different computational
approaches.
Computer-based modelling is a fast growing field in materials science, as
demonstrated by the large recent literature. The authors have combined expertise
in titanium and model development. Therefore, this book fills a gap of the
book literature in the application of modelling techniques in titanium research,
both hot topics in contemporary materials research, whilst at the same time
documenting the latest research in this area. A large chunk of this latest
research is from the authors themselves, based on their leading position in
this research area, but the book also covers important relevant research by
Preface
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Prefacexiv
others. Much of the microstructural modelling is about phase transformations
and kinetics.
The book has a clearly defined audience. It is primarily intended for
researchers involved with either titanium or modelling, or both. The titanium
expert will be able to learn modelling and apply the increasingly important
modelling techniques in their titanium materials research and development.
The modelling expert will be able to apply their modelling expertise to the
remarkable material that is titanium. Combining modelling and titanium into
one publication is the idea behind this book which is its strength.
Chapters on modelling will be about using these techniques on titanium
only. Computer modellers have lots of options on entire books that are
devoted to each of the modelling chapters in the book, but not applied to
titanium. The research papers listed at the end of the preface are used in this
book, but the underlying structure of the book is based on the techniques of
the modelling. It is intended that each chapter can be read largely independently.
Funding from the following is acknowledged:
• EPSRC, for research grants, and for the provision of Synchrotron Radiation
Source (SRS) beam time.
• The UK Royal Academy of Engineering, Global Research Award Scheme.
• The UK Royal Society, short-term study visit to the UK award scheme.
The following individuals are also acknowledged:
• All co-authors in the papers list at the end of this preface.
• Dr Veneta Yanakieva for her work on IMI 367 alloy.
• Mr Trevor Rathbone of the X-ray diffraction group at UK Daresbury
Laboratory for his technical support in setting up the furnace.
• Dr Yu. N. Akshentsev for his help in growing the Ti
3
Al single crystals,
Dr V. P. Pilyugin and Mrs O. A. Elkina for their help in preparing the
samples and Dr J. M. Gregg for his help in the transmission electron
microscopy study.
Wei Sha, Professor of Materials Science,
Savko Malinov, Lecturer in Mechanical and Aerospace Engineering,
The Queen’s University of Belfast, Northern Ireland
Research papers used in the preparation of this book
1 X-ray diffraction, optical microscopy, and microhardness studies of gas nitrided
titanium alloys and titanium aluminide. W. Sha, M.A. Haji Mat Don, A. Mohamed,
X. Wu, B. Siliang, A. Zhecheva, Materials Characterization, 59, 2008, 229–40.
2 Modeling the effects of heat treatment on Ti alloys. N. Lynn, S. Malinov, C. Armstrong,
S. Parks, Heat Treating Progress, 7(3), 2007, 32–34.
3 Titanium alloys after surface gas nitriding. A. Zhecheva, S. Malinov and W. Sha,
Surface and Coatings Technology, 201, 2006, 2467–74.
Preface xv
4 Fabrication of Ti–Al coatings by mechanical alloying method. S. Romankov, W.
Sha, S.D. Kaloshkin and K. Kaevitser, Surface and Coatings Technology, 201,
2006, 3235–45.
5 Modelling of kinetics of nitriding titanium alloys. A. Zhecheva, S. Malinov, I.
Katzarov, W. Sha, Surface Engineering, 22, 2006, 452–4.
6 Numerical simulation of the kinetics of gas nitriding of titanium alloys. A. Zhecheva,
S. Malinov, I. Katzarov and W. Sha, Proceedings of Advances in Materials and
Processing Technologies (AMPT), 30 July – 3 August 2006, Las Vegas, Nevada.
7 Transmission electron microscopy of microstructural evolution in a TiAl alloy. T.
Novoselova, S. Malinov, W. Sha, T.S. Rong, Microscopy and Analysis, 20(5), 2006,
15–7 (UK).
8 A phase-field model for computer simulation of lamellar structure formation in γ-
TiAl. I. Katzarov, S. Malinov and W. Sha, Acta Materialia, 54, 2006, 453–63.
9 Crack geometry for basal slip of Ti
3
Al. L. Yakovenkova, S. Malinov, L. Karkina
and T. Novoselova, Scripta Materialia, 52, 2005, 1033–8.
10 Corrosion behavior and surface characterization of Ti-6Al-2Sn-4Zr-2Mo and Ti-
8Al-1Mo-1V alloys after gas nitriding. A. Zhecheva, S. Malinov and W. Sha,
Proceedings of the 16th International Corrosion Congress, Beijing, China, 19–24
September 2005, paper P-03-Ti-01.
11 Microstructure and microhardness of gas nitrided surface layers in Ti-8Al-1Mo-1V
and Ti-10V-2Fe-3Al alloys. A. Zhecheva, S. Malinov and W. Sha, Surface Engineering,
21, 2005, 269–78.
12 Simulation of microhardness profiles of titanium alloys after surface nitriding using
artificial neural network. A. Zhecheva, S. Malinov, W. Sha, Surface and Coatings
Technology, 200, 2005, 2332–42.
13 Modelling, simulations and monitoring of lamella structure formation in titanium
alloys controlled by diffusion redistribution. S. Malinov, I. Katzarov and W. Sha,
Defect and Diffusion Forum, 237–40, 2005, 635–46.
14 Modelling beta transus temperature of titanium alloys using artificial neural network.
Z. Guo, S. Malinov, W. Sha, Computational Materials Science, 32, 2005, 1–12.
15 Fracture behavior of Ti
3
Al single crystals for the basal slip orientation. L. Yakovenkova,
S. Malinov, T. Novoselova, L. Karkina, Intermetallics, 12, 2004, 599–605.
16 Modelling tensile properties of gamma-based titanium aluminides using artificial
neural network. J. McBride, S. Malinov and W. Sha, Materials Science and
Engineering A, 384, 2004, 129–37.
17 Surface morphology, microstructure and phase modifications after gas nitriding of
a Ti-6Al-2Sn-4Zr-2Mo alloy. A. Zhecheva, S. Malinov, W. Sha and R. Turner,
Proceedings of the International Symposium on Light Metals and Metal Matrix
Composites, 43rd Annual Conference of Metallurgists, August 22–25, 2004, Hamilton,
Canada, eds. D. Gallienne and R. Ghomashchi, The Canadian Institute of Mining,
Metallurgy and Petroleum, Montreal, pp. 269–81.
18 Application of artificial neural networks for modelling correlations in titanium
alloys. S. Malinov and W. Sha, Materials Science and Engineering A, 365, 2004,
202–11.
19 High-temperature synchrotron X-ray diffraction study of phases in a gamma TiAl
alloy. T. Novoselova, S. Malinov, W. Sha, A. Zhecheva, Materials Science and
Engineering A, 371, 2004, 103–12.
20 Experimental and modelling studies of the thermodynamics and kinetics of phase
and structural transformations in a gamma TiAl-based alloy. S. Malinov, T. Novoselova,
W. Sha, Materials Science and Engineering A, 386, 2004, 344–53.
Prefacexvi
21 Experimental study and computer modeling of the isothermal beta to alpha
transformation kinetics in titanium alloys. P.E. Markovsky, S. Malinov and W. Sha,
Ti-2003, Science and Technology, Proceedings of the 10th World Conference on
Titanium, 13–18 July 2003, Hamburg, eds. G. Luetjering and J. Albrecht, Wiley-
VCH Verlag GmbH, Weinheim, Vol. 2, 2004, pp. 1131–8.
22 Atomistic simulations of γ/α
2
interfaces and dislocations relevant to lamellar titanium
aluminides. M. Finnis and W. Sha, Research Proposal – UK Engineering and Physical
Sciences Research Council (EPSRC) Grant Ref. EP/C015649/1, 2004.
23 Software products for modelling and simulation in materials science. S. Malinov
and W. Sha, Computational Materials Science, 28, 2003, 179–98.
24 Relationships between processing parameters, microstructure and properties after
gas nitriding of commercial titanium alloys. S. Malinov, A. Zhecheva and W. Sha,
Proceedings of the 9th International Seminar of the International Federation for
Heat Treatment and Surface Engineering (IFHTSE): Nitriding Technology – Theory
and Practice, 23–25 September 2003, Warsaw, Institute of Precision Mechanics,
311–22.
25 Experimental study of the effects of heat treatment on microstructure and grain size
of a gamma TiAl alloy. T. Novoselova, S. Malinov and W. Sha, Intermetallics, 11,
2003, 491–9.
26 Modelling the nitriding in titanium alloys. S. Malinov, A. Zhecheva and W. Sha,
Surface Engineering Coatings and Heat Treatments (Proceedings from the 1st
International Surface Engineering Congress and the 13th IFHTSE Congress, 7–10
October 2002, Columbus, Ohio), Eds: O. Popoola, N.B. Dahotre, J.O. Iroh, D.H.
Herring, S. Midea, and H. Kopech, ASM International, Materials Park, OH, 2003,
pp. 344–52.
27 Surface gas nitriding of Ti-6Al-4V and Ti-6Al-2Sn-4Zr-2Mo-0.08Si alloys. A.
Zhecheva, S. Malinov and W. Sha, Zeitschrift für Metallkunde, 94, 2003, 19–24.
28 Experimental study and computer modelling of β⇒α + β phase transformation in
β21s alloy at isothermal conditions. S. Malinov, W. Sha and P. Markovsky, Journal
of Alloys and Compounds, 348, 2003, 110–8.
29 Thermodynamic calculation for precipitation hardening steels and titanium aluminides.
Z. Guo and W. Sha, Intermetallics, 10, 2002, 945–50.
30 In situ high temperature microscopy study of the surface oxidation and phase
transformations in titanium alloys. S. Malinov, W. Sha and C.S. Voon, Journal of
Microscopy, 207, 2002, 163–8.
31 Microstructure evolution and phase transformation during heat treatment of a gamma
TiAl alloy. T. Novoselova, S. Malinov and W. Sha, Proceedings of Third European
Conference on Advanced Materials and Technologies (Euro-TECHMAT 3), Bucharest,
8–12 September 2002, Proceedings on CD ROM, Stefania Stoleriu, Bucharest.
32 Synchrotron X-ray diffraction study of the phase transformations in titanium alloys.
S. Malinov, W. Sha, Z. Guo, C.C. Tang and A.E. Long, Materials Characterization,
48, 2002, 279–95.
33 Finite element modeling of the morphology of β to α phase transformation in Ti-
6Al-4V alloy. I. Katzarov, S. Malinov and W. Sha, Metallurgical and Materials
Transactions A, 33A, 2002, 1027–40.
34 Experimental study of the effects of hydrogen penetration on gamma titanium
aluminide and beta 21S titanium alloys. W. Sha and C.J. McKinven, Journal of
Alloys and Compounds, 335, 2002, L16–20.
Preface xvii
35 Resistivity study and computer modelling of the isothermal transformation kinetics
of Ti-8Al-1Mo-1V alloy. S. Malinov, P. Markovsky and W. Sha, Journal of Alloys
and Compounds, 333, 2002, 122–32.
36 Predictive modelling of microstructural evolution and plastic flow of polycrystalline
materials during thermomechanical processing. Z.X. Guo, W. Sha and A.E. Long,
Final Report – UK Engineering and Physical Sciences Research Council (EPSRC)
Grant Ref. GR/M22574/01, 2002.
37 Computer modelling of the kinetics of phase transformation in Ti-46Al-2Mn-2Nb
titanium alloy. S. Malinov and W. Sha, Annual Scientific Session, 11–13 October
2001, The Technical University of Varna, Bulgaria, Proceedings, pp. 29–34.
38 Simulation of fatigue stress life (S-N) diagrams for Ti-6Al-4V alloy by application
of artificial neural network. S. McShane, S. Malinov, J.J. McKeown and W. Sha,
Computational Modeling of Materials, Minerals, and Metals Processing, Proceedings
of TMS Fall Extraction and Process Metallurgy Meeting: Conference on
Computational Modeling of Materials, Minerals and Metals Processing, San Diego,
CA, 23–26 September 2001, ed: M. Cross, J.W. Evans and C. Bailey, The Minerals,
Metals & Materials Society (TMS), Warrendale, PA, pp. 653–62.
39 Modelling the correlation between processing parameters and properties in titanium
alloys using artificial neural network. S. Malinov, W. Sha and J.J. McKeown,
Computational Materials Science, 21, 2001, 375–94.
40 Microstructural characterisation and modelling of a Ti-6Al-4V alloy during
thermomechanical processing in the β phase field. R. Ding, Z.X. Guo, W. Sha and
A. Wilson, Titanium Alloys at Elevated Temperature: Structural Development and
Service Behaviour, International Conference, University of Birmingham, Birmingham,
England, 11–12 September 2000, Microstructure of High Temperature Materials,
Number 4, ed: M.R. Winstone, IoM Communications, London, 2001, pp. 29–39.
41 Differential scanning calorimetry study and computer modelling of β ⇒ α phase
transformation in Ti-6Al-2Sn-4Zr-2Mo alloy. S. Malinov, Z. Guo, W. Sha, Z.X.
Guo and A.F. Wilson, Titanium Alloys at Elevated Temperature: Structural
Development and Service Behaviour, International Conference, University of
Birmingham, Birmingham, England, 11–12 September 2000, Microstructure of High
Temperature Materials, Number 4, ed: M.R. Winstone, IoM Communications, London,
2001, pp. 69–88.
42 Differential scanning calorimetry study and computer modeling of β ⇒ α phase
transformation in a Ti-6Al-4V alloy. S. Malinov, Z. Guo, W. Sha and A. Wilson,
Metallurgical and Materials Transactions A, 32A, 2001, 879–87.
43 Resistivity study and computer modelling of the isothermal transformation kinetics
of Ti-6Al-4V and Ti-6Al-2Sn-4Zr-2Mo-0.08Si alloys. S. Malinov, P. Markovsky,
W. Sha and Z. Guo, Journal of Alloys and Compounds, 314, 2001, 181–92.
44 Application of artificial neural network for prediction of time-temperature-
transformation diagrams in titanium alloys. S. Malinov, W. Sha and Z. Guo, Materials
Science and Engineering A, 283, 2000, 1–10.
1
1
Introduction to titanium alloys
Abstract: This is a concise introduction to titanium alloys and focuses on
the most relevant aspects for the book, namely the effect of the
thermomechanical processing of titanium alloys and aluminides. The chapter
includes a section on the most common alloys, as the large number of alloys
found in the literature can be very confusing. It includes, for example, Ti-
6Al-2Sn-4Zr-6Mo (Ti-6246), which is becoming increasingly important for
the aero engine industry.
Key words: titanium alloys, titanium aluminides, thermomechanical
processing, properties, applications.
1.1 Introduction
In recent decades, a generic class of titanium-based materials has been
developed for a range of applications. Titanium and titanium alloys are
currently finding increasingly widespread use in many industries for the
production of a variety of components and workpieces due to their desirable
and versatile combination of good mechanical and chemical properties.
Stimulus for the development of titanium alloys during the past sixty years
came initially from the aerospace industry when there was a critical need for
new materials with higher strength to weight ratios. The advantages of titanium
alloys include: (i) low densities, which fall between those of aluminium and
iron and give very attractive strength to weight ratios allowing lighter and
stronger structures; (ii) superior corrosion and erosion resistance in many
environments, in particular to pitting and corrosion cracking; (iii) high
temperature capability in the range of 300–600 °C. They also have high
toughness making them useful materials for precision mechanism gears,
turbine engine components, and biomedical prosthesis devices. However,
titanium alloys possess some disadvantages. One of the most significant
disadvantages is their cost.
Today, titanium alloys have many applications, from structural components
in the aerospace and automobile industries to corrosion resistance materials
in the chemical and marine sectors and medical device manufacturing (Guleryuz
and Cimenoglu, 2005; Škorić et al., 2004). It is believed that the expansion
of titanium alloys usage will continue for the forthcoming years. Although
the titanium materials are still considered as expensive materials, for many
applications the cost of titanium alloys can be justified from a material
selection viewpoint on the basis of their desirable properties.
The mechanical properties of titanium alloys, such as strength, ductility,
creep resistance, fracture toughness and crack propagation resistance, depend
Titanium alloys: modelling of microstructure2
essentially on the microstructure, which is formed during the thermomechanical
processing and thermal treatment procedures. It is therefore very important
to understand the nature of the phase transformations taking place at different
heat treatment conditions.
1.2 Conventional titanium alloys
1.2.1 Microstructure and properties
The physical metallurgy of titanium is both complex and interesting. The
metal is stable only at certain temperature ranges. At a temperature of 882 °C,
known as the β-transus temperature, pure titanium undergoes a phase
transformation from a low temperature stable, modified hexagonal close
packed structure (hcp) (α) to a body centred cubic phase (bcc) (β) that
remains stable up to the melting point of 1678 °C. The main characteristics
for a crystal structure are the plastic deformation capability and diffusion.
The diffusion rate depends on the lattice microstructure (Leyens and Peters,
2003). Titanium and its alloys react with several interstitial elements including
the gases oxygen, nitrogen and hydrogen. Such reactions may occur at
temperatures well below the melting points.
The type of phases present, grain size and grain shape, morphology and
distribution of the fine microstructure (for example, α + β colonies) determine
the properties and therefore the application of titanium alloys. The technical
titanium-rich alloys can be classified into these categories: α, near-α, α + β,
near-β, metastable β and stable β, depending on their composition, the ratio
of the amounts of the α and β phases, and the position in the pseudo binary
β-isomorphous phase diagram. The subclasses near-α and near-β refer to
alloys with compositions which place them near to α/(α + β) or (α + β)/β
phase boundaries, respectively.
α and near-α titanium alloys have mainly α structure and depending on
the processing conditions may have different microstructural grain
morphologies, ranging from equiaxed to acicular (martensitic). These
classes of titanium alloys are preferred for high temperature applications.
β titanium alloys contain a balance of β stabilisers to α stabilisers which is
sufficient to ensure that a fully β phase microstructure can be retained on
fast cooling (slow cooling, in furnace, for instance, causes β-phase
decomposition). In this condition, the metastable β alloys are generally
thermodynamically unstable. This can be used as an advantage (for cold
deformation before ageing, for example) by allowing some decomposition
reactions (α precipitation) during an ageing treatment in order to provide
secondary strengthening. As a result, the metastable β titanium alloys generally
have higher strength, higher toughness and improved formability at room
temperature as compared to the α and α + β titanium alloys, although the