thermo mechanical processing of Ti alloys

1. Thermo-mechanical
processing of Ti alloys
SUBMITTED TO
PROF. B. P. KASHYAP
PROFESSOR-IN-CHARGE
SUBMITTED BY
ADARSH BHARTI
MP19MT002
DEPARTMENT OF METALLURGICAL & MATERIALS ENGINEERING
INDIAN INSTITUTE OF TECHNOLOGY JODHPUR

2. Abstract
Titanium alloys is used in many engineering applications. It is very strong and
high corrosion strength and can perform well at high temperature up to
600°C. Because of its high strength, low weight ratio and corrosion resistance
ratio it is used in many aerospace and marine applications. The specific
properties of titanium is very good so that it is cost effective. In engineering
applications, titanium takes over heavier, serviceable and less cost effective
materials. It has excellent mechanical properties and machinability. Titanium
has very high application in medicine. Also, the biocompatibility of Ti alloys is
very good so it is used in body implants where it has direct contact with bone
and muscles.

3. Introduction
Crystal structure – BCC, FCC
Density(g/cc) - 4.54
Melting point - 1667°C
Atomic diameter - 0.32A°
Properties
• Experiences allotropic transformation at
882.5°C.
• React with oxygen, nitrogen, carbon and
hydrogen.
• Extraction is difficult & costly.
• High strength and toughness.
• Used in advance application.

4. Advantages of Ti alloys
Advantages
• More used in aircraft because of its high-strength to
weight ratio.
• Used in engines (fans and compressor) because of high
temperature resistance.
• High corrosion resistance
• Low specific gravity.
• Non-magnetic property.
• High specific strength.
• Bio-compatible material
• Fatigue property is more than steel.
• Good fabrication ability.

5. Application of titanium alloys
a)Titanium cladded
museum
b)hip-joint component c)Turbine blades
Aerospace
• Civil
• Military
• Space
Medical
• Orthopedic Implants
• Bone screws
• Trauma Plates
• Dental fixtures
• Surgical instruments
Industrial
• Petrochemical
• Offshore
• Subsea
• Metal Finishing
• Pulp & Paper
• General Engineering
Specialist
• Body jewelry
• Ultrasonic welding
• Motor racing
• Marine
• Bicycle
• Sport equipment

7. 882.3°C
Transformation
Alloying elements
• Alpha stabilizers- Al, O, N
• Beta stabilizers-
• Neutral- Zr, Si, Sn
1. Isomorphous – Mo, V, Wb, Nb, Ta
2. Eutectoid – Fe, Cr, Cu, Ni, Co, Mn
Phase diagram of Ti alloys

8. Classification of titanium alloys
Titanium alloys
Commercially pure
titanium alloys
Alpha-beta titanium
alloys
Beta titanium alloys
 Generally non-heat treatable
and weldable
 Medium strength
 Good creep resistance
 Good corrosion resistance
 Heat treatable
 Good forming properties
 Medium to high strength
 Good creep resistance
 Heat treatable
 formable
 Very high strength
 Low ductility

9. Classification with examples
•Commercially Pure – ASTM grades 1,2,3,4
•Ti/Pd Alloys- ASTM grades 7 and 11
Alpha Alloys
•Ti-2.5%Cu- IMI 230Alpha + compound
•Ti-8%Al-1%Mo-1%V
•Ti-6%Al-5%Zr-0.5%Mo-0.2%Si- IMI 685
•Ti-6%Al-2%Sn-4%Zr-2%Mo-0.80%Si
Near alpha Alloys
•Ti-6%Al-4%V
•Ti-4%Al-4%Mo-2%Sn-0.5%Si
•Ti-6%Al-4%Mo-4%Sn-0.5%Si –IMI 551
Alpha-Beta Alloys
•Ti-3%Al-8%V-6%Cr-4%Zr-4%Mo- Beta C
•Ti-15%Mo-3%Al-0.2%Si- Timetal 21 S
Metastable Beta Alloys

10. Classification by strength
•ASTM grades 1,2,3,7 and 11Low strength
•ASTM grades 4,5 and 9
•Ti-2.5%Cu
•Ti-8%Al-19%Mo-0.1%V
Medium strength
•Ti-3%Al-8%V-6%Cr-4%Zr-4%Mo
•Ti-4%Al-4%Mo-2%Sn-0.5%Si
•Ti-6%Al-6%V-2.5%Sn
High strength
•Ti-10%V-2%Fe-3%Al
•Ti-4%Al-4%Mo-4%Sn-0.5%Si
Very high strength

11. Heat treatment
It is applied to α/β and β Ti alloys due to α-β transformation
Heat treatment diagram for β-titanium
alloys
Effect
• Strength of annealed alloys increases with alloys contents
• Quenching from β phase gives a martensitic transformation with
improved strength.
• For lowly alloyed Ti alloys, rapid quenching from the β phase gives
maximum strength.
• For highly alloyed Ti alloys, rapid quenching from β phase gives lowest
strength but after aging gives maximum strength.
• For highly alloyed Ti alloys, rapid quenching from β phase gives lowest
strength but after aging gives maximum strength.

12. Commercially pure titanium alpha/near
alpha alloys
Microstructure contains HCP α phase and can be divided into:-
Commercially pure titanium alloys
Alpha titanium alloys
Near alpha titanium alloys
Characteristics
Non-heat
treatable
weldable
Medium
strength
Good notch
toughness
Good creep
resistance Phase diagram of α-
stabilized Ti alloy

13. Microstructure of CP titanium alloys
HCP alpha phase structure
a) Purity of 99-99.5%
b) HCP structure
c) Main elements are Fe and interstitial
elements like C,O,N and H
d) O content determine the grade and
strength.
e) C,N,H are impurities.

14. Properties and application of CP Ti
Lower strength depending on content of O & N
Corrosion resistance to nitric acid, moist chlorine.
Less expensive
0.2% Pd addition improves corrosion resistance
Applications
airframes
Surgical
implants
chemical marine
Heat
exchanger

15. Alpha Titanium Alloys
1. Al and O are the main alloying elements, which provide solid
solution strengthening. O and N gives interstitial hardening.
2. The amount of α stabilizers should not exceed 9%.
%𝐴𝑙 𝑒𝑞𝑢𝑖𝑣𝑎𝑙𝑒𝑛𝑡 = 𝐴𝑙 + 0.33𝑆𝑛 + 0.167𝑍𝑟 + 10 𝑂 + 𝐶 + 2𝑁 ≤ 9%
3. 5-6% Al can lead to finely dispersed, ordered phase (α2), which is
coherent to lattice.
4. Sn and Zr are also added to stabilize the phase and give strength.

16. Microstructure, properties and
application
•Moderate strength
•Strength depend on O and Al content.
•Al reduces the density.
•Good oxidation resistance
PROPERTIES
•Aircraft engine compressor blades
•Sheet metal parts
•High pressure cryogenic vehicle at -423°C.
APPLICATION
•Ti-5%Al-2.5%Sn alloy in sheet form
•Sn is added to improve ductility.
MICROSTRUCTURE

17. Heat treatment of CP and alpha
titanium alloys
Annealing of CP Ti at high
temperature gives HCP 𝛼-phase
Quenching of CP Ti alloy from β
phase change the HCP structure
to hexagonal martensitic phase
with remaining β phase.
Air cooling of CP Ti from β phase
field produces widmanstatten
plates.

18. Near alpha Titanium Alloys
1. Small amount of β stabilizer(Mo, V) is added
for microstructure of β phase dispersed in α-
structure.
2. Sn and Zr are added to compensate Al
contents while maintaining strength and
ductility.
3. Show greater creep strength than fully α Ti
alloy up to 400°C.
4. Ti-8Al-1Mo-1V and Ti-6Al-2Sn-4Zr-Mo alloys
are the most commonly used for aerospace
applications, i.e., airframe and engine parts.
a) Duplex annealed Ti-8Al-1Mo-1V
b) Forged compressor disc made
from neat alloy IMI 685

19. Heat treatment of near alpha titanium
alloys
Heat treatment of 𝛼 + 𝛽 phase field
• Alloys should contain high amount of 𝛼
stabilizers without severe loss of ductility.
• Small amount of Mo or V are added to
promote the response to heat treatment.
• The alloy is heated up to T to obtain equal
amount of 𝛼 and β phases.
• Air cooling gives equi-axed primary 𝛼 phase
Widmanstätten formed by nucleation and
growth from the β phase.
• Faster cooling transforms β in to martensitic 𝛼
to give higher strength.
Pseudo-binary diagram for Ti-8%Al with
Mo and V addition.
Air cooled from
𝛼 + 𝛽 phase to
primary 𝛼 and
windmanstattan 𝛼.

20. Heat treated from 𝛽 phase field
• Quenching from the β phase field produces laths
of martensitic α’ , which are delineated by thin
films of β phase.
• Aging causes precipitation of fine 𝛼 phase
dispersion.
• Air-cooling from the 𝛽 phase field gives a basket
weave structure of 𝛼 phase delineated by 𝛽 phase.
(a) Near 𝛼-Ti oil quenched
(b) Quenched from 𝛽 phase field and aged at 850°C
Near 𝛼-Ti air cooled from
the 𝛽 phase field.

21. Effect of cooling rate from 𝛽 phase field in lamellar microstructure
Increasing cooling rate

22. Properties And Application
Properties
• Moderately high strength at RT
and relatively good ductility
(~15%).
• High toughness and good creep
strength at high temperatures.
• Good weld-ability.
• Good resistance to salt-water
environment
Application
• Airframe and jet engine
parts requiring high
strength, good creep and
toughness.
• Parts and cases for jet
engine compressors, air-
frame skin components.

23. Alpha beta titanium alloys
• Alpha-beta titanium alloys contains both 𝛼 𝑎𝑛𝑑 𝛽.
• 𝛼 stabilizers are used to give strength with 4-6% 𝛽
stabilizers to allow the β phase to retain at RT after
quenching from β or 𝛼 + 𝛽 phase field.
• Improved strength and formability to 𝛼-Ti alloys.
• Microstructure depends on chemical composition,
processing history and heat treatments i.e. annealing,
quenching and tempering.
• Heat treatment can be done to achieve desired
microstructure and properties.

24. Annealing from 𝛽 and 𝛼 + 𝛽 phase field
Annealing from β phase field causes a
transformation from β to 𝛼 microstructure
containing lamellar structure of similar crystal
orientation
Annealing from 𝛼 + 𝛽 phase field produces
microstructure approaching equilibrium equi-axed
primary 𝛼 phase surrounded with retained 𝛽
phase.

25. Air Cooling from 𝛽 and 𝛼 + 𝛽 phase field
• Air cooling provides intermediate cooling rates.
• Air cooling from the 𝛽 phase field produces fine acicular 𝛼, which is transformed
from the 𝛽 phase by nucleation and growth.
• Air cooling from 𝛼 + 𝛽 𝑝ℎ𝑎𝑠𝑒 𝑓𝑖𝑒𝑙𝑑 provide equi-axed primary 𝛼 𝑝ℎ𝑎𝑠𝑒 in a matrix
of transformed 𝛽 phase.
Air-cooled from β phase field
giving transformed β phase
(acicular)
Air-cooled from 𝛼 + 𝛽 phase field,
showing primary 𝛼 grains in a matrix of
transformed 𝛽(acicular).

26. Heat treatment of alpha-beta titanium
alloy
 Annealing from the β
and α+β phase field.
 Air cooling from the
β and α+β phase
field.
 Quenching from β
and α+β phase fields.
 Tempering of
titanium martensite.
 Decomposition of
metastable β

27. Composition and application of Ti
alloys
Alloy composition
• 6% Al, 4% V
• 6% Al, 4% V(low O2)
• 6% Al, 6%V, 2% Sn
• 8% Mn
• 3% Al, 2.5% V
Condition
• Annealed(solution + age)
• Annealed
• Annealed (solution + age)
• Annealed
• Annealed
Application
• Rocket motor cases, blades and disk, turbines and
compressors, pressure vessels
• High pressure cryogenic vessels
• Rocket motor cases, aircraft parts, landing gears, good
hardenability.
• Aircraft sheet components, structural sections, good
formability and moderate strength.
• Aircraft hydraulic tubing, foil; combines strength, weld-
ability and formability .

28. Quenching from 𝛽 phase field
• Martensite of different crystal structure.
• Increasing solute, 𝛼′ to 𝛼“.
𝛽
𝛼′(martensite)
Lath martensite
colonies
Lenticular or
twinned martensite
𝛼”(𝑚𝑎𝑟𝑡𝑒𝑛𝑠𝑖𝑡𝑒)
𝛼”′(martensite)
𝑚𝑒𝑡𝑎𝑠𝑡𝑎𝑏𝑙𝑒 𝛽
Possible reaction due to
quenching from the 𝛽 phase
field.
Increasing
solute content
Hexagonal 𝛼’ lath, (b) hexagonal
lenticular 𝛼’, (c) orthorhombic 𝛽’’

29. Tempering of Ti martensite
 Decomposition of martensitic structure occurs when a quenched alloy is
subjected to elevated temperature treatment.
 Decomposition reaction depends on martensite crystal structure and alloy
composition.
𝛼′
martensite
𝛽-isomorphous alloys
𝛽 eutectoid alloys
Alloys with slow
eutectoid reaction
𝛼′
→ 𝛼 + 𝛽
→ 𝛼 + 𝑐𝑜𝑚𝑝𝑜𝑢𝑛𝑑
Alloys with fast
eutectoid reaction
𝛼′
→ 𝛼 +
𝑐𝑜𝑚𝑝𝑜𝑢𝑛𝑑

30. Decomposition of metastable 𝛽
 Retained 𝛽 obtained after quenching
decomposes when subjected to aging
at elevated temperature→developing
high tensile strength.
 The metastable 𝛽 is transformed into
equilibrium 𝛼 phase at high aging
temperature due to difficulty in
nucleating HCP 𝛼 phase on BCC 𝛽
matrix.
𝛽 isomorphous alloy phase diagram
Medium alloy content
100-500°C
𝛽 → 𝛽 + 𝜔 → 𝛽 + 𝛼
Concentrated alloys
200-500°C
𝛽 → 𝛽 + 𝛽1 → 𝛽 + 𝛼

31. Double solution treatment

32. Microstructure vs Heat treatment

33. Beta Titanium Alloys
Beta stabilizers are sufficiently added to retain a fully β structure when
quenched from β phase field.
Moeqiv%= 1.0Mo+ 0.67V +0.44W -0.28Nb +0.22Ta +1.6Cr+…-1.0Al
Metastable β alloys : Mo eq. <25
Stable 𝛽 alloys : Mo eq. 25-40

34. 𝛽 titanium alloys
 It posses BCC crystal structure which is cold worked in beta phase field.
 Microstructure after quenching contains equi-axed 𝛽 phase.
 After solution heat treating and quenching, it gives very high strength.
 Metastable 𝛽 titanium alloys are hardenable while stable 𝛽Ti alloys are non-hardenable.
Flow stress of Ti alloys hot workedTi alloy heat treated and water quenched

35. • Most β titanium alloys are metastable and transform
into:-
1. Coarse 𝛼 platets after heat treated in the 𝛼 + 𝛽 phase
field
2. 𝛼 phase precipitation after long term aging at elevated
temperature.
High strength causes
embrittlement that is not required

36. Advantages
• High strength to density ratio
• Low modulus
• High strength/toughness
• High fatigue strength
• Good deep hardenability
• Low forging temperature
• Easy to heat treat
• Excellent corrosion resistance
• Excellent combustion resistance
Disadvantages
• High density
• Low modulus
• Poor low and high temperature properties
• Small processing window
• High formulation cost
• Segregation problems
• High spring-back
• Poor corrosion resistance
• Interstitial pick-up
• Microstructural instabilities

37. TMP of β titanium
𝛽 annealing
𝛽 −annealed microstructure Ti-6246
TMP for β annealing
Step 1
• Homogenization
treatment above
β transus
temperature.
• Depending on
the cooling rate
from
homogenization
temperature the
grain boundary 𝛼
layer form
Step 2
• Aging at high
temperature
• High
temperature
aging will
produce coarse
alpha precipitate
throughout the
matrix.
Step 3
• Aging at low
temperature
• Low temperature
aging will
produce dine
alpha precipitate
in the matrix.

38. Processing bi-modal microstructure
Bi-modal processing route
Bimodal microstructure
𝛼 + 𝛽 microstructure
• The processing consists of homogenization in
the β phase field, deformation in the 𝛼 + 𝛽
phase field.
• After cooling from homogenization
temperature and heating to deformation
temperature, large equiaxed β grains with grain
boundary 𝛼 and 𝛼-plates within the grain.
• The next step is deformation in the 𝛼 + 𝛽 phase
field, the structure is deformed to higher
degree.
• Then it is deformed so that complete
recrystallization of the phase occurs.
• Aging is done to precipitate the particles of
different sizes according to temperature
decrease.

39. 𝛽 processing
Ingot breakdown
Hot working is
done in β phase
field
After finishing the
deformation, fast
cooling is applied
so that no
recrystallization
happens
𝛽 processed microstructure (a)LM (b)TEM

40. Through transus processing
Necklace microstructure
• Time temperature control of the deformation
process is presented. When temperature
drops under 𝛽 transus, 𝛼 phase start to
precipitate at 𝛽 grain boundaries.
• Due to high dislocation density the 𝛼 phase
precipitate in the form of round particles at 𝛽
grain boundaries. That is why it called
necklace.
• Deformation is two step. High temperature
aging leads to precipitation of 𝛼 − plates
within 𝛽 grains. The dislocation density is so
high that plates are small.
• Low temperature aging leads to precipitation
of small secondary 𝛼 platelates to harden the
alloy

41. Fatigue Properties
S-N curve β-Cez
S-N curve Ti -6246
• The high cycle fatigue properties of different
microstructure is compared by anisotropy
characteristics of β- grains.
• The crack plane and β grain boundary for ST
orientation and 45° orientation.
• The S-N curve of β processed condition of β-
Cez and Ti-6246.
• The 45° orientation exhibit the lowest HCF
strength for both alloys.
• For 𝛽-cez, the ST direction shows highest HCF
strength and vice versa of Ti-6246.
• Also the bi-modal microstructure shows
highest HCF strength. Fatigue cracks in the
microstructure nucleates at coarse 𝛼-plates in
the matrix. The small dimension of plates lead
to small maximum slip length and high HCF
strength.

42. Deformation of titanium alloys
HCP 𝛼 Ti alloys
Deformation is limited on available slip
planes and relies on twinning.
BCC β Ti alloys
Deformation relies on more slip system with
limited twinning deformation.

43. Forging of Ti alloys
 Ti alloys have much higher flow stress than Al alloys or
steels requiring high forging pressure, capacity.
 Near net shape is obtained using precision die forging.
 Initial working is done about 150°C above the beta
transient temperature to about 28-38% strain, depending
on alloy types and prior heat treatments. Subsequent
deformation processes can be done in the α+β region

44. Rolling of Ti alloys
 Packed to avoid surface oxidation.
 group of titanium sheet blanks are sealed with
steel retort and rolled as a group.
 Parting agent is filled between individual blanks
to prevent sheet bonding.
 After hot rolling, the sheets are extracted,
pickled and flattened for finishing process
Hot-rolled Ti clad steel plates used
in condenser in power station
Titanium ring rolling

45. Machining of Ti alloys
 These alloys are more difficult to machine
compared to steel and conventional alloys for
milling, drilling, turning, etc.
 Titanium’s low thermal conductivity reduces
heat dissipation at metal-workpiece interface
decreased tool life, welding or galling at tool-
workpiece interface.
 Machining tools are critical carbide or ceramic
toolings.
 Avoid loss of surface integrity due to tool
damage dramatically reduce properties
especially fatigue.

46. Powder metallurgy of Ti alloys
 Titanium PM parts are made from
pressing and sintering, giving near-net
shape products.
 Production of titanium powder is quite
difficult due to high reactivity of
titanium with oxygen.
 The whole process (atomisation,
pressing and sintering) requires
prevention from atmospheric
contamination.
a)Ti-6Al-4V alloy
produced from CIPing
and sintering of blended
CP sponge and ALV
master alloy
b)Same material after
HIPing, showing no
porosity

47. Properties of Ti alloys
Alloying
(chemistry)
• density
• Precipitation hardening
• Solid solution hardening
• Ordered structure
• Stiffness
• Thermal expansion
• Corrosion behavior
• Oxidation behavior
Processing
(microstructure)
• Hardening
• Thermo-mechanical
treatment
• Stress corrosion cracking
• SPF(grain size)
• Rapid solidification
• Mechanical alloying
• HIP(PM, casting)
• consolidation
Composites
(MMC)
• density
• Stiffness
• Strength
• Wear
• Fatigue
• Thermal expansion
• Oxidation resistance
• Corrosion protection
Specific proof stress of
various materials

48. Strength and toughness of Ti alloys
Tensile strength of different Ti alloys
at a range of temperatures

49. Microstructural and tensile properties
of Ti alloys
• Bimodal microstructure is more
resistant to fracture due to equaixed α
phase giving higher strength.
• Equiaxed α phase is also more resistant
to nucleation of voids higher ductility.

50. Microstructure and fracture toughness
properties of Ti alloy
Coarse lamellar and fine lamellar
• More torturous path in coarse lamellar microstructure leads to
higher energy dissipation during fracture higher toughness.

51. Fatigue properties of Ti alloys
 Smaller equiaxed α grains are
more beneficial to fatigue
strength.
 Crack nucleates within the
lamellar region more easily
than in the equiaxed α phase
region.
 But crack propagation is more
difficult in the lamellar
structure
Crack initiation at lamellar region in bi-modal
microstructure
Crack propagation paths in (a) lamellar and (b)
bi-modal structures

52. GUM TITANIUM
• It is a beta titanium based alloys having
excellent mechanical behavior at room
temperature.
• It exhibit high yield stress(1Gpa) and very
good elongation before failure (upto 35%)
• The governing mechanism is still unclear.
• Observation revealed that there is existence of
micro-meter size 2-D band like feature that
shows local shear.

53. Titanium alloy for biomedical
applications
• Hip and knee prostheses
• Good corrosion stability in human body
• High fatigue resistance
• High strength to weight ratio
• Good ductility
• Low elastic modulus
• Excellent wear resistance
• Low cyto-toxicity
• Less tendency for allergic reactions

54. Deformation behavior of alpha and
near alpha Ti alloys
Flow stress of CP Ti at various
temperature.
Flow stress of Ti-5Al-2.5Sn at
800°C and various strain rate.
Flow stress of IMI 834 at 1000°C at
various strain rate

55. Observation from deformation curve
• Stress-strain curve show initial work
hardening.
• Higher peak stress are observed at higher
strain and low temperatures.
• Flow stress increases with increase in strain at
given temperature.
• Increase in flow stress with increase in
substitutional solute strengthening.
• Below beta transus temperature, material is
undergoing dynamic recovery in which rate
of hardening is balanced by rate of softening
by dislocation anhilation.

56. Stress temperature map of Ti

57. TMP of 𝛽-Ti
TMP process
Step1- Heating at 10Ks-1 at 1223K and hold
on for 12
Step2- Step1+ cooling at 35Ks-1 from 1223K
to 1173K where 25% deformation occurs.
Step3- Step2 + Cooling at 35Ks-1 from 1173K
to 1023K, 1800s soaking
Step4- Step3 + 40% Deformation at 1023K

58. Grain boundary variation width
Variation of width of the grain
boundary α-phase with TMP

59. Distribution of alloying elements
between the phases after TMP
Elemental map of Ti-55511 after TMP
(a)Ti (b)Al (c)Mo (d)V (e)Cr (f)Fe
Elemental map of Ti-55521 after TMP
(a)Ti (b)Al (c)Mo (d)V (e)Cr (f)Fe

60. TMP for tri-modal properties (strength,
ductility and rupture) of Ti
Step 1
• Homogenization
and primary hot
rolling
Step 2
• Secondary hot
rolling
Step 3
• Solution
annealing
Step 4
• aging

61. Microstructure after TMP
Optical micrographs of Ti-6242S alloy with (a) widmanstätten, (b)
bimodal and (c) trimodal microstructures

62. Effect of microstructure on strength
Parameter for mechanical properties
• Volume fraction of alpha and beta transformed
phase
• Colony size
• Alloying element partitioning effect
Volume fraction of alpha and beta transformed phase
• Volume fraction of alpha phase has limited slip
system compared to that of beta phase
• The ratio of alpha to beta is used to determine
strength of alloy.

63. Colony size
• Several colonies with alpha/beta layers.
• Alpha/beta interfaces are not effective barrier
to slip and slip expand rapidly.
• Every colony has distinct orientation that act
barrier for slip. These colony size is important
for mechanical properties.
• Beta grain size is important factor since beta
grain size acts as barrier to slip and limits the
colony size.beta grain size in the
widmanstätten microstructure was about
• 600 μm, while the similar value for bimodal
microstructure is about 16 μm. There is a
significant difference in beta grain size in
widmanstätten and bimodal microstructure.
Based on hall-petch relation, reduction in
grain size improves the yield and ultimate
strength
Alloying element partitioning effect
• Cooling from solution annealing temperature
and formation of alpha phase, alloying
element partitioning take place.
• By an increase in alloying element
partitioning, the transformed beta regions will
be poor in
• alpha stabilizer elements
• The element which are strong alpha
stabilizers will partition into two phases.
• precipitation of these particles is related to
the concentration of alpha stabilizer elements.
This led to decrease in strength.
• A significant part of alpha stabilizer elements
in the trimodal microstructure is consumed to
stabilize the globular and lamellar alpha
phases. Hence, concentration of these
elements in the transformed beta regions of
trimodal microstructure is certainly lower than
the bimodal microstructure

64. Mechanism of globularization of
widmanstatten 𝛼 in 𝛼/𝛽 Ti alloys
 The globularization of both the lamellar plates
within the prior-beta grains as well as grain-
boundary alpha.
 Initially, recrystallized alpha grains are formed
within the alpha plate.
 Surface tension requirements do not permit a 180 ~
dihedral angle to exist between the alpha/alpha
boundary and the beta plate boundary.
 Driving force is provided for the movement of some
beta phase into the alpha/beta boundaries and a
simultaneous to rotation of the alpha/beta
boundaries toward one another.
 Rotation enlarges the recrystallized alpha grain to a
size larger than the original plate thickness, bringing
it into contact with the adjacent alpha plate, which
may or may not have recrystallize

65. Effect of deformation on volume
fraction of 𝛼-phase
• The volume fraction of globular 𝛼-phase increases
from zero in un-deformed sample to about 10% in
deformed sample at strain of 1.
• Under deformation condition, the kinetics of 𝛽 𝑡𝑜 𝛼
phase transformation increases due to
deformation strain induced transformation.
• The fraction of globular 𝛼-phase, which result from
deformation is high enough to provide 𝛼 + 𝛽 grain
microstructure.
• Under TMP condition, the high critical strain
initiate transformation to very large 𝛽 grain size.
• By increasing the strain beyond critical point, the
serration of 𝛽 grain boundary increase, increases
the nucleation opportunities around 𝛼 phase.

66. Effect of slow cooling on volume fraction and morphology
of deformed and un-deformed sample

67. Microstructure development during slow cooling of
deformed and un-deformed sample
Initial microstructure before deformation consists of large and equi-axed grains of β-phase.
Deformation causes elongation of β grains and serration of their boundaries.
Transformation initiates by nucleation of 𝛼 grains and plates along the serrated boundaries of β grains
The volume fraction of acicular and globular 𝛼 increases in the course of deformation.
On the deformation completion there is some 𝛼 grains with β grains.

68. Application of titanium alloys
Aero-engine
Automotive and road
transport
Dental alloys
Nuclear and
environmental safety
Geothermal plant condensers Heat exchangers
Offshore production
tubulars
Pulp and paper
Metal extraction
equipment
Jewelry manufacture
Cryogenic logging
tool
Medical implants Military hardware
Electrochemical
anode

69. Summary
1. Titanium is the most rarest element and fourth most abundant structural
metal.
2. The type and quantity of alloying element make the alloy specific.
3. Because of its physical and mechanical properties titanium has high
melting temperature and lightweight compared to steel.
4. Some Ti alloys used in cryogenic applications because they do not have
ductile to brittle transition.
5. Titanium alloys have high fatigue strength.

70. Doubt
 Grain boundary width variation
 How deformation introduces phase transformation?
 Did not understood Grain boundary width variation with TMP concept.