Post on 05-Oct-2018
Phase transformation kinetics in a near-β titanium alloy
Pere Barriobero Vila
pere.vila@tuwien.ac.at
Trnava, 15.11.2012
1- Goal 2- Experimental 2.1. Material
2.2. Techniques: - In Situ High Energy Synchrotron X-ray Diffraction (XRD) - Differential Scanning Calorimetry (DSC)
3- Results 3.1. Bimodal microstructure
3.2. Lamellar microstructure 3.3. Beta quenched microstructure
4- Summary
Content
2/15
1- Goal
To study the phase transformation kinetics during continuous heating of a near-β titanium alloy with
different initial microstructures
Methods Differential Scanning Calorimetry (DSC) Identification of precipitation and dissolution processes In situ High Energy Synchrotron X-ray diffraction (XRD) Identification AND quantification of microstructural phases
3/15
β transus
Temperature
Mo eq. (wt.%)
β Stabilizers Characteristics Aplications
808ºC 10,81%
• Excellent
Forgeability
• High strength
• High toughness
(air, salt water)
Aerospace industry
(variety of components)
2- Experimental
Ti-10V-2Fe-3Al
Near-β alloy
Leyens, 2003
2.1. Material
Handbook of Titanium Alloys, 2007
R.R. Boyer, JOM 2010
Boeing 777
Lütjering, 2007
β transus
α phase
β phase T (°C)
4/15
2- Experimental 2.1. Material: Initial microstructures
50µm 40µm
Large α Lamellae
Lamellar
5 k/min
T (°C)
t (min)
TβTRANSUS
Ar Atmosphere
10µm
Small α Lamellae
Bimodal
3µm
T (°C)
t (h)
TβTRANSUS 763°C / 2 h
510°C / 8 h
Ar Atmosphere
Secondary α-lamellae
Primary α
50µm
Metastable β grains
Beta quenched
α‘‘ martensite
Water
quenching
T (°C)
t (min)
TβTRANSUS
Ar Atmosphere
ωath
β
5/15
2- Experimental 2.2. Techniques: In Situ High Energy X-ray Diffraction
E. Aeby-Gautier, JOM 2007
20 k/min
T (°C)
t (min)
TβTRANSUS
Ar Atmosphere
900ºC ID15-ESRF
E= 87keV ʎ= 0.1426Å
Slit size = 0.3x0.3 mm²
Acquisition time = 2s
Readout time = 1s
Sample size = 4x4x10 mm³
MAUD
Quantitative
phase analysis
(Rietveld)
Image
processing
2D analysis
(calibration/integration/
image analysis)
Data processing
6/15
Reference Sample
Alumina
Crucible
Alumina
Ti1023
Sample
Ø=5mm
L=1,6mm
2- Experimental 2.2. Techniques: DSC
20 k/min
T (°C)
t (min)
TβTRANSUS
Ar Atmosphere
900ºC
7/15
3- Results
Bimodal
f (T)
2-Theta (°)
T (°C)
α (100)
α (002)
β (110)
α (101)
α (100)
α (002)
β (110)
α (101)
α+β→ β
Lamellar
f (T)
T (°C)
2-Theta (°)
Beta quenched
f (T)
T (°C)
2-Theta (°) α‘‘ (110)
α (100)
α (002)
α (101)
α‘‘ (020)
β (110)
α‘‘ (002)
α‘‘ (111)
TβTRANSUS α+β→ β
8/15
3- Results 3.1. Bimodal microstructure
Two dissolution processes may indicate sequential dissolution of α secondary α primary
Ti64, P. Barriobero Vila, Master‘s
Thesis
Start α+β→ β DSC T~ 425-450 °C XRD T~ 450-500°C
End α+β→ β DSC T~ 875°C
aβ shows a sudden increase
at T=500°C Diffusion of alloying elements
Primary α
50µm
3µm
Secondary α-lamellae
exo
9/15
50µm 40µm
Large α Lamellae
10µm
Small α Lamellae
3- Results 3.2. Lamellar microstructure
Assymetric endotermic peak may indicate sequential dissolution of smaller and larger lamellae
Ti17, E. Aeby-Gautier, JOM 2007
Stabilization of alpha content between ~400<T<575ºC increase from ~ 65wt% to ~75wt%
exo
Start α+β→ β DSC T~ 500-550°C XRD T ~ 575°C
End α+β→ β DSC T~ 875°C
aβ shows a sudden increase at
T=500°C
Diffusion of alloying elements
10/15
900°C β
exo
Metastable β grains
α‘‘ martensite
ω
282°C ω+β +α’’
Start α+β→ β DSC T~ 575 °C
End α+β→ β DSC T~ 855°C XRD: Beta quenched microstructure shows the
presence of stable α and β
plus metastable ωath, ω, α’’, α’’iso phases at different stages during heating
3- Results 3.3. Beta quenched microstructure
390°C ω+β +α’’
α
577°C β+α
437°C β + α’’iso.
• Ivasishin, Materials
Science and
Engineering 2005
• E. Aeby-Gautier,
Journal of Alloys and
Compounds 2012
Azim
uth
(°)
2-Theta (°)
150°C
β α‘‘
ωath.(TEM)+β+α’’
11/15
Metastable β grains
α‘‘ martensite
3- Results 3.3. Beta quenched microstructure
12/15
5k/min 390°C
20°C 390°C 425°C 540°C
5 k/min
4- Summary
• In Situ High Energy XRD:
Reveals the phases and its weight/volume fraction as f(T)
The faster increase of the aβ cell parameter at a threshold temperature of 500ºC
may be due to the diffusion of alloying elements into β phase (Al, Fe and/or V)
• DSC:
Reveals that the α phase (identified by XRD) dissolves at different stages
depending on its morphology fine lamella start to dissolve earlier than coarse
lamellae or globular α
- The bimodal and lamellar microstructures show the presence of α and β
phases at different stages during heating (no metastable phases were
observed)
- The beta quenched microstructure presents a much more complex phase
transformation kinetics as a consequence of the formation of the metastable
phases α’’, α’’iso, ωath, ω 13/15
4- Summary
Bimodal starts earlier due to the presence of smaller α-lamellae higher surface energy
Outlook:
- Metallography of microstructures frozen at different stages during
heating to confirm the dissolution sequence of the different α
morphologies
- The complex phase transformation kinetics of the Beta quenched
microstructure will be quantified by Rietveld analysis.
Microstructure
Start α+β→ β Temperature (ºC)
aβ Increasing
temperature
(ºC)
End α+β→ β Temperature (ºC)
DSC XRD DSC
Bimodal 425-450 450-500 500 875
Lamellar 500-550 575 500 875
Beta quenched 575 - - 850
14/15
David Lorrain (DSC), Georg Fiedler (Programming), David
Canelo (XRD data processing), Martin Stockinger (Ti-alloys),
Sabine Schwarz (TEM), Fernando Warchomicka, Guillermo
Requena
Beamline Scientist:
Thomas Buslaps (ESRF-ID15)
Acknowledgements
15/15