Prediction and Mechanism of Tensile Strengthening inSingle β-phase Ti-Ta Alloys with Oxygen Solutes
K.Yokota1, K.Shitara2,3 A.Bahador2, J.Umeda2 and K.Kondoh2
1Department of Mechanical Engineering, Graduate School of Osaka University
2Joining and Welding Research Institute, Osaka University
3Research and Service Division of Materials Data and Integrated System Center, National Institute for Materials ScienceIntroduction

Oxygen solid solution is known as one of strengthening mechanisms in Ti alloys. The lattice distortion owing to solidsolution is the key point in this strengthening mechanism and can be theoretically analyzed by first-principles
calculations. In this poster, the local structure of solutes oxygen and the lattice distortion in β-Ti alloy model werecomputationally elucidated by using first-principles calculations. In addition, the increment of 0.2% yield strength of
β-Ti alloy model was estimated by combining these results with the Labusch model, the theory of solid solution
strengthening. These increments of 0.2% yield strength were validated by experiments. The single β-phase Ti alloys
with various oxygen concentrations were fabricated by powder metallurgy and a series of heat treatment, and theirmicrostructure and mechanical properties were characterized.
Calculation conditions
2×2×2 model

3×3×3 model

Experimental procedure
Ti powderFirst-principles calculations
・VASP code
・Cutoff energy : 520 eV・K-point spacing : 0.15 Å-1

Substitution site

Substitution site

Tetrahedral site

Tetrahedral site

Octahedral site
Octahedral site
Ti or Ta atoms
O atom50 μm

𝜏𝑆

TiO2 powder

Mixed powder

Ball milling : 1 hr
Rocking milling : 3 hr

1 𝐹 𝑐 𝑤
4𝐺𝑏𝑆

Ti-35Ta+xO

1 μm x=1.5, 2.4, 3.6 at.%50 μm① Mixing

Labusch model𝛥𝜎Ta powder

10 μmpowder

Pressure : 30 MPa
VacuumChamber

Diameter : 42 mm

𝜏
1 𝐹 𝑐 𝑤
𝑆4𝐺𝑏𝑆
Increment of 0.2%YS by solid solution
estimated from theoretical method
𝛥𝜎Tetrahedral model
After calculation(2x2x2)

Increment of 0.2% YS by O solid
solution (calculation), ΔσYS(SS)/MPa

Octahedral model
After calculation(2x2x2)

Ti

2

2×2×2

1.5
10.5

3×3×3
Tetrahedral site Octahedral site Substitudted site

Validation by Experiments

3.6 at.% O2.4 at.% O
1.5 at.% O3040506070
Diffraction angle, 2θ/deg.

80

Fabricated specimens have single β phase.

Lattice constants, a/ÅIntensity (a.u.)

β-Ti
Resin

800
600
400
200
0024
Oxygen content (at.%)

6

Increment of 0.2%YS by O solution
could be theoretically estimated.

Lattice constant

3.335

XRD

1000

Solute oxygen is most stable atthe octahedral site in both results.

0Temp. : 1773 K
Time : 1 hr

Labusch model

Increment of 0.2%YS by O solution
350

3.315

Experimental

3.295
3.275

Calculation

3.255
024
Oxygen content (at.%)

6Increment of 0.2%YS by
O solid solution, ΔσYS(SS)/MPa

Relative energy (eV/detect)

2.5⑤ Quenching

Pressure

Theoretical results by using First-principles calculations and the Labusch model
Relative energy

Temp. : 1373 K
Time : 5 min
Load : 1650 kNTime : 1 hr

Results –lattice distortion and mechanical properties

3④ Hot forging

Temp. : 1373 K

PulsedDC power
supplyTemp. : 1773 K
Time : 12 hr

TiO2 particle② Spark plasma sintering (SPS)τ0 : Shear stress
SF : Schmid factor
Fm : Maximum interaction force
between solute atom and dislocationc : Solute atom concentration
w : The range of the interaction
G : Modulus of rigidityb : Burgers vector size

③ Homogenizing

The experimental lattice constants are in a goodagreement with calculation results.

300
250

ΔσYS(SS) Experimental
ΔσYS(SS) Computational

200
150
100500Standard（0MPa）
1.5

2.4
Oxygen content (at.%)

3.6

The increments of 0.2% YS were validated.