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At room temperature and ambient pressure, Ti (titanium) has a hexagonal close-packed structure (called α-phase) with the lattice constants listed in Table 1721a. Its unit cell has two atoms at (1/3, 2/3, 1/4) and (2/3, 1/3, 3/4) and the space group number is 194 (P63/mmc). At room temperature and high pressure, it changes to the ω-phase [1,2] with the lattice constants listed in Table 1721b. Its unit cell has three atoms at (0, 0, 0), (1/3, 2/3, 1/2), (2/3, 1/3, 1/2) and the space group is P6/mmm. The α → ω transition in Titanium is a typical example of martensitic transformation.
Table 1721a. Structural properties of poly-crystalline α-titanium.
Property |
|
Reference |
Lattice constants |
a (Å) |
b (Å) |
c/a |
2.951 |
4.684 |
1.5873* |
* Smaller than the ideal ratio of 1.633 for HCP
|
|
|
Mean number of faces per grain |
14.2 |
[3] |
Grain boundary with the greatest relative area |
28°/[0001] misorientation and (31-40) and (7-2-50) grain boundary planes |
[3] |
Table 1721b. Lattice constants of ω-titanium at 25 °C.
a (Å) |
b (Å) |
c/a |
4.598 |
2.822 |
~ 0.61 |
Table 1721c. Lattice constants of β-titanium.
a (Å) |
b (Å) |
c (Å) |
3.32 |
3.32 |
3.32 |
Table 1721d. Properties of Ti metal.
Density (g-cm-3) |
4.51 |
Valence states |
3s, 3p, 3d, 4s |
Reference configuration |
3s23p63d24s0 |
Core radii for angular waves (a.u.) |
rs=1.25, rp=1.25, rd=1.65 |
Specific heat (cp, Jkg-1K-1)
|
520 |
Heat conductivity (kh,Wcm-1K-1)
|
0.17 |
Melting temperature (Tm, °C)
|
1668 |
Vaporization temperature (Tv, °C)
|
3280 |
|
403 |
Vaporization heat (Qv, J-g-1)
|
8790 |
Absorption (1-R) |
0.40 for 1 µm light |
Phase transformation |
at ~882 °C, from bcc (β-phase) at higher temperatures to hcp (α-phase) at lower temperatures |
Figure 1721a shows the solid solubility of some impurities (including Ti) in silicon.
![Solid solubility of impurities in silicon](image2/3228.PNG)
Figure 1721a. Solid solubility of impurities in silicon.
Figure 1721b shows the solubility for impurities (including Ti) in SiC.
![Solubility for impurities in SiC](image2/2089b.PNG)
Figure 1721b. Solubility for impurities in SiC.
Table 1721e. Most closed packed d-spacing and planes in Ti and Ti-based crystals.
[1] Jamieson J.C., Science, 1963, 140, 72; doi:10.1126/science.140.3562.72.
[2] Sikka S.K., Vohra Y.K., Chidaraman R., Prog. Mater. Sci., 1982, 27, 245.
[3] Madeleine N. Kelly, Krzysztof Glowinski, Noel T. Nuhfer, Gregory S. Rohrer, The five parameter grain boundary character distribution of a-Ti determined from three-dimensional orientation data, Acta Materialia 111 (2016) 22-30.
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