Titanium is a chemical element with the symbol Ti and atomic number 22. Sometimes called the “space age metal”, it has a low density and is a strong, lustrous, corrosion-resistant (including sea water,
aqua regia and chlorine) transition metal with a silver color.
Titanium can be alloyed with iron, aluminium, vanadium, molybdenum, among other elements, to produce strong lightweight alloys for aerospace (jet engines, missiles, and spacecraft), military, industrial process (chemicals and petro-chemicals, desalination plants, pulp, and paper), automotive, agri-food, medical prostheses, orthopedic implants, dental and endodontic instruments and files, dental implants, sporting goods, jewelry, mobile phones, and other applications. Titanium was discovered in England by William Gregor in 1791 and named by Martin Heinrich Klaproth for the Titans of Greek mythology.
The element occurs within a number of mineral deposits, principally rutile and ilmenite, which are widely distributed in the Earth's crust and lithosphere, and it is found in almost all living things, rocks, water bodies, and soils. The metal is extracted from its principal mineral ores via the Kroll process or the Hunter process. Its most common compound, titanium dioxide, is used in the manufacture of white pigments. Other compounds include titanium tetrachloride (TiCl4) (used in smoke screens/skywriting and as a catalyst) and titanium trichloride (TiCl3) (used as a catalyst in the production of polypropylene).
The two most useful properties of the metal form are corrosion resistance and the highest strength-to-weight ratio of any metal. In its unalloyed condition, titanium is as strong as some steels, but 45% lighter. There are two allotropic forms and five naturally occurring isotopes of this element; 46Ti through 50Ti, with 48Ti being the most abundant (73.8%). Titanium's properties are chemically and physically similar to zirconium.
Pure Titanium
Titanium is a light metal having a density of about 4540 kg/m3. This compares to steel at 7900 kg/m3 and Aluminium at 2710kg/m3. Titanium has a melting point of about 1668oC which is higher than iron at1560oC. Titanium has a Modulus of Elasticity of 110 x 109 Pa. compared to steel at 210 x 109 Pa. Therefore Titanium has a significantly high deflection under the same load than steel. Pure Titanium can be cold rolled to 90% reduction in thickness at room temperatures without cracking.
There are a number of grades of commercially pure (unalloyed) titanium as identified in ASTM B265 (Gr,1,2,3,4,7,11,and 12) (see table below for Gr 1 to 4)). Each grade has a different amount of impurity content (Grade 1 have lowest impurities). Grade 1 to 4 are classified as pure even though grade 4 is much stronger and less ductile than grade 1. Grade 4 contains higher levels of oxygen which is classified ( for pure titanium ) as an alloying element. Oxygen and Nitrogen and Carbon are all interstitial alloys (they insert themselves in the crystal intertices of the crystals and prevent relative sliding). They therefore increase the hardness and reduce the ductility. Oxygen is the main element controlling the strength of unalloyed titanium.
Titanium Alloys
Titanium Alloys are generally divided into three groups (Alpha, Alpha-Beta and Beta). The Alpha group contain most importantly aluminum and tin. They can also contain molybdenum, zirconium, nitrogen, vanadium, columbium, tantalum, and silicon. Alpha alloys are not suitable for heat treatment. Alpha alloys are used for aircraft parts and cryogenic equipment.
The Alpha-Beta group can be strengthened by heat treatment. The alloys are used in aircraft and aircraft turbine parts, chemical processing equipment, marine hardware.
The Beta Alloys have good hardenability. Beta alloys are slightly more dense than other titanium alloys, having densities ranging from 4800 to 5050 kg/m3. They are the least creep resistant alloys, they are weldable, and can have yield strengths up to 1345 x 106 Pa.(Solution treated and age hardened) Beta alloys are the smallest group. They are used for heavier duty purposes on aircraft.
Mechanical Properties
Properties |
Conditions |
T (°C) |
Treatment |
Density (×1000 kg/m3) |
4.51 |
25 |
|
Poisson's Ratio |
0.34 |
25 |
|
Elastic Modulus (GPa) |
104.1 |
25 |
|
Tensile Strength (Mpa) |
310 |
315 more |
annealed |
Yield Strength (Mpa) |
172 |
Elongation (%) |
25 |
Reduction in Area (%) |
70 |
Hardness (HB) |
265 |
25 |
annealed |
Impact Strength (J)
(Charpy) |
20 |
25 |
annealed |
Thermal Properties
Properties |
Conditions |
T (°C) |
Treatment |
Thermal Expansion (10-6 ºC) |
8.6 |
20-100 more |
|
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