Why Titanium ??

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 1668^oC which is higher than iron at1560^oC. 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.

Titanium does not occur free in Nature. However, when combined with other elements, it is quite abundant, occurring in small amounts in most of the volcanic, sedimentary and metamorphic rocks.
Its more important minerals are ilmenite, rutile, arizonite (iron titanate), brookite, anatase, leucochene (titanium dioxide), perovskite (calcium titanate), and others. The first two have commercial importance, and can be found in deposits spread all over the world. There are important rutile and ilmenite deposits in Australia, Argentina, USA, Central Africa, Brazil, Canada, Egypt, India and Norway. The largest well-known deposits of rutile are located in Australia.
Titanium and its alloys are relatively new engineering metals since they have been in use only since about 1952. They are extremely attractive materials for engineers because they have a high strength to weight ratio, high elevated temperature properties to about 550^oC, and excellent corrosion resistance particularly in oxidising acids and chloride media.  This metal is being increasingly used for marine applications. Its resistance to seawater attack combined with its mechanical properties make it a prime choice for equipment operating within the sea or transferring seawater.
Titanium is not an 'exotic' metal, it is the fourth most abundant structural metal in the earth's crust, and the ninth industrial metal. This metal has become the prime selection for a wide range of critical and demanding applications.

Titanium Alloys

There are two crystallographic forms of titanium:

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      α-titanium, in which atoms are arranged in Hexagonal Closest Packing (HCP) crystal lattice;

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      β-titanium, in which atoms are arranged in Cubic Body Centered (BCC)crystal lattice;

Pure titanium exists in form of α-phase at temperatures above 1621°F (883°C) and in form of β-phase at temperatures below 1621°F (883°C).

The temperature of allotropic transformation of α-titanium to β-titanium is called Beta Transus Temperature.

Alloying elements in titanium alloys may stabilize either α-phase or β-phase of the alloy.

Aluminum (Al), gallium (Ga), Nitrogen (N), Oxygen (O) stabilize α-phase.

Molybdenum (Mo), vanadium (V), tungsten (W), tantalum (Ta), silicon (Si) stabilize β-phase.

Titanium alloys are classified into four groups according to their phase composition:

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      Commercially pure and low alloyed titanium alloys

Commercially pure titanium consists of grains of α-phase and dispersed spheroid particles of β-phase. Small amounts of iron, present in the alloys, stabilize β-phase.

Commercially pure titanium has relatively low mechanical strength and good corrosion resistance.

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      Titanium alpha and near-alpha alloys

α-alloys consist entirely of α-phase. They contain aluminum as the major alloying element, stabilizing α-phase.

α-alloys have good Fracture Toughness and Creep resistance combined with moderate mechanical strength, which is retained at increased temperatures.

They are easily welded, but their workability in hot state is poor.

Near α-alloys contain small amount of ductile β-phase. Besides α-phase stabilizer (aluminum), near α-alloys are alloyed by 1-2% of β-phase stabilizers (molybdenum, silicon).

Mechanical properties of near α-alloys are similar to those of α-alloys, however due to the presence of β-phase these alloys may be heat-treatable and are forged in hot state.

        

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Titanium alpha-beta alloys

α-β alloys contain 4-6% of β-phase stabilizers; therefore they consist of a mixture of α and β phases.

α-β alloys are heat-treatable. They have high mechanical strength and good hot formability.

Creep resistance of the alloys is lower, than that of α- and near α-alloys.

   * Titanium beta alloys

β-alloys are rich of β-phase. They contain substantial amount of β-phase stabilizers, preventing β-α transformation at high cooling rates of quenching.

β–alloys are heat-treatable to very high strength and have good hot formability.

Ductility and fatigue strength of the alloys in heat-treated conditions are low.

Titanium alloys are designated according to their compositions:

Ti-5Al-2.5Sn identifies titanium alloy, containing 5% of aluminum and 2.5% of tin.

Ti-6Al-4V identifies titanium alloy, containing 6% of aluminum and 4% of vanadium.

In parallel to this designation system other systems for designation titanium alloys exist (ASTM, IMI, military system).

Notice

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.