Titanium is the fourth most abundant
structural metal in the earth's crust and is the ninth industrial metal. No
other engineering metal has risen so swiftly to pre-eminence in critical and
demanding markets. Titanium is number 22 on the Periodic Table, has an atomic
weight of 47.90, and is represented by the symbol ※Ti§. It has a density of
4.54g/cm3, a melting point of roughly 1,667∼C and a boiling point of 3,287∼C. Rutile
and ilmenite, the two primary minerals which contain titanium, make up 24% of
the earth*s crust, thus making titanium the ninth most abundant element on the
planet. Titanium alloys are widely used in the aerospace, chemical, auto,
medical industries.
To produce the metal, the rutile is
combined with coke/tar, and chlorine gas and then is heated to create titanium
tetrachloride (TiCl4). The TiCl4 is then converted through a chemical process
to a ※sponge§ product which is then melted into an ingot form. Titanium is
melted either by the vacuum arc remelting (VAR) process, or by utilization of a
cold hearth furnace process. If the grade of titanium being melted is an
※alloyed§ grade, the alloying agents are added during the compacting process.
The ingot is then processed into various forms of mill products by standard equipment of metal working.
Titanium Chemical Composition: palladium
(Pd) and ruthenium (Ru), nickel (Ni) and molybdenum (Mo) are elements which can
be added to pure titanium in order to obtain a significant improvement of
corrosion resistance particularly in slightly reducing environments where
titanium otherwise might face some problems due to insufficient conditions for
formation of the necessary protective oxide film on the metal surface. The
formation of a stable and substantially inert protective oxide film on the
surface is otherwise the secret behind the extraordinary corrosion resistance
of titanium.
The mechanical properties of
commercially pure titanium are in fact controlled by "alloying" to
various levels of oxygen and nitrogen to obtain strength level varying between
approximately 290 and 550 MPa. For alloying elements of higher strength levels,
elements e.g. Al and V have to be added. Ti 3AL 2.5V has a tensile strength of
minimum 620 MPa in annealed condition and minimum 860 MPa in cold-worked and stress-relieved
condition. The CP-titanium grades are nominally all alpha in structure, whereas
many of the titanium alloys have a two phase alpha + beta structure. There are
also titanium alloys with high-alloying additions having an entire beta phase
structure. While alpha alloys cannot be heat treated to increase strength, the
addition of 2.5% copper would result in a material which responds to solution
treatment and ageing in a similar way to aluminum-copper.
Titanium alloys can be grouped into
four main categories. Their properties depend on their basic chemical structures
and the way they are manipulated during the process of manufacturing. Some
elements used for making alloys include aluminum, molybdenum, cobalt,
zirconium, tin and vanadium. Alpha phase alloys have the lowest strength but
are formable and weldable. Alpha plus beta alloys have high strength. Near
alpha alloys have medium strength but have good creep resistance. Beta phase
alloys have the highest strength of any titanium alloys but they also lack
ductility.
Titanium Benefit:
High strength,
High resistance to pitting, crevice
corrosion resistance,
High resistance to stress corrosion
cracking, corrosion fatigue and erosion,
Cold bending for complex piping bends
without fittings or flanges, high strength-to-weight ratio.
Weight saving possibilities,
Low modulus, high fracture toughness
and fatigue resistance,
Suitability for coiling and laying on
seabed,
Ability to withstand hot/dry and
cold/wet acid gas loading,
Excellent resistance to corrosive and
erosive action of high-temperature acid steam and brine,
Good workability and weldability.
Its weight-to-strength ratio is one of
the most attractive properties of titanium. This metal is as strong as steel
and 45% lighter, but while it's twice as strong as aluminum, it is 60% heavier.
This ratio is what makes it so ideal for aerospace and other applications, but
there are many other properties that make it such an important resource.
Tensile Strength 每 The tensile
strength of titanium and its alloys range from 20,000 psi to more than 200,000
psi, but most commercial grade titanium averages around 63,000 psi.
Fatigue Strength 每 A titanium alloy
can have a very high-cycle fatigue strength. The actual strength can be
determined by the surface finish, which is why care must be taken to avoid
stress concentrators.
Coefficient of Thermal Expansion 每 The
thermal expansion properties of titanium are lower than steel, copper and
aluminum. The size changes very little under extreme temperature changes.
Electrical Conductivity 每 Titanium is
not a good conductor of electricity. As a comparison, if copper were to have
100% conductivity, titanium would be around 3%.
Corrosion Resistance 每 A chemically
inert oxide film forms on the surface of the metal, creating a high level of
corrosion resistance to most mineral acids and chlorides.
Toxicity 每 This metal is non-toxic in
the human body and biologically compatible with human tissue and bone.
Magnetics 每 Commercially pure titanium
and all its associated alloys are non-magnetic.