| How does Titanium compare with Steel? |
| The density of Titanium is
60% that of steel. The strength of titanium and titanium alloys
compares favorably with steel and as such titanium has a much higher
strength to weight ratio. Titanium is far more corrosion resistant
than many stainless steels particularly in seawater applications.
Titanium has been found to be more bio-compatible than steel due
to its resistance to many corrosive human body fluids. As a design
material for aircraft, medical devices, sporting goods, industrial
tools, marine hardware, jewelry and reciprocating components, titanium
proves superior to steel where high strength, light weight or corrosion
resistance are beneficial.
Titanium is often confused with the pure
metal, but like iron, it is the base for many useful alloys. Just
like iron based alloys (steel), titanium based alloys are tailored
to a variety of different applications that require high strength,
elevated temperature resistance, resistance to corrosion in harsh
environments or a combination of these requirements. The most common
titanium alloy is Ti 6Al-4V (6% Aluminum, 4% Vanadium, Balance Titanium)
which has properties comparable to 300 series stainless steels.
High strength alloys such as Ti 15-3-3-3 or Beta-C compare with
high strength stainless steels such as 17-4Ph. High temperature
alloys such as Ti 6-2-4-2, Ti-1100 or IMI 834 are superior to stainless
steel where lighter weight is required. For high performance applications,
intermetallics such as gamma titanium aluminides show great promise
at operating temperatures beyond the capability of steel alloys. |
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| What is the history of Titanium? |
| The word titanium comes from the Greek
word titanos meaning Titans from Greek mythology. Although originally
discovered in ilmenite by Reverend William Gregor in 1791 in England,
it was then rediscovered in rutile ore in 1795 by the German chemist
Martin Heinrich Klaproth who subsequently named the element titanium.
It wasn’t until 1910 that titanium metal was successfully
extracted from the ore by M.A. Hunter, an American chemist.
The Hunter process as it became known, reduced
rutile to make titanium tetrachloride which was subsequently reacted
with metallic sodium to form the pure metal. In 1946, Dr. Wilhelm
Kroll substituted magnesium for sodium in the final reduction stage
which proved more economical. The Kroll process is still used today. |
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| Why is Titanium Corrosion Resistant? |
| Titanium is very high on the nobility scale
and is almost as corrosion resistant as platinum. It is highly reactive
and forms an oxide coating in air which inhibits corrosion. The metal
is protected by a thin oxide layer of TiO2 which is highly adherent
and chemically stable, in fact, the metal is able to instantly re-heal
itself as long as water and oxygen are present, even in small quantities.
The protective layer is successful in environments ranging from highly
oxidizing (highly acidic) to mildly reducing (partially alkali) environments,
even when exposed to high temperatures. Titanium’s resistance
to aqueous chlorides such as brine, and strong acids (e.g nitric acid)
place it a cut above steels and copper/nickel alloys which suffer
greatly in these conditions. Titanium can however suffer in solutions
of HCl, HF or HBr, the addition of small amounts of oxygen and oxidizing
compounds can aid in prolonging the life of the metal by aiding in
preserving its protective oxide skin. For extreme conditions brought
about by high temperatures, titanium is alloyed with metals such as
palladium or molybdenum. |
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| How does titanium compare with aluminum? |
Aluminum and titanium are both
metals that occur naturally in the Earth’s crust. Aluminum
and titanium are known for their high strength-to-weight ratio.
Aluminum is lightweight, durable, soft and malleable, whereas titanium
is stronger with higher density. Aluminum is silvery grey, and titanium
is matte grey color. Titanium has a high melting point of over 1,649°C
or 3,000°F, and is a reactive metal, whereas aluminum melts
at 933°C or 1,200°F and is less reactive in the molten state.
Aluminum is non-sparking while titanium gives off intense white
sparks when abraded. Aluminum and titanium are both nonmagnetic.
Aluminum is soluble in various aqueous solutions
but titanium is insoluble in almost all solvents including concentrated
acids. Aluminum is ductile and more easily machined when compared
to titanium. Titanium has more resistance to corrosion compared
to aluminum. Aluminum has a low metal density, whereas titanium
is 60% denser. Titanium has a much stronger strength to weight ratio
than aluminum. Aluminum is an excellent conductor of heat and electricity,
whereas titanium is a poor conductor.
Both aluminum and titanium are used in structural
components vital to the aerospace, transportation, electronics and
marine industries. Aluminum is in abundance on Earth, as it is the
most abundant metal and the 3’rd most abundant element; whereas,
titanium is the 9th most abundant element, and 7th most abundant
metal. Titanium is commercially produced by the Kroll process, a
complex series of reactions followed by electrolysis and is one
of the most expensive metals. Aluminum is reduced from the ore using
the less expensive Hall process which reduces the ore through electrolysis. |
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| What is investment casting? |
Investment casting, also known as lost
wax casting, is a precision casting process to fabricate near-net-shaped
metal parts from almost any alloy. Historically used to produce
artwork and jewelry, it is evolved over many years and has become
most commonly used to produce components that require complex and
sometimes thin-walled net shapes.
A wax pattern of the desired metal shape
is created by injecting a specific type of casting wax into a fabricated
metal mold die. Once a wax replica is produced, it is assembled
into a cluster and repeatedly dipped into a ceramic slurry, covered
with a sand stucco, and dried. Successive layers of ceramic are
built up until the wax mold is completely covered by a ceramic shell
approximately 1/4 to 3/8 inches thick. After sufficient drying time,
the wax is quickly removed by placing the assembly in a steam autoclave.
Following this step, the shell mold is placed in a furnace where
any residual wax is lost and the ceramic is cured to a high strength
by fusion bonding or sintering. The mold is then preheated to a
specific temperature before being filled with molten metal. Once
the metal casting has cooled, the ceramic shell is chipped away
revealing an exact replica of the expendable wax pattern. Final
finishing processes include sandblasting, belt sanding and machining.
Reactive metals such as titanium require
melting to be done in a vacuum which prevents oxidation (burning)
at elevated temperatures. Special refractories are used to prevent
titanium from reacting with the mold and allow the process to yield
useful, high quality components. Minimal machining is then required
to finish the part with very little metal removal. For complex components,
investment casting of titanium is far more economical than machining
from bar or plate due to the more efficient use of titanium alloy. |
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