Technical
Capabilities of Titanium
General Corrosion
Uniti Titanium supplies and markets commercially pure titanium products
that have excellent resistance to corrosion in a wide variety of
environments including seawater, salt brines, inorganic salts, bleaches,
wet chlorine, alkaline solutions, oxidizing acids, and organic acids.
Titanium is incompatible with fluorides, strong reducing acids, very
strong caustic solutions, and anhydrous chlorine. Due to its combustibility,
titanium is not suitable for pure oxygen service. Titanium does not
release any toxic ions into aqueous solutions, which would contribute
to pollution.
Crevice Corrosion Cracking
Uniti Titanium products have excellent resistance to crevice corrosion
cracking in salt solutions and generally outperform stainless
steels. Unalloyed titanium products (grades 1, 2, 3 and 4) typically
do not suffer crevice corrosion at temperatures below 80°C
(175°F) at any pH. Palladium alloyed CP titanium products
(grades 7, 11, 16 and 17) are more resistant and typically do
not suffer crevice corrosion at temperatures below 250°C
(480°F) at pH greater than 1.
Microbiologically Influenced
Corrosion (MIC)
Titanium alloys appear to be immune to MIC. They do suffer bio-fouling,
but this can be controlled by chlorination (which does not impair
titanium).
Galvanic Corrosion
Although it is a reactive metal, due to the extreme stability of
the passive film which forms on its surface, titanium typically
exhibits noble behavior. Thus it functions as the cathode when
coupled with other metals. Titanium is not affected by galvanic
corrosion, but can accelerate corrosion of other metals.
Stress Corrosion Cracking
Uniti Titanium products have excellent resistance to stress corrosion
cracking in hot chloride salt solutions.
Erosion Corrosion
Titanium alloys exhibit excellent resistance to flow induced and
erosion corrosion at velocities to above 40 m/sec.
Hydrogen Embrittlement
Titanium alloys are susceptible to hydrogen embrittlement under
some circumstances. This is generally less of a problem for the
low-strength grade 1 and grade 2 titanium alloys than for higher
strength titanium alloys. Absorption of hydrogen by titanium
normally occurs when the temperature is above 80°C (175°F),
and the titanium is galvanically coupled to an active metal or
an impressed current or the pH is less than 3 or greater than
12.
Welding
Uniti Titanium CP products are readily weldable using GTAW (gas
tungsten arc welding) or TIG (tungsten inert gas) processes if
adequate shielding is provided using pure inert gas (argon or
helium). Use of a trailing shield is recommended. Titanium must
be free of oil, grease or other contamination before welding.
Pre-heat or post-heat are not required. Friction welding, laser
welding, resistance welding, plasma arc welding, electron beam
welding, and diffusion bonding can also be used.
Formability
Uniti Titanium is readily formed at room temperature, using techniques
and equipment suitable for steel. When correct parameters have
been established, tolerances similar to those attainable with
stainless steel are possible with titanium and its alloys.
Three factors make forming
of titanium somewhat different from forming
of other metals.
- The room temperature ductility
of titanium, as measured by uniform elongation,
may be less than that of other common structural
metals. This means that titanium may require
more generous bend radii and has lower stretch
formability.
- The modulus of elasticity
of titanium is about half that of steel.
This causes significant spring back after
forming titanium for which compensation must
be made.
- The galling tendency of
titanium is greater than that of stainless
steel. This necessitates close attention
to lubrication in any forming operation in
which titanium is in contact (particularly
moving contact) with metal dies or other
forming equipment. The various grades of
titanium exhibit differences in formability.
Grades 1, 11 and 17 titanium, which are the
softest and most ductile grades, exhibit
the greatest formability. The slightly greater
strengths of Grades 2, 7 and 16 titanium
are still quite formable, but less so than
Grades 1, 11 or 17. The higher strength of
Grade 4 titanium makes it the least formable
of the CP titanium alloys. Normally, titanium
surfaces are acceptable for forming operations
as received from the mill. Gouges and other
surface marks introduced during handling
should be removed by sanding. To prevent
edge cracking, burred and sharp edges should
be filed smooth before forming.
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