Bill,
A titanium rotor would be 58% to 66% the weight of cast iron and more than
twice as strong as aluminum. With the casting price plus machining the
item gets pricey. If they could retail for under $500 each would there be a
market for them? Units sales would have to be over 500 pieces a year to
offset the price of the expensive mold. Would have to depend on the auto
racers no doubt.
A large part of the rotor weight still contains the inner gear of which how
much I would like to know. Can anyone weigh it for me? But lets say by
making it out of a titanium/aluminum alloy we can lower the total weight to
at least 6 lbs. What does a lighter rotor do for our aircraft engines?
Allows them to run at higher rpms and hence higher HP. Disavantageous? We
need with a 3:1 or higher gearbox to handle the rpms.
Why not make it out of aluminum and strengthen it with the carbide flame
spray method? Titanium would be less expensive because of the high force
aluminum "Squeeze casting" techniques needed to insure a part without
inclusions. IMHO I believe the flame spray technique would involve more
production steps at different locations, and labor costs as well.
TITANIUM: (Pulled from some long forgotten website)
" Depending on the predominant phase or phases in their microstructure,
titanium alloys are categorized as alpha, alpha-beta, and beta. This natural
grouping not only reflects basic titanium production metallurgy, but it also
indicates general properties peculiar to each type. The alpha phase in pure
titanium is characterized by a hexagonal close-packed crystalline structure
that remains stable from room temperature to approximately 1,620$B!<(JF. The beta
phase in pure titanium has a body-centered cubic structure, and is stable
from approximately 1,620$B!<(JF to the melting point of about 3,040$B!<(JF.
Adding alloying elements to titanium provides a wide range of physical and
mechanical properties. Certain alloying additions, notably aluminum, tend to
stabilize the alpha phase; that is, they raise the temperature at which the
alloy will be transformed completely to the beta phase. This temperature is
known as the beta-transus temperature.
Alloying additions such as chromium, columbium, copper, iron, manganese,
molybdenum, tantalum, and vanadium stabilize the beta phase by lowering the
temperature of transformation from alpha to beta. Some elements, notably tin
and zirconium, behave as neutral solutes in titanium and have little effect
on the transformation temperature, acting instead as strengtheners of the
alpha phase.
Alpha alloys: The single-phase and near-single-phase alpha alloys of
titanium have good weldability. The generally high aluminum content of this
group of alloys ensures good strength characteristics and oxidation
resistance at elevated temperatures (in the range of 600 to 1,100$B!<(JF). Alpha
alloys cannot be heat treated to develop higher mechanical properties
because they are single-phase alloys.
Alpha-beta alloys: The addition of controlled amounts of beta-stabilizing
alloying elements causes the beta phase to persist below the beta transus
temperature, down to room temperature, resulting in a two-phase system.
These two-phase titanium alloys can be strengthened significantly by heat
treatment consisting of a quench from some temperature in the alpha-beta
range, followed by an aging cycle at a somewhat lower temperature.
Beta-phase transformation, which would normally occur on slow cooling, is
suppressed by the quenching. The aging cycle causes the precipitation of
some fine alpha particles from the metastable beta, imparting a structure
that is stronger than the annealed alpha-beta structure. Although
heat-treated alpha-beta alloys are stronger than the alpha alloys, their
ductility is proportionally lower.
Beta alloys: The high percentage of beta-stabilizing elements in these
alloys results in a microstructure that is substantially beta. The
metastable beta can be strengthened considerably by heat treatment.
Titanium is used in corrosive environments or in applications that require
light weight, high strength-to-weight ratio, and nonmagnetic properties.
While commercially available in many alloys, most requirements can be met by
a grade of commercially pure titanium, titanium-0.2% palladium alloy, or by
the high-strength Ti-Al-V-Cr (beta type) alloys. These grades, which are
available in most common wrought mill forms, are covered by ASTM-AMS
specifications and, in most cases, by a similar ASME specification.
Beta-21S is a new beta alloy developed as an oxidation-resistant aerospace
material and as a matrix for metal-matrix composites. Composition is
Ti-15Mo-2.7Nb-3Al-0.2Si, with molybdenum and niobium working synergistically
to raise corrosion resistance to very high levels. It also offers one of the
lowest hydrogen uptake efficiency levels of any titanium alloy. The
combination of high strength and high corrosion resistance make it an ideal
candidate for orthopedic implants, deep sour oil wells, and geothermal brine
wells.
Like stainless steel, titanium sheet and plate work harden significantly
during forming. Minimum bend-radius rules are nearly the same for both,
although springback is greater for titanium. Commercially pure grades of
heavy plate are cold formed or, for more severe shapes, warm formed at
temperatures to about 800$B!<(JF. Alloy grades can be formed at temperatures as
high as 1,400$B!<(JF in inert-gas atmospheres. Tube can be cold bent to radii
three times the tube OD, provided that both inside and outside surfaces of
the bend are in tension at the point of bending. In some cases, tighter
bends can be made.
Despite their high strength, some alloys of titanium have superplastic
characteristics in the range of 1,500 to 1,700$B!<(JF. The alloy used for most
superplastically formed parts is the standard Ti-6Al-4V alloy. Several
aircraft manufacturers are producing components formed by this method. Some
applications involve assembly by diffusion bonding.
Titanium plates or sheets can be sheared, punched, or perforated on standard
equipment. Titanium and Ti-Pd alloy plates can be sheared subject to
equipment limitations similar to those for stainless steel. The harder
alloys are more difficult to shear, so thickness limitations are generally
about two-third those for stainless steel.
Titanium and its alloys can be machined and abrasive ground; however, sharp
tools and continuous feed are required to prevent work hardening. Tapping is
difficult because the metal galls. Coarse threads should be used where
possible.
Titanium castings can be produced by investment or graphite-mold methods.
Casting must be done in a vacuum furnace, however, because of the highly
reactive nature of titanium in the presence of oxygen. Typical applications
for titanium castings are surgical implants and hardware for marine and
chemical equipment such as compressors and valve bodies.
Generally, titanium is welded by gas-tungsten arc (GTA) or plasma-arc
techniques. Metal inert-gas processes can be used under special conditions.
Thorough cleaning and shielding are essential because molten titanium reacts
with nitrogen, oxygen, and hydrogen, and will dissolve large quantities of
these gases, which embrittles the metal. In all other respects, GTA welding
of titanium is similar to that of stainless steel. Normally, a sound weld
appears bright silver with no discoloration on the surface or along the
heat-affected zone..."
Doug in Japan