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Appendix K
TONNAGE POWDER METALLURGY
DIJ PONT TITANIUM TONNAGE POWDER METALLURGY
The barrier to important lower cost titanium mill products, based on
du Pont's investigations In the 1950s and 1960s and highlighted in
Chapter 11, may be the economical production of titanium powder
containing less than 50 parts per million of by-product chloride. Du
Pont did not solve this problem and, consequently, stopped its titanium
TPM development in 1962. Its technologic achievements on the remainder
of the TPM processes were considerable, however, and are outlined in thi s
appendix.
this problem and,
Du Po nt f ound i t
that, when ground in the presence of salt, produced a high purity,
acicular powder. This powder was ideally suited for processing it
directly to mill products (USP 2984560 and USP 30723473. - -
could produce a f riable sponge from sodium reduction
Du Pont then
experimented with compacting these powders directly in the nip of a
rolling mill to produce sheet and with the extrusion of green compacted
billets to bar, tubing, and shapes.
These experiments were so promising that du Pont proceeded to scale
up powder manufacture to tonnage size batches. It established a direct
powder conversion process for mill product manufacture at a
commercial-size facility in Baltimore, Maryland. Sheet was produced by
compacting powder continuously in the nip between two rolls. Through the
development of a feed hopper and an edge control system, sheet with high
green strength was produced (U. S . Patent 3530210 and U. S . Patent
3478136~. Sheet formed in these nips was 75 percent of theoretical
density at a minimum. When the powders used were optimum in particle
size distribution, the as-compacted density was in excess of 90 percent
of theoretical.
In contrast to the free-flowing microspheres required for the
precision molding process, the du Pont direct powder rolling process
requires dendritically shaped particles that interlock. The green sheet
was coiled and sintered of f line in a continuous, inert gas, Wintering
furnace. The sheet then was finished cold with intermediate anneals as
necessary . Excellent control of final gauge was achieved along with high
ductility and superior surface finish. Since all mill processing was
done at room temperature, the hardness of the sheet was dependent only on
the purity of the starting powder, the quality of the sintering
atmosphere, and the time at temperature.
207
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208
The process also proved to be successful for producing continuou s
6A1-4V alloy sheet. Elemental powders were blended with master alloy
powders and fed to the roll ni p through a hopper that prevented
segregation of the master alloy powder. Most of the deformation
necessary to reach f inal dimensions in the alloy sheet could be carried
out through the ductile matrix of a partially homogenized alloy. Final
homogenization through a 4-hour treatment at 1100°C, followed by finish
rolling resulted in high-strength alloy foils with typical 6-4
properties. This sheet could readily be formed and spot welded into
high-strength honeycomb structures (U. S. Patent 3084042) .
Bars, tubing, and shapes were produced by ache extrusion of
hydrostatically compacted billets. In some cases, extrusion was to
finished dimensions; in others, to near finished dimensions followed by
heat treatment and either rolling or drawing. Essential to the extrusion
of these products was a lubrication process that served to permit
streamlined flow of the billet through the die during extrusion (U.S.
Patent 3481762~. Most titanium and blended titanium alloy billets were
extruded below 400°C and contamination was not detectable. Billets up to
12 inches in diameter by 24 inches long were extruded. Reduction ratios
of up to 40:1 were accomplished. Hydrostatic pressures of up to 8000 psi
gave compacted densities as high as 97 percent. Theoretical density was
readily achieved upon extrusion. Alloys extruded in the partially
homogenized condition could be completely homogen] zed by annealing at
temperatures of 1100°C for 4 hours either prior to or after redrawing.
Du Pont tests could detect no differences in the mechanical properties
between these materials and those from melted and wrought products of
equivalent hardness. Tons of titanium powder were processed by du Pont.
Du Pont never test marketed these metal products because there was
one flaw that, in du Pont's judgment, would make their product
noncompetitive with melted and wrought products. The titanium and
titanium alloy mill products produced from powders contained very small
quantities of chlorides trapped within the microstructure. These
chlorides volatilized rapidly during welding and caused a buildup of
salts on the tungsten welding electrode that resulted in an unstable
arc. Chlorides in these products ranged f ram 0.05 percent to 0.01
percent. Experiments involving the dilution of these chloride levels
with powder produced from hydrided and ground pure titanium that had been
previously arc melted to remove the chlorides resulted in a judgment that
satisfactory weldability would be reached at a chloride level of 0.005
percent or less. Achieving these chloride levels was judged at that time
to be impractical f ram the manuf acturing standpoint . Theref ore, the
entire program was discontinued based on the conviction that a marginally
weldable product would not be acceptable commercially.
Technology has advanced significantly since du Pont's work In the
late 1950s. Twenty years of technical advances all over the world may
well contain the clue to the manufacture of chloride-f ree powder.
Indeed, D-H Titanium Company's report on its electrolytic titanium powder
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at the May 1980 Kyoto conference stated: "The low chloride content
assures clean melting characteristics and makes the metal ideal for
conversion into powder for use in powder metallurgy applications
re quiring products f ree of internal porosity and having good
weldability." New personnel, with new technical information and new
viewpoints might well solve the trace chloride problem in titanium powder.
Vacuum arc melting and large ingot technology have stood the test of
time f or important parts of the broad titanium field (e.g. for large
forgings and for thick plates), but for strip, particularly alloy strip,
and for tubing, bars and shapes, direct powder conversion would appear to
have signif icant advantages . As described in Chapter 10 sour-crude
tubing could lead to a much larger titanium industry based on civilian
demand and, thus, provide the capacity fly-wheel needed in case of a
national emergency.
Buchovecky, K. E., and Patton,
REFERENCES
Du Pant Patent s
L. W., U.S. Patent 3478136, 11/11/69.
Dombrowski, H. S., U.S. Patent 2984560, 5/16/61.
Dombrowski, H. S., U.S. Patent 3072347, 1/8/63.
Patton, W. L., U.S. Patent 3530210, 9/22/70.
Wartel, W. S ., Wasilewski, R. J., and Pollock, W. I., U. S. Patent 3084042
4/2/63.
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Representative terms from entire chapter:
direct powder
9
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BIBLlOGRAPHIC DATA
SHEET
4. ' ~1c Anti Subtitle
~1.~
Ti tani~nn: Pas t, Present, and Future
7 Auchot(s ) Panel on Assessment of Titanium Availability:
Current and Future Needs
_ .
9. Pcrforming, Organ~zar~on.Name and Address
Nat tonal Materials Advisory Board
National Research Council
2101 Constitution Avenue, N.W.
Washington, D. C. 20418
_
12. Sponsoring Organization .~;ame and Address
Federal Emergency Management Agency
SOO C Street, S.W.
Washington, D. C. 20472
5. S~ppiomentary Notes
16. Abstracts
_
2.
-
3. P
