Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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RD-2Q,40
T~BE F ~ RI ~ TION WIT~ R~LE MUUNDRE~
~a~R~N~ OF THE INVENTION
The present ir.vention relates generally to the fab-
rication of tubes through plasma spray techniques. More par-
ticularly, it relates to the plasma spray forming of articles
of generally tubular configuration employing a reusable man-
drel.
It is known that the plasma spray forming technol-
ogy can be employed in forming articles of a variety of con-
figurations. A number of patents `concern the process of
plasma spray forming of articles employing RF plasma as the
plasma medium. The preparation of titanium alloy base foils,
sheets, and similar articles and of reinforced structures in
which silicon carbide fibers are embedded in a titanium base
alloy are described in U.S. Patents 4,775,547; 4,782,884;
4,786,566; 4,805,294; 4,805,833; and 4,838,337; assigned to
the same assignee as the subject application. The texts of
these patents are incorporated herein by reference.
Preparation of composites as described in these
patents is the subject of intense study inasmuch as the com-
posites have very high strength properties in relation totheir weight. One of the properties which is particularly
desirable is the high tensile properties imparted to the
structures by the high tensile proper~ies of the silicon car-
bide fibers or filaments. The tensile properties of the
structures are related to the rule of mixtures. According to
this rule the proportion of the property, such as tensile
property, which i3 a~tributed to the filament, as contras~ed
with the matrix, is de~ermined by the volume percent of the
filament present in the structure and by the tensile strength
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RD-20,403
of the filament itself. Similarly, the proportion of the
same tensile property which is attributed to the matrix is
determined by the volume percent of the matrix present in the
structure and the tensile strength of the matrix itself.
Prior to the development of the processes described
in the above-referenced patents, such structures were pre-
pared by sandwiching the reinforcing filaments between foils
of titanium base alloy and pressing the stacks of alternate
layers of alloy and reinforcing filament until a composite
structure was formed. However, that prior art practice was
found to be less than satisfactory when attemp~s were made to
form ring structures in which the filament was an internal
reinforcement for the entire ring.
The structures taught in the above-referenced
patents and the methods by which they are formed, greatly
improved over the earlier practice of forming sandwiches of
matrix and reinforcing filament by compression.
Later it was found that while the structures pre-
pared as described in the above-referenced patents have prop-
erties which are a great improvement over earlier structures,the attainment of the potentially very high ultimate tensile
strength of these structures did not measure up to the values
theoretically possible. The testing of composites formed
according to the methods taught in the above patents has
demonstrated that although modulus values are generally in
good agreement with the rule of mixtures predictions, the
ultimate tensile strength is usually much lower than pre-
dicted by the underlying properties of the individual ingre-
dients to the composite. A number of applications have been
filed which are directed toward overcoming the problem of
lower than expected tensile properties and a number of these
applications are copending. These include applications
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Serial No. 445,203, filed December 4, 1989; Serial
No.459,894, filed January 2, 1990; and Serial Nos. 455,041 &
455,048, both filed December 22, 1989. The texts of these
applications are incorporated herein by reference.
One of the structures which has been found to be
particularly desirable in the use of the technology of these
reference patents is an annular article having a metal matrix
and having silicon carbide filament reinforcement extending
many times around the entire ring. Such ring structures have
very high tensile properties relative to their weight partic-
ularly when compared to structures made entirely of metal.
However, it has been found difficult, particularly because of
the very high temperatures which ~ust be used in forming such
articles to produce a ring structure which is dimensionally
very precise in its internal dimensions. Such structures
must be precise in their internal dimensions in order for the
structures to be used most effec~ively in end use applica-
tions inasmuch as the structures are often used as part of a
more complex structure and for this purpose are fitted over
one or a number of elements in a circular form in order to
serve as a reinforcing ring.
One of the structures which is formed has the rein-
forcing filament wound many times and in many layers around
the circumference is a reinforced ring structure. The rein-
forced ring can be used for example as a reinforcing ring forthe compressor blades of a compressor disk of a jet engine.
In order to serve to hold the blades in a compressor stage of
a jet engine a large number of layers of reinforcing fila-
ments are required. It has been found that it is very diffi-
cult to continue to add more and more layers of filamentreinforcement to a ring structure because of differences in
thermal expansion coefficient and other factors. One way in
which this problem has been solved is descri~ed in copending
2 ~ 3 ~ 2 ~33
application Serial No. (Attorney Docket RD-20,406)
filed , the text of which is incorporated herein
, _ .
by reference. The method described in the copending applica-
tion is carried out by forming a series of concentric rings
S which are then assembled together to provide a reinforced
ring structure having more than 100 layers of reinforcement.
Such ring structures may be of quite large diameter of the
order of a foot or several feet and must nevertheless be
nested together within very close ~olerances of only a few
thousands of an inch.
In order to form a nest of reinforced ring struc-
tures, it is desirable to have a set of standard internal
diameters of the rings to be nested so that some standardiza-
tion of the ring structure dimensions can be employed to fac-
ilitate these manufacturing processes and achieve some econ-
omy in the ring manufacture. For example, if an overall
structure is to have an internal diameter of about one foot,
a number of rings having different starting diameters can be
employed to build a set of reinforced structures, each of
which has a thickness of about 0.200 inch. For example, if
an overall ring structure is to have an internal diameter of
12 inches and a total of over 100 plies, it may be desirable
to fabricate the structure using 5 nesting hoops, each having
20 individual plies. Since each ply is about 0.009-0.010
inches thick, each hoop would be -0.200 inch thick. Hence,
the initial ring structures to be nested would have inside
diameters of 12, 12.4, 12.8, 13.2, and 13.6 inches. Each of
these rings can be employed as the s~arting ring for the
deposit of reinforcement and matrix material in layers having
an overall thickness of about 0.200 inch.
What is needed, therefore, is a convenient and eco-
nomical method for producing sets of starting rings having
closely reproducible internaL diameters.
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It is accordingly one object of the present inven-
tion to provide a method by which a plasma spray deposited
ring structure can be produced economically and reliably.
Another object of the present invention is to pro-
vide a method which permits production of plasma spray
deposited ring structures having well defined internal diame-
ters.
Another object is to provide a method which lends
itself to the economic and reliable production of ring struc-
tures which reproducibly have defined internal dimensions.
Other objects and advantages of the present inven-
tion will be, in part, apparent and in part pointed out in
the description which follows.
In one of its broader aspects, objects of the pre-
sent invention can be achieved by providing a mandrel having
a relatively high coefficient of thermal expansion and having
external dimensions slightly smaller than the internal dimen-
sions of the ring structure to be formed. The mandrel is
heated in a plasma flame and is then plasma sprayed with a
protective oxide surface layer such as a layer of aluminum
oxide. Following the deposit of protective oxide on the man-
drel surface, a sprayed deposit of a matrix me~al having a
coefficient of thermal coexpansion substantially smaller than
that of the mandrel is applied to the oxide coated mandrel
surface. The oxide coated mandrel and deposited tube of
matrix metal is then allowed to cool to room temperature.
During the cooling, the mandrel shrinks away from the tube of
matrix metal because of the relatively large difference in
thermal coefficients of their respective materials. The
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oxide coated mandrel surface separates from the ring so that
the ring may be removed from the mandrel. It is observed
that the separation of the ring from the mandrel occurs in
the oxide layer so that the initial oxide layer must be par- -
tially replenished before a second matrix layer is deposited.
Following the removal of the ring of matrix metal, the man-
drel is again heated to a temperature at which a pl~sma spray
deposit of a protective oxide coating and of a matrix metal
layer can be formed on the mandrel. The second ring of
matrix metal is formed on the oxide coated mandrel and this
ring and the contained mandrel are permitted to cool to room
temperature to cause a separation of the ring from the oxide
coated surface.
The process of depositing ring structures on the
lS oxide coated surface is repeated whereby a plurality of
plasma sprayed ring structures having essentially the same
internal diameter is reliably and economically produced.
By providing a set of mandrels of different diame-
ters sets of rings of matrix metal having reproducible diame-
ters may be fabricated.
~RT~ ~L8L~DR~
The detailed description of the invention which
follows will be understood with greater clarity if reference
is made to the accompanying drawings in which:
~GURE 1 is a semischematic isometric illustration of a
mandrel to which a surface coating of a pro~ective oxlde has
been applied;
F~G~RY 2 is a semischematic isometric illustration of
the deposit on the oxide coated mandrel of Figure 1 of a
plasma spray deposit of a matrix metal; and
F~G~ 3 is a semischematic isometric illustration ofthe oxide coated mandrel of Figure 1 being removed from the
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~ O,~
plasma ~pray deposited ring structure after the structures
have been permitted to cool.
DE~T~,EL D~;SCRTPTION Ol~ Tt~E IN~ON
It is known that RF plasma spray deposit of tita-
nium base matrix metal material on a substrate can beemployed to form a foil of the matrix material. Such a pro-
cess is disclosed in U.S. Patent No. 4,838~337. Numerous
other structures have ~een formed by the plasma spray deposit
of a metal on a substrate and there is extensive patent and
technical literature on such processes. However, where the
substrate is a mandrel, the conventional process for removal
of the mandrel is either the machlning of the mandrel out
from within the plasma spray deposit or the chemical
dissolution of the mandrel from within the plasma spray
deposit.
The subject process is one by which the mandrel and
the deposited ring structure spontaneously and automatically
separate from each other so that the ring structure can be
removed from the mandrel on which it is deposited without re-
course to chemical dissolution agents or machining or othermetal working techniques.
The techniyue by which the accomplishment of the
production of a plurality of plasma spray deposited ring
structures with essentially the same internal dimensions is
achieved is dependent on a combination of actions. One such
action is the coating of the mandrel surface with an oxide
surface coating to serve as a release agent for the separa-
tion of a plasma spray deposited material from the substrate
on which it is deposited.
The second action on which the process depends is
the provision of a mandrel which ha-~ a sufficiently large
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thermal coefficient of expansion relative to that of the ma-
trix material which is plasma spray deposited thereon that
the mandrel tends to shrink away from the internal surface of
the plasma spray deposited ring structure formed thereon. It
is this combination of elements of the applicant's process
which makes possible the repeated production of ring struc-
tures having essentially the same internal diameter from a
single starting mandrel structure.
Some of the advantages of the present invention can
be best understood if considered in relation to a production
process with which the instant invention may advantageously
be used.
The illustration is gi~en above of the need for
production of a set of rings which may be nested together in
concentric fashion to produce a single ring having a rela-
tively large number of filament reinforcement layers in
excess of one hundred such layers. For this purpose a set of
five concentric rings each having about twen~y layers of fil-
ament reinforcement is illustratively discussed in the back-
ground statement of the invention. Each of the five ringshas a different interval diameter and differs by about 0.4
inch from the internal diameter of the ad~acent ring, whether
it is larger or smaller.
What i5 desired in order to produce such a set of
filament reinforced rings, and what is made possible by the
present invention, is the productlon of starting matrix
structures which have initial diameters which are reliably
reproducible within close tolerance of a predetermined ini-
tial diametric dimension. In other words if a ring structure
having a 12 inch ID (internal diameter) is sought the method
of the present invention provides for production of a ring
structure having an internal diameter of 12 inches within a
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R~-?0~403
very close tolerance. And the same production capability
exists for rings of 12.4; 12.8; 13.2 and 13.6 inches.
The production of a singie such ring structure is
described now with reference to the figures. Referring first
now to Figure 1 mandrel 10 is provided having an external
diameter slightly s~aller than the diameter of the ring to be
produced. The mandrel 10 is preferably thick walled or solid
as illustrated in Figure 1. This wall thickness is preferred
in order to avoid distortion of the mandrel shape to out-of-
round due to the sequence of heating and cooling steps as themandrel is used over and over again. The mandrel is first
plasma sprayed with a protective oxide layer using a conven-
tional plasma gun 12 and using an-oxide powder such as alumi-
num oxide, magnesium oxide or some similar oxide. To form an
oxide surface deposit 14 on mandrel 10 with the aid of a con-
ventional plasma flame 16. we have demonstrated such oxide
coatings to be adherent and to form a persistent coating on a
m~tal surface such as the surface of mandrel 10.
The oxide coated mandrel is next introduced into a
low pressure RF plasma deposition chamber (not shown) where
the mandrel 10 is mounted for rotary movement under a plasma
flame 20 emanating from an RF plasma gun 18. Such an RF gun
may be one as described in the patents, such as the U.S.
Patent 4,782,884, discussed in the background statement of
this application. Preferably it is one such as is described
in copending application Serial No. (Attorney Docket
RD-17,823), filed
The RF plasma gun 18 is used to deposit a layer 22
of a titanium base metal such as Ti-6242 (titanium 6 alum-
inum-2 tin-4 zirconium-2 cobalt) onto the oxide coated sur-
face 14 of mandrel 10. the layer formed may be for example
about 1/8 inch thick. The preferred thickness of the layer
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is dependent on a few factors. One factor is that the ring
formed must be self supporting and the thickness of the layer
must be sufficient so that it provides a ring with a wall
thickness sufficient to be supporting. Another factor is the
planned use of the ring. If the outer surface of the ring is
to be machined, an additional thickness to allow for the
metal to be removed by machining should be included.
For reasons explained more fully in copending
application Serial No. (Attorney Docket RD-20,406)
filed _ , the inner position of a deposited ring of
matrix metal is a sacrificial portion of a reinforced ring
structure to serve as one member of a set of rings to be
nested concentrically and to be HIP consolidated into a ring
of over 100 layers of filament reinforcement. It is a sacri-
ficial portion in that it is machined out of the interior ofa 20 layer component ring of the set after the 20 layers of
reinforcement have been added but before the five component
rings are assembled in concentric array and consolidated into
a super ring or a single ring of over 100 layers.
The innermost layer of the matrix m~tal of each of
the rings to be assembled is sacrificed, i.e., machined and
discarded, in order to increase th~ volume fraction of fila-
ment of each component ring of the set.
Following the deposit of the layer 22 of matrix
metal the ring and mandrel are allowed to cool. The ring 22
separates spontaneously from the mandrel and slides off the
mandrel as illustrated in Figure 3.
The subject method and the way it may be carried
into effect is illustrated by the following example:
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A hollow ring of mild steel having a length of 4"
and a diameter of 4" was provided. The steel had a coeffi-
cient of thermal expansion of approximately 14 x 10-6 c-i
The hollow ring was mounted for air plasma spray depositing
of a 0.003"-0.005" thick surface coating of aluminum oxide
thereon. The plasma gun employed was a Metco 3MB using the
spray conditions suggested by Metco.. The mandrel was first
heated with the plasma flame and then the layer of aluminum
oxide was spray deposited thereon.
Following the air deposition of the aluminum oxide,
the mandrel was introduced into a low pressure RF plasma
deposition chamber similar to those described in the U.S.
Patents and applications referred to in the background state-
ment above. The oxide coated hollow ring was again heated by
the plasma torch to a suitably high temperature for deposit
thereon of a matrix metal. The matrix metal applied was a
titanium base alloy and specifically Ti6242 (Ti-6Al-2Sn-4Zr-
2Mo). The thermal coefficient of expansion of the deposited
titanium base alloy matrix metal was approximately 11 x 10-6
C-1.
Follow~ng deposit of approximately 0.12S~ thickness
of the titanium base alloy matrix, the mandrel and lts coat-
ings of oxide and metal were allowed to cool to room tempera-
ture and were removed from ~he low pressure plasma deposition
chamber.
On removal from the cham~er, it was found that the
collar of matrix metal had separated spontaneously and auto-
matically from the oxide coated mandrel so that it was possi-
ble to s1ide the collar off the mandrel without the employ-
ment of chemical agents or machining or other destructive in-
vasive steps.
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It will be appreciated that the operation of the
present method is dependent both on the coating of the man-
drel with a nonreactive oxide coating and on the existence of
a significant difference in thermal coefficient of expansion
between the metal of the mandrel and the matrix metal
deposited on the oxide coated portion thereof. Significant
differences of thermal coefficient of expansion of are
required for satisfactory operation of the presen~ invention
and preferably the differences in thermal coefficient of
expansion should be as high as feasible.
Following the deposit of the titanium base metal
collar and its removal from the oxide coated mandrel, the
mandrel was again re-sprayed with additional A12O3 to make up
for the amount which was incorporated in the matrix ring when
it separated from the oxide coated mandrel. The mandrel wi~h
its fresh coating of oxide was introduced into the low pres-
sure plasma deposition chamber and heated in preparation for
deposit of a second collar of matrix metal thereon. The
matrix metal of the same titanium alloy was formed on the
surface of the mandrel and again the mandrel and collar were
permitted to cool to room temperature and then removed from
the low pressure plasma deposition chamber. Again, the col-
lar separated spontaneously from the oxide coated mandrel and
was removed from the mandrel without the aid of mechanic~l or
chemical agents.
The internal diameter of the two collars formed as
described in the example were measured and were found to be
the same within 0.003-0.005 inch.
The foregoing demonstrates that it is possible to
introduce a multiplicity of ring structures having essen-
tlally the same internal diameter by the process of the sub-
ject invention.
