Title of Invention

METHOD FOR THE MANUFACTURE BY POWDER METALLURGY OF SHAPED PARTS TO BE ASSEMBLED BY SELF-BRAZING AT A SPECIFIC TEMPERATURE WITH RECEIVING METAL PARTS MADE FROM SUPERALLOY

Abstract Method for the manufacture by powder metallurgy of shaped parts to be assembled by self-brazing at a specific temperature with receiving metal parts, made from superalloy, said manufacturing method using two metal powders, - a first alloy powder, called the "basic powder" making it possible to obtain the desired metallurgical characteristics and essentially not containing melting element - and a second alloy powder, called the "brazing powder" containing at least one so-called melting element with a content such that the liquidus temperature of the brazing powder alloy is lower than the solidus temperature of the basic powder alloy, said basic and brazing powders being chosen so that the liquidus temperature of the brazing powder is lower than the self-brazing temperature and the solidus temperature of the basic powder is above the self-brazing temperature, - said manufacturing method comprising the following stages: c) preparing of a homogeneous mixture of basic powder, brazing powder and a liquid binder or a binder in the melted state, wherein the chemical composition of the basic powder corresponds to a superalloy based on Ni, Co or Fe and that of the brazing powder to a basic alloy of Ni, Co or Fe in which the melting element is Si and/or B and wherein the binder is chosen so that it can assume a consistency under controlled conditions, d) moulding-injection of said mixture into a mould of the shaped part to be made, moulding being maintained under temperature, pressure and time conditions such that the binder assumes the consistency, c) extraction of the moulded blank from the mold, d) binder removal, e) sintering of the binder-removed blank at a temperature above the liquidus temperature of the brazing powder, but below the subsequent self-brazing treatment temperature so as to obtain a shaped part suitable for self-brazing and whose relative density is at least 95%, but lower than 100%.
Full Text

The present invention concerns a method using powder
metallurgy for producing moulded parts intended to be
assembled by self-brazing to metal parts capable of
receiving them and said receiving parts.
It also concerns a method for assembling such moulded
parts to receiving metal parts.
In the continuation of the present document, the term
"self-brazing" means the autogenous brazing of the moulded
part on the receiving metal part, the elements effecting
brazing being contained in the moulded part.
The operation of self-brazing of the moulded part on
the metal part may comprise or be followed by a diffusion
heat treatment in the solid state, thus constituting what
is commonly termed a brazing-diffusion operation, which
treatment is intended to homogenize the composition and the
structure of the moulded parts and of the area of
connection by self-brazing.
From Patent EP 0 075 497 there is known a method for
assembly by brazing-diffusion of metal parts, such as
components made of superalloy for gas turbines, which
consists in interposing between the surfaces to be
assembled a connecting layer of overall composition
corresponding to a superalloy, and in carrying out a
brazing-diffusion treatment on this assembly.
The connecting layer consists of an intimate mixture
of two alloy powders, the first powder, termed "basic
powder", being a superalloy powder, and the second powder
being a brazing powder of Ni-Co-Si-B alloy the liquidus
temperature of which is below the solidus temperature of
the mechanical parts and of the basic powder.
The relatively low melting temperature of the brazing

powder is provided by its content of Si and/or of B.
In the continuation of the present document, the term
"melting element" designates an element such as, by way of
non-limiting example, silicon or boron, which substantially
lowers the solidus temperature of the alloy into which it
is introduced.
The brazing-diffusion operation is carried out at a
temperature such that the brazing powder melts and, flowing
between the basic powder grains, makes it possible to
decrease the porosity very rapidly and to obtain a compact
connecting layer independently of the volume of powder
employed.
The application of the temperature is then maintained
to diffuse the melting element or elements B and Si. The
homogenization of the composition resulting from such
diffusion raises the liquidus temperature of the melted
areas which solidify while the temperature is maintained,
diffusion continuing in the solid state.
The result at the end of the brazing-diffusion
operation is a homogeneous and dense structure with an
absence of discontinuity between the parts to be assembled.
The same document EP 0 07 5 497 gives several examples of application to superalloys based oh nickel or based on
cobalt.
One of the examples concerns the reconditioning of a
fixed turbine blade, made of cobalt-based alloy KC25NW
according to the AFNOR designation, cracked by thermal
fatigue.
For that, a paste containing an intimate mixture of
the basic powder of Co superalloy, the brazing powder of
Ni-Co-Si-B alloy and a volatile binding agent is applied in
the previously cleaned and/or widened crack.
The binding agent of the type consisting of a solution
of acrylic resin in the monomer of the latter is eliminated
by pyrolysis during the brazing-diffusion treatment at
1200°C.

The document EP 0 075 497 also provides for it being
possible to apply, instead of a paste, a strip or tape
obtained by lamination of an intimate mixture of basic and
brazing powders and of acrylic resin.
Patent EP 0 075 497 also provides for it being
possible to add on an elementary part of simple shape in
the form of a pre-sintered blank obtained from the mixture
of basic and brazing powders, the surface of the pre-
sintered blank acting as the connecting layer.
The patent cites in particular as application the
plugging of hub support holes on hollow turbine blades,
made of alloy NK15CADT according to the AFNOR designation,
coming from the foundry. For that, there is introduced
into the hole a plug consisting of a pre-sintered blank
containing 75% by weight of basic powder of alloy NK17CDAT
according to the AFNOR designation, and 25% by weight of
brazing powder of Ni-Co-Si-B alloy, and self-brazing is
carried out at 1200°C for 15 minutes.
The use of the method described in that patent is
nevertheless subject to a certain number of limitations.
The use of pastes or tapes containing, in addition to
the basic and brazing powders, a binding agent which it is
necessary to decompose and the decomposition products of
which must be eliminated during brazing-diffusion, requires
the use of furnaces capable of eliminating large quantities
of gas coming from the pyrolysis of the binding agent.
Such furnaces are poorly suited to the brazing-diffusion
operation which takes placed at around 1200°C and generally
under vacuum.
Another problem to be solved is the production of
elementary parts in the form of pre-sintered blanks. The
document EP 0 075 497 does not indicate any method for
producing such blanks and envisages only simple shapes.
The shaping of the blanks may be envisaged by uniaxial
cold compacting, but this method does not make it possible
to produce very slender or thin shapes of homogeneous

density because of friction between powder grains or
between grains and walls of the compacting die. Moreover,
in order to limit the friction, lubricants of the zinc stearate type or similar are used as additive to the
powders; these lubricants are capable of introducing zinc
into the blank, this element having a harmful effect on the
service life of the superalloys.
Other methods for shaping the blanks are in fact used,
such as plasma spraying onto a rotating substrate and
cutting of tapes by laser.
Plasma sprayin makes it possible to produce blanks of
tubular shape generated by rotation, by spraying metal
powder onto a rotating cylindrical mandrel. Such a method
has a very low yield, around 90% of the sprayed powder
being sprayed elsewhere than onto the rotating mandrel,
which severely affects the cost of producing the blanks,
taking into account the extremely high cost of the metal
powders sprayed. Furthermore, this method does not ensure
clean edges at the end of the blank, which necessitates re-
cutting and further increases the cost of the parts.
The laser cutting of tapes obtained by slip casting,
elimination of the solvent and sintering, makes it possible
only to obtain relatively thin flat parts. The losses
resulting from the laser cutting, however, are high and
represent 2/3rds of the material employed.
The consolidation of self-brazing pre-sintered blanks obtained by powder metallurgy is described in US Patent
4. 937,042 which concerns the production of fixed facing
friction parts of the fins of gas turbines. The blanks
consist of a mixture of a first superalloy powder of the M-
Cr-Al or M-Cr-Al-Y type not containing Si, and of a second
powder of the M-Cr-Al-Si type containing around 10% by
weight of Si, the element Si being the melting element and
M representing the element Co or the element Ni or a
combination of these two elements. The blanks are pre-

sintered at a temperature below the solidus temperature of
the second powder.
The consolidation brought about by such pre-sintering
is very limited, taking into account the low sintering
capacity of the superalloys. The blanks thus obtained are
therefore not easily handled.
An endeavour has been made in the present invention to
produce moulded parts intended to be assembled by self-
brazing to receiving metal parts, the moulded parts being
able to be of very varied and even complex shapes and
having relatively precise dimensional characteristics, and
being obtained by a powder metallurgy method having a high
yield, that is to say, the ratio between the mass of the
moulded part obtained and the mass of metal powders
employed in order to do this is close to 1.
An endeavour has also been made to produce moulded
parts having a controlled relative density close to 1, the
density of which is homogenous in the volume of the part
and containing no harmful elements or "poisons" for the
wear characteristics of these parts.
An endeavour has also been made to produce relatively
slender solid moulded parts the length/width ratio of which
is, for example, at least 5 and relatively thin hollow
moulded parts the diameter/thickness ratio of which is, for
example at least 10.
The subject of the present invention is firstly a
method using powder metallurgy for manufacturing moulded
parts intended to be assembled by self-brazing to receiving
metal parts.
The method employs two metal powders, a first powder
termed "basic powder" making it possible to obtain the
desired metallurgical characteristics, and a second powder
termed "brazing powder" made of alloy including a melting
element at a content such that the liquidus temperature of
the brazing powder is below the solidus temperature of the
basic powder, the basic powder not including in its

chemical composition any voluntary addition of melting
element.
The chemical composition of the basic powder may if
necessary be obtained from a mixture of powders.
The chemical composition of the basic powder and that
of the brazing powder make it possible to define a self-
brazing temperature which is higher than the liquidus
temperature of the brazing powder and below the solidus
temperatures of the basic powder and the receiving part.
The method according to the invention comprises the
following sequence of steps:
a) a homogenous mixture of basic metal powder, brazing powder and a liquid binding agent is prepared.
By binding agent there is understood here a
constituent or a group of constituents making it possible
to bind the metal powder grains to one another to form a
mixture of homogeneous appearance.
The binding agent in the continuation of the present
document may comprise additives intended, for example, to
facilitate the dispersion, the suspension of the metal
powders, or to improve other characteristics of the
mixture.
The qualifying adjective "liquid" for the binding

agent comprises the molten state and corresponds to various consistencies that can be characterized by their viscosity.
The binding agent is selected to be able to gain
consistency when it is desired. By that there is to be
understood assuming a state capable of retaining a shape
contrary, for example, to the liquid state.
b) The mixture thus prepared is injected into a mould of
the moulded part to be produced, while applying an
appropriate pressure to the said mixture.

The geometry of the mould is adapted to that of the
moulded parts to be produced, taking into account the
dimensional variations resulting from the method, which
dimensional variations a person skilled in the art is able
to predict from experience or take account of from
preliminary tests.
The moulding is maintained in conditions of
temperature, injection pressure and time such that the
binding agent gains consistency.
c) Once the binding agent has become consistent, the
moulded blank is removed from the mould.
d) The binding agent is eliminated from the moulded blank
by a known appropriate means or combination of means such
as, for example, physical, thermal or chemical means. This
step is termed "binding agent elimination" and the blank
which emerges from it is termed "with binding agent
eliminated".
e) The blank with binding agent eliminated is subjected
to a sintering treatment intended to densify it to a
relative density of at least 95%,sintering being carried
out at a temperature higher than the liquidus temperature
of the brazing powder but below the temperature of the
subsequent self-brazing treatment.
The condition regarding the minimum sintering
temperature makes it possible to ensure the sintering in
the liquid phase necessary for obtaining moulded parts
having a relative density close to unity, even in the case
of basic powders having a low sintering capacity, a high
density after sintering making it possible to limit
dimensional changes during self-brazing.
The condition regarding the maximum sintering
temperature makes it possible to ensure the formation of a

sufficient quantity of liquid phase during self-brazing to
assemble the moulded part reliably to the receiving part.
The self-brazing conditions themselves are known to a
person skilled in the art of this type of assembly.
The sequence of steps of the method of the invention,
namely, preparation of an injectable mixture, moulding,
extraction, elimination of the binding agent and sintering,
corresponds schematically to those of a method for
injection moulding of powdery metallic materials, which
method is designated by MIM, an abbreviation of "metal
injection—moulding".
Variants of such MIM methods are described for example in the patents US 4,197,118, WO 88/07902 and WO 88/07903.
The MIM techniques described in those patents filed 10
to 20 years ago are used to produce finished parts having
a relative density very close to unity, and a person
skilled in the art was until now in no way incited to
transpose these techniques to obtain components having
characteristics opposed to the characteristics associated
with the products resulting from the MIM techniques, the
products obtained by the method of the invention being
"semi-finished", not completely densified and intended to
undergo partial fusion when they are made use of.
Advantageously, but not exclusively, the method of the
invention applies to basic metal powders of superalloys
based on Ni, Co or Fe. The brazing powder is then an alloy
of Ni, Co or Fe in which the melting element is Si, B or
both these elements at the same time.
Preferably, the brazing powder contains, in the case
where the element Si is used alone or in combination as
melting element, 2 to 12% by weight of Si.
Preferably, in the case where the element B is used
alone or in combination as melting element, the brazing
powder contains 1 to 5% by weight of B.
Preferably, the alloy of the brazing powder is
selected from the following list of alloys: Ni-Si, Ni-B,

Ni-Co-Si, Ni-Co-B, Ni-Co-Si-B, Ni-Cr-Al-Si, Ni-Co-Cr-Al-Si,
Ni-Cr-B, Ni-Co-Cr-B.
In the alloy of the brazing powder, the unspecified
elements are present in their customary content, taking
into account the base materials used and the methods for
preparation of the alloy.
Preferably, the percentage by weight of brazing powder
in relation to the whole of the two metal powders is
between 5 and 40% and depends on the nature of the two
powders.
Preferably again, the charge of metal powders is at
least 50% by volume in the mixture produced with the
binding agent.
As indicated above, different variants of the MIM
method may advantageously be employed in the method of the
invention.
The mechanism of gain of consistency of the blank in
the mould may, according to a first variant of the method
of the invention, be a physical liquid-solid change of
state of the binding agent obtained by maintaining the
mould at a temperature below the temperature of said change
of state.
The temperature of the mould is of course selected
such as to produce the solidification of the binding agent
in spite of any possible supercooling phenomena and while
taking account of the influence of the presence of any
additives in the binding agent.
According to a sub-variant of this first variant of
the method of the invention, the binding agent may be or
comprise a thermoplastic resin, the binding agent/metal
powders mixture then being prepared at a temperature higher
than the melting temperature of the binding agent and
injected into the mould also at a temperature higher than
this melting temperature.
According to another sub-variant of this first variant
of the method of the invention, the binding agent may be an

aqueous or non-aqueous system liquid at ambient
temperature, and the mixture prepared with the metal
powders is injected into a mould cooled to a temperature
below the solidification temperature of the binding agent.
The step of elimination of the binding agent in this
sub-variant comprises an operation of lyophilization or
sublimation of the binding agent.
According to another variant of the method of the
invention, the binding agent is a thermosetting resin and
the mechanism of gain of consistency of the binding agent
is an accelerated polymerisation of the resin, for example
in a heated mould.
According to yet another variant of the method of the
invention, the binding agent is capable of a sol-gel
reaction which is employed during the moulding step. The
step of elimination of the binding agent then comprises an
operation of putting the binding agent, or its essential
constituents, back into solution.
Advantageously, in these different variants of the
method of the invention, the step of elimination of the
binding agent may comprise an operation of putting into
solution at least one component of the binding agent by the
chemical action of a solvent of the component or
components.
When the binding agent comprises a polymer, the step
of elimination of the binding agent may advantageously
comprise an operation of depolymerisation of said polymer
by the chemical and/or catalytic action of a specific
agent.
Again advantageously, the step of elimination of the
binding agent may comprise more than one operation, the
final operation being an operation of thermal elimination
of the binding agent.
Very advantageously in this case, the operation of
thermal elimination of the binding agent continues up to a
temperature ensuring the start of consolidation or "pre-

sintering" of the metal powders. This pre-sintering makes
it possible to handle the blanks with binding agent
eliminated, without risk of breakage, before subjecting
them to the sintering step intended to densify them.
In the continuation of the present document, the term
"sintering" is reserved for the operation which transforms
the "blanks" with binding agent eliminated into low
porosity self-brazing moulded parts knowing that, during
self-brazing, the physical process of sintering and
elimination of the residual porosity continues in the
moulded parts.
Preferably, in order to permit the pre-sintering of
the blanks with binding agent eliminated, the thermal
elimination of the binding agent is terminated at a
temperature within the melting range of the brazing powder
and very preferably in the lower half of the range.
Still more preferably, the sintering step is carried
out at a temperature approximately 50°C below that of the
subseguent self-brazing operation.
Optionally, the operation of thermal elimination of
the binding agent and the sintering step may be carried out
successively in the same furnace without a return to
ambient temperature between these two operations or steps.
The moulded parts obtained after sintering have very
regular dimensions which reguire little or no dimensional
retouching by machining to be able to fit the receiving
parts and produce a solid self-brazed assembly.
Owing to the forced elimination of the binding agent
during binding agent elimination, the moulded parts
resulting from the method of the invention do not contain
any chemical element other than those which constitute the
metal powders employed.
The present invention also covers a method of assembly
of the self-brazing moulded parts, obtained by the
manufacturing method according to the invention, to
receiving parts which are superalloy components of


aeronautic or land gas turbines.

According to this method of assembly, the alloy of
which the basic powder consists is selected for its
compatibility with the superalloy of the receiving parts,
and the moulded part is pre-assembled to the receiving part
by arranging it in contact with or at a small clearance
from the receiving part. This may impose known conditions
regarding the shape and dimensions of the moulded part and
of the facing portions of the receiving part.
The pre-assembly between these two parts is then
brought to a temperature higher than the liquidus
temperature of the brazing powder and below the solidus
temperature of the basic powder and of the receiving part
in order to carry out self-brazing.
Preferably, and in particular during the application
of the method to the repair of parts, the self-brazing
treatment is followed directly, or after returning to
ambient temperature, by a diffusion treatment intended to
diffuse the chemical elements, and especially the melting
element or elements, and to homogenize the structure of the
repaired area.
The following figures illustrate in a non-limiting
manner an example of a moulded part and examples of
implementation of the manufacturing and assembly methods of
the invention.
Figure 1 shows a self-brazing moulded part of the
annular bush type made of superalloy.
Figure 2 is a diagram of the steps of a first variant
of the manufacturing method according to the invention of
the bush in Figure 1, which variant employs a thermoplastic
resin.
Figure 3 is a diagram of the steps of a second variant
of the manufacturing method according to the invention of
the bush in Figure 1, which variant also employs a
thermoplastic resin.
Figure 4 is a diagram of the steps of a third variant

of the manufacturing method according to the invention of
the bush in Figure 1, which variant employs a binding agent
liguid at ambient temperature.
Figure 1 shows a tubular self-brazing bush 1 made of
nickel-based superalloy.
Its outside diameter D is of the order of 12 mm and
its thickness e of the order of 0.6 mm. It is therefore a
thin part with a high D/e ratio, of the order of 20. Its
height h is of the order of 10 mm.
Since the bush is intended to be self-brazed in a
blind hole of an aeronautic gas turbine blade made of
superalloy having the commercial designation Rene 77 (Ni
alloy of type NK15CDAT) , the tolerance on its outside
diameter is very tight, of the order of a few hundredths of
a mm, so as to centre the bush perfectly, to limit its
geometric distortions during self-brazing and to facilitate
its connection to the receiving part, i.e. the turbine
blade.
The bush 1 is made of nickel-based superalloy by the
powder metallurgy method according to the invention by
means of two metal powders, a basic powder A and a brazing
powder B.
The basic powder A is a known alloy powder having the
commercial designation Astroloy (NK17CDAT according to the
AFNOR designation). This material is completely compatible
with the Rene 77 superalloy of the blade, especially from
the point of view of solidus temperature and mechanical
characteristics.
The solidus temperature of the basic powder A is
1240°C. Its liquidus temperature is 1280°C.
The brazing powder B used to carry out the sintering
of the Astroloy powder and self-brazing with the blade is
an Ni-Co-Si-B alloy powder containing, by weight, 17% Co,
4% Si, 2.7% B.
The solidus temperature of the brazing powder B is
965°C. Its liquidus temperature is 1065°C and is below the

solidus temperatures of the basic powder A and of the
blade.
These data make it possible to define a self-brazing
temperature of 1200°C which is higher than the liquidus
temperature of the brazing powder but which is below the
solidus temperature of the blade made of Rene 77 and that
of the Astroloy powder A.
Figure 2 describes a first variant of implementation
of the method according to the invention.
The two metal powders A and B are powders with
spherical grains atomized with argon and their particle
size grading is 53 µm or less.
The two metal powders A and B are pre-mixed with one
another under an inert atmosphere. The pre-mixing of the
two metal powders A and B is designated by (A+B).
The proportion by weight of Astroloy powder A to the
brazing powder B is 3:1, which corresponds to a percentage
by weight of 25% of powder B in the pre-mix (A+B) of the
two metal powders.
According to this first variant, a paste-like mixture
is prepared from the two pre-mixed metal powders (A+B) with
a binding agent L melted at around 180°C in a mixer under
inert gas.
The binding agent L consists of a mixture of wax C and
of thermoplastic resin R, for example of the polyethylene
or polypropylene type.
The charge by volume of metal powders (A+B) in the
mixture is 70%.
The homogeneous mixture obtained is cooled and ground
to constitute granulates.
The granulates obtained may be handled and stored
without any problem at ambient temperature, the grains of
metal powders being coated with solidified binding agent.
In the following step of injection moulding, the
granulates are introduced into the Archimedean screw of a
press of the type for injection moulding objects made of

synthetic material, the Archimedean screw being heated to
around 180-200°C so as to melt the binding agent of the
granulates and to obtain a metallic paste, the viscosity of
which is between 10' and 107 cpoise and which is therefore
suitable for being injected by the Archimedean screw into
a mould.
The mould, produced from tool steel, is composed of
two parts bearing one upon the other by a joining plane,
the two parts, when they are placed upon one the other,
delimiting an annular cavity or impression into which the
metallic paste is injected by means of the Archimedean
screw.
The dimensions of the impression of the mould are
those of the bush to be produced except for a coefficient,
the blank undergoing dimensional variations during the
subsequent manufacturing operations, especially shrinkage
during sintering.
In the case of the bushes in Figure 1, the impression
therefore has dimensions equal to 1.15 x those of the bush.
The shrinkage may not be isotropic; to define the
dimensions of the mould, different shrinkage coefficients
are then applied according to the directions.
A person skilled in the art can predict these
dimensional variations, if necessary by means of some
preliminary tests intended to take into account the
influence in particular of the characteristics of the metal
powders and of the binding agent used, of the charge of
metal powders in the mixture, and of the sintering
conditions.
The mould is maintained at the temperature of the
order of 45°C to permit both correct filling of the
impression and the solidification of the metallic paste in
about 1 minute.
Once the blank has solidified, the two parts of the
mould are separated and the blank is extracted from the
impression.

The construction of the mould should take into account
the constraint of being able to extract the moulded blanks
without damaging them, but taking into account such a
constraint is known in the field of injection moulding.
The following step of the method according to Figure
2 is the elimination of the binding agent, which is carried
out in two successive operations.
A first operation is chemical binding agent
elimination, DCS, by the action of a solvent which is
hexane and which dissolves the wax of the binding agent.
This binding agent elimination is carried out in the vapour
phase and in the liquid phase by immersion.
The second operation of binding agent elimination
carried out is thermal binding agent elimination, DT, in a
furnace under a hydrogen atmosphere.

This second operation first comprises a rise and then
maintaining around 400-500°C where pyrolysis of the
thermoplastic resin not dissolved by the hexane takes
place.
Pyrolysis in a hydrogenated medium leaves almost no
residue of the binding agent.
The blank is extremely porous at that moment, the
pores occupying the volume left free by the departure of
the binding agent. The grains of metal powders have only
a low cohesion between them, which means that the blank is
sensitive to shocks and is not easily handled.
The temperature is then raised in the thermal binding
agent elimination furnace to 1000°C in order to carry out
pre-sintering of the blanks with binding agent eliminated.
At this temperature, higher than the solidus temperature of
the brazing powder B (965°C) and located at l/3rd of its
melting range, the powder B melts partially and the liquid
phase from B infiltrates the surface of the unmelted powder grains, especially those of the basic powder A, forming
metallic bridges between the grains and thereby effecting
the consolidation of the structure.

The blanks are maintained at 1000°C for around 10
minutes, then cooled to ambient temperature.
Pre-sintering at a lower temperature, slightly below
the solidus temperature of the brazing powder B, for
example at 950°C, would not permit the formation of metallic
bridges and the blanks would be too fragile to be able to
be handled subsequently, taking into account their very
slight thickness, less than a mm.
Pre-sintering at a temperature higher than 1000°C would
result in the formation of too much liquid phase at the
pre-sintering stage.
A relatively slow rise to 1000°C also contributes to
the quality of the pre-sintering. A speed of the rise of the order of 500°C/hour gives satisfactory results.
After this operation of thermal elimination of the
binding agent, the blanks are introduced into the sintering
furnace, which is a vacuum furnace.
Sintering is carried out by a rise in stages to 800°C,
then by a rise to 1150°C, or a temperature above the
liquidus temperature of the brazing powder B and 50°C below
the temperature envisaged for the self-brazing of the
bushes on the blade made of Rene 77.
The bushes are maintained at 1150°C for 15 minutes.
These conditions are sufficient to obtain forced
densification of the parts to more than 96% while retaining
sufficient potential for formation of the liquid phase
during self-brazing.
After cooling to ambient temperature, accelerated by
the introduction of argon into the furnace, the annular
bushes are checked and if necessary retouched by
rectification if, in particular, their outside diameter is
too large for their use.
Figure 3 describes a second variant for manufacturing
the annular bushes in Figure 1.
A homogeneous mixture is prepared from the same two
metal powders (A+B) pre-mixed with a melted binding agent

L which this time consists of a thermoplastic resin,
polyacetal, the charge of metal powders being 65% by volume
in the mixture. The mixture is granulated as in the first
variant.
As in the first variant, the granulates are heated
until the binding agent melts and are injected into the
mould of an injection moulding press.
After their extraction from the mould, the solidified
moulded blanks undergo catalytic binding agent elimination,
DCa, at 110°C by means of gaseous HNO3.
This agent depolymerizes the polyacetal which is
transformed into a gaseous monomer, formaldehyde, which is
evacuated.
This step of catalytic elimination of the binding
agent makes it possible to eliminate the binding agent
almost completely, the operation of thermal elimination of
the binding agent therefore being rendered unnecessary.
The blank with binding agent eliminated is then directly sintered in a furnace under vacuum at 1150°C as for
the first variant.
Figure 4 describes a third variant for manufacturing
the annular bushes in Figure 1.
This time, a mixture is prepared from the same metal
powders (A+B) pre-mixed with a binding agent L which is
liquid at ambient temperature.
The binding agent L may be an aqueous or non-aqueous
system.
In the case where an aqueous system is used, the major
constituent of the binding agent is water, additives to the
water improving the dispersion and the suspension of the
metal powder grains, making it possible to condition the
viscosity of the mixture at ambient temperature or having
a cryo-protective role. Patent Application WO 88/07902
describes such aqueous systems.
The metallic slip thus constituted with the aqueous
system L and a charge of the order of 60% of metal powders

(A+B) has a viscosity of between 103 and 104 cpoise and may
be conserved in closed receptacles before injection
moulding.
The injection moulding operation is then carried out
in a mould made of tool steel cooled to -40°C or to a lower
temperature.
Patent EP 587 483 describes a press for injecting such
slips and in particular the injection head of the press. Patent EP 626 224 describes a device for carrying out
the moulding of such slips at temperatures below ambient
temperature without causing frosting of the surface of the
impression or of the joining plane of the mould.
The use of a non-aqueous system as an alternative to
an aqueous system is described in Patent Application WO
88/07903.
It is possible, for example, to use cyclohexane with
additives such as a dispersant for dispersing the metal
powders, and a colloid for conditioning the viscosity of
the mixture.
The mould is in this case maintained at a temperature
of the order of -20°C.
Whether the binding agent L is an aqueous system or a
non-aqueous system, the metallic ice blocks extracted from
the mould after solidification of the slip are kept at a
low temperature and then the binding agent is eliminated in
two operations.
The first operation of elimination of the binding
agent is a known lyophilization operation, the water or the
cyclohexane being eliminated by sublimation during this
operation.
The second operation of elimination of the binding
agent is a thermal binding agent elimination which makes it
possible to burn the additives to the water or to the
cyclohexane which have not been eliminated during
lyophilization.
The thermal binding agent elimination is conducted in

the same manner as in the case of the variant of Figure 2,
and also makes it possible to pre-sinter the blanks
obtained by finally rising to 1000°C.
The sintering step is also carried out in the same
manner as for the variant of Figure 2.
The method for manufacturing self-brazing moulded
parts according to the invention is not of course limited
to the variants described above.
The results obtained on the annular bush in Figure 1
manufactured according to the invention by the variant of
Figure 2 are as follows:
Absolute density of the sintered bush : 7.83, or a
relative density of 98%.
Carbon content of the bush = 0.03%,
Grain size = n°6.5 according to specification ASTM
E112,
Typical deviation on inside diameter = 0.01 mm,
Mean deviation of circularity on inside diameter.
The deviation of circularity is taken as equal to the
difference between maximum diameter and minimum diameter
over a same section.
The mean deviation is taken as equal to the average of the
deviations over a same batch of parts.
The mean deviation of circularity on the inside diameter
measured at 25% of the height of the bush is 0.02 mm.
The mean deviation of circularity on the inside diameter
measured at 75% of the height of the bush is 0.03 mm.
A rapid description will now be given of the method of
assembly according to the invention by means of the same
example.
There is produced in the turbine blade made of Rene 77
superalloy a bore of very precise diameter, with a
tolerance of a few hundredths of a mm, for example, and the
outside diameter of the bush in Figure 1 is retouched if
necessary to allow it to be force-fitted into the bore of
the blade.

This force-fit pre-assembly is then brought under
vacuum to 1200°C, maintained at this temperature for 15
minutes, then cooled to ambient temperature.
The quality of the assembly obtained can then be
checked.
It is also possible to carry out a diffusion treatment
in the solid state for 2 hours at 1200°C, either in the
self-bra2ing furnace or subsequently after a return to
ambient temperature.
Finally, a quality heat treatment can be carried out
on the assembly produced.

WE CLAIM:
1) Method for the manufacture by powder metallurgy of shaped parts to be
assembled by self-brazing at a specific temperature with receiving metal parts,
made from superalloy, said manufacturing method using two metal powders,
- a first alloy powder, called the "basic powder" making it possible to obtain
the desired metallurgical characteristics and essentially not containing
melting element
- and a second alloy powder, called the "brazing powder" containing at least
one so-called melting element with a content such that the liquidus
temperature of the brazing powder alloy is lower than the solidus
temperature of the basic powder alloy,
said basic and brazing powders being chosen so that the liquidus
temperature of the brazing powder is lower than the self-brazing temperature
and the solidus temperature of the basic powder is above the self-brazing
temperature,
- said manufacturing method comprising the following stages:
a) preparing of a homogeneous mixture of basic powder, brazing powder and
a liquid binder or a binder in the melted state,
wherein the chemical composition of the basic powder corresponds to a
superalloy based on Ni, Co or Fe and that of the brazing powder to a basic
alloy of Ni, Co or Fe in which the melting element is Si and/or B and
wherein the binder is chosen so that it can assume a consistency under
controlled conditions,

b) moulding-injection of said mixture into a mould of the shaped part to be
made, moulding being maintained under temperature, pressure and time
conditions such that the binder assumes the consistency,
c) extraction of the moulded blank from the mold,
d) binder removal,
e) sintering of the binder-removed blank at a temperature above the liquidus
temperature of the brazing powder, but below the subsequent self-brazing
treatment temperature so as to obtain a shaped part suitable for self-brazing
and whose relative density is at least 95%, but lower than 100%.

2) Method for the manufacture of shaped parts as claimed in claim 1 wherein the
brazing powder alloy contains 2 to 12 wt.% Si.
3) Method for the manufacturing of shaped parts as claimed in claims 1 or 2,
wherein the brazing powder alloy contains 1 to 5 wt.% B.
4) Method for the manufacture of shaped parts as claimed in any one of the
claims 1 to 3, wherein the brazing powder alloy is chosen from within the
following list of alloys: Ni-Si, Ni-B, Ni-Co-Si, Ni-Co-B, Ni-Co-Si-B, Ni-Cr-AI-Si, Ni-
Co-Cr-AI-Si, Ni-Cr-B, Ni-Co-Cr-B.
5) Method for the manufacture of shaped parts as claimed in any one of the
claims 1 to 4, wherein the brazing powder weight percentage in the combined
two metal powders is between 5 and 40%.

6) Method for the manufacture of shaped parts as claimed in any one of claims 1
to 5 wherein the metal powder charge in the mixture with the binder is at least 50
vol.%.
7) Method for the manufacture of shaped parts as claimed in any one of claims 1
to 6 wherein the assuming of consistency of the binder in the mould is a physical
liquid-solid state change of the binder obtained by maintaining the mould at a
temperature below said state change temperature.
8) Method for the manufacture of shaped parts as claimed in claim 7, wherein the
binder incorporates a thermoplastic resin.

9) Method of manufacture as claimed in claim 7, wherein the binder is an
aqueous or non-aqueous system liquid at ambient temperature and in that binder
removal stage comprises an operation of lyophilizing or sublimating the main
constituent of the binder.
10) Method of manufacture as claimed in any one of the claims 1 to 6 wherein
the binder essentially incorporates a thermosetting resin and that the taking on of
consistency of the binder in the mould is obtained by polymerizing said resin.
11) Method of manufacture as claimed in any one of claims 1 to 6 wherein the
taking on of consistency of the binder during the moulding stage is obtained by a
sol-gel reaction said binder and in that the binder removal stage comprises an
operation of redissolving the gel obtained.
12) Method for manufacturing shaped parts as claimed in claim 9 or 10, wherein
the binder removal stage comprises a chemical operation of dissolving at least
one component of the binder by the action of a solvent with respect to said
component or components.

13) Method for manufacturing shaped parts as claimed in claim 8 or 10, the
binder incorporating a polymer, the binder removal stage comprises an operation
for depolymerizing the same.
14) Method of manufacture as claimed in any one of claims 1 to 13, wherein the
binder removal stage consists of or finally comprises a thermal binder removal
operation.
15) Method of manufacture as claimed in claim 14, wherein the thermal binder
removal operation continues up to a temperature ensuring a presintering of the
binder-removed blanks.
16) Method of manufacture as claimed in claim 15, wherein presintering is
terminated at a temperature in the brazing powder melting range.
17) Method of manufacture as claimed in claim 15 or 16 wherein presintering is
terminated at a temperature in the lower brazing powder melting half-range.
18) Method of manufacture as claimed in any one of claims 15 to 17, wherein the
thermal binder removal operation and the sintering stage are performed
successively in the same furnace without any return to ambient temperature
between two said operations or stages.
19) Method of manufacture as claimed in any one of claims 1 to 18 wherein the
sintering stage is performed at a temperature approximately 50°C below the
temperature of assembling the shaped parts by self-brazing.

20) Method for the assembly of self-brazing shaped parts obtained according to
the manufacturing method as claimed in any one of the claims 1 to 19 with
superalloy receiving parts, wherein the receiving parts are aeronautical or
terrestrial gas turbine components, wherein the basic powder from which said
shaped parts are made is an alloy compatible with the superalloy of said
receiving parts, wherein said shaped parts have shapes and dimensions
permitting their preassembly with said receiving parts and wherein the shaped
pars are self-brazed to the receiving parts at a temperature above the liquid
temperature of the brazing powder and below the solidus temperature of the
basic powder and the receiving part.
21) Method of assembly as claimed in claim 20, wherein the self-brazing
treatment is followed directly or following a return to ambient conditions by a solid
state diffusion treatment.
22) Method for repairing gas turbines as claimed in claims 20 or 21, wherein the
receiving parts are made from an alloy carrying the trade name Rene 77, in that
the shaped parts are made from an alloy carrying the trade name Astroloy and in
that the self-brazing treatment is performed at 1200°C.



ABSTRACT


Title: Method for the manufacture by powder metallurgy of shaped parts to be
assembled by self-brazing at a specific temperature with receiving metal parts
made from superalloy.
Method for the manufacture by powder metallurgy of shaped parts to be
assembled by self-brazing at a specific temperature with receiving metal parts,
made from superalloy, said manufacturing method using two metal powders,
- a first alloy powder, called the "basic powder" making it possible to obtain
the desired metallurgical characteristics and essentially not containing
melting element
- and a second alloy powder, called the "brazing powder" containing at least
one so-called melting element with a content such that the liquidus
temperature of the brazing powder alloy is lower than the solidus
temperature of the basic powder alloy,
said basic and brazing powders being chosen so that the liquidus temperature of
the brazing powder is lower than the self-brazing temperature and the solidus
temperature of the basic powder is above the self-brazing temperature,
- said manufacturing method comprising the following stages:
c) preparing of a homogeneous mixture of basic powder, brazing powder and
a liquid binder or a binder in the melted state,
wherein the chemical composition of the basic powder corresponds to a
superalloy based on Ni, Co or Fe and that of the brazing powder to a basic
alloy of Ni, Co or Fe in which the melting element is Si and/or B and
wherein the binder is chosen so that it can assume a consistency under
controlled conditions,
d) moulding-injection of said mixture into a mould of the shaped part to be
made, moulding being maintained under temperature, pressure and time
conditions such that the binder assumes the consistency,
c) extraction of the moulded blank from the mold,
d) binder removal,
e) sintering of the binder-removed blank at a temperature above the liquidus
temperature of the brazing powder, but below the subsequent self-brazing
treatment temperature so as to obtain a shaped part suitable for self-brazing
and whose relative density is at least 95%, but lower than 100%.

Documents:

IN-PCT-2001-507-KOL-ABSTRACT-1.1.pdf

in-pct-2001-507-kol-abstract.pdf

IN-PCT-2001-507-KOL-ASSIGNMENT.pdf

IN-PCT-2001-507-KOL-CANCELLED PAGES.pdf

IN-PCT-2001-507-KOL-CLAIMS-1.1.pdf

in-pct-2001-507-kol-claims.pdf

IN-PCT-2001-507-KOL-CORRESPONDENCE 1.1.pdf

in-pct-2001-507-kol-correspondence.pdf

in-pct-2001-507-kol-description (complete).pdf

in-pct-2001-507-kol-drawings.pdf

in-pct-2001-507-kol-examination report.pdf

IN-PCT-2001-507-KOL-FORM 1 1.1.pdf

in-pct-2001-507-kol-form 1.pdf

in-pct-2001-507-kol-form 18.pdf

IN-PCT-2001-507-KOL-FORM 2 1.1.pdf

in-pct-2001-507-kol-form 2.pdf

in-pct-2001-507-kol-form 26.pdf

IN-PCT-2001-507-KOL-FORM 3 1.1.pdf

in-pct-2001-507-kol-form 3.pdf

IN-PCT-2001-507-KOL-FORM 5 1.1.pdf

in-pct-2001-507-kol-form 5.pdf

IN-PCT-2001-507-KOL-FORM 6.pdf

IN-PCT-2001-507-KOL-GRANTED-ABSTRACT.pdf

IN-PCT-2001-507-KOL-GRANTED-CLAIMS.pdf

IN-PCT-2001-507-KOL-GRANTED-DESCRIPTION (COMPLETE).pdf

IN-PCT-2001-507-KOL-GRANTED-DRAWINGS.pdf

IN-PCT-2001-507-KOL-GRANTED-FORM 1.pdf

IN-PCT-2001-507-KOL-GRANTED-FORM 2.pdf

IN-PCT-2001-507-KOL-GRANTED-FORM 3.pdf

IN-PCT-2001-507-KOL-GRANTED-FORM 5.pdf

IN-PCT-2001-507-KOL-GRANTED-SPECIFICATION-COMPLETE.pdf

IN-PCT-2001-507-KOL-INTERNATIONAL SEARCH REPORT & OTHERS.pdf

IN-PCT-2001-507-KOL-OTHERS.pdf

IN-PCT-2001-507-KOL-PA.pdf

IN-PCT-2001-507-KOL-PETITION UNDER RULE 137.pdf

in-pct-2001-507-kol-priority document.pdf

in-pct-2001-507-kol-reply to examination report.pdf

in-pct-2001-507-kol-specification.pdf

in-pct-2001-507-kol-translated copy of priority document.pdf


Patent Number 257999
Indian Patent Application Number IN/PCT/2001/507/KOL
PG Journal Number 48/2013
Publication Date 29-Nov-2013
Grant Date 26-Nov-2013
Date of Filing 09-May-2001
Name of Patentee METALS PROCESS SYSTEMS
Applicant Address 130 RUE DE SILLY, F-92100 BOULOGNE-BILLANCOURT
Inventors:
# Inventor's Name Inventor's Address
1 LEROY YVES 3, RUE D'ANJOU, F-14400 BAYEUX
2 DAVID FRANCOIS 10, AVENUE JEAN VILAR F-14123 IFS
3 HUCHIN JEAN-PIERRE 29, RUE-AUGUSTIN NEVEU F-86100 CHATELLERAULT
4 MALIE ANDRE 17 RUE ROBERT DESNOS F-86100 TARGE
PCT International Classification Number B22F 1/00
PCT International Application Number PCT/FR1999/02747
PCT International Filing date 1999-11-09
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 98/14119 1998-11-10 France