METHOD FOR ASSEMBLING TWO BLADES OF A TURBOMACHINE
NOZZLE
5 TECHNICAL FIELD OF THE INVENTION
10
The invention pertains to the general field of
aeronautics. It relates to methods for manufacturing
nozzle vanes, and more particularly methods for
assembling two blades forming a nozzle.
TECHNOLOGICAL BACKGROUND OF THE INVENTION
Current foundry know-how does not enable a onepiece
monocrystalline nozzle to be obtained. Thus, it
is conventional to assemble two blades cast separately
15 to form a nozzle4 The assembly is generally carried out
by a brazing/diffusion method, which is the most widely
used method for the assembly of parts made of
superalloy.
20 The brazing/diffusion technique consists. in
assembling parts, generally metal, using filler metal,
in the form of powder or strip, placed between the
parts to join together. The melting temperature of the
filler met-al is below that of the parts to join
25 together. A first step, known as brazing, consists in
subjecting the parts and the filler metal to a brazing
temperature. The brazing temperature is determined such
as to be below the melting temperature of the parts to
join together. The increase in temperature to reach the
30 brazing temperature is carried out in stages. The parts
and the filler metal are then maintained at the brazing
2
temperature for several tens of minutes. During
brazing, an atomic diffusion takes place in a zone
forming a brazed joint linking the two parts. A second
step, called diffusion step, consists in carrying out a
5 diffusion heat treatment in an oven, under controlled
10
atmosphere for several hours, so as to assure
sufficient homogenisation of the material situated at
the level of the brazed joint.
In the light of the severe thermodynamic
conditions to which the parts of a turbomachine are
subjected in operation, the most suitable filler metal
for assembling two blades is of composition
NiCoSiB1060. The particularity of this filler metal is
15 that it comprises silicon and boron which guarantee a
good chemical bond between the blades to assemble.
However, a major defect of this component is the
formation of zones of low mechanical and environmental
20 resistances. Environmental resistance is taken to mean
the capacity to withstand oxidation and corrosion. Yet,
this type of both mechanical and environmental damage
is very detrimental, leading to accelerated degradation
of the ·'hr:azed joint and leading to the disassembly of
25 the two blades.
The rupture is generally located at less than one
millimetre from the brazed joint, but rarely on the
joint. This localisation lS linked to diffusional
30 phenomena on both side of the joint, which can exceed a
hundred microns. The diffusion is notably exacerbated
3
when the superalloy constituting the blades has grain
joints, as is the case of polycrystalline superalloys.
GENERAL DESCRIPTION OF THE INVENTION
5 The invention offers a solution to the
aforementioned problems, by proposing a method for
assembling two blades, avoiding the formation of zones
of low mechanical and environmental resistances.
10 The invention thus essentially relates to a method
15
20
for assembling two blades of a turbomachine nozzle,
comprising:
positioning of a first surface of a first
blade and a second surface of a second blade
facing one another, said first and second
surfaces being spaced apart from one another
by an assembly clearance,
vapour phase aluminising of the first and
second surfaces, such as to fill the assembly
clearance.
The method according to the invention comprises an
aluminising step. The technique of aluminising is
commonly used to protect parts from oxidation. This
25 technique is well known, reference may in particular be
made to the document FR1433497. It consists in placing
the part to protect in a chamber in which circulates a
gaseous mixture including a compound of aluminium, such
as a halide, and a dilution gas or carrier gas. The
30 halide is produced by reaction between a halogen, for
example chlorine or fluorine, and a metal donor
4
containing aluminium, for example a metal alloy of
aluminium with one or more of the metal constituents of
the material of the part to protect. The carrier gas
assures the dilution and the driving of the gaseous
5 mixture to bring the halide into contact with the part
in order to form a deposit, a coating, on the surface
thereof. The coating formed has the particularity of
protecting from oxidation. It may be noted that the
carrier gas commonly used is argon.
10
During the aluminising step, a homogeneous
deposition of aluminium is formed on the first blade
and on the second blade, and notably on the first
surface and on the second surface. At the end of the
15 aluminising step, the initial assembly clearance is
filled by these deposits.
The method according to the invention thus enables
chemical coupling between the blades, making the use of
20 a filler metal comprising silicon or boron no longer
necessary. Thus, the formation of zones of low
mechanical and environmental resistances, due to boron
or to silicon, is avoided.
25
30
Furthermore, an additional
the end of the aluminising step,
the two blades assembled,
antioxidant coating.
advantage is
the nozzle,
lS covered
that at
formed by
with an
Apart
mentioned
from the
in the
characteristics that
preceding paragraph,
have been
the method
5
5
according to the invention may have one or more
additional characteristics among the following,
considered individually or according to any technically
possible combinations thereof.
In a non-limiting embodiment, the method comprises
a step of implanting solder beads in the first surface
and second surface, such as to maintain the
positioning, between the positioning step and the
10 aluminising step. In a non-limiting embodiment, said
beads are constituted of nickel.
In a non-limiting embodiment, the method comprises
a diffusion step, following the aluminising step. This
15 makes it possible to avoid the formation of an overstoichiometric
aluminium phase. In fact, such a phase
is fragile.
In a non-limiting embodiment, the method comprises
20 a step of depositing a layer favouring aluminising.
This layer is intended to favour the deposition of
aluminium.
In ,a ,.aon-limiting embodiment, the layer is
25 obtained by electrolytic route, for example of platinum
or palladium.
30
In a non-limiting embodiment, the
obtained by physical vapour deposition.
layer is
6
In a non-limiting embodiment, the method according
to the invention comprises a step preceding the
positioning step: a surface treatment of the first and
second surfaces. This surface preparation is intended
5 to prepare and clean the first and the second surfaces
in order to favour aluminising.
In a non-limiting embodiment, the surface
treatment comprises degreasing the first and second
10 surfaces with acetone under ultrasonic agitation.
In a non-limiting embodiment, the surface
treatment comprises chemical dissolution of the surface
oxides of the metals constituting the first and second
15 blades.
In a non-limiting embodiment, the method comprises
a step of masking at least one zone of the first blade,
preceding the positioning step. This makes it possible
20 to avoid deposition of aluminium on certain zones of
the nozzle, for example at the blade root.
In a non-limiting embodiment, the method comprises
a step ·Of ,dei.J>e·rmining the assembly clearance, preceding
25 the positioning step. In fact, the binder layer of
aluminium must not be too thick, to avoid a reduction
in the mechanical properties. It may be noted that the
evolution of the deposited thickness as a function of
the parameters of time, temperature and pressure,
30 follows a parabolic law. The assembly clearance is of
the order of several tens of micrometres.
5
7
The invention and its different applications will
be better understood on reading the description that
follows and by examining the figures that accompany it.
BRIEF DESCRIPTION OF THE FIGURES
The figures are only presented for indicative
purposes and in no way limit the invention. The figures
show:
10 In figure 1, a schematic representation of a first
blade of a nozzle
In figure 2, a schematic representation of a second
blade of a nozzle
In figure 3, a schematic representation of a nozzle
15 formed of the association of the first blade of
figure 1 and the second blade of figure 2
20
25
In figure 4, a schematic representation of the steps
of a method for assembling according to a nonlimiting
embodiment of the invention.
DETAILED DESCRIPTION OF AT LEAST ONE EMBODIMENT OF THE
INVENTION
Unless stated otherwise, a same element appearing
in different figures has a single reference.
With reference to figures 1, 2 and 3, the method
according to the invention aims to assemble a first
surface 20 of a first blade 21 and a second surface 22
of a second blade 23, in order to form a turbomachine
30 nozzle 24, for example a nozzle of a high pressure
turbine used in civil and military engines. The alloys
5
10
cormnonly
turbines
8
employed in high pressure and
are nickel based superalloys.
low pressure
However, the
method according to the invention is also applicable to
cobalt based superalloys.
The method implements a vapour phase aluminising
step, as is detailed hereafter.
With
according
steps:
reference to figure 4'
to the invention comprises
the method 10
the following
according to a first step 11, masking at least one
zone of the first blade 21 and/ or one zone of the
second blade 23. In fact, it is important to protect
15 certain sensitive zones from the aluminising, for
example a blade root. It may be noted that the first
step is optional: it is not present in another
embodiment of the invention. The masks used are
20
25
metal elements covering
guaranteeing sealing to
conventionally used in the
and
Masks
be used
certain zones
aluminising.
prior art may
because the temperature of vapour phase aluminising
according to the invention is equivalent to that of
convent:ional aluminising.
According to a second step 12, surface treatment of
the first surface 20 and the second surface 22. The
surface treatment serves to prepare the surfaces to
assemble. The surface treatment comprises for
30 example simple degreasing with acetone under
ultrasonic agitation, or instead chemical
9
dissolution of the surface oxides of the metals
constituting the first and second blades 21, 2 3.
Chemical dissolution comprises conditioning of the
oxides ln alkaline bath, followed by chemical
5 activation by acid, then bleaching in alkaline bath.
It may be noted that this second step is optional:
it lS not present in another embodiment of the
invention. It may also be noted that in another
embodiment, the second step 12 is carried out before
10 the first step 11.
According to a third step 13, a deposition of a
layer favouring aluminising. The deposition is for
example obtained by electrolytic route of platinum
15 or palladium or any other combination known to
favour deposition of aluminium. The layer may also
be deposited by physical vapour deposition, or take
the form of a strip. It may be noted that the third
step is optional: it is not present in another
20 embodiment of the invention.
According to a fourth step 14, determination of an
assembly clearance E, said assembly clearance E
corresponding to the distance separating the first
25 surface 2 0 of the first blade 21 and the second
surface 22 of the second blade 23 when said first
and second surfaces are positioned facing one
another in order to undergo aluminising. The
assembly clearance E is determined as a function of
30 the material constituting the blades, the shape of
the blades, the aluminising treatment conditions,
10
etc. The assembly clearance E is of the order of
several tens of micrometres, it is for example
comprised between thirty and one hundred and fifty
micrometres. The assembly clearance E is for example
5 from forty to fifty micrometres, which is a usual
order of magnitude retained for operations of
brazing-diffusion for nickel based alloys.
According to a fifth step 15, positioning the first
10 surface 2 0 of the first blade 21 and the second
surface 22 of the second blade 23 facing one
another, said first and second surfaces being spaced
apart from one another by the assembly clearance E.
15 According to a sixth step 16, implanting solder
beads in the first and second surfaces 20, 22, such
as to maintain the positioning. In the case of
nickel based superalloys, the beads are constituted
of nickel. The number and the spacing between the
20 beads depend on the shapes of the blades to
assemble. This technology operates by storing the
welding current in capacitors. The discharge of the
capacitors releases the current in a very rapid
pulse. It is thus possible to produce extreme
25 welding currents of several 100 kA in an extremely
short time lapse, which makes it possible in the
case of nickel beads to melt them in order that said
30
beads maintain in position the surfaces before
assembly.
According to a seventh step 17, the vapour phase
aluminising of the first and second surfaces, such
I,1-
5
10
15
20
25
30
11
as to fill the assembly clearance E. This step
comprises the following sub-steps:
o Placing the assembly formed of the first blade
21' the second blade 23, and beads, in a
thermochemical installation. In this
thermochemical installation, called chamber,
circulates a gaseous mixture comprising an
aluminium compound, such as a halide, and a
dilution gas or carrler gas. The halide is
produced by reaction between a halogen, for
example based on chlorine and/or fluorine, and
a metal donor containing aluminium, for example
a metal alloy of aluminium with one or more of
the metal constituents of the material of the
part to protect. In an embodiment of the
invention, the metal donor containing aluminium
is of weight composition CrAl20 or CrAl30 • In
another embodiment of the invention, the donor
is a ternary or quaternary cement as described
in the document FR2950364. In this case, it is
possible to obtain, in addition to aluminium, a
doping with reactive elements (such as hafnium,
zirconium, etc.) known as beneficial for
GKi-dation resistance. In an embodiment of the
invention, the halogen is fluorine and the
halide produced is of composition NH4F or HF.
In an embodiment of the invention, the halogen
is chlorine and the halide produced is of
composition In an embodiment, the
dilution gas used is argon. In an embodiment,
the partial pressure of argon in the chamber is
! t5
10
15
20
25
30
12
of the order of 100 mBar. This pressure is
advantageously a lower limit. It may be noted
that it lS important to find a compromise
between the partial pressure of dilution gas
(in Bars), the useful volume of the chamber (in
dm3 ) , and the quantity of halide (in grammes) ,
in order to optimise aluminising. In an
embodiment, the operating ranges are comprised
between 10-2 and 140 g/Bar/dm3 • More precisely,
in an embodiment, the operating ranges are
comprised between 0.1 and 20 g/Bar/dm3 •
o A heat treatment of the assembly in the
chamber. In an embodiment in which the third
step is not carried out, the heat treatment is
carried out for six hours at a temperature of
1100 degrees Celsius. In an embodiment in which
the third step is carried out, the heat
treatment is carried out for six hours at a
temperature of 1080 degrees Celsius. These
conditions of temperature and duration are not
limiting. In another embodiment, the
temperature is comprised between 950 and 1200
degrees Celsius. In another embodiment, the
·duratien of the heat treatment is comprised
between two and twelve hours. At the end of the
heat treatment, a homogeneous deposit 25 of
aluminium is obtained on the first surface 20
and the second surface 22, said deposit 25
filling the assembly clearance E. Thus, thanks
to the deposit 25, the two blades 21, 23 are
assembled.
13
According to an eighth step 18, a diffusion
treatment in order to avoid the formation of a phase
of nickel aluminide in over-stoichiometric quantity,
5 which is fragile. In an embodiment, the diffusion
treatment is carried out under vacuum, at a
temperature of 1100 degrees Celsius, for a duration
of one hour or more. It may be noted that this
eighth step lS optional, it is not present in
10 another embodiment of the invention.
The method thus consists in assembling the blades
during the formation of a coating of nickel aluminide.
This type of assembly has interesting characteristics
15 ln terms of mechanical resistance and in terms of
oxidation resistance.

CLAIMS
1. Method for assembling ( 10) two blades of a
turbomachine nozzle, comprising:
5 positioning (15) of a first surface (20) of a
10
first blade (21) and a second surface (22) of a second
blade ( 2 3) facing one another, said first ( 2 0) and
second (22) surfaces being spaced apart from one
another by an assembly clearance (E)
vapour phase aluminising ( 17)
(20) and second (22) surfaces, such as
assembly clearance (E) .
of the first
to fill the
2. Method for assembling ( 10) according to the
15 preceding claim, characterised in that it comprises a
step of implanting (16) solder beads in the first (20)
and second (22) surfaces, such as to maintain the
positioning between the positioning step ( 15) and the
aluminising step (17).
20
25
30
3. Method for assembling ( 10) according to
of the preceding claims, characterised in that
comprises a diffusion
alumin±s~ng step (17).
step ( 18) f following
one
it
the
4. Method for assembling (10) according to one
of the preceding claims, characterised in that it
comprises a step of depositing (13) a layer favouring
aluminising, preceding the positioning step (15).
5
15
5. Method for assembling ( 10) according to the
preceding claim, characterised in that the layer is
obtained by electrolytic route.
6. Method for assembling (10) according to claim
4, characterised in that the layer is obtained by
physical vapour deposition.
7. Method for assembling ( 10) according to one
10 of the preceding claims, comprising a step of surface
treatment (12) of the first (20) and second (22)
surfaces, preceding the positioning step (15).
8. Method for assembling (10) according to the
15 preceding claim, characterised in that the surface
treatment (12) comprises degreasing the first (20) and
second (22) surfaces with acetone under ultrasonic
agitation.
20
25
9. l'1ethod for assembling (10) according to one
of the preceding claims, characterised ln that it
comprises a step of masking ( 11) at least one zone of
the first blade ( 21) , preceding the positioning step
( 15) .
10. Method for assembling (10) according to one
of the preceding claims, characterised in that it
comprises a step of determining (14) the assembly
30 clearance (E), preceding the positioning step (15).