A METHOD OF COATING A FIBER WITH PRE-COATING
The present invention lies in the field of
fabricating parts out of metal matrix composite material.
The invention relates to a method of depositing a coating
5 of a first metal alloy on a fiber extending in a main
direction D, the method comprising the following steps:
a) providing a first mass of a first metal alloy and
heating the first mass to above its melting temperature
so that this alloy is in the liquid state and occupies a
10 space E; and
b) causing the fiber to move in translation from
upstream to downstream through the liquid first mass
along the direction in which the fiber extends at a first
speed V1 such that the fiber becomes covered over at
15 least a portion of its length by a coating of the first
alloy, which coating presents a non-zero thickness over
the entire periphery of the fiber in a plane
perpendicular to the main direction D.
In certain applications, in particular in aviation
20 for turbine engine parts, parts made of metal matrix
composite material reinforced by fibers, e.g. ceramic
fibers, present very considerable potential.
Such composites present performance in terms of
stiffness and mechanical strength that is high, with the
25 fiber reinforcement enabling weight to be saved compared
with a part of equivalent performance but made of the
same metal alloy without fiber reinforcement.
Such a composite is fabricated from a semi-finished
product constituted by fiber reinforcement coated in a
30 metal coating forming a sheath around the fiber. The
alloy of the metal cdating is the same as the alloy of
the matrix in which the fibers sheathed in this way are
to be embedded during the subsequent manufacturing step.
In order to coat the fiber in the metal alloy, it is
35 possible for example to deposit the alloy by chemical
vapor deposition in an electric field, by thermal
evaporation, or by electrophoresis from a metal powder.
In the description below, the terms "upstream" and
"downstream" are defined relative to the direction in
which the fiber moves in translation.
Patent EP 0 931 846 describes a method of depositing
5 alloy on afiber by a liquid technique (referred to as
"coating" the fiber). That device is described with
reference to Figure 3.
A mass 120 of the alloy is heated until it becomes
liquid, and then a fiber 110 is moved in translation
10 along its main direction (central axis of the fiber)
through the liquid mass 120. The fiber 110 extends
between an upstream pulley 141 and a downstream pulley
142 that is situated on either side of the mass 120, with
the fiber being suitable for traveling relative to the
15 pullies. In order to avoid leaving the fiber 110 in
contact with the molten metal alloy 120 for too long with
the risk of damaging it, the fiber 110 is initially held
away from the alloy mass 120 while the mass 120 is being
heated by using a pulley 148 that is situated on the
20 portion of the fiber 110 that extends between the
upstream pulley 141 and a downstream pulley 142. The
fiber 110 thus does not touch the alloy mass 120. Once
the mass 120 is liquid, the fiber 110 is caused to travel
between the two pulleys from the upstream pulley 141
25 towards the downstream pulley 142, and the fiber 110 is
moved progressively towards the alloy mass 120 by moving
the pulley 148 in translation until the fiber 110 comes
into contact with the mass 120, as shown in Figure 3 (the
double-headed horizontal arrow shows the movement in
30 translation of the pulley 148, which pulley no longer
touches the fiber 110 at the end of its movement). The
portion of the fiber 110 that has passed through the
liquid mass 120 then becomes covered by an alloy coating
125 of given thickness.
35 In that technology, the liquid mass 120 is kept
levitated in a crucible 130 in which it is heated by a
heater 135, thereby presenting the advantage that the
alloy mass 120 is not contaminated by the material
constituting the crucible 130.
That method nevertheless presents drawbacks. In
order to obtain an alloy coating 125 on the fiber within
5 a certain range of thicknesses (e.g. thicknesses of about
50 micrometers (pm)), it is necessary for the fiber 110
to pass through the liquid mass 120 of alloy at a high
speed. Unfortunately, when the speed of the fiber 110
through the liquid mass 120 of alloy is too fast (more
10 than several meters per second), the time of contact
between the fiber 110 and the alloy is too short for the
fiber to be completely wetted by the liquid alloy,
thereby having the consequence of preventing the fiber
110 from penetrating into the alloy mass 120, such that
15 the fiber 110 remains at the periphery of the alloy mass
120. Thus, by that method, at most approximately threefourths
of the periphery of the fiber 10 becomes coated
(three-fourths in a cross-section plane perpendicular to
the rectilinear fiber).
20 In order to improve the wetting of the fiber 110 at
high speeds, one solution consists in depositing a
compound that is wettable by the metal of the alloy on
the fiber 110 by means of reactive chemical vapor
deposition (RCVD). That method is described in patent
25 FR 2 891 541.
It is then possible to cause the fiber 110 to pass
through (the middle) of the alloy mass 120, as shown in
Figure 3, and to obtain a deposit of alloy on the fiber
110.
30 Nevertheless, that method presents drawbacks.
Specifically, sporadic alloy-expulsion phenomena occur at
the exit from the mass 120, thereby leading to droplets
of alloy becoming formed on the fiber 110 at more or less
regular intervals.
35 This situation is shown in Figure 4, which shows a
fiber 110 in longitudinal section on exiting the alloy
mass 120, together with droplets 128.
Such droplets 128 are undesirable, in particular
because they prevent fibers 110 being distributed
uniformly within the composite material once they are
embedded in the matrix. Furthermore, they lead to the
5 fiber breaking when they reach the downstream pulley 142.
The present invention seeks to remedy those
drawbacks.
The invention seeks to provide a method enabling the
formation of these droplets to be prevented while
10 continuing to ensure that the fiber passes through the
alloy mass, even at high speeds.
This object is achieved by the fact that, prior to
step a), the following steps are performed:
i) providing a second mass of a second metal alloy
15 having a melting temperature T,, that is strictly higher
than the melting temperature T,, of the first alloy;
j) heating the second mass to above its melting
temperature so that the second alloy is in the liquid
state and occupies a space E2, and then moving the fiber
20 in translation from upstream to downstream through the
second alloy, this translation taking place at a second
speed V2 which is such that the condition under which the
second alloy is taken up during this translation lies
under visco-capillary conditions, such that the fiber
25 becomes covered, over this portion of its length, by a
coating of the second alloy, which coating presents a
non-zero thickness over the entire periphery of the
fiber; and
k) cooling the coating of the second alloy until it
30 becomes solid.
By means of these provisions, since the fiber is
coated in the second alloy, it is well wetted by the
first alloy on passing through the first alloy, and the
coating of first alloy on the fiber is of thickness that
35 is uniform along the entire fiber, without droplets being
formed. It is thus possible to coat a fiber with the
first alloy even at high speeds (faster than 1 meter per
second (m/s)), with a desired coating thickness, and with
good adhesion of the coating, and good soundness for the
fiber as coated in this way.
Advantageously, the second alloy does not form
5 embrittling phases with the first alloy.
Thus, the second alloy and the first alloy present
between them adhesion that is strong and tough, and the
resulting composite tends to be stronger.
The invention can be well understood and its
10 advantages appear better on reading the following
detailed description of an implementation shown by way of
non-limiting example. The description refers to the
accompanying drawings, in which:
Figure 1 is a diagrammatic view of a device using
15 the method of the invention for covering a fiber by a
liquid alloy;
Figure 2 is a section on line 11-11 of Figure 1
showing a fiber coated in alloy by using the method of
the invention;
20 Figure 3, described above, is a diagrammatic view
of a device using the prior art method for covering a
fiber by a liquid alloy; and
Figure 4, described above, is a longitudinal
section of a fiber coated in an alloy by using the prior
25 art method.
There follows a description of the method of the
invention for coating a fiber 10.
By way of example, the fibers 10 are made of
ceramic.
30 In particular, the fibers 10 are made of silicon
carbide (Sic) surrounding a core of tungsten or of
carbon.
In general, each fiber 10 presents a pyrolitic
carbon layer having a thickness of a few micrometers.
35 This layer is advantageous since firstly it protects the
Sic fiber chemically by acting as a diffusion barrier
between the Sic fiber and the metal material external to
the fiber, which material is often highly reactive, and
secondly it protects the Sic fiber mechanically against
the propagation of microdefects by limiting the effects
of a nick and making it possible to avoid possible
5 cracking, mainly as a result of the stratified
configuration of the fine layer of pyrolitic carbon (see
description below).
The term "coating" is used to mean depositing an
alloy on a substrate as a result of moving the substrate
10 (here a fiber) in contact with the alloy while the alloy
is in liquid form, the alloy being solid at ambient
temperature. The term "alloy" is used to include a pure
metal, i.e. a metal that (ignoring trace elements) is
constituted by a single element from the periodic table
15 of the element (Mendeleev's table).
A certain quantity (a first mass) of a first alloy
is provided, and this first mass 20 of this first alloy
is heated until it is liquid (step a)).
This heating is performed by placing a quantity of
20 this first alloy in a container, e.g. a crucible 30, and
heating it by means of a heater 35 until the temperature
throughout the first alloy is higher than its melting
temperature T,,. In known manner, the liquid first mass
20 of this first alloy is kept levitated in the crucible
25 30, thus presenting the advantage that the first mass 20
does not touch the crucible 30 and is therefore not
contaminated by the material from which the crucible 30
is made.
By way of example, the heater 35 is an inductor
30 arranged around the crucible 30, the inductor also
keeping the first mass 30 of this first alloy in
levitation.
Once liquid, this first mass 20 occupies a space El,
i.e. the first mass 20 completely fills this space El,
35 but does not extend beyond it.
If the first alloy is not a pure metal, then the
melting temperature T, is the liquidus temperature for the
particular composition of the alloy.
By way of example, the first metal alloy is a
5 titanium alloy.
For example, this first alloy may be Ti-6242 having
the following composition by weight:
6%A1 + 2%Sn + 4%Zn + 2%Mo
the balance being Ti.
10 A fiber 10 is placed in such a manner as to extend
between an upstream pulley 41 and a downstream pulley 42,
between which it is suitable for traveling from the
upstream pulley 41 towards the downstream pulley 42 in a
direction given by arrow F in Figure 1.
15 The fiber 10 thus moves in translation along the
main direction D in which it extends, in such a manner
that between a first instant tl and a subsequent instant
t2 an arbitrary first section S1 of the fiber 10 (other
than its downstream end) moves so as to occupy at the
20 subsequent instant t2 the position that was occupied at
the first instant tl by a second section S2 of'the fiber
10 situated downstream from the first section S1.
Between two pulleys, the fiber 10 is tensioned and
therefore extends along a main direction D that is the
25 same for each cross-section of the fiber 10. For other
portions of the fiber 10, the fiber 10 need not
necessarily be rectilinear and its main direction D may
vary along the fiber 10, e.g. the fiber 10 (and its main
direction) follows a circular arc around a pulley.
30 The upstream pulley 41 is situated upstream from the
mass 20 and the downstream pulley 42 is situated
downstream from the first mass 20.
The upstream pulley 41 and the downstream pulley 42
form part of a drive mechanism 40 for driving the fiber
35 10, the fiber 10 being driven for example by a motor (not
shown) included in the drive mechanism 40.
The upstream pulley 41 and the downstream pulley 42
are positioned in such a manner that when the fiber
extends in rectilinear manner from one pulley to the
other (i.e. when it extends along a straight line
5 interconnecting these two pulleys), the fiber 10 passes
through (the middle) of the first mass 20 of the first
alloy, and thus through the space El (step b)).
The drive mechanism 40 may include a guide mechanism
other than pulleys for guiding the fiber 10, providing
10 the fiber 10 passes through the first mass 20 as
described above.
Advantageously, the main direction D of the fiber 10
is constant (the fiber 10 is rectilinear) between a point
upstream from the space El and a point downstream from
15 the space El. The fiber thus tends to conserve a
rectilinear shape once it has been coated.
In order to coat the first alloy on a portion of the
length of the fiber 10 (e.g. the majority thereof), this
portion is caused to pass through the first mass 20 and
20 the space El as described above. A coating 25 of first
alloy is then deposited on the fiber 10.
The fiber 10 passes through the first mass 20 of
alloy at a first speed of translation V1. In the method
of the invention, this first speed V1 is high, e.g.
25 faster than 2 m/s.
In the invention, before coating the fiber 10 as
described above, the fiber 10 is subjected to pre-coating
(steps i), j), and k ) ) .
This pre-coating is performed in a manner similar to
30 the above-described coating, but nevertheless with
differences.
Firstly, the pre-coating takes place through a
second liquid mass 220 of a second alloy that is
different from the first alloy of the first mass 20. The
35 second alloy thus differs in composition from the first
alloy, i.e. it is not made up of the same chemical
elements, or it is made up of the same chemical elements
but in different proportions.
Furthermore, this pre-coating takes place at a speed
of translation V2 (second speed V2) that is such that the
5 condition under which the second alloy is taken up
during this translation lies under visco-capillary
conditions of taking-up of the alloy by the fiber 10.
Such visco-capillary conditions correspond to the
situation in which the thickness of the alloy that is
10 taken up by a fiber (i.e. that becomes deposited on and
that remains on the fiber - this being then called the
taking-up of the alloy) is proportional to the two-thirds
power of the speed V (i.e. proportional to V2I3) . The
thickness of the alloy that is taken up is small, being
15 of the order of a few micrometers (vm) .
Advantageously, the coating speed V1 is strictly
faster than the pre-coating speed V2, i.e. the precoating
speed V2 is strictly slower than the coating
speed V1. It is thus possible to deposit a coating of
20 first alloy of desired thickness on the fiber 10, e.g.
thickness of the order of 50 pm, and to do so without
droplets forming along the fiber 10.
For example, the speed V2 is equal to 1 m/s or
slower.
25 In certain configurations, it is desired for the
volume fraction of fibers 10 in the final composite
material (i.e. after the fibers 10 have become embedded
in the metal matrix) to be as high as possible, in order
to obtain superior mechanical performance. For this
30 purpose, the total thickness of the coating deposited on
the fiber 10 during the pre-coating and during the
coating should be as small as possible. To obtain a
thickness of first alloy 25 (as deposited during coating)
that is as slow as possible, the first speed V1 should be
35 as small as possible. The speed V1 is then under certain
circumstances slower than the second speed V2, and lies
within visco-capillary conditions.
Figure 1 is a diagram showing the fiber 10 being
subjected to this method of being pre-coated with the
second alloy, the second mass 220 of the second alloy
being situated in a crucible 230 heated by a heater 235
5 to a temperature higher than its melting temperature T,,.
The fiber 10 is tensioned between a third pulley 243
situated upstream from the second mass 220 and a fourth
pulley 244 situated downstream from the second mass 220.
The fiber is moved in translation from the upstream
10 pulley 243 to the downstream pulley 244 and it passes
through the second mass 220 of the second alloy, which
mass occupies a space E2. The fiber extends along a main
direction D2.
While the second mass 220 of alloy is being heated,
15 the portion of the fiber 10 between the third pulley 243
and the fourth pulley 244 is held away from the mass 20
of alloy by an intermediate pulley (not shown), after
which it is moved towards the second mass 220 of alloy
(in a method similar to that for the pulley 148 described
20 with reference to Figure 3).
Given that the second speed V2 lies in viscocapillary
conditions, the fiber 10 is well wetted by the
second alloy, and the fiber penetrates fully into the
second mass 220. On leaving the second mass 220, the
25 fiber 10 presents a coating 225 of second alloy of
thickness that is substantially constant over its entire
circumference and over the entire length of the portion
that is to be coated. This thickness is small relative
to the diameter of the fiber 10, i.e. less than one-tenth
30 of this diameter.
Once the entire portion of fiber 10 that is it
desirable to coat has become coated in the second alloy,
the coating is allowed to cool so that it becomes solid
(step k)).
3 5 In order to accelerate this cooling, it is
advantageous to use a cooler that cools the second alloy
on this portion of fiber 10.
The cooler is thus situated on the path of the fiber
10 downstream from the space E2 (and upstream from the
subsequent coating device, and possibly from the fourth
pulley 244, such that the second alloy is solid when it
5 comes into contact with the fourth pulley 244).
By way of example, the cooler is a sheath through
which the fiber 10 passes, and it delivers a stream of
gas or air (e.g. at ambient temperature) filling the
inside of the sheath and in which the fiber 10 is
10 immersed so as to be cooled.
Thereafter the fiber 10, as already coated in this
coating 225 of the second alloy, is coated in the first
alloy. For this purpose, the fiber 10 is caused to pass
through the first mass 20 of the alloy at a speed V1,
15 using the method described above.
On exiting the first mass 20, the coating 225 of
second alloy on the fiber 10 presents a coating 25 of a
substantially constant thickness of the first alloy over
its entire circumference and along the entire length of
20 the portion that is to be coated.
Given that the downstream pulley 42 is touched by
the fiber 10 carrying the coating 25, it is necessary for
the coating 25 to be solid when it comes into contact
with the downstream pulley 42.
25 After coating, in order to cool the coating 25
sufficiently for it to be solid when it comes into
contact with the d~ownstream pulley 42, a cooler 60 is
used, which cooler is then situated downstream from the
space El and upstream from the pulley 42. By way of
30 example, the cooler is similar to the above-described
cooler downstream from the pre-coating operation.
The second alloy presents a melting temperature T,,
that is higher than the melting temperature T,, of the
first alloy.
35 Surprisingly, tests undertaken by the inventors have
shown that when the melting temperature T,, of the second
alloy is lower than the melting temperature T,, of the
first alloy, the coating 25 of the first alloy and the
fiber 10 run the risk of being embrittled. Furthermore,
the coating 25 of first alloy does not wet the surface of
the coating 225 of second alloy in uniform manner, i.e.
5 certain portions of the coating 225 of second alloy are
not covered by the first alloy.
This is due to the fact that while passing through
the mass of the first alloy (coating), the second alloy
is heated to above its melting temperature T, and the
10 second alloy (as deposited during pre-coating) remelts
and becomes dissolved in the first alloy, and the second
alloy shrinks by the capillary effect, thereby laying
bare the surface of the fiber 10. Furthermore, since the
second alloy is in liquid form, it reacts with the first
15 alloy, which is likewise in liquid form, so as to form
chemical compounds that, during subsequent cooling of the
first and second alloys, serve to embrittle the coating
25 of the first alloy and to ernbrittle the fiber 10.
For example, for a fiber made of silicon carbide
20 (Sic) that is to be embedded in a matrix of Ti-6242
titanium alloy (first alloy) having a melting temperature
T,, of 1670°C, and with a second alloy of zirconiumvanadium
Zr-V with a melting temperature T,, of 1500°C, it
is observed after pre-coating (step k ) ) that carbides
25 (Zr, Ti-C) form during coating (step b)) around the fiber
10 and at the old P grain boundaries of the titanium
first alloy.
These carbides embrittle the coating 25 of first
alloy. Furthermore, remelting the coating 225 of second
30 alloy tends to embrittle the fiber 10.
Surprisingly, tests undertaken by the inventors have
shown that when the melting temperature T,, of the second
alloy is equal to the melting temperature T,, of the first
alloy, i.e. when the second alloy and the first alloy are
35 identical, the fiber 10 is not completely covered by
alloy.
This is due to the fact that the layer of alloy
deposited on the fiber 10 during pre-coating is thin
(because of the low speed at which the fiber passes
through the alloy) and tends to fracture during
5 subsequent cooling. In addition, this layer can become
dissolved during the subsequent coating operation.
Consequently, the coating that is performed subsequently
is not effective, with regions of the fiber 10 that are
laid bare being poorly wetted.
10 For example, for a fiber made of silicide carbide
(Sic) that is to be embedded in a matrix made of Ti-6242
titanium alloy, after the pre-coating, a brittle layer of
Tic is formed on the surface of the fiber 10. During
subsequent cooling, this layer breaks because of its
15 small thickness. Decohesion thus occurs between the
fiber 10 and the coating 225 of the second alloy, leaving
regions of the fiber 10 that are bare. These bare
regions of the fiber 10 are poorly wetted during the
coating operation, and consequently the fiber 10 is not
20 covered by alloy in some locations.
In contrast, when pre-coating is performed with a
second alloy having a melting temperature T,, that is
strictly higher than the melting temperature T,, of the
first alloy used during the subsequent coating operation,
25 then a coating 25 of first alloy is obtained that is of
uniform thickness over the entire surface of the coating
225 of second alloy that covers the fiber 10, i.e. over
the entire periphery of the fiber 10 in a plane
perpendicular to the main direction D.
30 This situation is shown in Figure 2 which is a
cross-section of the fiber 10 (i.e. a section in a plane
perpendicular to the direction in which this portion of
the fiber 10 extends (main direction D)) after it has
been coated.
35 During pre-coating, the second alloy wets the fiber
10 well since the second speed V2 is slow.
During subsequent coating through the first alloy,
the first alloy wets the second alloy coating 225 well
and a first alloy coating 25 of uniform thickness becomes
formed over the entire surface of the second alloy
5 coating 225, which coating adheres thereto. Because the
melting temperature T,, of the alloy is higher than the
melting temperature T,, of the first alloy, the coating
225 of the second alloy remains solid throughout coating,
thereby protecting the fiber 10. When present, the
10 pyrolytic carbon layer at the surface of the fiber 10 is
not damaged during this coating operation.
Thus, the wetting of the fiber 10 by the first alloy
is improved relative to a prior art method without precoating,
thereby enabling the fiber 10 to penetrate fully
15 into the first mass 20 of alloy even at speeds that are
fast (several meters per second), thereby covering the
fiber over its entire surface without forming droplets.
Advantageously, the second alloy (of the precoating)
does not form embrittling phases with the first
20 alloy (of the coating).
Thus, the interface between the coating of the
second alloy and the coating of the first alloy does not
present any phases (i.e. metallurgical phases or
compounds) that embrittle this interface, and there is no
25 risk of the interface becoming a zone that generates
breaks or decohesion between these coatings.
For example, the second alloy (of the pre-coating)
contains at least one chemical element that is present in
the first alloy (of the coating).
30 Thus, the matrix of the composite (which matrix is
made of the first alloy) is not modified chemically in
harmful manner in the vicinity of the fiber 10.
Alternatively, the chemical element has a betagenerating
effect on titanium, i.e. it presents a body
35 centered cubic structure like that of niobium.
Alternatively, this chemical element has an alphagenerating
effect.
For example, with a fiber made of silicon carbide
(Sic) that is embedded in a matrix of Ti-6242 titanium
alloy (first alloy) having a melting temperature T,, of
1670°C, the second alloy is selected to be a titanium
5 niobium alloy (Ti-Nb) comprising 51% by weight of Ti and
49% by weight of Nb, and having a melting temperature T,,
of 1870°C.
During pre-coating, the second alloy wets the fiber
10 well because the second speed V2 is slow (equal to
10 about 1 m/s or slower), and a coating 225 of this second
alloy is formed over the entire surface of the fiber 10
with a constant thickness of 4 pm, and this coating
adheres to the fiber 10. This coating 225 is made up of
grains of beta phase titanium with the carbides Tic and
15 NbC at the boundaries between grains.
During the subsequent coating, the Ti-Nb alloy is
well wetted by the titanium alloy. Little niobium
diffuses into the titanium, thereby avoiding the
appearance of a supercooling phenomenon such as a
20 eutectic phenomenon (a portion of the alloy going to the
liquid state).
Advantageously, the niobium content in the second
alloy is greater than 3% in order to obtain some beta
phase in the titanium of the second alloy (below which
25 content the titanium is entirely in alpha phase), and
less than 50% in order to avoid overheating the fiber 10
during pre-coating (since the melting temperature T,,
increases with the percentage of niobium).
Alloys other than Nb-Ti that are suitable for pre-
30 coating Sic fibers when the first alloy is a titanium
alloy are alloys of titanium and one (or more) additional
element(s) present in the first alloy. The melting
temperature of the additional element should be higher
than the melting temperature T,, of the first alloy.
35 Advantageously, the additional element does not form
a eutectic with titanium, and on the contrary it forms a
total solid solution (a single solid phase below the
solidus temperature in the phase diagram), or else it
generates a peritectic reaction.
Such additional elements are as follows: zirconium
(Zr) , chromium (Cr) , vanadium (Va), hafnium ( H f ) ,
5 molybdenum (Mo), tantalum (T), rhenium (Re), and tungsten
(W).
Thus, and advantageously, when the first alloy is
Ti-6242 titanium alloy, the second alloy (or pre-coating)
includes at least one of the elements in the group
10 constituted by Nb, Zr, Cr, V, Hf, Mo, Ta, Re, W.
The second alloy may thus be an alloy of titanium
with a plurality of elements from this group, such as
Ti-Nb-Zr, Ti-Nb-V, Ti-Ta-Zr.
In a variant, after the fiber 10 has been pre-
15 coating with the second alloy and before the fiber 10 is
coated with the first alloy, the fiber 10 (with its
coating of second alloy) is subjected to a second precoating
operation with a third alloy having a melting
temperature TF3 that is strictly lower than the melting
20 temperature T,, of the second alloy and strictly higher
than the melting temperature T,, of the first alloy.
Thus, after step k), and before step a), the
following steps are performed:
i?) providing a third mass of a third metal alloy
25 having a melting temperature T,, that is strictly lower
than the melting temperature T,, of the second alloy and
that is strictly higher than the melting temperature TF1
of the first alloy;
m) heating the third mass to above its melting
30 temperature so that the third alloy is in the liquid
state and occupies a space E3, and then moving the fiber
from upstream to downstream in translation through the
third alloy, this translation taking place at a third
speed V3 that is faster than the second speed V2, which
35 is slower than the first speed V1, and that is such that
the condition under which the third alloy is taken up
during this third translation.lies under visco-capillary
conditions, such that the fiber becomes covered over a
portion of its length (already coated in the second
alloy), by a coating of the third alloy presenting a
thickness that is not zero and occupying its entire
5 periphery; and
n) cooling the coating of the third alloy until it
becomes solid.
The method of the invention is applicable to any
combination of fibers, in particular ceramic fibers, and
10 of metal alloy constituting the matrix in which the
fibers are embedded.
CLAIMS
1. A method of depositing a coating of a first metal
alloy on a fiber (10) extending in a main direction D,
the method comprising the following steps:
5 a) providing a first mass (20) of a first metal
alloy and heating said first mass (20) to above its
melting temperature so that this alloy is in the liquid
state and occupies a space El; and
b) causing said fiber (10) to move in translation
10 from upstream to downstream through said liquid first
mass (20) along the direction in which said fiber (10)
extends at a first speed V1 such that said fiber (10)
becomes covered over at least a portion of its length by
a coating (25) of said first alloy, which coating
15 presents a non-zero thickness over the entire periphery
of the fiber in a plane perpendicular to said main
direction D,
which method is characterized in that, prior to step
a), the following steps are performed:
20 i) providing a second mass (220) of a second metal
alloy having a melting temperature .T,, that is strictly
higher than the melting temperature T,, of said first
alloy;
j ) heating said second mass (220) to above its
25 melting temperature so that the second alloy is in the
liquid state and occupies a space E2, and then moving
said fiber (10) in translation from upstream to
downstream through said second alloy, this translation
taking place at a second speed V2 which is such that the
30 condition under which the second alloy is taken up during
this translation lies under visco-capillary conditions,
such that the fiber (10) becomes covered, over said
portion of its length, by a coating (225) of said second
alloy, which coating presents a non-zero thickness over
35 the entire periphery of the fiber; and
k) cooling said coating (225) of the second alloy
until it becomes solid.
2. The method according to claim 1, characterized in that
said pre-coating speed V2 is strictly slower than said
coating speed Vl.
3. The method according to claim 1 or claim 2,
characterized in that said second alloy does not form
ernbrittling phases with said first alloy.
4. The method according to claim 3, characterized in that
said second alloy contains at least one chemical element
that is present in said first alloy.
5. The method according to any one of claims 1 to 4,
characterized in that said first alloy is a titanium
alloy.
6. The method according to claim 5, characterized in that
said first alloy is the Ti-6242 titanium alloy, said
second alloy including at least one of the elements from
the group constituted by Nb, Zr, Cr, V, Hf, Mo, Ta, Re,
and W.