FR2738017A1 - METHOD FOR COATING A CARBIDE OR A MIXED CARBONITRIDE OF TI AND ZR BY CHEMICAL VAPOR DEPOSITION (CVD) AND DEVICE FOR FORMING A CERAMIC COATING FROM AT LEAST TWO METALLIC PRECURSORS - Google Patents

Abstract

A method for coating a metallic or ceramic substrate (15) with a complex metallic or ceramic material from two or more organometallic precursors by chemical vapour deposition includes decomposing the two organometallic precursors by sublimation in two separate crucibles (16) in a reactor (6) into which a suitable gas is fed, while simultaneously rotating said substrates (15) above the two crucibles (16), and reacting these components at the surface of the substrate, heated to a temperature of about 650 DEG to 850 DEG C. Each of the precursors is sublimated at a suitable temperature according to the desired proportion of the two components in the coating.

Description

PROCESS FOR COATING A CARBON OR A MIXED CARBONITRIDE
Of Ti and Zr by Chemical Vapor Deposition (CVD) and
DEVICE FOR FORMING A CERAMIC COATING FROM
AT LEAST TWO METAL PRECURSORS
The present invention relates to a process for coating a carbide or a mixed carbonitride of Ti and
Zr by chemical vapor deposition on a metal or ceramic substrate, and a device for forming a ceramic coating of at least two metal precursors by the CVD technique.

 Ceramic coatings made by the CVD technique are well known. The precursors used to make these coatings are generally in the form of halides which are decomposed hot and whose metal elements are reacted with oxygen, a hydrocarbon and / or nitrogen to form oxides, carbides, nitrides or carbonitrides. The advantage of this coating technique is to give excellent adhesion of the coating to the substrate. This is the reason why CVD is used especially for the coating of cutting tools.

 The disadvantage of this technique is that it requires heating the substrate at temperatures of the order of 1000 ° C. and higher, thereby limiting the nature of the substrates on which CVD coatings can be made.

 It has been proposed to lower the temperature of the substrate by replacing the precursors in the form of halides with organometallic precursors. Thus, J. Slifirski (Perpignan thesis, 1993, N 257C) proposed depositing TiC, TiN or TiCN on a metal substrate starting from a sublimed Ti (CgH5) 2C12 organometallic precursor in a fed reactor. in H2 with a certain percentage of N2.

 It is also known that a solid solution of mixed carbonitride Ti and Zr can further increase the mechanical properties, including hardness. It is further presumed that it has excellent resistance to hot oxidation, even in an aggressive environment and gives good resistance to aqueous corrosion.

 The object of the present invention is precisely to produce such a coating.

 For this purpose, the subject of the present invention is a process for coating a Ti or Zr mixed carbide or carbonitride by chemical vapor deposition (CVD) on a metal or ceramic substrate, characterized in that on the one hand, an organometallic precursor of Ti is decomposed at its sublimation temperature and, on the other hand, an organometallic precursor of Zr at its sublimation temperature in a reactor fed with H2 and, in the case of carbonitride deposition, in NH 3 as a nitrogen precursor and that a relative displacement between the precursors of Ti and Zr on the one hand, and the heated substrate between approximately 650 and 850 on the other hand, to bring alternatively this substrate with respect to each of said precursors of Ti and Zr, the speed of this displacement being chosen so that the reaction between the components forms on this substrate a mixed deposition of carbide or carbonitride of the two elements.

 The accompanying drawing illustrates the process and the results obtained using the deposition method of the present invention.

 Figure 1 is a schematic sectional view of the experimental sublimator used to produce the examples.

Figure 2 is a diagram of the% at. of Zr compared to
Ti according to the mesh parameter determined by RX.

 Figure 3 is an X-ray image showing the distribution of the elements in the depot.

 Figure 4 is a schematic elevational view of the sublimator for the implementation of the method of the invention.

 The following examples were made in a cold-wall CVD deposition apparatus with sublimator in the reactor. The distance between the sublimator and the substrate is 40 mm.

FIG. 1 illustrates the sublimator used to carry out these examples and which comprises two crucibles A1203, an external crucible 1 and an inner crucible 2. A space is provided between the two crucibles to receive the precursor TiCp2Cl2 (Cp: cyclo pentadienyl C5Hg), while the precursor ZrCp2C12 is placed in the inner crucible 2. The crucibles are surrounded by a heating coil 3. A cover 4 in
A1203 pierced with a central opening 5 is placed on the outer crucible 1 while the edge of the inner crucible 2 is spaced from the cover 4 to allow the passage of the precursor TiCp2C12 vapor to the substrate disposed 40 mm above .

The examples were conducted according to the following protocol:
The substrate and the precursors are introduced into the reactor which is evacuated for about 2 hours. The pumping is then stopped to fill the hydrogen reactor until the pressure reaches the atmospheric pressure at which the deposition process takes place.

 The sublimator is heated until the temperature reaches 240 C by means of the heating coil 3.

 At the same time the substrate is heated using an HF generator until its temperature Ts reaches between 650 and 850-.

 When the temperature of the precursor reaches 240 ° C., the gas phase ammonia flow rate is adjusted to the desired value and the process lasts 3 hours from this moment. The voltage across the heating winding 3 must be monitored at least during the first hour so as to achieve a good thermal equilibrium.

 During the cooling phase following the shutdown of the HF generator and the voltage at the terminals of the heating winding 3, the flow rates of hydrogen and ammonia are stopped and replaced by 100 sccm of argon for at least 1 hour. so as to purge the ammonia flow meter and the reactor before disassembly.

The experimental sublimator, illustrated in FIG. 1, made it possible to sublimate precursor fractions of the order of 3. The melting temperature of the TiCp2C12 is 265-270 ° C. (supplier: Fluka) and an optimal sublimation rate. is obtained at 240 C without decomposition of the precursor (a first fragmentation is observed from 290'C). By analogy, we assume that there is no decomposition of
ZrCp2C12 below its melting temperature which is given by the supplier (Aldrich) at 240 ° C. Under these conditions, the two precursors are sublimated at the same temperature.

 Since all the aforementioned parameters are fixed, the examples given in the table below vary only as a function of the temperature Ts of the tungsten carbide substrate with cobalt binder and the gas phase ammonia X mixed with hydrogen. It is indeed these two parameters that have the greatest influence on the composition of the deposit. The results of the examples come from the RX and MEB-EDX (surface) analyzes.

 MEB-EDX: Atomic percentages are from a surface (magnification 100) in the center of the sample.

Growth rates were measured on polished sections.

RX: the mesh parameter is calculated from the only line (200) of the deposit which is not disturbed by the lines of the substrate. Beforehand, the spectrum is recaled on the line (110) of the WC of the substrate (20 = 63.977).

<Tb>

## EQU1 ##
<tb> 850 <SEP> 10 <SEP> 11 <SEP> 83 <SEP> 4.640 <SEP> 1.38
<tb> 2 <SEP> 750 <SEP> 10 <SEP> 9 <SEP> 77 <SEP> 4.656 <SEP> 0.78
<tb> 3 <SEP> 850 <SEP> 10 <SEP> 6 <SEP> 84 <SEP> 4.524 <SEP> 2.25
<tb> 4 <SEP> 850 <SEP> 20 <SEP> 6 <SEP> 86 <SEP> 4.557 <SEW> 1.58
<Tb>
The atomic percentages in this table are derived from a surface analysis. It has been verified that the results are identical on polished cut, which shows the uniformity of the distribution of the elements in depth. We have been able to draw figure 2 which represents the atomic percentage of Zr as a function of the mesh parameter, using a ratio of Ti and Zr on polished section and RX results.

The boundaries, delimited by the theoretical parameters,
TiN, ZrN, TiC and ZrC are also indicated in this diagram of FIG.

The results in the table above and the diagram in Figure 2 allow us to make various observations:
The growth rates are generally lower than those observed during the deposition of Ti carbonitride from the same precursor. This suggests that the conversion rate of ZrCp2C12 is lower than that of TiCp2C1 at the same pyrolysis temperature.

 An NH 3 percentage of 10% seems to be quite sufficient, since at 850 ° C. an additional excess has a growth inhibiting effect, as has been observed during the deposition of titanium carbonitride alone, from the same precursor.

 The area covered by the examples is in the zone rich in Zr which is related to the physiognomy of the assembly which does not allow to independently heat the two precursors.

On the other hand, the variation of the substrate temperature only affects the growth rate and not the Zr content of the deposit. Under these conditions, the sublimation temperature of the products would affect the ratio
Zr / (Zr + Ti) whereas that of the substrate would only influence the growth rate.

 FIG. 3 is an X-ray imaging made on a sample according to Example 1 of the above table and showing a good distribution of the elements of the deposit.

 The foregoing examples all relate to mixed carbonitrides of Ti and Zr. It is obvious to those skilled in the art that mixed carbides of Ti and Zr can also be obtained. For this purpose, it suffices simply to suppress the supply of ammonia in the H2.

 As indicated, the sublimator illustrated in FIG.

1 was used to obtain the above examples. Another type of sublimator or even the use of two sublimators, one for each precursor, is contemplated in order to vary the Ti and Zr concentrations in the deposit.

FIG. 4 schematically illustrates the installation used to allow the proportions of
Ti and Zr, since the preceding examples, carried out using the reactor of FIG. 1, do not make it possible to modify the Zr / Ti ratio which remains around 9/1. This is because the sublimation temperature of Ti is substantially higher than that of Zr. This is why the precursor of
Ti was put in the outer crucible and that of Zr in the inner crucible. However, this measure was not enough. The fact of putting the two precursors in two separate crucibles, separated from each other, poses a problem of homogenization of the mixed compound Ti, Zr. In this case, on the one hand, TiC or TiCN is obtained, on the other hand, ZrC or ZrCN.If the two crucibles are too close to each other, the problem is not solved. for all that and in addition there is heat transfer by radiation between the two crucibles.

 The installation illustrated in FIG. 4, making it possible to solve the problem of the variation of the Zr / Ti ratio, in carbide or carbonitride coatings from solid organometallic precursors comprises a tubular tubular enclosure 6 whose base is fixed with known waterproof way to a base plate 7 pierced with several openings, including the openings 8.9 for supplying the gas enclosure. In this example, these gases, in the case of carbonitride, are H 2 and the nitrogen precursor NH 3. Other openings are provided for the connection of crucible heating and that of thermocouples as will be seen later. The upper end (not shown) is connected in the usual way to a vacuum pump. An opening 10, formed in the center of the base plate 7, serves for the sealed passage of a shaft 11, the inner portion 11a is in alumina, extending coaxially with the axis of revolution of this tubular enclosure 6. The lower end of the inner portion 11a is engaged with a connecting sleeve 12, while the upper end carries a disc 13 of support substrates. This disc 13 is graphite passivated SiC. In this example, it has four openings 14 each having a shoulder 14a serving as support for the substrate 15 to be coated. An electric winding 27 connected to a high-frequency RF power source surrounds tubular enclosure 6 at the disk 13 to heat the substrates 15 through the graphite disk.

Crucibles 16, four in number in this example, are distributed at equal angular distance from each other around the axis of revolution of the tubular enclosure 6. These crucibles 16 are positioned in cavities 17 formed in a support 18 fixed to four feet 19 placed in blind positioning holes 20 formed on the base plate 7,
An alumina lid 21 pierced with openings 22 corresponding to the openings of the crucibles 16 is placed thereon. Heating bodies 23 and thermocouples 24 serve for controlled heating of each of the crucibles.These heating bodies and these thermocouples are connected outside the sealed tubular enclosure 6 by openings formed through the base plate 7, the passage of the connection son through these openings being made in a sealed manner by the means usually used in the reactors for CVD.

The connection sleeve 12 comprises several screws 25 which make it possible to fix the shaft 11a at variable heights and therefore to adjust the author of the support disk 13 of the substrates 15 and thus to vary the distance between the crucibles 16 and the substrates 15. The lower end of the connection sleeve 12 is fixed to the shaft 11 which is that of a variable speed motor 26. In this case, this speed can vary from 30 to 300 RPM in order to rotate the disc 13 and therefore the substrates 15 to be coated with respect to the crucible and thereby produce a combined deposition of the various precursors contained in the crucibles, whether or not also reacting with a gaseous precursor, in this example, with NH3A using of the installation of FIG. 4, a TiZrCN coating was carried out at atmospheric pressure from the abovementioned precursors TiCp2Cl2 and ZrCp2Cl2 respectively located in two of the four crucibles 16 at 180 from each other. We feed the enclosure 6 in H2 and 5X
NH3.

The TiCp2Cl2 was heated to 240 ° C., the ZrCp2Cl2 was heated to 210 ° C. while the substrates were heated to 700 ° C. The substrate-carrying disc 13 was driven at a speed of the order of 1 to 2 revolutions / second, ie 0.2 to 0.4 m / s, which makes it possible to obtain a TiZrCN coating in which
X at Ti
= 1
X at Zr
% at Ti
= 1
% at C
In general, the temperature of the TiCp2C12 can vary between 240 ° and 270 ° C., that of the ZrCp2Cl2 between 210 ° and 240 ° C. and that of the substrate between 650 ° and 850 °. The rotational speed of the disc 13 can vary between 30 and 300 ° C. RPM which corresponds, given the diameter at the center of the substrate at 0.1 to 1 m / s. In general, increasing the temperature of one of the precursors relative to the other increases the proportion of the metal of this precursor in the coating relative to the metal of the other precursor. The variation of the precursor and substrate temperatures also makes it possible to modify the growth rate of the coating. The rotation of the disc 13 makes it possible to better homogenize the gaseous system coming from sources that are separated and distant from each other so that each substrate does not receive alternately a gas then the other and so on, but constantly a mixture caused by the stirring generated by the rotation of the disc. Therefore, it is possible to obtain a homogeneous and untreated coating of successive layers of TiCN and ZrCN.

 Among the substrates which can be coated by means of the method described, mention may be made of WC-Co for cutting tools with a view to increasing their hardness, alloys for electrical resistances to increase besides their hardness, their resistance to high temperature oxidation and / or their resistance to aqueous corrosion for heating elements in an aggressive medium such as fluidized beds or for chemical or underwater installations. It is also possible to coat substrates made of steel or cast iron, in particular to make cast iron molds for polymers or glass. Of course, the substrates mentioned here, as well as the applications are not limiting, but only mentioned by way of examples.

 Among the advantages of the process described above, besides the possibility of varying the ratios Ti, Zr at will, it is also possible to report the fact of working at atmospheric pressure and even 1 to 2 mm Hg above, the continuous input H2, NH3 gases causing a slight overpressure. Therefore, the risk of a leak accidentally returning oxygen which would cause oxidation of the coating is avoided. Given the very slight overpressure, a leak would result in a gas outlet of the chamber 6 thus avoiding the risk of oxidation.

 In the case of coatings of substrates of complex shapes, the disc 13 can be replaced by a tubular cylinder whose inner wall has fastening means suitable for the substrates to be coated.

 In addition to the method mentioned above, the installation of FIG. 4 can be used for any ceramic layer deposition on substrates from two solid precursors.

 Alternatively, it is possible, by rotating the substrate support 13, disc or cylinder, and passing only once in front of each crucible 16 to form several successive layers, as many as there are crucibles with different precursors. Thus one could form two superimposed layers TiN / Al203 as found on the cutting tools.

Claims (7)

 1. A process for coating a Ti or Zr carbide or a mixed carbonitride by chemical vapor deposition (CVD) on a metallic or ceramic substrate, characterized in that one decomposes on the one hand a organometallic precursor of Ti at its sublimation temperature and, on the other hand, an organometallic precursor of Zr at its sublimation temperature in a reactor fed with H2 and, in the case of carbonitride deposition, with NH3 as precursor of nitrogen and that one produces a relative displacement between the precursors of Ti and Zr on the one hand, and the heated substrate between approximately 650 and 850 on the other hand, to bring alternately this substrate vis-à-vis each of said precursors of Ti and Zr, the speed of this displacement being chosen so that the reaction between the components forms on this substrate a mixed deposition of carbide or carbonitride of the two elements.  2. Method according to claim 1, characterized in that one fixes the proportion of NH3 between 0 and 20X of the flow rate of H2.  3. Method according to claim 1, characterized in that it takes place at atmospheric pressure.  4. Method according to claim 1, characterized in that the organometallic precursors are respectively ZrtCsH6) 2Cl2 and Ti (C5H5) 2Cl2.  5. Method according to claim 4, characterized in that the Zr precursor is heated between 210 and 240 and the Ti precursor between 240 and 270 ° C.  6. Method according to claim 4, characterized in that said moving speed is between 0.1 and 1 m / s.  7. Apparatus for forming a ceramic coating from at least two solid metal precursors by chemical vapor deposition (CVD) on a metal or ceramic substrate inside a sealed enclosure provided with openings for connecting this chamber has gas sources determined with a view to creating a controlled atmosphere in this chamber, characterized in that it comprises:  a support member of said substrate,  guide means engaged with this support defining a determined displacement trajectory located substantially in a horizontal plane,  driving means engaged with this support to move it along this path,  a crucible for each of said precursors disposed below a portion of said trajectory  means for heating each of said crucibles and means for heating said substrate.