FR3153352A1 - Part having an external surface, said external surface being covered with a multi-layer coating - Google Patents

Abstract

The present invention relates to a part (1) having an external surface (1a), said external surface (1a) being covered with a coating (2) comprising at least: a) a first layer (3), deposited on the external surface (1a) of the part (1), comprising at least two sub-layers (3a, 3b): i) a first sub-layer (3a) made of a material comprising at least one element chosen from chromium, nickel, cobalt, phosphorus, nitrogen, niobium, their alloys and their mixtures; ii) a second sub-layer (3b), deposited on the first sub-layer (3a), made of a material comprising at least two elements chosen from chromium, nickel, tungsten, cobalt, carbon, nitrogen, their alloys and their mixtures; and b) a second layer (4), deposited on the first layer (3), being a layer of amorphous carbon. Figure for abstract: Fig. 1

Description

Part having an external surface, said external surface being covered with a multi-layer coating

The invention relates to the technical field of parts of an engine reducer, in particular an aircraft engine, such as a bearing of an aircraft engine reducer.

State of the art

The role of a reducer, particularly a mechanical reducer, is to modify the speed and torque ratio between the input shaft and the output shaft of a mechanical system.

New generations of dual-flow turbomachines, particularly those with a very high bypass ratio, include a mechanical reducer to drive the fan shaft. Typically, the reducer's purpose is to transform the so-called fast rotation speed of a power turbine shaft into a slower rotation speed for the shaft driving the fan.

Such a reducer comprises a central pinion, called a sun gear, a crown gear and pinions called planet gears, which are meshed between the sun gear and the crown gear. The planet gears are held by a frame called a planet carrier. The sun gear, the crown gear and the planet carrier are planet gears because their axes of revolution coincide with the longitudinal axis X of the turbomachine. The planet gears each have a different axis of revolution equally distributed over the same operating diameter around the axis of the planet gears. These axes are parallel to the longitudinal axis X.

There are several gearbox architectures. In the state of the art of double-flow turbomachinery, gearboxes are of the planetary or epicyclic type. In other similar applications, there are so-called differential or compound architectures.

On a planetary gearbox, the planet carrier is fixed and the crown constitutes the output shaft of the device which rotates in the opposite direction to the solar.

On an epicyclic reducer, the crown is fixed and the planet carrier constitutes the output shaft of the device which rotates in the same direction as the sun.

In a differential gearbox, no element is fixed in rotation. The crown rotates in the opposite direction to the sun gear and the planet carrier.

Gearboxes can be composed of one or more meshing stages. This meshing is ensured in different ways such as by contact, friction or even magnetic fields. There are several types of contact meshing such as straight, helical or herringbone teeth.

The bearings of a reducer, in particular the plain bearings of an aircraft engine reducer, have various advantages, including limited space requirements, a capacity to withstand high radial loads at high speeds, but also a significant gain in reliability and dynamics.

Currently, bearings, particularly the plain bearings of a reducer, particularly an aircraft engine, can be covered with coatings of different types, in order to limit their wear, the consequences of friction between mechanical parts thus limiting the risks of seizure.

For example, copper-lead or copper-bismuth coatings are used to cover the surface of bearings, such as a plain bearing. Coatings comprising a zinc-tin-lead alloy can also be cited as an example. These coatings have a Young's modulus much lower than that of steel, which causes the coating to flake off in the event of deformation of the substrate, and limits the service life of such a coating. Similarly, the coefficient of thermal expansion of these coatings is very different from that of steel, which can cause flaking in the event of heating of the system.

These coatings are therefore not entirely satisfactory, in particular, the seizure limit is quite low, the negative consequences are quickly observed. This therefore reduces the longevity of the part.

There is therefore a real need to provide a part, such as a bearing, particularly a plain bearing, with improved wear resistance.

To this end, the present invention relates to a part having an external surface, said external surface being covered with a coating comprising at least:

(a) a first layer, deposited on the external surface of the part, comprising at least two sub-layers:

(i) a first underlayer made of a material comprising at least one element chosen from chromium, nickel, cobalt, phosphorus, nitrogen, niobium, their alloys and their mixtures;

(ii) a second sub-layer, deposited on the first sub-layer, made of a material comprising at least two elements chosen from chromium, nickel, tungsten, cobalt, carbon, nitrogen, their alloys and their mixtures;

b) a second layer, deposited on the first layer, being a layer of amorphous carbon.

Thanks to the part according to the invention, an improvement in wear resistance is obtained with a coating having a Young's modulus and a coefficient of expansion close to that of steel, for example during the different operating cycles. In addition, the coefficient of friction is minimized thanks to the part according to the invention. Thus, thanks to the invention, the longevity of the part is increased.

Furthermore, thanks to the undercoats of the invention, the adhesion of the coating to the surface of the part is ensured. In addition, in the event of tearing, the undercoats can also act as a solid lubricant, thus extending the life of the coating on the part, and therefore increasing the life of the part according to the invention.

Preferably, the material of the first underlayer comprises at least one element chosen from chromium, nickel, phosphorus, nitrogen, niobium, their alloys and their mixtures.

Advantageously, the material of the second sub-layer comprises at least two elements chosen from chromium, nickel, tungsten, carbon, nitrogen, their alloys and their mixtures.

Preferably, the first underlayer and the second underlayer are different. In other words, the material of the first underlayer and the material of the second underlayer are preferably of different natures.

According to a preferred embodiment, the second layer is a layer of hydrogenated or non-hydrogenated amorphous carbon, preferably a layer of hydrogenated amorphous carbon.

Amorphous carbon, also called DLC for “Diamond Like Carbon”, is a family of coatings based on carbon atoms.

Thus, preferably, the second layer is a hydrogenated amorphous carbon (a-c:H) layer.

Thanks to the amorphous carbon layer, wear resistance is further improved and the coefficient of friction is minimized.

Preferably, the ratio of sp ² /sp ³ carbon-carbon bonds in the amorphous carbon layer is from 1 to 3.

Thanks to this particular ratio, wear resistance is further improved.

Advantageously, the coating has a thickness ranging from 0.5 µm to 50 µm.

According to a preferred embodiment, the hardness of the second layer is greater than or equal to, more preferably strictly greater than, the hardness of the first layer.

Advantageously, the hardness of the second layer is greater than or equal to, more preferably strictly greater than, the hardness of the second sub-layer.

Thus, preferably, the coating has a hardness gradient and preferably a modulus gradient.

The coating preferably has a hardness ranging from 1000 to 4000 Hv (Vickers hardness). The Vickers hardness is determined experimentally by nano-indentation or micro-durometer, according to a conventional method well known to those skilled in the art.

The coating preferably has a Young's modulus ranging from 170 to 250 GPa. The Young's modulus is determined experimentally by nano-indentation.

According to a particular embodiment, the first layer further comprises:

iii) a third sub-layer, deposited on the second sub-layer, made of a material comprising at least one element chosen from chromium, nickel, titanium, silicon, cobalt, phosphorus, nitrogen, their alloys and their mixtures.

Advantageously, the hardness of the second layer is greater than or equal to, more preferably strictly greater than, the hardness of the third sub-layer.

According to another particular embodiment, the first layer further comprises:

iv) a fourth sub-layer, deposited on the third sub-layer, made of a material comprising at least one element chosen from chromium, nickel, titanium, silicon, cobalt, phosphorus, nitrogen, their alloys and their mixtures.

Advantageously, the hardness of the second layer is greater than or equal to, more preferably strictly greater than, the hardness of the fourth sub-layer.

According to yet another particular embodiment, the first layer further comprises:

(v) a fifth sub-layer, deposited on the fourth sub-layer, made of a material comprising at least one element chosen from chromium, nickel, titanium, silicon, cobalt, phosphorus, nitrogen, their alloys and their mixtures.

Advantageously, the hardness of the second layer is greater than or equal to, more preferably strictly greater than, the hardness of the fifth sub-layer.

Advantageously, the part is a bearing, such as a plain bearing.

Another object of the invention is a method of manufacturing the part according to the invention comprising the following steps:

(a) providing a part according to the invention having an external surface;

(b) forming on the external surface at least the first sub-layer and the second sub-layer to obtain the first layer, as defined previously;

(c) forming on the first layer the second layer as defined previously to obtain the coating.

The present invention also relates to an aircraft comprising at least one part according to the invention as defined above.

Other aims, advantages and characteristics will emerge from the description which follows, given purely for illustrative purposes and with reference to the attached drawings in which:

FIG. 1 represents a part having an external surface being covered with a multi-layer coating according to a first embodiment in accordance with the invention;

FIG. 2 represents a part having an external surface being covered with a multi-layer coating according to a second embodiment in accordance with the invention;

FIG. 3 represents a part having an external surface being covered with a multi-layer coating according to a third embodiment in accordance with the invention;

FIG. 4 represents a part having an external surface being covered with a multi-layer coating according to a fourth embodiment in accordance with the invention.

In what follows, the limits of a domain of values are included in this domain, notably in the expressions “between … and …” and “… from … to …”.

Furthermore, the expression “at least one” used in this description is equivalent to the expression “one or more”.

Detailed description of implementation methods

There FIG. 1 illustrates a part 1 having an external surface 1a which is covered with a coating 2 according to a first embodiment according to the invention.

The coating 2 comprises a first layer 3, deposited on the external surface 1a of the part 1, and a second layer 4 deposited on the first layer 3.

The first layer 3 comprises a first sub-layer 3a made of a material comprising at least one element chosen from chromium, nickel, cobalt, phosphorus, nitrogen, niobium, their alloys and their mixtures. The first sub-layer 3a is deposited on the external surface 1a of the part 1.

Preferably, the material of the first sub-layer 3a comprises at least one element chosen from chromium, nickel, phosphorus, nitrogen, niobium, their alloys and their mixtures.

The material of the first sub-layer 3a may be a metal, a doped metal or a ceramic containing chromium, a nickel alloy, such as a chromium-nickel alloy or a nickel-phosphorus alloy, a mixture of nitrogen and chromium, such as chromium nitride.

The first layer 3 further comprises a second sub-layer 3b, deposited on the first sub-layer 3a, made of a material comprising at least two elements chosen from chromium, nickel, tungsten, cobalt, carbon, nitrogen, their alloys and their mixtures.

The material of the second sub-layer 3b may be a nickel alloy, such as a chromium-nickel alloy, a mixture of nitrogen and chromium, a mixture of carbon and tungsten, such as tungsten carbide.

Additionally, the material of the second sub-layer 3b may be doped with an element, such as carbon, or a metallic element, such as silicon, chromium, or titanium.

The first sub-layer 3a and the second sub-layer 3b may be different. Preferably, they are different. In other words, the material of the first sub-layer 3a and the material of the second sub-layer 3b are preferably of different natures.

For example, if the material of the first sub-layer 3a is a chromium-nickel alloy, then the material of the second sub-layer 3b will be a material different from the chromium-nickel alloy in this embodiment.

Advantageously, the second layer 4 is a layer of hydrogenated or non-hydrogenated amorphous carbon, preferably a layer of hydrogenated amorphous carbon (a-c:H).

Preferably the ratio of carbon-carbon sp ² /sp ³ bonds in the second layer 4 ranges from 1 to 3.

Preferably, the coating 2 has a thickness ranging from 0.5 µm to 50 µm.

The part 1 comprising the coating 2 according to the invention can be manufactured according to a method comprising the following steps:

(a) provide part 1 having external surface 1a;

(b) forming on the external surface 1a the first sub-layer 3a and the second sub-layer 3b to obtain the first layer, as defined previously.

The sub-layers 3a and 3b are for example deposited by physical vapor deposition (PVD) or by plasma-enhanced chemical vapor deposition (PECVD or PAVCD); the second layer 4 is deposited by PACVD or PECVD to obtain a better surface finish and a higher deposition speed.

(c) forming on the first layer the second layer as defined previously to obtain the coating.

There FIG. 2 illustrates a part 1 having an external surface 1a which is covered with a coating 2 according to a second embodiment according to the invention.

Just like the part 1 as described in the first embodiment, the coating 2 comprises a first layer 3, deposited on the external surface 1a of the part 1, and a second layer 4 deposited on the first layer 3.

The first layer 3 also comprises at least a first sub-layer 3a and a second sub-layer 3b.

The same preferred modes as described in the first embodiment are valid for this second embodiment.

The first layer 3 further comprises a third sub-layer 3c, deposited on the second sub-layer 3b, made of a material comprising at least one element chosen from chromium, nickel, cobalt, phosphorus, titanium, silicon, nitrogen, their alloys and their mixtures.

In this second mode, the second layer 4 is deposited on the third sub-layer 3c.

There FIG. 3 illustrates a part 1 having an external surface 1a which is covered with a coating 2 according to a third embodiment according to the invention.

Just like the part 1 as described in the second embodiment, the coating 2 comprises a first layer 3, deposited on the external surface 1a of the part 1, and a second layer 4 deposited on the first layer 3.

The first layer 3 also comprises at least a first sub-layer 3a, a second sub-layer 3b and a third sub-layer 3c.

The same preferred modes as described in the first and second embodiments are valid for this third embodiment.

The first layer 3 further comprises a fourth sub-layer 3d, deposited on the third sub-layer 3c, made of a material comprising at least one element chosen from chromium, nickel, titanium, silicon, cobalt, phosphorus, nitrogen, their alloys and their mixtures.

In this third mode, the second layer 4 is deposited on the fourth sub-layer 3d.

There FIG. 4 illustrates a part 1 having an external surface 1a which is covered with a coating 2 according to a fourth embodiment according to the invention.

Just like the part 1 as described in the third embodiment, the coating 2 comprises a first layer 3, deposited on the external surface 1a of the part 1, and a second layer 4 deposited on the first layer 3.

The first layer 3 also comprises at least a first sub-layer 3a, a second sub-layer 3b, a third sub-layer 3c and a fourth sub-layer 3d.

The same preferred modes as described in the first, second and third embodiments are valid for this fourth embodiment.

The first layer 3 further comprises a fifth sub-layer 3e, deposited on the fourth sub-layer 3d, made of a material comprising at least one element chosen from chromium, nickel, cobalt, phosphorus, nitrogen, titanium, silicon, their alloys and their mixtures.

In this fourth mode, the second layer 4 is deposited on the fifth sub-layer 3e.

Example

Five steel pieces were used, hereinafter referred to as pieces 1 to 5.

Disc pin tests were performed according to DIN 50324-07, ASTM G99-05 or ISO 18535 standards, generating the results available in Table 1.

All pins are made of low alloy steel and have a ground surface, with the particularities of Table 1. The discs are all identical, made of low alloy steel with a ground surface.

Part 1 has undergone a thermochemical surface hardening treatment.

Part 2 was used as is and did not undergo thermochemical treatment.

Rooms 3 to 5 were covered with coatings of different types. All the information can be found in Table 1 below.

P room 1 2 3 4 5 Thermal treatment YES NO - - - Coating - - CuPb ₁₈ Sn CuPb Typical multi-layer coating of the application

Thus, parts 1 to 4 are comparative parts. Part 5 is a part according to the invention, coated with a layer of amorphous carbon with sub-layers with a thickness of 0.5 µm to 50 µm, by PVD and PACVD.

Then these parts were subjected to a test to assess the wear rate.

The results are presented in Table 2 below. The wear rate is expressed in µm/s.

P room 1 2 3 4 5 Wear rate (µm/s) 0.5 2.5 1.4 0.25 0.05

It is clear that part 5 according to the invention has a significantly lower wear rate than that of comparative parts 1 to 4.

Thus, the part according to the invention makes it possible to improve wear resistance.

Claims (11)

Aircraft comprising at least one part (1) having an external surface (1a), said external surface (1a) being covered with a coating (2) comprising at least:
a) a first layer (3), deposited on the external surface (1a) of the part (1), comprising at least two sub-layers (3a, 3b):
i) a first sub-layer (3a) made of a material comprising at least one element chosen from chromium, nickel, cobalt, phosphorus, nitrogen, niobium, their alloys and their mixtures;
ii) a second sub-layer (3b), deposited on the first sub-layer (3a), made of a material comprising at least two elements chosen from chromium, nickel, tungsten, cobalt, carbon, nitrogen, their alloys and their mixtures;
b) a second layer (4), deposited on the first layer (3), being a layer of amorphous carbon. Aircraft according to claim 1, characterized in that the material of the first sub-layer (3a) comprises at least one element chosen from chromium, nickel, phosphorus, nitrogen, niobium, their alloys and their mixtures. Aircraft according to claim 1 or 2, characterized in that the material of the second sub-layer (3b) comprises at least two elements chosen from chromium, nickel, tungsten, carbon, nitrogen, their alloys and their mixtures. Aircraft according to any one of the preceding claims, characterized in that the first sub-layer (3a) and the second sub-layer (3b) are different. Aircraft according to any one of the preceding claims, characterized in that the second layer (4) is a layer of hydrogenated or non-hydrogenated amorphous carbon, preferably a layer of hydrogenated amorphous carbon. Aircraft according to any one of the preceding claims, characterized in that the ratio of carbon-carbon sp ² /sp ³ bonds in the second layer (4) ranges from 1 to 3. Aircraft according to any one of the preceding claims, characterized in that the coating (2) has a thickness ranging from 0.5 µm to 50 µm. Aircraft according to any one of the preceding claims, characterized in that the first layer (3) further comprises:
iii) a third sub-layer (3c), deposited on the second sub-layer (3b), made of a material comprising at least one element chosen from chromium, nickel, titanium, silicon, cobalt, phosphorus, nitrogen, their alloys and their mixtures. Aircraft according to claim 8, characterized in that the first layer (3) further comprises;
iv) a fourth sub-layer (3d), deposited on the third sub-layer (3c), made of a material comprising at least one element chosen from chromium, nickel, titanium, silicon, cobalt, phosphorus, nitrogen, their alloys and their mixtures. Aircraft according to claim 9, characterized in that the first layer (3) further comprises:
v) a fifth sub-layer (3e), deposited on the fourth sub-layer (3d), made of a material comprising at least one element chosen from chromium, nickel, titanium, silicon, cobalt, phosphorus, nitrogen, their alloys and their mixtures. Aircraft according to any one of the preceding claims, characterized in that the part (1) is a bearing.