FR2745300A1 - Protecting engine parts against wear and thermal shock - Google Patents

Abstract

Coating for protecting vehicle engine parts against wear and thermal shock comprises an alloy, preferably aluminium based, of which at least 50% comprises one or more quasicrystalline phases. Also claimed are the use of such a coating for protecting engine parts and the application of such a coating using a plasma torch, a plasma arc, cathode spluttering, welding or vapour deposition.

Description

Anti-wear and / or thermal protection coatings for parts
such as motor vehicle engine parts
The subject of the invention is anti-wear and / or thermal protection coatings which can be used in particular, but not exclusively, for the protection of motor vehicle engine parts.

In operation, the parts of an engine (which are generally made of cast iron or steel) are highly stressed, on the one hand because they are subjected to high temperatures, and on the other hand because a certain number of 'between them are in motion with respect to each other with friction contact, such as for example the pistons in the cylinders, or undergo mutual shocks such as the valves and their seats.

This is why we have sought various means to improve the life of engine parts, in particular by reducing the wear of those which are subjected to friction or shock.

Among the solutions proposed, mention may be made of ceramic coatings or surface treatments such as carbonitriding, hard chromium plating or the deposition of molybdenum by plasma. However, these methods are either difficult to implement or very expensive.

The invention aims to remedy these drawbacks by providing an anti-wear and / or thermal protection coating consisting of a quasicrystalline alloy containing one or more quasicrystalline phases whose total volume fraction is greater than or equal to 50%.

In the present text, the expression "quasicrystalline phase" includes: 1) - The phases presenting symmetries of rotation normally incompatible
with translational symmetry, i.e. axis of rotation symmetries
of order 5, 8, 10 and 12, these symmetries being revealed by the diffraction of the
radiation. By way of example, mention may be made of the icosahedral phase I of
point group m3 5 (cf. D. Shechtman, I. Blech, D. Gratias, JW Cahn,
Metallic Phase with Long-Range Orientational Order and No Translational
Symmetry, Physical Review Letters, Vol. 53, no. 20, 1984, pages 1951-1953)
and the decagonal phase D of point group 10 / mmm (cf. L. Bendersky,
Quasicrystal with One Dimensional Translational Symmetry and a Tenfold
Rotation Axis, Physical Review Letters, Vol. 55, no. 14, 1985, pages 1461
1463) .The X-ray diffraction diagram of a decagonal phase
true was published in "Diffraction approach to the structure of decagonal
quasicrystals, JM Dubois, C. Janot, J. Pannetier, A. Pianelli, Physics
Letters A 117-8 (1986) 421-427 ".

2) - The approximate phases or approximate compounds which are
true crystals insofar as their crystallographic structure remains
compatible with translational symmetry, but which, in the
electron diffraction plate, diffraction figures whose symmetry
is close to the axes of rotation 5, 8, 10 or 12.

Among these phases, we can cite as an example the orthorhombic phase
1, characteristic of an alloy of the prior art having the composition
atomic A165Cu20FelOCrS, whose mesh parameters are
ao (l) = 2.366, b0 (1) = 1.267, c0 (1) = 3.252 in nanometers. This phase
orthorhombique O 1 is said to be approximate of the decagonal phase. She
is also so close that it is not possible to distinguish its diagram
of X-ray diffraction from that of the decagonal phase.

We can also cite the rhombohedral phase with parameters = = 3.208 nm, a = 36, present in alloys of similar composition
of A164Cu24Fe 12 in number of atoms (M. Audier and P. Guyot,
Microcrystalline AlFeCu Phase of Pseudo Icosahedral Symmetry, in
Quasicrystals, eds. MV Jaric and S. Lundqvist, World Scientific, Singapore,
1989).

 This phase is an approximate phase of the icosahedral phase.

We can also cite orthorhombic phases 2 and O3 of parameters
respective to (2) = 3.83; b0 (2) = 0.41; c0 (2) = 5.26 and au (3) = 3.25
b0 (3) = 0.41; cl (3) = 9.8 in nanometers present in an alloy of
composition Al63Cu17,5Co17,5Si2 in number of atoms or the phase
orthorhombic O4 of parameters a0 (4) = 1.46; b0 (4) = 1.23; c0 (4) = 1.24
in nanometers which is formed in the alloy of composition A163CugFel2Crl2
in number of atoms. The orthorhombic approximants are described by
example in C. Dong, JM Dubois, J. Materials Science, 26 (1991), 1647.

We can also cite a phase C, with a cubic structure, very often
observed in coexistence with the approximate or quasicrystalline phases
true. This phase which is formed in certain Al-Cu-Fe alloys and
Al-Cu-Fe-Cr, consists of a super-structure, by chemical effect of
alloying elements with respect to aluminum sites, a phase of
Cs-CI type structure and network parameter al = 0.297 nm.

A diffraction diagram of this cubic phase has been published (C. Dong,
JM Dubois, M. de Boissieu, C. Janot; Neutron diffraction study of the
peritectic growth of the A165Cu20Fe15 icosahedral quasicrystal; J. Phys.

Condensed Matte 2 (1990), 6339-6360) for a phase sample
pure cubic composition A165Cu20Fe15 in number of atoms.

We can also cite a phase H of hexagonal structure which derives
directly from phase C as shown by the epitaxy relationships
observed by electron microscopy between crystals of phases C and H and
the simple relations which connect the parameters of the crystal lattices, namely aH = 3 w / (to within 4.5%) and CH = 3 v / 2 (to within 2.5%).

This phase is isotype of a hexagonal phase, noted + AlMn, discovered
in Al-Mn alloys containing 40% by weight of Mn [MA Taylor,
Intermetallic phases in the Aluminum-Manganese Binary System, Acta
Metallurgica 8 (1960) 256].

The cubic phase, its substructures and the phases derived from them, constitute
a class of approximate phases of the quasicrystalline phases of
neighboring compositions.

According to other characteristics of the coating which is the subject of the invention:
- the alloy has the following composition, in atomic percentage
.7 7 to 27.5% copper
6 to 15% iron
0 to 15% chromium
. boron present up to 7%. 0 to 4% tungsten
base: aluminum;
- the alloy has the following composition, in atomic percentage:
22.5 to 27.5% copper
. 11 to 14% iron. 0 to 0 to 1.5% chromium
e of boron present up to 7%
. 0 to 0.7% tungsten
base: aluminum;
- The alloy has the following composition: A159CU25,5Fel2,5B3;
- the alloy has the following composition, in atomic percentage:
.7 7 to 11% copper
6 to 15% of iron
6 to 15% chromium
boron present up to 2%
. 0 to 4% tungsten
base: aluminum;
- The alloy has the following composition: A166CU9Fe10,5Cr10,5B1W3;
- the total proportion of boron and tungsten is less than or equal to 8%.

The invention also relates to the use of such a coating for the protection of parts such as motor vehicle engine parts.

The parts in question can be friction parts and / or subjected to shocks such as the parts of the distribution (tappets, rocker arms, camshafts, valves, valve seats) or of the crankshaft (barrels of the crankcase, pistons, segments, connecting rods, crankshafts), or essentially thermally stressed parts such as the piston heads, the cylinder head, the exhaust components such as the manifold.

Finally, the subject of the invention is also a method of depositing such an alloy on a part to be protected, this deposit possibly being carried out by one of the following methods: thermal spraying using a plasma torch, thermal spraying using transferred arc plasma, sputtering, welding, vapor deposition.

Other objects, characteristics, details and advantages of the invention will emerge from the description which follows, given solely by way of example, of tests carried out with coatings according to the invention, this description being given with reference to the drawings annexed, in which
- Figure 1 is a schematic view in vertical section of an assembly
used to perform wear tests;
- Figure 2 is a table giving the results of tests carried out with the
assembly of Figure 1;
- Figure 3 is a schematic perspective view of an assembly used
to perform thermal shock tests; and
- Figure 4 is a graph giving the temperature inside a head of
piston during such a test depending on whether the piston head is covered or
not a coating according to the invention.

The assembly of FIG. 1 essentially consists of an enclosure 1 inside which a roller 2 is rotatably mounted around a horizontal axis 3. A support 4, mounted on an axis 5 and placed above the roller , has a cylindrical lower face 6 of shape complementary to that of the roller and extending substantially over a third of the circumference thereof. Two housings are provided on the underside of the support 4 for samples 7. 8 to be tested, these being held by screws such as 9 and protruding from the surface 6 by a few millimeters.

The roller is rotated while the support is biased downwards so that samples 7 and 8 are applied to the roller with a given force. It will be noted that the support is symmetrical with respect to a vertical plane P containing the horizontal axis of rotation of the roller and that the lubrication is ensured by an oil bath whose level at rest is indicated in H. The samples used are from parallelepiped shape and arranged so that their planes of symmetry intersect along the axis of rotation of the roller and are perpendicular to each other. The drive means of the roller and the device for applying the support to the roller have not been shown in FIG. 1.

Various tests have been carried out with 10 × 10 × 6 mm samples of 16MC5 steel (used for certain parts of the distribution of a motor vehicle engine) coated with a layer of 300 micrometers of an M59Cu23.5Fe12 alloy, 5B3. Each test was carried out at a temperature of 80 "C for 24 hours, the applied loads being constant and between 10 and 180 kgs. The roller was made of GL cast iron and the lubrication was provided by a motor vehicle engine oil.

The results are given in the table in FIG. 2. There is good resistance to wear since the loss of mass of the samples, if it increases with the load, remains moderate. Note, however, that this is especially true for loads of 40 to 180 kg: indeed, the value of 10 kg seems too low because it results in too great a dispersion of the results. As for the friction coefficients, they remain low, even at high loads.

We will now describe thermal shock tests carried out on pistons of an aluminum-based alloy commonly used for this use, the head of which was covered or not with a layer of alloy A170CugFe10, gCr105 whose thickness varied from 500 at 800 micrometers because of the unevenness due to the presence of a combustion bowl at this location.

Two types of treatment were carried out, namely:
1) - 2000 cooling cycles between temperatures of 400 and 600
C, the passage from one temperature to the other taking place in 10 seconds.

2) - 500 cooling cycles between 750 and 17 C, the passage of a
temperature to the next being done in 1 second.

The assembly used is illustrated in FIG. 3. It can be seen that the piston 10 is mounted at the end of an arm 11 fixed on a wheel 12 driven by a stepping motor 13. An arm 11a, opposite to the arm 11, used for balancing the assembly.

The heating is obtained by an oxyacetylene torch 14, the cooling taking place in air in the first case, by passing through a water tank in the second.

FIG. 3 also shows a water tank 15 and a control module 16. It will also be noted that it is the active face of the piston head which is directed towards the torch 14.

The diagram in FIG. 4 shows the temperature in the mass of the piston head as a function of the distance from the active face once the maximum temperature has been reached. On the left side of the figure, there is shown very schematically a half-sectional view of the head of the piston 10, the coating being indicated at 17 and the grooves for the segments at 1 0a. Curve C1 corresponds to uncoated pistons and curve C2 to coated pistons, these curves having been determined by a finite element method from measurements carried out using thermocouples placed inside the piston. It can be seen that the temperature decreases much faster in the case of coated pistons, which shows the high efficiency of the coatings of the invention as a thermal barrier.

The coatings of the invention therefore have particularly advantageous advantages since they provide both anti-wear protection and thermal protection of the parts on which they are deposited. The manufacturing cost of the motors is thus reduced since the same material can be deposited on all the parts which need to be protected, whether they are moving parts and therefore subject to wear, or thermally stressed parts. , which can be fixed or mobile.

These coatings are therefore well suited for thermal protection of pistons, both for two-stroke and four-stroke engines. The coating insulates the part, reduces its operating temperature and increases its service life. In addition, in the case of diesel engines, the application of the insulating coating on the surfaces of the combustion chamber leads to an increase in the power of the engine.

Claims (16)

1. Anti-wear and / or thermal protection coating for parts such as motor vehicle engine parts, characterized in that it consists of a quasicrystalline alloy containing one or more quasicrystalline phases, the total volume fraction of which is greater than or equal to 50%. 2. Coating according to claim 1, characterized in that the alloy has the following composition, in atomic percentage:  .7 7 to 27.5% copper 6 to 15% iron  0 to 15% chromium  o boron present up to 7%  .O at 4% tungsten  base: aluminum. 3. Coating according to claim 2, characterized in that the alloy has the following composition, in atomic percentage:  22.5 to 27.5% copper  11 to 14% of iron  0-1.5% chromium  boron present up to 7% 0 to 0.7% tungsten  base: aluminum. 4. Coating according to claim 3, characterized in that the alloy has the following composition: Al59Cu25,5Fe12,5B3. 5. Coating according to claim 2, characterized in that the alloy has the following composition:  7 to 11% copper. 6 6 to 15% iron  6 to 15% chromium  boron present up to 2%. 0 0 to 4% tungsten  base: aluminum. 6. Coating according to claim 5, characterized in that the alloy has the following composition: A166CU9Fel0,5BlW3 7. Coating according to any one of the preceding claims, characterized in that the total proportion of boron and tungsten is less than or equal to 8%. 8. Use of a coating according to any one of claims 1 to 7 for the protection of parts such as motor vehicle engine parts. 9. Use according to claim 8, characterized in that said parts are parts subjected to friction and / or shock. 10. Use according to claim 9, characterized in that said parts are parts of the distribution of a motor vehicle engine. 11. Use according to claim 10, characterized in that said parts belong to the group comprising: tappets, rocker arms, camshaft, valves and valve seats. 12. Use according to claim 9, characterized in that said parts are parts of the crankshaft of a motor vehicle engine. 13. Use according to claim 12, characterized in that said parts belong to the group comprising: the barrels of the cylinder block, the pistons, the segments, the connecting rods and the crankshaft. 14. Use according to claim 8, characterized in that said parts are essentially thermally stressed parts. 15. Use according to claim 14, characterized in that said parts belong to the group comprising the piston head, the cylinder head and the components of the exhaust, in particular the manifold. 16. A method of depositing a coating according to any one of claims 1 to 7 on a part to be protected, characterized in that it is chosen from the following methods thermal spraying using a plasma torch, thermal spraying using transferred arc plasma, sputtering, welding, vapor deposition.