FR3132716A1 - Textured composite material and associated method of manufacture - Google Patents

Abstract

Composite material comprising a metal matrix (3) made of an iron or copper-based alloy, fillers (4) made of material having a hardness greater than the hardness of the metal matrix (3), and a surface texture comprising protrusions ( 5) formed by said fillers (4) highlighted on all or part of the surface of the composite material. Figure for abstract: Figure 1

Description

Textured composite material and associated manufacturing process

The present invention relates, in general, to wear linked to friction between two solids and, more precisely, to the optimization of friction between two solids to reduce wear phenomena, in particular in a motor vehicle combustion engine at operating speed. lubricated.

More particularly, the invention relates to a composite material comprising a surface texture and a method of manufacturing such a composite material.

In order to reduce friction in a motor vehicle combustion engine, such as the friction of a piston in the cylinder bore, the lubricating oils generally used are increasingly fluid.

However, the reduction in oil viscosity leads to an increase in friction between the solids used, leading to their premature wear.

Conventionally, friction modifier additives, such as ZnDDP or MoDTC, are therefore added to oils to allow the creation of tribofilm whose function is to protect surfaces and thus improve friction.

However, the materials and coatings used in engines for rubbing contacts are not optimized for these low viscosity oils containing these additives.

The invention therefore aims to remedy these drawbacks and to propose a composite material making it possible to optimize friction between two solids, in particular adapted to friction in a lubricated regime in the presence of a low viscosity oil loaded with friction modifier additives.

It is therefore proposed a process for manufacturing a composite material comprising a metal matrix made of an alloy based on iron or copper, and material fillers having a hardness greater than the hardness of the metal matrix, the process comprising the development a surface texture comprising the formation of protuberances by highlighting said charges on all or part of the surface of the composite material by mechanical abrasion or chemical attack.

The filler material has mechanical resistance properties to mechanical abrasion or chemical attack carried out on all or part of the surface of the composite material.

On the contrary, the metal matrix, of hardness lower than the hardness of the filler material, does not have sufficient mechanical resistance properties allowing it to resist mechanical abrasion or chemical attack carried out on all or part of the surface of the composite material. .

Preferably, the hardness of the material of the fillers is greater than or equal to 550 Hv.

According to one embodiment, the metal matrix is made of steel, preferably steel comprising between 11.5 and 13.5% by weight of chromium, between 0 and 1% by weight of manganese, between 0 and 1 % by weight of silicon, between 0 and 0.04% by weight of phosphorus, between 0 and 0.03% by weight of carbon, between 0 and 0.03% by weight of sulfur and the remainder of iron.

Advantageously, the charges can be made of a metallic material, preferably a steel, more preferably a tool steel comprising between 5.5 and 6.75% by weight of tungsten, between 4.5 and 5.5% by weight of molybdenum, between 3.75 and 4.5% by weight of chromium, between 1.75 and 2.20% by weight of vanadium, between 0.8 and 1% by weight of carbon, between 0.20 and 0.45 % by weight of silicon, between 0.15 and 0.4% by weight of manganese, between 0 and 0.03% by weight of phosphorus, between 0 and 0.03% by weight of sulfur and the remainder of iron.

The invention also relates to a method of depositing a composite material as defined above on a substrate to form a coating, in which the deposition is carried out by thermal projection, such as by dynamic projection by cold gas, plasma or flame. high-speed oxygen, or produced by laser reloading.

The invention also relates to a composite material comprising a metal matrix made of an iron or copper-based alloy, material fillers having a hardness greater than the hardness of the metal matrix, and a surface texture comprising protrusions formed by said fillers highlighted on all or part of the surface of the composite material.

Advantageously, the metal matrix can be made of steel, preferably a steel comprising between 11.5 and 13.5% by weight of chromium, between 0 and 1% by weight of manganese, between 0 and 1% by weight of silicon, between 0 and 0.04% by weight of phosphorus, between 0 and 0.03% by weight of carbon, between 0 and 0.03% by weight of sulfur and the remainder of iron.

Advantageously, the fillers can be made of a metallic material, preferably a steel, more preferably a tool steel comprising between 5.5 and 6.75% by weight of tungsten, between 4.5 and 5.5% by weight of molybdenum, between 3.75 and 4.5% by weight of chromium, between 1.75 and 2.20% by weight of vanadium, between 0.8 and 1% by weight of carbon, between 0.20 and 0.45% by weight weight of silicon, between 0.15 and 0.4% by weight of manganese, between 0 and 0.03% by weight of phosphorus, between 0 and 0.03% by weight of sulfur and the remainder of iron.

The invention also relates to a substrate coated with a composite material as described above.

The invention also relates to a system comprising a first part comprising a composite material as described above, all or part of the protuberances of said composite material being arranged opposite a second part, and an oil with a viscosity less than or equal to 5W30 arranged between said composite material and the second part.

By lubricating oil with a viscosity less than or equal to 5W30, we mean a lubricating oil with a viscosity less than or equal to 5 measured in centistokes at -18°C and a viscosity less than or equal to 30 measured in centistokes at 100°C.

According to one characteristic, all or part of the protuberances of said composite material being placed in contact with the second part, and said oil comprises at least one friction modifier additive, preferably chosen from ZnDDP and MoDTC.

According to one embodiment, the first part can be a friction element of a motor vehicle, such as a cylinder bore, a bearing, a crankshaft bearing, a camshaft bearing or a cam.

The invention also relates to a motor vehicle comprising a composite material as described above.

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

is a sectional view of a cylinder bore for a motor vehicle combustion engine according to one embodiment of the invention.

, , And illustrate a system comprising a cylinder bore made of textured composite material in contact with a piston, represented respectively at times T0, T1, T2 and T3.

represents the evolution of the friction coefficient as a function of time measured during an alternating pin-plane friction test.

In what follows, the limits of a domain of values are included in this domain, in particular in the expression “between”.

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

There illustrates a first part 1 comprising a coating 2 made of a composite material comprising a metal matrix 3, fillers 4 and a surface texture comprising protuberances 5.

In the example developed below, the first part 1 is a cylinder bore of a motor vehicle combustion engine intended to cooperate with a second part 6 formed by a piston.

According to another embodiment, the first part 1 can be another friction element, for example a bearing, a crankshaft bearing, a camshaft bearing or even a motor vehicle cam.

The metal matrix 3 is formed by an alloy chosen from an iron-based alloy, or a copper-based alloy.

In addition, the fillers 4 are formed of a material whose hardness is greater than the hardness of the material of the metal matrix.

In addition, the surface texture includes protrusions 5 formed by the charges 4 highlighted on a surface of the composite material.

According to one aspect, the invention relates to a method of manufacturing a composite material comprising a metal matrix 3 made of an alloy based on iron or copper, and fillers 4 made of material having a hardness greater than the hardness of the matrix metallic.

In addition, the manufacturing process includes the development of a texture comprising the formation of protuberances 5 by highlighting the fillers 4 on all or part of the surface of the composite material.

By protuberance is meant an eminence or projection formed by a load 4 of the composite material from a surface of the composite material.

The texture is developed by mechanical abrasion or chemical attack.

Mechanical abrasion can be carried out using at least one of: a lapping, polishing or smoothing process. A portion of the metal matrix 3 is thus mechanically removed so as to reveal the charges 4 present on the surface 2a of the coating 2.

The highlighting of the charges 4 to form protrusions 5 by chemical means can be carried out by using a solution making it possible to dissolve the material of the metal matrix 3 at the level of the surface 2a of the composite material, without dissolving the material of the protrusions 5.

In addition, the fillers 4 are formed of a material whose hardness is greater than the hardness of the material of the metal matrix.

The hardness of the metal matrix 3 does not confer sufficient mechanical resistance properties to resist mechanical abrasion or chemical attack carried out on all or part of the surface 2a of the composite material.

On the contrary, the hardness of the material of the fillers 4 gives the fillers 4 properties of mechanical resistance to mechanical abrasion or chemical attack carried out on all or part of the surface 2a of the composite material.

In this way, during the mechanical abrasion or chemical attack step, only the metal matrix is removed, revealing the charges 4 arranged on the surface of the composite material, and thus forming protuberances 5 projecting from the surface 2a of the material. composite.

In order to allow the fillers 4 to resist mechanical abrasion or chemical attack, the minimum hardness value of the material of the fillers 4 is preferably equal to 550 Hv.

Preferably, the metal matrix 3 comprises a steel, more preferably a steel comprising between 11.5 and 13.5% by weight of chromium, between 0 and 1% by weight of manganese, between 0 and 1% by weight of silicon, between 0 and 0.04% by weight of phosphorus, between 0 and 0.03% by weight of carbon, between 0 and 0.03% by weight of sulfur and the remainder of iron, known as 410L stainless steel and ferritic structure.

The charges 4, and consequently the protuberances 5, are made from materials of hardness greater than the hardness of the material of the metal matrix 3. The hardness differential allows natural and easier relief during mechanical abrasion or chemical attack.

Preferably, the charges 3 are made of a metallic material based on iron, more preferably steel. Iron-based materials make it possible to obtain good reactions in lubricated applications, particularly with friction modifier additives added to lubricating oils, and facilitate the creation of a tribofilm.

The material of the charges 4 may comprise a tool steel meeting the NF EN ISO 4957 standard, such as a tool steel comprising between 5.5 and 6.75% by weight of tungsten, between 4.5 and 5.5 % by weight of molybdenum, between 3.75 and 4.5% by weight of chromium, between 1.75 and 2.20% by weight of vanadium, between 0.8 and 1% by weight of carbon, between 0.20 and 0.45% by weight of silicon, between 0.15 and 0.4% by weight of manganese, between 0 and 0.03% by weight of phosphorus, between 0 and 0.03% by weight of sulfur and the remainder of iron, generally known as M2 tool steel.

The mass content of each chemical element is indicated in relation to the total weight of the steel considered.

According to another embodiment, the charges 4 can be made of a metallic material based on Nickel or based on Cobalt.

According to another embodiment, the fillers 4 can be made of a ceramic material, for example Al2O3, TiO2, ZrO2, or Cr2O3.

Preferably, the average diameter or average equivalent diameter of the protuberances 5 is between 5µm and 200µm.

The shape of the protuberances 5 can be spherical, irregular or form spherical segments.

In the example illustrated in , the charges 4 are substantially spherical particles so that the protuberances 5 are also spherical or forming spherical segments.

Obtaining spherical segments can be the result of the step of developing the texture, in particular when this is produced by mechanical abrasion, and/or the result of friction between the first and second parts 1 and 6, leading to the flattening of the loads 4 protruding from the surface 2a of the composite material covering.

Preferably, the ratio between protuberances 5 and metal matrix 3 on the surface 2a of the composite material is between 4% and 30%.

Preferably, the average height difference between the protuberances 5 and the textured surface 2a of the composite material is between 0.02µm and 2µm.

Preferably, the roughness Rz of the surface 2a of the composite material is between 0.1 μm and 1 μm.

Another aspect of the invention relates to a method of depositing a composite material as described above on a substrate to form a coating 2.

According to one embodiment, the deposition can be carried out by thermal projection, such as by dynamic projection by cold gas, plasma or even high speed oxygen flame called HVOF projection for “High Velocity Oxygen Fuel”.

According to another embodiment, the deposition can be carried out by a laser cladding technique, also known as “Laser Cladding”.

In the example illustrated, the composite material takes the form of a coating 2, and the deposition of the coating 2 in composite material on the substrate, which in this example is the first part 1 formed by a cylinder bore, is carried out by dynamic projection by cold gas.

By dynamic projection by cold gas, we mean a metallization process, more commonly called “Cold Spray coating” in which a gas is accelerated to supersonic speeds in a “De Laval” type nozzle. The metal composite material in powder form is introduced into a high pressure part of the nozzle and projected towards the substrate.

Above a certain speed, which is characteristic for each sprayed material/substrate pair, the particles form a dense and very adherent coating 2 on impact.

For this, the particles must undergo plastic deformation. The propellant gas is heated. When its temperature increases, the speed of the gas increases, which accelerates the particles. The relative increase in the temperature of the powder particles contributes to their deformation at the point of impact.

Deposition by cold gas dynamic spraying leads to a homogeneous microstructure of the metallic composite material with a low porosity rate and significant anchoring to the substrate.

The dynamic projection technique using cold gas which makes it possible to obtain a composite material comprising charges 4 distributed homogeneously in the metal matrix 3, thus leads to a homogeneous distribution of the protuberances 5 on the surface 2a of the coating 2.

According to an alternative, the first part 1 can be formed by a solid material made of composite material.

The solid composite material can be made by foundry or by powder sintering.

Figures 2A, 2B, 2C and 2D illustrate a system comprising a cylinder bore comprising a coating 2 of composite material arranged opposite a piston, represented at different times T0, T1, T2 and T3.

The bore and the piston, forming first and second parts 1 and 6, are in contact so that the piston forms an element rubbing against the composite material. The protuberances 5 of the textured composite material are arranged opposite the piston.

According to one example, the second part 6 can be formed by a material comprising steel. The material of the second part 6 may be treated or untreated, and may be coated or uncoated.

In addition, a lubricating oil with a viscosity less than or equal to 5W30, comprising at least one friction modifier additive, is placed between the bore and the piston for the formation of a protective film also called tribofilm.

By 5W30, we mean an oil where 5 corresponds to the viscosity at -18°C measured in centistokes and 30 corresponds to the viscosity measured at 100°C in centistokes.

By lubricating oil with a viscosity less than or equal to 5W30, we mean a lubricating oil with a viscosity less than or equal to 5 measured in centistokes at -18°C and a viscosity less than or equal to 30 measured in centistokes at 100°C.

According to one example, the lubricating oil is an oil with a viscosity less than or equal to 0W20 oil where 0 corresponds to the viscosity at -18°C measured in centistokes and 20 corresponds to the viscosity measured at 100°C in centistokes.

Preferably, the friction modifier additives are chosen from ZnDDP and MoDTC.

The system is illustrated in Figures 2A to 2C in a boundary, mixed, or elastohydrodynamic lubrication regime in which the cylinder bore and piston are in contact.

There illustrates the system in an initial state at time T0.

As illustrated in the , at time T1, tribofilm forms on the protrusions 5. The tribofilm forms under the effect of pressure and shear in the tribological contact from the friction modifier additives. Once this is formed, the coefficient of friction stabilizes.

At time T2, illustrated in , tribofilm is also formed in the valleys, that is to say on the metal matrix 3 placed between the protuberances 5, either by formation directly in them, or by formation on the protuberances 5 then scanning in the valleys.

Finally, at time T3, illustrated in , the tribofilm is totally or partially eliminated from the protuberances 5. The tribofilm in the valleys therefore reaches the height of the protuberances 5 and the system is stabilized. The coefficient of friction is very low and there is no longer any wear linked to friction between the cylinder bore and the piston.

Example 1

A first part 1 is covered by a coating 2 of composite material comprising a metal matrix 3 of 410L stainless steel with a ferritic structure and an average hardness of 335 Hv _0.01 , and loads 4 made of M2 tool steel with an average hardness of 719 Hv _0.01 .

Coating 2 was deposited by dynamic projection using cold gas.

The development of a texture on surface 2a of coating 2 was then carried out by polishing using a SiC1200 abrasive.

The textured composite material obtained has a roughness Rz of 0.5µm and a porosity rate of 3%.

The average diameter of the particles of charges 4 is 22µm and the charges 4 have a quasi-spherical shape.

The ratio between protuberances 5 and metal matrix 3 on the surface 2a of the coating 2 in composite material is 11.1%.

The average height difference between protuberances 5 and metal matrix 3 on surface 2a of coating 2 in composite material is 102 nm.

Surface 2a of coating 2 in composite material was subjected to an alternative pin-plane friction test, facing a counter-sample of 100C6 steel and in a 0W16 oil bath containing friction modifier additives ZnDDP and MoDTC.

There represents the evolution of the friction coefficient as a function of time.

We can see on the that the instant T3 in which the system is stabilized is reached after only 800 seconds of testing. Friction takes place on the protuberances 5 and on the tribofilm which protects the metal matrix 3. The coefficient of friction is extremely low and stable over time. Wear is virtually zero thanks to the tribofilm thus formed.

The texturing of the composite material comprising the protuberances 5 therefore allows a significant improvement in the performance of combustion engines, and consequently a reduction in their CO2 emissions, thanks to the reduction in friction.

It also allows increased durability of the first and second parts 1 and 6 involved in friction thanks to tribofilm protection which leads to a reduction in wear.

In a hydrodynamic regime (not shown), in which the cylinder bore and the piston do not touch, it is the oil which exerts the friction depending on its thickness.

In the case of friction in hydrodynamic regime, the two solids of the system are not in contact because the thickness of the oil is significant, for example in the middle of the stroke in the cylinder where the speed of the piston is very high. The friction is then due to the shearing of the oil. The greater the oil film thickness, the greater the forces required, and therefore the greater the coefficient of friction.

In hydrodynamic regime, there is no formation of tribofilm because the solids are not in contact. The initial texture formed by the protuberances 5 will therefore not be modified. The presence of protuberances 5 of the composite material allows local reductions in shear forces.

In a lubrication regime where the first and second parts 1 and 6 touch, the protuberances 6 of the textured composite material therefore allow the formation of a tribofilm and thus a reduction in friction.

In a lubrication regime where the first and second parts 1 and 6 do not touch, the protuberances 6 of the textured composite material allow a reduction in shear forces and thus also a reduction in friction.

Claims (12)

Method for manufacturing a composite material comprising a metal matrix (3) made of iron or copper-based alloy, and fillers (4) made of material having a hardness greater than the hardness of the metal matrix (3), the method comprising the development of a surface texture comprising the formation of protuberances (5) by highlighting said fillers (4) on all or part of the surface of the composite material by mechanical abrasion or chemical attack. Method according to claim 1, in which the metal matrix (3) is made of steel, preferably a steel comprising between 11.5 and 13.5% by weight of chromium, between 0 and 1% by weight of manganese, between 0 and 1% by weight of silicon, between 0 and 0.04% by weight of phosphorus, between 0 and 0.03% by weight of carbon, between 0 and 0.03% by weight of sulfur and the remainder of iron. Method according to claim 1 or 2, in which the charges (4) are made of a metallic material, preferably a steel, more preferably a tool steel comprising between 5.5 and 6.75% by weight of tungsten, between 4 .5 and 5.5% by weight of molybdenum, between 3.75 and 4.5% by weight of chromium, between 1.75 and 2.20% by weight of vanadium, between 0.8 and 1% by weight of carbon, between 0.20 and 0.45% by weight of silicon, between 0.15 and 0.4% by weight of manganese, between 0 and 0.03% by weight of phosphorus, between 0 and 0.03% by weight of weight of sulfur and the rest of iron. Method for depositing a composite material according to any one of the preceding claims on a substrate (1) to form a coating (2), in which the deposition is carried out by thermal spraying, such as by dynamic spraying by cold gas, plasma or high-speed oxygen flame, or made by laser cladding. Composite material comprising a metal matrix (3) made of iron or copper-based alloy, fillers (4) made of material having a hardness greater than the hardness of the metal matrix (3), and a surface texture comprising protuberances ( 5) formed by said fillers (4) raised on all or part of the surface of the composite material. Composite material according to claim 5, in which the metal matrix (3) is made of steel, preferably comprising between 11.5 and 13.5% by weight of chromium, between 0 and 1% by weight of manganese, between 0 and 1 % by weight of silicon, between 0 and 0.04% by weight of phosphorus, between 0 and 0.03% by weight of carbon, between 0 and 0.03% by weight of sulfur and the remainder of iron. Composite material according to claim 5 or 6, in which the fillers (4) are made of metallic material, preferably a steel, more preferably a tool steel comprising between 5.5 and 6.75% by weight of tungsten, between 4, 5 and 5.5% by weight of molybdenum, between 3.75 and 4.5% by weight of chromium, between 1.75 and 2.20% by weight of vanadium, between 0.8 and 1% by weight of carbon , between 0.20 and 0.45% by weight of silicon, between 0.15 and 0.4% by weight of manganese, between 0 and 0.03% by weight of phosphorus, between 0 and 0.03% by weight sulfur and the rest of iron. Substrate coated with a composite material according to any one of claims 5 to 7. System comprising a first part (1) comprising a composite material according to any one of claims 5 to 7, all or part of the protuberances (5) of said composite material being arranged opposite a second part (6), and an oil of viscosity less than or equal to 5W30 placed between said composite material and the second part (6). System according to claim 9, in which all or part of the protrusions (5) of said composite material being arranged in contact with the second part, and said oil comprises at least one friction modifier additive, preferably chosen from ZnDDP and MoDTC. System according to claim 9 or 10, in which the first part (1) is a friction element of a motor vehicle, such as a cylinder bore, a bearing, a crankshaft bearing, a camshaft bearing or a cam. Motor vehicle comprising a composite material according to any one of claims 5 to 7.