Textured composite material and associated manufacturing process

Abstract

The invention relates to a composite material comprising a metal matrix (3) made of an iron-based or copper-based alloy, fillers (4) made of a 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 over all or part of the surface of the composite material.

Description

[0001] TITLE: Textured composite material and associated manufacturing process

[0002] 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 combustion engine of a motor vehicle in lubricated mode.

[0003] More particularly, the invention relates to a composite material comprising a surface texture and a method of manufacturing such a composite material.

[0004] 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 becoming more and more fluid.

[0005] However, the decrease in oil viscosity leads to an increase in friction between the solids used, leading to their premature wear.

[0006] Conventionally, friction modifying additives, such as ZnDDP or MoDTC, are therefore added to oils to enable the creation of tribofilms whose function is to protect surfaces and thus improve friction.

[0007] However, the materials and coatings used in engines for frictional contacts are not optimized for these low viscosity oils containing these additives.

[0008] The invention therefore aims to remedy these drawbacks and to propose a composite material making it possible to optimize friction between two solids, particularly suitable for friction in lubricated conditions in the presence of a low-viscosity oil loaded with friction-modifying additives.

[0009] A method is therefore proposed for manufacturing a composite material comprising a metal matrix made of an iron- or copper-based alloy, and fillers made of a material having a hardness greater than the hardness of the metal matrix, the method comprising the development of a surface texture comprising the formation of protuberances by highlighting said fillers on all or part of the surface of the composite material by mechanical abrasion or chemical attack.

[0010] 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 lower hardness than the hardness of the filler material, does not have sufficient mechanical resistance properties to enable it to resist mechanical abrasion or chemical attack carried out on all or part of the surface of the composite material.

[0011] Preferably, the hardness of the filler material is greater than or equal to 550 Hv.

[0012] 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.

[0013] Advantageously, the fillers may 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.

[0014] 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 high-speed oxygen flame, or carried out by laser cladding.

[0015] The invention also relates to a composite material comprising a metal matrix made of an iron- or copper-based alloy, fillers made of a material having a hardness greater than the hardness of the metal matrix, and a surface texture comprising protuberances formed by said fillers raised on all or part of the surface of the composite material.

[0016] Advantageously, the metal matrix may 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.

[0017] Advantageously, the fillers may be 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 of sulfur and the remainder of iron.

[0018] The invention also relates to a substrate coated with a composite material as described above.

[0019] 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.

[0020] Lubricating oil with a viscosity less than or equal to 5W30 means 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.

[0021] According to one characteristic, all or part of the protuberances of said composite material being arranged in contact with the second part, and said oil comprises at least one friction modifying additive, preferably chosen from ZnDDP and MoDTC.

[0022] According to one embodiment, the first part may be a friction element of a motor vehicle, such as a cylinder bore, a bearing, a crankshaft bearing, a camshaft bearing or a cam.

[0023] The invention also relates to a motor vehicle comprising a composite material as described above.

[0024] 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:

[0025] [Fig 1] is a sectional view of a cylinder bore for a motor vehicle combustion engine according to one embodiment of the invention.

[0026] [Fig 2A], [Fig 2B], [Fig 2C] and [Fig 2D] 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.

[0027] [Fig 3] represents the evolution of the coefficient of friction as a function of time measured during an alternating pin-plane friction test. In what follows, the limits of a range of values ​​are included in this range, in particular in the expression "between".

[0028] Furthermore, the expression "at least one" used in this description is equivalent to the expression "one or more".

[0029] Figure 1 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.

[0030] 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.

[0031] According to another embodiment, the first part 1 may be another friction element, for example a bearing, a crankshaft bearing, a camshaft bearing or even a motor vehicle cam.

[0032] The metal matrix 3 is formed by an alloy chosen from an iron-based alloy or a copper-based alloy.

[0033] Furthermore, the fillers 4 are formed from a material whose hardness is greater than the hardness of the metal matrix material.

[0034] In addition, the surface texture comprises protrusions 5 formed by the fillers 4 raised on a surface of the composite material.

[0035] According to one aspect, the invention relates to a method for manufacturing a composite material comprising a metal matrix 3 made of an iron- or copper-based alloy, and fillers 4 made of a material having a hardness greater than the hardness of the metal matrix.

[0036] Furthermore, the manufacturing method comprises 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.

[0037] By protuberance is meant an eminence or projection formed by a charge 4 of the composite material from a surface of the composite material.

[0038] The texture is created by mechanical abrasion or chemical attack.

[0039] The mechanical abrasion can be carried out using at least one of the following methods: a lapping, polishing or buffing method. A portion of the metal matrix 3 is thus mechanically removed so as to reveal the fillers 4 present on the surface 2a of the coating 2. The chemical highlighting of the fillers 4 to form protuberances 5 can be carried out using a solution making it possible to dissolve the material of the metal matrix 3 at the surface 2a of the composite material, without dissolving the material of the protuberances 5.

[0040] Furthermore, the fillers 4 are formed from a material whose hardness is greater than the hardness of the metal matrix material.

[0041] The hardness of the metal matrix 3 does not provide 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.

[0042] 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.

[0043] In this way, during the mechanical abrasion or chemical attack step, only the metal matrix is ​​removed, revealing the fillers 4 arranged on the surface of the composite material, and thus forming protuberances 5 projecting from the surface 2a of the composite material.

[0044] In order to enable the charges 4 to resist mechanical abrasion or chemical attack, the minimum hardness value of the material of the charges 4 is preferably equal to 550 Hv.

[0045] 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 under the name of 410L stainless steel and of ferritic structure.

[0046] The charges 4, and consequently the protuberances 5, are made from materials of a hardness greater than the hardness of the material of the metal matrix 3. The hardness differential allows for natural and facilitated relief during mechanical abrasion or chemical attack.

[0047] Preferably, the fillers 3 are made of an iron-based metallic material, more preferably steel. Iron-based materials make it possible to obtain good reactions in lubricated applications, in particular with friction modifying additives added to lubricating oils and facilitate the creation of a tribofilm. The material of the fillers 4 may comprise a tool steel meeting the standard NF EN ISO 4957, 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 under the name M2 tool steel.

[0048] The mass content of each chemical element is indicated in relation to the total weight of the steel considered.

[0049] According to another embodiment, the charges 4 can be made of a metallic material based on Nickel or based on Cobalt.

[0050] According to another embodiment, the fillers 4 can be made of a ceramic material, for example A12O3, TiO2, ZrO2, or Cr2O3.

[0051] Preferably, the average diameter or average equivalent diameter of the protrusions 5 is between 5 pm and 200 pm.

[0052] The shape of the protrusions 5 can be spherical, irregular or form spherical segments.

[0053] In the example illustrated in Figure 1, the fillers 4 are substantially spherical particles so that the protuberances 5 are also spherical or form spherical segments.

[0054] Obtaining spherical segments may be the result of the texture development step, in particular when this is achieved by mechanical abrasion, and / or the result of friction between the first and second parts 1 and 6, leading to the flattening of the charges 4 projecting from the surface 2a of the composite material coating.

[0055] Preferably, the ratio between protrusions 5 and metal matrix 3 on the surface 2a of the composite material is between 4% and 30%.

[0056] Preferably, the average height difference between the protrusions 5 and the textured surface 2a of the composite material is between 0.02 pm and 2 pm.

[0057] Preferably, the roughness Rz of the surface 2a of the composite material is between 0.1 pm and 1 pm.

[0058] Another aspect of the invention relates to a method of depositing a composite material as described previously 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 known as HVOF projection for “High Velocity Oxygen Fuel”.

[0059] According to another embodiment, the deposition can be carried out by a laser cladding technique, also known as “Laser Cladding”.

[0060] 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.

[0061] Cold gas dynamic spraying is a metallization process, more commonly known as "Cold Spray Coating" in which a gas is accelerated to supersonic speeds in a "De Laval" type nozzle. The metallic composite material in powder form is introduced into a high-pressure part of the nozzle and projected towards the substrate.

[0062] Above a certain speed, which is characteristic for each projected material / substrate pair, the particles form a dense and very adherent coating 2 on impact.

[0063] To achieve this, the particles must undergo plastic deformation. The propellant gas is heated. As its temperature increases, the gas speed increases, which accelerates the particles. The relative increase in the temperature of the powder particles contributes to their deformation at the point of impact.

[0064] Cold gas dynamic spray deposition leads to a homogeneous microstructure of the metallic composite material with a low porosity rate and significant anchoring on the substrate.

[0065] The cold gas dynamic projection technique which makes it possible to obtain a composite material comprising fillers 4 distributed homogeneously in the metallic matrix 3, thus leads to a homogeneous distribution of the protuberances 5 on the surface 2a of the coating 2.

[0066] Alternatively, the first part 1 may be formed from a solid composite material.

[0067] The solid material made of composite material can be produced by casting or by sintering powders. Figures 2A, 2B, 2C and 2D illustrate a system comprising a cylinder bore comprising a coating 2 made of composite material arranged opposite a piston, shown at different times T0, T1, T2 and T3.

[0068] The bore and the piston, forming first and second parts 1 and 6, are in contact so that the piston forms a rubbing element against the composite material. The protrusions 5 of the textured composite material are arranged opposite the piston.

[0069] According to one example, the second part 6 may be formed from a material comprising steel. The material of the second part 6 may be treated or untreated, and may be coated or uncoated.

[0070] In addition, a lubricating oil with a viscosity less than or equal to 5W30, comprising at least one friction modifying additive, is placed between the bore and the piston for the formation of a protective film also called a tribofilm.

[0071] 5W30 means 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.

[0072] Lubricating oil with a viscosity less than or equal to 5W30 means 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.

[0073] 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.

[0074] Preferably, the friction modifying additives are selected from ZnDDP and MoDTC.

[0075] The system is illustrated in Figures 2A-2C in a boundary, mixed, or elastohydrodynamic lubrication regime in which the cylinder bore and piston are in contact.

[0076] Figure 2A illustrates the system in an initial state at time T0.

[0077] As illustrated in Figure 2B, at time T l , tribofilm forms on the protrusions 5. The tribofilm forms under the effect of pressure and shear in the tribological contact from the friction modifying additives. Once it is formed, the coefficient of friction stabilizes.

[0078] At time T2, illustrated in Figure 2C, tribofilm also forms in the valleys, i.e. on the metal matrix 3 arranged between the protuberances 5, either by formation directly in them, or by formation on the protuberances 5 then sweeping into the valleys.

[0079] Finally, at time T3, illustrated in Figure 2D, 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.

[0080] Example 1

[0081] A first part 1 is coated with a coating 2 in composite material comprising a metallic matrix 3 in 410L stainless steel with a ferritic structure and an average hardness of 335 Hvo,oi, and fillers 4 in M2 tool steel with an average hardness of 719 Hvo,oi.

[0082] Coating 2 was deposited by cold gas dynamic spraying.

[0083] The development of a texture on the surface 2a of the coating 2 was then carried out by polishing using a SiC 1200 abrasive.

[0084] The textured composite material obtained has a roughness Rz of 0.5 pm and a porosity rate of 3%.

[0085] The average diameter of charge 4 particles is 22 pm and charge 4 has a quasi-spherical shape.

[0086] The ratio between protrusions 5 and metal matrix 3 on the surface 2a of the coating 2 made of composite material is 1 1.1%.

[0087] The average height difference between protrusions 5 and metal matrix 3 on surface 2a of coating 2 made of composite material is 102nm.

[0088] Surface 2a of coating 2 made of composite material was subjected to an alternating pin-plane friction test, facing a counter-sample made of 100C6 steel and in a 0W 16 oil bath containing friction modifying additives ZnDDP and MoDTC.

[0089] Figure 3 shows the evolution of the friction coefficient as a function of time.

[0090] It can be seen in Figure 3 that the instant T3 in which the system is stabilized is reached after only 800 seconds of testing. The friction occurs 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 made almost 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.

[0091] It also allows increased durability of the first and second parts 1 and 6 involved in friction thanks to the tribofilm protection which leads to a reduction in wear.

[0092] 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.

[0093] 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 piston speed is very high. The friction is then due to the shearing of the oil. The greater the thickness of the oil film, the greater the forces required, and consequently the greater the coefficient of friction.

[0094] In the hydrodynamic regime, there is no tribofilm formation because the solids are not in contact. The initial texture formed by the protrusions 5 will therefore not be modified. The presence of the protrusions 5 of the composite material allows local reductions in shear forces.

[0095] In a lubrication regime where the first and second parts 1 and 6 touch, the protrusions 6 of the textured composite material therefore allow the formation of a tribofilm and thus a reduction in friction.

[0096] In a lubrication regime where the first and second parts 1 and 6 do not touch, the protrusions 6 of the textured composite material allow a reduction in shear forces and thus also a reduction in friction.

Claims

DEMANDS 1. A method for manufacturing a composite material comprising a metallic matrix (3) made of an iron or copper-based alloy, and fillers (4) of a material having a hardness greater than the hardness of the metallic matrix (3), the method comprising the development of a surface texture comprising the formation of protrusions (5) by raising said fillers (4) on all or part of the surface of the composite material by mechanical abrasion or chemical attack.

2. A method according to claim 1, wherein 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 iron.

3. A method according to claim 1 or 2, wherein 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 sulfur and the remainder iron.

4. Method of depositing a composite material according to any one of the preceding claims onto a substrate (1) to form a coating (2), in which the deposition is carried out by thermal projection, such as by dynamic projection by cold gas, plasma or high-speed oxygen flame, or carried out by laser loading.

5. Composite material comprising a metallic matrix (3) of iron or copper alloy, fillers (4) of material having a hardness greater than the hardness of the metallic matrix (3), and a surface texture comprising protrusions (5) formed by said fillers (4) raised on all or part of the surface of the composite material.

6. Composite material according to claim 5, wherein 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 rest iron.

7. Composite material according to claim 5 or 6, wherein the fillers (4) are 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 of sulfur and the remainder iron.

8. Substrate coated with a composite material according to any one of claims 5 to 7.

9. System comprising a first part (1) comprising a composite material according to any one of claims 5 to 7, all or part of the protrusions (5) of said composite material being disposed opposite a second part (6), and an oil of viscosity less than or equal to 5W30 disposed between said composite material and the second part (6).

10. System according to claim 9, wherein all or part of the protrusions (5) of said composite material being disposed in contact with the second part, and said oil comprises at least one friction modifier additive, preferably selected from ZnDDP and MoDTC. 1 1. System according to claim 9 or 10, wherein 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.

12. Motor vehicle comprising a composite material according to any one of claims 5 to 7.

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