Part coated with a metal matrix composite material and method for obtaining such a part

Abstract

Part comprising a coating of composite material having a metallic matrix and metallic reinforcements, the reinforcements having a hardness greater than or equal to 550 Hv.

Description

Title of the invention: Part coated with a metal matrix composite material and method for obtaining such a part

[0001] The present invention relates, in general, to the wear and coefficient of friction related to the friction of parts such as the cylinder block of an internal combustion engine of a motor vehicle and, more specifically, to the application of a coating to improve the wear resistance of such parts.

[0002] More particularly, the invention relates to a part coated with a metal matrix composite material and to a method for obtaining such a part.

[0003] In a motor vehicle, certain parts are subject to significant and continuous friction.

[0004] In particular, the friction of the pistons on the cylinder block represents about half of the friction occurring in an internal combustion engine.

[0005] An increase in the fuel consumption of the combustion engine results from these frictions and consequently leads to an increase in the rate of carbon dioxide emission by the motor vehicle.

[0006] Conventionally, a coating is applied to the bore surface of the cylinder block and makes it possible to improve the wear resistance properties of the cylinder block related to the friction generated during the movement of the pistons.

[0007] In particular, it is known to form a coating in metal matrix composite material loaded with solid lubricants.

[0008] Despite their significant benefit in reducing friction, such a coating is difficult to produce, and the cohesion between the matrix and the solid lubricants is unsatisfactory. The layered structure of the solid lubricants weakens or even prevents cohesion between the particles of the metallic matrix.

[0009] Another existing solution aims to form a ductile coating with hard reinforcements. In this regard, particles of ceramic material, in particular alumina and zirconia, are incorporated into a metallic matrix, generally made of steel or aluminum.

[0010] However, the hard ceramic particles are nonetheless brittle and eventually fracture during coating application and under the action of friction. Furthermore, given their limited affinity, the ceramic particles detach from the metallic matrix, leading to significant wear of the cylinder block.

[0011] According to a conventional technique, the bore surface of the cylinder housing is coated by a projection process called "Bore spray coating".

[0012] However, the Bore Spray coating process is difficult to industrialize, costly and limits the types of coatings that can be used.

[0013] The invention therefore aims to remedy these drawbacks and to offer a composite material coating designed to improve the resistance properties against friction wear and the coefficients of friction of the part on which it is applied, which can be easily manufactured in large series in order to be industrialized, is inexpensive, benefits from an optimized cohesion between matrix and reinforcements, and whose ductility is improved.

[0014] A part is therefore proposed comprising a coating of composite material having a metallic matrix and metallic reinforcements, the reinforcements having a hardness greater than or equal to 550 Hv.

[0015] It was found that the optimized cohesion between the metallic matrix and the metallic reinforcements led to the obtaining of a coating with improved wear resistance properties.

[0016] In addition, the ductility and hardness of the metallic reinforcements prevent their fracture and improve the wear resistance properties of the coating.

[0017] The invention also relates to a method of obtaining a part coated with a composite material comprising a metallic matrix and metallic reinforcements, the reinforcements having a hardness greater than or equal to 550 Hv, and the metallic matrix and the metallic reinforcements being projected in powder form onto the part by dynamic projection with cold gas.

[0018] Cold gas dynamic spraying refers to a metallization process, more commonly known as "Cold Spray Coating," in which a powdered material contained in a De Laval-type nozzle is sprayed at supersonic speed onto a surface by a pressurized gas. The operating temperature is below 450°C at the De Laval nozzle outlet.

[0019] It has been found that Cold Spray coating provides a significant tri-bological gain by improving the wear resistance properties of the coating.

[0020] In addition, Cold Spray coating provides a significant advantage for large-scale industrialization, particularly through simple and inexpensive manufacturing of coated parts.

[0021] The invention also relates to a motor vehicle comprising a part coated with a composite material having a metallic matrix and metallic reinforcements, the reinforcements having a hardness greater than or equal to 550 Hv.

[0022] Other purposes, advantages and characteristics will become apparent from the description that follows, given for illustrative purposes only.

[0023] In what follows, the bounds of a domain of values ​​are included in that domain, in particular in the expression "between".

[0024] The example developed below relates to a cylinder block for an internal combustion engine of a motor vehicle having a bore surface configured to cooperate with a plurality of pistons for the operation of the internal combustion engine.

[0025] The bore surface is coated with a composite material comprising a metallic matrix and metallic reinforcements, the reinforcements having a hardness greater than or equal to 550 Hv.

[0026] According to one embodiment, the coating is applied to a part made of aluminum or aluminum alloy.

[0027] It may be envisaged that the coating may be applied to another part of a motor vehicle subject to friction, lubricated or unlubricated, or a part not belonging to a motor vehicle.

[0028] Preferably, the projected powder is spherical and the D50 particle size of the powder is between 5 pm and 30 pm so as to allow an industrial yield.

[0029] More preferably, the D50 particle size of the powder between 10 pm and 25 pm for optimal projection.

[0030] The presence of very fine particles less than 1 pm is also preferably avoided in order to present a homogeneous powder flow during projection.

[0031] Metallic matrix

[0032] According to one embodiment, the material of the metallic matrix may comprise steel.

[0033] According to one example, the material of the metallic matrix may consist of steel.

[0034] Steel has sufficiently high mechanical properties to prevent sagging of the metal reinforcements in the metal matrix.

[0035] Preferably, the carbon content of the steel is less than 0.1% by weight so that the metal matrix powder is sufficiently ductile to deform on impact during dynamic cold gas projection.

[0036] Advantageously, the metal matrix material, which in one example may be steel, further comprises chromium with a content of between 0 and 16% by weight, preferably between 10 and 16% by weight.

[0037] The presence of chromium makes it possible to improve the friction wear resistance properties of the coating by preventing any seizing phenomenon.

[0038] According to one embodiment, the metal matrix material may comprise 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, generally known as 410L stainless steel, of ferritic structure.

[0039] According to another embodiment, the metal matrix material may comprise a copper alloy, for example bronze or brass.

[0040] 410L stainless steel and copper alloy are particularly suitable for cold spray coating and their hardness prevents sagging of the metal reinforcements within the matrix.

[0041] According to another embodiment, the metal matrix material may comprise a cobalt alloy or a nickel alloy.

[0042] Metal reinforcements

[0043] The HV hardness or Vickers hardness of the reinforcements is greater than or equal to 550 Hv, which improves the wear resistance of the coating.

[0044] Preferably, the content of reinforcements in the deposited coating is between 5% and 30%, preferably between 8% and 15%

[0045] In one embodiment, the material of the metal reinforcements comprises steel.

[0046] According to one example, the reinforcement material may consist of steel.

[0047] According to one embodiment, the reinforcement material comprises a tool steel conforming to the NF EN ISO 4957 standard and whose toughness and hardness make it possible to improve the wear resistance of the coating.

[0048] According to one example, the reinforcement material may comprise 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, generally known as M2 tool steel.

[0049] According to another embodiment, the reinforcement material may comprise or consist of steel comprising between 12 and 14% by weight of chromium, between 0 and 1% by weight of manganese, between 0 and 1% by weight of silicon, between 0.15 and 0.4% by weight of carbon, 0.04% by weight of oxygen, between 0 and 0.04% by weight of phosphorus, between 0 and 0.03% by weight of sulfur and the remainder iron, generally known as 420 stainless steel.

[0050] It may be provided that the part also includes a lubricant on the surface of the composite material coating.

[0051] It may also be provided that the metal matrix composite material with metal reinforcements having a hardness greater than or equal to 550 Hv may, in addition, comprise additional reinforcements selected from: copper or copper alloy particles, molybdenum or molybdenum alloy particles, solid lubricants or a mixture thereof.

[0052] The addition of copper is particularly advantageous for giving improved thermal properties to the coating.

[0053] The addition of molybdenum and solid lubricants is particularly advantageous for improving wear resistance properties related to friction and reducing the coefficient of friction. Example 1

[0054] 410L stainless steel metal matrix

[0055] The metal matrix material is a ferritic structure steel, known as 410L stainless steel, and comprises 11.9% by weight of chromium, 0.67% by weight of manganese, 0.56% by weight of silicon, 0.014% by weight of phosphorus, 0.013% by weight of carbon, 0.005% by weight of sulfur and the remainder iron.

[0056] The hardness of 410L stainless steel is approximately 335 Hvo,oi.

[0057] The metallic matrix is ​​in the form of a spherical powder having a particle size D50 of 21.2 pm, D10 of 12.1 pm and D90 of 35.9 pm.

[0058] Metal reinforcements made of M2 tool steel

[0059] The material of the metal reinforcements is a tool steel known as M2 tool steel, and comprises 6.29% by weight of tungsten, 4.8% by weight of molybdenum, 4.31% by weight of chromium, 1.97% by weight of vanadium, 0.9% by weight of carbon, 0.28% by weight of silicon, 0.26% by weight of manganese, 0.024% by weight of phosphorus, 0.008% by weight of sulfur and the remainder iron.

[0060] The hardness of M2 tool steel is approximately 719 Hvo,oi.

[0061] The reinforcements are in the form of spherical powder having a particle size D50 of 22 pm, D10 of 13.7 pm and D90 of 33.7 pm.

[0062] Coating made of 410L+M2 composite material obtained

[0063] The powder mixture comprising 80% by weight of 410L stainless steel metal matrix and 20% of M2 tool steel reinforcements, contained in a De Laval type nozzle, is projected onto the surface of a part by dynamic cold gas projection known as "Cold Spray" at supersonic speed by a pressurized gas.

[0064] The temperature and projection pressure upstream of the De Laval nozzle are respectively greater than 800°C and 40 bar.

[0065] The final content of the coating applied to the part is 90% by weight of 410L stainless steel metal matrix and 10% of M2 tool steel reinforcements.

[0066] It has been observed that the hard particles of M2 tool steel reinforcements are effectively anchored in the 410L stainless steel matrix, reflecting significant cohesion between the matrix and the reinforcements.

[0067] Localized mechanical tests have shown that the 410L stainless steel die has sufficient mechanical properties to prevent the M2 tool steel reinforcements from sinking. In particular, no die sagging is observed for pressures of 1400 MPa, that is, pressure values ​​well beyond the pressures exerted in a combustion engine.

[0068] Mechanical tests have also shown that the benefits of the 410L+M2 coating obtained on the resistance of the part to friction are significant.

[0069] Therefore, the composite material coating with a 410L stainless steel matrix and M2 tool steel reinforcements is particularly suitable for coating the bore surface of a cylinder housing. Example 2

[0070] 410L stainless steel metal matrix

[0071] The metallic matrix of Example 2 is identical to the metallic matrix of Example 1.

[0072] 420 stainless steel metal reinforcements

[0073] The material of the metal reinforcements is a stainless steel known as 420 stainless steel, and comprises 12.9% by weight of chromium, 0.7% by weight of manganese, 0.7% by weight of silicon, 0.38% by weight of carbon, 0.04% by weight of oxygen, 0.011% by weight of phosphorus, 0.008% by weight of sulfur and the remainder iron.

[0074] The hardness of 420 stainless steel is approximately 680 Hvo,oi.

[0075] The reinforcements are in the form of spherical powder having a D50 particle size of approximately 22 pm.

[0076] Coating made of 410L+420 composite material obtained

[0077] The powder mixture comprising 80% by weight of 410L stainless steel metal matrix and 20% of 420 stainless steel reinforcements.

[0078] The projection of the composite material powder comprising the 410L stainless steel metal matrix and the 420 stainless steel metal reinforcements is projected onto the surface of a part by dynamic cold gas projection under conditions identical to Example 1.

[0079] The final content of the coating applied to the part is 90% by weight of 410L stainless steel metal matrix and 10% of 420 stainless steel reinforcements.

[0080] The significant cohesion between 410L stainless steel and 420 stainless steel leads to effective anchoring of the reinforcements in the matrix.

[0081] Localized mechanical tests have shown sufficient mechanical properties of the 410L stainless steel metal matrix to prevent the 420 stainless steel reinforcements from sinking. The composite material coating with a 410L stainless steel matrix and 420 stainless steel reinforcements is particularly suitable for coating the bore surface of a cylinder housing.

[0082] Mechanical tests have also shown that the benefits of the re The 410L+420 garment obtained based on the resistance of the piece to friction are significant.

[0083] Study of the wear resistance properties of three coatings

[0084] The performance with respect to wear by friction of three coatings was studied, in an oil at a temperature of 20°C and at a temperature of 100°C.

[0085] A first coating is applied to a first part by projection according to a Bore Spray coating process of a 13Mn6 steel.

[0086] The 13Mn6 material is a steel comprising between 1.6 and 1.8% by weight of manganese, between 0.25 and 0.40% by weight of silicon, between 0.10 and 0.13% by weight of carbon, between 0 and 0.04% by weight of phosphorus, between 0 and 0.03% by weight of sulfur and the remainder iron.

[0087] A second coating is applied to a second part by projection according to a Cold Spray coating process of a stainless steel powder without reinforcements.

[0088] A third coating similar to Example 1 is applied to a third part by projection according to a Cold Spray coating process of a powder of composite material comprising a 410L stainless steel matrix and M2 tool steel reinforcements.

[0089] Results

[0090] The results of the wear tests carried out on the three coatings at 20°C and 100°C are presented, respectively, in Tables 1 and 2 below. Table 1:

[0091] Temperature 20°C Spraying Method: Bore Spray, Cold Spray, Cold Spray Coating Material: 13Mn6 410L 410L+20%M2 Wear Depth: 1 µm, 0.2 µm, 0.2 µm Wear Width: 0.95 µm, 1.18 µm, 1.14 µm Wear Condition: Medium Abrasion Wear, Light Abrasion Wear, Light Abrasion Wear Table 2:

[0092] Temperature 100°C Projection Method Bore Spray Cold Spray Cold Spray Coating Material 13Mn6 410L 410L+20%M2 Wear Depth 2.5 pm 14.9 pm 0.6 pm Wear width 0.94 µm 1.89 µm 0.64 µm Wear condition High abrasion wear Adhesion and seizing Low abrasion wear

[0093] According to the results presented in Table 1, at 20°C, the wear of the second and third coatings applied by cold spray coating is limited compared to the first coating applied by boron spray coating, reflecting a tribological advantage obtained with the cold spray coating process compared to the boron spray coating process. However, at 20°C, the hard M2 tool steel particles do not appear to be essential.

[0094] In contrast, according to the results presented in Table 2, at 100°C, the second 410L stainless steel coating without reinforcement, i.e., without hard particles, seizes, resulting in very significant wear. The addition of hard M2 tool steel particles prevented seizing and limited wear to very superficial levels compared to the first coating applied by boron spray coating.

[0095] The third coating has increased durability and is particularly suitable, according to one example, for coating a bore surface of a cylinder block of an internal combustion engine.

[0096] The coefficient of friction of the first and third coatings was also compared, in an oil at 20°C and 100°C.

[0097] At 20°C, it was observed that the coefficient of friction of the third coating 410L+M2 is lower than that of the first coating 13Mn6 at low speed, but that these equalize at higher speed.

[0098] Conversely, at 100°C, it was found that the coefficient of friction of the third coating 410L+M2 is significantly lower than that of the first coating 13Mn6, and this across the entire operating speed range. The observed reduction is approximately 70%, which allows for a significant reduction in CO2 emissions when the third coating is applied to the bore surface of a cylinder block in an internal combustion engine.

Claims

Demands

1. Part comprising a composite material coating having a metallic matrix and metallic reinforcements, the reinforcements having a hardness greater than or equal to 550 Hv, the metallic matrix material comprising steel, the carbon content of the steel in the metallic matrix being less than 0.1% by weight.

2. Part according to claim 1, wherein the steel of the metal matrix comprises chromium, the chromium content being between 0 and 16% by weight.

3. Part according to any one of claims 1 or 2, wherein the metal matrix material comprises 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.

4. Part according to claim 1, wherein the metal matrix material comprises a copper alloy, such as bronze or brass, a cobalt alloy or a nickel alloy.

5. Part according to any one of the preceding claims, wherein the content of metal reinforcements is between 5% and 30%, preferably between 8% and 15%.

6. A part according to any one of the preceding claims, wherein the material of the metal reinforcements comprises steel, preferably tool steel.

7. Part according to claim 6, wherein the reinforcement material comprises a 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. Part according to any one of the preceding claims, wherein the composite material of the coating further comprises reinforcements selected from: copper or copper alloy particles, molybdenum or molybdenum alloy particles, solid lubricants or a mixture thereof.

9. A method for obtaining a part coated with a composite material according to any one of the preceding claims, the metal matrix and metal reinforcements being projected in powder form onto the part by dynamic cold gas projection.

10. A method for obtaining according to claim 9, wherein the projected powder is spherical, the D50 particle size of the powder being between 5 pm and 30 pm, preferably between 10 pm and 25 pm.

11. Motor vehicle comprising at least one part according to any one of claims 1 to 8.