CN113831138B - Carbon nanotube modified composite material piston for engine and preparation method and application thereof - Google Patents
Carbon nanotube modified composite material piston for engine and preparation method and application thereof Download PDFInfo
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
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Abstract
The invention relates to a carbon nano tube modified composite material piston for an engine and a preparation method and application thereof, belonging to the technical field of piston materials and piston design and processing. The preparation method comprises the following steps: designing and preparing a prefabricated body structure; high-temperature heat treatment; preparing a low-density C/C porous body by adopting a CVI method; C/C porous body high-temperature heat treatment; machining the piston blank into a piston blank at one time, and growing a carbon nano tube in situ in the pores of the C/C porous body by adopting a normal-pressure CVD method; the piston blank is densified by an RMI method, and secondary machining is carried out according to the size requirement of a finished piston; and coating an anti-oxidation coating on the piston combustion chamber and the piston top position after finishing finish machining to obtain a nano tube modified composite material piston finished product. The composite material piston provided by the invention has positive significance for improving the output power of an engine, reducing oil consumption, reducing noise, prolonging the service life of the piston, reducing emission and improving the environment.
Description
Technical Field
The invention relates to the field of engine parts, in particular to a piston and a preparation method and application thereof.
Background
The piston, known as the engine's "heart", is one of the most important parts in the engine. Its function is to withstand the gas pressure and to drive the crankshaft in rotation, transmitted to the connecting rod by the piston pin. In the working process of the engine, the engine is required to bear not only the heat load generated by top gas, but also mechanical loads such as explosion pressure, reciprocating inertia force, lateral force, friction force and the like, so that the performance requirement on the material is high, and the service life of the piston determines the working reliability and the use durability of the engine to a great extent. However, as the engine is continuously developed towards high power, light oil consumption, low noise, long service life, low emission, environmental friendliness and the like, the traditional piston made of cast iron, cast steel, aluminum alloy and the like reaches or approaches the use limit, and the requirement of the engine on rapid development is increasingly not met. Therefore, there is a trend toward developing new material pistons with better high temperature mechanical properties and lighter mass.
Disclosure of Invention
Aiming at the defects in the prior art, the invention aims to provide the carbon nanotube modified composite material piston for the high-power high-detonation pressure engine so as to improve the output power of the engine, reduce oil consumption and noise, prolong the service life of the piston, reduce emission and improve the environment.
The second purpose of the invention is to provide a preparation method of the carbon nano tube modified composite material piston for the engine.
The invention also aims to provide an application of the carbon nano tube modified composite material piston for the engine on the engine.
In order to realize the purpose, the technical scheme provided by the invention is as follows:
(1) Designing and preparing a piston preform structure: according to the cylindrical structure of the piston, the annular needling structure preform for the piston is designed and prepared. Specifically, a unit layer is formed by compounding a carbon fiber mesh tire with carbon fiber non-woven cloth in the axial direction of a prefabricated body through needling, another unit layer is formed by compounding a carbon fiber mesh tire through continuously winding carbon fiber in the circumferential direction through needling, and the unit layer are alternately superposed and continuously needled. Wherein the final density of the preform is 0.4-0.6 g/cm 3 The carbon fiber can be T700, T800, T1000 or any other grade, and the tow can be 6K or 12K.
(2) High temperature heat treatment
And (3) carrying out heat treatment on the prepared piston preform for 1-2 h in the inert gas protective atmosphere, removing the protective adhesive on the surface of the carbon fiber, improving the graphitization degree of the carbon fiber, and relieving the mechanical stress introduced in the preparation process of the preform. The heat treatment temperature is 1950-2300 deg.C, and the inert gas can be argon or helium.
(3) Preparation of carbon fiber reinforced matrix carbon porous body
The piston carbon fiber preform is subjected to pyrolytic carbon densification by adopting a rapid CVI method to obtain the carbon fiber preform with the density of 1.15-1.55 g/cm 3 Carbon fiber reinforced matrix carbon porous bodies (i.e., C/C porous bodies) in between. Wherein the carbon source gas for chemical vapor deposition is natural gas, propane, propylene, acetylene or their mixture, and the diluent gas is nitrogen, hydrogen orThe volume ratio of the source gas to the diluent gas is 1:1-14, the infiltration time is 100-500 h, the retention time is 0.6-2.5 s, the infiltration temperature is 860-1050 ℃, and the pressure is 1000-5000 Pa.
(4) High temperature heat treatment of C/C porous bodies
In order to remove non-carbon impurities in the pores of the carbon fiber reinforced matrix carbon porous body, the pores are reopened and are subjected to heat treatment at a high temperature. Specifically, the heat treatment temperature is 2000-2450 ℃, the pressure is 500-5000 Pa, the heat treatment time is 0.5-5 h, and the inert gas is used for protection. Wherein the inert gas can be argon or helium.
(5) And (4) machining the carbon fiber reinforced matrix carbon (C/C) porous body (C/C porous body for short) subjected to high-temperature heat treatment in the step (4) according to the size of the piston to obtain a piston blank. Wherein, the inner cavity of the piston blank is processed according to the deviation under the drawing size, and the allowance of 0.05-0.2 mm is reserved at the top, the head and the skirt of the piston. The piston top includes the processing at positions such as combustion chamber, combustion chamber throat, valve pit, and the piston head includes the processing at positions such as firepower bank, annular, ring bank, and piston skirt portion includes the processing at positions such as face window, pinhole, jump ring groove, oil spout breach, and the piston inner chamber includes the processing at positions such as key seat, pillar. The machining can adopt a combined machining mode of a lathe and a machining center.
(6) In-situ growth of carbon nanotubes
In order to improve the interface bonding property between the carbon substrate and the SiC substrate prepared by reaction, relieve the thermal stress generated by mismatching of thermal expansion coefficients in the cooling process, eliminate or reduce residual silicon, and prepare the carbon nano tube in the pores of the piston blank in an in-situ growth mode. The specific method comprises the following steps: putting the piston blank in an absolute ethyl alcohol solution (namely a mixed solution) of a catalyst precursor, performing ultrasonic treatment for 3-8H, putting the mixture in a blast oven at 60-80 ℃, drying, then transferring the dried mixture into a normal-pressure chemical vapor deposition furnace, reducing the mixture for 1-3H at 300-500 ℃ in an H2 atmosphere, closing hydrogen, introducing shielding gas, continuously heating to 650-980 ℃, introducing a carbon source gas and diluent gas to grow the carbon nanotube in situ in the C/C material pore, depositing for 30-180 min, closing the carbon source gas and the diluent gas, and introducing protective gas to cool the carbon nanotube to room temperature. Wherein the catalytic precursor can be nickel nitrate or cobalt acetate, the solvent is ethanol, the catalytic precursor is dissolved in the ethanol to prepare a mixed solution, and the concentration of the mixed solution is 0.5-2.5 mol/L; the protective gas can be nitrogen, argon or helium; the carbon source gas can be methane, propane, propylene, acetylene or a mixed gas thereof, the diluent gas can be hydrogen, nitrogen or a mixed gas thereof, and the ratio of the source gas to the diluent gas is 1:1-10.
(7) Piston blank densification
And placing the piston blank after in-situ growth of the carbon nano tube in a graphite crucible filled with silicon powder to perform melting siliconizing in a high-temperature furnace, and infiltrating the C/C porous body by melting Si at high temperature and reacting with the contacted C to generate SiC to generate volume expansion for densification. Wherein the melt siliconizing process parameter is that the temperature is kept constant at 1450-1650 ℃ for 30-150 min under the inert gas protective atmosphere, and the density of the piston blank after melt siliconizing is 1.95-2.2 g/cm 3 The purity of the silicon powder is more than 99 percent, the granularity is 100 to 300 meshes, and the inert gas can be argon or helium.
(8) Finish machining
The densified piston blank is subjected to secondary machining (i.e., finishing). The method comprises processing the head, skirt and inner cavity of the piston according to the size requirement of the drawing of the piston, and reserving the thickness of an anti-oxidation coating, which is generally 0.08-0.2 mm, for performing anti-oxidation treatment on the top of the piston. The piston head comprises a firepower bank, a ring groove, a ring bank and the like, the piston skirt comprises a face window, a pin hole, a clamp spring groove, an oil injection notch and the like, and the piston inner cavity comprises a pin seat and a strut. The machining can adopt a combined machining mode of a lathe and a machining center.
(9) Anti-oxidation treatment for piston top
Because the piston top is directly contacted with high-temperature fuel gas in the moving process, the top of the piston needs to be subjected to anti-oxidation treatment in order to prevent the C matrix in the composite material matrix from being oxidized at high temperature.
The piston is prepared by combining the structural design of a piston preform, the densification of a matrix and the processing and forming. The invention has the following advantages:
(1) Compared with the traditional aluminum alloy piston, the C/C-SiC composite piston prepared by the invention has the advantages that the mass is reduced by 20-30%, the generated reciprocating motion inertia force and inertia moment are reduced, and the oil consumption of an engine is reduced; the mechanical strength is high, the high temperature is not attenuated, the long-time working at the high temperature of more than 1000 ℃ can be met, the fuel efficiency and the engine power are greatly improved, the fuel consumption and the tail gas emission are reduced, and the service life of a piston is prolonged; the linear thermal expansion coefficient is low, the dimensional stability is good, and the matching size of the piston and the cylinder wall can be reduced, so that the fuel efficiency and the output power of an engine are improved, and the noise is reduced; the C in the matrix has good self-lubricating property, so that the faults of cylinder scuffing and the like can be effectively avoided under the condition of poor lubricating condition, the fault rate of an engine is reduced, and the service life of the piston is prolonged.
(2) According to the invention, the carbon nano tube is prepared in the pores of the C/C porous body in an in-situ growth mode, and on one hand, the preparation of the carbon nano tube can adjust the size and the distribution of the pore diameter of the C/C porous body, improve the densification degree, improve the distribution uniformity of SiC and reduce or even eliminate the residual Si of a brittle phase; on the other hand, the carbon nano tube connects the matrix carbon and the SiC, so that the interface bonding property between the carbon matrix and the SiC matrix prepared by reaction can be effectively improved, the thermal stress generated by mismatching of thermal expansion coefficients in the cooling process is relieved, the crack is stopped or deflected, the strength of the composite material piston is improved, and the service life of the piston is prolonged.
(3) According to the piston structure and the stress characteristics, a novel annular needling prefabricated body suitable for the movement of the piston is designed and prepared, so that the reinforcing body fibers can better bear the force generated in the working process of the piston, and the adaptability of the composite material piston to the use environment is improved.
Drawings
FIG. 1 is a flow chart of the production process of the present invention;
FIG. 2 is a schematic structural diagram of a carbon nanotube modified composite piston for an engine according to an embodiment of the present invention;
FIG. 3 is a schematic representation of a carbon nanotube modified composite piston for an engine according to an embodiment of the present invention;
fig. 4 is a second schematic diagram of a carbon nanotube modified composite piston for an engine according to an embodiment of the present invention.
Detailed Description
The invention is further illustrated with reference to the following figures and examples.
In fig. 1, the preparation method of the present invention is: designing and preparing a prefabricated body structure (designing and preparing an annular prefabricated body according to a cylindrical structure of a piston); high-temperature heat treatment; preparing a low-density C/C porous body by adopting a CVI method; carrying out high-temperature heat treatment on the C/C porous body; machining the piston blank into a piston blank at one time, and growing a carbon nano tube in situ in the pores of the C/C porous body by adopting a normal-pressure CVD method; the piston blank is densified by an RMI method, and secondary machining (namely finish machining) is carried out according to the size requirement of a finished piston; and (3) coating an anti-oxidation coating on the piston combustion chamber and the piston top position after finishing finish machining to obtain a nano tube modified composite material piston finished product (shown in figures 2, 3 and 4).
Example 1:
(1) Adopting 12K T700 carbon fiber non-woven cloth to compound a layer of carbon fiber net tire to form a unit layer by needling in the axial direction, adopting 12K T700 carbon fiber to continuously wind and compound a layer of carbon fiber net tire to form another unit layer by needling in the circumferential direction, alternately superposing the unit layers and the unit layers to continuously needle, and preparing the carbon fiber net tire with the density of 0.40g/cm 3 Carbon fiber preforms (i.e., piston preforms);
(2) Carrying out heat treatment on the carbon fiber preform at 2100 ℃ for 1h under the helium protective atmosphere;
(3) The mixed gas of natural gas and propane is used as a carbon source gas to prepare the carbon source gas with the density of 1.35g/cm 3 The C/C porous body of (1), wherein the natural gas: propane: the volume ratio of nitrogen is 4:1:6, the infiltration time is 300h, the retention time is 1.8s, the infiltration temperature is 1030 ℃, and the pressure is 2000Pa;
(4) Carrying out heat treatment on the C/C porous body for 2h at the temperature of 2150 ℃ and the pressure of 1500Pa in a helium atmosphere;
(5) Machining the C/C porous body subjected to the high-temperature heat treatment in the step (4) according to the size of the piston to obtain a piston blank; processing the contour dimension of the piston excircle by using a lathe, then processing the piston inner cavity by using a processing center according to the deviation of the piston drawing dimension, and reserving a margin of 0.1mm at the top, the head and the skirt part of the piston;
(6) Placing the processed piston blank in 1.5mol/L nickel nitrate ethanol solution (namely mixed solution) for ultrasonic treatment for 5H, drying in a blast oven at 60 ℃ for 2H, then preparing the carbon nano tube in a normal pressure chemical vapor deposition furnace, specifically, heating to 400 ℃ in nitrogen atmosphere, closing nitrogen and introducing H 2 And H is closed after 1.5H 2 Continuously introducing N2, heating to 750 ℃, then closing N2, introducing methane and nitrogen with the volume ratio of 1;
(7) Placing the piston blank body in a graphite crucible filled with silicon powder, melting and siliconizing in a high-temperature furnace, specifically, keeping the temperature at 1450 ℃ for 90min under Ar atmosphere, wherein the purity of the silicon powder is 99.95 percent, the granularity is 200 meshes, and the density of the piston blank body after melting and siliconizing is 2.12g/cm 3 ；
(8) Machining the excircle of the piston by using a lathe according to the drawing size requirement, and then machining the rest sizes by using a machining center, wherein the piston is machined to 0.12mm more;
(9) And (4) carrying out anti-oxidation treatment on the top of the piston.
Example 2:
(1) Adopting 12K T800 carbon fiber non-woven cloth to compound a layer of carbon fiber net tire needling in the axial direction, adopting 12K T1000 carbon fiber to continuously wind and compound a layer of carbon fiber net tire needling in the circumferential direction, alternately superposing unit layers and continuously needling to prepare the carbon fiber net tire with the density of 0.55g/cm 3 A carbon fiber preform;
(2) Carrying out heat treatment on the carbon fiber preform at 2000 ℃ for 0.5h under the argon protective atmosphere;
(3) The mixed gas of propane and nitrogen is used as a gas source to prepare the product with the density of 1.35g/cm 3 The C/C porous body of (1), wherein the volume ratio of propane to nitrogen is 1:8, the infiltration time is 500h, the residence time is 2.0s, the infiltration temperature is 1050 ℃, and the pressure is 2500Pa;
(4) Carrying out heat treatment on the C/C porous body for 2h at 2250 ℃ and 1500Pa in a helium atmosphere;
(5) Machining the C/C porous body subjected to the high-temperature heat treatment in the step (4) according to the size of the piston to obtain a piston blank; machining the outline size of the piston excircle by using a lathe, then machining the piston inner cavity by using a machining center according to the deviation of the piston drawing size, and reserving a margin of 0.08mm at the top, the head and the skirt part of the piston;
(6) Placing the processed piston blank in 1.0mol/L nickel nitrate ethanol solution, performing ultrasonic treatment for 5H, drying in a blast oven at 60 ℃ for 2H, and then preparing the carbon nano tube in a normal-pressure chemical vapor deposition furnace, specifically, heating to 360 ℃ in nitrogen atmosphere, closing nitrogen, and introducing H 2 And after 2H, H is turned off 2 Continuously introducing N2, heating to 700 ℃, then closing N2, introducing methane and nitrogen with the volume ratio of 1:8 for 150min, then closing, introducing N2, and cooling to room temperature;
(7) Placing the piston blank body in a graphite crucible filled with silicon powder, melting and siliconizing in a high-temperature furnace, specifically, keeping the temperature at 1500 ℃ for 90min under Ar atmosphere, wherein the purity of the silicon powder is 99.95 percent, the granularity is 200 meshes, and the density of the piston blank body after melting and siliconizing is 2.15g/cm 3 ；
(8) According to the requirements of drawing dimensions, processing the excircle of the piston by using a lathe, and then processing the rest dimensions by using a processing center, wherein the piston is processed by 0.10mm more;
(9) And (4) carrying out anti-oxidation treatment on the top of the piston. The prepared composite material piston for the high-power high-detonation-pressure engine is subjected to 1:1 integral piston test, and the test results are as follows:
Claims (8)
1. a preparation method of a carbon nano tube modified composite material piston for an engine is characterized by comprising the following steps: the method comprises the following steps:
1) Piston preform preparation
According to the cylindrical structure of the piston, a carbon fiber non-woven fabric is compounded with a carbon fiber net tire in the axial direction to form a unit layer by needling, carbon fiber is continuously wound and compounded with a carbon fiber net tire in the circumferential direction to form another unit layer by needling, and the unit layers are alternately superposed and continuously needled to form an annular needling structure piston prefabricated body for the piston; wherein piston preform density0.4 to 0.6g/cm 3 ；
2) High temperature heat treatment
Carrying out heat treatment on the piston preform prepared in the step 1) for 1 to 2h under the protection atmosphere of inert gas, wherein the heat treatment temperature is 1950 to 2300 ℃, and the inert gas is argon or helium;
3) Preparation of carbon fiber reinforced matrix carbon porous body
Carrying out pyrolytic carbon densification on the piston preform subjected to the high-temperature heat treatment in the step 2) by adopting chemical vapor deposition to prepare a carbon fiber reinforced matrix carbon porous body; the carbon source gas for chemical vapor infiltration is natural gas, propane, propylene, acetylene or a mixed gas thereof, the diluent gas is nitrogen, hydrogen or a mixed gas thereof, the volume ratio of the carbon source gas to the diluent gas is 1 to 14, the infiltration time is 100 to 500h, the residence time is 0.6 to 2.5s, the infiltration temperature is 860 to 1050 ℃, and the pressure is 1000 to 5000Pa;
4) High-temperature heat treatment of carbon fiber reinforced matrix carbon porous body
Processing at 2000-2450 ℃ under the protection of inert gas, at 500-5000 Pa, and for 0.5-5h;
5) Piston blank machining
Machining the carbon fiber reinforced matrix carbon porous body subjected to the high-temperature heat treatment in the step 4) according to the size of the piston to obtain a piston blank;
6) In-situ growth of carbon nanotubes
The catalytic precursor is nickel nitrate or cobalt acetate, the solvent is ethanol, the catalytic precursor is dissolved in the ethanol to prepare a mixed solution, and the concentration of the mixed solution is 0.5 to 2.5mol/L; putting the piston blank into the mixed solution, performing ultrasonic treatment for 3 to 8 hours, putting the piston blank into a blast oven at the temperature of between 60 and 80 ℃, drying the piston blank, and then transferring the piston blank into a normal-pressure chemical vapor deposition furnace at the temperature of between 300 and 500 ℃ in H 2 Reducing for 1 to 3 hours under the atmosphere, closing hydrogen, introducing protective gas, continuously heating to 650 to 980 ℃, introducing carbon source gas and diluent gas to grow the carbon nano tube in situ in the C/C material pore, depositing for 30 to 180min, closing the carbon source gas and the diluent gas, and introducing protective gas to cool to room temperature;
7) Piston green body densification
Placing the piston blank after in-situ growth of the carbon nano tube in a graphite crucible filled with silicon powder to perform melting siliconizing in a high-temperature furnace; the melt siliconizing process parameter is that the temperature is kept constant at 1450 to 1650 ℃ for 30 to 150min under the protection atmosphere of inert gas, the purity of the silicon powder is more than 99 percent, the granularity is 100 to 300 meshes, and the inert gas is argon or helium;
8) Finish machining
Performing finish machining on the piston blank densified in the step 7) according to the size requirement of a finished piston;
9) And (4) carrying out anti-oxidation treatment on the top of the piston.
2. The method for preparing a carbon nanotube modified composite piston for an engine according to claim 1, wherein: the density of the carbon fiber reinforced matrix carbon porous body in the step 3) is 1.15 to 1.55g/cm 3 。
3. The method for preparing a carbon nanotube modified composite piston for an engine according to claim 1, wherein: the inert gas in the step 4) is argon or helium.
4. The method for preparing a carbon nanotube modified composite piston for an engine according to claim 1, wherein: the protective gas in the step 6) is nitrogen, argon or helium; the carbon source gas is methane, propane, propylene, acetylene or a mixed gas thereof, the diluent gas is hydrogen, nitrogen or a mixed gas thereof, and the volume ratio of the carbon source gas to the diluent gas is 1 to 10.
5. The method for preparing a carbon nanotube modified composite piston for an engine according to claim 1, wherein: the density of the piston blank after the melting siliconizing in the step 7) is 1.95 to 2.2g/cm 3 。
6. The method for preparing a carbon nanotube modified composite piston for an engine according to claim 1, wherein: the anti-oxidation treatment method for the top of the piston blank in the step 9) comprises the following steps: and coating a ceramic coating with heat insulation and self-healing functions on the top of the piston and the combustion chamber, wherein the ceramic coating is a phosphate coating, a borate coating and/or a mixed coating thereof.
7. A piston made by the method for preparing the carbon nanotube modified composite piston for the engine as claimed in any one of claims 1 to 6.
8. Use of the piston of claim 7 in an engine.
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