CN108728804B - CrAlN thermal insulation coating for aluminum alloy piston combustion chamber surface and preparation method thereof - Google Patents

CrAlN thermal insulation coating for aluminum alloy piston combustion chamber surface and preparation method thereof Download PDF

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CN108728804B
CN108728804B CN201811058209.8A CN201811058209A CN108728804B CN 108728804 B CN108728804 B CN 108728804B CN 201811058209 A CN201811058209 A CN 201811058209A CN 108728804 B CN108728804 B CN 108728804B
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craln
aluminum alloy
coating
thermal insulation
combustion chamber
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CN108728804A (en
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齐福刚
李贝贝
欧阳晓平
赵镍
曹红帅
罗文忠
钟向丽
陈静
刘应都
王冰
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Xiangtan University
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    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
    • C23C14/22—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the process of coating
    • C23C14/24—Vacuum evaporation
    • C23C14/32—Vacuum evaporation by explosion; by evaporation and subsequent ionisation of the vapours, e.g. ion-plating
    • C23C14/325—Electric arc evaporation
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
    • C23C14/0021—Reactive sputtering or evaporation
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
    • C23C14/02—Pretreatment of the material to be coated
    • C23C14/024—Deposition of sublayers, e.g. to promote adhesion of the coating
    • C23C14/025—Metallic sublayers
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
    • C23C14/06—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the coating material
    • C23C14/0641—Nitrides

Abstract

The invention discloses a CrAlN thermal insulation coating for an aluminum alloy piston combustion chamber surface and a preparation method thereof. The method adopts a magnetic filtration cathode vacuum arc method, uses CrAl alloy target materials (Cr and Al metal target materials) as a cathode, deposits a CrAl coating on the surface of the aluminum alloy to form a transition layer, then uses nitrogen as working gas, and uniformly coats the CrAlN coating on the surface of the obtained transition layer to form a heat insulation layer. The invention not only solves the problem of poor bonding force and bearing capacity caused by larger difference of basic physical properties of the CrAlN coating and the aluminum alloy substrate material, but also has uniform and compact coating, good film-substrate bonding state, hardness as high as 40GPa, and good high-temperature heat insulation and thermal shock resistance in a piston thermal load test. The invention obviously improves the performance reliability and the service life of the aluminum alloy piston and can meet the development requirements of high power and low emission of modern engines.

Description

CrAlN thermal insulation coating for aluminum alloy piston combustion chamber surface and preparation method thereof
Technical Field
The invention relates to the field of piston surface treatment, in particular to a CrAlN thermal insulation coating for an aluminum alloy piston combustion chamber surface and a preparation method thereof.
Background
The piston is the 'heart' of the engine and is an important component for transmitting energy of the engine, and the quality of the piston directly influences the usability, the economy and the service life of the engine. When the combustion chamber surface of the piston is positioned at the top dead center, the combustion chamber surface is above the top surface of the piston and below the bottom surface of the cylinder cover, and the combustion chamber surface is used for mixing gas and organizing airflow and providing space for combustion. However, diesel fuel of the diesel engine has high viscosity and is not easy to evaporate, the autoignition temperature of the diesel fuel is lower than that of gasoline, and the working property of piston compression ignition endows a combustion chamber with a worse service environment. When the piston of the diesel engine works, diesel oil can form fine oil particles, the fine oil particles are mixed with high-pressure and high-temperature air, instantaneous high temperature and gas pressure are further generated in the compression process, and ablative gases such as nitrogen, oxygen, sulfur, oxygen and the like are generated at the same time; under the working cycle of four strokes of air inlet, compression, work application and air exhaust, the combustion chamber surface not only bears alternating mechanical load and cyclic thermal shock, but also enables the piston base material to directly contact with high-temperature fuel gas in a mode of fuel and air mixed working, and the combustion chamber surface is very easy to have failure behaviors of thermal load, thermal fatigue, thermal corrosion and the like. The combustion chamber surface of the piston of the diesel engine is a non-geometric surface, and the shape of the combustion chamber of the piston not only influences the efficiency of the diesel engine, but also has considerable influence on the heat intensity of the piston. With the development of technology, the geometry of combustion chambers is becoming more complex, but in general, the unified development of perfect combustion efficiency, piston thermal strength and emission standards is not achieved. One of the effective ways to improve the base material of the piston at present is to improve the local performances of the piston, such as thermal shock resistance, high-temperature oxidation resistance, corrosion resistance and the like, by a surface coating technology. However, in consideration of the special service condition of the combustion chamber surface of the piston of the diesel engine, the traditional surface coating process has poor diffraction performance, and a uniform and compact film layer with good bonding performance with a base material is difficult to prepare, so that the effect of protecting the base material and strengthening the base material cannot be achieved.
The CrAlN coating has good mechanical property and machining characteristic, and can form inert Al at high temperature2O3、Cr2O3The mixed oxide film has a low heat conductivity coefficient, and has great application advantages in the field of high-temperature protection. For example, patent with publication number CN108266287A discloses a wear-resistant coating of a piston ring, which is composed of four layers, sequentially including a bonding layer, a main wear-resistant layer, an auxiliary wear-resistant layer and a buffer layer from inside to outside; the main wear-resistant layer is a CrAlN layer and a WS layer2CrAlN/WS alternately formed in layers2A multi-layer coating, wherein the auxiliary wear-resistant layer is a Cr layer and a CrO layer which are alternately formed to Cr-A CrO multilayer coating. The wear-resistant coating disclosed by the patent has better mechanical property and wear resistance. However, the CrAlN coating is mainly used in the wear-resistant field by being combined with base materials such as Si, tool and die steel, and the like, and the high-hardness CrAlN coating and the aluminum alloy piston base material have great difference in hardness, thermal expansion coefficient and structure, so that the binding force and bearing capacity between the CrAlN heat-insulating coating and the base material are limited, and the failure behaviors such as heat load, thermal fatigue, thermal corrosion and the like caused when the coating is applied to a combustion chamber surface cannot be avoided.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to provide a CrAlN thermal insulation coating for an aluminum alloy piston combustion chamber surface and a preparation method thereof, and solves the problem of failure behaviors of a piston, such as thermal load, thermal fatigue, thermal corrosion and the like caused by a severe service environment due to poor bonding force of a base material aluminum alloy and the thermal insulation coating.
In order to solve the technical problems, the invention adopts the following technical scheme: a CrAlN heat insulation coating for an aluminum alloy piston combustion chamber surface sequentially comprises a transition layer and a heat insulation layer from inside to outside, wherein the transition layer is a CrAl coating, and the heat insulation layer is a CrAlN coating.
Thus, a CrAl transition layer with high Al content is arranged between the CrAlN layer with high hardness and the base material aluminum alloy, so that the adaptability between the CrAlN coating and the aluminum alloy base material can be improved, the difference of properties such as chemical bonds, thermal expansion coefficients and the like can be relieved, and the effect of reducing stress is achieved. Effectively avoiding the problems of poor binding force and poor bearing capacity caused by the great difference between the basic physical properties of the CrAlN coating and the aluminum alloy substrate.
Further, the thickness of the transition layer is 0.4-2 mu m, the thickness of the heat insulation layer is 2-5 mu m, and the ratio of the thickness of the transition layer to the thickness of the heat insulation layer is 1: 4-6.
Therefore, the heat-insulating coating has better strengthening effect and effectively protects the base material; but also can fully play the binding role of the transition layer.
The preparation method of the CrAlN thermal insulation coating for the combustion chamber surface of the aluminum alloy piston comprises the following steps:
1) preparation of the transition layer
Depositing CrAl on the surface of the aluminum alloy piston combustion chamber by adopting a magnetic filtration cathode vacuum arc method and taking Cr and Al metal targets as double cathodes or a CrAl alloy target as a cathode to obtain a transition layer;
2) preparation of thermal insulation layer
And (2) continuously adopting a magnetic filtration cathode vacuum arc method on the transition layer obtained in the step 1), and depositing CrAlN on the transition layer by taking Cr and Al metal target materials as double cathodes or CrAl alloy target materials as cathodes and nitrogen as working gas to obtain a heat insulation layer, thus obtaining the CrAlN heat insulation coating for the surface of the aluminum alloy piston combustion chamber.
Thus, a CrAl layer and a CrAlN layer are deposited on the surface of a piston combustion chamber of the diesel engine by adopting a magnetic filtration cathode vacuum arc method, the deposition rate is high, the metal beam flow and the magnetic field are controllable, a 180-degree straight pipe and a 90-degree bent pipe are adopted as magnetic filtration devices, large particles during film formation can be effectively filtered, and the prepared coating is uniform and compact and has few defects; and the binding force of the heat-insulating coating and the aluminum alloy substrate material is greatly improved due to the binding effect of the CrAl transition layer with high Al content.
The general formula of the CrAl alloy target is CrxAlyThe x is 20-30, and the y is 70-80. When the Cr and Al metal target materials are used as double cathodes, the arcing current on the Al is larger than that on the Cr.
Thus, the CrAl compound with high Al content is between the critical solid solubility of the phase change of the face-centered cubic structure and the hexagonal structure of CrAlN, and coating products applied in different fields are optimally designed through parameters of a deposition process: such as high Cr content for CrAlN coatings resistant to hot corrosion or high Al content for CrAlN coatings resistant to high temperature oxidation.
Further, in the magnetic filtration cathode vacuum arc method, the arcing current is 60-130A, the positive bias voltage is 1.8-3.0V, the upper deflection current is 1.5A-3.5A, the lower deflection current is 1.5-3.5A, the negative bias voltage is 30-200V, and the duty ratio is 20-90%.
Preferably, the arcing current in the magnetic filtration cathode vacuum arc method is 90-110A, the positive bias is 2.4V, the upper deflection current is 2.4A, the lower deflection current is 3.2A, the negative bias is 30-120V, and the duty ratio is 86.2 +/-0.1%.
Further, the transition layer is prepared by the following method: adjusting the arcing current, controlling the negative bias of the base material, depositing a CrAl transition layer on the surface of the pretreated piston in a sputtering mode by sequentially adopting negative pressure points from high to low, keeping each negative pressure point for 30-60 s, and then selecting a proper negative bias to continuously deposit CrAl to form the transition layer; the negative pressure points are-600V, -500V, -400V, -300V and-200V.
Like this, adopt in proper order from high negative pressure point to low negative pressure point, can play the abluent effect of sputter on the one hand, on the other hand can strengthen the cohesion between transition layer and the aluminum alloy substrate.
Further, the deposition time in the step 2) is 10-30 min.
Further, the ventilation amount of the nitrogen in the step 3) is 60-160 sccm, and the deposition time is 20-70 min.
Further, the ventilation amount of the nitrogen in the step 3) is changed in a gradient manner, and a plurality of CrAlN gradient coatings with different N contents are obtained in the direction vertical to the coatings.
Therefore, the compactness of the coating can be improved, the defects are reduced, the hardness of the coating is improved, the stress accumulation of the coating at an interface can be reduced, and the binding force is improved.
Furthermore, the gradient variation range of the nitrogen ventilation amount is 60-160 sccm, and each gradient is maintained for 20-40 min.
Thus, CrAlN coatings with different N contents can be obtained by controlling the nitrogen gas ventilation quantity to change in a gradient way.
The invention has the following function principle:
(1) the invention adopts the magnetic Filtration Cathode Vacuum Arc (FCVA) deposition technology to prepare the CrAlN thermal insulation coating on the surface of the aluminum alloy piston combustion chamber, adds a magnetic filtration plasma bent pipe on the basis of vacuum cathode arc ion plating, almost can completely filter neutral and large particles generated by cathode arc discharge, ensures that only high-energy plasma exists in the plasma, has the advantages of high ionization rate, high ion energy, high deposition rate and the like, has good diffraction, can be plated with wide materials, has controllable magnetic field, and is beneficial to the application of the CrAlN thermal insulation coating on the surface of the diesel engine piston combustion chamber with irregular non-geometric surface.
(2) The thermal property and the mechanical property of the aluminum alloy substrate material and the CrAlN coating are greatly different, so that the interface bonding performance of the two materials is influenced, and the film thickness is limited. According to the invention, the CrAl transition layer is deposited between the aluminum alloy piston substrate and the CrAlN heat-insulating coating, and the adaptability of the hard coating and the substrate can be improved by adopting one (or more) intermediate layer systems to act between the hard coating and the substrate, so that the difference of properties such as chemical bonds, thermal expansion coefficients and the like is relieved, and the effect of reducing stress is achieved; or the parameter gradient is controlled to reduce the accumulation of coating stress on the interface, thereby improving the binding force.
(3) When the piston combustion chamber works, the thermal load failure of the coating is easily caused by the cyclic thermal shock effect. Therefore, the invention adopts FCVA deposition technology to prepare the CrAlN thermal insulation coating. The CrAlN coating has low intrinsic heat conductivity coefficient, good high-temperature thermal stability and high-temperature oxidation resistance, and can further obtain a special columnar crystal morphology through process parameter optimization, thereby further reducing the heat conductivity of the coating; and has larger strain tolerance, thereby having better thermal shock resistance.
Compared with the prior art, the invention has the following beneficial effects:
1. compared with other physical vapor deposition methods such as vacuum evaporation plating and vacuum sputtering plating, the preparation method has the advantages of the two methods, high deposition rate, high ionization rate and controllable metal beam and magnetic field, and can effectively filter large particles during film forming by adopting a 180-degree straight pipe and a 90-degree bent pipe as magnetic filtering devices, so that the obtained film is uniform and compact, has fewer defects and is good in interface bonding state. The equipment is simple to operate, the process is mature, the batch production can be realized, and the method has wide application value in industrialization. The piston surface treatment technology belongs to the vacuum plasma category, is green and environment-friendly, and cannot cause pollution to the ecological environment.
2. According to the invention, by adopting a CrAl compound with high Al content as a transition layer, the internal stress of an aluminum alloy substrate material and the film layer of CrAlN can be effectively released, and the film-substrate binding force is enhanced; by adopting the structural design of the parameter gradient coating, the mechanical property changes along with the gradient of the coating thickness, the stress of the CrAlN coating at the interface is relieved, and the CrAlN coating with higher thickness can be prepared by 5-15 mu m; by the design of a film layer structure and the optimization of deposition parameters, the heat-insulating coating prepared by the method disclosed by the invention shows a good film-substrate bonding state of HF 1-HF 3 grade, and the hardness is up to 40 GPa.
3. The CrAlN heat insulation coating prepared by the invention has the characteristic columnar crystal appearance which is vertical to the heat flow direction and blocks heat flow transmission, effectively avoids direct contact of high-temperature fuel gas and a piston substrate, obviously improves the heat insulation property and the heat stability (more than 800 ℃) of the aluminum alloy piston, greatly improves the comprehensive performance of the aluminum alloy piston, and can meet the development requirements of high power and low emission of modern vehicles.
Drawings
FIG. 1 is a schematic structural diagram of a CrAlN thermal insulation coating used on the combustion chamber surface of an aluminum alloy piston;
FIG. 2 shows SEM images of the surface and back reflection of a CrAlN thermal insulation coating for the combustion chamber surface of an aluminum alloy piston prepared in example 1;
FIG. 3 is an SEM cross-sectional view of a CrAlN thermal insulation coating for a combustion chamber surface of an aluminum alloy piston prepared in example 1;
in the figure, 1 is a heat insulation layer, 2 is a transition layer, and 3 is an aluminum alloy base material;
FIG. 4 is a TEM image of a CrAlN thermal barrier coating cross-section prepared for the combustion chamber face of an aluminum alloy piston in example 2;
in the figure, 1 is a heat insulation layer, 2 is a transition layer, and 3 is an aluminum alloy base material; FIG. A is a selected area electron diffraction pattern;
FIG. 5 is a schematic diagram of a rock pit for preparing a CrAlN thermal insulation coating for a combustion chamber surface of an aluminum alloy piston in examples 1-4;
FIG. 6 is a graph showing the hardness changes of CrAlN thermal insulation coatings for the combustion chamber surface of the aluminum alloy piston prepared in examples 1 to 4;
FIG. 7 is a graph comparing the thermal insulation performance of CrAlN thermal barrier coatings and uncoated coatings prepared for the combustion chamber face of an aluminum alloy piston in example 5;
FIG. 8 is a DSC chart of CrAlN thermal barrier coating for the combustion chamber face of an aluminum alloy piston prepared in example 5.
Detailed Description
The present invention will be described in further detail with reference to examples.
The CrAlN heat-insulating coating for the surface of the aluminum alloy piston combustion chamber sequentially comprises a transition layer and a heat-insulating layer from inside to outside, wherein the transition layer is a CrAl coating, and the heat-insulating layer is a CrAlN coating.
The invention provides a CrAlN thermal insulation coating for an aluminum alloy piston combustion chamber surface, and in order to realize the purpose of the invention, the technical scheme of the invention mainly comprises two steps: firstly, a pretreatment process; the second is a preparation process. The pretreatment process has the same operation in each embodiment, and specifically comprises the following steps:
(1) wet grinding an aluminum alloy piston base material with 400#, 800#, 1000#, 2000# and 5000# abrasive paper in sequence, and then respectively carrying out ultrasonic cleaning on the base material for 10-15 min by taking an appropriate amount of acetone solution and anhydrous ethanol solution in sequence;
(2) before the aluminum alloy piston base material is placed in a magnetic filtration cathode arc vacuum chamber device, a dust collector is adopted to completely absorb dust and attachments remained in the magnetic filtration cathode arc vacuum chamber, and a sample table is wiped by absolute ethyl alcohol and gauze;
(3) before coating, controlling the vacuum degree in a magnetic Filtration Cathode Vacuum Arc (FCVA) deposition system to be 3.5 multiplied by 10-3Pa ~4.5×10-3And Pa, regulating the bias voltage of glow cleaning to be 800-1000V, and cleaning for 10 min by using plasma.
The preparation process will be described below by way of specific examples.
Example 1
1) Preparation of the transition layer
Placing the pretreated aluminum alloy piston into a magnetic filtration cathode vacuum chamber, adjusting the positive bias voltage to 2.4V, the upper deflection current to 2.4A, the lower deflection current to 3.2A and the duty ratio to 86.2 +/-0.1 percent, and taking Cr as a reference25Al75The target material is used as a cathode, the arc starting current is adjusted to be 100A, 5 negative pressure points of-600V, -500V, -400V, -300V and-200V are adopted in sequence, a CrAl transition layer is deposited on the surface of the pretreated base material in a sputtering mode, each negative pressure point is kept for 30 s-60 s, and thenAnd (3) continuously depositing a CrAl transition layer by selecting negative bias as-50V, wherein the deposition time is 20min, and the CrAl is deposited on the surface of the aluminum alloy piston to form the transition layer.
2) Preparation of thermal insulation layer
Continuously adopting a magnetic filtration cathode vacuum arc method on the transition layer obtained in the step 1), wherein the positive bias voltage is 2.4V, the upper deflection current is 2.4A, the lower deflection current is 3.2A, the duty ratio is 86.2 +/-0.1 percent, and Cr is used25Al75The target is a cathode, the arc starting current is adjusted to be 100A, a gas flow switch is opened, the reaction gas nitrogen is slowly introduced, the ventilation amount is adjusted to be 100 +/-2 sccm, the deposition time is 40min, and the CrAlN is deposited on the transition layer to obtain a heat insulation layer, so that the CrAlN heat insulation coating for the surface of the aluminum alloy piston combustion chamber is obtained; and closing the gas flow switch, closing the arc source, recording data, closing the molecular pump, and taking out the sample.
The CrAlN thermal insulation coating for the combustion chamber surface of the aluminum alloy piston prepared in the embodiment is subjected to a film thickness test by a surface profiler, the thickness of the thermal insulation coating is 4.265 μm, the thickness of the transition layer is about 1 μm, and the thickness of the thermal insulation layer is about 3 μm.
The surface and the section of the CrAlN thermal insulation coating for the combustion chamber surface of the aluminum alloy piston, prepared in the embodiment, are observed by a scanning electron microscope, and the results are shown in FIGS. 2 and 3.
As seen from FIG. 2, the coating is uniform and dense, has no obvious component change, and has relatively uniform composition; as can be seen from FIG. 3, a very clear transition layer interface is formed between the aluminum alloy substrate and the CrAlN thermal insulation layer, and the adaptability of the CrAlN layer and the aluminum alloy substrate can be improved due to the fact that a CrAl compound with high Al content is used as the transition layer, and the obtained coating is uniform and compact.
Example 2
1) Preparation of the transition layer
Placing the pretreated aluminum alloy piston into a magnetic filtration cathode vacuum chamber, adjusting the positive bias voltage to 2.4V, the upper deflection current to 2.4A, the lower deflection current to 3.2A and the duty ratio to 86.2 +/-0.1 percent, and taking Cr as a reference25Al75The target is a cathode, the arc starting current is adjusted to be 100A, and the sequence adopts-600V, -500V, -400V, -300V anddepositing a CrAl transition layer on the surface of the pretreated base material in a sputtering mode at 5 negative pressure points of-200V, keeping each negative pressure point for 30-60 s, then selecting negative bias as-50V to continue depositing the CrAl transition layer for 20min, and depositing CrAl on the surface of the aluminum alloy piston to form the transition layer;
2) preparation of thermal insulation layer
Continuously adopting a magnetic filtration cathode vacuum arc method on the transition layer obtained in the step 1), wherein the positive bias voltage is 2.4V, the upper deflection current is 2.4A, the lower deflection current is 3.2A, the duty ratio is 86.2 +/-0.1 percent, and Cr is used25Al75The target is a cathode, the arc starting current is adjusted to be 100A, a gas flow switch is opened, the reaction gas nitrogen is slowly introduced, the ventilation amount is adjusted to be 140 +/-2 sccm, the deposition time is 40min, and the CrAlN is deposited on the transition layer to obtain a heat insulation layer, so that the CrAlN heat insulation coating for the surface of the aluminum alloy piston combustion chamber is obtained; and closing the gas flow switch, closing the arc source, recording data, closing the molecular pump, and taking out the sample.
The CrAlN thermal insulation coating for the combustion chamber surface of the aluminum alloy piston, prepared in the embodiment, is subjected to a film thickness test through a surface profiler, wherein the thickness of the transition layer is about 0.6-0.8 mu m, and the thickness of the thermal insulation layer is about 3 mu m.
The appearance of the section of the prepared CrAlN thermal insulation coating for the combustion chamber surface of the aluminum alloy piston is observed by a transmission electron microscope, and the result is shown in FIG. 4.
As can be seen from fig. 4, the CrAlN thermal barrier layer exhibits a fine columnar morphology with better strain tolerance, and selective electron diffraction indicates that the thermal barrier layer is not a single solid solution, but rather a heterogeneous competitive coating.
Example 3
1) Preparation of the transition layer
Placing the pretreated aluminum alloy piston into a magnetic filtration cathode vacuum chamber, adjusting the positive bias voltage to 2.4V, the upper deflection current to 2.4A, the lower deflection current to 3.2A and the duty ratio to 86.2 +/-0.1 percent, and taking Cr as a reference25Al75The target is a cathode, the arc starting current is adjusted to be 100A, 5 negative pressure points of-600V, -500V, -400V, -300V and-200V are adopted in sequence, and the surface of the pretreated base material is subjected to surface treatmentDepositing a CrAl transition layer in a sputtering mode, keeping each negative pressure point for 30-60 s, then selecting negative bias as-50V to continue depositing the CrAl transition layer, wherein the deposition time is 20min, and depositing CrAl on the surface of the aluminum alloy piston to form the transition layer;
2) preparation of thermal insulation layer
Continuously adopting a magnetic filtration cathode vacuum arc method on the transition layer obtained in the step 1), wherein the positive bias voltage is 2.4V, the upper deflection current is 2.4A, the lower deflection current is 3.2A, the duty ratio is 86.2 +/-0.1 percent, and Cr is used25Al75The target is a cathode, the arc starting current is adjusted to be 100A, a gas flow switch is opened, the reaction gas nitrogen is slowly introduced, the ventilation amount is adjusted to be 100 sccm, the deposition time is 20min, a 'first layer' of CrAlN coating is obtained, the ventilation amount is continuously set to be 120 sccm, the deposition is carried out for 20min, a 'second layer' of CrAlN coating is obtained, a CrAlN gradient coating is deposited on the transition layer to obtain a heat insulation layer, and the CrAlN heat insulation coating for the combustion chamber surface of the aluminum alloy piston is obtained; and closing the gas flow switch, closing the arc source, recording data, closing the molecular pump, and taking out the sample.
The prepared CrAlN thermal insulation coating for the combustion chamber surface of the aluminum alloy piston is subjected to a film thickness test by a surface profiler, and the film thickness of the thermal insulation coating is 3.880 mu m.
Example 4
1) Preparation of the transition layer
Placing the pretreated aluminum alloy piston into a magnetic filtration cathode vacuum chamber, adjusting the positive bias voltage to 2.4V, the upper deflection current to 2.4A, the lower deflection current to 3.2A and the duty ratio to 86.2 +/-0.1 percent, and taking Cr as a reference25Al75The target is a cathode, the arc starting current is adjusted to be 100A, 5 negative pressure points of-600V, -500V, -400V, -300V and-200V are sequentially adopted, a CrAl transition layer is deposited on the surface of the pretreated base material in a sputtering mode, each negative pressure point is kept for 30 s-60 s, then the negative bias is selected to be-50V, the CrAl transition layer is continuously deposited, the deposition time is 20min totally, and the CrAl is deposited on the surface of the aluminum alloy piston, namely the transition layer is formed;
2) preparation of thermal insulation layer
Continuing to adopt magnetic filtration cathode vacuum on the transition layer obtained in the step 1)Arc method, positive bias voltage of 2.4V, upper deflection current of 2.4A, lower deflection current of 3.2A, duty ratio of 86.2 + -0.1%, and Cr25Al75The target is a cathode, the arc starting current is adjusted to be 100A, a gas flow switch is opened, the reaction gas nitrogen is slowly introduced, the ventilation amount is adjusted to be 120 sccm, the deposition time is 20min, a 'first layer' of CrAlN coating is obtained, the ventilation amount is continuously set to be 140 sccm, the deposition is carried out for 20min, a 'second layer' of CrAlN coating is obtained, a CrAlN gradient coating is deposited on the transition layer to obtain a heat insulation layer, and the CrAlN heat insulation coating for the combustion chamber surface of the aluminum alloy piston is obtained; and closing the gas flow switch, closing the arc source, recording data, closing the molecular pump, and taking out the sample.
The prepared CrAlN thermal insulation coating for the combustion chamber surface of the aluminum alloy piston is subjected to a film thickness test by a surface profiler, and the film thickness of the thermal insulation coating is 3.717 mu m.
The CrAlN thermal insulation coating for the combustion chamber surface of the aluminum alloy piston, prepared in the embodiment 1-4, is subjected to a bonding force test, a hardness test and a thermal insulation effect test. The results are shown in FIGS. 5 and 6:
as can be seen from FIGS. 5 and 6, under the same deposition time, the bonding force and hardness of the coating are obviously improved through the nitrogen ventilation gradient structure design, wherein the bonding force of the coating in the embodiment 3 is between HF1 and HF2, and the hardness is as high as 40 GPa. The nitrogen content influences the performance of the coating by influencing the phase composition, internal stress and the like of the coating, and in addition, the nitrogen ventilation quantity is graded to form coatings with different nitrogen contents in the direction perpendicular to the growth direction of the film on the substrate, so that the accumulation of the stress of the coating on the interface can be reduced, and the binding force is increased. The piston without the coating is selected as a comparison group to perform a piston heat load experiment on the CrAlN heat insulation coating on the surface of the aluminum alloy piston combustion chamber prepared in the embodiment 1-4, 30 thermal shock cycles are performed at the same temperature range of 100-300 ℃, the time required by the coating for the piston without the coating is respectively reduced by 55 s, 42 s, 60s and 59 s, and the CrAlN heat insulation coating for the surface of the piston combustion chamber is designed by a nitrogen ventilation gradient structure, so that the CrAlN heat insulation coating has a good heat insulation effect.
Example 5
1) Preparation of the transition layer
Placing the pretreated aluminum alloy piston into a magnetic filtration cathode vacuum chamber, adjusting positive bias to 2.4V, upper deflection current to 2.0A, lower deflection current to 2.0A and duty ratio to 86.2 +/-0.1%, respectively adjusting arcing current to 70A and 90A by taking Cr and Al metal targets as double cathodes, sequentially adopting 5 negative pressure points of-600V, -500V, -400V, -300V and-200V, depositing a CrAl transition layer on the surface of the pretreated base material in a sputtering mode, keeping each negative pressure point for 30-60 s, then selecting negative pressure to be-50V to continuously deposit the CrAl transition layer for 20min, and depositing CrAl on the surface of the aluminum alloy piston to form the transition layer;
2) preparation of thermal insulation layer
Continuously adopting a magnetic filtration cathode vacuum arc method on the transition layer obtained in the step 1), wherein the positive bias voltage is 2.4V, the upper deflection current is 2.4A, the lower deflection current is 2.4A, the duty ratio is 86.2 +/-0.1%, Cr and Al metal target materials are used as double cathodes, the arcing currents are respectively adjusted to be 70A and 90A, a gas flow switch is opened, the reaction gas nitrogen is slowly introduced, the ventilation quantity is adjusted to be 50 sccm, the deposition time is 40min, and a thermal insulation layer is obtained by depositing CrAlN on the transition layer, so that the CrAlN thermal insulation coating for the combustion chamber surface of the aluminum alloy piston is obtained; and closing the gas flow switch, closing the arc source, recording data, closing the molecular pump, and taking out the sample.
The piston without the coating is selected as a comparison group to carry out a piston heat load experiment on the piston and the piston, 30 heat shock cycles are carried out at the same temperature range of 100-300 ℃, and it can be seen from figure 7 that the time required by the coated piston is 60-70 s more than that of the piston without the coating, which shows that the CrAlN heat insulation coating for the piston combustion chamber surface prepared by the embodiment has a good heat insulation effect; the thermal stability test of the coating prepared in the embodiment is carried out in Ar atmosphere, and the DSC chart of the CrAlN thermal insulation coating on the combustion chamber surface of the aluminum alloy piston can be seen from figure 8, and the thermal stability of the coating is as high as 800 ℃.
The above description is only exemplary of the present invention and should not be taken as limiting, and any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (7)

1. The CrAlN thermal insulation coating for the surface of the aluminum alloy piston combustion chamber is characterized by sequentially comprising a transition layer and a thermal insulation layer from inside to outside, wherein the transition layer is a CrAl coating, and the thermal insulation layer is a CrAlN coating;
the preparation method of the thermal insulation coating comprises the following steps:
1) preparation of the transition layer
Depositing CrAl on the surface of the aluminum alloy piston combustion chamber by adopting a magnetic filtration cathode vacuum arc method and taking a CrAl alloy target as a cathode to obtain a transition layer;
2) preparation of thermal insulation layer
Continuously adopting a magnetic filtration cathode vacuum arc method on the transition layer obtained in the step 1), taking a CrAl alloy target as a cathode and nitrogen as a working gas, and depositing CrAlN on the transition layer to obtain a heat insulation layer, thus obtaining a CrAlN heat insulation coating for the surface of the aluminum alloy piston combustion chamber;
the general formula of the CrAl alloy target is CrxAlyX is 20-30, and y is 70-80;
the ventilation quantity of the nitrogen is changed in a gradient manner, and a plurality of CrAlN gradient coatings with different N contents are obtained in the direction vertical to the coatings.
2. The CrAlN thermal insulation coating for the combustion chamber surface of the aluminum alloy piston as claimed in claim 1, wherein the thickness of the transition layer is 0.4-2 μm, the thickness of the thermal insulation layer is 3-7 μm, and the thickness ratio of the transition layer to the thermal insulation layer is 1: 4-8.
3. The method for preparing a CrAlN thermal insulation coating for the combustion chamber face of the aluminum alloy piston as claimed in claim 1, wherein the magnetic filtration cathode vacuum arc method is characterized in that the arc starting current is 60-130A, the positive bias is 1.8-3.0V, the upper deflection current is 1.5A-3.5A, the lower deflection current is 1.5-3.5A, the negative bias is 30-200V, and the duty ratio is 20-90%.
4. The method for preparing the CrAlN thermal insulation coating for the combustion chamber surface of the aluminum alloy piston as claimed in claim 1, wherein the deposition time in the step 1) is 10-30 min; and 2) ventilating the nitrogen gas at a rate of 60-160 sccm, and depositing for 20-70 min.
5. The preparation method of the CrAlN thermal insulation coating for the combustion chamber surface of the aluminum alloy piston as claimed in claim 1, wherein the transition layer is prepared by the following specific method: adjusting the arcing current, controlling the negative bias of the base material, depositing a CrAl transition layer on the surface of the pretreated piston in a sputtering mode by sequentially adopting negative pressure points from high to low, keeping each negative pressure point for 30-60 s, and then selecting a proper negative bias to continuously deposit CrAl to form the transition layer.
6. The method for preparing the CrAlN thermal insulation coating for the combustion chamber face of the aluminum alloy piston as claimed in claim 5, wherein the negative pressure point is-600V, -500V, -400V, -300V and-200V.
7. The method for preparing a CrAlN thermal insulation coating for the combustion chamber surface of the aluminum alloy piston as claimed in claim 1, wherein the nitrogen gas ventilation amount has a gradient ranging from 60 to 160 sccm, and each gradient is maintained for 20 to 40 min.
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