A low stress anti-coking alternating laminated film for engine intake and exhaust valves and method of making

Abstract

The application discloses a low-stress anti-coking alternate laminated film for engine intake and exhaust valves and a preparation method thereof. The film comprises, from bottom to top, a CrN film, a CrAlN film, a TiO2 film, a CrN film, a CrAlN film and a TiO2 film arranged on a substrate in sequence. The structure effectively balances the tensile stress and compressive stress inside the film through multiple alternate deposition of CrN, CrAlN and TiO2 layers, significantly reduces stress concentration and thermal residual stress during use. The CrN layer serves as a bottom layer and a transition layer, enhancing the adhesion of the film to the substrate and the interlayer. The CrAlN layer provides high hardness and high-temperature resistance. The TiO2 layer endows the film with excellent anti-coking performance. Through reasonable structural design and stress distribution control, the alternate laminated film exhibits excellent anti-coking and anti-oxidation performance in a high-temperature and oxygen-containing environment, significantly prolonging the service life of the intake and exhaust valves.

Description

Technical Field

[0001] The present invention relates to the field of surface engineering technology, and in particular to a low-stress anti-coking alternately laminated film for engine intake and exhaust valves and a preparation method thereof. Background Art

[0002] As a type of internal combustion engine, engines are widely used in industries such as industry, transportation, and power generation. During engine operation, the intake and exhaust valves are key components that control the flow of gas into and out of the combustion chamber. They operate in a high-temperature, high-pressure, and corrosive gas environment, subjecting them to extreme thermal and mechanical loads. Especially during the exhaust process, the exhaust valves are directly exposed to high-temperature exhaust gases, reaching temperatures of 600-800°C, while the intake valves are relatively cooler, at approximately 300-400°C. This high-temperature environment makes it very easy for severe coking and deposition to form on the material surface. Long-term carbon deposition not only increases airflow resistance and reduces engine performance, but can also lead to excessive valve temperatures, accelerating oxidation and mechanical fatigue, seriously affecting the engine's operating efficiency and service life.

[0003] In recent years, due to the high temperature, high oxidation and complex dynamic thermomechanical environment of engine intake and exhaust valves, higher requirements have been placed on the anti-oxidation and anti-coking properties of surface coatings. Studies have shown that single-layer coatings often exhibit problems of decreased adhesion and coating peeling due to the combined effects of thermal stress and high-temperature oxidation. Patent CN114959574A points out that CrAlN coatings are prone to decomposition under high temperature conditions, generating wurtzite AlN and cubic Cr structures, accompanied by the loss of nitrogen. This microstructural change directly weakens the hardness and wear resistance of the coating, significantly limiting its long-term application in engine intake and exhaust valves. In order to improve the shortcomings of single-layer coatings, double-layer coating technology has been proposed. Patent CN117344274A describes a TiN transition layer and an AlTiN functional layer alternately stacked coating prepared by an arc ion plating process, which improves the adhesion of the coating by reducing the interface stress. However, under the extreme dynamic operating conditions of the engine intake and exhaust valves, the double-layer coating still has the problem of interface stress mismatch, which may lead to delamination or cracking. Furthermore, patent CN109468614A proposes an Al2O3 / TiO2 nano-alternating layered coating based on atomic layer deposition technology. The bottom layer of Al2O3 is used to block carbon penetration, while the surface layer of TiO2 reduces the catalytic effect of carbon deposition. Although this double-layer coating shows improvements in oxidation resistance and coking resistance, its interfacial stability under complex dynamic thermomechanical environments still needs further optimization.

[0004] The coating prepared by the above method has not yet been able to completely solve the problem of coking of the engine intake and exhaust valves under high-temperature working conditions. Summary of the Invention

[0005] To overcome the problem of coking easily occurring on engine intake and exhaust valves in existing high-temperature operating environments, the present invention aims to provide a low-stress, anti-coking alternating laminated film for engine intake and exhaust valves and a preparation method. This method prepares a multi-layer alternating structure of chromium nitride (CrN), chromium aluminum nitride (CrAlN), and titanium dioxide (TiO2). Through a multi-level stress balance design, the compressive stress characteristics of the CrN and CrAlN layers and the tensile stress characteristics of the TiO2 layer are fully utilized to achieve internal stress balance in the film in a high-temperature environment. This low-stress design can effectively reduce the risk of film peeling under high-temperature oxidation and mechanical loads, while significantly improving the film's anti-coking performance, thereby providing an efficient solution for the long-term protection of engine intake and exhaust valves.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A low-stress anti-coking alternately laminated film for engine intake and exhaust valves comprises a CrN film, a CrAlN film, a TiO2 film, a CrN film, a CrAlN film and a TiO2 film which are sequentially arranged on a substrate from bottom to top.

[0008] Furthermore, the thickness of the CrN films is 0.2 to 0.5 μm;

[0009] The thickness of CrAlN films is 2 to 4 μm;

[0010] The thickness of TiO2 films is 50 to 150 nm.

[0011] Furthermore, the total thickness of the low-stress anti-coking alternately laminated film is 5 to 9 μm.

[0012] A method for preparing a low-stress, anti-coking alternately laminated film for an engine intake and exhaust valve comprises the following steps:

[0013] A CrN film is first deposited on the substrate surface, a CrAlN film is deposited on the CrN film, and a TiO2 film is prepared on the CrAlN film;

[0014] A CrN film is deposited on a TiO2 film, a CrAlN film is deposited on a CrN film, and a TiO2 film is prepared on a CrAlN film to obtain a low-stress anti-coking alternately stacked film for an engine intake and exhaust valve.

[0015] Furthermore, the thickness of the CrN films is 0.2 to 0.5 μm;

[0016] The thickness of CrAlN films is 2 to 4 μm;

[0017] The thickness of TiO2 films is 50 to 150 nm;

[0018] The total thickness of the low-stress anti-coking alternate laminated film is 5-9 microns.

[0019] Further, the preparation process of the CrN film is as follows: a Cr target is used, the multi-arc ion plating process parameters are as follows: the arc current of the CrAl target is 70-100 A, the deposition bias voltage is 100-300 V, the cavity pressure is 1-5 Pa, the nitrogen flow rate is 1300-1500 sccm, and the deposition temperature is about 350 DEG C.

[0020] Further, the CrAl target is an alloy target with the atomic percentage of Cr being 60-75%.

[0021] Further, the preparation process of the CrAlN film is as follows: a CrAl target is used, the multi-arc ion plating process parameters are as follows: the arc current is 70-100 A, the bias voltage is 50-80 V, the cavity pressure is 1-5 Pa, the nitrogen flow rate is 1300-1500 sccm, and the deposition temperature is about 350 DEG C.

[0022] Further, the preparation process of the TiO2 film is as follows: titanium isopropoxide is used as the titanium source precursor, hydrogen peroxide is used as the oxygen source, nitrogen is used as the purging gas in a single cycle of the atomic layer deposition process, and the time of the titanium source precursor injection, nitrogen purging, oxygen source injection and nitrogen purging is 1-2 s, 25-35 s, 0.1-0.3 s and 20-35 s, respectively; the total cycle number of the atomic layer deposition process is 2000.

[0023] Further, the temperature of the titanium source precursor is 70-90 DEG C, the plating film area temperature is 200-250 DEG C, the base vacuum is lower than 50mtorr, and the nitrogen purging working pressure is 100-200mtorr.

[0024] Compared with the prior art, the present application has the following beneficial effects:

[0025] The low-stress, anti-coking alternating laminated film of the present invention is designed for engine intake and exhaust valves. By rationally designing the alternating laminated structure of the film, the CrN, CrAlN and TiO2 layers are alternately arranged, which effectively regulates the distribution of stress within the film and significantly reduces the internal stress level of the film. In this alternating laminated film structure, the CrAlN layer usually generates compressive stress during the deposition process due to its high hardness and strong high temperature resistance. This compressive stress helps to improve the hardness and wear resistance of the film, reduce thermal fatigue and wear in high temperature environments, and thus enhance the stability and durability of the film. In contrast, the TiO2 layer usually generates tensile stress during the deposition process due to its relatively brittle nature. This tensile stress helps to improve the adhesion of the film to a certain extent, especially to improve the bonding strength between the TiO2 layer and the CrAlN layer, while enhancing the anti-coking performance of the film. By arranging the CrN layer as a transition layer between the substrate and the CrAlN layer, and between the first layer of TiO2 and the second layer of CrAlN, the stress distribution of the film is further optimized. The CrN layer can effectively alleviate the stress concentration caused by the difference in thermal expansion coefficient between the substrate and the hard CrAlN layer, and also regulate the tensile stress of the TiO2 layer, thereby achieving a balanced distribution of stress. This reasonable stress ratio not only avoids brittle cracking or peeling of the film under high temperature conditions, but also improves the overall fatigue resistance of the film and extends its service life. In a high-temperature, oxygen-containing working environment, the high hardness and high-temperature resistance of the CrAlN layer effectively protect the intake and exhaust valves from wear and oxidation corrosion during high-temperature combustion. The TiO2 layer exerts its excellent anti-coking function, significantly reduces carbon accumulation, keeps the valve surface clean, thereby ensuring smooth airflow and improving engine combustion efficiency and power output. The low-stress design of the alternating laminated film optimizes the bonding between the film and the substrate, reduces the risk of peeling and wear, and reduces the maintenance and replacement frequency of the film. The low-stress anti-coking alternating laminated film of the present invention not only improves the anti-coking ability of the intake and exhaust valves under high temperature conditions, but also significantly extends the service life of the film through reasonable stress design, optimizes the overall performance and emission control of the engine, and helps diesel engines meet increasingly stringent environmental emission standards. The film has good compatibility with engine materials and does not affect the mechanical properties and structural integrity of the intake and exhaust valves, ensuring stable operation of the engine under high temperature and high pressure. It has broad application prospects and significant economic benefits.

[0026] The method of the present invention combines multi-arc ion plating and atomic layer deposition (ALD) technology. First, a CrN transition layer and a CrAlN hard layer are sequentially deposited on the surfaces of the intake and exhaust valves using the multi-arc ion plating process. The CrN layer enhances adhesion between the film and the substrate, further optimizing the film's stress distribution, while the CrAlN layer significantly improves the film's hardness and wear resistance. ALD technology is then used to uniformly deposit a TiO2 nanofilm on the surface of the CrAlN layer. The TiO2 layer effectively inhibits the accumulation of coking materials and exhibits excellent oxidation resistance in high-temperature environments.

[0027] Furthermore, the thickness of the TiO2 layer is between 50 and 150 nm to ensure high temperature anti-coking effect and overall stability of the film.

[0028] Furthermore, in the present invention, the deposition temperature of the CrN and CrAlN layers is controlled at 350° C. to ensure the density and stability of the film. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Schematic diagram of the structure of the engine intake and exhaust valve test piece, where (a) is a schematic diagram of the intake valve; (b) is a schematic diagram of the exhaust valve;

[0030] Figure 2 Schematic diagram of the hierarchical structure of low-stress alternating stacked films;

[0031] Figure 3 This is a comparison of the mass changes of the uncoated and alternately laminated thin film test pieces before and after the anti-coking experiment;

[0032] Figure 4 Comparison chart of film stress changes. DETAILED DESCRIPTION

[0033] To facilitate understanding of the present invention, the present invention will be described more fully below with reference to the accompanying drawings. The accompanying drawings illustrate preferred embodiments of the present invention. However, the present invention may be implemented in a variety of different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and comprehensive understanding of the disclosure of the present invention.

[0034] The present invention's method for preparing a low-stress, anti-coking alternating laminated film for engine intake and exhaust valves combines multi-arc ion plating and atomic layer deposition (ALD) processes. Multi-arc ion plating is first used to form an intermediate layer on a substrate surface. The intermediate layer comprises a CrN film and a CrAlN film. ALD is then used to form a high-quality TiO2 film with anti-coking properties on the surface of the CrAlN film. These steps are then repeated to alternately deposit CrN, CrAlN, and TiO2 films, thereby forming an alternating laminated film with low-stress, anti-coking properties on the substrate.

[0035] Preferably, the method for preparing the alternating stacked thin film specifically comprises the following steps:

[0036] 1) The substrate is sequentially ground, polished, cleaned, and dried to clean the substrate surface to ensure the initial adhesion of the film; then, a CrN film is first deposited on the clean substrate surface with a thickness of 0.2 to 0.5 μm, and then a CrAlN film is deposited thereon to obtain a substrate coated with CrAlN;

[0037] 2) The CrAlN-plated substrate is cleaned and then dried.

[0038] 3) A TiO2 film is deposited on the CrAlN-coated substrate by atomic layer deposition to form a CrAlN / TiO2 alternating layered film. Steps 2) through 3) are then repeated to alternately deposit CrN, CrAlN, and TiO2 films, thereby forming a low-stress, anti-coking alternating layered film on the substrate for engine intake and exhaust valves.

[0039] Preferably, in step 1), the ground and polished substrate is ultrasonically cleaned with anhydrous ethanol for 10 minutes and then blown dry with nitrogen.

[0040] Preferably, in step 1), the multi-arc ion plating process parameters for preparing a CrN film with a thickness of 0.1 to 0.5 μm using a pure Cr target are: arc current of 70 to 100 A, deposition bias of 100 to 300 V; chamber pressure of 1 to 5 Pa, nitrogen flow rate of 1300 to 1500 sccm, and deposition temperature of approximately 350°C.

[0041] Preferably, in the step 1), the multi-arc ion plating process parameters for preparing a CrAlN film with a thickness of 3 to 4 μm using a CrAl target are: arc current of 70 to 100 A, bias voltage of 50 to 80 V, chamber pressure of 1 to 5 Pa, nitrogen flow rate of 1300 to 1500 sccm, and deposition temperature of approximately 350°C.

[0042] Preferably, the CrAl target is an alloy target with an atomic percentage of Cr of 60% to 75%.

[0043] Preferably, in the step 3), titanium isopropoxide is used as the titanium source precursor and hydrogen peroxide (aqueous H2O2 solution with a mass fraction of 24% to 35%) is used as the oxygen source to prepare a TiO2 film with a thickness of 50 to 150 nm; nitrogen is used as the purge gas in a single cycle of the atomic layer deposition process, and the times for titanium source precursor injection, nitrogen purge, oxygen source injection, and nitrogen purge are 1 to 2 s, 25 to 35 s, 0.1 to 0.3 s, and 20 to 35 s, respectively; the total number of cycles of the atomic layer deposition process is 2000 times.

[0044] Preferably, in step 3), the temperature of the titanium source precursor is 70-90° C., the temperature of the coating area is 200-250° C., the background vacuum is lower than 50 mtorr, and the nitrogen purge working pressure is 100-200 mtorr.

[0045] In the present invention, before each deposition of the TiO2 layer, the surface of the underlying CrAlN layer is cleaned and dried to improve the adhesion of the TiO2 layer.

[0046] In the present invention, the thickness of the TiO2 layer is between 50 and 150 nm to ensure the high-temperature anti-coking effect and the overall stability of the film.

[0047] In the present invention, the deposition temperature of the CrN and CrAlN layers is controlled at 350° C. to ensure the density and stability of the films.

[0048] The film of the present invention is formed by alternating layers of CrN layer, CrAlN layer and TiO2 layer on a substrate. The above-mentioned alternatingly stacked film has excellent high-temperature anti-stripping and anti-coking properties, and can be used on the intake and exhaust valves of the engine to passivate the surface of the exhaust valve and protect against high-temperature coking. The interface bonding strength of the film is high, which can effectively reduce the stress concentration of the film in a high-temperature working environment, improve the stability and anti-coking performance, and thus extend the service life of the film.

[0049] The alternating laminated film in the present invention improves structural stability and anti-stripping performance through a balanced design of compressive stress and tensile stress under high temperature environment, thereby effectively inhibiting coking accumulation and significantly improving the durability and operating efficiency of the engine.

[0050] The method of the present invention combines multi-arc ion plating and atomic layer deposition (ALD) technology. First, a CrN transition layer and a CrAlN hard layer are sequentially deposited on the surfaces of the intake and exhaust valves using the multi-arc ion plating process. The CrN layer enhances adhesion between the film and the substrate, further optimizing the film's stress distribution, while the CrAlN layer significantly improves the film's hardness and wear resistance. ALD technology is then used to uniformly deposit a TiO2 nanofilm on the surface of the CrAlN layer. The TiO2 layer effectively inhibits the accumulation of coking materials and exhibits excellent oxidation resistance in high-temperature environments.

[0051] A key innovation of this invention lies in the low-stress design of the film structure. By alternately depositing CrN, CrAlN, and TiO2 layers and introducing the CrN layer as a transition layer, the film's internal stress is effectively regulated. The CrN layer, acting as a transition layer, mitigates stress concentration caused by differences in physical properties between the different layers, preventing the film from peeling or cracking due to excessive internal stress. Furthermore, the CrAlN layer further enhances the film's resistance to high-temperature peeling and provides a stable substrate for the TiO2 layer, ensuring good adhesion even in high-temperature, oxygen-rich environments.

[0052] The finally formed alternating laminated film structure is "substrate-CrN-CrAlN-TiO2-CrN-CrAlN-TiO2", which not only has good anti-coking performance, but also significantly improves the durability and reliability of the intake and exhaust valves in high temperature environment. The low stress design ensures that the film works stably under high temperature operating conditions of the engine, avoids film peeling or damage due to excessive internal stress, thereby prolonging the service life of the engine metal structure and improving the safety and reliability of the engine metal structure in severe working environment.

[0053] Example 1

[0054] (I) Alternating laminated film preparation experiment

[0055] Referring to Figure 1 Figs. 1 and 2, the experimental pieces are the intake and exhaust valves, which are flat-topped valve head type intake and exhaust valves. Among them, the outer diameter B1 of the intake valve is 23 mm, the total height A is 61 mm, and the thickness C is 5 mm. The outer diameter B2 of the exhaust valve is 20 mm, the total height A is 61 mm, and the thickness C is 5 mm.

[0056] Referring to Figure 2 Fig. 3, it is a schematic diagram of the "CrN-CrAlN-TiO2-CrN-CrAlN-TiO2" low-stress anti-coking alternating laminated film structure prepared for the experiment. The film includes CrN film, CrAlN film, TiO2 film, CrN film, CrAlN film and TiO2 film arranged on the substrate from bottom to top.

[0057] The low-stress anti-coking alternating laminated film is prepared on the substrate of the intake and exhaust valves, and the specific process is as follows:

[0058] Step 1: The substrate is polished with 400, 800, 1200 and 2000 grit sandpaper in turn, and then polished with a polishing machine. Then the polished and polished substrate is ultrasonically cleaned with anhydrous ethanol for 15 min, then dried with high-purity nitrogen (purity 99.99%) and the inner wall of the vacuum cavity is cleaned with anhydrous ethanol.

[0059] Step 2: After sandblasting the surface of the substrate, it is placed in a vacuum coating equipment, and vacuumed to less than 5.0x10 - 3 Pa, and the substrate is heated to 400℃ and kept for 40 min. Then open the inlet valve, fill in 400sccm of argon, set the target bias voltage to 800V for 8min for glow cleaning to remove the surface material of the target. Change the argon flow to 70sccm, adjust the substrate bias voltage to 500V and 300V in turn for Ar + ion bombardment cleaning (30min in total), so that the surface of the substrate is clean.

[0060] The CrN transition layer was then deposited using 99.99% pure nitrogen gas, an arc current of 100A for the Cr target, a bias voltage of 100V, a nitrogen flow rate of 1450sccm, an intra-chamber pressure of 3Pa, a process time of approximately 18 minutes, and a deposition temperature of 350°C. The resulting metallic CrN transition layer had a thickness of 0.4μm.

[0061] Next, a CrAlN film was deposited using 99.99% pure nitrogen gas, a CrAl target (70% Cr:30% Al atomic percentage), an arc current of 90A, a bias voltage of 60V, a nitrogen flow rate of 1450sccm, an intracavity pressure of 4Pa, a process time of approximately 120 minutes, a deposition temperature of 350°C, and a 3.5μm thickness. This resulted in a CrAlN-coated substrate.

[0062] Step 3: Use anhydrous ethanol to ultrasonically clean the CrAlN-plated substrate for 15 minutes, and then blow dry with nitrogen.

[0063] Step 4: Prepare a TiO2 thin film on a CrAlN-coated substrate using an atomic layer deposition device.

[0064] The CrAlN-coated substrate was transferred to a coating chamber and evacuated to a chamber pressure of 50 mtorr. The temperature was then programmed to 200°C and held for 30 minutes. Titanium isopropoxide was then used as the titanium source precursor (70°C), hydrogen peroxide (a 30% H2O2 aqueous solution) was used as the oxygen source, and high-purity nitrogen (99.999%) was used as the purge gas. The high-purity nitrogen flow rate was adjusted by a needle valve, and the operating pressure during the high-purity nitrogen purge was 200 mtorr. In a single cycle of the atomic layer deposition process, the titanium source precursor, high-purity nitrogen, hydrogen peroxide, and high-purity nitrogen were introduced for 1.5 seconds, 30 seconds, 0.2 seconds, and 20 seconds, respectively, for a total of 2000 cycles. This resulted in a 150nm thick TiO2 layer deposited on the CrAlN-coated substrate.

[0065] Step 5: Repeat steps 1 to 4 to obtain a low-stress, anti-coking alternating stacked film with a structure of "CrN-CrAlN-TiO2-CrN-CrAlN-TiO2" on the substrate surface.

[0066] (2) Film anti-coking protection test

[0067] In order to test the anti-coking performance of the film, the test piece with the alternating laminated film was placed in a circular tube with a diameter of 30 mm and faced the flow direction of the hydrocarbon fuel. The experiment adjusted the flow rate of the fuel through a flow control device. After the fuel was output by the delivery device, it was first heated through the preheating section and then entered the circular tube of the experimental section. The test piece was then subjected to an anti-coking protection test for 1 hour at a temperature of 800K. In the experimental section pipeline, the flow channel of the hydrocarbon fuel simulates the flow channel shape of the engine intake and exhaust valves. This setting is intended to simulate the fuel flow and heat treatment process of the engine intake and exhaust valves in actual work, so as to evaluate the anti-coking performance of the alternating laminated film under high temperature and high pressure environment. Before and after the experiment, the mass changes of the test pieces without coating and with alternating laminated films were measured.

[0068] See also Figure 3 , comparing the weight changes of the test pieces before and after the anti-coking experiment, the results showed that under the same test conditions, the weight increase of the test pieces with alternating laminated films was 0.1 mg, while the weight increase of the test pieces without coating protection was 1.0 mg, reflecting the anti-coking effect of the alternating laminated films.

[0069] (3) Film anti-peeling test

[0070] The test piece coated with the alternating laminated film was heated to 850°C in a tube furnace at a heating rate of 8°C / min. After holding for 1.5 hours, it was cooled to room temperature in the furnace to complete the annealing. The sample was annealed in air (850°C, 1.5 hours). The observation results showed that the alternating laminated film on the surface of the sample remained intact, without any damage or peeling. This result shows that the alternating laminated film has a good protective effect on the substrate and effectively improves the substrate's anti-coking performance.

[0071] (IV) Stress test experiment before and after coating

[0072] The internal stress of substrates under three different treatment conditions was measured using the FST2000 thin film stress tester (curvature method). The experimental samples included: uncoated substrates, substrates coated with "CrN-CrAlN-TiO2" alternating stacked films, and substrates coated with "CrN-CrAlN-TiO2-CrN-CrAlN-TiO2" alternating stacked films. First, the film thickness of each sample was measured using an ellipsometer to ensure that the thickness of each film met the predetermined requirements. Then, stress tests were performed on uncoated substrates, substrates coated with single-layer alternating stacked films, and substrates coated with multi-layer alternating stacked films, and the baseline data was recorded and compared.

[0073] See also Figure 4The test results show that the internal stress of the uncoated substrate is higher, while the internal stress of the substrate coated with the "CrN-CrAlN-TiO2" alternating stacked film is reduced, indicating that the single-layer alternating stacked film can effectively relieve internal stress. Furthermore, the substrate coated with the "CrN-CrAlN-TiO2-CrN-CrAlN-TiO2" multi-layer alternating stacked film showed the most significant reduction in internal stress, indicating that the structure more effectively disperses internal stress through the alternating stacking design. All samples also underwent high-temperature treatment at 850°C for 1.5h and then cooled in the furnace. The stress test results after high-temperature treatment showed that the internal stress of the film changed little, indicating that the low-stress design has good stability in high-temperature environments.

[0074] Example 2

[0075] Step 1: Grind the substrate with 400, 800, 1200, and 2000 sandpaper in turn, then polish it with a polishing machine, and then use anhydrous ethanol to ultrasonically clean the ground and polished substrate for 15 minutes, then blow it dry with high-purity nitrogen (purity is 99.99%), and wipe the inner wall of the vacuum chamber with anhydrous ethanol.

[0076] Step 2: After sandblasting the substrate surface, place it in the vacuum coating equipment and evacuate the vacuum to less than 5.0×10 - 3 Pa, heat the substrate to 400℃ and keep it warm for 40min. Then open the gas inlet valve, fill it with 400sccm of argon, set the target bias voltage to 800V and perform glow cleaning for 8min to remove the surface material of the target. Change the argon flow rate to 70sccm, adjust the substrate bias voltage to 500V and 300V in turn for Ar + Bombardment cleaning (30 min in total) cleans the substrate surface.

[0077] Then, a CrN transition layer was prepared: nitrogen gas with a purity of 99.99% was introduced, the arc current of the Cr target was 70A, the deposition bias was 300V, the nitrogen flow rate was 1300sccm, the pressure in the chamber was 2Pa, the process time was about 15min, the deposition temperature was 350°C, and the deposition thickness of the obtained metal CrN transition layer was 0.2μm.

[0078] Next, a CrAlN film was deposited using 99.99% pure nitrogen gas, a CrAl target (atomic percentage 60% Cr:40% Al), an arc current of 70A, a bias voltage of 60V, a nitrogen flow rate of 1300sccm, an intracavity pressure of 1Pa, a process time of approximately 120 minutes, a deposition temperature of 350°C, and a 4μm thickness. This resulted in a CrAlN-coated substrate.

[0079] Step 3: Use anhydrous ethanol to ultrasonically clean the CrAlN-plated substrate for 15 minutes, and then blow dry with nitrogen.

[0080] Step 4: Prepare a TiO2 thin film on a CrAlN-coated substrate using an atomic layer deposition device.

[0081] The CrAlN-coated substrate was transferred to a coating chamber and evacuated to a chamber pressure of 50 mtorr. The temperature was then programmed to 200°C and held for 30 minutes. Titanium isopropoxide was then used as the titanium source precursor (70°C), hydrogen peroxide (a 24% H2O2 aqueous solution) was used as the oxygen source, and high-purity nitrogen (99.999%) was used as the purge gas. The high-purity nitrogen flow rate was adjusted via a needle valve, and the operating pressure during the high-purity nitrogen purge was 150 mtorr. In a single cycle of the atomic layer deposition process, the titanium source precursor, high-purity nitrogen, hydrogen peroxide, and high-purity nitrogen were introduced for 1.5 seconds, 15 seconds, 0.3 seconds, and 20 seconds, respectively, for a total of 2000 cycles. This resulted in a 100nm thick TiO2 layer being deposited on the CrAlN-coated substrate.

[0082] Step 5: Repeat steps 1 to 4 to obtain a low-stress, anti-coking alternating stacked film with a structure of "CrN-CrAlN-TiO2-CrN-CrAlN-TiO2" on the surface of the substrate.

[0083] The test results show that the internal stress of the alternating stacked film prepared in Example 3 is 83 MPa. The film anti-stripping test results show that the film on the sample surface does not show any damage or peeling.

[0084] Example 3

[0085] Step 1: Grind the substrate with 400, 800, 1200, and 2000 sandpaper in turn, then polish it with a polishing machine, and then use anhydrous ethanol to ultrasonically clean the ground and polished substrate for 15 minutes, then blow it dry with high-purity nitrogen (purity is 99.99%), and wipe the inner wall of the vacuum chamber with anhydrous ethanol.

[0086] Step 2: After sandblasting the substrate surface, place it in the vacuum coating equipment and evacuate the vacuum to less than 5.0×10 - 3 Pa, heat the substrate to 400℃ and keep it warm for 40min. Then open the gas inlet valve, fill it with 400sccm of argon, set the target bias voltage to 800V and perform glow cleaning for 8min to remove the surface material of the target. Change the argon flow rate to 70sccm, adjust the substrate bias voltage to 500V and 300V in turn for Ar + Bombardment cleaning (30 min in total) cleans the substrate surface.

[0087] Then, a CrN transition layer was prepared: nitrogen gas with a purity of 99.99% was introduced, the arc current of the Cr target was 100A, the bias voltage was 150V, the nitrogen flow rate was 1500sccm, the pressure in the chamber was 5Pa, the process time was about 20min, the deposition temperature was 350°C, and the deposition thickness of the obtained metal CrN transition layer was 0.5μm.

[0088] Next, a CrAlN film was deposited using 99.99% pure nitrogen gas, an arc current of 80A for a CrAl target (75% Cr:25% Al atomic percentage), a bias voltage of 50V, a nitrogen flow rate of 1400sccm, an intracavity pressure of 5Pa, a process time of approximately 100 minutes, a deposition temperature of 350°C, and a 3μm thickness. This resulted in a CrAlN-coated substrate.

[0089] Step 3: Use anhydrous ethanol to ultrasonically clean the CrAlN-plated substrate for 15 minutes, and then blow dry with nitrogen.

[0090] Step 4: Prepare a TiO2 thin film on a CrAlN-coated substrate using an atomic layer deposition device.

[0091] The CrAlN-coated substrate was transferred to a coating chamber and evacuated to a chamber pressure of 50 mtorr. The temperature was then programmed to 200°C and held for 30 minutes. Titanium isopropoxide was then used as the titanium source precursor (70°C), hydrogen peroxide (a 35% H2O2 aqueous solution) was used as the oxygen source, and high-purity nitrogen (99.999%) was used as the purge gas. The high-purity nitrogen flow rate was adjusted by a needle valve, and the operating pressure during the high-purity nitrogen purge was 100 mtorr. In a single cycle of the atomic layer deposition process, the titanium source precursor, high-purity nitrogen, hydrogen peroxide, and high-purity nitrogen were introduced for 1.5 seconds, 15 seconds, 0.2 seconds, and 30 seconds, respectively, for a total of 2000 cycles. This resulted in a 50nm thick TiO2 layer being deposited on the CrAlN-coated substrate.

[0092] Step 5: Repeat steps 1 to 4 to obtain a low-stress, anti-coking alternating stacked film with a structure of "CrN-CrAlN-TiO2-CrN-CrAlN-TiO2" on the substrate surface.

[0093] The test showed that the internal stress of the alternating stacked film prepared in Example 3 was 90 MPa. The film anti-stripping test results showed that the film on the sample surface did not show any damage or peeling.

[0094] Example 4

[0095] Step 1: Grind the substrate with 400, 800, 1200, and 2000 sandpaper in turn, then polish it with a polishing machine, and then use anhydrous ethanol to ultrasonically clean the ground and polished substrate for 15 minutes, then blow it dry with high-purity nitrogen (purity is 99.99%), and wipe the inner wall of the vacuum chamber with anhydrous ethanol.

[0096] Step 2: After sandblasting the substrate surface, place it in the vacuum coating equipment and evacuate the vacuum to less than 5.0×10 - 3 Pa, heat the substrate to 400℃ and keep it warm for 40min. Then open the gas inlet valve, fill it with 400sccm of argon, set the target bias voltage to 800V and perform glow cleaning for 8min to remove the surface material of the target. Change the argon flow rate to 70sccm, adjust the substrate bias voltage to 500V and 300V in turn for Ar + Bombardment cleaning (30 min in total) cleans the substrate surface.

[0097] Then, a CrN transition layer was prepared: nitrogen gas with a purity of 99.99% was introduced, the arc current of the Cr target was 80A, the bias voltage was 300V, the nitrogen flow rate was 1400sccm, the pressure in the chamber was 5Pa, the process time was about 10min, the deposition temperature was 350°C, and the deposition thickness of the obtained metal CrN transition layer was 0.2μm.

[0098] Next, a CrAlN film was deposited using 99.99% pure nitrogen gas, a CrAl target (atomic percentage 65% Cr:35% Al), an arc current of 70A, a bias voltage of 70V, a nitrogen flow rate of 1500sccm, an intracavity pressure of 3Pa, a process time of approximately 90 minutes, a deposition temperature of 350°C, and a CrAlN film thickness of 2.5μm. This resulted in a CrAlN-coated substrate.

[0099] Step 3: Use anhydrous ethanol to ultrasonically clean the CrAlN-plated substrate for 15 minutes, and then blow dry with nitrogen.

[0100] Step 4: Prepare a TiO2 thin film on a CrAlN-coated substrate using an atomic layer deposition device.

[0101] The CrAlN-coated substrate was transferred into a coating chamber, and vacuumed to a chamber pressure of 50 mtorr, while programmed to warm up to 200℃ and keep for 30 min. Then, isopropyl titanate was used as the titanium source precursor (temperature of 70℃), hydrogen peroxide (27% H2O2 aqueous solution) was used as the oxygen source, and high-purity nitrogen (purity of 99.999%) was used as the purge gas. The flow of the high-purity nitrogen was adjusted by a needle valve. The working gas pressure was 200 mtorr when the high-purity nitrogen was purged. In a single cycle of the atomic layer deposition process, the titanium source precursor, the high-purity nitrogen, the hydrogen peroxide, and the high-purity nitrogen were sequentially introduced for 1.5 s, 15 s, 0.1 s, and 20 s, respectively. The total cycle number was 2000, so as to prepare a TiO2 layer with a thickness of 80 nm on the surface of the CrAlN-coated substrate.

[0102] Step five: steps one to four were repeated to obtain a low-stress anti-coking alternating layer stack with a structure of "CrN-CrAlN-TiO2-CrN-CrAlN-TiO2" on the surface of the substrate.

[0103] It was tested that the internal stress of the alternating layer stack prepared in Example 4 was 87 MPa. The film anti-peeling test results showed that the surface film of the sample did not appear to be damaged or peeled off.

[0104] Example 5

[0105] Step one: the substrate was polished using 400, 800, 1200, and 2000 grit sandpaper in sequence, and then polished using a polishing machine. Then, the substrate after polishing was ultrasonically cleaned with anhydrous ethanol for 15 min, and then dried with high-purity nitrogen (purity of 99.99%) and the inner wall of the vacuum chamber was cleaned with anhydrous ethanol.

[0106] Step two: after sandblasting the surface of the substrate, it was placed into a vacuum coating device, and vacuumed to less than 5.0 x 10 - 3 Pa, and the substrate was heated to 400℃ and kept for 40 min. Then, the gas inlet valve was opened, 400 sccm of argon was filled, and the target bias was set to 800 V for glow cleaning for 8 min to remove the surface substances of the target. The argon flow was changed to 70 sccm, and the substrate bias was adjusted to 500 V and 300 V in sequence for Ar + bombardment cleaning (30 min in total), so as to clean the surface of the substrate.

[0107] Then, a CrN transition layer was prepared: nitrogen with a purity of 99.99% was introduced, the arc current of the Cr target was 70 A, the deposition bias was 250 V, the nitrogen flow was 1350 sccm, the chamber gas pressure was 4 Pa, the process time was about 18 min, the deposition temperature was 350℃, and the deposition thickness of the obtained metal CrN transition layer was 0.3 μm.

[0108] Next, a CrAlN film was deposited using 99.99% pure nitrogen gas, a CrAl target (atomic percentage 60% Cr:40% Al) arc current of 100A, a bias voltage of 80V, a nitrogen flow rate of 1350sccm, an intracavity pressure of 2Pa, a process time of approximately 80 minutes, a deposition temperature of 350°C, and a CrAlN film thickness of 2μm. This resulted in a CrAlN-coated substrate.

[0109] Step 3: Use anhydrous ethanol to ultrasonically clean the CrAlN-plated substrate for 15 minutes, and then blow dry with nitrogen.

[0110] Step 4: Prepare a TiO2 thin film on a CrAlN-coated substrate using an atomic layer deposition device.

[0111] The CrAlN-coated substrate was transferred to a coating chamber and evacuated to a chamber pressure of 50 mtorr. The temperature was then programmed to 220°C and held for 30 minutes. Titanium isopropoxide was then used as a titanium source precursor (temperature 90°C), hydrogen peroxide (a 27% H2O2 aqueous solution) was used as an oxygen source, and high-purity nitrogen (99.999%) was used as a purge gas. The high-purity nitrogen flow rate was adjusted by a needle valve, and the operating pressure during the high-purity nitrogen purge was 100 mtorr. In a single cycle of the atomic layer deposition process, the titanium source precursor, high-purity nitrogen, hydrogen peroxide, and high-purity nitrogen were introduced for 1 second, 25 seconds, 0.3 seconds, and 35 seconds, respectively, for a total of 2000 cycles, resulting in a 50nm thick TiO2 layer deposited on the CrAlN-coated substrate.

[0112] Step 5: Repeat steps 1 to 4 to obtain a low-stress, anti-coking alternating stacked film with a structure of "CrN-CrAlN-TiO2-CrN-CrAlN-TiO2" on the surface of the substrate.

[0113] Example 6

[0114] Step 1: Grind the substrate with 400, 800, 1200, and 2000 sandpaper in turn, then polish it with a polishing machine, and then use anhydrous ethanol to ultrasonically clean the ground and polished substrate for 15 minutes, then blow it dry with high-purity nitrogen (purity is 99.99%), and wipe the inner wall of the vacuum chamber with anhydrous ethanol.

[0115] Step 2: After sandblasting the substrate surface, place it in the vacuum coating equipment and evacuate the vacuum to less than 5.0×10 - 3Pa, heat the substrate to 400℃ and keep it warm for 40min. Then open the gas inlet valve, fill it with 400sccm of argon, set the target bias voltage to 800V and perform glow cleaning for 8min to remove the surface material of the target. Change the argon flow rate to 70sccm, adjust the substrate bias voltage to 500V and 300V in turn for Ar + Bombardment cleaning (30 min in total) cleans the substrate surface.

[0116] The CrN transition layer was then deposited using 99.99% pure nitrogen, a 90A arc current for the Cr target, a 200V deposition bias, a nitrogen flow rate of 1500 sccm, an intra-chamber pressure of 1 Pa, a process time of approximately 20 minutes, and a deposition temperature of 350°C. The resulting metallic CrN transition layer had a thickness of 0.4 μm.

[0117] Next, a CrAlN film was deposited using 99.99% pure nitrogen gas, a CrAl target (70% Cr:30% Al atomic percentage), an arc current of 70A, a bias voltage of 50V, a nitrogen flow rate of 1500sccm, an intracavity pressure of 1Pa, a process time of approximately 90 minutes, a deposition temperature of 350°C, and a CrAlN film thickness of 2.5μm. This resulted in a CrAlN-coated substrate.

[0118] Step 3: Use anhydrous ethanol to ultrasonically clean the CrAlN-plated substrate for 15 minutes, and then blow dry with nitrogen.

[0119] Step 4: Prepare a TiO2 thin film on a CrAlN-coated substrate using an atomic layer deposition device.

[0120] The CrAlN-coated substrate was transferred to a coating chamber and evacuated to a chamber pressure of 50 mtorr. The temperature was then programmed to 250°C and held for 30 minutes. Titanium isopropoxide was then used as the titanium source precursor (at 80°C), hydrogen peroxide (a 27% H2O2 aqueous solution) was used as the oxygen source, and high-purity nitrogen (99.999%) was used as the purge gas. The high-purity nitrogen flow rate was adjusted by a needle valve, and the operating pressure during the high-purity nitrogen purge was 150 mtorr. In a single cycle of the atomic layer deposition process, the titanium source precursor, high-purity nitrogen, hydrogen peroxide, and high-purity nitrogen were introduced for 2 seconds, 35 seconds, 0.1 seconds, and 20 seconds, respectively, for a total of 2000 cycles. A 100nm thick layer of TiO2 was deposited on the CrAlN-coated substrate.

[0121] Step 5: Repeat steps 1 to 4 to obtain a low-stress, anti-coking alternating stacked film with a structure of "CrN-CrAlN-TiO2-CrN-CrAlN-TiO2" on the substrate surface.

[0122] Comparative Example 1

[0123] Step 1: Grind the substrate with 400, 800, 1200, and 2000 sandpaper in turn, then polish it with a polishing machine, and then use anhydrous ethanol to ultrasonically clean the ground and polished substrate for 15 minutes, then blow it dry with high-purity nitrogen (purity is 99.99%), and wipe the inner wall of the vacuum chamber with anhydrous ethanol.

[0124] Step 2: Use atomic layer deposition equipment to directly prepare TiO2 thin film on the substrate.

[0125] The substrate was transferred to the coating chamber and evacuated to a chamber pressure of 50 mtorr. The temperature was then programmed to 200°C and maintained for 30 minutes. Titanium isopropoxide was then used as the titanium source precursor (temperature 60°C), hydrogen peroxide (a 27% H2O2 aqueous solution by mass) was used as the oxygen source, and high-purity nitrogen (99.999% purity) was used as the purge gas. The flow rate of high-purity nitrogen was adjusted by a needle valve, and the operating pressure during the high-purity nitrogen purge was 200 mtorr. In a single cycle of the atomic layer deposition process, the introduction time of the titanium source precursor, high-purity nitrogen, hydrogen peroxide, and high-purity nitrogen was 1.5s, 30s, 0.1s, and 30s, respectively, with a total number of cycles of 2000 times, thereby preparing a layer of TiO2 with a thickness of 54 nm on the substrate surface.

[0126] The internal stress of the single-layer TiO2 film prepared in Comparative Example 1 was 282 MPa. The results of the film anti-stripping test showed that the single-layer TiO2 film on the sample surface was damaged and peeled to a certain extent, and could no longer perform its anti-coking protection function.

[0127] Comparative Example 2

[0128] Step 1: Grind the substrate with 400, 800, 1200, and 2000 sandpaper in turn, then polish it with a polishing machine, and then use anhydrous ethanol to ultrasonically clean the ground and polished substrate for 15 minutes, then blow it dry with high-purity nitrogen (purity is 99.99%), and wipe the inner wall of the vacuum chamber with anhydrous ethanol.

[0129] Step 2: After sandblasting the substrate surface, place it in a vacuum coating machine and evacuate to less than 5.0×10-3Pa. Heat the substrate to 400°C and maintain this temperature for 40 minutes. Then, open the gas inlet valve, introduce 400 sccm of argon, and set the target bias voltage to 800V for glow cleaning for 8 minutes to remove the target surface material. Change the argon flow rate to 70 sccm, and adjust the substrate bias voltage to 500V and then 300V for Ar+ bombardment cleaning (a total of 30 minutes) to clean the substrate surface.

[0130] Then, a CrN transition layer was prepared: nitrogen gas with a purity of 99.99% was introduced, the arc current of the Cr target was 90A, the bias voltage was 200V, the nitrogen flow rate was 1400sccm, the pressure in the chamber was 5Pa, the process time was about 25min, and the deposition thickness of the obtained metal CrN transition layer was 0.5μm.

[0131] Next, a CrAlN film was deposited using 99.99% pure nitrogen gas, a CrAl target (70% Cr:30% Al atomic percentage) arc current of 60A, a bias voltage of 40V, a nitrogen flow rate of 1500sccm, and a chamber pressure of 3Pa. The process took approximately 100 minutes, resulting in a 2.5μm thick CrAlN film. This resulted in a CrAlN-coated substrate.

[0132] Step 3: Use anhydrous ethanol to ultrasonically clean the CrAlN-plated substrate for 15 minutes, and then blow dry with nitrogen.

[0133] Step 4: Prepare a TiO2 thin film on a CrAlN-coated substrate using an atomic layer deposition device.

[0134] The CrAlN-coated substrate was transferred to a coating chamber and evacuated to a chamber pressure of 50 mtorr. The temperature was then programmed to 200°C and held for 30 minutes. Titanium isopropoxide (60°C) was used as the titanium source precursor, hydrogen peroxide (a 27% H2O2 aqueous solution) was used as the oxygen source, and high-purity nitrogen (99.999%) was used as the purge gas. The high-purity nitrogen flow rate was adjusted via a needle valve, and the operating pressure during the high-purity nitrogen purge was 200 mtorr. In a single cycle of the atomic layer deposition process, the titanium source precursor, high-purity nitrogen, hydrogen peroxide, and high-purity nitrogen were introduced for 1.5 seconds, 30 seconds, 0.1 seconds, and 30 seconds, respectively, for a total of 2000 cycles. A 60nm thick TiO2 layer was deposited on the CrAlN-coated substrate. A thin film with a "CrN-CrAlN-TiO2" structure was obtained on the substrate surface.

[0135] The test showed that the internal stress of the "CrN-CrAlN-TiO2" film prepared in Comparative Example 2 was 175 MPa. The film anti-stripping test results showed that the film on the sample surface was slightly damaged and peeled.

[0136] In Comparative Example 1, the single-layer TiO2 film failed to effectively achieve the anti-coking protection function. In Comparative Example 2, although a "CrN-CrAlN" composite layer was added to the film and the film stress was effectively reduced, breakage and peeling still occurred. In contrast, the low-stress alternating laminated films prepared in Examples 1 to 4 exhibited anti-coking protection performance that was significantly better than that of the comparative experiment, successfully avoided breakage and peeling, and had better stability and durability. Therefore, the low-stress alternating laminated film of the present invention not only performs well in anti-coking protection function, but also has obvious advantages in improving the long-term durability and reliability of the film.

[0137] The present invention forms an alternating stack of thin films through multiple deposition processes. Specifically, a CrN transition layer, a CrAlN hard layer, and a TiO2 anti-coking functional layer are first deposited sequentially on the substrate surface to form a first layer of alternating stacked structures. The same "CrN-CrAlN-TiO2" layer is then deposited again on top of this structure, achieving a multi-layered, alternating arrangement of thin films. This dual deposition strategy effectively optimizes the internal stress distribution of the thin film. By compensating for interlayer stresses, it significantly reduces the overall internal stress of the film, thereby improving the film's adhesion, spalling resistance, and high-temperature stability, further enhancing the anti-coking performance of the intake and exhaust valves.

[0138] The above description is merely a description of the preferred embodiment of the present invention and is not to be construed as limiting the claims. The present invention is not limited to the above embodiment, and variations in the specific structure are permitted. Any variations made within the scope of the independent claims of the present invention are also within the scope of protection of the present invention.

[0139] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this invention pertains. The terms used herein in the specification of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

Claims

1. A low stress anti-coking alternately laminated film for engine intake and exhaust valves, characterized in that: The method comprises a CrN film, a CrAlN film, a TiO2 film, a CrN film, a CrAlN film and a TiO2 film which are sequentially arranged on a substrate from bottom to top; The CrN transition layer and CrAlN hard layer were prepared by multi-arc ion plating process; TiO2 thin films were prepared by atomic layer deposition; The thickness of the CrN films is 0.2~0.5 μm; The thickness of CrAlN films is 2~4 μm; The thickness of TiO2 films is 50~150 nm; The total thickness of the low-stress anti-coking alternately laminated film is 5-9 μm.

2. A method for preparing a low-stress anti-coking alternately laminated film for engine intake and exhaust valves according to claim 1, characterized in that: The following steps are involved: A CrN film is first deposited on the substrate surface, a CrAlN film is deposited on the CrN film, and a TiO2 film is prepared on the CrAlN film; A CrN film is deposited on a TiO2 film, a CrAlN film is deposited on a CrN film, and a TiO2 film is prepared on a CrAlN film to obtain a low-stress anti-coking alternately stacked film for an engine intake and exhaust valve.

3. The method for preparing a low-stress anti-coking alternately laminated film for engine intake and exhaust valves according to claim 2, characterized in that: The CrN film was prepared using a Cr target and the multi-arc ion plating process parameters were as follows: arc current of 70-100 A, deposition bias of 100-300 V, chamber pressure of 1-5 Pa, nitrogen flow rate of 1300-1500 sccm, and deposition temperature of 350 °C.

4. The method for preparing a low-stress anti-coking alternately laminated film for engine intake and exhaust valves according to claim 2, characterized in that: The preparation process of CrAlN film is as follows: using CrAl target, the multi-arc ion plating process parameters are: arc current of 70~100 A, bias voltage of 50~80 V, chamber pressure of 1~5 Pa, nitrogen flow rate of 1300~1500 sccm, and deposition temperature of 350 ℃.

5. The method for preparing a low-stress anti-coking alternately laminated film for engine intake and exhaust valves according to claim 4, characterized in that: The CrAl target uses an alloy target with an atomic percentage of Cr of 60% to 75%.

6. The method for preparing a low-stress anti-coking alternately laminated film for engine intake and exhaust valves according to claim 2, characterized in that: The preparation process of TiO2 thin film is as follows: titanium isopropoxide is used as the titanium source precursor and hydrogen peroxide is used as the oxygen source. Nitrogen is used as the purge gas in a single cycle of the atomic layer deposition process. The time for titanium source precursor injection, nitrogen purge, oxygen source injection, and nitrogen purge are 1~2 s, 25~35 s, 0.1~0.3 s, and 20~35 s, respectively; the total number of cycles of the atomic layer deposition process is 2000 times.

7. The method for preparing a low-stress anti-coking alternately laminated film for engine intake and exhaust valves according to claim 6, characterized in that: The temperature of the titanium source precursor is 70~90 ℃, the temperature of the coating area is 200~250 ℃, the background vacuum is lower than 50mtorr, and the nitrogen purge working pressure is 100~200 mtorr.

Images