Composite coating suitable for alkalescent urea environment, preparation method and urea nozzle ball valve

Abstract

The invention relates to the technical field of composite coatings, in particular to a composite coating suitable for an alkalescent urea environment, a preparation method of the composite coating and a urea nozzle ball valve. The invention relates to a composite coating suitable for a weakly alkaline urea environment. The composite coating comprises a chromium base layer, a CrN transition layer, a WC-DLC composite coating and a diamond-like carbon layer from an inner coating substrate to the outside in sequence. According to the urea nozzle ball valve prepared through coating of the composite coating, the corrosion resistance of the urea nozzle ball valve is greatly improved, and the service life of the urea nozzle ball valve is greatly prolonged.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of composite coating, in particular to a composite coating suitable for weak alkaline urea environment, a preparation method thereof and a urea nozzle ball valve. BACKGROUND

[0002] Selective catalytic reduction technology (SCR) is to reduce the emission of NOx in diesel exhaust by spraying reducing agent (such as NH3, liquid ammonia, urea) to reduce it into N2 and H2O under the action of catalyst, so as to achieve the effect of energy saving and emission reduction. The SCR urea nozzle ball valve coupling is a precision part of the selective catalytic reduction system. The surface of the ball valve is coated with a wear-resistant coating-diamond-like carbon (DLC) coating, which can improve the wear resistance of the ball valve, prolong the service life and the stability of the function. The tungsten carbide transition layer is used to solve the problems of large stress, low adhesion and easy peeling of the coating caused by the large difference in material expansion coefficient and lattice constant between the DLC coating and the ball valve matrix.

[0003] The hard alloy of composite carbide WTiTaC and binder metal cobalt (Co) is the most widely used adhesive in the sintering forming process of tungsten carbide (WC) target material, which can be used to eliminate the residual porosity of WC material and reduce the brittleness of WC material to achieve high strength and toughness value. However, with the identification of cobalt (Co) as an inhalable carcinogen and the increasing demand for WC purity in the industry, the material composition of WC target material has changed. Specifically, the WTiTaC component is cancelled, and only <0.05% of cobalt is retained, which is called cobalt-free tungsten carbide target material. This weakens the effect of improving the brittleness of WC target material, increases the stress of the coating, and easily causes peeling under load.

[0004] The SCR urea nozzle ball valve coupling is used in weak alkaline and high temperature environment, and the coating structure prepared by the old target material is Cr-Cr / WC-WC:CH-DLC. When preparing the Cr / WC transition layer, the Cr content gradually decreases and the WC content gradually increases from the inside to the outside wall, until the outermost side is close to pure WC material. The cobalt in WC can quickly react with the corrosive solvent of weak alkaline urea, leaving a loosely woven tungsten carbide grain skeleton, which causes large-area coating peeling under load and functional failure.

[0005] Due to the change of tungsten carbide raw material, the existing coating structure of the SCR urea nozzle ball valve currently processed has large-area coating peeling during use, affecting its service life. In order to solve this problem, a new coating structure must be developed. SUMMARY

[0006] In order to solve the above technical problems in the prior art, the application provides a composite coating suitable for a weak alkaline urea environment and a preparation method thereof, and a urea nozzle ball valve.

[0007] The technical scheme for solving the above technical problems of the application is as follows: The first aspect of the application is to provide a composite coating suitable for a weak alkaline urea environment, which comprises, from inside to outside, a chromium primer layer, a CrN transition layer, a WC-DLC composite coating and a diamond-like layer in sequence on a coating substrate.

[0008] The composite coating provided by the application removes the Cr / WC layer and improves the service life by designing a new composite coating. Specifically, the chromium primer layer has excellent wear resistance, strong oxidation resistance, good bonding performance with the steel substrate, and good transition with the upper coating layer. The CrN transition layer has strong adhesion with the chromium primer layer and is not easy to peel off. Meanwhile, the dense columnar crystal structure of the CrN transition layer has excellent wear resistance and can withstand a certain impact damage. The WC-DLC composite coating cooperates with other layers to ensure the bonding strength of the coating, improve the corrosion resistance and service life of the composite coating.

[0009] Further, the preparation raw material of the WC-DLC composite coating comprises WC and C2H2.

[0010] The beneficial effects of the above further technical scheme are that the Cr / WC layer is removed and replaced by the WC-DLC composite coating to avoid the existence of pure WC.

[0011] Further, the thickness of the chromium primer layer is 0.2 um, the thickness of the CrN transition layer is 1.0 um, the thickness of the WC-DLC composite coating is 0.3 um, and the thickness of the diamond-like layer is 1.0 um.

[0012] The second aspect of the application is to provide a preparation method of the composite coating suitable for a weak alkaline urea environment according to the first aspect of the application, which comprises the following steps: S1, depositing a chromium primer layer on a coating substrate; S2, depositing a CrN transition layer on the chromium primer layer; S3, depositing a WC-DLC composite coating on the CrN transition layer; S4, depositing a diamond-like layer on the WC-DLC composite coating.

[0013] Further, in step S1, the chromium primer layer is deposited by a magnetron sputtering method, the magnetron sputtering power is controlled to be 5-7Kw, the Ar flow rate ratio is controlled to be 200-400 sccm, the temperature is controlled to be 180-200℃, and the deposition time is controlled to be 0.1-0.3h.

[0014] Further, in step S2, a CrN transition layer is deposited by a magnetron sputtering physical vapor deposition method, the bias voltage is controlled to be 200 V, the flow rate ratio of N2 and Ar is controlled to be 150 sccm and 300 sccm respectively, the temperature is controlled to be 160-200 ℃, and the deposition time is controlled to be 1-2 h.

[0015] Further, in step S3, a WC-DLC composite coating is deposited by a magnetron sputtering method, the flow rate of C2H2 is controlled to be increased from 5 sccm to 150 sccm within 30 minutes, and then the flow rate of C2H2 is controlled to be increased from 70 sccm to 150 sccm within 15 minutes; the magnetron sputtering power is controlled to be 5-7 Kw, the flow rate ratio of Ar is controlled to be 200-400 sccm, the temperature is controlled to be 160-200 ℃, and the deposition time is controlled to be 0.3-0.6 h.

[0016] The beneficial effects of the above further technical solutions are that the flow rate of C2H2 at the beginning and the stable time and the time required for stabilization are controlled, so that the amount of pure WC in the transition layer is reduced as much as possible, the content of C2H2 in the WC-DLC composite coating is increased, and coating peeling is avoided; in addition, by increasing the flow rate of C2H2, the WC-DLC composite coating is directly and excessively formed as much as possible, so that the corrosion rate of Co in an alkaline solvent such as urea and the peeling of WC are reduced, and coating peeling is avoided.

[0017] Further, in step S4, a diamond-like layer is deposited by a magnetron sputtering method, the flow rate of C2H2 is controlled to be 400-600 sccm, the flow rate ratio of Ar is controlled to be 200-400 sccm, the temperature is controlled to be 200-220 ℃, the bias voltage is controlled to be 600-800 V, and the deposition time is controlled to be 0.4-0.6 h.

[0018] Another aspect of the present application is to provide a urea nozzle ball valve, the surface of which is coated with the composite coating suitable for a weak alkaline urea environment provided by the first aspect of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 A picture of urea immersion of a sample block coated with the composite coating of the embodiment of the present application after being damaged by a ball pressure; Figure 2 A picture of durability test of a urea nozzle ball valve of the embodiment of the present application; Figure 3 A picture of urea immersion of a sample block coated with the composite coating of the comparative example of the present application after being damaged by a ball pressure; Figure 4 A picture of durability test of a urea nozzle ball valve of the comparative example of the present application; Figure 5 A picture of Figure 4 An electron microscope graph of the part circled by a red frame; Figure 6 A picture of Figure 4The energy spectrum of the part circled by the red frame. DETAILED DESCRIPTION

[0020] The following description will be made to the embodiments of the present application by specific examples, and other advantages and effects of the present application can be easily understood by those skilled in the art from the disclosure. Although the description of the present application will be introduced in combination with the preferred embodiments, this does not mean that the features of the present application are limited to the embodiments. On the contrary, the purpose of introducing the present application in combination with the embodiments is to cover other options or modifications that can be extended based on the claims of the present application. In order to provide a deep understanding of the present application, many specific details will be included in the following description. The present application can also be implemented without using these details. In addition, in order to avoid confusion or obscure the focus of the present application, some specific details will be omitted in the description. It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict.

[0021] EMBODIMENT A magnetron sputtering method was used to coat a chromium primer layer, a CrN transition layer, a WC-DLC composite coating and a diamond-like layer on the urea nozzle ball valve substrate in sequence: S1, depositing a chromium primer layer on the coated substrate: controlling the magnetron sputtering power to be 6Kw, the Ar flow ratio to be 300sccm, the temperature to be 190℃, and the deposition time to be 0.1h; S2, depositing a CrN transition layer on the chromium primer layer: the bias voltage is 200V, the N2 flow ratio is 150sccm, the Ar flow ratio is 300sccm, the temperature is 180℃, and the deposition time is 1.5h; S3, depositing a WC-DLC composite coating on the CrN transition layer: the C2H2 initial flow rate is increased from 5sccm to 150sccm within 30 minutes, and then changed to be increased from 70sccm to 150sccm within 15 minutes, the magnetron sputtering power is 6Kw, the Ar flow ratio is 300sccm, the temperature is 180℃, and the deposition time is 0.5h; S4, depositing a diamond-like layer on the WC-DLC composite coating: a diamond-like layer is deposited by a magnetron sputtering method, the C2H2 flow rate is controlled to be 500sccm, the Ar flow ratio is 300sccm, the temperature is 210℃, the bias voltage is 700V, the deposition time is 0.5h, and a urea nozzle ball valve coated with a composite coating is obtained.

[0022] COMPARATIVE EXAMPLE A magnetron sputtering method was used to coat a chromium primer layer, a Cr / WC layer, a WC-DLC composite coating and a diamond-like layer on the urea nozzle ball valve substrate in sequence.

[0023] PERFORMANCE TEST Ball pressure immersion: First, a circular pit is pressed into the surface of the sample using a Rockwell hardness tester. The sample is then placed in a container containing pure urea at 80°C and left for 80 hours. Finally, the sample is removed and inspected for signs of flaking around the pit.

[0024] Durability test: The SCR ball valve coated with the composite coating is assembled into a complete SCR urea injector, placed in a test device, and subjected to 100 million urea injections according to the following test conditions set by software control, with the flow rate, leakage rate, etc. checked every 24 hours during the process; test conditions: urea solution temperature 80°C, cooling liquid temperature 80°C, urea solution flow rate 3 kg / h, cooling liquid flow rate 120 L / h, urea solution pressure 6 / 7 / 8 bar, injection frequency 100 HZ, constant injection time 4 ms, drive voltage 13.8 V.

[0025] The performance test results of the examples and comparative examples are shown in Tables 1 and Figures 1-6

[0026] Table 1 Performance test results of examples and comparative examples

[0027] The above description is merely preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.​

Claims

1. A composite coating suitable for use in a weakly alkaline urea environment, characterized in that, The Cr undercoat layer, the CrN transition layer, the WC-DLC composite coating and the diamond-like carbon layer are sequentially arranged from the inner side of the coating substrate to the outer side.

2. The composite coating suitable for weakly alkaline urea environment according to claim 1, characterized in that, The preparation raw material of the WC-DLC composite coating comprises WC and C2H2.

3. The composite coating suitable for weakly basic urea environment according to claim 1, characterized in that, The thickness of the Cr undercoat layer is 0.2 um, the thickness of the CrN transition layer is 1.0 um, the thickness of the WC-DLC composite coating is 0.3 um, and the thickness of the diamond-like carbon layer is 1.0 um.

4. A method for producing a composite coating suitable for use in a weakly alkaline urea environment according to any one of claims 1 to 3, characterized in that The method comprises the following steps: S1, depositing a Cr undercoat layer on the coating substrate; S2, depositing a CrN transition layer on the Cr undercoat layer; S3, depositing a WC-DLC composite coating on the CrN transition layer; S4, depositing a diamond-like carbon layer on the WC-DLC composite coating.

5. The method of claim 4, wherein the method is characterized by, In step S1, the Cr undercoat layer is deposited by a magnetron sputtering method, the magnetron sputtering power is controlled to be 5-7Kw, the Ar flow ratio is controlled to be 200-400sccm, the temperature is controlled to be 180-200℃, and the deposition time is controlled to be 0.1-0.3h.

6. The method of claim 4, wherein the composite coating is prepared by the steps of: In step S2, the CrN transition layer is deposited by a magnetron sputtering physical vapor deposition method, the bias voltage is controlled to be 200V, the flow ratio of N2 and Ar is controlled to be 150sccm and 300sccm respectively, the temperature is controlled to be 160-200℃, and the deposition time is controlled to be 1-2h.

7. The method of claim 4, wherein the composite coating is prepared by the steps of: In step S3, the WC-DLC composite coating is deposited by a magnetron sputtering method, the C2H2 flow is controlled to be increased from 5sccm to 150sccm within 30 minutes and then controlled to be increased from 70sccm to 150sccm within 15 minutes, the magnetron sputtering power is controlled to be 5-7Kw, the Ar flow ratio is controlled to be 200-400sccm, the temperature is controlled to be 160-200℃, and the deposition time is controlled to be 0.3-0.6h.

8. The method for preparing a composite coating suitable for a weakly alkaline urea environment according to claim 4, characterized in that, In step S4, the diamond-like carbon layer is deposited by a magnetron sputtering method, the C2H2 flow is controlled to be 400-600sccm, the Ar flow ratio is controlled to be 200-400sccm, the temperature is controlled to be 200-220℃, the bias voltage is controlled to be 600-800V, and the deposition time is controlled to be 0.4-0.6h.

9. A urea nozzle ball valve characterized by, Coating the surface with the composite coating suitable for weak alkaline urea environment according to any one of claims 1 to 3.

Images