A composite CVD coating, its preparation method and application

Abstract

This invention relates to the field of coating technology, and discloses a composite CVD coating, its preparation method, and its application. The coating comprises, from the inside out, a base layer, a first spacer layer, a first composite layer, and a second composite layer, arranged sequentially on the surface of a substrate. The first composite layer consists of a transition layer and a second spacer layer; the second composite layer consists of a third spacer layer and a surface layer; both the base layer and the surface layer are TiN; the first, second, and third spacers are MT-TiCN, κ-Al₂O₃, and TiC, respectively; the transition layer includes HT-TiCN and TiCO. The coating provided by this invention has good adhesion, strong resistance to crack propagation, and excellent overall coating quality; simultaneously, the coating particles are fine, and the surface roughness is low, which is more conducive to chip removal during processing.

Description

Technical Field

[0001] This invention relates to the field of coating technology, specifically to a composite CVD coating, its preparation method, and its application. Background Technology

[0002] Coating is one of the key technologies in modern cutting tool manufacturing. Technological advancements in manufacturing, the continuous emergence of new materials, and increasingly stringent requirements for processing efficiency have placed ever higher demands on cutting tool coatings.

[0003] Cutting tools endure immense mechanical and thermal loads during machining, making them highly susceptible to wear and causing a sharp decline in their service life. This is especially true when machining difficult-to-machine materials, where the loss of service life is even more severe. Therefore, surface modification of cutting tools to improve their surface properties is crucial for extending their lifespan. Currently, surface coating technology is commonly used to enhance the cutting performance and service life of cutting tools, thereby enabling them to achieve superior overall performance and significantly improve machining efficiency.

[0004] Chemical vapor deposition (CVD) coatings are widely used in the cutting tool industry today. These coatings are formed through gaseous chemical reactions at high temperatures (800-1200 degrees Celsius), resulting in coatings with consistent thickness and performance, and capable of meeting the requirements of complex shapes. Although new technologies are constantly emerging, the core coating components and structures that play a major role have remained largely unchanged. The current mainstream coating structure is still TiN+MT-TiCN+transition layer+Al2O3+TiN. Among these, the Al2O3 coating, due to its excellent heat insulation and wear resistance, has always been a core research focus and hot topic in the CVD field. It exhibits multiple phase structures, such as α phase, κ phase, and γ phase, each with its own advantages.

[0005] Compared to α-Al₂O₃, κ-Al₂O₃ has slightly higher hardness, finer and defect-free particles, and lower thermal conductivity, thus providing stronger thermal protection to the substrate. However, κ-Al₂O₃ is an unstable phase and transforms into stable α-Al₂O₃ at high temperatures, accompanied by a volume change of approximately 7%, leading to poorer coating adhesion and premature coating failure. Furthermore, its resistance to rake face wear is lower than that of α-Al₂O₃, thus limiting its application areas. However, through optimization of the growth process and techniques, its application range is being further broadened, particularly in water-cooled (or oil-cooled) machining and stainless steel processing. Existing process optimization schemes include alternating growth schemes of TiN (four layers) + κ-Al₂O₃ (five layers) coatings and multi-layer alternating growth schemes of TiAlCNO + κ-Al₂O₃, which can expand the application areas of κ-Al₂O₃ and improve coating life to some extent. However, in practical applications, the coating obtained based on the above optimization scheme will still have poor adhesion during machining, affecting the coating life. Summary of the Invention

[0006] The present invention aims to provide a composite CVD coating, its preparation method and application. The coating has good adhesion, strong resistance to crack propagation, superior overall coating quality and long service life. At the same time, the coating particles are fine and the surface roughness is low, which is more conducive to chip removal during the processing.

[0007] To achieve the above objectives, the basic solution provided by this invention is as follows:

[0008] Option 1

[0009] A composite CVD coating includes an underlayer, a first spacer layer, a first composite layer, and a second composite layer, which are sequentially disposed from the inside to the outside on the surface of a substrate. The first composite layer consists of a transition layer and a second spacer layer. The second composite layer consists of a third spacer layer and a surface layer. The underlayer and the surface layer are both TiN. The first spacer layer, the second spacer layer, and the third spacer layer are MT-TiCN, κ-Al2O3, and TiC, respectively. The transition layer includes HT-TiCN and TiCO.

[0010] The working principle and advantages of this solution are as follows:

[0011] First, the TiN underlayer on the substrate surface effectively ensures the adhesion between the substrate and the coating. The first spacer layer, MT-TiCN, placed above the underlayer, possesses high hardness, serving as a wear-resistant layer and providing ample support for the subsequent first composite layer. The first composite layer consists of a transition layer and a second spacer layer. The transition layer effectively ensures the adhesion between the MT-TiCN and κ-Al2O3 coatings, guaranteeing a tight bond between the layers. κ-Al2O3 exhibits excellent thermal insulation properties, acting as a heat-insulating layer to protect the substrate. Simultaneously, its high hardness allows it to serve as a wear-resistant layer, contributing to improved wear resistance. The second composite layer consists of a third spacer layer and a top layer. The combination of TiC and TiN effectively increases the coating's resistance to crack propagation; furthermore, the golden-yellow color of TiN allows it to serve as a marker layer, facilitating observation of coating wear.

[0012] In particular, this solution employs a composite CVD coating with two composite layers (a first composite layer and a second composite layer), resulting in better overall coating adhesion, stronger resistance to crack propagation, superior overall coating quality, and a longer service life. Specifically, in the first composite layer, a transition layer comprising HT-TiCN and TiCO is incorporated, upon which κ-Al2O3 grows. Compared to conventional coating designs, conventional solutions often limit the application of Al2O3 to a single coating (as in existing mainstream coating structures) or directly utilize the nucleation and growth characteristics of κ-Al2O3 on TiN, TiC, and TiCN surfaces, combining κ-Al2O3 directly with TiN, TiC, or TiCN (as in existing process optimization schemes). While these conventional solutions optimize the wear resistance and heat insulation of the coating using κ-Al2O3, the coating is still prone to premature failure. In fact, existing solutions do not address the contact issue between κ-Al2O3 and other interfaces; the formation of pores at the TiCN-κ-Al2O3 interface significantly impacts coating quality. This solution addresses this problem by specifically improving the composition of the transition layer and κ-Al2O3. The nucleation layers of TiCO and κ-Al2O3 are connected, effectively reducing interfacial porosity, enhancing coating adhesion, and resulting in better coating quality. In the second composite layer, the combination of TiC and TiN, compared to traditional single-layer TiN coatings, effectively reduces coating particle size, increases crack propagation resistance, and reduces surface roughness to facilitate chip removal during processing.

[0013] Option 2

[0014] A method for preparing a composite CVD coating, used to prepare a composite CVD coating as described in Scheme 1; comprising the following steps:

[0015] Step 1: Select the substrate material; place the substrate material into a chemical vapor deposition apparatus for coating deposition;

[0016] Step 2: Deposit a base layer on the substrate material;

[0017] Step 3: Deposit a first spacer layer on the base layer; deposit a first composite layer and a second composite layer sequentially on the first spacer layer.

[0018] The advantages and benefits of this approach are: the coating is deposited sequentially using chemical vapor deposition, the preparation method is simple and easy to operate.

[0019] Option 3

[0020] An application of a composite CVD coating, wherein a composite CVD coating as described in Scheme 1 is applied to the surface of a cutting tool.

[0021] The effects and advantages of this solution are as follows: using this coating as the surface coating of cutting tools can significantly enhance the wear resistance of cutting tools and extend their service life. Furthermore, due to the finer coating particles and lower surface roughness, this coating is more conducive to chip removal during the machining process and helps to improve cutting quality. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the coating structure of a composite CVD coating, its preparation method, and its application embodiments according to the present invention.

[0023] Figure 2 This is a schematic diagram of the coating structure of a composite CVD coating, its preparation method, and its application embodiments according to the present invention.

[0024] Figure 3 This is a schematic diagram of the morphology and particle size of κ-Al2O3 in a composite CVD coating, its preparation method, and application examples of the present invention.

[0025] Figure 4 This is a schematic diagram of the coating structure for Comparative Example 1;

[0026] Figure 5 This is a schematic diagram of the morphology and particle size structure of κ-Al2O3 in Comparative Example 1. Detailed Implementation

[0027] The following detailed explanation illustrates the specific implementation methods:

[0028] The basic implementation examples are as follows: Figure 1 As shown: A composite CVD coating includes an underlayer, a first spacer layer, a first composite layer and a second composite layer, which are sequentially disposed from the inside to the outside on the surface of a substrate.

[0029] In this embodiment, the substrate surface can be the surface of various materials such as high-speed steel, stainless steel, WC-based cemented carbide, ZrO2, silane ceramics, Si3N4 ceramics, TiCN ceramics, Al2O3 ceramics, CBN ceramics, and diamond.

[0030] The first composite layer consists of a transition layer and a second spacer layer; the second composite layer consists of a third spacer layer and a surface layer; the underlayer and the surface layer are both TiN; the first spacer layer, the second spacer layer and the third spacer are MT-TiCN, κ-Al2O3 and TiC respectively; the transition layer includes HT-TiCN and TiCO.

[0031] In the first composite layer, the transition layer and the second spacer layer are alternately stacked to form (transition layer + κ-Al2O3). x Alternating composite coatings, with a second spacer layer as the top layer.

[0032] Here, the transition layer consists of HT-TiCN and TiCO, and κ-Al2O3 is deposited on the TiCO base. Compared to conventional processes, κ-Al2O3 can directly nucleate on the surfaces of TiN, TiC, and TiCN, so conventional processes often choose to deposit it directly on these surfaces. However, in reality, localized reactions easily occur at the interface between these surfaces and κ-Al2O3, causing pores at the TiCN-κ-Al2O3 interface, significantly affecting coating quality. This solution addresses this problem by specifically improving the composition of the transition layer and κ-Al2O3, with TiCO and the κ-Al2O3 nucleation layer joining together. This effectively reduces interface pores, enhances coating adhesion, and results in better coating quality.

[0033] Furthermore, based on the multi-layered alternating transition layer and κ-Al2O3, by controlling the deposition time of each single layer, the particle size of the coating can be effectively reduced, and the coating's resistance to crack propagation can be increased. At the same time, through the optimized design of the coating composition, the porosity between different coating interfaces can be effectively reduced, the interfacial bonding can be strengthened, and the coating's adhesion can be increased.

[0034] In the second composite layer, the third spacer layer and the surface layer are alternately stacked to form (TiC+TiN). y An alternating composite coating is used, with the surface layer as the top layer. Here, based on a multi-layer alternating TiC and TiN structure, compared to the single-layer TiN structure in conventional coating designs, this scheme can further reduce the coating particle size, increase the coating's resistance to crack propagation, and reduce the coating surface roughness to facilitate chip removal during processing.

[0035] Specifically, the thickness of the single-layer transition layer is 0.1–0.3 μm, and the thickness of the single-layer κ-Al₂O₃ is 0.2–0.4 μm; the value of x is 4–12. The thickness of the single combination of the third spacer layer and the surface layer is 0.2–0.5 μm; the value of y is 2–5. Under the above parameter conditions, the overall thickness values ​​of the first composite layer and the second composite layer are optimal, resulting in good wear resistance (if the coating thickness is too small, the wear resistance will be insufficient) and a low risk of coating cracking (if the coating thickness is too large, the stress will increase, and the risk of coating cracking during use will be higher).

[0036] The overall structure of the coating is TiN+MT-TiCN+(transition layer+κ-Al2O3). x +(TiC+TiN) y Corresponding to the appendix. Figure 1 In the diagram, A represents the substrate, and a coating layer is deposited on top of A. B1 is the base layer TiN, C1 is the first spacer layer MT-TiCN, D11 (HT-TiCN) and D12 (TiCO) together form D1 (transition layer), ending with D12. E11 (nucleation layer) and E12 (growth layer) together form E1 (κ-Al2O3), ending with E12. E1 and D1 form the first composite layer. G1 (TiN) and F1 (TiC) form the second composite layer, ending with G1.

[0037] The overall coating thickness is 3–18 μm. In this embodiment, it is preferably set to 5–8 μm. A smaller coating thickness helps ensure the sharpness of the substrate material (for example, when the coating is applied to a cutting tool, it minimizes the loss of tool sharpness, thus improving the tool's cutting performance). The thickness of the underlayer (TiN) is 0.3–2 μm, preferably 0.5–1 μm in this embodiment; under these parameters, the underlayer thickness is moderate and effectively ensures the adhesion between the subsequent coating and the substrate material. The thickness of the first spacer layer (MT-TiCN) is 1–10 μm, preferably 3–8 μm in this embodiment; under these parameters, the coating exhibits optimal performance, good wear resistance, and a low risk of cracking.

[0038] This embodiment also provides a method for preparing a composite CVD coating, used to prepare a composite CVD coating as described in Scheme 1; including the following steps:

[0039] Step 1: Select the substrate material; place the substrate material into a chemical vapor deposition apparatus for coating deposition.

[0040] Specifically, the substrate material is placed in a hot-wall chemical vapor deposition furnace for coating deposition.

[0041] Step 2: Deposit a base layer on the substrate material; the deposition temperature of the base layer is set to 900-1000℃, and the deposition pressure is set to 100-500mbar.

[0042] Step 3: Deposit a first spacer layer on the substrate; the deposition temperature of the first spacer layer is set to 800-920℃ and the deposition pressure is set to 60-200mbar.

[0043] A first composite layer and a second composite layer are sequentially deposited on a first spacer layer. The deposition temperature of the first composite layer is set to 950–1050℃ and the deposition pressure is set to 60–120 mbar; the deposition temperature of the second composite layer is set to 950–1050℃ and the deposition pressure is set to 200–800 mbar.

[0044] Specifically, during the deposition of the first composite layer, the monolayer composite layer includes a transition layer and κ-Al2O3. When depositing the monolayer composite layer, the HT-TiCN and TiCO in the transition layer are deposited sequentially first, followed by the deposition and growth of κ-Al2O3.

[0045] In this composite layer, the κ-Al₂O₃ consists of a nucleation layer and a growth layer. Under the gaseous conditions of H₂, CO₂, and AlCl₃, a very thin nanoscale κ-Al₂O₃ layer is first deposited on the TiCO oxide of the transition layer as a nucleation layer. After a preset time, the nucleation layer is completely deposited. Here, the preset time is set to be greater than 5 minutes to ensure sufficient deposition of the nucleation layer and to ensure that the subsequent coating quality meets the standards. Then, H₂S is added to promote the chemical reaction process, allowing the κ-Al₂O₃ to begin the formal epitaxial formation process on the nucleation layer.

[0046] This embodiment also provides an application of a composite CVD coating, which is applied to the surface of a cutting tool as described in Scheme 1.

[0047] The effectiveness of this solution will be further illustrated below with comparative examples:

[0048] The coating structure in this embodiment is TiN+MT-TiCN+(transition layer+κ-Al2O3). x +(TiC+TiN) y The solid coating structure is shown in the attached figure. Figure 2 As shown in the figure (the thickness of each coating is indicated), the morphology, structure, and particle size of κ-Al2O3 in the coating are as follows. Figure 3 As shown.

[0049] The preparation process and coating size settings are shown in Table 1:

[0050] Table 1

[0051] Element TiN MT-TiCN <![CDATA[Intermediate layer + κ-Al2O3]]> TiC+TiN temperature 900℃ 880℃ 1000℃ 1000℃ pressure 160mbar 80mbar 70mbar 600mbar thickness 0.5μm 5μm 3μm 0.5μm

[0052] Comparative Example 1

[0053] The coating structure is TiN+MT-TiCN+ bonding layer+κ-Al2O3+TiN. The solid coating structure is shown in the attached figure. Figure 4 As shown in the figure (the thickness of each coating is indicated), the morphology, structure, and particle size of κ-Al2O3 in the coating are as follows. Figure 5 As shown.

[0054] This coating structure is the mainstream coating structure for existing κ-Al2O3 applications. The difference between this coating structure and the one described in this embodiment lies in the configuration of the (bonding layer + κ-Al2O3 + TiN) portion. The preparation process and coating size settings are shown in Table 2, where the process parameters are set to be consistent with those in this embodiment.

[0055] Table 2

[0056] Element TiN MT-TiCN bonding layer <![CDATA[κ-Al2O3]]> TiN temperature 900℃ 880℃ 1000℃ 1000℃ 1000℃ pressure 160mbar 80mbar 70mbar 70mbar 600mbar thickness 0.5μm 4.5μm 0.5μm 2.3μm 0.9μm

[0057] Based on this scheme and Comparative Example 1, this scheme utilizes (transition layer + κ-Al2O3) x +(TiC+TiN) y The multilayer composite coating structure design effectively reduces the particle size of κ-Al2O3. In Comparative Example 1, the particle size of κ-Al2O3 is 1.5 μm (as shown in the attached figure). Figure 5 As shown in the attached diagram), in this scheme, the particle size of κ-Al2O3 is reduced to 0.5 μm (as shown in the attached diagram). Figure 3 As shown, the labeled particle sizes include 336.9 μm, 361.6 μm, 421.9 μm, 423.3 μm, 433.2 μm, and 466.9 μm, etc. (the particle size can be reduced to below 0.5 μm), achieving a reduction in particle size by several times. This solution, through further reduction in particle size, enables stronger bonding of κ-Al2O3, enhances the coating's resistance to crack propagation, and effectively extends the coating's lifespan.

[0058] Comparative Example 2

[0059] The coating structure is PVD-TiAlN.

[0060] The coating thickness is 3μm.

[0061] The coating structure is a conventional coating structure without κ-Al2O3 in the coating body. This comparative example is introduced here to compare the lifespan of various coatings.

[0062] Based on the coating structures and related preparation processes of this scheme, Comparative Example 1, and Comparative Example 2, coatings were applied to the same substrate material (a cemented carbide turning tool, model SNMG120404-HA), and cutting tests were conducted using the coated substrate material (i.e., the coated cutting tool) under the same experimental environment. The cutting test data are shown in Table 3.

[0063] Table 3

[0064]

[0065] Table 3 shows that, under the condition that all cutting test parameters remain consistent, the service life of the cutting tool obtained using the coating and preparation process of this scheme is 300 m, while the service life of the cutting tool corresponding to Comparative Example 1 is 180 m, and the service life of the cutting tool corresponding to Comparative Example 2 is 105 m. The service life of the cutting tool corresponding to this scheme is significantly better than that of the comparative scheme. Therefore, it can be seen that the coating quality of this scheme is better, the coating life is longer, and the durability is stronger.

[0066] This embodiment provides a composite CVD coating, its preparation method, and its application. The coating has good adhesion, strong resistance to crack propagation, and excellent overall coating quality. At the same time, the coating particles are fine and the surface roughness is low, which is more conducive to chip removal during the processing.

[0067] The above descriptions are merely embodiments of the present invention. Commonly known structures and characteristics of the solutions are not described in detail here. Those skilled in the art are aware of all common technical knowledge in the field prior to the application date or priority date, are aware of all existing technologies in that field, and have the ability to apply conventional experimental methods prior to that date. Those skilled in the art can, under the guidance of this application, improve and implement this solution in combination with their own capabilities. Some typical known structures or methods should not be obstacles for those skilled in the art to implement this application. It should be noted that those skilled in the art can make several modifications and improvements without departing from the structure of the present invention. These should also be considered within the scope of protection of the present invention, and will not affect the effectiveness of the implementation of the present invention or the practicality of the patent.

Claims

1. A composite CVD coating, characterized in that, The substrate includes a base layer, a first spacer layer, a first composite layer, and a second composite layer, arranged sequentially from the inside out on the substrate surface. The first composite layer consists of a transition layer and a second spacer layer. The second composite layer consists of a third spacer layer and a surface layer. Both the base layer and the surface layer are TiN. The first spacer layer, the second spacer layer, and the third spacer layer are MT-TiCN, respectively. TiC; the transition layer includes HT-TiCN and TiCO; In the first composite layer, the transition layer and the second spacer layer are alternately stacked to form Alternating composite coatings, with a second spacer layer as the top layer; sediment At that time, deposition and growth were carried out on TiCO base; In the second composite layer, the third spacer layer and the surface layer are alternately stacked to form Alternating composite coatings, with the surface layer as the top layer.

2. The composite CVD coating according to claim 1, characterized in that, The coating thickness is 3~18μm.

3. The composite CVD coating according to claim 1, characterized in that, The value of x is 4~12; the value of y is 2~5.

4. The composite CVD coating according to claim 1, characterized in that, The thickness of the base layer is 0.3~2μm; the thickness of the first spacer layer is 1~10μm; the thickness of the single-layer transition layer is 0.1~0.3μm, and the single-layer... The thickness of the first layer is 0.2~0.4μm; the thickness of the single combination of the third spacer layer and the surface layer is 0.2~0.5μm.

5. A method for preparing a composite CVD coating, characterized in that, A method for preparing a composite CVD coating as described in any one of claims 1-4; comprising the following steps: Step 1: Select the substrate material; place the substrate material into a chemical vapor deposition apparatus for coating deposition; Step 2: Deposit a base layer on the substrate material; Step 3: Deposit a first spacer layer on the base layer; deposit a first composite layer and a second composite layer sequentially on the first spacer layer.

6. The method for preparing a composite CVD coating according to claim 5, characterized in that, The deposition temperature for the first layer is set to 900~1000℃, and the deposition pressure is set to 100~500mbar; the deposition temperature for the first spacer layer is set to 800~920℃, and the deposition pressure is set to 60~200mbar; the deposition temperature for the first composite layer is set to 950~1050℃, and the deposition pressure is set to 60~120mbar; the deposition temperature for the second composite layer is set to 950~1050℃, and the deposition pressure is set to 200~800mbar.

7. The method for preparing a composite CVD coating according to claim 5, characterized in that, During the deposition of the first composite layer, while performing During growth, first in Deposition was carried out under gaseous conditions, and after a preset time interval, more gas was added. They are deposited together.

8. An application of a composite CVD coating, characterized in that, The composite CVD coating as described in any one of claims 1-4 is applied to the surface of a cutting tool.

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