A wear-resistant coating for extrusion die surfaces and a method for producing and using the same

Abstract

The application discloses an extrusion die surface wear-resistant coating and a preparation method and application thereof. The wear-resistant coating comprises an intermediate transition layer and a wear-resistant covering layer. The intermediate transition layer is composed of TiC, Ti(CN) and TiN which are gradually distributed from inside to outside. The total carbon-nitrogen ratio of the intermediate transition layer is 0

Description

Technical Field

[0001] This invention relates to the field of extrusion die coatings, specifically to a wear-resistant coating for the surface of an extrusion die, its preparation method, and its application. Background Technology

[0002] An extrusion die is a tool used to slowly extrude heated metal material through a die orifice of a specific shape under high pressure, resulting in plastic deformation and producing metal profiles with specific cross-sectional shapes and dimensions. Therefore, extrusion dies are required to possess good thermal strength, toughness, and resistance to thermal fatigue. Furthermore, the high pressure conditions during extrusion create strong friction and shear forces between the metal material and the die, necessitating exceptional wear resistance on the die surface. A typical extrusion die is a Cr-Mo-V alloy die with a wear-resistant coating on its surface, exhibiting good heat resistance and heat treatment properties, allowing for long-term use at certain high temperatures. However, due to friction and shear forces, the wear-resistant coating on the die surface gradually wears away, leading to dimensional changes in the extruded profile and making it difficult to meet the requirements of high-precision profile production. For example, thin-walled porous microchannel aluminum flat tube profiles have wall thicknesses as thin as 0.2 mm and precision requirements of less than 0.05 mm, with processing accuracy even required to be below 10 μm. This means that the orifices of the extrusion dies used for their production are extremely small, and the friction and shear forces between the aluminum alloy material and the extrusion die are also much greater. Testing has shown that in actual production, the extrusion ratio of thin-walled porous microchannel aluminum flat tube profiles is often over 500 times, with extrusion pressures exceeding 200 MPa, resulting in extremely high shear friction. Existing extrusion dies are difficult to adapt to these extrusion conditions for extended periods; the coating on the dies is easily peeled off, requiring frequent shutdowns for maintenance and die replacement, which not only increases production costs but also seriously affects product quality and production efficiency.

[0003] Chemical vapor deposition (CVD) is a technique that uses gaseous precursors to react chemically on a substrate surface to generate a solid deposit film. Due to its ability to deposit multi-component and multi-layer coating materials onto substrate surfaces, it is the most widely used technique for coating molds and cutting tools. However, existing CVD processes for producing wear-resistant coatings still have the following drawbacks:

[0004] First, as mentioned above, the CVD process involves introducing a precursor gas to undergo a chemical reaction under certain conditions, depositing a thin film on the substrate surface. This is equivalent to simply putting a "coat" on the substrate surface without considering the intrinsic connection between the deposited film and the substrate. That is, the connection between the coating and the steel substrate is not tight enough. When there is huge shear stress at the interface, the wear-resistant layer is easy to separate from the mold body. For example, when extruding profiles such as thin-walled porous microchannel aluminum flat tubes, the coating is prone to peeling and failure under high temperature and high pressure cyclic loads.

[0005] Secondly, because the deposited wear-resistant layer components (such as Al2O3 ceramics) often have poor adhesion to the metal mold substrate, existing technologies address this issue by introducing an intermediate transition film between the coating and the substrate. For example, Chinese patent document CN103748264B discloses a method for generating a coating on an extrusion tool, which deposits a Ti(CN) component on the substrate to connect with the outer wear-resistant coating layer. However, to provide sufficient support for the upper wear-resistant coating layer, the deposited Ti(CN) component has a high C content; for example, the aforementioned patent requires the C / N ratio of the Ti(CN) layer to be greater than 1, preferably greater than 2. This requires the prolonged introduction of a large amount of carbon source gas during the preparation process, which can lead to decarburization of the carbon-containing metal substrate surface, reducing the substrate's hardness. Consequently, the coating on the mold surface is easily peeled off under high-temperature and high-pressure cyclic extrusion loads, affecting the mold's lifespan. Moreover, the coefficient of thermal expansion (CTE) of the Ti(CN) layer differs significantly from that of the steel substrate and the ceramic wear-resistant layer. This CTE mismatch leads to a large stress concentration at the interface, which becomes the origin of coating crack initiation. Under harsh extrusion conditions, the coating is also prone to peeling and failure.

[0006] Furthermore, when depositing a wear-resistant coating layer on a transition film layer, if the surface of the transition film layer is too smooth, the adhesion of the wear-resistant layer above it will be insufficient. However, while an uneven surface of the transition film layer is beneficial for the adhesion of the upper film material, it can also easily lead to uneven deposition of the wear-resistant coating layer. For example, in the aforementioned Chinese patent document CN103748264B, the deposited Ti(CN) component forms a large number of adjacent and parallel cylindrical or columnar structures on the substrate surface. Although this is beneficial for the adhesion of the upper functional layer, it is difficult for the wear-resistant layer component to fill the gaps in these cylindrical or columnar structures, resulting in more pores and defects inside the film, insufficient film density, and a decrease in wear resistance.

[0007] There are also reports in the industry of depositing multiple intermediate transition layers on the surface of steel substrates to improve the adhesion between Al2O3 and other coatings and the steel substrate. For example, Zhang Jin, Xue Qi, and others proposed using chemical vapor deposition to prepare a Ti(CN) / TiC / Al2O3 multilayer coating structure on the surface of 42CrMo steel substrate, claiming to improve the interfacial adhesion between the coating and the substrate. However, when the transition film is deposited in multiple layers, there will inevitably be abrupt changes in the coefficient of thermal expansion between the layers, which makes the interlayer CTE mismatch problem more likely to occur, and the interfacial stress concentration phenomenon will also exist more. Therefore, the improvement of the interfacial adhesion between the coating and the substrate by using multiple transition layers is limited (about 62N), and the overall film is poor. Under the high temperature and high pressure of extrusion, the coating is still prone to cracking and peeling.

[0008] Therefore, how to ensure that the wear-resistant layer deposited by CVD is tightly bonded to the extrusion die body, further alleviate the interfacial stress between the coating and the substrate and between coatings, and ensure the density and integrity of the superimposed deposited film to meet the heavy-duty requirements of production of profiles including thin-walled and porous structures, remains an urgent problem to be solved. Summary of the Invention

[0009] To address the aforementioned problems such as insufficient bonding between the CVD-deposited wear-resistant layer and the extrusion die body, high interfacial stress between the coating and the substrate, and between coatings themselves, lack of overall integrity and density of the film, easy peeling, and difficulty in adapting to the extrusion conditions of thin-walled and porous profiles, this invention proposes a wear-resistant coating for the surface of an extrusion die, its preparation method, and its application. The intermediate transition layer is designed as a continuous gradient deposition layer of TiC→Ti(CN)→TiN. First, a dense TiC layer is formed on the substrate surface by the reaction of C in the extrusion die body with TiCl4, increasing the bonding between the deposited film and the extrusion die body while protecting the substrate. Through the continuous gradient deposition of TiC→Ti(CN)→TiN, the coefficient of thermal expansion is progressively increased to match the coefficient of thermal expansion of the wear-resistant layer, effectively alleviating interfacial stress. Furthermore, TiN spike structures are induced on the surface of the intermediate transition layer, and the subsequently deposited wear-resistant coating fully fills the spike gaps, forming a three-dimensional mechanical interlocking structure, greatly reducing the risk of coating peeling under heavy loads. The specific technical solution is as follows:

[0010] First, the present invention provides a wear-resistant coating for extrusion dies, comprising an intermediate transition layer and a wear-resistant covering layer, wherein the intermediate transition layer is located between the wear-resistant covering layer and the extrusion die body; the intermediate transition layer is composed of three components, TiC, Ti(CN), and TiN, which are gradually distributed from the inside to the outside; specifically, the interface deposit in contact with the extrusion die body is TiC; as it moves away from the extrusion die body, the C content in the deposit gradually decreases and the N content gradually increases, and the deposit smoothly transitions from carbon-rich Ti(CN) to nitrogen-rich Ti(CN); then, as it continues to move away from the extrusion die body, the deposit becomes pure TiN, and a jagged TiN spike protrusion structure is formed on the surface.

[0011] The aforementioned wear-resistant coating is provided in which the extrusion die body is made of heat-resistant tool steel with a carbon content of 0.05 to 0.5 wt%, preferably 0.05 to 0.25 wt%.

[0012] The aforementioned wear-resistant coating has an intermediate transition layer with a thickness of 4–8 μm, preferably 5–7 μm; a total carbon-nitrogen ratio of 0 < C / N < 1, preferably 0 < C / N < 0.5; a surface TiN spike height of no more than 3 μm, preferably 0.5–2.5 μm; and a spike aspect ratio of ≤2:1, preferably ≤1.5:1.

[0013] The aforementioned wear-resistant coating, wherein the wear-resistant covering layer is composed of Al2O3 ceramic and has a thickness of 2-6 μm, preferably 3-4 μm; the wear-resistant covering layer fully fills the gaps between the TiN spikes on the surface of the intermediate transition layer and is tightly overlapped and embedded on the intermediate transition layer; the thickness of the portion where the wear-resistant covering layer meets the intermediate transition layer is not less than 0.5 μm, preferably not less than 1 μm.

[0014] Secondly, the present invention provides a method for preparing the aforementioned wear-resistant coating, comprising the following steps:

[0015] S1: Preheating and activation: After pretreatment, the extrusion die body is loaded into the CVD furnace for preliminary preheating and reduction. Then, the temperature is increased and plasma is turned on for sputter cleaning to activate its surface.

[0016] S2: Deposition of intermediate transition layer: Turn off plasma, adjust deposition process parameters, and constantly introduce TiCl4 and H2. While maintaining stable TiCl4 and H2 flow rates, introduce CH4 and N2, and independently control the CH4 and N2 flow rates in reverse to make the intermediate C / N ratio in the deposition layer continuously and gradually change, and deposit TiC→Ti(CN)→TiN composition in a gradient, and induce TiN spike formation in the later stage of TiN composition deposition;

[0017] S3: Deposition of wear-resistant coating layer: After the intermediate transition layer is deposited, adjust the temperature, shut off the TiCl4, N2 and H2 gas flow, and introduce aluminum source and oxygen source gas to deposit the wear-resistant coating layer on the intermediate transition layer. After filling the spike gaps on the intermediate transition layer, it is tightly embedded and covers the intermediate transition layer.

[0018] S4: Restorative heat treatment: After the wear-resistant coating is deposited, it is cooled to a safe temperature under a protective atmosphere, and then transferred to a heat treatment furnace for tempering to restore the properties of the substrate and improve the adhesion of the coating.

[0019] As a preferred technical solution, in step 1), the preheating and activation specifically include:

[0020] S1-1: Load the pretreated extrusion die body into the CVD furnace and evacuate to a vacuum level below 5.0 × 10⁻⁶. -3 Pa, fill the furnace with H2 or H2 / Ar mixed gas until the pressure inside the furnace reaches 100-150 Pa, then evacuate and refill the furnace again, repeating this process 2-3 times;

[0021] S1-2: After the final vacuuming, H2 is introduced to bring the furnace pressure to 1.5-3 kPa. Then, the furnace temperature is raised to 500-600℃ at a rate of 10℃ / min and held for 30-120 min to preheat and reduce the extrusion die body.

[0022] S1-3: Start the radio frequency plasma source with a power of 300-500W and apply a bias voltage of -350-450V. Continue to raise the temperature to 750-850℃ at a rate of 10℃ / min and hold for 15-30min to perform sputter cleaning and activation on the surface of the extrusion die body.

[0023] As a preferred technical solution, in step 2), the deposition temperature of the intermediate transition layer is controlled at 800–1050℃, and the deposition pressure is controlled at 8–10 kPa; the flow rate of TiCl4 is controlled at 100–300 SCCM, and the flow rate of H2 is controlled at 2000–3000 SCCM; the flow rates of CH4 and N2 are independently and in reverse controlled to perform gradient deposition, as follows:

[0024] S2-1: First stage: CH4 is introduced and the CH4 flow rate is controlled to increase linearly from 0 SCCM to 40-60 SCCM within 20 min at a rate of 2-3 SCCM, so as to deposit TiC on the surface of the extrusion die body.

[0025] S2-2: Second stage: Control the CH4 flow rate, linearly decreasing it from 40-60 SCCM to 0 SCCM at a rate of 0.6 SCCM over 100 min; simultaneously, control the N2 flow rate, linearly increasing it from 0 SCCM to 60-80 SCCM over 100 min at a rate of 0.6-0.8 SCCM; to gradually change the deposition composition from carbon-rich Ti(CN) to nitrogen-rich Ti(CN);

[0026] S2-3: Third stage: When the CH4 flow rate is 0 SCCM and the N2 flow rate reaches 60-80 SCCM, the radio frequency plasma is started with a power of 350-450 W and a bias voltage of -150--250 V is applied and maintained for 5-10 min to deposit TiN composition; then the pressure is controlled at 5-6 kPa, the radio frequency power is 550-650 W, and the bias voltage is -350-380 V, and deposition is carried out for 10-15 min to induce the formation of TiN spike structures; then the pressure is adjusted to 8-10 kPa, the bias voltage is reduced to -300-330 V, and deposition is carried out for 5-10 min to control the morphology of TiN spikes.

[0027] As a preferred technical solution, in step 3), the process of depositing the wear-resistant coating is as follows:

[0028] S3-1: Pretreatment of deposition surface: After the intermediate transition layer is deposited, the TiCl4, N2 and H2 gas flow is turned off, the furnace temperature is controlled at 800-1050℃, and then Ar gas is introduced at a flow rate of 450-550 SCCM. Radio frequency plasma is started at a power of 300-500W, and sputter cleaning is performed for 5-10 minutes to activate the TiN spike surface.

[0029] S3-2: Initial nucleation stage: Turn off the radio frequency plasma, maintain the temperature at 800-1050℃, control the pressure at 30-50Pa, introduce aluminum source and oxygen source gas, and the molar flow ratio of aluminum source and oxygen source is 1:15-20, deposit for 15-30min, and uniformly generate Al2O3 crystal nuclei on the TiN spike surface.

[0030] S3-3: Main growth stage: Continue to maintain the temperature at 800-1050℃, increase the furnace pressure to 100-200Pa, adjust the molar flow ratio of aluminum source and oxygen source gas to 1:10-15, and deposit for 2-4 hours to allow Al2O3 to grow in a shape-preserving manner, fill the gaps between TiN spikes, and uniformly cover the intermediate transition layer.

[0031] As a preferred technical solution, in step 4), the restorative heat treatment specifically includes:

[0032] S4-1: Homogenization and Austenitization: After the wear-resistant coating is deposited, the aluminum and oxygen sources are shut off, the furnace temperature is controlled at 450-550℃, only Ar gas is introduced at a flow rate of 500-800 SCCM, the positive pressure inside the furnace is maintained at 1-5 kPa, and this is maintained for 10-15 min to ensure uniform mold temperature; then, the furnace temperature is reheated to 1020-1200℃ at a rate of 8-10℃ / min and held for 30-40 min.

[0033] S4-2: Gas quenching: After the heat preservation is completed, turn off the Ar gas source, quickly fill the furnace with N2 to a pressure of 5-10 bar, turn off the heater, start the high-speed airflow circulation system, and gas cool the mold; the cooling rate is controlled to be not less than 25℃ / min, and the mold temperature is cooled to below 40℃.

[0034] S4-3: High-temperature tempering: Transfer the gas-quenched mold to a vacuum tempering furnace, evacuate to below 1×10-2 Pa, and perform tempering according to the set program: heat to 550~650℃ at a rate of ≤5℃ / min, hold for 2~3h, and then cool to room temperature at a cooling rate of ≤5℃ / min; repeat 2~3 times; after the last cooling to room temperature, fill with Ar or N2 to atmospheric pressure and remove from the furnace.

[0035] Secondly, the present invention provides an aluminum alloy extrusion die for extruding thin-walled, porous aluminum profiles, the surface of which is deposited with the aforementioned wear-resistant coating, the total thickness of which is 5 to 13 μm, and the interfacial bonding force between the intermediate transition layer of which is wear-resistant coating and the substrate and wear-resistant cover layer is ≥90N, preferably ≥100N.

[0036] The beneficial effects of this invention are:

[0037] 1) This invention is the first to design the transition layer between the wear-resistant coating layer and the extrusion die body as an intermediate transition layer with a continuous and gradual change from TiC to Ti(CN) to TiN. That is, the interface with the die body is TiC, and as it moves away from the die body, the C content in the deposited layer gradually decreases and the N content gradually increases, and its composition smoothly transitions from carbon-rich Ti(CN) to nitrogen-rich Ti(CN); then, as it continues to move away from the die body, the deposit becomes pure TiN. The internal TiC component serves as the starting point of the gradient transition layer, enabling it to bond well with the steel matrix. Furthermore, some of the carbon sources in TiC originate from the matrix, resulting in stronger interfacial bonding. In addition, the coefficient of thermal expansion increases sequentially from TiC to Ti(CN) to TiN. The CTE of the TiN component is similar to that of the wear-resistant coating layer (Al2O3), allowing the coefficient of thermal expansion to gradually and continuously transition from the steel matrix to the level of the external wear-resistant coating layer (Al2O3). This effectively reduces stress concentration caused by abrupt changes in material properties, alleviates interfacial stress, and improves the temperature and wear resistance and service life of the extrusion die.

[0038] 2) Since some of the carbon source in the TiC component inside the intermediate transition layer of this invention comes from the extrusion die body, it enhances the bonding force between the coating and the extrusion die body; the TiN component outside can react with the oxygen source to generate TiO2 in the early stage of Al2O3 capping layer deposition, which not only facilitates Al2O3 nucleation and growth, but also forms Ti-O-Al ion-covalent bonds with Al2O3, making the bond between the intermediate transition layer and the wear-resistant capping layer stronger and tougher; the toughness and hardness of the intermediate Ti(CN) component are between TiC and TiN, so that the toughness of the entire intermediate transition layer can be smoothly transitioned; and the C / N ratio in the intermediate transition layer of this invention is continuously changing, so that Ti(CN) exhibits good thermodynamic stability and mechanical properties, providing sufficient support for the upper structure, and further improving the temperature resistance, wear resistance and service life of the extrusion die.

[0039] 3) This invention is the first to incorporate a TiN-based spiked protrusion structure on the intermediate transition layer. This not only facilitates the adhesion of the wear-resistant coating, but the TiN component also possesses excellent toughness and strength, enabling it to form a three-dimensional mechanical interlocking mosaic effect with the subsequently deposited wear-resistant coating. This effect counteracts interfacial shear stress and further improves the wear resistance and service life of the extrusion die. Furthermore, this invention further limits the height of the spikes to no more than 3 μm and the aspect ratio to ≤2:1, preferably ≤1.5. This balances the spike structure between strength and stability, avoiding the problem of high spikes being prone to breakage and low spikes having insufficient anchoring force, thus ensuring mechanical interlocking strength and structural stability. It also facilitates the deposition and filling of Al2O3 into the spike gaps, allowing the wear-resistant coating to overlap and cover the spikes, thereby improving the interfacial bonding strength between the intermediate transition layer and the wear-resistant coating. This helps to cope with the extrusion stress of the thin-walled profile in the channel and avoids the risk of coating peeling and failure.

[0040] 4) The extrusion die body of the present invention is made of steel with a low carbon content (0.05-0.5wt%, preferably 0.05-0.25wt%), which provides an adhesion base for the transition layer and is conducive to controlling the formation of TiC at the interface of the transition layer; and the carbon-nitrogen ratio in the intermediate transition layer of the present invention is controlled within the range of 0 < C / N < 1 (preferably 0 < C / N < 0.5), so that the coating achieves a balance between hardness and toughness, improves the crack resistance of the coating, and forms a strong and flexible transition support system, effectively connecting the wear-resistant coating and the die body into a stable whole, thereby effectively relieving interface stress and extending the die life.

[0041] 5) The preparation method of this invention achieves a continuous gradual change in the composition of the intermediate transition layer from TiC to Ti(CN) to TiN by precisely controlling the gas flow rate and deposition time, thereby realizing the transition from the metallic bonds of the matrix to the covalent bonds of the ceramic. Furthermore, this invention induces the generation of TiN spikes on the surface of the intermediate transition layer by combining high-energy ion bombardment and bias voltage induction. By controlling the deposition parameters of the wear-resistant coating in segments, Al2O3 crystal nuclei are first uniformly generated on the surface of the TiN spikes, and then the TiN spike gaps are filled by conformal growth and tightly overlapped on the intermediate transition layer, thereby improving the density, continuity and integrity of the coating.

[0042] 6) In this invention, the intermediate transition layer is deposited in stages, and the flow rates of CH4 and N2 are independently and in reverse controlled to continuously adjust the C / N ratio, ensuring that the deposited intermediate transition layer achieves the desired structure and function. Specifically, in the first stage, the CH4 flow rate is slowly increased at a rate of 5 SCCM, allowing the titanium source in TiCl4 to preferentially combine with the C released from the substrate surface at high temperatures, improving the adhesion between the coating and the substrate. Furthermore, the slow increase in the externally input CH4 flow rate helps form a dense TiC layer on the substrate surface, effectively isolating the substrate from subsequent decarburization attacks by the high CH4 and H2 atmosphere, protecting the strength and hardness of the substrate. The first stage is completed within 20 minutes, ensuring that the deposited TiC layer thickness is appropriate (approximately several hundred nanometers), sufficient for strong interfacial bonding without becoming brittle due to excessive carbon content. In the second stage, the CH4 flow rate was linearly reduced from 40–60 SCCM to 0 SCCM within 100 min at a rate of 0.6 SCCM, while the N2 flow rate was linearly increased from 0 SCCM to 60–80 SCCM within 100 min at a rate of 0.6–0.8 SCCM. This achieved a continuous C / N gradient change and provided sufficient deposition time for the reaction deposits to be Ti(CxNy) phases (x+y=1) corresponding to the gas ratio at that time. This ensured that the final deposits formed a true gradient with continuous compositional changes, rather than a simple stacked structure of three thin layers of "TiC / Ti(CN) / TiN". This ensured that the intermediate transition layer had high bonding capacity and effectively reduced the stress at each interface.

[0043] In summary, the intermediate transition layer designed in this invention effectively alleviates interfacial stress. During the initial deposition phase, carbon diffused into the substrate and a low-concentration atmosphere provide an environment where carbon reacts with TiCl4 to form a dense TiC layer on the substrate surface. This increases the bonding between the deposited film and the extrusion die body, and protects the strength and hardness of the substrate. By independently and precisely controlling the flow rates of CH4 and N2 gases and the deposition time, the intermediate transition layer achieves a continuous gradient from TiC to Ti(CN) to TiN, providing a good transition effect. The TiN spike structure generated on the surface of the intermediate transition layer guides the subsequent deposition of the wear-resistant coating layer to fill the TiN spike structure, forming a three-dimensional mechanical interlocking effect and improving the shear resistance of the wear-resistant layer. Furthermore, the intermediate transition layer designed in this invention facilitates the deposition and bonding of the wear-resistant coating layer, improving the density and integrity of the entire wear-resistant coating, significantly reducing the risk of peeling off the wear-resistant coating under heavy loads, and enabling the extrusion die to adapt to the extrusion of thin-walled, porous profiles. This invention has good prospects for promotion and application value. Attached Figure Description

[0044] Figure 1 This is a schematic cross-sectional view of the wear-resistant coating structure on the surface of the extrusion die of the present invention;

[0045] Figure 2This is a physical diagram of the extrusion die body structure of the present invention;

[0046] Figure 3 A cross-sectional micrograph of the wear-resistant layer of the extrusion die prepared in Example 1 of this invention;

[0047] Figure 4 These are sample points from the cross-sectional elemental distribution detection map of the wear-resistant layer of the extrusion die prepared in Example 1 of this invention;

[0048] Figure 5 This is a cross-sectional microstructure photograph of the wear-resistant layer of the extrusion die prepared in Comparative Example 4 of the present invention;

[0049] Figure 6 This is a cross-sectional microstructure photograph of the extrusion die matrix prepared in Example 1 of the present invention;

[0050] Figure 7 The results of microscopic examination of the banded structure of the extrusion die matrix prepared in Example 1 of this invention;

[0051] Figure 8 The results of microscopic examination of the spheroidized structure of the extrusion die matrix prepared in Example 1 of this invention;

[0052] Figure 9 The results of microscopic detection of non-metallic inclusions in the extrusion die matrix prepared in Example 1 of this invention;

[0053] Figure 10 This is a schematic diagram of the cross-section of the extruded thin-walled porous aluminum flat tube profile, which is an example of the effect of the present invention (Example 2).

[0054] Figure 11 Example 2 shows a comparison between the wear-resistant coating of the present invention and the coating of comparative product 4 after continuous extrusion for 48 hours.

[0055] Figure 12 Example 2 shows a comparison of the longitudinal sections of the mold of the present invention and the mold of the comparative product 4 after continuous extrusion for 48 hours. Detailed Implementation

[0056] To address the problems of insufficient bonding between the wear-resistant layer and the extrusion die body in existing CVD-deposited materials, high interfacial stress between the coating and the substrate and between coatings, lack of overall integrity and density of the film, and easy peeling of the wear-resistant coating on the die under heavy loads of thin-walled porous profile extrusion, this invention proposes a wear-resistant coating for the surface of extrusion dies, its preparation method and application.

[0057] The wear-resistant coating of this invention includes an intermediate transition layer and a wear-resistant cover layer, wherein the intermediate transition layer is located between the wear-resistant cover layer and the extrusion die body. The extrusion die body is made of heat-resistant tool steel, and the carbon content in the extrusion die body, which serves as the substrate for the wear-resistant coating, is controlled to be 0.05–0.5 wt%, preferably 0.05–0.25 wt%. This is not only to facilitate control of the carbon content of the intermediate transition layer and improve the bonding force between the substrate and the intermediate transition layer, but also to improve the toughness of the substrate at high temperatures, providing a solid inherent foundation for the preparation of a high-quality wear-resistant coating.

[0058] It should be noted that DIN 1.2888 steel (C: 0.17-0.22%) exhibits excellent high-temperature performance, enabling long-term stable operation within a temperature range of 700-800℃. Furthermore, its austenitizing temperature is between 1100-1150℃, which is well-suited to the deposition temperature of this invention, resulting in a superior coating structure while maintaining the substrate's excellent hardness and deformation resistance. Therefore, it is the chosen substrate material. Of course, other durable, heat-resistant, and high-temperature-resistant low-carbon steel materials can also be used as the substrate for the wear-resistant coating of this invention, such as H13 (C: 0.38-0.42%). The key is to select an appropriate deposition temperature (e.g., controlled at 850℃) during the wear-resistant layer deposition process, and to choose suitable quenching and tempering temperatures during the recovery heat treatment stage, so that the substrate recovers its performance after the wear-resistant coating is deposited.

[0059] The intermediate transition layer in the wear-resistant coating of this invention is composed of TiC, Ti(CN), and TiN, which are gradually distributed from the inside out. Figure 1 As shown, the interface deposition composition between the intermediate transition layer and the mold body is TiC. As the distance from the mold body increases, the C content in the deposition layer gradually decreases, while the N content gradually increases, resulting in a smooth transition from carbon-rich Ti(CN) to nitrogen-rich Ti(CN). Then, further away from the mold body, the C content gradually decreases to 0, and the deposit becomes pure TiN. The advantages of this design are as follows:

[0060] (1) In this invention, the carbon in the innermost TiC component of the intermediate transition layer originates from the extrusion die body. That is, Ti forms Ti-C with the C on the surface of the extrusion die body. The Ti-C bond is a typical covalent bond with higher bond energy and stability (compared to the Ti-CN bond), which effectively enhances the mechanical interlocking force between the coating and the substrate and improves the bonding strength between the transition layer and the substrate. At the same time, by controlling the deposition parameters, the TiC in this invention is an extremely thin layer (about several hundred nanometers) and is very dense, with more stable performance. It effectively isolates the substrate from the decarburization attack of the high CH4 and H2 atmosphere during the subsequent deposition process, thereby protecting the strength and hardness of the substrate.

[0061] (2) The intermediate transition layer of the present invention is Ti(CN) with a continuous gradient change in carbon-nitrogen ratio (C / N) in the middle. This makes the transition layer composition deposited in the present invention a true gradient transition layer with a continuous gradient change from TiC to Ti(CN) to TiN, rather than a simple superposition of three thin layers of "TiC / Ti(CN) / TiN". This is the fundamental guarantee that the transition layer of the present invention can effectively eliminate the interlayer stress. It not only alleviates the interlayer stress between the capping layer and the substrate and achieves a better connection effect, but also makes there almost no interlayer stress inside it, so that the entire transition layer forms a good support transition system, and the toughness of the entire intermediate transition layer can be smoothly transitioned, and can provide good support for the upper structure, greatly improving the stability and integrity of the coating.

[0062] (3) The outermost intermediate transition layer of the present invention is composed of TiN, whose coefficient of thermal expansion (CTE) is closer to that of the Al2O3 wear-resistant coating layer, which can effectively reduce interfacial stress. Moreover, the spikes formed on the surface of TiN can not only form a three-dimensional mechanical interlocking stereo-embedded effect with the subsequently deposited Al2O3 wear-resistant coating layer, but also ensure that the spikes formed have good toughness. At the same time, in the initial stage of coating layer deposition, TiN can react with oxygen source to generate TiO2, which is not only conducive to Al2O3 nucleation and growth, but also can form Ti-O-Al ion-covalent bonds with Al2O3, making the combination of intermediate transition layer and wear-resistant coating layer stronger and tougher, effectively resisting interfacial shear stress, and further improving the wear resistance and service life of the coating.

[0063] (4) The C distribution trend in the intermediate transition layer of the present invention is that it first increases and then decreases from the matrix outwards, while the N distribution trend is that it starts to enter and gradually increases from the point when the carbon content begins to decrease. The total carbon-nitrogen ratio of the entire transition layer is controlled at 0 < C / N < 1, preferably at 0 < C / N < 0.5, so that the intermediate transition layer forms a strong and flexible transition support system, improves the crack resistance of the coating, effectively connects the wear-resistant coating with the mold body into a stable whole, and achieves the effects of relieving interface stress, reducing the risk of coating peeling, and extending the mold life.

[0064] In addition, this invention also provides a matching preparation method for achieving the above-mentioned wear-resistant coating. First, to ensure good bonding between the substrate and the coating, the extrusion die body is preheated and activated. This involves pre-treating the extrusion die body to remove oil contaminants, then placing it in a CVD furnace for preliminary preheating and reduction. Next, the temperature is increased and plasma is activated for sputter cleaning, activating its surface in preparation for deposition. Specifically:

[0065] 1-1) Load the pre-treated extrusion mold body into the CVD furnace, evacuate to below 5.0×10-3Pa, and fill with H2 or H2 / Ar mixed gas until the furnace pressure reaches 100-150Pa. Then evacuate and fill with gas again to repressurize. Repeat this process 2-3 times.

[0066] 1-2) After the last vacuuming, H2 is introduced to make the pressure inside the furnace reach 1.5-3 kPa. Then, the furnace temperature is raised to 500-600℃ at a rate of 10℃ / min and held for 30-120 min to preheat and reduce the extrusion die body.

[0067] 1-3) Start the radio frequency plasma source with a power of 300-500W and apply a bias voltage of -350-450V. Continue to raise the temperature to 750-850℃ at a rate of 10℃ / min and hold for 15-30min. Sputter clean and activate the surface of the extrusion die body in preparation for the deposition of the intermediate transition layer.

[0068] Because the intermediate transition layer designed in this invention has a true gradient of continuous change from the inside to the outside of TiC→Ti(CN)→TiN, to achieve this effect, this invention innovatively performs a three-stage gradient deposition of the transition layer. During the deposition process, the flow rates of CH4 and N2 are independently and inversely controlled to achieve continuous adjustment of the C / N ratio, ensuring that the deposited intermediate transition layer composition reaches the desired structure and function. During the deposition process of the intermediate transition layer, the temperature is controlled at 800–1050℃, the pressure at 8–10 kPa, and TiCl4 and H2 are constantly introduced; wherein, H2 is used as the carrier gas for TiCl4, with an evaporation temperature of 35–45℃ and a flow rate controlled at 100–300 SCCM; H2 is used as both the carrier gas and the functional gas, with a flow rate controlled at 2000–3000 SCCM. The independent and inverse control of the CH4 and N2 flow rates for staged deposition is as follows:

[0069] 2-1) First stage: The flow rate of CH4 is slowly increased from 2 to 3 SCCM to 40 to 60 SCCM, so that the titanium source in TiCl4 preferentially combines with the C released from the substrate surface at high temperature to form TiC; at the same time, the slow increase of the external CH4 flow rate is conducive to the formation of a dense TiC layer on the substrate surface; the deposition time of this stage is controlled to be completed within 20 minutes to ensure that the thickness of the deposited TiC layer does not exceed 1 micrometer (about several hundred nanometers), so that it can play a strong interfacial bonding role without being brittle and broken due to excessive carbon content, which would affect subsequent use.

[0070] 2-2) The second stage: The CH4 flow rate is controlled at a rate of 0.6 SCCM to linearly decrease from 40-60 SCCM to 0 SCCM within 100 min; at the same time, the N2 flow rate is controlled at a rate of 0.6-0.8 SCCM to linearly increase from 0 SCCM to 60-80 SCCM within 100 min; thus achieving a continuous gradient deposition of C / N, and having sufficient deposition time so that the reaction deposits are all Ti(CxNy) phases (x+y=1) corresponding to the gas ratio at that time, forming a continuous gradient structure of TiC→Ti(CN)→TiN. This is the key to ensuring that the intermediate transition layer can effectively reduce interfacial stress and improve the interfacial adhesion of the coating.

[0071] 2-3) Third stage: A combination of radio frequency plasma and pressure control is used to generate unevenly distributed TiN spikes on the surface of the intermediate transition layer, and the spike morphology is controlled by adjusting the pressure and bias voltage. Specifically: after the N2 flow rate reaches 60-80 SCCM, the radio frequency plasma is started with a power of 350-4500W and a bias voltage of 150--250V is applied and maintained for 5-10 min to deposit TiN. Then, the pressure is controlled to 5-6 kPa, the radio frequency power is increased to 550-650W, and a bias voltage of -350-380V is applied for deposition for 10-15 min to induce the formation of spike structures. Subsequently, the pressure is adjusted to 8-10 kPa, the bias voltage is reduced to -300-330V, and deposition is carried out for 5-15 min. It should be explained that the spikes formed in this way are not uniform, but staggered. However, the overall height of the spikes does not exceed 3μm, preferably 0.5 to 2.5μm. The aspect ratio of the spikes is ≤2:1, preferably ≤1.5:1, so that the thickness of the part where the wear-resistant coating layer meets the intermediate transition layer is not less than 1μm. This achieves a balance between strength and stability, avoids the problem of high spikes being prone to breakage and low spikes having insufficient anchoring force, ensures the mechanical interlocking strength and structural stability formed with the subsequently deposited wear-resistant coating layer, further improves the coating's performance in coping with interfacial shear stress, and improves the wear resistance and service life of the extrusion die.

[0072] To ensure that the Al2O3 wear-resistant coating can fully fill the gaps between the TiN spikes and tightly overlap and embed on the intermediate transition layer, this invention also optimizes the Al2O3 deposition method. Specifically:

[0073] 3-1) Pretreatment of deposition surface: After the intermediate transition layer is deposited, the TiCl4, N2 and H2 gas flow is turned off, the furnace temperature is controlled at 800-1050℃, and then Ar gas is introduced at a flow rate of 450-550 SCCM. Radio frequency plasma is started at a power of 300-500W, and sputter cleaning is performed for 5-10 minutes to activate the TiN spike surface.

[0074] 3-2) Initial nucleation stage: Turn off the radio frequency plasma, maintain the temperature at 800-1050℃, control the pressure at 30-50Pa, introduce aluminum source and oxygen source gas, and the molar flow ratio of aluminum source and oxygen source is 1:15-20, deposit for 15-30min, and uniformly generate Al2O3 crystal nuclei on the surface of TiN spikes.

[0075] 3-3) Main growth stage: The temperature is maintained at 800-1050℃, the furnace pressure is increased to 100-200Pa, the molar flow ratio of aluminum source and oxygen source gas is adjusted to 1:10-15, and deposition is carried out for 2-4 hours to allow Al2O3 to grow in a shape-preserving manner to fill the gaps between TiN spikes and evenly cover the intermediate transition layer.

[0076] It should be noted that the present invention uses Al2O3 as the component of the wear-resistant coating layer because it not only has good wear resistance, but more importantly, it has good thermal insulation properties. Al2O3 has extremely low thermal conductivity (approximately 7-30 W / mK), and the coating structure it forms can effectively block heat conduction. This low thermal conductivity forms an effective thermal barrier between the mold and the high-temperature aluminum billet, significantly reducing the temperature of the mold substrate, increasing the hardness of the substrate and the service life of the coating, and ensuring that both the coating itself and the mold substrate can work in the best condition, thereby maximizing the life of the extrusion mold.

[0077] Furthermore, after the coating of this invention is deposited, a recovery heat treatment is required to ensure the performance of the mold substrate. Specifically, the recovery heat treatment includes:

[0078] 4-1) Homogenization and Austenitization: After the wear-resistant coating is deposited, the aluminum and oxygen sources are shut off, the furnace temperature is controlled at 450-550℃, pure Ar gas is introduced at a flow rate of 500-800 SCCM, and the positive pressure inside the furnace is maintained at 1-5 kPa for 10-15 min to ensure uniform mold temperature. Subsequently, the furnace temperature is reheated to 1020-1200℃ at a rate of 8-10℃ / min (the specific temperature is selected and controlled according to the austenite transformation temperature of the matrix material) and held for 30-40 min to allow the matrix structure to completely and uniformly transform into austenite, preparing for subsequent quenching. As mentioned earlier, different steel matrices require different quenching and tempering temperatures, mainly because their austenitizing temperatures differ. For example, using DIN 1.2888 material as the matrix, the austenitizing temperature needs to be selected as 1100–1200℃; while using H13 as the matrix, the austenitizing temperature needs to be selected as 1020–1050℃.

[0079] 4-2) Gas quenching: After the heat preservation is completed, turn off the Ar gas source, quickly fill the furnace with N2 to a pressure of 5-10 bar, turn off the heater, start the high-speed airflow circulation system in the furnace, and force gas cooling of the mold; control the cooling rate to be not less than 25℃ / min, preferably 30-40℃ / min, and continue cooling until the mold temperature is below 40℃;

[0080] 4-3) High-temperature tempering: Transfer the gas-quenched mold to a vacuum tempering furnace and evacuate it to a vacuum level of 1×10⁻⁶. -2 Below Pa, tempering is performed according to the set procedure: heat to 580-620℃ at a rate of ≤5℃ / min, hold for 2-3 hours, and then cool to room temperature at a rate of ≤5℃ / min. The high-temperature tempering cycle should be repeated at least 2-3 times to ensure the recovery of the matrix properties. After the final cooling to room temperature, Ar or N2 is introduced to atmospheric pressure, and the furnace is removed.

[0081] The thickness of the intermediate transition layer of the wear-resistant coating of the present invention is preferably 4-8 μm, more preferably 6-7 μm; the thickness of the wear-resistant capping layer is preferably 2-6 μm, more preferably 3-4 μm; the thickness of the overlapping portion between the transition layer and the capping layer is not less than 1 μm (controlled by the morphology and height of the TiN spikes), ensuring sufficient mechanical interlocking force and interfacial bonding force between the capping layer and the transition layer. Therefore, the total thickness of the wear-resistant coating of the present invention is approximately 5-13 μm, preferably 8-11 μm, the thickness of the portion where the wear-resistant capping layer and the intermediate transition layer meet is not less than 0.5 μm, preferably not less than 1 μm, and the interfacial bonding force between the intermediate transition layer and the substrate and the wear-resistant capping layer is ≥90N, preferably ≥100N; it can be used as a coating for thin-walled, porous profile extrusion dies, and has good promotion prospects and application value.

[0082] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with embodiments. All pharmaceuticals involved in the embodiments are commercially available, and those without a purity label are industrial or reagent grade. Specific embodiments are as follows:

[0083] Example 1

[0084] The extrusion die in this embodiment, such as Figure 2As shown, the die consists of an upper die and a lower die, used for extruding thin-walled, porous microchannel aluminum flat tube profiles (outer wall thickness approximately 0.20 mm, middle partition wall thickness approximately 0.18 mm). Due to the extremely thin wall thickness of the produced profiles and the very high extrusion pressure and frictional shear forces during the extrusion process, ordinary extrusion dies are difficult to adapt to the extrusion conditions. In this embodiment, the extrusion die body is made of DIN 1.2888 steel, which serves as the substrate on which a wear-resistant layer is deposited. The deposition equipment used in this embodiment is a customized integrated multi-functional thermochemical vapor deposition (PECVD) system equipped with plasma-enhanced (PE) functionality (purchased from Shanghai Dezhuxin Technology Co., Ltd.). The specific preparation method of the wear-resistant layer in this embodiment is as follows:

[0085] S1: Preheating and Activation: The extrusion die body is pretreated by sequentially ultrasonically cleaning with acetone and anhydrous ethanol for 15 minutes each to thoroughly remove surface oil and impurities. After oil removal, it is dried with high-pressure nitrogen and immediately placed in the CVD equipment sample chamber for preheating and activation. Details are as follows:

[0086] S1-1: Place the pre-treated extrusion die body into the homogenization zone of the CVD furnace and evacuate to 1.0×10⁻⁶. -3 Pa, H2 was introduced until the furnace pressure reached 120 Pa, then a vacuum was drawn again to 1.0 × 10 Pa. -3 Pa, then charge H2 again until the furnace pressure reaches 120 Pa, repeat this process three times;

[0087] S1-2: After the final vacuuming, pure H2 (purity above 99.999%) is introduced to bring the furnace pressure to 2 kPa. Then the heater is turned on, and the furnace temperature is raised to 600℃ at a rate of 10℃ / min. The temperature is held for 30 minutes to preheat and reduce the extrusion die body.

[0088] S1-3: Start the radio frequency plasma source with a power of 300W and apply a bias voltage of -400V. Continue to raise the temperature to 800℃ at a rate of 10℃ / min, hold for 15min, and perform sputter cleaning on the surface of the extrusion die body to obtain a highly activated clean surface.

[0089] S2: Deposition of the intermediate transition layer: The plasma was turned off, and the deposition process parameters were adjusted to a temperature of 1020℃ and a pressure of 8kPa. TiCl4 and H2 were introduced in two constant streams; one stream introduced TiCl4-H2, i.e., H2 as the carrier gas (evaporation temperature of 45℃), with the TiCl4-H2 carrier gas flow rate controlled at 300 SCCM; the other stream introduced pure H2 with a flow rate controlled at 2000 SCCM. While maintaining stable TiCl4 and H2 flow rates, CH4 and N2 were introduced, and the CH4 and N2 flow rates were independently and in reverse phases to continuously and gradually change the C / N ratio in the deposition layer, resulting in a gradient deposition of TiC→Ti(CN)→TiN composition. During the later stages of TiN deposition, cooling was used to induce spike formation. Details are as follows:

[0090] S2-1: First stage: CH4 is introduced and the CH4 flow rate is controlled to increase linearly from 0 SCCM to 60 SCCM within 20 minutes at a rate of 3 SCCM, so as to deposit a thin layer of TiC composition (about 500 nm thick) on the extrusion die body.

[0091] S2-2: Second Stage: The CH4 flow rate was linearly decreased from 60 SCCM to 0 SCCM over 100 min at a rate of 0.6 SCCM, while the N2 flow rate was linearly increased from 0 SCCM to 80 SCCM over 100 min at a rate of 0.8 SCCM. This caused a continuous and gradual change in the C / N ratio of the sedimentary composition, resulting in a gradual decrease in carbon (C) content and a gradual increase in nitrogen (N) content in the sedimentary layer. The sedimentary composition transitioned from carbon-rich Ti(C) to a more refined composition. x N 1-x The sediment composition smoothly transitions from TiC to Nitrogen-rich Ti(CxN1−x) (where x is close to 1) to Nitrogen-rich Ti(CxN1−x) (where x is close to 0). During this stage, the CH4 flow rate decreases linearly while the N2 flow rate increases linearly, and the sediment composition transitions from TiC to TiN; the reaction formula is: TiCl4 + CH4 + N2 → Ti(CxN1−x) + 4HCl; as the CH4 flow rate decreases and the N2 flow rate increases, the value of x gradually decreases, ranging from 1 to 0, and the sediment composition transitions from carbon-rich to nitrogen-rich.

[0092] S2-3: Third stage: After the N2 flow rate reaches 80 SCCM, the radio frequency plasma is started with a power of 400W and a bias voltage of -200V is applied and held for 10 min to deposit a TiN composition; then the pressure is reduced to 5 kPa, the radio frequency power is increased to 600W, and a bias voltage of -350V is applied for deposition for 15 min to induce the formation of spike structures; then the pressure is adjusted to 8 kPa, the bias voltage is reduced to -300V, and deposition is carried out for 10 min to control the spike morphology (aspect ratio).

[0093] S3: Deposition of Wear-Resistant Coating: After the intermediate transition layer is deposited, the temperature is adjusted, the gas is switched, and a wear-resistant coating is deposited on the intermediate transition layer, filling the spiked gaps and tightly embedding it onto the intermediate transition layer. Details are as follows:

[0094] S3-1: Pretreatment of the deposition surface: After the intermediate transition layer is deposited, the TiCl4, N2 and H2 gas flow is turned off, the furnace temperature is kept at 1020℃, Ar gas is introduced at a flow rate of 500 SCCM, radio frequency plasma is started at a power of 400W, sputter cleaning is performed for 5 minutes to activate the TiN spike surface.

[0095] S3-2: Initial nucleation stage: The radio frequency plasma was turned off, the temperature was maintained at 1020℃, and the pressure was controlled at 50Pa. An aluminum source and an oxygen source were introduced. The aluminum source was TMA, and the oxygen source was N2O, both carried by Ar carrier gas bubbling. The molar flow ratio of the aluminum source to the oxygen source was approximately 1:15. After 20 minutes of deposition, Al2O3 crystal nuclei were uniformly generated on the surface of the TiN spikes.

[0096] S3-3: Main growth stage: The temperature is maintained at 1020℃, the furnace pressure is increased to 200Pa, the molar flow ratio of aluminum source and oxygen source gas is adjusted to about 1:20, and deposition is carried out for 3 hours to allow Al2O3 to grow in a conformal manner to fill the gaps between TiN spikes and overlap and cover the intermediate transition layer, at which point recovery heat treatment can be performed.

[0097] S4: Restorative Heat Treatment: After the wear-resistant coating is deposited, it is quenched, then cooled to a safe temperature under a protective atmosphere, and then transferred to a heat treatment furnace for high-temperature tempering to restore the substrate properties, improve the coating adhesion, and reduce the internal stress of the coating; specifically:

[0098] S4-1: Homogenization and Austenitization: After the Al2O3 wear-resistant coating is deposited, the aluminum and oxygen sources are shut off, the furnace temperature is controlled at 1020℃, the Ar gas flow rate is maintained at 500 SCCM, and the positive pressure inside the furnace is maintained at 5 kPa for 10 min to ensure uniform mold temperature. Subsequently, the furnace temperature is reheated to 1150℃ at a rate of 10℃ / min and held for 40 min to allow the matrix structure to completely and uniformly transform into austenite, preparing for subsequent quenching.

[0099] S4-2: Gas quenching: After the heat preservation is completed, turn off the Ar gas flow, quickly fill the furnace with N2 to a pressure of 5 bar, turn off the heater, start the high-speed airflow circulation system in the furnace, and force gas cooling of the mold; control the cooling rate at 30℃ / min, and continue cooling until the mold temperature is about 30℃;

[0100] S4-3: High-temperature tempering: Transfer the gas-quenched mold to a vacuum tempering furnace, evacuate to below 0.01 Pa, and perform tempering according to the set program: heat to 580℃ at a rate of ≤5℃ / min, hold for 3 hours, and then cool to room temperature at a cooling rate of ≤5℃ / min to restore the matrix properties. Repeat the high-temperature tempering operation 3 times; after the last cooling to room temperature, fill with N2 to atmospheric pressure, remove from the furnace, and you will get the finished extrusion mold 1 with a wear-resistant layer (referred to as invention product 1).

[0101] The cross-sectional morphology of the coating was observed using a Zeiss EVO-18 scanning electron microscope (SEM), such as... Figure 3 As shown. From Figure 3 Microscopic images show that the inner and outer coating interfaces of the wear-resistant coating are irregularly interwoven. The thickness of the surface Al2O3 wear-resistant coating layer is 3.30±0.61μm, and the thickness of the intermediate transition layer is approximately 6.80±0.71μm. The height of the spikes on the surface is mainly distributed in the range of 0.5 to 1.5μm, and the aspect ratio is distributed between 1:1.5 and 1:2. Furthermore, from... Figure 3 It can be seen that the interface between the intermediate transition layer and the substrate of the product of the present invention is smooth and there is no decarburization phenomenon; at the same time, the intermediate transition layer and the Al2O3 wear-resistant coating layer are tightly interlocked, and TiN spikes are interlocked and covered on the spikes.

[0102] The elemental distribution on the coating cross-section was detected using an Energy 350 (INCA) X-ray energy dispersive spectrometer (EDS). The distribution of the detected spectral points is shown in the image. Figure 4 As shown in Table 1, the elemental distribution detection results on the coating cross-section are as follows.

[0103] Table 1. Elemental distribution detection results on the cross-section of the coating of the present invention

[0104]

[0105] As can be seen from the test results in Table 1, the C element distribution in the layer increases first and then decreases from bottom to top, while the N element distribution gradually increases from the C peak in spectrum 8, which is consistent with the control of carbon and nitrogen gas sources. Spectrum 4 is the overlapping area of ​​TiN spikes and Al2O3 capping layer, and the sampling point is at the junction of TiN spikes and Al2O3 wear-resistant capping layer. The test results are consistent with the corresponding deposition composition. From the above test results, it can be clearly seen that the interface between the intermediate transition layer and the mold body of the present invention is TiC. As it moves away from the mold body, the C content in the deposition layer gradually decreases and the N content gradually increases, and its composition smoothly transitions from carbon-rich Ti(CN) to nitrogen-rich Ti(CN). Then, as it continues to move away from the mold body, the deposition becomes pure TiN. This proves that the intermediate transition layer of the present invention is a true gradient transition layer with a continuous and gradual change from TiC→Ti(CN)→TiN.

[0106] Example 2

[0107] The difference from Example 1 is that the substrate is made of H13 steel. Due to its slightly weaker temperature resistance, the temperature control during the deposition of the transition layer is lower. Specifically, the deposition temperature of the intermediate transition layer is controlled at 880℃ throughout; the deposition temperature of the Al2O3 wear-resistant layer is controlled at 900℃ throughout; the quenching temperature is controlled at 1030℃ (austenitizing temperature); the tempering temperature is controlled at 580℃, and the remaining parameters are the same as in Example 1. The resulting extrusion die is designated as Invention Product 2.

[0108] Comparative Example 1: Matrix content higher than 0.5 wt%

[0109] The difference from Example 1 is that the substrate is made of 5Cr4Mo2W2SiV steel (carbon content: 0.55wt%). The deposition temperature of the intermediate transition layer is controlled at 880℃ throughout the process; the deposition temperature of the Al2O3 wear-resistant layer is controlled at 900℃ throughout the process; the quenching temperature is controlled at 1030℃ (austenitizing temperature); the tempering temperature is controlled at 580℃; the remaining parameters are the same as in Example 1, and the obtained comparative mold 1 is referred to as comparative product 1.

[0110] Comparative Example 2: The transition layer composition is gradually varied, but without spike structures.

[0111] This embodiment also describes the preparation of a wear-resistant coating for the surface of an extrusion die. Except for the composition and structure of the intermediate transition layer, which differs from Example 1, the composition of the substrate and the wear-resistant capping layer are the same as in Example 1. Specifically, the substrate is made of 1.2888 steel; the wear-resistant capping layer is an Al2O3 ceramic, and the aluminum source and oxygen source are TMA and N2O, respectively. The intermediate transition layer of this wear-resistant coating also has a TiC→Ti(CN)→TiN continuous gradient structure, but without the spike structure. The entire preparation process is the same as in Example 1, except that the intermediate transition layer deposited in step S2 differs from that in Example 1. Specifically, the preparation method of the wear-resistant coating in this embodiment differs from Example 1 only in the third stage of step S2, namely, in the third stage of step S2-3: after the N2 flow rate reaches 80 SCCM, it is maintained for 30 min to deposit a TiN layer without inducing the formation of spike structures.

[0112] Step S3 is performed directly on the deposited TiN composition, and the deposition process is the same as in Example 1. Then, step S4 is performed to obtain the comparative mold 2, which is referred to as the comparative product 2.

[0113] Comparative Example 3: The transition layer is a simple stack of three thin layers, "TiC / Ti(CN) / TiN", with a spiked structure.

[0114] This embodiment also describes the preparation of a wear-resistant coating for the surface of an extrusion die. Except for the composition and structure of the intermediate transition layer, which differs from Example 1, the composition of the substrate and the wear-resistant capping layer are the same as in Example 1. Specifically, the substrate is made of 1.2888 steel; the wear-resistant capping layer is composed of Al2O3 ceramic, and the aluminum source and oxygen source are TMA and N2O, respectively. The intermediate transition layer of this wear-resistant coating is also composed of TiC, Ti(CN), and TiN, but it is not a continuous gradient structure. Instead, it is a structure of three thin layers stacked together: TiC / Ti(CN) / TiN, and its surface also has TiN spike structures. The entire preparation process is the same as in Example 1, except that the transition layer deposited in step S2 differs from that in Example 1.

[0115] In this embodiment, the method for preparing the wear-resistant coating, step S2, the deposition of the transition layer, is carried out as follows: The plasma is turned off, and the deposition process parameters are adjusted: temperature 1020℃, pressure 8kPa. TiCl4 and H2 are introduced in two constant streams; one stream introduces TiCl4-H2, i.e., H2 as the carrier gas (evaporation temperature 45℃), with the TiCl4-H2 carrier gas flow rate controlled at 300 SCCM; the other stream introduces pure H2, with the flow rate controlled at 2000 SCCM. While maintaining stable TiCl4 and H2 flow rates, CH4 and N2 are introduced, and the CH4 and N2 flow rates are independently controlled. TiC, Ti(CN), and TiN components are deposited sequentially, and spike formation is induced in the later stages of TiN component deposition. Details are as follows:

[0116] S2-1: First stage: First, CH4 is introduced at a flow rate of 60 SCCM and deposited for 20 min to deposit a thin TiC layer on the extrusion die body;

[0117] S2-2: Second stage: Maintain CH4 flow rate at 60 SCCM, while simultaneously introducing N2 flow rate at 80 SCCM, and deposit for 100 min to deposit a uniform Ti(CN) thin layer;

[0118] S2-3: Third stage: Same as in Example 1, deposit a layer of TiN composition and induce the formation of spike structures.

[0119] Then, steps S3 and S4 are performed to obtain the comparison mold 3, which is denoted as the comparison product 3.

[0120] Comparative Example 4: The transition layer has a uniform Ti(CN) composition with a C / N ratio of 60:40 and no spiked structures.

[0121] This embodiment also describes the preparation of a wear-resistant coating for the surface of an extrusion die. Except for the composition and structure of the intermediate transition layer, the composition of the substrate and the wear-resistant capping layer are the same as in Example 1. Specifically, the substrate is made of 1.2888 steel; the wear-resistant capping layer is an Al2O3 ceramic, and the aluminum source and oxygen source are TMA and N2O, respectively. The intermediate transition layer of this wear-resistant coating has a uniform Ti(CN) composition with a C / N ratio of 60:40. The deposition process is the same as in Example 1 except for step S2. Therefore, the preparation method of the wear-resistant coating in this embodiment is as follows: Step S1 is the same as in Example 1.

[0122] Step S2, the deposition of the transition layer, is carried out as follows: After preheating and activation, the plasma is turned off, and the deposition process parameters are set as follows: temperature 1020℃, pressure 8kPa, and constant flow of TiCl4, H2, TiCl4 and N2; wherein, the introduced TiCl4 is TiCl4-H2, that is, the carrier gas is H2 (evaporation temperature is 45℃), and the TiCl4-H2 carrier gas flow rate is controlled at 300SCCM; there is also a separate channel for pure H2, with the flow rate controlled at 2000SCCM; the flow rate of CH4 is 210SCCM, and the flow rate of N2 is 70SCCM, so that the C / N ratio in the deposition composition is 60:40, and the deposition is carried out for 150min to form a transition layer consisting of Ti(CN) (C / N is 60:40).

[0123] Steps S3 and S4 are performed identically to those in Example 1, and the resulting comparative mold 4 is designated as comparative product 4. The cross-sectional morphology of the coating is observed using a Zeiss EVO-18 field emission scanning electron microscope (SEM), as shown below. Figure 5 As shown.

[0124] Example 1: Performance Testing

[0125] This embodiment tests the interfacial adhesion of the wear-resistant coatings of the inventive products 1-2 prepared in Examples 1-2 and the comparative products 1-4 prepared in Comparative Examples 1-4, as well as the matrix properties of the extrusion dies in Examples 1-2 and Comparative Example 1. Wherein:

[0126] The interfacial adhesion test method for the coating is as follows: The interfacial adhesion of the coating of each product is tested using an MFT-4000 multifunctional surface mechanical property tester. During the test, the coating surface is fixed on the sample stage with the surface facing upward. The scratch loading speed is 50 N / min, the scratch length is 5 mm, and the termination load is 150 N. The critical load value Lc of each product coating is recorded. When the acoustic emission signal suddenly increases and the friction coefficient fluctuates by more than 15%, the coating is judged to be in failure.

[0127] Matrix performance testing includes:

[0128] 1) Metallographic structure inspection: Refer to the standard ASTM E3-11 (R2017), use an OLYMPUS BX53M upright metallographic microscope to inspect the grain size and banded structure;

[0129] 2) Inspection of non-metallic inclusions: Refer to standard ASTM E45-2018, and use an OLYMPUS BX53M upright metallographic microscope for testing.

[0130] 3) Hardness testing: Refer to the standard ASTM E18-20, and use the Aolongxingdi MHRS-150 PLUS digital display Rockwell hardness tester and Aolongxingdi HBS-3000 digital display Brinell hardness tester; each test group consists of 3 samples, and the average value of the results is used.

[0131] 4) Charpy Impact Test: Sample preparation standard: ASTM A370-20, test standard: ASTM E23-18, test instruments: PTM2152-C microcomputer-controlled metal pendulum impact tester, MTS-ZBC2602 impact tester; sampling instructions: 7*10*55mm transverse unnotched impact specimens and 10*10*55mm transverse V-notched (wire cut) impact specimens are taken respectively; 5 specimens are set for each test group, and the average value of the result (J) is taken.

[0132] The experimental results are shown in Table 2 and Figures 6 to 9 As shown.

[0133] Table 2. Test results of wear-resistant layer and matrix properties of each extrusion die

[0134]

[0135] From Table 2 and Figures 6 to 9 The results show that the interfacial bonding force of the wear-resistant coating of the present invention is greater than 90N, with the interfacial bonding force of Example 1 being 105N and Example 2 being 95N, which is superior to the products of Comparative Examples 1 to 4. This indicates that the intermediate transition layer of the present invention does indeed provide a good bonding effect for the coating, significantly improving the bonding between the substrate and the wear-resistant coating. Furthermore, the substrate performance test results of the present invention show that its hardness and impact strength are at the expected levels; in particular, the 1.2888 steel substrate has an annealed hardness of 309HB; a heat-treated Rockwell hardness of 50.9HRC; an impact resistance of 12.8J for notched samples and 401J for unnotched samples; and microstructure examination shows no obvious banded segregation, only a small amount of granular structure in the annealed structure, no non-metallic inclusions, and no coarsening of the structure. This indicates that the substrate after the wear-resistant coating deposition treatment of the present invention still has good mechanical properties and can well adapt to subsequent extrusion conditions.

[0136] Example 2: Application Effect

[0137] The extrusion dies prepared in Examples 1-2 and the comparative dies 1-4 prepared in Comparative Examples 1-4 were used for extruding thin-walled, porous, flat tubular aluminum profiles. Figure 10 As shown, the blank for this microchannel aluminum flat tube profile is AA1100 aluminum alloy, with an outer wall thickness of approximately 0.20 mm and a middle partition wall thickness of approximately 0.18 mm. Each die product was continuously extruded for 48 hours according to the extrusion process parameters shown in Table 3.

[0138] Table 3. Process parameters for extruding microchannel aluminum flat tube profiles using various extrusion dies

[0139]

[0140] The bonding strength between the coating and the die substrate of each extrusion die was tested, and the presence of defects such as blistering, cracking, and peeling in the wear-resistant coating of the extrusion die was observed. The bonding strength testing method was the same as in Example 1. The test and observation results are shown in Table 4 and... Figure 11 and Figure 12 As shown.

[0141] Table 4. Performance changes of microchannel aluminum flat tube profiles after extrusion using various extrusion dies

[0142]

[0143] From Table 4 and Figure 11 and Figure 12 The results show that the wear-resistant coating of the present invention still exhibits good interfacial adhesion after 48 hours of continuous extrusion production. The change in interfacial adhesion is only 10N, and no blistering, cracking or peeling occurs. The products from Comparative Examples 1 to 4 showed significant variations in interfacial bonding strength, with the largest reaching 35 N. All exhibited varying degrees of blistering, cracking, and peeling. Comparative Example 1, with a substrate containing more than 0.5 wt% carbon, showed obvious blistering, cracking, and complete coating peeling, highlighting the crucial importance of substrate selection. Comparative Example 1, with a gradient transition layer composition but no spiked structure, only showed slight blistering and cracking, but its surface layer showed significant peeling, indicating that the TiN spiked structure significantly contributes to the mechanical bonding force of the wear-resistant layer. The transition layer, using a three-layer superposition of "TiC / Ti(CN) / TiN," still showed some blistering and cracking despite the presence of spikes, and also exhibited coating peeling and cracking. The transition layer using only a uniform Ti(CN) composition (C / N 60:40) was essentially scrapped after 48 hours of continuous extrusion production.

[0144] Therefore, summarizing the above results, it can be confirmed that this invention, by designing the intermediate transition layer as a TiC→Ti(CN)→TiN continuous gradient deposition layer, utilizes the reaction of C in the extrusion die body with TiCl4 to form a dense TiC layer on the substrate surface, increasing the bonding between the deposited film and the extrusion die body while protecting the substrate; and through the continuous gradient deposition of TiC→Ti(CN)→TiN, the coefficient of thermal expansion is progressively increased to match the coefficient of thermal expansion of the wear-resistant layer, effectively alleviating interfacial stress; simultaneously, TiN spike structures are induced on the surface of the intermediate transition layer, and the subsequently deposited wear-resistant coating fully fills the spike gaps, forming a strong three-dimensional mechanical interlocking structure. With the combination of multiple methods, the bonding between the wear-resistant coating and the substrate is improved, interlayer stress is reduced, the density and integrity of the entire wear-resistant coating are improved, the risk of peeling off the wear-resistant coating under heavy loads is greatly reduced, the service life of the die is greatly extended, and the extrusion die can adapt to the extrusion of thin-walled, porous profiles, showing good prospects for promotion and application value.

[0145] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered exemplary and not restrictive in all respects. Furthermore, it should be understood that although this specification describes embodiments, it does not encompass only one technical solution. This descriptive method is merely for clarity, and those skilled in the art should consider the specification as a whole. The technical solutions in the embodiments can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A wear-resistant coating for an extrusion die, comprising an intermediate transition layer and a wear-resistant covering layer, wherein the intermediate transition layer is located between the wear-resistant covering layer and the extrusion die body; characterized in that: The intermediate transition layer is composed of TiC, Ti(CN), and TiN, which are gradually distributed from the inside out. Specifically, the deposit at the interface with the extrusion die body is TiC. As the distance from the extrusion die body increases, the C content in the deposit gradually decreases and the N content gradually increases, and the deposit gradually transitions from carbon-rich Ti(CN) to nitrogen-rich Ti(CN). Then, as the distance from the extrusion die body continues, the deposit becomes pure TiN, and a jagged TiN spike protrusion structure is formed on the surface of the intermediate transition layer. The extrusion die body is made of heat-resistant tool steel, and the carbon content of the heat-resistant tool steel is 0.05-0.5 wt%. The thickness of the intermediate transition layer is 4 to 8 μm, and the total carbon-nitrogen ratio in the intermediate transition layer is 0 < C / N < 1. The height of the TiN spikes on its surface does not exceed 3 μm, and the aspect ratio is ≤ 2:

1. The wear-resistant coating is composed of Al2O3 ceramic and has a thickness of 2-6 μm. The wear-resistant coating fully fills the gaps between the TiN spikes on the surface of the intermediate transition layer and is tightly overlapped and embedded on the intermediate transition layer, and the thickness of the overlapping part with the intermediate transition layer is not less than 0.5 μm.

2. A method for preparing the wear-resistant coating according to claim 1, characterized in that: Includes the following steps: S1: Preheating and activation: After pretreatment, the extrusion die body is loaded into the CVD furnace for preliminary preheating and reduction. Then, the temperature is increased and plasma is turned on for sputter cleaning to activate its surface. S2: Deposition of intermediate transition layer: Turn off plasma, adjust deposition process parameters, and constantly introduce TiCl4 and H2. While maintaining stable TiCl4 and H2 flow rates, introduce CH4 and N2, and independently control the CH4 and N2 flow rates in reverse to make the C / N ratio in the deposition layer continuously and gradually change. The TiC→Ti(CN)→TiN composition is deposited in a gradient, and spike formation is induced in the later stage of TiN composition deposition. S3: Deposition of wear-resistant coating layer: After the intermediate transition layer is deposited, adjust the temperature, shut off the TiCl4, N2 and H2 gas flow, and introduce aluminum source and oxygen source gas to deposit the wear-resistant coating layer on the intermediate transition layer. After filling the spike gaps on the intermediate transition layer, it is tightly embedded and covers the intermediate transition layer. S4: Restorative heat treatment: After the wear-resistant coating is deposited, it is cooled to a safe temperature under a protective atmosphere, and then transferred to a heat treatment furnace for tempering to restore the properties of the substrate and improve the adhesion of the coating.

3. The method for preparing the wear-resistant coating according to claim 2, characterized in that: In step S1, the preheating and activation specifically include: S1-1: Load the pretreated extrusion die body into the CVD furnace and evacuate to a vacuum level below 5.0 × 10⁻⁶. -3 Pa, fill the furnace with H2 or H2 / Ar mixed gas until the pressure inside the furnace reaches 100-150 Pa, then evacuate and refill the furnace again, repeating this process 2-3 times; S1-2: After the final vacuuming, H2 is introduced to bring the furnace pressure to 1.5-3 kPa. Then, the furnace temperature is raised to 500-600℃ at a rate of 10℃ / min and held for 30-120 min to preheat and reduce the extrusion die body. S1-3: Start the radio frequency plasma source with a power of 300-500W and apply a bias voltage of -350-450V. Continue to raise the temperature to 750-850℃ at a rate of 10℃ / min and hold for 15-30min to perform sputter cleaning and activation on the surface of the extrusion die body.

4. The method for preparing the wear-resistant coating according to claim 3, characterized in that: In step S2, the deposition temperature of the intermediate transition layer is controlled at 800–1050℃, and the deposition pressure is controlled at 8–10 kPa; the flow rate of TiCl4 is controlled at 100–300 SCCM, and the flow rate of H2 is controlled at 2000–3000 SCCM; gradual deposition is performed by independently and in reverse controlling the flow rates of CH4 and N2; specifically as follows: S2-1: First stage: CH4 is introduced and the CH4 flow rate is controlled to increase linearly from 0 SCCM to 40-60 SCCM within 20 min at a rate of 2-3 SCCM, so as to deposit TiC on the surface of the extrusion die body. S2-2: Second stage: Control the CH4 flow rate, linearly decreasing it from 40-60 SCCM to 0 SCCM at a rate of 0.6 SCCM over 100 min; simultaneously, control the N2 flow rate, linearly increasing it from 0 SCCM to 60-80 SCCM over 100 min at a rate of 0.6-0.8 SCCM; to gradually change the deposition composition from carbon-rich Ti(CN) to nitrogen-rich Ti(CN); S2-3: Third stage: When the CH4 flow rate is 0 SCCM and the N2 flow rate reaches 60-80 SCCM, the radio frequency plasma is started with a power of 350-450 W and a bias voltage of -150--250 V is applied and maintained for 5-10 min to deposit TiN composition; then the deposition pressure is controlled at 5-6 kPa, the radio frequency power is controlled at 550-650 W, and the bias voltage is controlled at -350-380 V, and deposition is carried out for 10-15 min to induce the formation of TiN spike structures; then the pressure is adjusted to 8-10 kPa, the bias voltage is reduced to -300-330 V, and deposition is carried out for 5-10 min to control the morphology of TiN spikes.

5. The method for preparing the wear-resistant coating according to claim 4, characterized in that: In step S3, the process of depositing the wear-resistant coating is as follows: S3-1: Pretreatment of the deposition surface: After the intermediate transition layer is deposited, the TiCl4, N2 and H2 gas flow is turned off, the furnace temperature is controlled at 800~1050℃, Ar gas is introduced at a flow rate of 450~550SCCM, radio frequency plasma is started at a power of 300~500W, sputter cleaning is performed for 5~10min to activate the TiN spike surface. S3-2: Initial nucleation: Turn off the radio frequency plasma, maintain the temperature at 800-1050℃, control the pressure at 30-50Pa, introduce aluminum source and oxygen source gas, and the molar flow ratio of aluminum source and oxygen source is 1:15-20, deposit for 15-30min, and uniformly generate Al2O3 crystal nuclei on the TiN spike surface. S3-3: Main body growth: Continue to maintain the temperature at 800-1050℃, increase the furnace pressure to 100-200Pa, adjust the molar flow ratio of aluminum source and oxygen source to 1:10-15, and deposit for 2-4 hours to allow Al2O3 to grow in a conformal manner to fill the gaps between TiN spikes and evenly cover the intermediate transition layer.

6. The method for preparing the wear-resistant coating according to claim 5, characterized in that: In step S4, the restorative heat treatment specifically includes: S4-1: Homogenization and Austenitization: After the wear-resistant coating is deposited, the aluminum and oxygen sources are shut off, and the furnace temperature is lowered to 450-550°C. Only Ar gas is introduced at a flow rate of 500-800 SCCM, and the positive pressure inside the furnace is maintained at 1-5 kPa for 10-15 minutes to ensure uniform mold temperature. Subsequently, the furnace temperature is raised back to 1020-1200°C at a rate of 8-10°C / min and held for 30-40 minutes. S4-2: Gas quenching: After the heat preservation is completed, turn off the Ar gas, quickly fill the furnace with N2 to a pressure of 5-10 bar, turn off the heater, start the high-speed airflow circulation system, and gas quench the mold. The cooling rate is not less than 25℃ / min, and the mold temperature is cooled to below 40℃. S4-3: High-temperature tempering: Transfer the gas-quenched mold to a vacuum tempering furnace and evacuate it to 1×10⁻⁶. -2 Below Pa, tempering is performed according to the set program: heat to 550~650℃ at a rate of ≤5℃ / min, hold for 2~3h, and then cool to room temperature at a cooling rate of ≤5℃ / min; repeat 2~3 times; after the last cooling to room temperature, charge Ar or N2 to atmospheric pressure and remove from the furnace.

7. An aluminum alloy extrusion die, characterized in that: The mold is used to extrude thin-walled, porous aluminum profiles, and its surface is deposited with the wear-resistant coating as described in claim 1. The total thickness of the wear-resistant coating is 5 to 13 μm, and the interfacial bonding force between the intermediate transition layer of the wear-resistant coating and the substrate and the wear-resistant cover layer is ≥90N.

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