High-pressure hot-pressing die surface coating and preparation method thereof

Abstract

The application relates to the technical field of surface engineering, and particularly discloses a high-pressure and high-temperature press mold surface coating and a preparation method thereof. The preparation method of the high-pressure and high-temperature press mold surface coating comprises the following steps: (1) H13 steel substrate pretreatment; (2) depositing a Cr layer, a CrN layer and a TiAlN layer on the surface of the pretreated H13 steel in sequence by using a magnetron sputtering method to form a Cr-CrN-TiAlN composite coating; and (3) placing the substrate after coating in a high-voltage electric field for treatment to obtain the high-pressure and high-temperature press mold surface coating. The high-pressure and high-temperature press mold surface coating prepared by the application improves the bonding force between the substrate and the coating.

Description

Technical Field

[0001] The present application relates to the field of surface engineering technology, and more specifically, to a high-pressure hot-pressing mold surface coating and a preparation method thereof. Background Art

[0002] As the manufacturing industry evolves towards higher-end, more sophisticated production, hot stamping dies are increasingly being used in aerospace, automotive, and electronic packaging. Under high-temperature and high-pressure conditions, H13 steel stands out as a material for high-pressure hot stamping dies due to its excellent overall performance. Its alloying elements, such as Cr, Mo, and V, form stable carbides, imparting excellent hardenability and high-temperature strength. Its yield strength remains ≥1000 MPa at temperatures between 500 and 600°C, and it can withstand transient pressures exceeding 1500 MPa, effectively resisting plastic deformation under high pressure. Compared to traditional materials, H13 steel offers longer service life, lower maintenance costs, and more stable forming accuracy in high-pressure hot stamping applications such as hot forging and powder metallurgy. However, under high-pressure hot stamping conditions, H13 steel is susceptible to surface wear due to friction with the billet, oxidation and die sticking in high-temperature environments, and thermal fatigue cracking caused by repeated heating and cooling, shortening die life and compromising workpiece quality.

[0003] Surface coating technology has become a key means of improving mold performance. Applying high-hardness, high-modulus ceramic coatings (such as TiN, ZrB2-SiC), metal-ceramic composite coatings (Ti(C, N)-Ni), or functionally gradient coatings to the mold surface can significantly improve the compressive strength and wear resistance of the mold surface. For example, patent application publication number CN102650029A discloses a method for preparing a nano-ceramic composite coating material for a hot-working mold surface, including steps for preparing a spray feed, pretreating an H13 steel substrate, preparing a transition layer, and preparing a nano-ceramic composite layer. In this patent application, during the plasma spraying process, the interface between the nickel-clad aluminum transition layer and the H13 steel substrate forms only a localized micrometallurgical bond (e.g., a Ni-Fe solid solution), but the overall bond is primarily mechanical. Due to the differences in the physical and chemical properties of the metal and ceramic (e.g., poor wettability and difficulty in element diffusion), the interface between the ceramic layer and the transition layer has almost no metallurgical bond, relying solely on mechanical interlocking and the surface roughness of the transition layer to maintain the bond. This makes it susceptible to failure under cyclic thermal stress and mechanical loads. Therefore, the development of new coating materials and preparation processes with high compressive strength, excellent thermal stability and strong interface bonding between the coating and the substrate is of great significance to improving the service performance and service life of hot pressing molds. Summary of the Invention

[0004] In order to improve the interfacial bonding strength between the prepared coating and the substrate, the present application provides a high-pressure hot pressing mold surface coating and a preparation method thereof.

[0005] The application provides a preparation method of a high-pressure hot-pressing die surface coating.

[0006] The preparation method of the high-pressure hot-pressing die surface coating comprises the following steps:

[0007] (1) H13 steel substrate pretreatment;

[0008] (2) depositing a Cr layer, a CrN layer and a TiAlN layer on the surface of the pretreated H13 steel in sequence by using a magnetron sputtering method to form a Cr-CrN-TiAlN composite coating;

[0009] (3) placing the coated substrate in a high-voltage electric field to obtain the high-pressure hot-pressing die surface coating.

[0010] By using the above technical scheme, on the one hand, the electric field force drives the directional migration of the charged defects in the coating, which helps to release the residual stress and promote the diffusion of the interface elements, forms a transition layer with a gentle composition gradient, and further reduces the interface brittleness caused by stress concentration and composition mutation; on the other hand, the electric field can optimize the microstructure of the coating,

[0011] By reducing the porosity, refining the grains and improving the density, the mechanical biting effect is enhanced; in addition, it is possible to promote the formation of stronger chemical bonds at the interface, so as to upgrade the simple mechanical combination to the synergistic effect of chemical and mechanical combination, and finally improve the interface bonding strength of the substrate and the coating.

[0012] Preferably, the step (3) is specifically: placing the coated substrate in a high-voltage electric field composed of two parallel metal plates, one of which is grounded, and the other is connected to a high-voltage electric field generator, and the distance between the coated surface of the substrate and the metal plate is greater than 1 mm.

[0013] By using the above technical scheme, the parallel metal plates can form a uniform direct-current electric field between the plates, ensuring that the interface between the coating and the substrate is subjected to stable electric field effect; the coating surface does not contact the plate, which can prevent local discharge, short circuit or mechanical friction damage to the coating between the plate and the coating, while ensuring that the electric field can penetrate the coating and act on the interface; in addition, the distance between the coated surface of the substrate and the metal plate is greater than 1 mm, which can avoid air breakdown of the coating caused by too small distance.

[0014] Preferably, the distance between the coated surface of the substrate and the metal plate is 2-4 mm, the voltage of the high-voltage electric field is 5-50 kV, and the treatment time is 5-30 min.

[0015] By adopting the technical scheme, the electric field needs to provide sufficient driving force to promote the directional migration of the charged defects in the coating, so as to effectively release the residual stress; if the voltage is too low, the migration driving force of the defects is insufficient, the stress is difficult to relieve, and the interface bonding cannot be improved; at the same time, the electric field assisted diffusion of the interface elements needs to overcome the energy barrier of atomic migration, and the electric field voltage needs to reach a level that can reduce the diffusion activation energy, so as to promote diffusion at a lower temperature and form an effective transition layer; if the voltage is insufficient, the diffusion effect is weak, and a gradient interface cannot be formed; on the contrary, when the voltage is too high, the defects such as micropores and cracks in the coating or local strong electric field caused by electric field distortion cause stress concentration, leading to defect diffusion or even coating peeling, and damaging the coating and substrate structure.

[0016] The processing time needs to ensure the sufficiency of element diffusion and stress release; if the processing time is too short, the interface diffusion layer is not formed, and the residual stress is not completely released; and if the processing time is too long, excessive diffusion occurs, Cr, Ti and Al in the coating migrate to the substrate in large quantities, damaging the composition and structure of the coating itself, or accumulating additional stress due to the continuous electric field effect, thereby weakening the bonding.

[0017] If the distance between the coating surface on the substrate and the metal electrode plate is too small, the substrate and the electrode plate will discharge, causing local damage; and if the distance is too large, a higher voltage is needed to maintain the effective strength, which not only increases the equipment load, but also causes uneven strength distribution due to the divergence of the electric field, thereby weakening the driving effect on the migration of interface defects and the diffusion of elements.

[0018] Preferably, in step (3), the processing environment during the high-voltage electric field processing is an inert gas atmosphere, and the gas pressure is 20-30 Pa.

[0019] By adopting the above technical scheme, the inert gas atmosphere is selected during processing, which can effectively isolate oxygen and impurities, prevent the oxidation reaction of easily oxidized elements (such as Al, Ti and Cr) in the coating and the H13 steel substrate, and avoid the formation of brittle oxide layers that hinder element diffusion; at the same time, it can inhibit the reaction of impurities such as water and CO2 with the coating or substrate to form brittle phases, ensuring the purity of the interface; in addition, the inert gas has high ionization energy, which can stabilize the high-voltage electric field distribution and reduce the damage of electric arc discharge to the coating.

[0020] Preferably, the processing temperature during the high-voltage electric field processing is 200-400℃.

[0021] By adopting the above technical scheme, the temperature needs to be lower than the tempering temperature of H13 steel to avoid softening of the substrate due to overheating (reducing the support strength of the substrate); at the same time, it is lower than the significant oxidation temperature of TiAlN; at the same time, low-temperature heat treatment under the assistance of the electric field can relieve the internal stress generated during the deposition process of the coating, and refine the grains, thereby improving the hardness, wear resistance and anti-peeling performance of the coating.

[0022] Preferably, the specific method for pretreating the H13 steel substrate is to sequentially use ultrasonic sand blasting, ultrasonic shot peening and plasma cleaning to pretreat the surface of the H13 steel substrate.

[0023] By using the above technical solution, sand blasting provides a mechanical bonding basis, shot peening refines grains and strengthens the stress state, and cleaning eliminates interface barriers, and the three form a progressive pretreatment system of "coarsening-strengthening-cleaning" to construct an ideal substrate with mechanical anchoring, metallurgical diffusion, stress balance and high surface energy on the surface of the H13 steel, which provides a basis for strong interface bonding for subsequent coatings, and significantly improves the service life of the mold under high pressure working conditions.

[0024] Preferably, it further includes vacuum annealing strengthening treatment, specifically, the mold after high-voltage electric field treatment is treated in an inert atmosphere at 300-400℃ for 2-3h.

[0025] By using the above technical solution, high-voltage electric field treatment may induce lattice distortion due to strong electric field force, resulting in local residual stress; at the same time, the rapid diffusion driven by the electric field may form a metastable phase. Annealing treatment can eliminate the residual stress caused by lattice distortion through atomic thermal motion, avoid interface cracking caused by stress concentration; promote the metastable phase to transform into an equilibrium phase, enhance the structural matching of the coating and the substrate; and further strengthen the diffusion channels formed by the electric field pretreatment with the help of thermal driving, so that element diffusion is more sufficient, and the interface metallurgical bonding is improved.

[0026] Preferably, in step (2), the thickness of the Cr layer is 1.1-3.4μm, the thickness of the CrN layer is 3.2-5.8μm, and the thickness of the TiAlN layer is 4.9-7.2μm.

[0027] By using the above technical solution, the Cr layer is used to relieve the physical property difference between the substrate and the subsequent head layer, and reduce the interface stress through "metallurgical grade" interface bonding. The Cr layer needs to be thick enough to cover the substrate and buffer the stress, but cannot be too thick to cause internal stress accumulation. The role of the CrN intermediate layer is to connect the Cr layer and the TiAlN outer layer, and its performance is between the two, which needs to be moderate in thickness to realize performance transition, avoid interface mutation caused by too thin, or stress concentration caused by too thick. The TiAlN outer layer is the "functional layer" of the coating, and the influence of its thickness on the bonding mainly reflects through internal stress accumulation and "pulling effect" on the lower layer, which needs to be controlled within the functional requirements to prevent excessive thickness from causing overall stress overrun. By optimizing the thickness ratio of each layer, the interface compatibility of the Cr-CrN-TiAlN coating and the H13 steel substrate can be further improved.

[0028] Preferably, in step (2), the power of the Cr target used in the magnetron sputtering method is 200-300 W, the power of the TiAl target is 300-500 W, the distance between the target material and the substrate is 8-12 cm; the substrate temperature is 200-400 DEG C, and the substrate bias voltage is-50--100 V when depositing the Cr layer, the substrate bias voltage is-80--120 V when depositing the CrN layer, and the substrate bias voltage is-100--150 V when depositing the TiAlN layer.

[0029] By using the above technical solution, the target power determines the deposition rate and the coating structure, the appropriate distance between the target material and the substrate can balance the particle energy and the deposition uniformity, the appropriate substrate temperature can not only ensure the crystallinity of the coating but also avoid the softening of the substrate; the layered bias voltage optimizes the stress distribution and the interfacial adhesion of each layer by regulating the ion bombardment intensity, and the above parameters optimize the performance of the Cr-CrN-TiAlN coating and the H13 steel substrate through interaction.

[0030] In a second aspect, the application provides a high-pressure hot-pressing die surface coating, which adopts the following technical solution,

[0031] A high-pressure hot-pressing die surface coating is prepared by using the above preparation method.

[0032] In summary, the application has the following beneficial effects:

[0033] 1. The preparation method of the application adopts a magnetron sputtering method to deposit a composite coating on the surface of H13 steel and then performs high-voltage electric field treatment. The high-voltage electric field not only promotes the diffusion of interfacial elements to form a transition layer, but also promotes the formation of chemical bonds at the interface, thereby improving the adhesion between the substrate and the coating.

[0034] 2. The application further improves the effect of the electric field on the coating and the substrate by optimizing the electric field strength, treatment time, treatment environment and treatment temperature and other process parameters during high-voltage electric field treatment, thereby further improving the adhesion between the two.

[0035] 3. The application further performs annealing treatment after high-voltage electric field treatment of the coating. The annealing treatment not only eliminates the lattice distortion caused by the high-voltage electric field, but also further strengthens the diffusion channels formed by the electric field pretreatment, thereby improving the metallurgical adhesion of the interface. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 A cross-sectional morphology diagram of the high-pressure hot-pressing die surface coating prepared for Example 12;

[0037] Figure 2 An energy spectrum diagram of the high-pressure hot-pressing die surface coating prepared for Example 12. DETAILED DESCRIPTION

[0038] The application will be further described in detail in conjunction with the examples below.

[0039] The raw materials of the examples and comparative examples of the present application are all ordinary commercial products unless otherwise specified.

[0040] Example 1

[0041] The present example provides a preparation method of the high-pressure hot-pressing mold surface coating, comprising the following steps:

[0042] (1) The H13 steel mold substrate is treated by supersonic sandblasting with 20-40 μm Al2O3 abrasive, pressure 0.6 MPa, spraying distance 80 nm, and treatment time 3 min, to obtain an H13 steel mold with surface roughness Ra=5-8 μm; then the H13 steel mold is treated by WC-Co pellet with 1 mm diameter, frequency 20 kHz, and amplitude 30 μm for 10 min, to obtain an H13 steel mold with nanocrystalline layer of 50-100 nm in surface layer; the treated H13 steel mold is installed and fixed on the substrate holder of the vacuum chamber, and connected to the cathode of the bias power supply; the Cr target and TiAl target required for coating are respectively installed and fixed on the cathode of the evaporation source, and the distance between the mold and the target is 10 cm, while the mold is pasted with a mask on the non-cavity surface, and the evaporation source base is connected to the anode; the door of the vacuum chamber is closed, the mechanical pump is started to vacuumize to an air pressure less than 0.1 Pa, then the molecular pump is started to vacuumize to a base vacuum less than 3×10 -4 Pa; the substrate heating table is started, and the temperature is raised to 300℃ and kept for 30 min; then Ar gas with a flow rate of 15 sccm is introduced, and the pressure in the vacuum chamber is adjusted to 0.4 Pa; the mold is applied with a negative bias of 400 V, and the auxiliary anode is started to generate Ar + particles to bombard the mold surface, and etch for 20 min;

[0043] (2) the Cr target is started, Ar gas is introduced, and the working pressure in the vacuum chamber is maintained at 0.4 Pa; the Cr target power is 250 W, the bias is -80 V, and the deposition is carried out for 30 min to obtain a Cr transition layer with a thickness of 2.3 μm; the Cr target is kept open, 20 sccm of Ar is introduced, 10 sccm of N2 is introduced into the vacuum chamber, the gas pressure in the vacuum chamber is maintained at 0.4 Pa, the Cr target power is 250 W, the bias is -100 V, and the deposition is carried out for 60 min to obtain a CrN layer with a thickness of 4.6 μm; the Cr target is closed, the TiAl target is started, 20 sccm of Ar and 30 sccm of N2 are introduced, and the working pressure in the vacuum chamber is maintained at 0.4 Pa; the TiAl target power is 400 W, the bias is -120 V, and the deposition is carried out for 90 min to obtain a TiAlN layer with a thickness of 6.1 μm; after the deposition is completed, the target power and gas are closed, the vacuum state of the vacuum chamber is maintained, the furnace is cooled to below 100℃, Ar gas is filled to normal pressure, and the mold is taken out;

[0044] (3) A closed cavity made of polytetrafluoroethylene material is used, and an electrode interface is reserved in the cavity. Two metal plates are fixed in the center of the cavity in a parallel manner from top to bottom, wherein the lower plate is connected to the external ground electrode through an insulating sleeve in the cavity via a grounding wire, and the wire of the other metal plate is connected to the high-voltage power supply through an insulating sleeve in the cavity wall. A vacuum pump is connected to the gas interface. The mold is placed between the two plates, specifically: the distance between the upper mold and the lower mold is 10 mm, and the two are fixed in the cavity by an insulating support; the cavity surface of the upper mold is opposite to the lower plate with a distance of 2 mm, and one end of a copper sheet with a thickness of 0.1 mm is fixed on the lower plate, and the other end is pressed on the non-coating surface of the upper mold by an insulating clamp; the cavity surface of the lower mold is opposite to the upper plate with a distance of 2 mm. Start the high-voltage power supply and set the voltage to 5 kV. Continue processing for 30 min. After processing is completed, turn off the high-voltage power supply and open the cavity to take out the mold.

[0045] Example 2

[0046] This example is basically the same as Example 1, except that in step (3), a closed cavity made of polytetrafluoroethylene material is used, and an electrode interface is reserved in the cavity. Two metal plates are fixed in the center of the cavity in a parallel manner from top to bottom, wherein the lower plate is connected to the external ground electrode through an insulating sleeve in the cavity via a grounding wire, and the wire of the other metal plate is connected to the high-voltage power supply through an insulating sleeve in the cavity wall. A vacuum pump is connected to the gas interface. The mold is placed between the two plates, specifically: the distance between the upper mold and the lower mold is 10 mm, and the two are fixed in the cavity by an insulating support; the cavity surface of the upper mold is opposite to the lower plate with a distance of 3 mm, and one end of a copper sheet with a thickness of 0.1 mm is fixed on the lower plate, and the other end is pressed on the non-coating surface of the upper mold by an insulating clamp, and the cavity surface of the lower mold is opposite to the upper plate with a distance of 3 mm. Start the high-voltage power supply and set the voltage to 30 kV. Continue processing for 20 min. After processing is completed, turn off the high-voltage power supply and open the cavity to take out the mold.

[0047] Example 3

[0048] The embodiment is basically the same as embodiment 1, except that: in step (3), a closed cavity made of polytetrafluoroethylene is used, and an electrode interface is reserved in the cavity; two metal plates are fixed in the center of the cavity in a parallel manner from top to bottom by an insulating support, wherein the lower plate is connected to an external ground electrode through an insulating sleeve in the cavity by a grounding wire, and the wire of the other metal plate is connected to a high-voltage power supply through an insulating sleeve in the cavity wall, and a gas interface is connected to a vacuum pump; the mold is placed between the two plates, specifically: the distance between the upper mold and the lower mold is 10 mm, and the two are fixed in the cavity by an insulating support; the cavity surface of the upper mold is opposite to the lower plate with a distance of 4 mm, and one end of a copper sheet with a thickness of 0.1 mm is fixed on the lower plate, and the other end is pressed on the non-coating surface of the upper mold by an insulating clamp; the cavity surface of the lower mold is opposite to the upper plate with a distance of 4 mm; start the high-voltage power supply, set the voltage to 50 kV, and continue to process for 30 min; after the processing is completed, the high-voltage power supply is turned off, and the cavity is opened to take out the mold.

[0049] Embodiment 4

[0050] The embodiment is basically the same as embodiment 2, except that: in step (3), a closed cavity made of polytetrafluoroethylene is used, and an electrode interface, a gas interface and a vacuum exhaust port are reserved in the cavity; the gas interface is connected to an argon purifier, the vacuum exhaust port is connected to a vacuum pump, a closed cavity made of polytetrafluoroethylene is used, and an electrode interface is reserved in the cavity; two metal plates are fixed in the center of the cavity in a parallel manner from top to bottom by an insulating support, wherein the lower plate is connected to an external ground electrode through an insulating sleeve in the cavity by a grounding wire, and the wire of the other metal plate is connected to a high-voltage power supply through an insulating sleeve in the cavity wall, and a gas interface is connected to a vacuum pump; the mold is placed between the two plates, specifically: the distance between the upper mold and the lower mold is 10 mm, and the two are fixed in the cavity by an insulating support; the cavity surface of the upper mold is opposite to the lower plate with a distance of 3 mm, and the cavity surface of the lower mold is opposite to the upper plate with a distance of 3 mm, and one end of a copper sheet with a thickness of 0.1 mm is fixed on the lower plate, and the other end is pressed on the non-coating surface of the upper mold by an insulating clamp; start the vacuum pump, and the pressure in the cavity is extracted to 1x10 -3 Pa, maintain for 5 min to exclude residual air, turn off the vacuum pump, and introduce argon to the pressure in the cavity to 25 Pa, and stabilize for 10 min; start the high-voltage power supply, set the voltage to 30 kV, and continue to process for 20 min; after the processing is completed, the high-voltage power supply is turned off, and the cavity is opened to take out the mold.

[0051] Embodiment 5

[0052] The embodiment is basically the same as embodiment 4, except that in step (3), a closed cavity made of polytetrafluoroethylene material is used, and the cavity is pre-provided with electrode interfaces, temperature measuring holes, gas path interfaces and vacuum gas exhaust ports. The gas path interfaces are connected with an argon purifier, the vacuum gas exhaust ports are connected with a vacuum pump, an armored electric heating wire is wound outside, and a K-type thermocouple is embedded inside the cavity. Two metal plates are fixed in the center of the cavity in a parallel manner from top to bottom by an insulating support. The lower plate is connected to an external ground electrode through an insulating sleeve in the cavity via a grounding wire, and the wire of the other metal plate is connected to a high-voltage power supply through an insulating sleeve in the cavity wall. The gas path interfaces are connected with a vacuum pump. The mold is placed between the two plates, specifically: the distance between the upper mold and the lower mold is 10 mm, and the two are fixed in the cavity by an insulating support; the cavity surface of the upper mold is opposite to the lower plate with a shortest distance of 4 mm, and the cavity surface of the lower mold is opposite to the upper plate with a shortest distance of 4 mm. One end of a 0.1 mm thick red copper sheet is fixed on the lower plate, and the other end is pressed on the non-coating surface of the upper mold by an insulating clamp. Start the vacuum pump, and the pressure in the cavity is pumped to 1x10 -3 Pa, maintain for 5 min to exclude residual air, close the vacuum pump, and introduce argon to the pressure in the cavity to 25 Pa, stabilize for 10 min, and heat to 300℃ at a rate of 10℃ / min. After constant temperature for 10 min, start the high-voltage power supply, set the voltage to 30 kV, and continue to process for 20 min. After the processing is completed, the high-voltage power supply is turned off, the argon flow is kept, and the mold is naturally cooled to room temperature. Open the cavity and take out the mold.

[0053] Example 6

[0054] The embodiment is basically the same as embodiment 5, except that in step (3), a closed cavity made of polytetrafluoroethylene material is used, and the cavity is pre-provided with electrode interfaces, temperature measuring holes, gas path interfaces and vacuum gas exhaust ports. The gas path interfaces are connected with an argon purifier, the vacuum gas exhaust ports are connected with a vacuum pump, an armored electric heating wire is wound outside, and a K-type thermocouple is embedded inside the cavity. Two metal plates are fixed in the center of the cavity in a parallel manner from top to bottom by an insulating support. The lower plate is connected to an external ground electrode through an insulating sleeve in the cavity via a grounding wire, and the wire of the other metal plate is connected to a high-voltage power supply through an insulating sleeve in the cavity wall. The gas path interfaces are connected with a vacuum pump. The mold is placed between the two plates, specifically: the distance between the upper mold and the lower mold is 10 mm, and the two are fixed in the cavity by an insulating support; the cavity surface of the upper mold is opposite to the lower plate with a shortest distance of 4 mm, and the cavity surface of the lower mold is opposite to the upper plate with a shortest distance of 4 mm. One end of a 0.1 mm thick red copper sheet is fixed on the lower plate, and the other end is pressed on the non-coating surface of the upper mold by an insulating clamp. Start the vacuum pump, and the pressure in the cavity is pumped to 1x10 -3Pa, maintain 5 min to exclude residual air, close the vacuum pump, and pass argon into the cavity until the pressure is 20 Pa. After stabilizing for 10 min, increase the temperature to 400℃ at a rate of 10℃ / min. After constant temperature for 10 min, start the high-voltage power supply, set the voltage to 30 kV, and continue processing for 20 min. After processing is completed, close the high-voltage power supply, keep the argon flowing, and wait for the mold to cool to room temperature naturally. Open the cavity and take out the mold.

[0055] Example 7

[0056] This example is basically the same as Example 5, except that step (3) uses a closed cavity made of polytetrafluoroethylene material. The cavity has reserved electrode interfaces, temperature measurement holes, gas interface, and vacuum exhaust port. The gas interface is connected with an argon purifier, and the vacuum exhaust port is connected with a vacuum pump. The outside is wrapped with armored heating wire, and a K-type thermocouple is embedded inside the cavity. Two metal plates are fixed in the center of the cavity in a parallel manner from top to bottom by an insulating support. The lower plate is connected to the external ground electrode through an insulating sleeve in the cavity. The wire of the other metal plate is connected with the high-voltage power supply through an insulating sleeve in the cavity wall. The gas interface is connected with a vacuum pump. The mold is placed between the two plates, specifically: the distance between the upper and lower molds is 10 mm, and both are fixed in the cavity by an insulating support. The cavity surface of the upper mold is opposite to the lower plate with a shortest distance of 4 mm, and the cavity surface of the lower mold is opposite to the upper plate with a shortest distance of 4 mm. A 0.1 mm thick copper sheet is fixed on the lower plate at one end and pressed on the non-coated surface of the upper mold by an insulating clamp at the other end. Start the vacuum pump and exhaust the cavity to 1×10 -3 Pa, maintain 5 min to exclude residual air, close the vacuum pump, and pass argon into the cavity until the pressure is 20 Pa. After stabilizing for 10 min, increase the temperature to 400℃ at a rate of 10℃ / min. After constant temperature for 10 min, start the high-voltage power supply, set the voltage to 30 kV, and continue processing for 20 min. After processing is completed, close the high-voltage power supply, keep the argon flowing, and wait for the mold to cool to room temperature naturally. Open the cavity and take out the mold.

[0057] Example 8

[0058] This example is basically the same as Example 5, except that it further includes step (4), which is: placing the mold treated by the electric field into a vacuum annealing furnace, closing the furnace door, starting the vacuum pump, and exhausting to 1×10 -3 Pa. Increase the temperature to 300℃ at a rate of 5℃ / min, and keep the temperature for 10 min. Continue to increase the temperature to 350℃ at a rate of 3℃ / min, and keep the temperature for 2.5 h. Cool the furnace to room temperature, open the furnace door, and take out the mold.

[0059] Example 9

[0060] The embodiment is basically the same as embodiment 8, except that in step (4), the mold after electric field treatment is placed in a vacuum annealing furnace, the door is closed, the vacuum pump is started, and the vacuum is pumped to 1x10 -3 Pa, the temperature is raised to 200℃ at a rate of 5℃ / min, and the temperature is kept for 10 min, then the temperature is raised to 300℃ at a rate of 3℃ / min, and the temperature is kept for 3h, the furnace is cooled to room temperature, the door is opened, and the mold is taken out.

[0061] Example 10

[0062] The embodiment is basically the same as embodiment 8, except that in step (4), the mold after electric field treatment is placed in a vacuum annealing furnace, the door is closed, the vacuum pump is started, and the vacuum is pumped to 1x10 -3 Pa, the temperature is raised to 300℃ at a rate of 5℃ / min, and the temperature is kept for 10 min, then the temperature is raised to 400℃ at a rate of 3℃ / min, and the temperature is kept for 2h, the furnace is cooled to room temperature, the door is opened, and the mold is taken out.

[0063] Example 11

[0064] The embodiment is basically the same as embodiment 8, except that in step (2), the Cr target is turned on, Ar gas is introduced, and the working pressure in the vacuum chamber is maintained at 0.4Pa, the Cr target power is 200W, the bias voltage is -50V, and the deposition is carried out for 30min to obtain a Cr transition layer with a thickness of 1.1μm; the Cr target is kept on, 20sccm of Ar is introduced, 10sccm of N2 is introduced into the vacuum chamber, the gas pressure in the vacuum chamber is maintained at 0.4Pa, the Cr target power is 200W, the bias voltage is -80V, and the deposition is carried out for 60min to obtain a CrN layer with a thickness of 3.2μm; the Cr target is turned off, the TiAl target is turned on, 20sccm of Ar and 30sccm of N2 are introduced, and the working pressure in the vacuum chamber is maintained at 0.4Pa, the TiAl target power is 300W, the bias voltage is -100V, and the deposition is carried out for 90min to obtain a TiAlN layer with a thickness of 4.9μm; after the deposition is completed, the target power supply and the gas are turned off, the vacuum chamber is kept in a vacuum state, the furnace is cooled to below 100℃, Ar gas is filled to normal pressure, and the mold is taken out.

[0065] Example 12

[0066] The embodiment is basically the same as embodiment 8, except that in step (2), the Cr target is turned on, Ar gas is introduced, and the working pressure in the vacuum chamber is maintained at 0.4 Pa, the Cr target power is 300 W, the bias voltage is -100 V, and the deposition is performed for 30 min to obtain a Cr transition layer with a thickness of 3.4 μm; the Cr target is kept on, 20 sccm of Ar is continuously introduced, 10 sccm of N2 is introduced into the vacuum chamber, the gas pressure in the vacuum chamber is maintained at 0.4 Pa, the Cr target power is 300 W, the bias voltage is -120 V, and the deposition is performed for 60 min to obtain a CrN layer with a thickness of 5.8 μm; the Cr target is turned off, the TiAl target is turned on, 20 sccm of Ar and 30 sccm of N2 are introduced, and the working pressure in the vacuum chamber is maintained at 0.4 Pa, the TiAl target power is 500 W, the bias voltage is -150 V, and the deposition is performed for 90 min to obtain a TiAlN layer with a thickness of 7.2 μm; after the deposition is completed, the target power supply and the gas are turned off, the vacuum chamber is kept in a vacuum state, the furnace is cooled to below 100 °C, Ar gas is filled to the normal pressure, and the mold is taken out.

[0067] Comparative example 1

[0068] The present comparative example provides a preparation method of the high-pressure hot-pressing mold surface coating described above, which comprises the following steps:

[0069] (1) The H13 steel mold substrate is treated by supersonic sand blasting with 20-40 μm Al2O3 abrasive, a pressure of 0.6 MPa, a spraying distance of 80 nm, and a treatment time of 3 min to obtain an H13 steel mold with a surface roughness of Ra=5-8 μm; then the H13 steel mold is treated by using 1 mm diameter WC-Co pellets at a frequency of 20 kHz and an amplitude of 30 μm for 10 min to obtain an H13 steel mold with a nanocrystalline layer of 50-100 nm in the surface layer; the treated H13 steel mold is installed and fixed on the substrate holder of the vacuum chamber and connected to the cathode of the bias power supply; the Cr target material and the TiAl target material required for coating are respectively installed and fixed on the cathode of the evaporation source, the mold is 10 cm away from the target material, and the mold non-cavity surface is pasted with a mask, the evaporation source base is connected to the anode; the vacuum chamber door is closed, the mechanical pump is started to vacuum to a gas pressure of less than 0.1 Pa, then the molecular pump is started to vacuum to a base pressure of less than 3×10 -4 Pa; the substrate heating table is turned on, the temperature is raised to 300 °C, and the temperature is maintained for 30 min; then 15 sccm of Ar gas is introduced, and the vacuum chamber pressure is adjusted to 0.4 Pa; a negative bias of 400 V is applied to the mold, the auxiliary anode is turned on, Ar + particles bombard the mold surface, and etching is performed for 20 min;

[0070] (2) open the Cr target, pass in Ar gas, and maintain the working pressure in the vacuum chamber at 0.4 Pa, deposit a Cr transition layer with a thickness of 2.3 μm at a Cr target power of 250 W and a bias voltage of -80 V for 30 min; continue to keep the Cr target open, keep 20 sccm of Ar passing in, and pass in 10 sccm of N2 into the vacuum chamber, maintain the gas pressure in the vacuum chamber at 0.4 Pa, deposit a CrN layer with a thickness of 4.6 μm at a Cr target power of 250 W and a bias voltage of -100 V for 60 min; turn off the Cr target, open the TiAl target, pass in 20 sccm of Ar and 30 sccm of N2, and maintain the working pressure in the vacuum chamber at 0.4 Pa, deposit a TiAlN layer with a thickness of 6.1 μm at a TiAl target power of 400 W and a bias voltage of -120 V for 90 min; after the deposition is completed, turn off the target power supply and the gas, keep the vacuum chamber in a vacuum state, cool to below 100℃ with the furnace, fill in Ar gas to normal pressure, and take out the mold.

[0071] Performance detection

[0072] Bonding force test: a WS-2005 coating adhesion automatic scratch tester was used to test the bonding force between the coating and the substrate of the hot-pressing mold prepared in Examples 1-12 and Comparative Example 1, and the test results are recorded in Table 1.

[0073] Microhardness test: a HWV-IT microhardness tester was used to test the microhardness of the coating of the hot-pressing mold prepared in Examples 1-12 and Comparative Example 1, and the test results are recorded in Table 1.

[0074] Wear resistance test: a HT-500 high-temperature friction and wear testing machine was used to test the coating of the hot-pressing mold prepared in Examples 1-12 and Comparative Example 1, and the test results are recorded in Table 1.

[0075] Service life: the hot-pressing mold prepared in Examples 1-12 and Comparative Example 1 was heated to 1000℃ and kept for 5 min, then taken out and quickly put into 25℃ water for cooling, and the process was repeated until 5% of the coating on the surface of the mold peeled off, at which time the coating was determined to be invalid, and the number of cycles was recorded in Table 1.

[0076] Table 1 Performance detection data of the surface coating of the high-pressure hot-pressing mold in Examples 1-12 and Comparative Example 1

[0077]

[0078] Referring to Table 1 and Figures 1-2 , in combination with Examples 1-12 and Comparative Example 1, it can be seen that, from Figure 1It can be seen from the figure that the coating structure is dense, the interface between the layers is blurred, and the transition is "sawtooth-shaped". Compared with the traditional coating interface which presents a "straight line type" mutation boundary, the interface of the coating prepared by the method of the present application presents a "sawtooth-shaped" transition. The interface of the coating prepared by the method of the present application is smoother than the interface of the coating prepared by the traditional method. Figure 2 It can be seen from the figure that the Cr-CrN-TiAlN composite coating after high-voltage electric field treatment mainly contains N, Cr, Ti and Al elements. Although the electric field promotes the diffusion of Fe atoms in the substrate to the Cr layer, the diffusion range is limited and below the detection threshold, so the above EDS figure does not contain Fe elements. The reason is that: in the present application, the mold after coating is treated by high-voltage electric field, the electric field force not only can drive the directional migration of charged defects in the coating and release residual stress, but also can promote the diffusion of interface elements, form a transition layer with a gentle composition gradient, and reduce the interface brittleness caused by stress concentration and composition mutation; and the electric field can optimize the microstructure of the coating, reduce the porosity, refine the grains, improve the density, enhance the mechanical biting effect, and may promote the interface to form stronger chemical bonds, improve the bonding strength of the substrate and the coating, and thus improve the service life of the mold.

[0079] Referring to Table 1, in combination with Examples 1 and 4, it can be seen that the present application selects to perform the high-voltage electric field treatment in an inert atmosphere, which effectively isolates oxygen and impurities, prevents the oxidation reaction of easily oxidizable elements (such as Al, Ti, Cr) in the coating and the H13 steel substrate, avoids the formation of a brittle oxide layer that hinders element diffusion; at the same time, it can inhibit the reaction of moisture, CO2 and other impurities with the coating or substrate to form brittle phases, and ensure the purity of the interface; in addition, the inert gas has high ionization energy, which can stabilize the high-voltage electric field distribution, reduce the damage of electric arc discharge to the coating, and finally improve the comprehensive performance of the mold.

[0080] Referring to Table 1, in combination with Examples 4 and 5, it can be seen that in the present application, the high-voltage electric field treatment is selected to be performed at an environment of 300°C. This temperature is not only lower than the tempering temperature of H13 steel, avoiding the softening of the substrate due to overheating (reducing the support strength of the substrate); but also lower than the significant oxidation temperature of TiAlN; and the low-temperature heat treatment assisted by the electric field can relieve the internal stress generated during the deposition process of the coating, refine the grains, and thus improve the hardness, wear resistance and anti-peeling performance of the coating.

[0081] Referring to Table 1, in combination with Examples 5 and 8, it can be seen that the present application further performs annealing strengthening treatment on the mold after high-voltage electric field treatment. The annealing treatment not only can eliminate the residual stress caused by the lattice distortion of the high-voltage electric field through atomic thermal motion, avoiding the interface cracking caused by stress concentration; but also can promote the metastable phase formed by the high-voltage electric field to transform into a balanced phase, enhancing the structural matching of the coating and the substrate; at the same time, with the help of heat driving, the diffusion channels formed by the electric field pretreatment are further strengthened, making the element diffusion more sufficient, improving the interface metallurgical bonding, and further improving the comprehensive performance of the mold.

[0082] The embodiments are only illustrative of the present application, and are not intended to limit the present application, and those skilled in the art can make modifications to the embodiments without creative contribution after reading the specification, but as long as the modifications are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A method for preparing a surface coating of a high-pressure hot-pressing mold, characterized in that: The following steps are involved: (1) Pretreatment of H13 steel substrate; (2) Cr layer, CrN layer and TiAlN layer were deposited in sequence on the pretreated H13 steel surface by magnetron sputtering to form a Cr~CrN~TiAlN composite coating; (3) placing the coated substrate in a high-voltage electric field consisting of two parallel metal plates, one of which is grounded and the other is connected to a high-voltage electric field generator, with the coating surface on the substrate and the metal plate spaced 2 to 4 mm apart, the voltage of the high-voltage electric field being 5 to 50 kV, and the treatment time being 5 to 30 min; the treatment environment during the high-voltage electric field treatment is an inert gas atmosphere with a gas pressure of 20 to 30 Pa; and the treatment temperature during the high-voltage electric field treatment is 200 to 400 °C; It also includes vacuum annealing strengthening treatment, specifically: the mold treated with a high voltage electric field is treated at 300-400°C in an inert atmosphere for 2-3 hours.

2. The method for preparing a high-pressure hot-pressing mold surface coating according to claim 1, characterized in that: In step (1), the specific method of pre-treating the H13 steel substrate is: pre-treating the surface of the H13 steel substrate by supersonic sandblasting, ultrasonic shot blasting and plasma cleaning in sequence.

3. The method for preparing a high-pressure hot-pressing mold surface coating according to claim 1, characterized in that: In step (2), the thickness of the Cr layer is 1.1-3.4 μm, the thickness of the CrN layer is 3.2-5.8 μm, and the thickness of the TiAlN layer is 4.9-7.2 μm.

4. The method for preparing a high-pressure hot-pressing mold surface coating according to claim 1, characterized in that: In step (2), the power of the Cr target used in the magnetron sputtering method is 200~300W, the power of the TiAl target is 300~500W, and the distance between the target and the substrate is 8~12cm; the substrate temperature is 200~400℃, and the substrate bias is -50~-100V when depositing the Cr layer, the substrate bias is -80~-120V when depositing the CrN layer, and the substrate bias is -100~-150V when depositing the TiAlN layer.

5. High-pressure hot-pressing mold surface coating, characterized in that: It is prepared by the method for preparing the surface coating of a high-pressure hot-pressing mold according to any one of claims 1 to 4.

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