Preparation method of titanium nitride aluminum coating for hot extrusion dies

Abstract

This invention belongs to the field of coating technology, specifically relating to a method for preparing a titanium aluminum nitride coating for hot extrusion dies. The preparation method includes the following steps: (1) heating the die; (2) pre-bombardment; (3) coating deposition: nitrogen gas is introduced into the coating chamber to maintain the total pressure of the mixed gas at 1×10⁻⁶. ‑1 -5×10 ‑1 Pa, the substrate bias voltage of the titanium-aluminum alloy target is 20-30V, and a titanium-aluminum nitride coating with a thickness of 3-4μm is deposited; (4) Quenching: Quenching is performed at a temperature of 700-800℃; (5) Die cooling: The hot extrusion die is first cooled to 400-500℃, held for 30-60min, and then naturally cooled to obtain the titanium-aluminum nitride coating. The titanium-aluminum nitride coating obtained by this invention has an aluminum content of 55-60%, a high temperature resistance of over 900℃, and a hardness of over 3300HV, which improves the service life of the hot extrusion die.

Description

Technical Field

[0001] This invention belongs to the field of coating technology, specifically relating to a method for preparing a titanium nitride aluminum coating for hot extrusion dies. Background Technology

[0002] Many non-ferrous metal and steel profiles, pipes, and special-shaped profiles are formed using hot extrusion processes. Hot extrusion dies operate under harsh conditions such as high temperature, high pressure, wear, and thermal fatigue. For hot extrusion dies that experience severe wear under high-temperature conditions, especially those extruding complex-shaped workpieces, a coating is typically added to the surface to extend their service life. Currently, tungsten carbide coatings are common for hot extrusion dies. The highest hardness of tungsten carbide coatings suitable for hot extrusion dies is around 75 HRC. Hardness below 75 HRC significantly reduces wear resistance, while hardness above 75 HRC makes them prone to cracking, leading to coating failure.

[0003] Nitride coatings are obtained by nitriding the surface of a mold. Nitriding is a chemical heat treatment process that allows nitrogen atoms to penetrate into the surface layer of a workpiece at a specified temperature in a certain medium. Mold products treated with nitriding exhibit excellent wear resistance, fatigue resistance, corrosion resistance, and high-temperature resistance. It can effectively reduce the coefficient of friction on the mold surface, extend the service life of the mold, and reduce production costs.

[0004] Among them, titanium aluminum nitride (TiAlN) coatings, due to the nano-sized deposition particles, can enhance the bonding strength between the coating and the substrate, as well as between layers. Simultaneously, they can reduce surface roughness, increase surface smoothness, and enhance surface corrosion resistance and wear resistance. Therefore, titanium aluminum nitride coatings are widely used in metallurgical molds, hardware molds, medical devices, artificial joints, and other fields.

[0005] However, existing titanium aluminum nitride coatings have a low aluminum content. To improve the coating's hardness and high-temperature resistance, other elements are often added to enhance its overall performance. For example, patent CN113151781A discloses a titanium aluminum nitride type superhard coating and its preparation method. The superhard coating includes a titanium aluminum nitride layer and a functional layer deposited on the titanium aluminum nitride layer. The functional layer contains 8-12 at% tungsten and 8-12 at% silicon. The preparation method involves sequentially performing substrate pretreatment, vacuum heating treatment, ion bombardment, deposition, and cooling. This titanium aluminum nitride type superhard coating improves the coating's hardness and high-temperature resistance by doping with tungsten and silicon. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a method for preparing a titanium aluminum nitride coating for hot extrusion dies, wherein the aluminum content of the obtained titanium aluminum nitride coating is 55-60%, the high temperature resistance reaches above 900℃, the hardness reaches above 3300HV, and the service life of hot extrusion dies is improved.

[0007] The method for preparing the titanium aluminum nitride coating for hot extrusion dies according to the present invention includes the following steps:

[0008] (1) Mold heating: Place the cleaned and dried hot extrusion mold in the coating chamber and heat it to 180-220℃ at a rate of 2-5℃ / min under vacuum conditions;

[0009] (2) Pre-bombardment: Argon gas is introduced into the coating chamber until the vacuum level reaches 1×10⁻⁶. -1 -5×10 -1 Pa, activate the arc source to perform ion bombardment;

[0010] (3) Coating deposition: Nitrogen gas is introduced into the coating chamber to maintain the total pressure of the mixed gas at 1×10⁻⁶. -1 -5×10 - 1 Pa, the arc current of the titanium-aluminum alloy target is set to 60-80A, the substrate bias voltage is 20-30V, and a titanium-aluminum nitride coating with a thickness of 3-4μm is deposited on the surface of the hot extrusion die.

[0011] (4) Quenching: The hot extrusion die with the titanium aluminum nitride coating deposited on the surface is quenched at a temperature of 700-800℃;

[0012] (5) Die cooling: After quenching, the hot extrusion die is first cooled to 400-500℃, kept at that temperature for 30-60 minutes, and then cooled naturally to obtain a titanium nitride aluminum coating for hot extrusion dies.

[0013] In step (1), the hot extrusion mold is ultrasonically cleaned in anhydrous ethanol for 5-30 minutes during cleaning.

[0014] In step (1), the drying process is carried out at 50-80℃ for 10-30 minutes.

[0015] In step (1), the vacuum level in the coating chamber is maintained at 1×10 during heating. -4 -1×10 -3 Pa. In this invention, the temperature is raised to 180-220°C at a rate of 2-5°C / min under vacuum conditions. The heating rate is slow to ensure that the temperature inside and on the surface of the hot extrusion die rises uniformly, which is beneficial to the uniform deposition of the coating.

[0016] In step (2), the ion bombardment time is 5-15 min.

[0017] In step (3), the aluminum content in the titanium-aluminum alloy target is 55-60 at.%.

[0018] This invention incorporates Al into TiN. In the TiAlN crystalline film, Al atoms replace some of the Ti atoms in TiN, causing lattice distortion. Coatings with high lattice distortion have more grain boundaries and more dislocations that are less prone to sliding, thereby increasing the coating's hardness. Furthermore, Al can significantly reduce oxidative wear of the TiN coating during cutting. When the mold temperature exceeds approximately 749°C, the outer surface of the coating transforms into aluminum oxide, which can prevent further oxidation and protect the mold, thus extending its service life.

[0019] The hardness of TiAlN coatings changes with the Al content. Pure TiN has a hardness of approximately 2000 HV, and theoretically, the hardness of TiAlN should increase with increasing Al content. However, during our research, we found that the hardness of TiAlN reaches its maximum when the Al:Ti ratio is 6:4. When the Al content exceeds 60%, the hardness begins to decrease. This is because when the Al content is less than 60%, columnar structures exist in the microstructure; while when the Al content exceeds 60%, these columnar structures disappear, and the grain size decreases. This change in lattice structure affects the hardness of the coating.

[0020] In step (3), the deposition time of the titanium nitride aluminum coating is 90-120 min.

[0021] In the current industry practice, bias voltages above 100V are generally used for the deposition of TiAlN coatings via cathodic arc evaporation. However, during the research process, this invention discovered that the bias voltage significantly affects the Al content in the coating. When the bias voltage exceeds 100V, the reactive ion yield is low, significant self-sputtering occurs on the substrate surface, the deposition rate decreases, and the film surface is etched, becoming rough and dull. By reducing the bias voltage, the wear resistance of the coating can be improved, with the best wear resistance observed when the bias voltage is between 20-30V. As the bias voltage increases, the Al content in the final titanium aluminum nitride coating will gradually decrease. This is mainly due to the following two reasons: (1) There is a difference in the ionization degree of Ti and Al. The ionization rate of Ti is as high as 80%, while that of Al is 50%. Highly ionized Ti ions are preferentially attracted to the substrate. (2) The difference in sputtering coefficients of Ti ions and Al ions and the difference in their own charges lead to the above results. Backsputtering increases with the increase of bias voltage. Since Ti atoms are heavier than Al atoms, Al atoms are more likely to undergo backsputtering than Ti atoms.

[0022] In step (4), quenching is carried out in quenching oil for 30-60 minutes. This invention performs re-quenching treatment on hot extrusion dies after the surface is coated with titanium aluminum nitride. On the one hand, this can improve the bonding force between the coating and the die substrate. On the other hand, the quenching and heat preservation can make the hardness distribution of the coating uniform and reduce the occurrence of deformation and cracking under high temperature conditions.

[0023] In step (5), after quenching, the temperature is lowered by quenching oil cooling. In this invention, when cooling the hot extrusion die after depositing a titanium aluminum nitride coating on the surface, a segmented cooling method is adopted to further improve the bonding force between the coating and the die substrate and the hardness of the coating.

[0024] The titanium nitride aluminum coating for hot extrusion dies prepared by the preparation method described in this invention has a thickness of 3-4 μm, a bonding strength between the titanium nitride aluminum coating and the hot extrusion die greater than 60 N, a high temperature resistance of over 900℃, a hardness of over 3300 HV, and a steel friction coefficient of less than 0.3.

[0025] The purpose of this invention is to improve the hardness and high-temperature resistance of TiAlN coatings, and extend the service life of hot extrusion dies under harsh conditions such as high temperature, high pressure, wear, and thermal fatigue, solely through the design of element content and improvements in coating preparation processes. In some embodiments, Si can be added to the TiAlN coating to refine the grains and increase hardness, while Y and Cr can be added to improve oxidation resistance, or V and Zr can be added to improve wear resistance, and so on.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] (1) This invention reduces the oxidative wear of TiAlN coating during cutting by increasing the content of Al element in TiAlN coating, while keeping the content of Al element in TiAlN coating no higher than 60%, so that columnar structure is retained in the microstructure of coating and the grain size does not change significantly, thereby maximizing the hardness of coating.

[0028] (2) In the present invention, when depositing TiAlN coating by cathode arc evaporation, a lower bias voltage is used. By reducing the bias voltage, the ionization rate of Al and the degree of back sputtering are reduced, thereby avoiding the reduction of Al content in the coating and improving the wear resistance of the coating.

[0029] (3) The present invention employs a process of slow heating, step-by-step cooling, coating, and then quenching, which significantly improves the surface hardness, wear resistance, and high-temperature resistance of the mold. The bonding strength between the coating and the mold is greater than 80 N / m. 2 It has a high temperature resistance of over 900℃, a hardness of over 3300HV, and a steel friction coefficient of less than 0.3, which greatly extends the service life of hot extrusion dies. Detailed Implementation

[0030] The present invention will be further described below with reference to the embodiments. Unless otherwise specified, the raw materials used in the embodiments are all commercially available conventional raw materials; unless otherwise specified, the process methods used in the embodiments are conventional methods in the art.

[0031] Example 1

[0032] A method for preparing a titanium nitride aluminum coating for hot extrusion dies includes the following steps:

[0033] (1) Mold heating: After ultrasonically cleaning the hot extrusion mold in anhydrous ethanol for 20 min, dry it at 60℃ for 20 min, and then place it in the coating chamber, maintaining the vacuum degree of the coating chamber at 1×10 -4 Pa, heated to 220℃ at a rate of 5℃ / min;

[0034] (2) Pre-bombardment: Argon gas is introduced into the coating chamber until the vacuum level reaches 1×10⁻⁶. -1 Pa, turn on the arc source to bombard ions for 10 min;

[0035] (3) Coating deposition: Nitrogen gas is introduced into the coating chamber to maintain the total pressure of the mixed gas at 1×10⁻⁶. -1 Pa, the arc current of the titanium-aluminum alloy target (aluminum content of 60 at.%) is set at 70A, the substrate bias voltage is 25V, and the titanium-aluminum nitride coating with a thickness of 4μm is deposited on the surface of the hot extrusion die for 120min.

[0036] (4) Quenching: The hot extrusion die with the surface coated with titanium aluminum nitride was quenched in quenching oil at 800℃ for 50 minutes.

[0037] (5) Die cooling: After quenching, the hot extrusion die is first cooled to 450°C in quenching oil, kept at that temperature for 40 minutes, and then cooled naturally to obtain a titanium nitride aluminum coating for hot extrusion dies.

[0038] Example 2

[0039] A method for preparing a titanium nitride aluminum coating for hot extrusion dies includes the following steps:

[0040] (1) Mold heating: After ultrasonically cleaning the hot extrusion mold in anhydrous ethanol for 5 min, dry it at 50℃ for 30 min, and then place it in the coating chamber, maintaining the vacuum degree of the coating chamber at 1×10 -3 Pa, heated to 180℃ at a rate of 2℃ / min;

[0041] (2) Pre-bombardment: Argon gas is introduced into the coating chamber until the vacuum degree reaches 5×10⁻⁶. -1Pa, turn on the arc source and perform ion bombardment for 5 minutes;

[0042] (3) Coating deposition: Nitrogen gas is introduced into the coating chamber to maintain the total pressure of the mixed gas at 5 × 10⁻⁶. -1 Pa, the arc current of the titanium-aluminum alloy target (aluminum content of 55 at.%) is set at 60A, the substrate bias voltage is 30V, and the titanium-aluminum nitride coating with a thickness of 3μm is deposited on the surface of the hot extrusion die for 90min.

[0043] (4) Quenching: The hot extrusion die with the surface coated with titanium aluminum nitride was quenched in quenching oil at 700℃ for 60 minutes.

[0044] (5) Die cooling: After quenching, the hot extrusion die is first cooled to 400°C in quenching oil, kept at that temperature for 60 minutes, and then cooled naturally to obtain a titanium nitride aluminum coating for hot extrusion dies.

[0045] Example 3

[0046] A method for preparing a titanium nitride aluminum coating for hot extrusion dies includes the following steps:

[0047] (1) Mold heating: After ultrasonically cleaning the hot extrusion mold in anhydrous ethanol for 30 min, dry it at 80℃ for 10 min, and then place it in the coating chamber, maintaining the vacuum degree of the coating chamber at 1×10 -3 Pa, heated to 200℃ at a rate of 4℃ / min;

[0048] (2) Pre-bombardment: Argon gas is introduced into the coating chamber until the vacuum level reaches 1×10⁻⁶. -1 Pa, turn on the arc source to bombard ions for 15 minutes;

[0049] (3) Coating deposition: Nitrogen gas is introduced into the coating chamber to maintain the total pressure of the mixed gas at 1×10⁻⁶. -1 Pa, the arc current of the titanium-aluminum alloy target (aluminum content of 58 at.%) is set at 80A, the substrate bias voltage is 20V, and the titanium-aluminum nitride coating with a thickness of 4μm is deposited on the surface of the hot extrusion die for 120min.

[0050] (4) Quenching: The hot extrusion die with the surface coated with titanium aluminum nitride was quenched in quenching oil at 800℃ for 30 minutes.

[0051] (5) Die cooling: After quenching, the hot extrusion die is first cooled to 500°C in quenching oil, kept at that temperature for 30 minutes, and then cooled naturally to obtain a titanium nitride aluminum coating for hot extrusion dies.

[0052] Comparative Example 1

[0053] The only difference between this comparative example and Example 1 is that the aluminum content in the titanium-aluminum alloy target used during coating deposition is 40 at.%.

[0054] Comparative Example 2

[0055] The only difference between this comparative example and Example 1 is that the substrate bias voltage is 100V during the deposition of the coating.

[0056] Comparative Example 3

[0057] The only difference between this comparative example and Example 1 is that, after the deposition coating is performed, quenching is not performed, and the material is directly cooled naturally to obtain a titanium nitride aluminum coating for hot extrusion dies.

[0058] Comparative Example 4

[0059] The only difference between this comparative example and Example 1 is that, after quenching, segmented cooling is not performed; instead, the material is directly cooled naturally to obtain a titanium nitride aluminum coating for hot extrusion dies.

[0060] The performance of the titanium nitride aluminum coatings prepared in each embodiment and comparative example was tested, and the test results are shown in Table 1.

[0061] Table 1

[0062]

[0063] As can be seen from the test results in Table 1, the titanium aluminum nitride coating for hot extrusion dies prepared in Examples 1-3 of this invention has a bonding strength with the hot extrusion die greater than 80 N / m. 2 It exhibits high temperature resistance exceeding 900℃, a hardness exceeding 3300HV, and a steel friction coefficient below 0.3, significantly extending the service life of hot extrusion dies. However, reducing the aluminum content in the titanium nitride aluminum coating or increasing the bias voltage noticeably decreases the coating's hardness and heat resistance. Furthermore, incomplete quenching or failure to perform segmented cooling after quenching significantly reduces the bonding strength with the hot extrusion die, and the coating's hardness and heat resistance also slightly decrease.

Claims

1. A method for producing a titanium aluminum nitride coating for a hot extrusion die, characterized by: The method comprises the following steps: (1) mold temperature rise: the hot extrusion mold after cleaning and drying is placed in a coating chamber, and is heated at a rate of 2-5 ℃ / min to 180-220 ℃ under vacuum; (2) Pre-ionization: argon gas is introduced into the coating chamber to reach a vacuum degree of 1 x 10 -1 -5 x 10 -1 Pa, and ion bombardment is performed by turning on the arc source. (3) Deposited coating: nitrogen gas was introduced into the coating chamber, so that the total pressure of the mixed gas was kept at 1x10 -1 -5x10 -1 Pa, the arc current of the titanium-aluminum alloy target was set to 60-80 A, the substrate bias was 20-30 V, and a titanium-aluminum nitride coating with a thickness of 3-4 μm was deposited on the surface of the hot extrusion die, wherein the proportion of aluminum in the titanium-aluminum alloy target was 55-60 at.%. (4) quenching: the hot extrusion mold after the surface is deposited with the titanium aluminum nitride coating is quenched at a temperature of 700-800 ℃, the quenching is performed in quenching oil, and the quenching time is 30-60 min; (5) mold temperature drop: after the quenching is completed, the hot extrusion mold is cooled in the quenching oil, is cooled to 400-500 ℃ first, is kept for 30-60 min, and is naturally cooled, so that the hot extrusion mold is obtained and is coated with the titanium aluminum nitride coating; The prepared hot extrusion die is coated with titanium aluminum nitride layer with thickness of 3-4 μm, and the bonding strength between the titanium aluminum nitride layer and the hot extrusion die is greater than 80 N / m 2 , the high temperature resistance reaches above 900℃, the hardness reaches above 3300HV, and the steel friction coefficient is below 0.

3.

2. The method for producing a titanium aluminum nitride coating for a hot extrusion die according to claim 1, characterized by: In step (1), the hot extrusion mold is ultrasonically cleaned in anhydrous ethanol for 5-30 min during cleaning.

3. The method of producing a titanium aluminum nitride coating for a hot extrusion die according to claim 1, characterized by: In step (1), the hot extrusion mold is dried at 50-80 ℃ for 10-30 min during drying.

4. The method of claim 1, wherein the method is characterized by: In step (1), the vacuum degree in the plating chamber is kept at 1 x 10 -4 -1 x 10 -3 Pa during the temperature rise.

5. The method of claim 1, wherein the method is characterized by: In step (2), the ion bombardment time is 5-15 min.

6. The method of producing a titanium aluminum nitride coating for a hot extrusion die according to claim 1, characterized by: In step (3), the titanium aluminum nitride coating deposition time is 90-120 min.

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