High-temperature self-lubricating TiAlMoN / CrAlN multilayer hard coating and preparation method thereof

Abstract

The invention discloses a high-temperature self-lubricating TiAlMoN / CrAlN multilayer hard coating and a preparation method of the high-temperature self-lubricating TiAlMoN / CrAlN multilayer hard coating, and belongs to the field of cutter coatings. The comprehensive performance of the coating is remarkably improved through Mo element alloying and multi-layer structural design. Mo is subjected to solid solution in TiAlN crystal lattices, the large atomic radius of Mo causes crystal lattice distortion, dislocation motion is hindered, and then the mechanical strength of the coating is improved. The Mo element can form a self-lubricating Magneli phase in the friction process, has a slip plane structure easy to shear, and can improve the wear resistance of the coating. In the aspect of structural design, a nano-multilayer structure is deposited at a multilayer interface, and interlayer bonding strength is guaranteed through coincidence epitaxial growth. The high hardness of TiAlMoN and the strong oxidation resistance of CrAlN can be combined through the multilayer design, meanwhile, dislocation movement and crack expansion can be effectively hindered through the multilayer interface structure, the service temperature range of the coating is further expanded, and the service life of the coating is further prolonged.

Description

Technical Field

[0001] The invention belongs to the field of tool coatings, and in particular relates to a high-temperature self-lubricating TiAlMoN / CrAlN multilayer hard coating and a preparation method thereof. Background Art

[0002] As modern manufacturing rapidly develops toward high speed, precision, and environmental friendliness, cutting technology is placing increasingly stringent demands on tool performance. This is especially true in fields like aerospace and automotive manufacturing. The widespread use of difficult-to-machine materials (such as titanium alloys and high-temperature alloys) has further driven innovation in tool coating technology. As a core technology for improving tool life and machining efficiency, hard coatings must possess properties such as high hardness, excellent wear resistance, high-temperature oxidation resistance, and a low coefficient of friction. However, single coating systems often struggle to meet these multi-dimensional performance requirements, making the design of multilayer composite coatings a current research hotspot.

[0003] Traditional TiAlN coatings have become the mainstream choice for tool coatings due to their high hardness and age-hardening effect. However, their high friction coefficient results in insufficient wear resistance at room temperature, which limits their performance in high-speed cutting. In addition, the oxidation resistance temperature of TiAlN is only about 850°C, and phase transformation (cubic phase to hexagonal AlN transformation) is prone to occur at high temperatures, resulting in a sharp decline in mechanical properties. Although CrAlN coatings have better high-temperature oxidation resistance (>1000°C) and thermal stability, their hardness and wear resistance are lower than TiAlN, and they lack age-hardening effect. Brittle phases such as Cr2N may be generated at high temperatures, affecting the life of the coating. Existing studies have attempted to optimize performance through TiAlN / CrAlN multilayer structures, but most solutions have failed to effectively combine low friction and high-temperature stability, and the problem of insufficient interface bonding strength remains to be solved.

[0004] To address the frictional defects of TiAlN coatings, the introduction of Mo to form TiAlMoN coatings has become an effective solution. Research has shown that Mo exists as a solid solution in TiAlN, generating a self-lubricating Magnéli phase in situ during the friction process, significantly reducing the coefficient of friction while maintaining high hardness and reducing the wear rate. Furthermore, the addition of Mo further optimizes the thermal stability of the coating through solid solution strengthening, making it suitable for machining scenarios requiring higher cutting temperatures.

[0005] The core advantage of CrAlN coatings lies in their high-temperature oxidation resistance. At temperatures exceeding 1000°C, a dense mixed oxide layer of Cr2O3 and Al2O3 forms on the CrAlN surface, effectively blocking oxygen diffusion and delaying coating failure. However, the hardness and room-temperature wear resistance of a single CrAlN coating are insufficient, necessitating a multilayer design combined with other high-hardness coatings to balance high-temperature performance and mechanical strength. Summary of the Invention

[0006] Purpose of the invention: The present invention aims to provide a high-temperature self-lubricating TiAlMoN / CrAlN multilayer hard coating with high hardness, high stability and excellent wear resistance. The second purpose of the present invention is to provide a method for preparing the above-mentioned high-temperature self-lubricating TiAlMoN / CrAlN multilayer hard coating.

[0007] Technical solution: The high-temperature self-lubricating TiAlMoN / CrAlN multilayer hard coating of the present invention includes, from bottom to top, a Cr transition layer and several composite layers consisting of a CrAlN inner layer-a cyclic alternating layer-a TiAlMoN surface layer, wherein the alternating layer includes, from bottom to top, a TiAlMoN layer and a CrAlN layer.

[0008] Furthermore, the thickness of the multi-layer hard coating is 2-10 μm; the thickness of the Cr transition layer is 30-200 nm.

[0009] Furthermore, the thickness of the CrAlN inner layer is 150-300 nm, and the thickness ratio of the CrAlN inner layer to the TiAlMoN surface layer is 1:0.5-3.

[0010] Furthermore, in the alternating layers, the thickness of the TiAlMoN layer and the CrAlN layer are both in the range of 5-15 nm.

[0011] Furthermore, the number of cycles of the alternating layers is 2-4.

[0012] Furthermore, the number of the composite layers is 4-16.

[0013] In the present invention, TiAlMoN and CrAlN are combined into a multilayer structure. By introducing a Cr transition layer, the difference in thermal expansion coefficients between the substrate and the coating can be reduced, interfacial crack propagation can be suppressed, and bonding strength can be improved. The surface layer uses TiAlMoN to achieve low friction and high wear resistance, while the inner layer CrAlN provides high-temperature protection. At the same time, the cyclic alternating structure (interlayer nano-multilayer) can induce coherent epitaxial growth and enhance interfacial bonding. The age-hardening effect of TiAlMoN combined with the high-temperature oxidation resistance of CrAlN can expand the applicable temperature range of the coating and adapt to extreme processing environments above 1000°C.

[0014] The method for preparing the high-temperature self-lubricating TiAlMoN / CrAlN multilayer hard coating of the present invention comprises the following steps:

[0015] (1) Pretreatment of the substrate;

[0016] (2) Using a multi-arc ion plating machine for deposition treatment, the target materials are pure Cr target, CrAl target and TiAlMo target;

[0017] (3) After the test piece is clamped, it is heated to 400-500°C after vacuuming, argon gas is introduced, the DC power supply is turned on, and the substrate is filament cleaned;

[0018] (4) Turn off the DC power supply, turn on the Cr target, and deposit the Cr transition layer;

[0019] (5) Turn off the Cr target, introduce nitrogen, turn on the CrAl target, and deposit the CrAlN inner layer;

[0020] (6) Turn on the TiAlMo target, keep CrAl and TiAlMo co-depositing, and deposit cyclic alternating layers consisting of TiAlMoN layers and CrAlN layers;

[0021] (7) Turn off the CrAl target and deposit the TiAlMo surface layer;

[0022] (8) cyclically depositing a composite layer consisting of a CrAlN inner layer, a cyclic alternating layer, and a TiAlMoN surface layer;

[0023] (9) After the deposition is completed, wait for the test piece to cool down before taking it out.

[0024] Furthermore, in step (1), the substrate is high-speed steel or cemented carbide; in step (2), the CrAl target and the TiAlMo target are placed opposite each other; the Cr content in the CrAl target is 20-60 at.%; the Ti content in the TiAlMo target is 20-60 at.%, the Mo content is 2-20 at.%, and the rest is Al; in step (3), the process parameters for filament cleaning are: power bias of 500-600 V, cleaning time of 40-90 min, argon flow rate of 60-80 sccm, DC voltage of 30-60 V, and current of 10-20 A.

[0025] Furthermore, in step (1) and step (4), the deposition parameters of the Cr transition layer are: power bias voltage of 700-900 V, deposition time of 5-12 min, argon flow rate of 60-80 sccm, arc current of 50-100 A, and cooling for 5-10 min after completion; in step (5), the deposition parameters of the CrAlN inner layer are: power bias voltage of 50-100 V, deposition time of 5-20 min, argon flow rate of 400-500 sccm, arc current of 10 0-120A; in step (6), the deposition parameters of the TiAlMoN layer and the CrAlN layer are: power bias voltage of 50-100V, deposition time of 1-2min, argon flow rate of 400-500sccm, arc current of 100-120A; in step (7), the deposition parameters of the TiAlMo surface layer are: power bias voltage of 50-100V, deposition time of 5-20min, argon flow rate of 400-500sccm, arc current of 100-120A.

[0026] Principle of the invention: Mo element is introduced in the study of TiAlN modification. Mo exists in the TiAlN lattice in the form of solid solution. Its larger atomic radius can bring about lattice distortion and produce a solid solution strengthening effect, which effectively improves the strength of the TiAlN coating. The addition of Mo element prompts the coating to generate Magnéli phase in situ during the friction process, significantly reducing the friction coefficient and showing excellent tribological properties. Single-layer coatings often have problems such as excessive internal stress and coarse grains. The multi-layer coating of the present invention can combine the advantages of single-layer coating characteristics, using the CrAlN layer with excellent oxidation resistance and thermal stability as the template layer. In a high-temperature environment above 1000°C, the CrAlN coating can form a dense Cr2O3 and Al2O3 mixed oxide layer on its surface, which effectively blocks oxygen diffusion, delays coating failure, and makes up for the application defects of TiAlN. Through the multi-layer structure design, the internal stress of the coating is optimized, the growth of columnar crystals is blocked, and the problem of coarse grains is avoided. At the same time, by adjusting the thickness of the TiAlMoN layer, the advantages of the TiAlMoN layer and the CrAlN layer can be synergistically adjusted. The structure can be flexibly adjusted according to the application scenario. The high hardness of TiAlN and the oxidation resistance of CrAlN are combined, and the nano-multilayer structure between the two layers is used to ensure the interlayer bonding force. The interface effect is used to hinder the movement of dislocations to release internal stress and extend the coating life.

[0027] Beneficial effects: Compared with the existing technology, the present invention has the following significant advantages: (1) Through the solid solution strengthening effect brought about by Mo element alloying, the coating hardness is significantly improved, the thermal stability of the coating is optimized, and an oxidation phase with self-lubricating properties is generated at high temperature, which significantly improves the wear resistance; (2) The multi-layer structure design can block the growth of columnar crystals, refine the grains, and improve the hardness and toughness of the coating. The unique nano-multilayer interface design realizes co-epitaxial growth, ensures stress gradient transition, and improves the bonding between multiple layers. The thickness and thickness ratio of the sub-layers are adjusted according to the usage scenario between the multiple layers, and the performance advantages of TiAlMoN and CrAlN are combined to have excellent structural control capabilities. This technology can be widely used in surface strengthening fields such as high-speed cutting tools and precision molds. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Schematic diagram of the structure of the multi-layer hard coating in Example 1;

[0029] Figure 2 This is the XRD pattern of the multilayer hard coating prepared in Example 1;

[0030] Figure 3 This is a surface morphology image of the multilayer hard coating prepared in Example 1;

[0031] Figure 4 This is a cross-sectional morphology of the multilayer hard coating prepared in Example 1;

[0032] Figure 5 The hardness of the multilayer hard coating prepared in Example 1 and Example 2;

[0033] Figure 6 Room temperature wear morphologies of the multilayer hard coatings prepared in Examples 1 and 2, (a) is Example 1, (b) is Example 2;

[0034] Figure 7 These are the wear morphologies of the multilayer hard coatings prepared in Examples 1 and 2 at 500°C, (a) is Example 1, and (b) is Example 2. DETAILED DESCRIPTION

[0035] The present invention is further described below with reference to specific embodiments and accompanying drawings.

[0036] Example 1: Figure 1 As shown, the high-temperature self-lubricating TiAlMoN / CrAlN multilayer hard coating described in this embodiment has a cemented carbide substrate 1, and includes a Cr transition layer 2 and 7 composite layers consisting of a CrAlN inner layer 3-a cyclic alternating layer-a TiAlMoN surface layer 4 from bottom to top, and the alternating layer includes a TiAlMoN layer 4 and a CrAlN layer 3 from bottom to top.

[0037] The above coating preparation method comprises the following steps:

[0038] (1) Matrix pretreatment: ultrasonically clean the test piece with anhydrous ethanol and blow dry with cold air for later use;

[0039] (2) Use multi-arc ion plating machine for deposition treatment, and select pure Cr target, Cr 30 Al 70 Target and Ti 44 Al 44 Mo 12 Target, Cr 30 Al 70 Target and Ti 44 Al 44 Mo 12 The targets are placed relative to each other;

[0040] (3) After the specimen is clamped, the chamber is evacuated to below 0.03 Pa and heated to 450°C. The laminating equipment used is Quark A430A, and all components used are common components of the equipment.

[0041] (4) Argon gas was introduced, the DC power supply was turned on, and the substrate was cleaned with the following process parameters: power bias voltage of 500 V, cleaning time of 60 min, argon flow rate of 80 sccm, DC voltage of 40 V, and power supply of 15 A;

[0042] (5) Turn off the DC power supply, turn on the Cr target, and deposit the Cr transition layer. The deposition parameters are: power bias voltage 800 V, deposition time 5 min, argon flow rate 80 sccm, arc current 100 A, and cool for 10 min after completion.

[0043] (6) Turn off the Cr target, introduce nitrogen, turn on the CrAl target, and deposit the CrAlN inner layer. The deposition parameters are: power bias voltage 60 V, deposition time 5 min, argon flow rate 500 sccm, arc current 100 A;

[0044] (7) Turn on the TiAlMo target and keep co-depositing CrAl and TiAlMo. The deposition parameters are: power bias voltage of 60 V, argon flow rate of 500 sccm, arc current of 100 A, and deposition of cyclic alternating layers consisting of TiAlMoN layer and CrAlN layer. The deposition time is 1 min and the number of cycles is 2.

[0045] (8) The CrAl target was turned off and the TiAlMo surface layer was deposited. The deposition parameters were: power bias voltage 60 V, deposition time 5 min, argon flow rate 500 sccm, arc current 100 A;

[0046] (9) Repeating steps (6) to (8) alternately depositing a composite layer consisting of a CrAlN inner layer, a cyclic alternating layer, and a TiAlMoN surface layer, for 7 cycles, maintaining a total coating thickness of approximately 3 μm;

[0047] (10) After the deposition is completed, wait for the test piece to cool down before taking it out.

[0048] Example 2: The difference from Example 1 is that in step (8), the deposition time is controlled at 15 min. In step (8), the number of cycles is 4.

[0049] Comparative Example 1: The difference from Example 1 is that the target material is pure Cr target material, Cr 30 Al 70 Target and Ti 50 Al 50 The target material, the prepared coating is a TiAlN / CrAlN multilayer coating, which does not include the cyclic alternating layer in step (7).

[0050] Comparative Example 2: The difference from Example 1 is that the coating is a TiAlMoN / CrAlN nano-multilayer coating, which does not include the cyclic alternating layer in step (7).

[0051] The coatings of Examples 1-2 and Comparative Examples 1-2 were tested for performance, and the results are shown in Table 1.

[0052] Table 1 Summary of coating properties prepared in Example 1-Example 2 and Comparative Example 1-Comparative Example 2

[0053]

[0054] Figure 2 The XRD pattern of the multilayer hard coating prepared in Example 1 of the present invention shows that the main phase structure of the multilayer coating is the face-centered cubic solid solution fcc-(Al, Cr)N and fcc-(Ti, Al)N, which preferentially grow along the (111) plane.

[0055] Figure 3 This is a surface topography image of the multilayer hard coating prepared in Example 1 of the present invention. The coating's surface is relatively smooth, with relatively few large particles and cavities. This is due to the bombardment effect of the deposited atoms. The target contains 12% Mo, and the high Mo content bombards the coating surface with greater energy during deposition, effectively reducing large particle defects and surface roughness.

[0056] Figure 4 This is a cross-sectional morphology of the multilayer hard coating prepared in Example 1 of the present invention. The coating is tightly bonded to the substrate. The dark area in the figure is the CrAlN inner layer, and the bright area is the TiAlMoN surface layer. The nano-multilayer structure at the interface between the multiple layers is clearly displayed, and it is observed that the large particles generated during the multi-arc deposition process continuously affect the deposition of the multilayer structure.

[0057] Figure 5 The hardness of the multilayer hard coatings prepared in Examples 1 and 2 of the present invention is shown in the figure. The addition of Mo forms a (Ti,Al,Mo)N solid solution, which causes lattice distortion and increases resistance to dislocation motion, thereby improving hardness. However, as deposition time increases, the TiAlMoN surface layer thickness increases, the multilayer interface strengthening effect weakens, the grain refinement effect weakens, and the defect density increases, resulting in a decrease in the hardness of the multilayer coating.

[0058] Figure 6 The room temperature wear morphology of the multilayer hard coating prepared in Example 1 and Example 2 of the present invention shows that the wear scar surface is relatively smooth, with slight plowing grooves and no obvious cracks. This is because the overall hardness of the coating is relatively high, and high hardness can effectively improve wear resistance. It can also be seen from Table 1 that the coating exhibits a low friction coefficient. With the increase in the thickness of the TiAlMoN surface layer in Example 2, the wear scar becomes smooth and dense, the plowing groove phenomenon disappears, the wear scar narrows, only slight oxide adhesion occurs, and the wear rate decreases, indicating that the increase in the thickness of the TiAlMoN surface layer can improve the friction performance of the multilayer coating and reduce the loss of the coating.

[0059] Figure 7The 500°C wear morphology of the multilayer hard coating prepared in Example 1 and Example 2 of the present invention shows that the coating wear is aggravated compared to room temperature. However, Table 1 shows that the coating still maintains a low friction coefficient. This is because Mo is oxidized at high temperature to form MoO2 with lubricating effect. Its low shear strength and high-temperature chemical inertness can reduce the adhesion of wear debris, thereby offsetting the upward trend of the friction coefficient caused by high temperature and increased oxide film thickness. Example 2 has a thicker TiAlMoN surface layer thickness, and the coating wear is alleviated. The wear mark morphology becomes smooth and flat, without obvious plowing grooves and bonded oxides. At this time, the main wear form of the coating is oxidative wear, and the wear rate is reduced, showing excellent high-temperature self-lubrication.

Claims

1. A high-temperature self-lubricating TiAlMoN / CrAlN multilayer hard coating, characterized in that: From bottom to top, it comprises a Cr transition layer and several composite layers consisting of a CrAlN inner layer, a cyclic alternating layer and a TiAlMoN surface layer. The alternating layer comprises a TiAlMoN layer and a CrAlN layer from bottom to top.

2. The coating according to claim 1, characterized in that The thickness of the multi-layer hard coating is 2-10 μm; the thickness of the Cr transition layer is 30-200 nm.

3. The coating according to claim 1, characterized in that The thickness of the CrAlN inner layer is 150-300 nm, and the thickness ratio of the CrAlN inner layer to the TiAlMoN surface layer is 1:0.5-3.

4. The coating according to claim 1, characterized in that In the alternating layers, the thickness of the TiAlMoN layer and the CrAlN layer are both in the range of 5-15 nm.

5. The coating according to claim 1, characterized in that The number of cycles of the alternating layers is 2-4.

6. The coating according to claim 1, characterized in that The number of the composite layers is 4-16.

7. A method for preparing the high-temperature self-lubricating TiAlMoN / CrAlN multilayer hard coating according to claim 1, characterized in that: The following steps are involved: (1) Pretreatment of the substrate; (2) Using a multi-arc ion plating machine for deposition treatment, the target materials are pure Cr target, CrAl target and TiAlMo target; (3) After the test piece is clamped, it is heated to 400-500°C after vacuuming, argon gas is introduced, the DC power supply is turned on, and the substrate is filament cleaned; (4) Turn off the DC power supply, turn on the Cr target, and deposit the Cr transition layer; (5) Turn off the Cr target, introduce nitrogen, turn on the CrAl target, and deposit the CrAlN inner layer; (6) Turn on the TiAlMo target, keep CrAl and TiAlMo co-depositing, and deposit cyclic alternating layers consisting of TiAlMoN layers and CrAlN layers; (7) Turn off the CrAl target and deposit the TiAlMo surface layer; (8) cyclically depositing a composite layer consisting of a CrAlN inner layer, a cyclic alternating layer, and a TiAlMoN surface layer; (9) After the deposition is completed, wait for the test piece to cool down before taking it out.

8. The preparation method according to claim 7, characterized in that In step (1), the substrate is high-speed steel or cemented carbide; in step (2), the CrAl target and the TiAlMo target are placed opposite to each other.

9. The preparation method according to claim 7, characterized in that In step (3), the process parameters for filament cleaning are: power bias voltage of 500-600 V, cleaning time of 40-90 min, argon flow rate of 60-80 sccm, DC voltage of 30-60 V, and current of 10-20 A.

10. The preparation method according to claim 7, characterized in that In step (4), the deposition parameters of the Cr transition layer are: power bias of 700-900 V, deposition time of 5-12 min, argon flow rate of 60-80 sccm, arc current of 50-100 A, and cooling for 5-10 min after completion; in step (5), the deposition parameters of the CrAlN inner layer are: power bias of 50-100 V, deposition time of 5-20 min, argon flow rate of 400-500 sccm, and arc current of 100-120 A; in step (6), the deposition parameters of the TiAlMoN layer and the CrAlN layer are: power bias of 50-100 V, deposition time of 1-2 min, argon flow rate of 400-500 sccm, and arc current of 100-120 A; in step (7), the deposition parameters of the TiAlMo surface layer are: The power bias voltage is 50-100 V, the deposition time is 5-20 min, the argon flow rate is 400-500 sccm, and the arc current is 100-120 A.

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