A dual-gradient pure altin n hard metal cutter coating, a preparation method and application thereof

Abstract

This invention belongs to the technical field of tool coating preparation methods, specifically relating to a dual-gradient pure AlTiN cemented carbide tool coating, its preparation method, and its application. The coating is an AlTiN system, containing no other alloying elements. It forms a dual-gradient structure from the WC-Co cemented carbide substrate to the coating surface, combining a Ti content gradient and a thickness gradient: the bottom layer is 1.5 μm thick with a Ti content of 60-70 at.%; the intermediate transition layer is 1 μm thick with a Ti content that linearly decreases from the bottom layer to 40-50 at.%; and the top layer is 0.7 μm thick with a Ti content of 40-50 at.%. The coating is prepared using HiPIMS technology, achieving gradient deposition by linearly adjusting the pulse width from 100 μs to 200 μs, the bias voltage from -150V to -250V, and the Ar / N2 flow ratio from 3:2 to 2:3, at a deposition temperature ≤450℃. The resulting coating exhibits an adhesion strength Lc2 ≥120N, internal stress ≤-1.8 GPa, and hardness ≥30 GPa. This invention solves the problems of poor adhesion and high internal stress in pure AlTiN coatings without adding alloying elements.

Description

Technical Field

[0001] This invention belongs to the technical field of tool coating preparation methods, specifically relating to a dual-gradient pure AlTiN cemented carbide tool coating, its preparation method, and its application. Background Technology

[0002] AlTiN coatings are widely used for surface modification of cemented carbide cutting tools due to their high hardness, good wear resistance, and high-temperature stability. However, there is a significant interface abrupt change between traditional single-component pure AlTiN coatings and WC-Co cemented carbide substrates, resulting in a mismatch in thermal expansion coefficients. This leads to large residual stress within the coating and insufficient adhesion between the coating and the substrate, making it prone to failures such as peeling and cracking during high-speed cutting.

[0003] To address the aforementioned issues, existing technologies attempt to improve coating performance by adding additional alloying elements or designing gradient structures. Patent document CN111270202B discloses a dual-gradient functional coating for cutting tools, consisting of alternating deposition of TiAlMe′N (Me′ being toughening elements such as B, C, Ta, and Nb) and TiAlMe″N (Me″ being hardening elements such as Si and Zr). These two layers, exhibiting different properties, are deposited alternately on the substrate surface, with decreasing and increasing thicknesses, respectively. This approach achieves complementary performance by introducing multiple alloying elements; however, the large number of elements and high cost, coupled with the increased number of interfaces due to the alternating structure of the two coatings, necessitates stricter control over the adhesion.

[0004] Another patent document, CN103132019B, discloses an AlZrCrN composite dual-gradient coated cutting tool. The tool consists of a Cr transition layer, a gradient CrN transition layer, a gradient AlZrCrN transition layer, and an AlZrCrN layer, arranged sequentially outwards from the substrate. The compositional gradient is achieved through a linear gradual change in the target current. This approach also relies on multiple additive elements such as Cr and Zr, and employs conventional magnetron sputtering, resulting in a low ionization rate and limited precision in controlling the composition and thickness.

[0005] In summary, existing technologies improve the performance of AlTiN coatings by adding multiple alloying elements or using alternating multi-material stacked structures. However, these solutions increase material costs and production complexity, and fail to simultaneously address the issues of low adhesion, high internal stress, and easy peeling without altering the pure AlTiN system. Summary of the Invention

[0006] The purpose of this invention is to provide a dual-gradient pure AlTiN cemented carbide tool coating, its preparation method, and its application, in order to solve the technical problems of insufficient bonding between pure AlTiN coating and cemented carbide substrate, internal stress concentration, and easy peeling in the prior art, and to further solve the problems of increased cost and complicated process caused by the addition of multiple alloying elements in the existing improvement scheme.

[0007] The technical solution of the present invention is as follows: In the first aspect, a dual-gradient pure AlTiN cemented carbide tool coating is provided. The coating is deposited on the surface of a WC-Co cemented carbide substrate. The coating is an AlTiN system and does not contain any alloying elements other than Ti, Al, and N. A dual-gradient structure combining Ti content gradient and thickness gradient is formed from the WC-Co cemented carbide substrate to the coating surface, and the thickness is distributed in a decreasing manner. The coating comprises a base layer, an intermediate transition layer, and a top layer; The thickness of the bottom layer is 1.5 μm, and the Ti content of the bottom layer is 60-70 at.% and the Al content is 30-40 at.%. The intermediate transition layer has a thickness of 1 μm, and the Ti content of the intermediate transition layer linearly decreases from 60–70 at.% of the bottom layer to 40–50 at.%, while the Al content of the intermediate transition layer linearly increases from 30–40 at.% of the bottom layer to 50–60 at.%. The thickness of the top layer is 0.7 μm, and the Ti content of the top layer is 40-50 at.% and the Al content is 50-60 at.%.

[0008] Secondly, a method for preparing the dual-gradient pure AlTiN cemented carbide tool coating as described above is provided, which employs HiPIMS technology for deposition and includes the following steps: (1) Pretreatment of the substrate: The WC-Co carbide tool substrate is ground, polished, and ultrasonically cleaned in sequence, and then dried for later use. (2) HiPIMS plasma cleaning: The pretreated substrate is placed in the vacuum chamber of the HiPIMS deposition equipment and evacuated to a vacuum degree ≤ 5 × 10⁻⁶. -3 Pa, Ar gas is introduced to perform two-stage plasma cleaning; (3) Dual gradient pure AlTiN coating deposition, using a single TiAl alloy target, the Al / Ti atomic ratio of the TiAl alloy target is 1.0 to 1.5, Ar / N2 mixed gas is introduced, during the deposition process, the pulse width is linearly adjusted from 100 μs to 200 μs, the pulse frequency is maintained at 150 to 250 Hz, the bias voltage is linearly adjusted from -150V to -250V, the Ar / N2 mixed gas flow ratio is linearly transitioned from 3:2 to 2:3, the deposition temperature is ≤450℃ throughout, the bottom layer, the intermediate transition layer and the top layer are deposited in sequence, the deposition thickness of the bottom layer is 1.5 μm, the deposition thickness of the intermediate transition layer is 1 μm and the deposition thickness of the top layer is 0.7 μm; (4) Post-treatment: After deposition, the vacuum chamber is naturally cooled to room temperature to obtain a dual-gradient pure AlTiN cemented carbide tool coating.

[0009] Preferably, the two-stage plasma cleaning in step (2) includes: first-stage cleaning, bias voltage -700 to -900V, pulse frequency 50 to 100Hz, Ar gas flow rate 40 to 60sccm, and etching time 15 to 20min; second-stage cleaning, bias voltage -100 to -150V, pulse frequency 200 to 300Hz, Ar gas flow rate 40 to 60sccm, and activation time 5 to 10min.

[0010] Preferably, in step (3), the Al in the plasma is monitored in real time during the deposition process using spectral diagnostics. + Ti + N + Ion concentration, wherein the ion concentration fluctuation is ≤5%.

[0011] Preferably, in step (3), the total flow rate of the Ar / N2 mixed gas is 80–120 sccm, and the vacuum level is maintained at 1 × 10⁻⁶ during the deposition process. -2 ~5×10 -2 Pa.

[0012] Preferably, in step (3), the matrix rotation speed is 5 to 15 r / min.

[0013] Preferably, in step (4), the natural cooling rate is 5 to 10 °C / min.

[0014] Thirdly, a cemented carbide cutting tool is provided, wherein the substrate of the cemented carbide cutting tool is WC-Co cemented carbide, and the surface of the cemented carbide cutting tool has the above-mentioned dual-gradient pure AlTiN cemented carbide cutting tool coating, wherein the coating is prepared by any of the methods described above.

[0015] Preferably, the carbide cutting tool is a turning tool or a milling cutter.

[0016] Preferably, the coating adhesion force Lc2 of the carbide cutting tool is ≥120N, the internal stress is ≤-1.8GPa, the room temperature hardness is ≥30GPa, and the surface roughness Ra is ≤0.06μm.

[0017] Compared with the prior art, the advantages of the present invention are: (1) The pure AlTiN system is adopted without adding any additional alloying elements, which reduces the material cost and process complexity. Through the design of high Ti content (60-70 at.%) and thickness (1.5 μm) of the bottom layer, good interfacial wettability is formed with the WC-Co matrix, so that the bonding force Lc2 reaches more than 120 N.

[0018] (2) By setting an intermediate transition layer (1 μm thick), the Ti content decreases linearly from the bottom layer to 40-50 at.%, and the Al content increases accordingly, eliminating the abrupt change at the interface between the substrate and the coating, alleviating the stress concentration caused by the difference in thermal expansion coefficients, and reducing the internal stress of the coating to below -1.8 GPa.

[0019] (3) The top layer is 0.7 μm thick and is made of standard pure AlTiN, which ensures wear resistance while avoiding stress accumulation caused by excessive top layer thickness. The total coating thickness is 3.2 μm, and the thickness is distributed in a decreasing manner to achieve a balance between stress dispersion and wear resistance.

[0020] (4) HiPIMS technology is used to achieve gradient deposition through linear gradual changes in pulse width, bias voltage, and gas flow ratio. High ionization rate ensures dense coating and uniform composition. The low-temperature process of ≤450℃ throughout avoids the decrease in bending strength of the cemented carbide substrate. The preparation method is compatible with existing production equipment and does not require large-scale modification. Attached Figure Description

[0021] The present invention will be further described below with reference to the accompanying drawings and embodiments: Figure 1 This is a process flow diagram of the preparation method of the dual-gradient pure AlTiN cemented carbide tool coating described in this invention; Figure 2 This is a cross-sectional scanning electron microscope (SEM) image of the dual-gradient pure AlTiN cemented carbide tool coating prepared in Example 1 of this invention; Figure 3 This is a bar chart comparing the elastic modulus and resistance to plastic deformation of the embodiments and comparative examples described in this invention. Figure 4 This is a comparison chart of load-displacement curves between the embodiments and comparative examples described in this invention. Detailed Implementation

[0022] The present invention will be further described in detail below with reference to specific embodiments.

[0023] Example 1

[0024] I. Coating Structure A dual-gradient pure AlTiN carbide tool coating is deposited on the surface of a WC-Co carbide end mill substrate (substrate composition: WC-8wt.%Co). The layers from the substrate to the coating surface are as follows: 1. Bottom layer: 1.5 μm thick, Ti content 60 at.% %, Al content 40 at.%; 2. Intermediate transition layer: 1 μm thick, Ti content linearly decreases from 60 at.% to 40 at.%, Al content linearly increases from 40 at.% to 60 at.%; 3. Top layer: 0.7 μm thick, Ti content 40 at.%, Al content 60 at.%.

[0025] The total coating thickness is 3.2 μm, and the thickness error is ≤0.05 μm as measured by cross-sectional SEM.

[0026] II. Preparation Method The preparation process flow of this embodiment is as follows: Figure 1 As shown, the details are as follows: (1) Matrix pretreatment The WC-Co carbide end mill substrate was successively polished with 800#, 1000#, and 1200# sandpaper, and then polished with diamond polishing paste until the surface roughness Ra ≤ 0.02μm. The polished substrate was then placed in anhydrous ethanol and ultrasonically cleaned for 10 minutes at an ultrasonic power of 300W; after removal, it was placed in an 80℃ oven to dry for 20 minutes for later use.

[0027] (2) HiPIMS plasma cleaning The pretreated substrate was placed in the vacuum chamber of the HiPIMS deposition equipment, and the vacuum level was evacuated to 3 × 10⁻⁶. - 3 Pa. Ar gas with a purity of 99.999% is introduced for two-stage plasma cleaning: First-stage cleaning: bias voltage -700V, pulse frequency 50Hz, Ar gas flow rate 40sccm, etching time 15min. This step is used to remove residual oxide layer and oil on the substrate surface, while forming a nanoscale rough surface on the substrate surface, increasing the contact area between the coating and the substrate.

[0028] Second-stage cleaning: bias voltage -100V, pulse frequency 200Hz, Ar gas flow rate 40sccm, activation time 5min. This step is used to achieve atomic-level cleaning of the substrate surface and form uniform nucleation sites.

[0029] (3) Dual-gradient pure AlTiN coating deposition A single TiAl alloy target (99.9% purity, Al / Ti atomic ratio 1.0) was used, and an Ar / N2 mixed gas was introduced at a total flow rate of 80 sccm.

[0030] During deposition, the pulse width was linearly adjusted from 100 μs to 200 μs, while the pulse frequency was maintained at 150 Hz. Increasing the pulse width during HiPIMS deposition significantly improves the ionization rate of the target material, leading to an increase in the density of Ti and Al ions. The bias voltage was linearly adjusted from -150 V to -250 V (linear change rate: 0.33 V / min). Increasing the absolute value of the bias voltage enhances the ion bombardment energy and promotes coating densification; however, excessively high bias voltage can introduce excessive compressive stress. This invention controls the compressive stress level while improving the ionization rate through synchronous linear changes in bias voltage and pulse width.

[0031] The Ar / N2 mixed gas flow ratio transitions linearly from 3:2 to 2:3 (i.e., the Ar flow rate linearly decreases from 48 sccm to 32 sccm, the N2 flow rate linearly increases from 32 sccm to 48 sccm, and the total flow rate remains unchanged at 80 sccm). This change in the Ar / N2 flow ratio directly affects the reaction kinetics of Ti, Al, and N: as the N2 ratio increases, the activity of N increases, which is conducive to the formation of the AlTiN phase with a higher Al content.

[0032] The deposition temperature was maintained at 400℃, controlled by thermocouple temperature feedback. Al concentration in the plasma was monitored in real-time using spectral diagnostics. + (wavelength 396.1nm), Ti + (wavelength 334.9nm), N + The emission intensity at wavelength 391.4 nm was recorded every 30 seconds, and the calculated ion concentration fluctuation was ≤5%. The matrix rotation speed was 5 r / min (triaxial revolution + rotation), and the vacuum level was maintained at 1×10⁻⁶. -2 Pa.

[0033] Deposition time control: bottom layer deposition 45 min, intermediate transition layer deposition 30 min, top layer deposition 21 min. Total deposition time 96 min. Thickness was monitored in real time during deposition using a quartz crystal oscillating film thickness gauge.

[0034] (4) Post-processing After deposition, all arc sources and bias power supplies are turned off, the vacuum chamber temperature is maintained at 400℃ for 10 minutes to release residual stress, and then the end mill is naturally cooled to room temperature at a rate of 5℃ / min. The end mill is then removed to obtain a dual-gradient pure AlTiN carbide end mill coating.

[0035] III. Performance Testing like Figure 2As shown, this is a SEM image of the coating cross-section taken at an accelerating voltage of 15.0 kV, a working distance of 10.0 mm, a backscattered electron detector (BED-C), and a magnification of 10,000x. It shows the layers from the WC-Co cemented carbide substrate outwards as a bottom layer (approximately 1.5 μm thick), an intermediate transition layer (approximately 1 μm thick), and a top layer (approximately 0.7 μm thick). The interfaces between the three layers are continuous, with no obvious pores or cracks. There are contrast differences between the bottom layer and the intermediate transition layer, and between the intermediate transition layer and the top layer in the image; these differences originate from variations in Ti content.

[0036] The coating performance was tested using the following methods: (1) Coating thickness: The thickness of each layer was measured by cross-sectional SEM with an accelerating voltage of 15kV and a magnification of 10,000. Five different locations were selected on the cross-sectional image to measure the thickness of each layer, and the average value was taken. Results: bottom layer 1.51±0.02μm, middle layer 1.02±0.01μm, top layer 0.70±0.01μm.

[0037] (2) Bonding strength Lc2: A scratch tester was used with a loading rate of 10 N / min, an initial load of 1 N, an ending load of 200 N, and a scratch length of 5 mm. The Lc2 was determined by combining acoustic emission signals with microscopic observation. Each sample was tested 5 times, and the average value was taken. Result: 152 N (standard deviation ± 6 N).

[0038] (3) Internal stress: X-ray diffraction sin 2 The φ method was used, with the detection direction being the (220) crystal plane. The φ angle was 0°, 15°, 30°, and 45°. The test sample was a 20mm × 20mm × 3mm WC-Co sheet, and the coating was deposited under the same conditions. Result: -1.8GPa (standard deviation ±0.1GPa).

[0039] (4) Room temperature hardness: A nanoindenter was used with an indentation depth of 200 nm. Continuous stiffness mode was used, and 10 points were measured for each sample. The average value was taken. Result: 32 GPa (standard deviation ± 1.5 GPa).

[0040] (5) Surface roughness Ra: A white light interferometer was used, with a sampling length of 0.8 mm. Five regions were measured for each sample, and the average value was taken. Result: 0.06 μm (standard deviation ±0.005 μm).

[0041] (6) Tool life: Cutting conditions: workpiece material 45# carbon steel (hardness HB220), cutting speed 120m / min, feed rate 0.2mm / r, depth of cut 0.5mm, dry cutting, milling method is side milling. Tool failure criteria: flank wear VB reaches 0.3mm, or large-scale coating peeling or chipping occurs. Three tools were tested in each group, and the average value was taken. Result: 1840min (three test values: 1810min, 1860min, 1850min).

[0042] (7) Elastic modulus and resistance to plastic deformation: The elastic modulus E and reduced modulus Er of the coating were measured simultaneously using a nanoindenter (the same equipment used for hardness testing), and H / E (elastic strain failure resistance factor) and H were calculated. 3 / (Er) 2 (Resistance to plastic deformation factor). Ten points were measured for each sample, and the average value was taken.

[0043] Test results are as follows Figure 3 As shown. Figure 3 The H / E and H of Sample 1 (Comparative Example 1), Sample 2 (Example 2), and Sample 3 (Example 1) are given. 3 / (Er) 2 Compare the bar charts. From... Figure 3 As can be seen, the H / E and H in the embodiments of the present invention 3 / (Er) 2 The values ​​are all significantly higher than those of Comparative Example 1, indicating that the coating of the present invention has higher resistance to elastic failure and resistance to plastic deformation.

[0044] Figure 4 The corresponding load-displacement curves are shown. Sample 1 (Comparative Example 1) has the smallest indentation displacement under the same maximum load (approximately 53 mN), indicating that it has the highest hardness but is also more brittle. Sample 2 (Example 2) has an indentation displacement close to that of Sample 3, but its elastic recovery after unloading is moderate. Sample 3 (Example 1) has a slightly larger indentation displacement than Sample 1, but its elastic recovery after unloading is the most complete, indicating that it has better toughness and crack resistance.

[0045] comprehensive Figure 3 and Figure 4 The embodiments of the present invention significantly improve the coating's resistance to plastic deformation and toughness while maintaining high hardness.

[0046] Example 2

[0047] I. Coating Structure --A dual-gradient pure AlTiN carbide tool coating is deposited on the surface of a WC-Co carbide turning tool substrate (substrate composition: WC-10wt.%Co). The specific structure is as follows: 1. Bottom layer: 1.5 μm thick, Ti content 65 at.% %, Al content 35 at.%; 2. Intermediate transition layer: 1 μm thick, with Ti content linearly decreasing from 65 at.% to 45 at.% and Al content linearly increasing from 35 at.% to 55 at.%; 3. Top layer: 0.7 μm thick, Ti content 45 at.%, Al content 55 at.%.

[0048] The total coating thickness is 3.2 μm, and the thickness error is ≤0.05 μm.

[0049] II. Preparation Method (1) Matrix pretreatment The WC-Co carbide turning tool substrate was successively polished with 800#, 1000#, and 1200# sandpaper, and then polished with diamond polishing paste until the surface roughness Ra ≤ 0.02μm. The polished substrate was then placed in anhydrous ethanol and ultrasonically cleaned for 12 minutes at an ultrasonic power of 400W; after removal, it was placed in a 90℃ oven to dry for 25 minutes for later use.

[0050] (2) HiPIMS plasma cleaning The pretreated substrate was placed in the vacuum chamber of the HiPIMS deposition equipment, and the vacuum level was evacuated to 4 × 10⁻⁶. - 3 Pa. Introduce 99.999% pure Ar gas to flush the chamber three times, 8 minutes each time. Then perform two-stage plasma cleaning: First stage cleaning: bias voltage -800V, pulse frequency 80Hz, Ar gas flow rate 50sccm, etching time 18min; Second-stage cleaning: bias voltage -120V, pulse frequency 250Hz, Ar gas flow rate 50sccm, activation time 8min.

[0051] (3) Dual-gradient pure AlTiN coating deposition A single TiAl alloy target (99.9% purity, Al / Ti atomic ratio 1.2) was used, and an Ar / N2 mixed gas was introduced at a total flow rate of 100 sccm. The parameters changed linearly during deposition as follows: The pulse width was linearly adjusted from 100μs to 200μs; The pulse frequency is maintained at 200Hz; The bias voltage is linearly adjusted from -150V to -250V; The Ar / N2 mixed gas flow ratio transitions linearly from 3:2 to 2:3 (i.e., the Ar flow rate linearly decreases from 60 sccm to 40 sccm, and the N2 flow rate linearly increases from 40 sccm to 60 sccm).

[0052] The deposition temperature was maintained at 450℃. Al in the plasma was monitored in real-time using spectral diagnostics. + Ti + N + Ion concentration fluctuation was measured to be ≤5%. The matrix rotation speed was 10 r / min, and the vacuum level was maintained at 3 × 10⁻⁶. -2 Pa. Deposition time control: bottom layer deposition 42 min, intermediate transition layer deposition 28 min, top layer deposition 19.6 min. Total deposition time 89.6 min.

[0053] (4) Post-processing After deposition, the vacuum chamber temperature was maintained at 450℃ for 12 minutes, and then naturally cooled to room temperature at a rate of 8℃ / min. The cutting tool was then removed to obtain a double-gradient pure AlTiN cemented carbide cutting tool coating.

[0054] III. Performance Testing Using the same test method as in Example 1, the results are as follows: Coating thickness: bottom layer 1.51±0.01μm, intermediate layer 1.01±0.01μm, top layer 0.70±0.01μm; Bonding force Lc2: 128N (standard deviation ±5N); Internal stress: -1.6 GPa (standard deviation ±0.1 GPa); Room temperature hardness: 35 GPa (standard deviation ± 2 GPa); Surface roughness Ra: 0.05 μm (standard deviation ±0.005 μm); Tool life: Cutting conditions were the same as in Example 1 (45# carbon steel, 120m / min, 0.2mm / r, 0.5mm, dry cutting), with a life of 2080min (three test values: 2060min, 2100min, 2090min).

[0055] Comparative Example 1 The tool substrate of Comparative Example 1 was exactly the same as that of Example 1 (WC-Co carbide end mill, with the same pretreatment process). A single-component pure AlTiN coating was deposited using conventional DC magnetron sputtering (DCMS) with a TiAl alloy target (Al / Ti atomic ratio 1.0). The deposition parameters were: gas pressure 0.3 Pa, Ar / N2 flow ratio 1:1 (40 sccm each), bias voltage -80 V, deposition temperature 400 °C, deposition time 120 min, coating thickness 3.2 μm (controlled by deposition time), Ti content 50 at.%, and Al content 50 at.%. Post-treatment was the same as in Example 1.

[0056] Performance test results: bonding force Lc2 = 75 N (standard deviation ± 8 N), internal stress = -3.0 GPa (standard deviation ± 0.2 GPa), hardness = 33 GPa (standard deviation ± 2 GPa), surface roughness Ra = 0.12 μm (standard deviation ± 0.01 μm), tool life (same cutting conditions as in Example 1) = 800 min (three test values: 790 min, 810 min, 800 min).

[0057] Comparative Example 2 The tool substrate of Comparative Example 2 was exactly the same as that of Example 2. A single-component pure AlTiN coating was deposited using the conventional DCMS process. The target material was TiAl (Al / Ti atomic ratio 1.2), and the deposition parameters were the same as those of Comparative Example 1 (only the target material ratio was adjusted). The coating thickness was 3.2 μm, with a Ti content of 45 at.% and an Al content of 55 at.%. Performance test results: adhesion force Lc2 = 75 N, internal stress = -3.0 GPa, hardness = 33 GPa, surface roughness Ra = 0.12 μm, and tool life = 800 min (consistent with Comparative Example 1, due to the same composition and thickness).

[0058] Performance data summary and analysis To clearly compare the performance differences between the embodiments of the present invention and the comparative examples, the above test results are summarized in Table 1 below.

[0059] Table 1: Comparison of Coating Performance between Examples and Comparative Examples

[0060] Analysis of the data in Table 1 shows that: Adhesion strength: The adhesion strengths Lc2 of Examples 1 and 2 were 152 N and 128 N, respectively, significantly higher than the 75 N of Comparative Examples 1 and 2. This indicates that the high Ti content substrate design, combined with HiPIMS high ionization rate deposition, effectively enhances the interfacial bonding strength between the coating and the WC-Co substrate.

[0061] Internal stress: The compressive stress of the comparative coating is as high as -3.0 GPa, while the internal stress of Example 1 and Example 2 is reduced to -1.8 GPa and -1.6 GPa, respectively. This indicates that the stepless gradual change of composition in the intermediate transition layer eliminates abrupt interface changes and effectively alleviates stress concentration caused by the mismatch of thermal expansion coefficients.

[0062] Hardness: The hardness of Example 1 was 32 GPa, which was basically the same as the 33 GPa of the comparative example; the hardness of Example 2 reached 35 GPa, which was significantly higher than that of the comparative example. The difference in hardness mainly stemmed from the difference in Al content in the top layer (55 at.% in Example 2 and 60 at.% in Example 1) and deposition parameters, indicating that the technical solution of the present invention can optimize other properties while maintaining or improving the hardness of the coating.

[0063] Surface roughness: The Ra values ​​of Example 1 and Example 2 were 0.06 μm and 0.05 μm, respectively, which were significantly better than the 0.12 μm of the comparative example, indicating that the coating prepared by HiPIMS technology has higher density and fewer surface droplets and other defects.

[0064] Tool life: Under the same cutting conditions, the end mill life of Example 1 was 1840 min, which is 130% higher than that of Comparative Example 1 (800 min); the turning tool life of Example 2 was 2080 min, which is 160% higher than that of Comparative Example 2 (800 min). The significant increase in tool life is a comprehensive result of enhanced bonding force, reduced internal stress, and improved surface quality.

[0065] The above embodiments are merely illustrative of the technical concept and features of the present invention, intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly, and should not be construed as limiting the scope of protection of the present invention. It will be apparent to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments, and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects. The scope of the present invention is defined by the appended claims rather than the foregoing description, and thus all changes falling within the meaning and scope of the equivalents of the claims are intended to be included within the present invention.

Claims

1. A dual-gradient pure AlTiN cemented carbide tool coating, characterized in that, The coating is deposited on the surface of the WC-Co cemented carbide substrate. The coating is an AlTiN system and does not contain any alloying elements other than Ti, Al, and N. A dual gradient structure combining Ti content gradient and thickness gradient is formed from the WC-Co cemented carbide substrate to the coating surface, and the thickness is distributed in a decreasing manner. The coating comprises a base layer, an intermediate transition layer, and a top layer; The thickness of the bottom layer is 1.5 μm, and the Ti content of the bottom layer is 60-70 at.% and the Al content is 30-40 at.%. The intermediate transition layer has a thickness of 1 μm, and the Ti content of the intermediate transition layer linearly decreases from 60–70 at.% of the bottom layer to 40–50 at.%, while the Al content of the intermediate transition layer linearly increases from 30–40 at.% of the bottom layer to 50–60 at.%. The thickness of the top layer is 0.7 μm, and the Ti content of the top layer is 40-50 at.% and the Al content is 50-60 at.%.

2. The method for preparing a dual-gradient pure AlTiN cemented carbide tool coating according to claim 1, using HiPIMS technology for deposition, includes the following steps: (1) Pretreatment of the substrate: The WC-Co carbide tool substrate is ground, polished, and ultrasonically cleaned in sequence, and then dried for later use. (2) HiPIMS plasma cleaning: The pretreated substrate is placed in the vacuum chamber of the HiPIMS deposition equipment and evacuated to a vacuum degree ≤ 5 × 10⁻⁶. -3 Pa, Ar gas is introduced to perform two-stage plasma cleaning; (3) Dual gradient pure AlTiN coating deposition, using a single TiAl alloy target, the Al / Ti atomic ratio of the TiAl alloy target is 1.0 to 1.5, Ar / N2 mixed gas is introduced, during the deposition process, the pulse width is linearly adjusted from 100 μs to 200 μs, the pulse frequency is maintained at 150 to 250 Hz, the bias voltage is linearly adjusted from -150V to -250V, the Ar / N2 mixed gas flow ratio is linearly transitioned from 3:2 to 2:3, the deposition temperature is ≤450℃ throughout, the bottom layer, the intermediate transition layer and the top layer are deposited in sequence, the deposition thickness of the bottom layer is 1.5 μm, the deposition thickness of the intermediate transition layer is 1 μm and the deposition thickness of the top layer is 0.7 μm; (4) Post-treatment: After deposition, the vacuum chamber is naturally cooled to room temperature to obtain a dual-gradient pure AlTiN cemented carbide tool coating.

3. The method for preparing a dual-gradient pure AlTiN cemented carbide tool coating according to claim 2, characterized in that, The two-stage plasma cleaning in step (2) includes: first-stage cleaning, bias voltage -700 to -900V, pulse frequency 50 to 100Hz, Ar gas flow rate 40 to 60sccm, and etching time 15 to 20min; second-stage cleaning, bias voltage -100 to -150V, pulse frequency 200 to 300Hz, Ar gas flow rate 40 to 60sccm, and activation time 5 to 10min.

4. The method for preparing a dual-gradient pure AlTiN cemented carbide tool coating according to claim 2, characterized in that, In step (3), the Al in the plasma is monitored in real time during the deposition process using spectral diagnostics. + Ti + N + Ion concentration, wherein the ion concentration fluctuation is ≤5%.

5. The method for preparing a dual-gradient pure AlTiN cemented carbide tool coating according to claim 2, characterized in that, In step (3), the total flow rate of the Ar / N2 mixed gas is 80–120 sccm, and the vacuum level is maintained at 1 × 10⁻⁶ during the deposition process. -2 ~5×10 -2 Pa.

6. The method for preparing a dual-gradient pure AlTiN cemented carbide tool coating according to claim 2, characterized in that, In step (3), the matrix rotation speed is 5 to 15 r / min.

7. The method for preparing a dual-gradient pure AlTiN cemented carbide tool coating according to claim 2, characterized in that, In step (4), the natural cooling rate is 5 to 10 °C / min.

8. A cemented carbide cutting tool, characterized in that, The substrate of the cemented carbide tool is WC-Co cemented carbide, and the surface of the cemented carbide tool has the dual-gradient pure AlTiN cemented carbide tool coating as described in claim 1, wherein the coating is prepared by the method described in any one of claims 2-7.

9. The cemented carbide cutting tool according to claim 8, characterized in that, The carbide cutting tool is a lathe tool or a milling cutter.

10. The cemented carbide cutting tool according to claim 8, characterized in that, The cemented carbide cutting tool has a coating adhesion strength Lc2≥120N, internal stress≤-1.8GPa, room temperature hardness≥30GPa, and surface roughness Ra≤0.06μm.

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