Nano multilayer composite coating and its preparation method and cutting tool

Abstract

The present invention belongs to the field of coatings, and specifically relates to a nano multilayer composite coating, a preparation method thereof, and an application thereof. The nano multilayer composite coating comprises an A layer and a B layer, wherein the A layer and the B layer are arranged in a periodic A-B-A-B or B-A-B-A manner, and the A layer has a ZrAlN cubic phase as the main structure and its composition is represented by the chemical formula Zr x1 (Al x2 Hf x3 Me x4 )N x5 Indicates that the B layer has HfAlN cubic phase as the main structure and its composition is based on the chemical formula Hf y1 (Al y2 Zr y3 Me` y4 )N y5 The nano multi-layer composite coating provided by the present invention has super hardness, high toughness and high bonding strength, and thus has a long cutting life.

Description

Technical Field

[0001] The present invention belongs to the field of coatings, and in particular relates to a nano multi-layer composite coating and a preparation method and application thereof. Background Art

[0002] With the rapid development of cutting tool technology, people are placing higher demands on cutting tool materials and performance, demanding that cutting tools have a longer service life. Depositing coatings on tool surfaces using technologies such as physical vapor deposition (PVD) and chemical vapor deposition (CVD) has become an important development direction for modern cutting tools. As an important component of cemented carbide cutting tools, coatings, along with the substrate and groove type, are closely related to tool performance. Stable coatings can significantly improve cutting tool service life and processing efficiency.

[0003] As early as the 1990s, people developed and applied TiAlN coatings with higher hardness and higher wear resistance based on TiN, which greatly improved the cutting performance and service life of tools. In the 21st century, with the development of PVD coating technology and equipment, coatings continued to move from single layer to multilayer and nanostructure. Nanocomposite coatings with higher hardness, stronger wear resistance and special nanostructure were invented and paid attention to. To this end, TiN-TiAlN and TiN-TiAlN coatings were developed. 高 Al 低 N-Ti 低 Al 高 N, TiAlN-TiAlSiN and other nano multi-layer composite coating series with different structural components.

[0004] Nano-multilayer composite coatings generally refer to coating systems composed of alternating layers of different materials or structures at the nanometer scale. The coating exhibits nanometer-scale periodicity in the thickness direction, with a basic fixed period of double-layer thickness. Compared to single-layer and non-nano-multilayer composite coatings, nano-multilayer composite coatings exhibit ultra-hardness and supermodulus effects in mechanical properties due to the Hall-Petch effect caused by the nanoscale structure. These coatings possess a level of ultra-hardness not found in other coatings, enhancing wear resistance while significantly improving coating toughness. Due to the presence of multiple interfaces, nano-multilayer composite coatings can also enhance corrosion resistance, oxidation resistance, cracking resistance, and other properties.

[0005] In order to ensure the various high performances of nano multilayer composite coatings, it is necessary to ensure that there is a large composition, especially structural difference between the two nanoscale coatings of the nano multilayer composite coating, so as to have a clearer coating interface, thereby ensuring that the coating has high hardness and toughness, and at the same time, it is necessary to ensure that there is a certain similarity between the two nanoscale coatings to ensure that the coating has a strong bonding force. That is, hardness and toughness and bonding force have put forward completely different requirements for nano multilayer composite coatings. Due to the large structural difference between the two nanoscale coatings of the nano multilayer composite coating, the coating bonding force is insufficient. The existing nano multilayer coating system tends to have a certain similarity between the two nanoscale coatings, that is, to ensure the bonding force of the two coatings, only the composition of the two coatings is changed, and the structure is still the cubic phase of the same system, such as TiN cubic phase system, CrN cubic phase system, etc. Although this can ensure the bonding strength of the coating, the coating hardness and wear resistance are not significantly improved, and the cutting life of the final nano multilayer coating is short. For example, U.S. Patent No. 10596636B2 discloses a TiMN nano-multilayer composite coating, in which the Ti content of the two adjacent layers accounts for more than 57 at% of the metal elements. This indicates that the main structure of the two adjacent layers is a TiN cubic phase structure, without showing a large structural difference. The hardness and wear resistance potential of the nano-multilayer coating cannot be fully exerted, and the cutting life is short. Summary of the Invention

[0006] The first purpose of the present invention is to overcome the defect of the existing nano multi-layer composite coating having a short cutting life and to provide a nano multi-layer composite coating having a longer cutting life.

[0007] The second purpose of the present invention is to provide a method for preparing the nano multi-layer composite coating.

[0008] The third object of the present invention is to provide an application of the nano multi-layer composite coating in cutting tools.

[0009] Specifically, the nano multilayer composite coating provided by the present invention comprises an A layer and a B layer, wherein the A layer and the B layer are arranged on the substrate in a periodic ABAB or BABA manner, and the thickness of the single layer of the A layer and the B layer is independently 3-50 nm;

[0010] The A layer is composed of Zr x1 (Al x2 Hf x3 Me x4 )N x5composition, wherein 0.5≤x1≤0.8, 0.2≤x2≤0.5, 0≤x3≤0.2, 0≤x4≤0.2, 0.9≤x5≤1.1, x1+x2+x3+x4=1, and 0≤x3+x4≤0.2, Me is selected from at least one of Ti, V, Ta, Nb, Cr, W, Mn, Mo and Si, and the main phase structure of the A layer is a ZrAlN cubic phase;

[0011] The B layer is composed of Hf y1 (Al y2 Zr y3 Me` y4 )N y5 composition, wherein 0.47≤y1≤0.77, 0.23≤y2≤0.53, 0≤y3≤0.2, 0≤y4≤0.2, 0.9≤y5≤1.1, y1+y2+y3+y4=1, and 0≤y3+y4≤0.2, Me` represents at least one of Ti, V, Ta, Nb, Cr, W, Mn, Mo and Si, and the main phase structure of the B layer is HfAlN cubic phase.

[0012] After in-depth and extensive research, the inventors of the present invention found that the cutting life of cutting tools is affected by the substrate, groove type and coating, among which the coating effect is determined by the coating hardness, toughness and bonding strength. The present invention is based on the superhard effect and bonding strength mechanism of nano multi-layer composite coatings. ZrN cubic phase and HfN cubic phase are periodically deposited on the substrate. At the same time, a large amount of Al (20-50 at%) is alloyed and solid-dissolved in the ZrN cubic phase and a large amount of Al (23-53 at%) is alloyed and solid-dissolved in the HfN cubic phase. The resulting ZrAlN-HfAlN nano multi-layer composite coating with an optimized alloy ratio can not only perfectly exert the superhard effect of the nano multi-layer composite coating, making it have both superhardness and toughness, but also the high solid solubility and high affinity between the three elements Zr, Hf and Al enable the A layer and the B layer to have good solid solution bonding at the interface, ensuring the bonding strength of the nano multi-layer composite coating, and ultimately extending the cutting life of the nano multi-layer composite coating.

[0013] The nano-multilayer composite coating provided by the present invention is formed by alternating nano-sized Zr(AlHfMe)N-Hf(AlZrMe)N. The main phase structure of the Zr(AlHfMe)N layer is a ZrAlN cubic phase, and the main phase structure of the Hf(AlZrMe)N layer is a HfAlN cubic phase. Compared with the existing nano-multilayer coating system, the nano-multilayer coating can better exert the superhard effect of the nano-multilayer coating, and can obtain a clearer coating interface state at the nano-scale coating interface in terms of microscopic mechanism, better prevent the dislocation and defect slip of the coating, and improve the hardness and wear resistance of the coating; compared with the single-layer columnar crystal structure, the multiple interface structure can also improve the generation, expansion and growth direction of cracks and improve toughness; at the same time, the high solid solubility and high affinity between the three elements Zr, Hf and Al enable the A layer and the B layer to have good solid solution bonding at the interface, thereby ensuring the bonding strength of the nano-multilayer composite coating. In summary, the nano-multilayer composite coating provided by the present invention not only possesses exceptional hardness and toughness, but also possesses high bonding strength, enabling targeted strengthening according to specific working conditions, resulting in a longer cutting life in tool cutting conditions. Depositing this nano-multilayer composite coating on cutting tools can effectively inhibit and alleviate wear, corrosion, oxidation, fatigue, and crack initiation on the cutting tool substrate surface, thereby effectively improving the performance and life of the cutting tool, increasing metal removal rates, and enhancing the finish and machining accuracy of the machined surface. It has broad application prospects.

[0014] In a preferred embodiment, the A layer contains Hf and 0.03≤x3≤0.15, and the B layer contains Zr and 0.03≤y3≤0.15, which can further improve the similarity and interface solid solubility between the two coatings, thereby further improving the bonding strength of the nano multi-layer composite coating, and ultimately further extending the cutting life of the nano multi-layer composite coating.

[0015] In a preferred embodiment, the A layer contains Me and 0.03≤x4≤0.15, and the B layer contains Me` and 0.03≤y4≤0.15, which can further improve the cutting life of the nano multi-layer composite coating.

[0016] In a preferred embodiment, the A layer contains Hf and Me, the B layer contains Zr and Me`, and 0.03≤x3≤0.12, 0.03≤y3≤0.12, 0.03≤x4≤0.12, 0.03≤y4≤0.12, 0.06≤x3+x4≤0.15, 0.06≤y3+y4≤0.15, which can further improve the hardness, toughness and bonding strength of the nano multi-layer composite coating, thereby giving it a better cutting life.

[0017] In a preferred embodiment, Me and Me' are each independently selected from at least one of a combination of Ta and Nb, a combination of V and Cr, and a combination of Mo and W. When Me and Me' are a combination of Ta and Nb, the hardness attenuation of the coating at high temperatures can be reduced, the cutting life can be extended, and the nano-multilayer composite coating is more suitable for dry cutting without coolant; when Me and Me' are a combination of V and Cr, the coating grains can be further refined by mechanisms such as hindering the epitaxial growth of the coating, thereby improving the hardness of the nano-multilayer composite coating and extending the cutting life; when Me and Me' are a combination of Mo and W, the high solid solubility of Mo and W in the WC-based cemented carbide substrate can improve the matrix bonding strength between the coating and the substrate, thereby further extending the cutting life.

[0018] In a preferred embodiment, Me and Me' are both Si. Since Si is deposited to form Si3N4 nanocrystals, the coating grains can be further refined, so that the hardness of the nano multilayer composite coating can be further improved and the toughness can be further reduced, and the cutting life is longer.

[0019] In a preferred embodiment, the thickness of a single period AB is 6-100 nm.

[0020] In a preferred embodiment, the thickness of the nano multi-layer composite coating is 0.3-10 μm.

[0021] In an embodiment, the thickness a of the A layer and the thickness b of the B layer satisfy:

[0022]

[0023]

[0024] If the thickness of the single layer of layer A and layer B is too high, according to the expression of Hall-Petch relationship H=H0+kd -1 / 2 The larger the thickness d, the lower the coating hardness, which will significantly reduce the coating hardness. If the single layer thickness of layer A and layer B is too low, on the one hand, the thin film thickness will not be able to prevent dislocations from passing through the multilayer grain boundaries, making the Hall-Petch model inapplicable and reducing the coating hardness; on the other hand, too thin a film thickness also means more multilayer interfaces. Overly dense coating interfaces will lead to reduced coating adhesion and reduced coating performance stability. Similarly, when the thickness ratio of layer A and layer B differs too much, it not only means that one layer is too thick and the other is too thin. Under the condition that all other conditions are the same, the performance of the coating is inferior to that of a coating with similar film thickness of layer A and layer B.

[0025] In a preferred embodiment, the lattice constant of the ZrAlN cubic phase of the A layer is The lattice constant of the HfAlN cubic phase in the B layer is

[0026] The preparation method of the nano multi-layer composite coating provided by the present invention comprises:

[0027] The substrate to be coated is clamped on the rotating disk of the physical vapor deposition equipment, and the metal target A and the metal target B are placed around the rotating disk in the deposition order, and the physical vapor deposition is carried out by heating and passing N2;

[0028] When the substrate to be coated rotates to the metal target A area, layer A is deposited;

[0029] When the substrate to be coated rotates to the metal target B area, layer B is deposited;

[0030] The nano multilayer composite coating is obtained by deposition in a periodic ABAB or BABA manner through the rotation of the rotating disk.

[0031] In a preferred embodiment, the composition of the metal target material A is Zr a1 Al a2 Hf a3 Me a4 , wherein, 0.43≤a1≤0.75, 0.25≤a2≤0.57, 0≤a3≤0.17, 0≤a4≤0.17, 0≤a3+a4≤0.17; the composition of the metal target material B is Hf b1 Al b2 Zr b3 Me b4 , among which, 0.4≤b1≤0.72, 0.28≤b2≤0.6, 0≤b3≤0.17, 0≤b4≤0.17, 0≤b3+b4≤0.17.

[0032] In a preferred embodiment, the quantity ratio of the metal target material A to the metal target material B is 0.33-3:1.

[0033] In a preferred embodiment, the rotation speed of the rotating disk is 0.75-3 r / min.

[0034] In the present invention, the time the substrate stays in front of different metal targets can be controlled by adjusting the rotation speed of the rotating disk, thereby controlling the approximate thickness between the deposited A layer and the B layer; the approximate thickness relationship between the deposited A layer and the B layer can be controlled by changing the quantity ratio of the metal target material A to the metal target material B; and the overall thickness and thickness relationship between the A layer and the B layer can be further accurately controlled by adjusting the target current of the metal target material A and the metal target material B.

[0035] In the present invention, before physical vapor deposition, the substrate to be coated can be pretreated to obtain a surface to be coated that is more conducive to the deposition and adhesion of the coating. The pretreatment methods include but are not limited to: mechanical processing of the surface to be coated, sandblasting, demagnetization, cleaning, etc. Among them, the method of mechanical processing of the surface to be coated can be, for example, processing the substrate to be coated to the desired substrate shape and size through processes such as grinding and polishing, and smoothing the polished surface to improve the bonding strength between the coating and the substrate. The sandblasting method can be, for example, passivating the sharp and uneven edges of the surface of the substrate to be coated by dry spraying or wet spraying, reducing the internal stress generated by the coating film at the edge, reducing the generation of cracks and coating peeling, smoothing the surface to be coated, and reducing surface scratches to facilitate coating deposition. The demagnetization method can be, for example, applying a certain changing magnetic field to remove the magnetism of the substrate to be coated itself, reducing the adhesion of surface magnetic dust, reducing the influence of the magnetism of the substrate to be coated on the electromagnetic field distribution in the furnace, and improving the coating bonding, uniformity and stability. The cleaning method may be, for example, using pure water, alkaline cleaning agents, ultrasound, high-temperature drying, etc. to clean dirt and dust on the surface of the substrate to be coated, so as to facilitate the deposition and adhesion of the coating and improve the adhesion of the coating.

[0036] In a preferred embodiment, the temperature of the physical vapor deposition is 410-680° C., and the partial pressure of N 2 is 0.035-0.075 mbar.

[0037] In the present invention, pressure refers to the absolute pressure relative to vacuum in the physical vapor deposition equipment.

[0038] In a preferred embodiment, the excitation arc current of the metal target material A and the metal target material B is 120-230A, and the negative bias voltage is -30 to -200V.

[0039] In the present invention, the relative evaporation and ionization rates of each metal element in the metal target material are controlled by adjusting the target current intensity during the deposition process, and the relative combination deposition rates of each metal ion and the N element can be controlled by adjusting the substrate surface bias electric field intensity, the substrate deposition temperature, etc., thereby further modulating the composition of the metal target material to deposit a nano-multilayer composite coating with a special coating chemical element ratio and microstructure.

[0040] In the present invention, the deposition method may further include an etching step after heating and passing N2 and before physical vapor deposition. Specifically, ionized Ar ions or metal ions excited by the target are accelerated to bombard the substrate surface under high voltage electric field strength to sputter out residual gas substances on the surface of the substrate to be coated, clean and smooth the surface, facilitate coating deposition and enhance bonding strength.

[0041] In the present invention, the physical vapor deposition can adopt arc ion plating, and the metal target material A and the metal target material B are ionized by arc evaporation, so that the metal ions are accelerated to bombard the substrate surface under the voltage electric field strength, and react with N2 on the substrate surface to deposit and grow, thereby obtaining the nano multilayer composite coating.

[0042] In the present invention, the deposition method may further include a cooling step after physical vapor deposition. Specifically, the substrate temperature is reduced to below 100° C. or room temperature using a natural cooling mode or a rapid cooling mode of the physical vapor deposition equipment.

[0043] The present invention also provides an application of the nano multi-layer composite coating in a cutting tool. In a specific application process, the nano multi-layer composite coating can be deposited on the surface of a cutting tool or used as a part of the surface coating of a cutting tool.

[0044] The nano multi-layer composite coating provided by the present invention has superhardness, strong toughness and high bonding strength, and thus has a long cutting life. Among them, the hardness at room temperature can reach more than 28GPa, the toughness can reach more than 47%, the bonding strength can reach more than 65N, the high-temperature hardness can reach more than 26GPa, and the cutting life can reach more than 14min. DETAILED DESCRIPTION

[0045] The present invention will be described in detail below through examples.

[0046] In the following examples and comparative examples, the substrate to be coated was a WC-based cemented carbide insert sample, containing approximately 10% Co by weight, 0.2% VC by weight, and the balance being WC. The average particle size of the WC, Co, and VC raw material powders was approximately 0.8 microns, and the insert model was WNMG080408-LM.

[0047] Example 1

[0048] This embodiment provides a method for preparing a nano multi-layer composite coating, comprising the following steps:

[0049] The blades to be coated are first pretreated. Specifically, the sintered carbide blades are mechanically flat ground. A double-end face grinder equipped with a 600-mesh or higher diamond grinding wheel is used to polish the blades to a smooth, flat surface. The blades are then guaranteed to meet tolerances, with a tip clamping height of 4±0.01mm. A high-pressure water gun is used to spray a mixture of Al2O3 powder to passivate the blade edge radius to 20-40μm. The blades are then ultrasonically cleaned with high-purity water and dried at high temperature.

[0050] The metal target material A and the metal target material B are clamped in the target material position of the arc ion plating equipment in sequence according to the deposition order AB of the periodic coating unit. The composition of the metal target material A is Zr 0.5 Al 0.4 Hf 0.05 Nb 0.05 The metal target material B is composed of Hf 0.47 Al 0.43 Zr 0.05 Nb 0.05 The quantity ratio of the metal target material A to the metal target material B is 2:2.

[0051] The pre-treated blade substrate was clamped on a circular rotating disk, which was kept rotating at a speed of 2 r / min. The arc ion plating equipment furnace was vacuumed to 5×10 -4 mbar, and then the surface of the blade substrate is heated to 480℃ and kept stable by the heating device in the furnace of the arc ion plating equipment. Ar is introduced into the furnace of the arc ion plating equipment to maintain the Ar partial pressure in the furnace at 0.05mbar to maintain the generation of the metal target arc. The Ar ionization chamber switch is turned on and the negative bias voltage is set to -200V, so that the ionized Ar ions bombard the blade substrate at high speed under the action of the electric field and the etching continues for 30 minutes.

[0052] Maintaining the Ar partial pressure constant, N2 was introduced, maintaining the N2 partial pressure in the furnace at 0.05 mbar. A negative deposition bias of -100 V was applied to the blade substrate to be coated. The arc evaporation devices for metal targets A and B were started, and the currents for both targets A and B were set to 190 A. Under the action of the arc, the metal particles on the metal targets evaporated and ionized, and accelerated toward the blade substrate to be coated under the action of the negative bias electric field. They combined with N2 on the surface of the blade substrate to be coated, and the coating was deposited through reaction. When the blade substrate to be coated rotated to the metal target area A, layer A, namely the Zr(AlHfNb)N layer, was deposited; when the blade substrate to be coated rotated to the metal target area B, layer B, namely the Hf(AlZrNb)N layer, was deposited. Through the rotation of the rotating disk, after 60 minutes of periodic deposition, a Zr(AlHfNb)N-Hf(AlZrNb)N nano-multilayer composite coating was obtained. After stopping the deposition, Ar was introduced to maintain the pressure in the furnace at 200 mbar, and the circulation fan in the furnace was turned on to quickly cool the coating furnace.

[0053] Example 2-Example 19, Comparative Example 1-Comparative Example 15

[0054] The nano multilayer composite coating was prepared according to the method of Example 1, except that the target material composition and quantity and coating process parameters were different, and other conditions were the same as Example 1. The target material composition and quantity of each embodiment and comparative example are shown in Table 1, and the coating process parameters of each embodiment and comparative example are shown in Table 2.

[0055] Table 1

[0056]

[0057]

[0058] Table 2

[0059]

[0060]

[0061] Test Case

[0062] (1) Composition and thickness of layer A and layer B: The composition and thickness of the layer A and layer B were measured using a transmission electron microscope (TEM). The magnification of the TEM was set to 1.25 million times. In the field of view, a dark layer A and a bright layer B with different light and dark stripes were clearly observed. The EDS module of the TEM equipment was used to analyze the composition of the layer A and layer B respectively to obtain the atomic ratio content of each element in the coating. Five measurement points were selected and the average value was taken as the composition of each layer of the coating. Under the field of view of 1.25 million times, five areas were selected for photography. The thickness of the layer A and layer B in each figure was measured according to the ruler and the average value was taken as the thickness of each single layer of the coating. The results are shown in Tables 3 and 4.

[0063] (2) Total thickness of the nano-multilayer composite coating: Calculated using the following formula: Coating thickness = (A layer thickness a + B layer thickness b) * rotation speed * total deposition time. Taking Example 1 as an example, coating thickness = (14.4 + 13.7) * 2 * 60 nm = 3370 nm = 3.37 μm. Comparing this data with data typically obtained using SEM observations, the deviation is within 1%, demonstrating high reliability. Therefore, the results calculated using the above method are accurate and reliable as the total thickness of the coating of the present invention. The results are shown in Table 5.

[0064] (3) Lattice constant: The lattice constant of the coating grains was analyzed using X-ray diffraction (XRD). The coating was subjected to a 2θ scan using an incident angle of 1°, a scan range of 25–150°, a step size of 0.033°, and 1 s to obtain a raw spectrum. The peak shape of the spectrum was fitted and analyzed to determine the peak position of each coating component, and the lattice constant of the coating was calculated. The results are shown in Tables 3 and 4.

[0065] (4) Hardness at room temperature: using the nanoindenter Anton-PaarTriTec UNHT 3The coating hardness was measured with a maximum load of 20 mN, a loading and unloading time of 30 seconds, and a holding time of 5 seconds. The instrument measured the relationship between load force and penetration depth and automatically calculated the coating hardness (GPa). The measurement was repeated 16 times in a 4×4 matrix mode. Curves and values with excessive deviation were deleted, and the average value was taken as the room-temperature hardness. The results are shown in Table 5.

[0066] (5) Toughness: MDP is used to reflect the toughness of the coating, expressed in %. Specifically, the relationship curve between the indenter loading force and the indentation depth is measured by a nanoindenter. The indentation process curve can be used to integrate and calculate the total mechanical work done during the indentation process, which is recorded as Wt. The unloading process curve can be used to integrate and calculate the elastic recovery work We of the coating after unloading, and then calculate the energy consumed by the coating through plastic deformation Wp=Wt-We. MDP=Wp / Wt(%) can be used to represent the ratio of the energy consumed by the coating through plastic deformation during the indentation process to the total energy. The higher the value, the more conducive it is to the release of residual stress, and the more effectively it can prevent the brittle fracture of the coated carbide blade caused by excessive residual stress during the cutting process, and the higher the relative toughness of the coating. The results are shown in Table 5.

[0067] (6) High temperature hardness: Place the sample in the sample chamber of the nanoindenter and evacuate to a pressure of <5×10 -3 After heating the sample to 800°C, the indenter was used to perform indentation with a maximum load of 20 mN, a loading and unloading time of 30 seconds, and a holding time of 5 seconds. The measurement was repeated 16 times in a 4×4 matrix configuration. Curves and values with excessive deviations were deleted, and the average value was taken as the high-temperature hardness. The results are shown in Table 5.

[0068] (7) Adhesion strength: The TRIBO Millennium 200 scratch tester was used to measure the adhesion strength of the coating. Specifically, a conical diamond indenter with a smooth tip was used to scratch the coating surface at a certain speed while gradually increasing the vertical pressure of the indenter. The minimum pressure at which the coating cracked was used to characterize the film-based adhesion strength of the coating. The measurement parameters were: scratch length of 12 mm, scratch speed of 5 mm / min, indenter pressure of 0 N-120 N, and loading speed of 50 N / min. Based on the acoustic signal of coating cracking collected synchronously during the scratch loading test, the change in friction force of the indenter across the substrate, the cracking situation of the coating surface and the pressure corresponding to its position, etc., the critical load force when the coating cracked was determined. The average value of the three measurements was the coating-film-based adhesion strength of the present invention. The results are shown in Table 5.

[0069] (8) Cutting life: 304 stainless steel cutting test was carried out using the cemented carbide substrate and the WNMG080408-LM blade. The hardness of the 304 stainless steel substrate tested was 210-230HB, the cutting speed Vc=180m / min, the feed f=0.2mm / r, the cutting depth Ap=2mm, and water cooling was used during the cutting process. Pause after each 1 minute of cutting to observe whether the blade is chipped and whether the back face wear value exceeds 0.3mm. Continue cutting until the blade is chipped or the back face wear exceeds 0.3mm, which is recorded as the cutting life of the blade. Three blades were tested, and the average value was taken as the cutting life of the coating. The results are shown in Table 5.

[0070] Table 3: Composition, lattice constant and thickness of layer A

[0071]

[0072]

[0073] Table 4: Composition, lattice constant and thickness of B layer

[0074]

[0075]

[0076]

[0077] Table 5: Thickness ratio of layer A and layer B and other performance parameters of nano multilayer coating

[0078]

[0079]

[0080] Note: The qualified values of various properties should meet the following requirements: room temperature hardness H ≥ 28GPa, toughness MDP ≥ 47%, bonding force ≥ 65N, high temperature hardness ≥ 26GPa, cutting life ≥ 14min.

[0081] From the above examples and comparative examples, it can be seen that:

[0082] (1) The composition and thickness of Examples 1-19 meet the stated ranges, and all of their properties meet the requirements.

[0083] (2) Compared with Example 2, Example 1 adds Hf to the ZrAlN cubic phase of layer A, adds Zr to the HfAlN cubic phase of layer B, and adds the metal element Nb to both, which effectively improves the hardness, toughness and bonding strength. These performance improvements jointly improve the cutting life of the coating.

[0084] (3) Compared with Example 1, in which the special added element Me of layer A and the special added element Me' of layer B are both single Nb, the elements Me and Me' in Example 16 are different, namely Nb and Ta. On the one hand, the structural difference between the two coatings is increased, which slightly improves the room temperature hardness and toughness of the coatings. On the other hand, since Ta and Nb are elements of the same family, their similarity and solid solubility are relatively large, so Example 16 only slightly reduces the bonding force between the coatings compared with Example 1. It is important that Ta and Nb, as special metal elements, can significantly improve the red hardness of the coating, that is, slow down the hardness decay ability at high temperature. When the two elements are added at the same time, they can play a synergistic role, and the effect is more significant, so that the high temperature hardness of Example 16 is significantly improved compared with Example 1, which further improves the cutting life of the tool.

[0085] (4) Compared with Example 3, in which the special added element Me of layer A and the special added element Me' of layer B are both V, the elements Me and Me' in Example 17 are different, namely V and Cr. On the one hand, the structural difference between the two coatings is increased, which slightly improves the toughness of the coatings. On the other hand, since the atomic numbers of V and Cr are adjacent, their similarity and solid solubility are large, so Example 17 only slightly reduces the bonding force between the coatings compared with Example 3. It is important that V and Cr, as special metal elements, can precipitate different VN and CrN on the surface of the coating grains, which will interrupt and inhibit the epitaxial growth of the coating grains, thereby achieving the purpose of refining the coating grains. When the two elements are added at the same time, they can play a synergistic role, and the effect is more significant, so that the room temperature hardness and high temperature hardness of Example 17 are significantly improved compared with Example 3 due to grain refinement, further improving the cutting life of the tool.

[0086] (5) Compared to Example 9, in which the special added element Me of layer A and the special added element Me' of layer B were both Mo, the Me and Me' elements in Example 18 were different, namely Mo and W, which increased the structural difference between the two coatings, resulting in a slight improvement in the hardness and toughness of the coatings. Importantly, since the main component of the cemented carbide substrate is WC-Co, which has extremely high affinity and solid solubility with the special metal elements Mo and W, when the two elements are added simultaneously, they can play a synergistic role, with a more significant effect, greatly increasing the bonding strength between the coating and the substrate, comprehensively improving the overall bonding strength of the coating, and further improving the cutting life of the tool.

[0087] (6) Compared with Example 1 and Example 16, the special added element Me in the A layer of Example 19 is the same as the special added element Me' in the B layer, but it also contains Nb and Ta. Ta and Nb are elements of the same family, and their similarity and solid solubility are relatively large. Therefore, the room temperature performance is not much different from that of Example 1. It is important that Ta and Nb, as special metal elements, can significantly improve the red hardness of the coating, that is, the ability to slow down the hardness decay at high temperatures. When the two elements are added to the A layer and the B layer at the same time, they can play a synergistic role, and the effect is more significant, so that the high temperature hardness of Example 19 is significantly improved compared with Example 1 and Example 16, further improving the cutting life of the tool.

[0088] (7) Compared with Example 3, in Comparative Example 1, x1<0.5 and y1<0.47, which are smaller than the coating composition range. This results in insufficient Zr content in the main phase of layer A, and the coating cannot form a complete cubic ZrAlN main phase structure, resulting in the precipitation of hexagonal AlN and other impurity phases. Similarly, the Hf content in the main phase of layer B is insufficient, and a complete cubic HfAlN main phase structure cannot be formed, resulting in the precipitation of hexagonal AlN and other impurity phases. The precipitated hexagonal phase structure is softer than the cubic phase structure, resulting in the overall room temperature hardness and high temperature hardness of the coating being lower than the qualified values. At the same time, the presence of the impurity phase also affects the bonding strength of the coating, making it lower than the qualified value, which together leads to its cutting life not meeting the requirements.

[0089] (8) Compared with Example 4, in Comparative Example 2, x1>0.8 and y1>0.77, which are greater than the coating composition range, while x2<0.2 and y2<0.23, which are less than the coating composition range. This causes the relative content of Al in layer A to be too low, and the coating cannot be sufficiently alloyed and strengthened. Similarly, the alloying strengthening of layer B is also insufficient, causing the overall hardness and toughness of the coating to be lower than the qualified values, resulting in its cutting life not meeting the requirements.

[0090] (9) Compared with Example 5, in Comparative Example 3, x2<0.2 and y2<0.23, which are smaller than the coating composition range. The relative content of Al in layer A and layer B is too low, the coating alloying strengthening is insufficient, and the overall hardness and toughness are lower than the qualified values, resulting in its cutting life not meeting the requirements.

[0091] (10) Compared with Example 6, in Comparative Example 4, x2>0.5 and y2>0.53, which are greater than the coating composition range, while x1<0.5 and y1<0.47, which are less than the coating composition range. The main phase components of each layer of the coating are insufficient, and hexagonal AlN phase and other impurity phases are precipitated. The precipitated hexagonal phase structure is softer than the cubic phase structure, resulting in the overall room temperature hardness and high temperature hardness of the coating being lower than the qualified value. At the same time, the presence of impurity phases also affects the bonding strength of the coating, making it lower than the qualified value, resulting in its cutting life not meeting the requirements.

[0092] (11) Compared with Example 7, in Comparative Example 5, x3>0.2 and y3>0.2, which are larger than the coating composition range, so that an excessive amount of Hf is dissolved in the ZrAlN main phase of layer A, thereby precipitating HfAlN cubic phases of different contents in the ZrAlN cubic phase of layer A, that is, a phase with a portion of the composition of layer B is precipitated in layer A. Similarly, a phase with a portion of the composition of layer A is also precipitated in layer B. Unlike the different phases between multilayer interfaces, the distribution of precipitated phases in a single layer is uncontrollable and the number of interfaces is too dense, resulting in insufficient toughness and bonding strength of the coating, which are lower than the qualified value, resulting in its cutting life not meeting the requirements.

[0093] (12) Compared with Example 8, in Comparative Example 6, x4>0.2 and y4>0.23, which are larger than the coating composition range, this causes an excessive amount of Me to be dissolved in the ZrAlN main phase of layer A, resulting in the precipitation of different amounts of MeN cubic phase or MeN hexagonal phase in the ZrAlN cubic phase of layer A (the MeN phase structure varies depending on the Me composition). The same applies to layer B. The presence of the precipitated phase greatly increases the number of interfaces within the coating, resulting in insufficient toughness and bonding strength of the coating, which are lower than the qualified value, resulting in its cutting life not meeting the requirements.

[0094] (13) Compared with Example 9, in Comparative Example 7, x3+x4>0.2 and y3+y4>0.2, which are larger than the coating composition range. This causes excessive Hf and Me to be dissolved in the ZrAlN main phase of layer A, thereby precipitating different amounts of HfAlN, MeN cubic phase or MeN hexagonal phase in the ZrAlN cubic phase of layer A; similarly, ZrAlN, MeN cubic phase or MeN hexagonal phase precipitates in layer B. The presence of the precipitated phase greatly increases the number of interfaces inside the coating, making the toughness and bonding strength of the coating insufficient, lower than the qualified value, resulting in its cutting life not meeting the requirements.

[0095] (14) Compared with Example 10, in Comparative Example 8, x5<0.9 and y5<0.9, which are smaller than the coating composition range. The low N2 partial pressure during deposition results in too little N element in the coating. There are metal atoms in the coating that are not fully nitrided, and the number of ionic bonds is insufficient, resulting in the overall hardness of the coating being low, below the qualified line, resulting in its cutting life not meeting the requirements.

[0096] (15) Compared with Example 11, in Comparative Example 9, x5>1.1 and y5>1.1, which are larger than the coating composition range. The excessively high N2 partial pressure during deposition results in excessive N elements in the coating, and excessive N ion bonds in the coating, which increases the overall hardness of the coating, but reduces the toughness and bonding strength of the coating, which is lower than the qualified line, resulting in its cutting life not meeting the requirements.

[0097] (16) Compared with Example 12, the thickness of layer A and layer B in comparative example 10 is a<3nm and b<3nm, which is smaller than the thickness range of the coating. The excessively thin coating thickness leads to an excessively dense number of coating interfaces, which makes the overall toughness and bonding strength of the coating too low, below the qualified line, resulting in its cutting life not meeting the requirements.

[0098] (17) Compared with Example 13, the thickness of layer A and layer B in Comparative Example 11 is a>50nm and b>50nm, which is greater than the thickness range of the coating. The excessively thick single layer thickness weakens the superhard effect of the nano multilayer coating, reduces the hardness of the coating, and is below the qualified line, resulting in its cutting life not meeting the requirements.

[0099] (18) Compared with Example 14, the thickness relationship between layer A and layer B of Example 12 is a / (a+b)<0.25, which is less than the lower limit of the coating thickness relationship. This means that the thickness of layer A of the coating is too thin and layer B is too thick. The uneven thickness distribution makes the superhard effect of layer A significant while the interface is dense and the bonding strength is poor. The superhard effect of layer B is not obvious while the hardness is low. The overly unbalanced thickness ratio leads to poor stability in macroscopic performance. The overall hardness, toughness and bonding strength are all below the qualified line, resulting in its cutting life not meeting the requirements.

[0100] (19) Compared with Example 15, the thickness relationship between layer A and layer B in Example 13 is a / (a+b)>0.75, which is greater than the lower limit of the coating thickness relationship. This means that layer B of the coating is too thin and layer A is too thick. Similarly, its overall hardness, toughness, and bonding strength are all below the qualified line, resulting in its cutting life not meeting the requirements.

[0101] (20) Compared to the examples, the Zr content in both layer A and layer B of Comparative Example 14 is relatively high, resulting in the XRD peaks of the double-layer coating being the ZrAlN main phase. This is a ZrAlMeN nano-multilayer composite coating obtained by adjusting the relative contents of Zr and Al. Compared to the examples with different main phases, this nano-multilayer coating structure obtained by adjusting the element content has a smaller difference between the two layers. This results in its room temperature hardness and high temperature hardness being significantly lower than those of the examples, resulting in poor wear resistance of the tool and unsatisfactory cutting life.

[0102] (21) Compared with the examples, the Hf content in both layer A and layer B of Comparative Example 15 is relatively high, resulting in the XRD peaks of the double-layer coating being the HfAlN main phase. This is an HfAlMeN nano-multilayer composite coating obtained by adjusting the relative contents of Hf and Al. Compared with the examples with different main phases, this nano-multilayer coating structure obtained by adjusting the element content has a smaller difference between the two layers, which results in its room temperature hardness and high temperature hardness being significantly lower than the examples, resulting in poor wear resistance of the tool and unsatisfactory cutting life.

[0103] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention without departing from the principles and purpose of the present invention.

Claims

1. A nano multi-layer composite coating, characterized in that: The nano multilayer composite coating comprises an A layer and a B layer, wherein the A layer and the B layer are arranged in a periodic ABAB or BABA manner, and the thickness of each single layer of the A layer and the B layer is independently 3-50 nm; The A layer is composed of Zr x1 (Al x2 Hf x3 Me x4 )N x5 composition, wherein 0.5≤x1≤0.8, 0.2≤x2≤0.5, 0.03≤x3≤0.2, 0≤x4≤0.2, 0.9≤x5≤1.1, x1+x2+x3+x4=1 and 0≤x3+x4≤0.2, Me is selected from at least one of Ti, V, Ta, Nb, Cr, W, Mn, Mo and Si, and the main phase structure of the A layer is a ZrAlN cubic phase; The B layer is composed of Hf y1 (Al y2 Zr y3 Me` y4 )N y5 composition, wherein 0.47≤y1≤0.77, 0.23≤y2≤0.53, 0.03≤y3≤0.2, 0≤y4≤0.2, 0.9≤y5≤1.1, y1+y2+y3+y4=1 and 0≤y3+y4≤0.2, Me` is selected from at least one of Ti, V, Ta, Nb, Cr, W, Mn, Mo and Si, and the main phase structure of the B layer is HfAlN cubic phase.

2. The nano multi-layer composite coating according to claim 1, characterized in that: The A layer contains Hf and 0.03≤x3≤0.15, and the B layer contains Zr and 0.03≤y3≤0.

15.

3. The nano multi-layer composite coating according to claim 1, characterized in that: The A layer contains Me and 0.03≤x4≤0.15, and the B layer contains Me` and 0.03≤y4≤0.

15.

4. The nano multi-layer composite coating according to claim 3, characterized in that: The A layer contains Hf and Me, the B layer contains Zr and Me`, and 0.03≤x3≤0.12, 0.03≤y3≤0.12, 0.03≤x4≤0.12, 0.03≤y4≤0.12, 0.06≤x3+x4≤0.15, 0.06≤y3+y4≤0.

15.

5. The nano multi-layer composite coating according to claim 4, characterized in that: The Me and Me' are selected from at least one of a combination of Ta and Nb, a combination of V and Cr, and a combination of Mo and W.

6. The nano multi-layer composite coating according to claim 1, characterized in that: The thickness of the nano multi-layer composite coating is 0.3-10 μm.

7. The nano multi-layer composite coating according to claim 1, characterized in that: The thickness a of the A layer and the thickness b of the B layer satisfy:

8. The nano multi-layer composite coating according to claim 1, characterized in that: The lattice constant of the ZrAlN cubic phase in the A layer is The lattice constant of the HfAlN cubic phase in the B layer is 9. The method for preparing a nano multi-layer composite coating according to any one of claims 1 to 8, characterized in that: The preparation method comprises: The substrate to be coated is clamped on the rotating disk of the physical vapor deposition equipment, and the metal target A and the metal target B are placed around the rotating disk in the deposition order, and the physical vapor deposition is carried out by heating and passing N2; When the substrate to be coated rotates to the metal target A area, layer A is deposited; When the substrate to be coated rotates to the metal target B area, layer B is deposited; The nano multilayer composite coating is obtained by deposition in a periodic ABAB or BABA manner through the rotation of the rotating disk.

10. The method for preparing a nano multi-layer composite coating according to claim 9, characterized in that: The composition of the metal target material A is Zra1Al a2 Hf a3 Me a4 , wherein, 0.43≤a1≤0.75, 0.25≤a2≤0.57, 0≤a3≤0.17, 0≤a4≤0.17, 0≤a3+a4≤0.17; the composition of the metal target material B is Hf b1 Al b2 Zr b3 Me b4 , among which, 0.4≤b1≤0.72, 0.28≤b2≤0.6, 0≤b3≤0.17, 0≤b4≤0.17, 0≤b3+b4≤0.

17. 11 . The method for preparing a nano multi-layer composite coating according to claim 9 , wherein the quantitative ratio of the metal target material A to the metal target material B is 0.33-3:

1.

12. The method for preparing a nano multi-layer composite coating according to claim 9, characterized in that: The temperature of the physical vapor deposition is 410-680° C., and the partial pressure of N 2 is 0.035-0.075 mbar. 13 . The method for preparing a nano multi-layer composite coating according to claim 9 , wherein the excitation arc current of the metal target material A and the metal target material B is 120-230 A, and the negative bias voltage is -30 to -200 V.

14. The method for preparing a nano multi-layer composite coating according to claim 9, wherein the rotation speed of the rotating disk is 0.75-3 r / min.

15. A cutting tool, characterized in that: The surface of the cutting tool is provided with a coating, and the coating comprises the nano multi-layer composite coating according to any one of claims 1-8.

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