A high-toughness and wear-resistant α-Al2O3-based composite textured coating and its preparation method

Abstract

This invention relates to the field of surface coating technology for machining tools, and discloses a high-toughness and wear-resistant α-Al2O3-based composite textured coating and its preparation method. From the substrate surface outwards, the coating comprises, in sequence, an underlayer, an MT-TiCN layer, an HT-TiCN transition layer, a bonding layer, an oxide layer, a composite textured α-Al2O3 layer, and a top wear indicator layer. The composite textured α-Al2O3 layer is composed of multiple periodically stacked A-textured layers and B-textured layers. The A-textured layer has a (001) texture, and the B-textured layer has a (110) texture. Within one stacking cycle, the thickness ratio of the A-textured layer to the B-textured layer is 1:1.5 to 1:3. The number of stacking cycles is 2 to 20. The thickness of each single textured layer is 0.5-5 μm. The total thickness of the composite textured α-Al2O3 layer is 3-30 μm. While maintaining excellent wear resistance with a high texture coefficient, the coating achieves a synergistic improvement in toughness and wear resistance by utilizing the interlayer grain boundary deflection effect to deflect crack propagation paths.

Description

Technical Field

[0001] This invention relates to the field of surface coating technology for machining tools, specifically to a high-toughness and wear-resistant α-Al2O3-based composite textured coating and its preparation method. Background Technology

[0002] In modern machining, cemented carbide cutting tools are widely used in turning and milling of various steel parts, cast iron, stainless steel, and high-temperature alloys. During the cutting process, localized high temperatures, intense friction, and periodic mechanical impacts exist between the tool and the workpiece, making the tool prone to failure modes such as wear, chipping, and thermal cracking, severely affecting the surface quality and production efficiency. Depositing protective coatings on the tool surface is one of the key technologies for improving tool life. Among these, α-Al₂O₃ coatings prepared by chemical vapor deposition (CVD) have become an ideal choice for high-speed cutting tools due to their high hardness, excellent wear resistance, and outstanding resistance to high-temperature oxidation, and are widely used in the field of CNC cutting tools.

[0003] To further improve the wear resistance of α-Al2O3 coatings, those skilled in the art have prepared α-Al2O3 coatings with specific microtextures by controlling the directional growth of crystals. For example, US patents US2006 / 0199026A1, US7094447B2, and US7442431B2 have prepared single-orientation textured α-Al2O3 coatings such as (104), (012), (110), (116), and (001) by designing a transition layer with a gradient of Al content and an oxide layer containing Ti-O; European patent EP2570510B2 has prepared (001) textured α-Al2O3 by controlling sulfur doping in the growth process of α-Al2O3; Chinese patent CN115074696B has prepared (110) textured coatings with high texture coefficient (TC) by controlling the ratio of CO2 to AlCl3; and Chinese patent CN120905647A has prepared (001) textured α-Al2O3 coatings by designing an Al purging modification layer. Studies have shown that textured α-Al2O3 coatings, especially (001) preferred orientation coatings, have outstanding wear resistance, and tool life is increased by several to tens of times compared with untextured coatings.

[0004] However, the aforementioned existing technologies are all based on a single texture design, resulting in a straight-lined columnar crystal structure within the coating. Under conditions of heavy-duty cutting and intermittent cutting, where there is intense mechanical impact, once cracks initiate on the coating surface or interface, they can easily propagate rapidly along the straight grain boundaries that penetrate the coating, leading to large-area coating failure and severely limiting the reliability of the tool under harsh conditions. Chinese patent CN118880276A proposes a texture-reinforced α-Al2O3 coating, which gradually reduces the coating growth direction... <001> The angle between the crystal orientation and the surface normal achieves <110> → <001> The orientation gradient transition is gradual. However, the main body of the coating in this scheme is still vertical columnar crystals, which fails to fundamentally change the failure mode of rapid crack penetration along vertical grain boundaries. European patent EP2902528A1 prepared an α-Al2O3 coating with serrated grain boundaries by alternately depositing different textures, introducing a grain boundary orientation mechanism, but the coating texture coefficient is low (TC<7), and the improvement in coating toughness and wear resistance is limited. Summary of the Invention

[0005] This invention aims to provide a high-toughness and wear-resistant α-Al2O3-based composite textured coating and its preparation method, addressing the failure problem of single-textured α-Al2O3 coatings where cracks easily penetrate rapidly along straight grain boundaries under impact conditions such as heavy loads and intermittent cutting, leading to coating collapse, and the technical bottleneck of existing gradient textured coatings failing to fundamentally change the crack propagation mode along vertical grain boundaries. By constructing a composite textured structure with periodically alternating (001) and (110) textured layers, while maintaining excellent wear resistance with a high texture coefficient, the crack propagation path is deflected by the interlayer grain boundary turning effect, achieving a synergistic improvement in coating toughness and wear resistance.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: Option 1: A high-toughness and wear-resistant α-Al2O3-based composite textured coating, comprising, from the substrate surface outwards, an underlayer, an MT-TiCN layer, an HT-TiCN transition layer, a bonding layer, an oxide layer, a composite textured α-Al2O3 layer, and a top wear indicator layer; The composite textured α-Al2O3 layer is composed of multiple periodically stacked A-textured layers and B-textured layers; the A-textured layer is a (001) texture, and the B-textured layer is a (110) texture; within one stacking cycle, the thickness ratio of the A-textured layer to the B-textured layer is 1:1.5 to 1:3; the number of stacking cycles is 2 to 20; the thickness of each single-layer textured layer is 0.5-5 μm; and the total thickness of the composite textured α-Al2O3 layer is 3-30 μm.

[0007] Beneficial effects: By periodically stacking the (001) texture layer and the (110) texture layer, the crystallographic orientation difference between the (001) base plane and the (110) prism plane is used to form grain boundary orientation, which effectively deflects and inhibits the crack propagation along a single direction, significantly improving the coating's anti-chipping performance and fracture toughness; at the same time, the A texture layer, as the main bearing layer, retains the excellent thermal stability and wear resistance of the (001) texture, and the B texture layer, as the toughening functional layer, achieves crack deflection through grain boundary engineering. The synergistic effect of the two makes the coating have both high wear resistance and high toughness.

[0008] Furthermore, the thickness ratio of the A texture layer to the thickness of the B texture layer is 1:2.

[0009] Beneficial effects: By limiting the thickness ratio of texture layer A to texture layer B to 1:2, it is possible to provide a sufficiently large grain boundary turning angle to effectively deflect the crack propagation path while avoiding excessive thickness of texture layer B, which would weaken the overall (001) texture strength of the coating, thus achieving the optimal balance between toughness and wear resistance.

[0010] Furthermore, the bonding layer is a (Ti,Al)(C,N,O) layer with a thickness of 0.3-1 μm; the oxide layer is a Ti-containing oxide layer formed by oxidizing the bonding layer. x O y The aluminum oxide nucleation layer of the compound.

[0011] Beneficial effects: Using (Ti,Al)(C,N,O) as the bonding layer and forming Ti through oxidation treatment x O y The nucleation layer provides a high density of nucleation sites for the subsequent heterogeneous nucleation of α-Al2O3, reduces the nucleation barrier of α-Al2O3, promotes the vertical growth of columnar crystals, and enhances the bonding strength between the coating and the substrate.

[0012] Furthermore, in the composite textured α-Al2O3 layer, the texture coefficient TC(001) of the A textured layer is ≥8, and the texture coefficient TC(110) of the B textured layer is ≥5.

[0013] Beneficial effects: By limiting the A texture layer to have a high texture coefficient of TC(001)≥8, the coating body is ensured to have excellent high-temperature wear resistance and chemical stability with (001) orientation; at the same time, the B texture layer maintains a texture strength of TC(110)≥5, ensuring that the interlayer interface has a clear orientation difference to achieve grain boundary turning. The two work together to enable the coating to have both high wear resistance and anti-chipping properties under harsh cutting conditions.

[0014] Furthermore, the coating is suitable for heavy-duty cutting, intermittent cutting, high-speed cutting, or dry cutting.

[0015] Beneficial effects: By clearly linking the coating structure design with harsh working conditions such as heavy load, intermittent, high speed, and dry cutting, and utilizing the grain boundary turning mechanism of the composite texture to cope with the strong mechanical and thermal shocks under the above working conditions, the service life of the tool under extreme service conditions is significantly extended, and the application scenarios of α-Al2O3 coated tools are expanded.

[0016] Option 2: A method for preparing a high-toughness, wear-resistant α-Al2O3-based composite textured coating, comprising the following steps: Step 1, Substrate Pretreatment: Select cemented carbide, cermet or cubic boron nitride as the substrate, and perform polishing, sandblasting and cleaning. Step 2, Underlayer Deposition: Use TiN, TiC or ZrN as the underlayer, with a thickness of 0.2-2 μm, a gas composition of 0.8-1.8 vol% TiCl4, 20-40 vol% N2, and the balance H2, a temperature of 850-1000℃, a pressure of 100-300 mbar, and a deposition time of 10-30 min; Step 3, MT-TiCN layer deposition: Deposit an MT-TiCN support layer with a thickness of 3-10 μm, using a gas mixture of 0.5–1.5 vol% CH3CN, 1.5–2.5 vol% TiCl4, 10–25 vol% N2, 1–5 vol% HCl, and the balance H2, at a temperature of 800–900℃, a pressure of 50–200 mbr, and a deposition time of 1–10 h. Step 4, HT-TiCN transition layer deposition: Deposit a nitrogen-rich HT-TiCN transition layer with a thickness of 0.3-1 μm. The deposition gas is 1–2 vol% TiCl4, 2–5 vol% CH4, 0–2 vol% HCl, and 15–35 vol% N2. The temperature is 900–1050℃, the pressure is 100–500 mbar, and the deposition time is 10–60 min. Step 5, Deposition of the bonding layer: Deposit a (Ti,Al)(C,N,O) bonding layer with a thickness of 0.3-1μm. The gas composition is 1.5-2.5 vol% TiCl4, 1.5-3 vol% AlCl3, 1-3.5 vol% CO, 20-30 vol% N2, and the balance H2. The deposition temperature is 900-1050℃, the pressure is 50-200 mbar, and the deposition time is 10-30 min, during which the CO flow rate gradually increases with the deposition time.

[0017] Beneficial effects: By depositing a layered base layer, an MT-TiCN layer, an HT-TiCN transition layer, and a bonding layer, a gradient transition structure from the substrate to the α-Al2O3 coating is constructed. The thermal expansion coefficient and chemical composition are gradually adjusted, which effectively relieves the internal stress of the coating and improves the interfacial bonding strength of the multilayer structure, providing a stable foundation for the high-quality deposition of the subsequent composite textured α-Al2O3 layer.

[0018] Furthermore, following step five, a sixth step is included: alumina nucleation layer treatment. This involves oxidizing the bonding layer with a mixed gas containing 1.5–3.5 vol% CO2, 2.5–3.5 vol% CO, 20–30 vol% N2, and the balance H2, to form Ti. x O y The compound provides nucleation sites for subsequent α-Al2O3 deposition.

[0019] Beneficial effects: By using a mixed gas of CO2, CO, N2 and H2 in a specific ratio to oxidize the bonding layer, Ti can be controllably generated on the surface of the bonding layer through the synergistic regulation of the weak oxidizing property of CO2 and the reducing property of CO. x O y The compound has a matching crystal structure and lattice parameters with α-Al2O3, and can serve as a preferred nucleation substrate for heterogeneous nucleation of α-Al2O3, thereby increasing the nucleation density and promoting the vertical growth of columnar crystals, thus improving the density and bonding strength of the coating.

[0020] Furthermore, it also includes step seven, deposition of a composite textured α-Al2O3 layer: The composite textured α-Al2O3 layer is composed of multiple periodically stacked A textured layers and B textured layers, wherein the A textured layer is a (001) texture and the B textured layer is a (110) texture; When depositing the A texture layer, 2.5–5.5 vol% CO2, 1.5–3 vol% AlCl3, 1–9 vol% HCl, 1.5–10 vol% CO, 0–1 vol% H2S, and the balance H2 are introduced at a temperature of 900–1050℃ and a pressure of 50–200 mbar. When depositing the B texture layer, 1.4–3.5 vol% CO2, 1–4.5 vol% AlCl3, 1–3 vol% HCl, 0–1 vol% CO, 0–0.3 vol% H2S, and the balance H2 are introduced at a temperature of 900–1050°C and a pressure of 50–200 mbar. Within one stacking cycle, the thickness ratio of the A texture layer to the B texture layer is 1:1.5 to 1:3, the number of stacking cycles is 2 to 20, the thickness of the single texture layer is 0.5-5 μm, and the total thickness of the composite texture α-Al2O3 layer is 3-30 μm.

[0021] Beneficial effects: By differentially controlling the gas ratio of texture layer A and texture layer B, especially by introducing 1.5–10 vol% CO into texture layer A and 0–1 vol% CO into texture layer B, CO is used as a carbon source and oxygen partial pressure regulator. In texture layer A deposition, preferential growth of (001) crystal face is promoted, while in texture layer B deposition, the growth of (001) is inhibited and the development of (110) crystal face is promoted by reducing CO content. Thus, precise and controllable alternating deposition of the two textures is achieved. The interlayer grain boundaries formed by periodic stacking effectively deflect cracks and greatly improve the toughness of the coating.

[0022] Furthermore, the thickness ratio of the A texture layer to the thickness of the B texture layer is 1:2.

[0023] Beneficial effects: By limiting the thickness ratio to 1:2, while ensuring sufficient grain boundary turning angle, the (001) texture layer, as the main bearing layer, maintains a sufficient volume fraction, thus maintaining the overall high texture coefficient and excellent wear resistance of the coating, and avoiding a significant reduction in the wear resistance of the coating due to excessive thickness of the (110) texture layer.

[0024] Furthermore, it also includes step eight, deposition of the top wear indicator layer: depositing TiN, TiC, TiCN, ZrN or TiAlN as the top wear indicator layer on the surface of the composite textured α-Al2O3 layer, with a total thickness of 0.3-3 μm, a gas ratio of 0.8-1.8 vol% TiCl4, 20-40 vol% N2, and the balance H2, a temperature of 850-1000℃, a pressure of 200-800 mbar, and a deposition time of 30-120 min.

[0025] Beneficial effects: A top indicator layer with a distinct color difference from α-Al2O3 is deposited on the surface of the composite textured α-Al2O3 layer. This allows operators to visually judge the tool wear status by observing the wear of the indicator layer during the cutting process, enabling visualized monitoring of tool wear and timely tool replacement, thereby improving the controllability and safety of the machining process.

[0026] The advantages of this invention are: This invention utilizes precise control of the CVD deposition process to construct a composite textured α-Al2O3 coating on the tool surface, consisting of (001) textured layers and (110) textured layers stacked periodically in a specific thickness ratio. While maintaining excellent wear resistance due to its high texture coefficient, this structure leverages the crystallographic orientation difference between the (001) basal plane and the (110) prism facets to create significant grain boundary orientation between the layers. This effectively deflects and inhibits crack propagation along a single direction, fundamentally solving the inherent defect of insufficient toughness in single-textured coatings and achieving a synergistic enhancement of wear resistance and toughness.

[0027] The unexpected aspect of this invention in solving the technical problem lies in the fact that those skilled in the art generally recognize that the (001) texture of α-Al2O3 coatings has the best wear resistance. Therefore, existing technologies have focused on obtaining the purest possible (001) single texture through process optimization in order to maximize wear resistance. However, this approach leads to the formation of straight, columnar grain boundaries inside the coating, which become channels for rapid crack propagation under impact loads. This invention breaks through the technical bias that "a single high texture coefficient is optimal." By introducing a periodic alternation between a (110) texture layer and a (001) texture layer, it achieves a much higher-than-expected improvement in toughness while sacrificing some theoretical texture purity. Furthermore, since the (001) texture layer is still the main load-bearing layer, the overall wear resistance of the coating does not decrease significantly, thus realizing the long-sought-after goal of "wear resistance-toughness" synergistic optimization in this field.

[0028] The unexpected aspect of the technical means of this invention lies in the fact that the deposition process conditions for (001) texture and (110) texture are known in the art to be significantly different. It is generally believed that it is difficult to achieve the process of alternating two stable textures in the same coating, and the interlayer interface may cause severe stress concentration due to abrupt orientation changes. This invention achieves precise and controllable alternating deposition of the two textures by precisely controlling the key process parameter of CO content—using 1.5–10 vol% CO to promote (001) growth in the deposition of texture layer A, and using 0–1 vol% CO to inhibit (001) and promote (110) development in the deposition of texture layer B; at the same time, by limiting the thickness ratio to 1:1.5 to 1:3 and preferably 1:2, the interlayer orientation difference is large enough to achieve grain boundary turning, but the interface stress concentration caused by excessive orientation changes is avoided. The precise control of this process window is something that those skilled in the art cannot easily predict through conventional experiments. Attached Figure Description

[0029] Figure 1 This is a schematic diagram illustrating the design principle of the coating structure of this invention.

[0030] Figure 2 This is the XRD pattern of Embodiment 1 of the present invention.

[0031] Figure 3 This is the XRD pattern of Embodiment 2 of the present invention.

[0032] Figure 4 This is the XRD pattern of Comparative Example 1 of the present invention.

[0033] Figure 5 This is the XRD pattern of Comparative Example 2 of the present invention.

[0034] Figure 6 This is a cross-sectional topographic view of Embodiment 1 of the present invention.

[0035] Figure 7 This is a cross-sectional topographic view of Embodiment 2 of the present invention.

[0036] Figure 8 This is a cross-sectional topographic view of Comparative Example 1 of the present invention.

[0037] Figure 9 This is a cross-sectional topographic view of Comparative Example 2 of the present invention.

[0038] Figure 10 The image shows the EBSD diffraction pattern quality diagram (left) and crystal orientation distribution diagram (right) of Embodiment 1 of the present invention.

[0039] Figure 11 This is a comparison diagram of the indentation fracture toughness of the samples.

[0040] Figure 12 Comparison of wear morphology on the back face of the sample. Detailed Implementation

[0041] The following detailed description illustrates the specific implementation method: The composite textured alumina coating of this invention comprises, from the substrate surface outwards: an underlayer, an MT-TiCN layer, an HT-TiCN transition layer, a bonding layer, an oxide layer, a composite textured α-Al₂O₃ layer, and a top wear indicator layer. The overall structure is designed as follows: Figure 1 As shown; The composite textured α-Al2O3 layer consists of multiple periodically stacked A-textured layers and B-textured layers; wherein, the A-textured layer has a (001) texture and the B-textured layer has a (110) texture. EBSD analysis shows that the average grain boundary angle difference between adjacent periods is 80°–100°; EBSD phase analysis confirms that the composite coating is a pure α-Al2O3 phase, without κ-Al2O3 or θ-Al2O3 phases.

[0042] The composite texture has a thickness ratio of 1:1.5 to 1:3 between the thickness of texture layer A and texture layer B. A thickness ratio > 1:1.5 results in insufficient crack deflection, while a thickness ratio < 1:3 weakens the (001) texture strength. Preferably, the thickness ratio of texture layer A to texture layer B is set to 1:2 to provide a sufficiently large grain boundary orientation to deflect crack propagation paths, while avoiding excessive thickness of texture layer B, which would weaken the overall (001) texture strength of the coating. The number of stacking cycles is 2 to 20. A number of cycles < 2 results in no significant composite effect, while a number of cycles > 20 leads to excessive internal stress in the coating, making it prone to peeling.

[0043] The thickness of the single-layer composite texture is 0.5-5 μm, and the total thickness of the composite texture α-Al2O3 layer is 3-30 μm.

[0044] Before depositing the composite textured α-Al2O3 layer, an alumina nucleation layer treatment is required on the bonding layer. Specifically, the bonding layer is oxidized using a mixed gas containing CO2, CO, N2, and H2 to form Ti. x O y The compound provides nucleation sites for subsequent α-Al2O3 deposition.

[0045] The microscopic mechanism by which composite texture grain boundary orientation inhibits cracking and improves fracture toughness: α-Al₂O₃ belongs to the trigonal crystal system. Its (001) crystal plane is the basal plane, and the c-axis of the grains grows perpendicular to the coating surface, forming a columnar crystal morphology. The (110) crystal plane is a prismatic plane, and the grain orientation is perpendicular to the (001) layer, forming significant large-angle grain boundaries at the interface of alternating stacks. This specific crystallographic relationship constitutes the structural basis for crack deflection. When the crack tip encounters a grain boundary with abrupt orientation change, due to the significant difference in the slip system orientation of adjacent grains (the Schmid factor distributions of basal slip and prismatic slip are different), the crack cannot directly pass through the grain boundary to continue propagating in the original direction and is forced to deflect. This deflection forces the crack to turn along the grain boundary or along a more energy-consuming path, thereby effectively consuming the energy of crack propagation and enhancing the fracture toughness of the coating.

[0046] The detailed technical route of the composite textured alumina coating of this invention is as follows: 1. Substrate Selection and Treatment: Commonly used CVD high-temperature deposition substrates such as cemented carbide, cermet, or cubic boron nitride can be selected. This solution preferably uses WC-Co substrate, which is polished, sandblasted, and cleaned to ensure the surface roughness and cleanliness of the substrate.

[0047] 2. Underlayer Deposition: To improve the adhesion between the coating and the substrate, TiN, TiC, ZrN, etc., are selected as the underlayer. This scheme preferably uses TiN, with a thickness of 0.2-2 μm (preferably 0.5 μm). The gas composition is 0.8–1.8 vol% TiCl4, 20–40 vol% N2, with the balance being H2. The temperature is 850–1000℃, the pressure is 100–300 mbar, and the deposition time is 10–30 min.

[0048] 3. MT-TiCN layer deposition: Medium-temperature TiCN is selected as the support layer to enhance the toughness and wear resistance of the coating. The thickness is 3-10μm (preferably 6μm). The gas composition is 0.5–1.5 vol% CH3CN, 1.5–2.5 vol% TiCl4, 10–25 vol% N2, 1–5 vol% HCl, and the balance H2. The temperature is 800–900℃, the pressure is 50–200 mbr, and the deposition time is 1–10h.

[0049] 4. Deposition of N-rich HT-TiCN layer: High-temperature TiCN is used as a transition layer with a thickness of 0.3-1 μm (preferably 0.5 μm). The deposition gas is 1–2 vol% TiCl4, 2–5 vol% CH4, 0–2 vol% HCl, and 15–35 vol% N2. The temperature is 900–1050℃, the pressure is 100–500 mbar, and the deposition time is 10–60 min.

[0050] 5. Deposition of the bonding layer: Prepare a (T,Al)(C,N,O) bonding layer with a thickness of 0.3-1μm (preferably 0.5μm). The gas composition is 1.5-2.5 vol% TiCl4, 1.5-3 vol% AlCl3, 1-3.5 vol% CO, 20-30 vol% N2, and the balance H2. The deposition temperature is 900-1050℃, the pressure is 50-200 mbar, and the deposition time is 10-30 min, wherein the CO flow rate gradually increases with the deposition time.

[0051] 6. Alumina nucleation layer treatment: The bonding layer is oxidized using 1.5–3.5 vol% CO2, 2.5–3.5 vol% CO, 20–30 vol% N2, and the balance H2, with the aim of forming Ti. x O y The compound provides nucleation sites for α-Al2O3 deposition.

[0052] 7. Composite Textured α-Al₂O₃ Deposition: The bottom texture layer employs a 001 texture (A texture) to ensure the overall α-Al₂O₃ exhibits a 001 texture. The gas composition of the A texture layer is 2.5–5.5 vol% CO₂, 1.5–3 vol% AlCl₃, 1–9 vol% HCl, 1.5–10 vol% CO, 0–1 vol% H₂S, with the balance being H₂, at a temperature of 900–1050 °C and a pressure of 50–200 mbar. Since the 110 crystal plane is a typical prismatic face perpendicular to the 001 basal plane, a second layer employs a 110 texture (B texture) to achieve a larger grain boundary orientation. The gas composition of texture layer B is 1.4–3.5 vol% CO2, 1–4.5 vol% AlCl3, 1–3 vol% HCl, 0–1 vol% CO, 0–0.3 vol% H2S, with the balance being H2, at a temperature of 900–1050℃ and a pressure of 50–200 mbar. The stacking method for the composite textures is as follows: texture A + texture B constitutes one cycle, where the thickness ratio of texture A to texture B is 1:1.5, 1:2, or 1:3. This scheme prioritizes 1:2. The stacking cycle is 2–20 cycles, the thickness of a single texture layer is 0.5–5 μm, and the total thickness of the composite texture α-Al2O3 coating is 3–30 μm. The purpose of setting the above thickness ratio is to provide sufficiently large grain boundary deflection cracks while avoiding an excessively thick texture layer B that would reduce the strength of the 001 texture.

[0053] 8. Top Wear Indicator Layer Deposition: To assess the wear condition of the coating during cutting, a layer of TiN (preferably), TiC, TiCN, ZrN, TiAlN, etc., is deposited on top, with a total thickness of 0.3-3 μm, preferably 0.5 μm. The gas composition is 0.8–1.8 vol% TiCl4, 20–40 vol% N2, with the balance being H2. The temperature is 850–1000℃, the pressure is 200–800 mbar, and the deposition time is 30–120 min.

[0054] This invention constructs a composite structure by precisely controlling the deposition process and using special α-Al2O3 nucleation control, which consists of (001) texture layers and (110) texture layers stacked periodically in a specific thickness ratio. This structure can significantly enhance the (001) texture coefficient and utilize the significant grain boundary orientation effect formed between layers with different orientations to effectively deflect and suppress crack propagation within the coating, thereby greatly improving the toughness of the coating while retaining the excellent thermal stability and wear resistance of the (001) texture. The method is controllable and has good repeatability. The prepared coating is particularly suitable for tool surface protection under harsh conditions such as heavy-duty cutting, interrupted cutting, high-speed cutting, and dry cutting, and can significantly extend the tool life.

[0055] The specific implementation process is as follows: Example 1 This embodiment provides a specific method for preparing a high-toughness and wear-resistant α-Al2O3-based composite textured coating.

[0056] WC-8%Co cemented carbide was selected as the coating substrate, and the cutting tool model was WNMG080408-TM CNC cutting tool. The substrate was polished, sandblasted, cleaned and dried before use.

[0057] In an Ionbond 530 hot-wall CVD coating furnace, according to... Figure 1 The coating structure was designed and then fabricated. The sample has a multi-layer structure: from bottom to top, it consists of a TiN base layer, MT-TiCN, HT-TiCN, a bonding layer, an oxide layer, and a composite textured α-Al₂O₃ layer (see attached diagram). Figure 1 Multiple α-Al₂O₃ textured layers and a TiN wear indicator layer. The process parameters for each layer are as follows: TiN substrate: 1.48 vol% TiCl4, 23.5 vol% N2, balance H2, temperature 900℃, pressure 160 mbar, deposition time 60 min.

[0058] The MT-TiCN layer, also known as the MT-Ti(C,N) layer, consists of 0.7 vol% CH3CN, 1.9 vol% TiCl4, 21 vol% N2, 1–5 vol% HCl, and the balance H2. The deposition temperature is 880℃, the pressure is 100 mbr, and the deposition time is 5 h.

[0059] The HT-TiCN layer, also known as the HT-Ti(C,N) layer, consists of 1.8 vol% TiCl4, 3.5 vol% CH4, 0–2 vol% HCl, and 15.8→3.7 vol% N2, at a temperature of 1008 ℃, a pressure of 300 mbar, and a deposition time of 30 min.

[0060] The bonding layer consisted of 2.3 vol% TiCl4, 0.4 vol% AlCl3, 1→3 vol% CO, 24.5 vol% N2, and the balance H2. The deposition temperature was 1008℃, the pressure was 100 mbar, and the deposition time was 30 min.

[0061] Oxidation layer: 2 vol% CO2, 3 vol% CO, 26.5 vol N2, balance H2 were used to purge the bonding layer at a temperature of 1008℃, a pressure of 80 mbar, and a time of 5 min.

[0062] Composite texture α-Al2O3: The coating is formed by alternating stacking of 001 texture (A texture) and 110 texture (B texture) with a stacking cycle of 3. The process parameters of a single texture layer are shown in Table 1 below.

[0063] Table 1

[0064] The top wear indicator layer, TiN, consisted of 1.1 vol% TiCl4, 33 vol% N2, with the balance being H2. The deposition temperature was 950℃, the pressure was 650 mbar, and the deposition time was 60 min.

[0065] Example 2 This embodiment provides a specific implementation method for a high-toughness, wear-resistant α-Al₂O₃-based composite textured coating. This embodiment only changes the thickness and stacking cycle of a single textured layer compared to Example 1. The thickness ratio of texture A to texture B is 1:1.5, and the deposition times for the single textured layers are 40 min and 75 min, respectively; the stacking cycle is 8. Before depositing the α-Al₂O₃ composite texture, a bottom TiN layer, MT-TiCN, HT-TiCN layer, bonding layer, oxide layer, and a top TiN wear indicator layer are also included. The process parameters for each coating are the same as in Example 1 and will not be repeated here.

[0066] Comparative Example 1 To highlight the advantages of this technical solution, the present invention provides a comparative example, which includes only a single 001 texture (A texture) and a deposition time of 480 min. Before depositing the 001 texture, it also includes a bottom TiN, MT-TiCN, HT-TiCN, bonding layer, oxide layer and a top TiN wear indicator layer. The process parameters of each coating are the same as those in Example 1, and will not be repeated here.

[0067] Comparative Example 2 The present invention also provides a comparative example, which includes only a single 110 texture (B texture), with a deposition time of 300 min. Before depositing the 110 texture, it also includes a bottom TiN, MT-TiCN, HT-TiCN, bonding layer, oxide layer and a top TiN wear indicator layer. The process parameters of each coating are the same as those in Example 1, and will not be repeated here.

[0068] The following comparison and illustration of the embodiments and comparative examples are based on detailed structural characterization and performance test results: Structural characterization and performance testing: (1) Crystal structure analysis and texture coefficient calculation of the coating: The crystal structure of the coating was analyzed using an X-ray diffractometer (XRD, XPert Pro MPD). The radiation source was Cu Kα (λ=0.15406nm), the scanning mode was 2θ, and the scanning step size was 3° / min. The actual diffraction intensity of each diffraction peak of the α-Al2O3 coating was obtained using JADE software, and the TC value of each crystal plane was calculated. The calculation formula is as follows: (1) in, I(hkl) The actual measured intensity of the (hkl) reflective crystal plane; I 0 (hkl) The standard intensity of the (hkl) reflective crystal plane in JCPDF standard powder diffraction data; n The number of reflective crystal planes used in the calculation is (102), (104), (110), (006), (113), (024), (116), (214), (300). Figure 2 The XRD pattern is shown in Example 1. Figure 3 The XRD pattern is shown in Example 2. Figure 4 The image shows the XRD pattern of Comparative Example 1. Figure 5 The image shows the XRD pattern of Comparative Example 2. Figure 2-5 XRD patterns of Examples 1, 2, and the comparative example are shown. Analysis indicates that the diffraction peaks are mainly composed of WC-Co, Ti(C,N), α-Al₂O₃, and TiN crystal diffraction patterns, and the phase composition is consistent with the design scheme. The texture coefficient calculation results are shown in Table 2. It can be found that Examples 1 and Comparative Example 1 both have a 001 preferred orientation, while Example 2 has a 110 preferred orientation. The TC of Example 1... (006) =8.48, TC of Example 2 (006) =8.47, and all other texture indices are less than 0.5. TC of Comparative Example 1 (006) =8.23, TC of Comparative Example 1 (110) =5.22. Therefore, the technical solution provided by the present invention can further enhance the texture.

[0069] Table 2 Texture coefficient (TC) of the samples

[0070] (2) Characterization of coating cross-sectional morphology: The cross-sectional morphology of the embodiments and comparative examples of the present invention was characterized by scanning electron microscopy (ZEISS Sigma 300) at a voltage of 3-5 kV. Figure 6 The cross-sectional morphology of Example 1 is shown. Figure 7 The cross-sectional morphology of Example 2 is shown. Figure 8 The cross-sectional morphology is shown in Comparative Example 1. Figure 9 To show the cross-sectional morphology of Comparative Example 2, through Figure 6-9 The cross-sectional morphology of the coatings in Examples 1, 2 and the comparative examples is shown respectively. It can be found that the α-Al2O3 coatings in Examples 1 and 2 grow in a columnar shape and the grain boundaries are serrated, indicating that the orientation of the coatings changed periodically during the growth process; while Comparative Examples 1 and 2 have a single 001, 110 texture, and their grain boundaries have conventional vertical and curved features.

[0071] (3) EBSD Characterization: EBSD technology was used to perform crystallographic analysis on the cross-section of Example 1 to directly verify its unique grain boundary morphology and crystal orientation. The coating cross-section was cut out using a mechanical cutter, and after rough grinding to expose the coating cross-section, fine polishing was performed to eliminate mechanical damage. Subsequently, the sample was placed in the sample chamber of an argon ion polisher, and high-purity argon gas (purity ≥99.999%) was used as the sputtering gas to polish the sample cross-section. The accelerating voltage was 4-6kV and the ion beam current was 1-4mA. The polishing process was carried out in stages: first, the surface damage was removed at a larger angle (6°-10°) and a higher beam current (4mA), with a cumulative time of about 3-5 hours; then, the angle was reduced to 3°-5° and the beam current was reduced for final fine polishing, which lasted for 2-3 hours. The final coating cross-section should have a mirror-like gloss and be free of scratches. EBSD analysis of the coating cross-section was performed on a field emission scanning electron microscope (ZeissSigma 360) equipped with an Oxford Symmetry S2 system. The voltage was 15 kV, the sample tilt angle was 70°, and the scanning step size was 0.04 μm.

[0072] Figure 10 The EBSD diffraction pattern quality map (left) and crystal orientation distribution map (right) of Example 1 are shown. It can be observed that most grain boundaries are serrated; a small number of grains still exhibit vertical grain boundaries, which may be due to inhomogeneous furnace atmosphere. EBSD analysis shows that the average angle difference between adjacent grain boundaries is 80°–100°; EBSD phase analysis confirms that the composite coating is a pure α-Al₂O₃ phase, without κ-Al₂O₃ or θ-Al₂O₃ phases. Furthermore, the crystal orientation distribution map and the calculated pole figure show that the growth direction (Y direction) of the coating is 001, confirming that the coating has a 001 preferred orientation.

[0073] (4) Fracture toughness test: The toughness of the coating is tested using the indentation method. First, the coating surface is polished using diamond slurry with average particle sizes of 1μm and 0.5μm. The coating surface should be as smooth as possible to avoid excessive removal of delamination; therefore, the applied force in the normal direction should be sufficiently small. The indentation test is performed on a micro Vickers hardness tester with a load of 30-50kg and a holding time of 5s. When cracks are difficult to form, it is usually necessary to adjust the applied load. PThis allows for better crack propagation. The fracture toughness of the coating can be quantitatively calculated by measuring the crack length along the diagonal of the indentation, using the following formula: (2) H and E These represent the hardness and elastic modulus of the coating, respectively. P For load, α α is the geometric factor of the indentation; for Vickers indentations, α is typically taken as 0.016, and c is the crack length, i.e., the distance from the center of the indentation to the crack tip. The indentation fracture toughness of the examples and comparative examples is calculated as follows: Figure 11 As shown, K in Examples 1 and 2 Ic They were 8.4 ± 0.8 MPa•m respectively. 1 / 2 9.8±0.5MPa•m 1 / 2 Comparative Examples 1 and 2, K Ic They were 7.4 ± 0.9 MPa•m respectively. 1 / 2 5.7±0.8 MPa•m 1 / 2 Based on the above results, it can be seen that the technical solution of the present invention can significantly improve the fracture toughness of the coating, by at least 13.5% and 47.4% compared with the single 001 and 100 textured coatings, respectively.

[0074] (5) Cutting test: The cutting performance of the sample was evaluated by continuous turning of the steel part. According to GB / T16461-2016, the average wear band width VB=0.3 mm on the back face was used as the criterion for the end of tool life.

[0075] Blade type: WNMG080408-TM Workpiece: Cylindrical part Material: 45# steel Cutting speed: 300m / min Feed: 0.2mm / rev Depth of cut: 0.15mm Cutting method: continuous dry cutting The wear on the flank face was measured after 10 minutes and 20 minutes of continuous turning, as shown in Table 3. The wear condition of the flank face is as follows: Figure 12 As shown, the technical solution provided by the present invention significantly improves the wear resistance of the coating. Under the same continuous turning time, the wear on the back face of Examples 1 and 2 is lower than that of Comparative Example 1.

[0076] Table 3. Wear amount VB (mm) on the tool face after 10 minutes, 20 minutes, and 30 minutes of continuous turning.

[0077] The above descriptions are merely embodiments of the present invention, and common knowledge such as specific technical solutions and / or characteristics are not described in detail here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the technical solutions of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A high-toughness, wear-resistant α-Al₂O₃-based composite textured coating, characterized in that, From the substrate surface outwards, the layers are: underlayer, MT-TiCN layer, HT-TiCN transition layer, bonding layer, oxide layer, composite textured α-Al2O3 layer, and top wear indicator layer. The composite textured α-Al2O3 layer is composed of multiple periodically stacked A textured layers and B textured layers; the A textured layer is a (001) texture, and the B textured layer is a (110) texture; Within one stacking cycle, the thickness ratio of the A texture layer to the B texture layer is 1:1.5 to 1:3; the number of stacking cycles is 2 to 20; the thickness of the single texture layer is 0.5-5 μm; and the total thickness of the composite texture α-Al2O3 layer is 3-30 μm.

2. The composite textured coating according to claim 1, characterized in that, The thickness ratio of the A texture layer to the B texture layer is 1:

2.

3. The composite textured coating according to claim 1, characterized in that, The bonding layer is a (Ti,Al)(C,N,O) layer with a thickness of 0.3-1 μm; the oxide layer is a Ti-containing oxide layer formed by oxidizing the bonding layer. x O y The aluminum oxide nucleation layer of the compound.

4. The composite textured coating according to claim 1, characterized in that, In the composite textured α-Al2O3 layer, the texture coefficient TC(001) of the A texture layer is ≥8, and the texture coefficient TC(110) of the B texture layer is ≥5.

5. The composite textured coating according to claim 1, characterized in that, The coating is suitable for heavy-duty cutting, intermittent cutting, high-speed cutting, or dry cutting.

6. A method for preparing a high-toughness, wear-resistant α-Al₂O₃-based composite textured coating, characterized in that, Includes the following steps: Step 1, Substrate Pretreatment: Select cemented carbide, cermet or cubic boron nitride as the substrate, and perform polishing, sandblasting and cleaning. Step 2, Underlayer Deposition: Use TiN, TiC or ZrN as the underlayer, with a thickness of 0.2-2 μm, a gas composition of 0.8-1.8 vol% TiCl4, 20-40 vol% N2, and the balance H2, a temperature of 850-1000℃, a pressure of 100-300 mbar, and a deposition time of 10-30 min; Step 3, MT-TiCN layer deposition: Deposit an MT-TiCN support layer with a thickness of 3-10 μm, using a gas mixture of 0.5–1.5 vol% CH3CN, 1.5–2.5 vol% TiCl4, 10–25 vol% N2, 1–5 vol% HCl, and the balance H2, at a temperature of 800–900℃, a pressure of 50–200 mbr, and a deposition time of 1–10 h. Step 4, HT-TiCN transition layer deposition: Deposit a nitrogen-rich HT-TiCN transition layer with a thickness of 0.3-1 μm. The deposition gas is 1–2 vol% TiCl4, 2–5 vol% CH4, 0–2 vol% HCl, and 15–35 vol% N2. The temperature is 900–1050℃, the pressure is 100–500 mbar, and the deposition time is 10–60 min. Step 5, Deposition of the bonding layer: Deposit a (Ti,Al)(C,N,O) bonding layer with a thickness of 0.3-1μm. The gas composition is 1.5-2.5 vol% TiCl4, 1.5-3 vol% AlCl3, 1-3.5 vol% CO, 20-30 vol% N2, and the balance H2. The deposition temperature is 900-1050℃, the pressure is 50-200 mbar, and the deposition time is 10-30 min, during which the CO flow rate gradually increases with the deposition time.

7. The preparation method according to claim 6, characterized in that, Following step five is step six, an alumina nucleation layer treatment: the bonding layer is oxidized using a mixed gas containing 1.5–3.5 vol% CO2, 2.5–3.5 vol% CO, 20–30 vol% N2, and the balance H2, to form Ti. x O y The compound provides nucleation sites for subsequent α-Al2O3 deposition.

8. The preparation method according to claim 7, characterized in that, It also includes step seven, deposition of a composite textured α-Al2O3 layer: The composite textured α-Al2O3 layer is composed of multiple periodically stacked A textured layers and B textured layers, wherein the A textured layer is a (001) texture and the B textured layer is a (110) texture; When depositing the A texture layer, 2.5–5.5 vol% CO2, 1.5–3 vol% AlCl3, 1–9 vol% HCl, 1.5–10 vol% CO, 0–1 vol% H2S, and the balance H2 are introduced at a temperature of 900–1050℃ and a pressure of 50–200 mbar. When depositing the B texture layer, 1.4–3.5 vol% CO2, 1–4.5 vol% AlCl3, 1–3 vol% HCl, 0–1 vol% CO, 0–0.3 vol% H2S, and the balance H2 are introduced at a temperature of 900–1050 °C and a pressure of 50–200 mbar. Within one stacking cycle, the thickness ratio of the A texture layer to the B texture layer is 1:1.5 to 1:3, the number of stacking cycles is 2 to 20, the thickness of the single texture layer is 0.5-5 μm, and the total thickness of the composite texture α-Al2O3 layer is 3-30 μm.

9. The preparation method according to claim 8, characterized in that, The thickness ratio of the A texture layer to the B texture layer is 1:

2.

10. The preparation method according to claim 8, characterized in that, The process also includes step eight, deposition of a top wear indicator layer: depositing TiN, TiC, TiCN, ZrN or TiAlN as a top wear indicator layer on the surface of the composite textured α-Al2O3 layer, with a total thickness of 0.3-3 μm, a gas ratio of 0.8-1.8 vol% TiCl4, 20-40 vol% N2, and the balance H2, a temperature of 850-1000℃, a pressure of 200-800 mbar, and a deposition time of 30-120 min.

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