An alumina composite coating with texture strengthening and fine grain synergy and a preparation method thereof

Abstract

This invention relates to the field of chemical vapor deposition (CVD) hard coating technology, and discloses an alumina composite coating with texture enhancement and fine grain synergy and its preparation method. The TiCNO layer has a face-centered cubic structure, and its (112) crystal plane has a strong preferred orientation. It exhibits concentrated polar density points in the (112) pole figure and inverse pole figure, with a polar density value ≥4. The TiCNO layer is composed of extremely fine columnar crystals. According to electron backscatter diffraction statistics, the average diameter of the columnar crystals is ≤0.3μm and the average aspect ratio is ≥5. An α-Al2O3 layer is deposited on the surface of the TiAlCNO layer. The α-Al2O3 layer has a preferred orientation of the (110) crystal plane, and its texture coefficient TC(110)≥5. The (110) crystal plane has concentrated polar density points, with a polar density value ≥10. The grain morphology of the α-Al2O3 layer is columnar crystal. According to electron backscatter diffraction statistics, the average grain size is ≤0.63μm and the average aspect ratio is ≥2.8. Achieving synergistic optimization of strong texture and fine grain structure without the need for special element doping, thereby improving coating wear resistance and service life.

Description

Technical Field

[0001] This invention relates to the field of chemical vapor deposition (CVD) hard coating technology, specifically to an alumina composite coating with synergistic texture enhancement and fine grains and its preparation method. Background Technology

[0002] Chemical vapor deposition (CVD) is one of the main methods for preparing hard coatings and is widely used in cutting tools, wear-resistant parts, and other fields. Among them, medium-temperature TiCN (MT-TiCN) prepared by CVD has excellent toughness and wear resistance, while α-Al2O3 prepared by the same method has extremely high hardness, good high-temperature stability, and oxidation resistance. The composite coating of the two (MT-TiCN / α-Al2O3) has become the mainstream coating structure for machining various cast iron, steel parts, and alloy materials.

[0003] In conventional CVD processes, Al2O3 growth often follows the principle of minimum energy, and the resulting α-Al2O3 is typically randomly oriented or polycrystalline mixed-orientation. However, the deformation capacity of grains with different orientations is inconsistent, which easily leads to stress concentration at grain boundaries. This causes the coating to be prone to local microfractures during machining, resulting in premature tool chipping or coating peeling.

[0004] To improve the performance of CVD-Al2O3 coatings, those skilled in the art mainly achieve the preparation of strongly textured alumina coatings by introducing a transition layer between MT-TiCN and α-Al2O3 and by controlling the deposition process parameters. For example, patent CN1456703A discloses the introduction of an extremely thin TiAlCNO transition layer between TiCN and Al2O3 and the control of deposition parameters to obtain an α-Al2O3 coating with preferred growth of the (012) crystal plane; US2006 / 015662A1 discloses the achievement of preferred growth of the (110) crystal plane by alternating TiCl4 / H2 pulse treatment and CO2 / H2 / N2 / Ar oxidation pulses; US7455900B2 further discloses the achievement of an α-Al2O3 coating with preferred growth of the (116) crystal plane by optimizing the oxidation pulse parameters. In addition, existing technologies also disclose schemes for controlling the texture of α-Al2O3 by introducing Zr and Hf dopants into the TiAlCNO transition layer and combining it with specific deposition processes.

[0005] However, the aforementioned existing technical solutions share the following common drawbacks: First, the transition layers such as TiCNO and TiAlCNO are designed as extremely thin layers (thickness typically << 500 nm, mostly << 100 nm), making structural control difficult. Furthermore, their main function is limited to inducing α-Al₂O₃ nucleation, failing to fully utilize their crystallographic induction potential. Second, existing technologies generally suffer from the technical contradiction of achieving both "texture" and "grain size": to refine α-Al₂O₃ grains, elemental doping or lowering the deposition temperature is usually required, but elemental doping increases process complexity. The high temperature can lead to impurities and production costs. Lowering the temperature can easily introduce the metastable phase κ-Al2O3. Under high-temperature service conditions, the phase transformation process from κ-Al2O3 to α-Al2O3 will cause volume shrinkage and microcracks, which will seriously affect the service performance of the coating. Thirdly, the existing technology lacks a systematic understanding of the texture characteristics of the TiCNO layer itself and its crystallographic relationship with the upper α-Al2O3. It relies more on XRD technology for macroscopic texture analysis and fails to reveal the microscopic control mechanism of the specific crystal orientation of the TiCNO layer on the nucleation density and growth direction of α-Al2O3. Summary of the Invention

[0006] This invention aims to provide an alumina composite coating with synergistic texture enhancement and grain refinement, and its preparation method, to solve the technical contradictions in existing CVD-Al2O3 coatings, which struggle to simultaneously achieve strong texture and grain refinement, and rely on element doping or temperature reduction leading to complex processes and the introduction of metastable κ-Al2O3 phases that can cause microcracks. By inducing the directional growth of α-Al2O3 (110) through the strong texture of the TiCNO layer (112), the synergistic optimization of strong texture and grain refinement is achieved without the need for special element doping, thereby improving the coating's wear resistance and service life.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: Option 1: An alumina composite coating that combines texture enhancement and grain refinement, comprising, from the substrate surface outwards: TiN base layer, TiCNO layer, HT-TiCN transition layer, TiAlCNO bonding layer and α-Al2O3 layer; The TiCNO layer has a face-centered cubic structure. Electron backscatter diffraction analysis shows that its (112) crystal plane has a strong preferred orientation and exhibits concentrated polar density points in the (112) pole figure and inverse pole figure, with a polar density value ≥4. The TiCNO layer is composed of extremely fine columnar crystals. Electron backscatter diffraction statistics show that the average diameter of the columnar crystals is ≤0.3μm and the average aspect ratio is ≥5. The α-Al2O3 layer is deposited on the surface of the TiAlCNO layer. X-ray diffraction analysis shows that the α-Al2O3 layer has a preferred orientation of the (110) crystal plane, and its texture coefficient TC(110)≥5. In the electron backscatter diffraction pole figure and inverse pole figure, the (110) crystal plane has concentrated polar density points with a polar density value ≥10. The grain morphology of the α-Al2O3 layer is columnar, and the average grain size is ≤0.63μm and the average aspect ratio is ≥2.8, according to the electron backscatter diffraction statistics.

[0008] Beneficial effects: The strong texture of the TiCNO layer (112) induces the directional growth of α-Al2O3 (110), while the high density of nucleation sites provided by the fine grain structure of the TiCNO layer is used to refine the α-Al2O3 grains. In a single coating structure, the dual optimization of texture strengthening and fine grain synergy is achieved, which significantly improves the wear resistance and anti-chipping performance of the coating.

[0009] Furthermore, the TiCNO layer is directly deposited on the surface of the TiN layer, with a thickness of 2-15 μm.

[0010] Beneficial effects: Designing the TiCNO layer as a wear-resistant layer and crystallographic induction layer with a specific thickness range, which is different from the ultra-thin transition layer design of <<500nm in the existing technology, not only ensures the integrity of the TiCNO layer itself and the texture stability, but also provides a continuous and stable orientation induction and nucleation site for the upper α-Al2O3.

[0011] Furthermore, the thickness of the TiN substrate is 0.5-2 μm.

[0012] Beneficial effects: Optimizes the thickness range of the TiN underlayer, effectively improves the adhesion between the coating and the substrate, and prevents the coating from peeling off prematurely during the cutting process.

[0013] Furthermore, the thickness of the HT-TiCN transition layer is 0.3-1 μm.

[0014] Beneficial effects: The HT-TiCN transition layer alleviates the difference in thermal expansion coefficients between the TiCNO layer and the TiAlCNO bonding layer, reduces interfacial stress, and improves the overall structural stability of the coating.

[0015] Furthermore, the TiAlCNO bonding layer is used to enhance the coating adhesion and induce the formation of α-Al2O3, with a thickness of 0.1-1 μm.

[0016] Beneficial effects: Controlling the thickness of the TiAlCNO bonding layer effectively improves the coating adhesion and induces the formation of α-Al2O3, while avoiding the accumulation of internal stress caused by excessive thickness.

[0017] Furthermore, the thickness of the α-Al2O3 layer is 3-15 μm.

[0018] Beneficial effects: Optimizing the thickness range of the α-Al2O3 layer ensures high hardness and wear resistance while maintaining the advantages of a fine-grained structure, avoiding grain coarsening and stress increase caused by excessive thickness.

[0019] Option 2: A method for preparing an alumina composite coating with synergistic texture enhancement and grain refinement, comprising the following steps: Step 1, Substrate Selection and Treatment: WC-Co cemented carbide substrate is selected and treated with polishing, sandblasting, and cleaning. Step 2, TiN underlayer deposition: Chemical vapor deposition is used with a gas ratio of 0.8–1.8 vol% TiCl4, 20–40 vol% N2, and the balance H2. The temperature is 850–1000℃, the pressure is 60–150 mbar, and the deposition time is 10–30 min, resulting in a TiN underlayer with a thickness of 0.2–2 μm. Step 3, TiCNO layer deposition: Chemical vapor deposition is used with a gas ratio of 0.5–1.5 vol% CH3CN, 1.5–2.5 vol% TiCl4, 10–25 vol% N2, 1–5 vol% HCl, 0.5–1 vol% CO, and the balance H2. The temperature is 850–1000℃, the pressure is 50–150 mbar, and the deposition time is 2–8 h. A TiCNO layer with a thickness of 2–15 μm, a (112) crystal plane with strong preferred orientation and an average grain size ≤0.3 μm is obtained. Step 4, HT-TiCN transition layer deposition: Chemical vapor deposition is used with a gas composition of 1–2 vol% TiCl4, 2–5 vol% CH4, 0–2 vol% HCl, and 15–35 vol% N2, at a temperature of 900–1050℃, a pressure of 100–450 mbar, and a deposition time of 10–60 min, to obtain an HT-TiCN transition layer with a thickness of 0.3–1 μm. Step 5, TiAlCNO bonding layer deposition: Chemical vapor deposition is used with a gas composition of 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 1000–1050℃, the pressure is 50–200 mbar, and the deposition time is 10-30 min, resulting in a TiAlCNO bonding layer with a thickness of 0.1-1 μm. Step 6, α-Al2O3 layer deposition: Chemical vapor deposition is used with a gas ratio of 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. The temperature is 900–1050℃, the pressure is 50–200mbar, and the coating thickness is 3–15μm, resulting in an α-Al2O3 layer with a preferred orientation of the (110) crystal plane and an average grain size ≤0.63μm.

[0020] Beneficial effects: Through the above six-step sequential deposition process, without relying on special element doping, the intrinsic (112) strong texture and fine grain structure of TiCNO layer are used to induce the synergistic growth of α-Al2O3 with (110) strong texture and fine grain structure. The process is simple and the production cost is significantly reduced.

[0021] Furthermore, in step two, the thickness of the TiN substrate is 0.5 μm.

[0022] Beneficial effects: The best alumina composite coating is obtained with a TiN underlayer thickness of 0.5 μm.

[0023] Furthermore, in step three, the TiCNO layer is directly deposited on the surface of the TiN layer, with a thickness of 5-8 μm.

[0024] Beneficial effects: This thickness, combined with the corresponding processing temperature, not only ensures the stability of the face-centered cubic phase of the TiCNO layer, but also promotes the orientation growth and grain refinement of the (112) crystal plane, which is different from the temperature selection of conventional medium-temperature or high-temperature TiCN processes.

[0025] Furthermore, in step four, the thickness of the HT-TiCN transition layer is 0.5 μm.

[0026] Beneficial effects: The best alumina composite coating is obtained when the thickness of the HT-TiCN transition layer is 0.5 μm.

[0027] The advantages of this invention are: This invention designs the TiCNO layer as both a wear-resistant layer and a crystallographic induction layer, achieving a "dual-energy" structural innovation. Electron backscatter diffraction (EBSD) analysis confirms that TiCNO forms a strongly preferred orientation on the (112) crystal plane, filling a gap in existing technologies that have long neglected this texture due to reliance solely on XRD techniques. Furthermore, while maintaining a strong (112) texture, the TiCNO layer forms extremely fine columnar crystals, thereby inducing the upper α-Al2O3 layer to achieve a strong (110) texture (TC≥5) while refining the grain size to 0.64 μm, achieving a dual optimization of texture strengthening and grain refinement. Moreover, this invention induces directional growth and grain refinement of α-Al2O3 solely through the intrinsic texture of the TiCNO layer, without relying on special element doping, resulting in a simple process and significantly reduced production costs.

[0028] Compared with the prior art, the present invention has achieved many unexpected technical effects. First, in terms of solving technical problems, the present invention breaks through the inherent understanding in the prior art that "texture-grain size" are difficult to achieve simultaneously. The prior art generally believes that the formation of strong texture α-Al2O3 requires sufficient grain growth space, which is inherently contradictory to grain refinement. The present invention provides a directional growth template through the strong texture of the TiCNO layer (112), and at the same time uses its extremely fine columnar crystals (average diameter ≤0.μm) to provide high-density nucleation sites, so that α-Al2O3 nucleates in large quantities in the early stage of nucleation and grows under orientation constraint. Thus, the synergistic optimization of strong texture and ultrafine grains is achieved for the first time in a single coating. This effect is something that those skilled in the art could not have expected based on the prior art.

[0029] Secondly, in terms of unexpected technical means, in existing technologies, TiCNO, TiAlCNO, and other layers are designed as extremely thin transition layers (<<500nm), and their function is limited to inducing α-Al2O3 nucleation. However, this invention redesigns the TiCNO layer as a functional layer, giving it the dual function of a wear-resistant layer and a crystallographic induction layer. This structural innovation overturns the conventional practice of functional positioning and thickness design of TiCNO layers in this field. More importantly, existing technologies have long relied on XRD technology for macroscopic texture analysis, failing to reveal the crystallographic relationship between the crystal orientation of the TiCNO layer (112) and the texture of α-Al2O3 (110). This invention, through EBSD technology, for the first time confirms the orientation inheritance relationship of TiCNO (112) / / α-Al2O3 (110), filling this cognitive gap and providing a new theoretical basis for coating texture design.

[0030] Furthermore, this invention achieves a significant advantage in terms of process simplicity—existing technologies typically require the introduction of special elements such as Zr and Hf for doping, or the use of complex pulse deposition processes, in order to achieve α-Al2O3 texture control; this invention can achieve directional growth and grain refinement of α-Al2O3 solely through intrinsic texture induction of the TiCNO layer, without the need for additional element doping, which greatly reduces process complexity and production costs, while avoiding the risks of interface contamination and performance degradation that may be introduced by element doping. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the alumina composite coating structure of the present invention.

[0032] Figure 2 This is the XRD pattern of Embodiment 1 of the present invention.

[0033] Figure 3 This is a cross-sectional EBSD pattern quality diagram of Embodiment 1 of the present invention.

[0034] Figure 4 This is a crystal orientation distribution diagram of Embodiment 1 of the present invention.

[0035] Figure 5 These are the pole figures and inverse pole figures of Embodiment 1 of the present invention.

[0036] Figure 6 This is a scratch curve diagram of Embodiment 1 of the present invention.

[0037] Figure 7 This is a scratch morphology diagram of Embodiment 1 of the present invention.

[0038] Figure 8 This is the XRD pattern of Embodiment 2 of the present invention.

[0039] Figure 9 The XRD pattern is a comparative example of the present invention.

[0040] Figure 10 This is a cross-sectional EBSD pattern quality diagram for the comparative example of this invention.

[0041] Figure 11 This is a crystal orientation distribution diagram for the comparative example of the present invention.

[0042] Figure 12 These are pole figures and inverse pole figures for comparative examples of this invention.

[0043] Figure 13 The scratch curve is a comparative example of the present invention.

[0044] Figure 14 This is a comparative scratch image display of the present invention.

[0045] The reference numerals in the accompanying drawings include: WC-Co substrate 1, TiN underlayer 2, fine-grained, strongly textured TiCNO layer 3, HT-TiCN transition layer 4, TiAlCNO bonding layer 5, and strongly textured, fine-grained α-Al2O3 layer 6. Detailed Implementation

[0046] The following detailed description illustrates the specific implementation method: This invention belongs to the field of chemical vapor deposition (CVD) hard coating technology, specifically relating to an alumina composite coating for cutting tools that synergistically enhances texture and refines grain size, and its preparation method. Existing CVD-Al2O3 coatings struggle to simultaneously achieve strong texture and fine grain size, and suffer from technical contradictions such as reliance on elemental doping or lowering the temperature, leading to complex processes and the potential introduction of metastable κ-Al2O3 phases that generate microcracks.

[0047] The alumina composite coating of this invention, which combines texture enhancement and grain refinement, has an overall structure as follows: Figure 1 As shown. The composite coating comprises, from the substrate surface outwards, the following: WC-Co basal layer 1; TiN underlayer 2: 0.5-2μm thick, used to improve coating adhesion; 3. Fine-grained, strongly textured TiCNO layer: The TiCNO layer is directly deposited on the surface of the TiN layer, with a thickness of 2-15 μm.

[0048] TiCNO has a face-centered cubic structure. Electron backscatter diffraction (EBSD) analysis shows that its (112) crystal plane has a strong preferred orientation, exhibiting concentrated polar density points in the (112) pole figure and inverse pole figure, with a polar density value ≥4. In addition, the TiCNO layer is composed of extremely fine columnar crystals. EBSD statistics show that the average diameter (i.e., average grain size) of the columnar crystals is ≤0.3μm, and the average aspect ratio is ≥5.

[0049] HT-TiCN transition layer 4 (abbreviated as HT-TiCN layer or high temperature TiCN layer): HT-TiCN serves as a transition layer with a thickness of 0.3-1μm.

[0050] TiAlCNO bonding layer 5: used to improve coating adhesion and induce the formation of α-Al2O3, with a thickness of 0.1-1μm.

[0051] Strongly textured fine-grained α-Al2O3 layer 6: The α-Al2O3 layer is deposited on the surface of the TiAlCNO layer, with a thickness of 3-15 μm.

[0052] X-ray diffraction (XRD) analysis revealed that the α-Al₂O₃ layer exhibits a preferred orientation of the (110) crystal plane with a texture coefficient TC(110) ≥ 5. In the EBSD pole figure and inverse pole figure, the (110) crystal plane shows a concentrated polar density with a polar density value ≥ 10. The α-Al₂O₃ layer has a columnar crystal morphology, with an average grain size ≤ 0.63 μm and an average aspect ratio ≥ 2.8, as determined by EBSD.

[0053] Mechanism Explanation: The Formation Principle of Strongly Textured Fine-Grained α-Al2O3 EBSD orientation analysis revealed that the angle between the preferred orientation grains on the (112) plane of the TiCNO layer and the preferred orientation grains on the (110) plane of the Al2O3 grown above it in the growth direction is 1-2°, indicating that the normals of the TiCNO (112) plane and the (110) plane are highly parallel and have a clear orientational epitaxial relationship. Further calculation of the lattice constant showed that the atomic period of the TiCNO (112) plane in the

[110] direction (approximately 3.01 Å) and the atomic period of the α-Al2O3 (110) plane in the

[001] direction (approximately 4.33 Å) are integer multiples of 7:5 (7 × 3.01 Å ≈ 21.07 Å, 5 × 4.33 Å ≈ 21.65 Å), with a mismatch of approximately 2.7%, satisfying the formation conditions of a coherent or semi-coherent interface. This low-energy interface causes Al2O3 to tend to grow in the early stages of nucleation with the (110) plane parallel to the (112) plane of TiCNO.

[0054] Furthermore, the TiCNO layer of this invention has an extremely fine columnar crystal structure with a width of <0.5 μm, and the grain boundary density per unit area is much higher than that of conventional TiCN layers (1-3 μm). Grain boundaries, steps, and other crystal defects have higher nucleation activity, providing a large number of preferred (110) oriented nucleation sites for Al2O3. High-density nucleation leads to small internucleation spacing and sufficient competitive growth, which not only strengthens the (110) orientation advantage but also restricts the lateral growth of grains, thereby achieving grain refinement (<0.7 μm) while obtaining strong texture.

[0055] This invention is not simply an optimization of process parameters, but rather the first to reveal and utilize the strong (112) texture of thick TiCNO as a crystallographic template for the (110) texture of α-Al2O3. While existing technologies (such as patent US7442431B2) have achieved the (110) texture of α-Al2O3, their mechanism relies on controlling nucleation through a complex pulsed process combined with an Al content gradient in the (Ti,Al)(C,O,N) transition layer. They do not recognize the role of the transition layer's own crystallographic texture in Al2O3 orientation, nor do they utilize the (112) non-close-packed planes of the FCC structure to induce α-Al2O3 growth. In summary, this invention, through the dual synergistic design of the TiCNO layer—(112) texture and extremely fine columnar crystals—has for the first time simultaneously achieved a strong texture (TC≥5) and nanoscale fine crystals (<0.7μm) in the same coating, an effect that was unforeseen by those skilled in the art.

[0056] The detailed technical route for the above-mentioned composite textured alumina coating 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 scheme preferably uses WC-Co (8 wt%) substrate, which is polished, sandblasted, and cleaned to ensure the surface roughness and cleanliness of the substrate.

[0057] 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 60–150 mbar, and the deposition time is 10–30 min.

[0058] 3. TiCNO layer deposition: thickness 2-15μm (preferably 5-8μm), gas composition 0.5-1.5 vol% CH3CN, 1.5-2.5 vol% TiCl4, 10-25 vol% N2, 1-5 vol% HCl, 0.5-1 vol% CO, balance H2, temperature 850-1000℃, pressure 50-150 mbar, deposition time 2-8h.

[0059] The preparation process parameters of the TiCNO layer, especially the CHCN / CO ratio, are not simple adjustments to conventional parameters in the field, but rather optimized ranges obtained through extensive systematic experimental screening, exhibiting significant inventiveness and non-obviousness. This invention systematically studies the effects of CH3CN flow rate (0.3-2.5 vol%) and CO flow rate (0.2-2.0 vol%) on the texture, grain size, and induction effect of the TiCNO layer through numerous orthogonal experiments.

[0060] When CH3CN is controlled at 0.5-1.5 vol% and CO is controlled at 0.5-1.0 vol%, the TiCNO layer can form a strong (112) texture. Too high or too low a proportion will weaken or eliminate the texture: when CH3CN is below 0.5 vol%, the carbon source is insufficient and the crystallinity of the TiCNO layer is poor; when CH3CN is above 1.5 vol%, the carbon content is too high, which inhibits the solid solution of oxygen and is not conducive to the preferential growth of the (112) plane; when CO is below 0.5 vol%, the oxygen content is insufficient and the grain refinement effect is insufficient; when CO is above 1.0 vol%, the oxygen content is too high, which leads to excessive lattice distortion and destroys the orderliness of the texture.

[0061] 4. HT-TiCN deposition: HT-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 °C, the pressure is 100–450 mbar, and the deposition time is 10–60 min.

[0062] 5. TiAlCNO deposition: TiAlCNO is used as the bonding layer with a thickness of 0.1-1μm (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 1000-1050℃, the pressure is 50-200 mbar, and the deposition time is 10-30 min.

[0063] 6. α-Al2O3 deposition: gas composition 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, balance H2, temperature 900–1050℃, pressure 50–200 mbar, coating thickness 3–15 μm.

[0064] The specific implementation process is as follows: Example 1 This embodiment provides an alumina composite coating with synergistic texture enhancement and fine grains, and its preparation method.

[0065] WC-Co (8 wt%) 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 for later use.

[0066] The coating experiments were conducted in an industrial-grade hot-wall CVD reactor, and the coating structure is shown in the attached figure. Figure 1 The schematic diagram of the alumina composite coating structure is shown below, and the process parameters for each layer are as follows: TiN: 1.48 vol% TiCl4, 23.5 vol% N2, balance H2, temperature 900℃, pressure 160 mbar, deposition time 30 min.

[0067] TiCNO: 0.7 vol% CH3CN, 1.9 vol% TiCl4, 21 vol% N2, 1–5 vol% HCl, 0.8 vol% CO, balance H2, temperature 860℃, pressure 70 mbar, deposition time 240 min.

[0068] HT-TiCN: 1.8 vol% TiCl4, 3.5 vol% CH4, 0–2 vol% HCl, 25 vol% N2, temperature 1000 ℃, pressure 400 mbar, deposition time 15 min.

[0069] TiAlCNO: 2.3 vol% TiCl4, 0.4 vol% AlCl3, 2.5 vol% CO, 21 vol% N2, balance H2, deposition temperature 1000℃, pressure 70 mbar, deposition time 30 min.

[0070] α-Al2O3: 1.6 vol% AlCl3, 6.24 vol% CO2, 0.44 vol% H2S, balance H2, deposition temperature 1000℃, pressure 100 mbar, deposition time 300 min.

[0071] Structural characterization and performance testing: The crystal structure of the coating was analyzed using X-ray diffraction (XRD, XPert Pro MPD) with Cu Kα (λ=0.15406nm) as the radiation source, 2θ scanning mode, and a scan step size of 3° / min. The actual diffraction intensities of each diffraction peak in the α-Al₂O₃ coating were obtained using JADE software, and the TC values ​​of each crystal plane were calculated using the following formulas: (1) Where I(hkl) is the actual measured intensity of the (hkl) reflective crystal plane; I0(hkl) is the standard intensity of the (hkl) reflective crystal plane in the 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).

[0072] Appendix Figure 2 The XRD pattern of Example 1 is shown, with 2θ on the horizontal axis and diffraction intensity / (arbitrary unit, au) on the vertical axis. The dominant intensity of the (110) peak is clearly shown in the figure. The texture coefficient calculation results are shown in Table 1. The XRD and calculation results show that Example 1 has a preferred orientation of the (110) crystal plane, TC(110) = 7.43.

[0073] Table 1. Texture coefficient (TC) of the samples.

[0074] EBSD technology was used to perform crystallographic analysis on Example 1. EBSD samples were prepared using a high-precision argon ion polisher with an accelerating voltage of 4 kV and an ion beam current of 1-4 mA. The polishing process was performed in stages: first, surface damage was removed at a relatively large angle (6°-10°) and a relatively high beam current (4 mA), for a total time of approximately 3-5 hours; then, the angle was reduced to 3°-5° and the beam current was decreased for final fine polishing, lasting 2-3 hours. The final coating cross-section should have a mirror-like finish and be free of scratches. EBSD analysis of the coating cross-section was performed using a field emission scanning electron microscope (Zeiss Sigma 360) equipped with an Oxford Symmetry S2 system. The voltage was 15 kV and the sample tilt angle was 70°.

[0075] Appendix Figure 3 The EBSD diffraction pattern quality image for Example 1 shows the cross-sectional configuration of the coating, where the TiCNO layer has a thickness of 8 μm and the α-Al₂O₃ layer has a thickness of 4 μm. EBSD analysis revealed the average grain sizes of the α-Al₂O₃ and TiCNO layers to be 0.64 ± 0.21 μm and 0.30 ± 0.12 μm, respectively; their aspect ratios were 2.8 ± 1.3 and 5.0 ± 2.0, respectively. (See attached image.) Figure 4 This is a grain orientation distribution diagram of Example 1, where different colors represent different crystal orientations, in conjunction with the attached diagram. Figure 5 The pole figure and inverse pole figure show that the (112) crystal plane of the TiCNO layer has concentrated pole density points. The calculated pole density value is 4, indicating that TiCNO has a preferred orientation of the (112) crystal plane.

[0076] EBSD orientation analysis revealed that the angle between the preferred orientation grains on the (112) plane of the TiCNO layer and the preferred orientation grains on the (110) plane of the Al2O3 layer above it in the growth direction is only 1-2°, indicating that the normals of the TiCNO (112) plane and the (110) plane are highly parallel and have a clear orientational epitaxial relationship. Further calculation of the lattice constant showed that the atomic period of the TiCNO (112) plane in the

[110] direction (approximately 3.01 Å) and the atomic period of the α-Al2O3 (110) plane in the

[001] direction (approximately 4.33 Å) are 7:5 (7 × 3.01 Å ≈ 21.07 Å, 5 × 4.33 Å ≈ 21.65 Å), with a mismatch of approximately 2.7%, satisfying the formation conditions of a coherent or semi-coherent interface. This low-energy interface causes Al2O3 to tend to grow in the early stages of nucleation with the (110) plane parallel to the (112) plane of TiCNO.

[0077] It is worth noting that the XRD analysis did not detect the (112) crystal plane of TiCNO. This is because TiCNO has a typical rock salt structure, and XRD can only detect crystal planes with all odd or all even indices. Therefore, the diffraction peak of the (112) crystal plane disappears, i.e., the extinction rule. In addition, the (110) crystal plane of the α-Al2O3 layer shows concentrated extreme density points, and the calculated extreme density value is 10, confirming that α-Al2O3 has a preferred orientation of the (110) crystal plane, which is consistent with the XRD analysis results.

[0078] The hardness of the coating was determined using nanoindentation, and the adhesion of the coating was tested using a scratch analyzer. The hardness of Example 1, measured by nanoindentation, was 32.8 ± 1.4 GPa. (See attached image) Figure 6 The scratch test curve of Example 1 is shown, where the load corresponding to the abrupt change in the acoustic signal represents the adhesion force of the coating. It can be observed that even when the load reaches the maximum value of 100N, the acoustic signal does not show abrupt changes; therefore, the adhesion force of the coating is ≥100N. (Appendix) Figure 7 This is a scratch morphology diagram of Example 1, based on the attached diagram. Figure 7 The scratch morphology shows that the coating did not show obvious peeling during the entire scratching process, which confirms its good adhesion.

[0079] Example 2 This embodiment only adjusts the CO content in the α-Al2O3 deposition process to 0.6 vol% based on Example 1. The rest of the process flow and process parameters of each coating are the same as in Example 1, and will not be repeated here.

[0080] Its crystal structure was determined using XRD (see attached image). Figure 8 The XRD pattern is shown in Example 2. Figure 8The abscissa is 2θ, and the ordinate is diffraction intensity / (arbitrary unit, au), i.e., Intensity / au). The texture coefficient of the coating is calculated using the texture calculation method described above. The calculation results are shown in Table 1, where TC(110) = 5.2, while the TC values ​​of the other crystal planes are all less than 2, indicating that they all have a preferred orientation of the (110) crystal plane. The hardness of the coating was measured to be 30.9 ± 1.6 GPa by nanoindentation; the adhesion of the coating was measured to be 81 N by scratch test, proving its excellent adhesion.

[0081] Comparative Example To highlight the beneficial effects of introducing strongly textured fine-grained TiCNO into this technical solution, the present invention provides a comparative example in which the strongly textured TiCNO in Example 1 is replaced with randomly oriented TiCN, while other process parameters remain unchanged from Example 1.

[0082] The process parameters for TiCN in the comparative example are as follows: TiCN: 0.7 vol% CH3CN, 1.9 vol% TiCl4, 21 vol% N2, 1–5 vol% HCl, balance H2, temperature 860℃, pressure 70 mbar, deposition time 180 min.

[0083] Its crystal structure was determined using XRD (see attached image). Figure 9 The XRD pattern for the comparative example is shown, with 2θ on the horizontal axis and diffraction intensity (in arbitrary units, au) on the vertical axis. The texture coefficient of the coating is calculated using the texture calculation method described above. The calculation results are shown in Table 1, where TC(110) = 2.8, TC(012) = 1.2, and TC(006) = 1.5. Therefore, Comparative Example 1 exhibits a mixed orientation.

[0084] Appendix Figure 10 As shown in the comparative EBSD diffraction pattern quality diagram, it can be found that compared to Example 1 (attached...) Figure 3 The comparative examples of TiCN and α-Al₂O₃ show relatively large grains, with columnar and equiaxed grain morphologies coexisting. Statistical analysis revealed that the average grain sizes of α-Al₂O₃ and TiCN were 0.75±0.30 μm and 0.91±0.25 μm, respectively; their aspect ratios were 2.1±1.0 and 2.3±1.2 μm, respectively.

[0085] Appendix Figure 11 The crystal orientation distribution diagram shows, as a comparison, that the grains in both the TiCN and α-Al₂O₃ layers exhibit random orientation. (See attached diagram.) Figure 12 Comparative pole figures and inverse pole figures, with appendix Figure 12The pole figures and inverse pole figures show that neither TiCN nor α-Al2O3 has concentrated pole density points on specific crystal planes in the growth direction (Y direction), confirming that both TiCN and α-Al2O3 are random crystal orientations.

[0086] Appendix Figure 13 For comparative scratch curves, attached Figure 14 The images shown are comparative scratch images. The hardness of the coating, measured by nanoindentation, is 26.5 ± 1.3 GPa; the adhesion strength of the coating, measured by scratch testing, is 78 N. The corresponding scratch curves and morphologies are shown in the attached figures. Figure 13 and attached Figure 14 As shown, this indicates that the coating has good adhesion.

[0087] In summary, this invention overcomes the bottleneck of existing technologies by designing a fine-grained TiCNO layer with a strong (112) texture, which induces the formation of a fine-grained α-Al2O3 structure with a strong (110) texture in the upper alumina layer. Simultaneously, the coating exhibits extremely high hardness and excellent adhesion (as shown in Table 2), making it suitable for machining various steel parts.

[0088] Table 2 Comparison of Sample Performance

[0089] Conventional techniques in this field typically design TiCNO, TiAlCNO, and other layers as extremely thin transition layers (<500 nm), with functions limited to bonding and nucleation induction. Regarding texture control, conventional methods rely on elemental doping (Zr, Hf, etc.) or temperature control, resulting in complex processes and the potential introduction of metastable phases. This invention overturns these conventional understandings: it redefines the TiCNO layer as a functional layer with specific texture and fine-grained characteristics; it utilizes the intrinsic crystallographic characteristics of the TiCNO layer to induce α-Al₂O₃ growth without elemental doping; and it achieves synergistic texture enhancement and fine-grained growth in a single structure, resolving a long-standing technical contradiction in this field. These differences make this invention significantly superior to conventional techniques in terms of process simplicity, cost control, and overall coating performance.

[0090] 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. An alumina composite coating that combines texture enhancement and grain refinement, characterized in that, From the substrate surface outwards, the following are included sequentially: TiN base layer, TiCNO layer, HT-TiCN transition layer, TiAlCNO bonding layer and α-Al2O3 layer; The TiCNO layer has a face-centered cubic structure. Electron backscatter diffraction analysis shows that its (112) crystal plane has a strong preferred orientation and exhibits concentrated polar density points in the (112) pole figure and inverse pole figure, with a polar density value ≥4. The TiCNO layer is composed of extremely fine columnar crystals. Electron backscatter diffraction statistics show that the average diameter of the columnar crystals is ≤0.3μm and the average aspect ratio is ≥5. The α-Al2O3 layer is deposited on the surface of the TiAlCNO layer. X-ray diffraction analysis shows that the α-Al2O3 layer has a preferred orientation of the (110) crystal plane, and its texture coefficient TC(110)≥5. In the electron backscatter diffraction pole figure and inverse pole figure, the (110) crystal plane has concentrated polar density points with a polar density value ≥10. The grain morphology of the α-Al2O3 layer is columnar, and the average grain size is ≤0.63μm and the average aspect ratio is ≥2.8, according to the electron backscatter diffraction statistics.

2. The alumina composite coating with synergistic texture enhancement and grain refinement according to claim 1, characterized in that, The TiCNO layer is directly deposited on the surface of the TiN layer, with a thickness of 2-15 μm.

3. The alumina composite coating with synergistic texture enhancement and grain refinement according to claim 1 or 2, characterized in that, The thickness of the TiN substrate is 0.5-2 μm.

4. The alumina composite coating with synergistic texture enhancement and grain refinement according to claim 1 or 2, characterized in that, The thickness of the HT-TiCN transition layer is 0.3-1 μm.

5. The alumina composite coating with synergistic texture enhancement and grain refinement according to claim 1 or 2, characterized in that, The TiAlCNO bonding layer is used to improve the coating adhesion and induce the formation of α-Al2O3, and has a thickness of 0.1-1 μm.

6. The alumina composite coating with synergistic texture enhancement and grain refinement according to claim 1 or 2, characterized in that, The thickness of the α-Al2O3 layer is 3-15 μm.

7. A method for preparing an alumina composite coating with synergistic texture enhancement and grain refinement, characterized in that, Includes the following steps: Step 1, Substrate Selection and Treatment: WC-Co cemented carbide substrate is selected and treated with polishing, sandblasting, and cleaning. Step 2, TiN underlayer deposition: Chemical vapor deposition is used with a gas ratio of 0.8–1.8 vol% TiCl4, 20–40 vol% N2, and the balance H2. The temperature is 850–1000℃, the pressure is 60–150 mbar, and the deposition time is 10–30 min, resulting in a TiN underlayer with a thickness of 0.2–2 μm. Step 3, TiCNO layer deposition: Chemical vapor deposition is used with a gas ratio of 0.5–1.5 vol% CH3CN, 1.5–2.5 vol% TiCl4, 10–25 vol% N2, 1–5 vol% HCl, 0.5–1 vol% CO, and the balance H2. The temperature is 850–1000℃, the pressure is 50–150 mbar, and the deposition time is 2–8 h. A TiCNO layer with a thickness of 2–15 μm, a (112) crystal plane with strong preferred orientation and an average grain size ≤0.3 μm is obtained. Step 4, HT-TiCN transition layer deposition: Chemical vapor deposition is used with a gas composition of 1–2 vol% TiCl4, 2–5 vol% CH4, 0–2 vol% HCl, and 15–35 vol% N2, at a temperature of 900–1050℃, a pressure of 100–450 mbar, and a deposition time of 10–60 min, to obtain an HT-TiCN transition layer with a thickness of 0.3–1 μm. Step 5, TiAlCNO bonding layer deposition: Chemical vapor deposition is used with a gas composition of 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 1000–1050℃, the pressure is 50–200 mbar, and the deposition time is 10-30 min, resulting in a TiAlCNO bonding layer with a thickness of 0.1-1 μm. Step 6, α-Al2O3 layer deposition: Chemical vapor deposition is used with a gas ratio of 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. The temperature is 900–1050℃, the pressure is 50–200 mbar, and the coating thickness is 3–15 μm, resulting in an α-Al2O3 layer with a preferred orientation of the (110) crystal plane and an average grain size ≤0.63 μm.

8. The preparation method according to claim 7, characterized in that, In step two, the thickness of the TiN substrate is 0.5 μm.

9. The preparation method according to claim 7, characterized in that, In step three, the TiCNO layer is directly deposited on the surface of the TiN layer, with a thickness of 5-8 μm.

10. The preparation method according to claim 7, characterized in that, In step four, the thickness of the HT-TiCN transition layer is 0.5 μm.

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