High-hardness and high-toughness TiN-Cu composite film
By introducing extremely low amounts of copper into TiN thin films to construct nanocomposite structures, the problem of insufficient toughness in TiN thin films is solved, achieving a synergistic improvement in high hardness and high toughness, which is suitable for cutting tools, precision molds and other fields.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-28
- Publication Date
- 2026-03-13
AI Technical Summary
Existing TiN films have high hardness but insufficient toughness. Existing modification methods are difficult to improve both hardness and toughness in a synergistic way, which leads to the coating being prone to peeling and failure under impact loads.
By introducing extremely low amounts of copper into TiN thin films, a nanocomposite structure is constructed, including TiN grains with nanotwins and copper in amorphous or nanocrystalline form filling the grain boundaries. The distribution of copper is controlled by magnetron co-sputtering, forming a unique 'grain boundary-twin' synergistic toughening mechanism.
The TiN-Cu composite film achieved high hardness (32 GPa) and high toughness (radial crack length less than 1.6 µm), changing the traditional perception that 'hardness is necessarily brittle' and possessing the potential for large-scale industrial production.
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Figure CN121653587A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of hard thin film materials, specifically to a titanium nitride-copper (TiN-Cu) composite thin film with a nanocomposite structure that simultaneously possesses enhanced hardness and toughness, and its preparation method. Background Technology
[0002] Titanium nitride (TiN) is a widely used material in the field of hard thin film materials. Due to its high hardness, excellent wear resistance, and outstanding chemical stability, TiN thin films are extensively used as surface strengthening coatings for cutting tools, precision molds, and wear-resistant parts. They also have applications in decorative coatings and the electronics industry.
[0003] However, TiN films in the current state of technology have significant limitations: despite their high hardness, their toughness (i.e., the material's ability to resist fracture) is relatively poor, exhibiting brittleness. This brittleness causes TiN coatings to easily develop microcracks and propagate rapidly during actual service, especially when subjected to impact loads or alternating stresses, ultimately leading to coating peeling and failure, severely shortening the service life of tools or components.
[0004] To resolve the inherent contradiction between hardness and toughness, the mainstream approach in this field is to introduce a metal phase with better toughness into the TiN matrix to form a composite film. Copper (Cu) is often chosen as the toughening additive phase due to its good toughness and its inability to form compounds with TiN. However, existing technologies, whether magnetron sputtering or arc ion plating, generally face a "seesaw effect" in the preparation of TiN-Cu composite films, meaning it is difficult to simultaneously optimize hardness and toughness. Typically, increasing the Cu content to improve toughness significantly reduces the film's hardness because the soft Cu phase weakens the overall load-bearing capacity, and vice versa. Existing research largely remains at the level of observation and empirical summarization, lacking in-depth and systematic elucidation of the specific form in which trace amounts of Cu exist in the film and how they affect TiN performance at the microscopic level. This results in a narrow process window and poor performance repeatability. Therefore, existing technologies have failed to propose a controllable solution for constructing specific microstructures to fundamentally solve the technical challenge of the trade-off between hardness and toughness in hard films. Summary of the Invention
[0005] This disclosure aims to address the technical problems of insufficient toughness in existing TiN hard films and the difficulty of synergistically improving hardness and toughness using existing modification methods. The objective is to provide a TiN-Cu composite film with a specific microstructure that can simultaneously achieve high hardness and high toughness, and its preparation method.
[0006] One aspect of this disclosure provides a titanium nitride-copper composite film having a nanocomposite structure. The nanocomposite structure comprises: titanium nitride grains containing a nanotwin structure; and amorphous or nanocrystalline copper filling the grain boundaries of the titanium nitride grains, wherein the atomic percentage of copper is in the range of 0.1 at.% to 2.0 at.% of the film.
[0007] According to embodiments of this disclosure, the cross-sectional morphology of titanium nitride grains is a dense columnar crystal structure.
[0008] According to embodiments of this disclosure, titanium nitride grains have a preferred orientation of (111).
[0009] According to embodiments of this disclosure, the atomic percentage of copper is 0.54 at.% of the thin film.
[0010] According to embodiments of this disclosure, the size of titanium nitride grains is in the range of 10 nm to 15 nm.
[0011] According to embodiments of this disclosure, the film has a hardness of 32 GPa and an elastic modulus of 292 GPa.
[0012] According to embodiments of this disclosure, the radial crack length of the film is less than or equal to 1.6 µm in a Vickers indentation test.
[0013] Another aspect of this disclosure provides a method for preparing a titanium nitride-copper composite thin film. The method is used to manufacture a titanium nitride-copper composite thin film with a nanocomposite structure, the nanocomposite structure comprising: titanium nitride grains containing a nanotwin structure and amorphous or nanocrystalline copper filling the grain boundaries of the titanium nitride grains. The atomic percentage content of copper in the thin film is in the range of 0.1 at.% to 2.0 at.%. The method is characterized by comprising: preparing a substrate and placing it in a processing chamber of a magnetron sputtering vacuum apparatus; preparing a titanium target and a copper target; forming a gas atmosphere comprising argon and nitrogen in the processing chamber; and inducing magnetron co-sputtering of the titanium and copper targets onto the substrate by providing electrical energy to the titanium and copper targets, thereby forming a titanium nitride-copper composite thin film on the surface of the substrate. Specifically, DC power is applied to the titanium and copper targets, a substrate bias voltage is applied to the substrate, the DC power of the titanium target is 400 W, the DC power of the copper target is greater than 15 W and less than 45 W, and the substrate bias voltage is -100 V.
[0014] According to embodiments of this disclosure, a reaction atmosphere comprising argon and nitrogen is formed in the processing chamber, comprising: controlling the argon flow rate in the gas atmosphere to be 20 sccm, the nitrogen flow rate to be 7 sccm, and the working pressure to be 0.3 Pa.
[0015] According to embodiments of this disclosure, after the step of preparing the substrate and before the steps of preparing the titanium target and the copper target, the preparation method further includes: forming an argon atmosphere in a processing chamber, turning on the titanium target, and sputtering and depositing a pure titanium metal transition layer on the surface of the substrate, the thickness of the transition layer being 10-100 nm.
[0016] According to one or more aspects of this disclosure, a titanium nitride-copper composite film capable of simultaneously improving hardness and toughness is provided. Trace amounts of amorphous or nanocrystalline copper effectively segregate and fill the grain boundary defects of the titanium nitride grains, significantly increasing the film density and suppressing crack initiation at its source. More importantly, the doping of trace amounts of Cu induces the formation of a high-density nanotwin structure within the TiN grains with high-level fault energy. These nanotwin boundaries effectively hinder dislocation movement and deflect microcrack propagation, forming a unique "grain boundary-twin" synergistic toughening mechanism with the flexible Cu phase at the grain boundaries. Based on this, the TiN-Cu composite film provided by this disclosure (preferably with a Cu content of 0.54 at.%) exhibits a hardness as high as 32 GPa, significantly improved compared to the hardness of pure TiN film (approximately 27 GPa). Simultaneously, in Vickers indentation testing, the radial crack length is reduced to less than or equal to 1.6 µm, demonstrating excellent toughness. The titanium nitride-copper composite thin film disclosed herein challenges the traditional perception that "hardness inevitably leads to brittleness" in hard thin films. Furthermore, the magnetron co-sputtering preparation method of this invention is simple, highly controllable, and reproducible, possessing the potential for large-scale industrial production. The toughening microstructure mechanism revealed in this invention also provides new ideas and clear theoretical guidance for achieving toughening in high-fault-energy ceramic materials. Attached Figure Description
[0017] The above and other aspects, features and advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings.
[0018] Figure 1 This is a schematic diagram of a magnetron co-sputtering system according to an embodiment of the present disclosure.
[0019] Figure 2 This is a flowchart of a method for preparing a titanium nitride-copper composite thin film according to an embodiment of the present disclosure.
[0020] Figure 3 This is an X-ray diffraction (XRD) pattern of a thin film prepared according to embodiments and comparative examples of this disclosure.
[0021] Figure 4 These are cross-sectional morphology diagrams of thin films prepared according to embodiments and comparative examples of this disclosure.
[0022] Figure 5 This is a transmission electron microscope image of the microstructure of the TiN-Cu composite film according to an embodiment of the present disclosure.
[0023] Figure 6 It is a graph showing the hardness and elastic modulus of the films prepared according to the embodiments and comparative examples of this disclosure.
[0024] Figure 7 The image shows the indentation pattern of a film prepared according to the embodiments and comparative examples of this disclosure after testing with a Vickers hardness tester. Detailed Implementation
[0025] The following detailed descriptions are provided to aid the reader in gaining a comprehensive understanding of the methods, apparatus, and / or systems described herein. However, various modifications, variations, and equivalents of the methods, apparatus, and / or systems described herein will be apparent to those skilled in the art. For example, the order of operations described herein is merely illustrative and is not limited to the order set forth herein; changes that will be apparent to those skilled in the art may be made, except for operations that must be performed in a specific order. Furthermore, for clarity and brevity, descriptions of features and structures well-known to those skilled in the art may be omitted. The features described herein may be implemented in different forms and will not be construed as being limited to the examples described herein. Rather, the examples provided herein make the invention thorough and complete, and will fully convey the scope of the invention to those skilled in the art.
[0026] This disclosure provides a high-hardness, high-toughness titanium nitride-copper (TiN-Cu) composite film with a specific nanocomposite structure and its preparation method, aiming to solve the technical problems of insufficient toughness in existing TiN hard films and the difficulty of existing modification methods in synergistically improving hardness and toughness. The core concept of this invention lies in: by introducing an extremely low content of copper into the TiN film and precisely controlling its existence form and distribution position in the film, a unique nanoscale composite microstructure is constructed, thereby breaking the "seesaw" relationship between hardness and toughness in traditional hard film materials and achieving synergistic enhancement of the two.
[0027] Embodiments of the present invention will now be described in detail with reference to the accompanying drawings. These embodiments will be explained in order to illustrate the present invention.
[0028] Figure 1 This is a schematic diagram of a magnetron co-sputtering system according to an embodiment of the present disclosure.
[0029] like Figure 1 As shown, the magnetron co-sputtering system consists of a vacuum chamber, multiple targets (Ti, Cu) located above, and a substrate located below. Magnetron sputtering is performed in the vacuum chamber. First, an inert gas (such as Ar and / or N2) is introduced into the vacuum chamber. Then, in the reaction atmosphere containing the inert gas, a glow discharge confined by a magnetic field generates plasma, Ar...+ The Ti and / or Cu targets are bombarded to sputter atoms, which then deposit onto the substrate surface under a negative bias. If the inert gas includes N2, the sputtered atoms will also be transported downwards along with the active nitrogen-containing material and deposited onto the substrate surface.
[0030] According to embodiments of this disclosure, a magnetron co-sputtering system includes at least one titanium (Ti) target and one copper (Cu) target for co-sputtering Ti and Cu. Although not shown, the magnetron co-sputtering system also includes components such as a substrate support, power supply, gas supply port, exhaust port, and vacuum pump to achieve precise control of the deposition environment (such as pressure, gas composition, bias voltage, and target power).
[0031] Figure 2 This is a flowchart of a method for preparing a titanium nitride-copper composite thin film according to an embodiment of the present disclosure.
[0032] Reference Figure 2 The method for manufacturing titanium nitride-copper composite films is used to manufacture films with nanocomposite structures.
[0033] In step S10, a substrate is provided.
[0034] In the embodiments, the substrate includes one of monocrystalline silicon, high-speed steel, cemented carbide, stainless steel, titanium alloy, and high-temperature alloy.
[0035] As an example, high-speed steel (HSS) is a high-carbon, high-alloy tool steel with high hardness, high wear resistance, and high toughness. Typical alloying elements include tungsten, molybdenum, chromium, and vanadium, which can form stable carbides. High-speed steels such as W18Cr4V and W6Mo5Cr4V2 are mainly used to manufacture cutting tools such as drills and end mills that maintain hardness under high-speed cutting conditions. Cemented carbide is an even harder material, prepared using powder metallurgy processes with a high-hardness refractory metal carbide (such as tungsten carbide WC) as a framework and iron group metals such as cobalt and nickel as binders. WC-Co cemented carbide is an example of this type and is widely used in the manufacture of high-strength cutting tools and wear-resistant parts. Furthermore, the substrate used in this disclosure is also applicable to stainless steel. Stainless steel is an Fe-based alloy steel designed primarily for corrosion resistance, generally containing ≥10.5 wt% Cr and ≤1.2 wt% C. Common 304 and 316 stainless steels are widely used in the chemical, medical, and food industries. They can be classified into different types based on their microstructure, such as austenitic, ferritic, and martensitic. Alongside stainless steel are superalloys, a class of metallic materials specifically designed for long-term operation in high-temperature environments above 600°C, maintaining high strength, oxidation resistance, and corrosion resistance. Superalloys typically use nickel, cobalt, or iron as a base material and contain various complex alloying elements to enhance their high-temperature performance. Examples include Inconel 718, which is a preferred material for key components in aerospace engines and gas turbines.
[0036] In the following embodiments, a single-crystal silicon (Si(100)) wafer will be used as the substrate material. The substrate will be ultrasonically cleaned in acetone and ethanol in sequence, dried, and then placed on a rotating substrate holder in the processing chamber of a magnetron sputtering vacuum equipment.
[0037] Start the vacuum system and evacuate the vacuum chamber to a background vacuum level better than 9.8 × 10⁻⁶. -4 Pa. Then, high-purity argon (Ar) gas is introduced, and the working pressure is adjusted to about 0.3 Pa. A negative bias voltage of -100V is applied to the substrate to perform glow discharge cleaning and Ar ion bombardment to remove surface contaminants and activate the surface.
[0038] Following the substrate preparation step, the manufacturing method further includes forming a Ti transition layer. The Ti transition layer formation step involves maintaining an argon atmosphere in a processing chamber, turning on a titanium target, and sputter-depositing a pure titanium metal transition layer on the substrate surface. The thickness of the transition layer is 10-100 nm. This enhances the adhesion between the subsequent thin film and the substrate.
[0039] In step S20, titanium and copper targets are prepared.
[0040] In step S30, a gaseous atmosphere comprising argon and nitrogen is formed in the processing chamber. High-purity nitrogen (N2) is introduced as the reaction gas based on the Ar atmosphere.
[0041] In step S40, by providing electrical energy to the titanium and copper targets, magnetron co-sputtering of the titanium and copper targets is induced and sputtered onto the substrate, thereby forming the titanium nitride-copper composite film on the surface of the substrate. In this embodiment, the Ti and Cu targets can be turned on simultaneously for reactive co-deposition. The process parameters are as follows: working gas pressure: 0.3 Pa, Ar flow rate: 20 sccm (standard cubic centimeters per minute), N2 flow rate: 7 sccm, substrate temperature: room temperature, substrate negative bias: -100 V, Ti target power: 400 W (DC power supply), Cu target power: greater than 15 W and less than 45 W (preferably 30 W) (DC power supply).
[0042] By precisely adjusting the Cu target power, the atomic percentage of Cu in the film can be controlled within the range of 0.1 at.% to 2.0 at.%. Although not shown in the figure, when the Cu target power is 15 W, a Cu atomic percentage of approximately 0.1 at.% can be obtained, for example, between 0.1 at.% and 0.12 at.%, while the deposition time is determined according to the desired thickness. The titanium nitride-copper composite film disclosed herein has a nanocomposite structure comprising: titanium nitride grains containing a nanotwinned structure; and amorphous or nanocrystalline copper filling the grain boundaries of the titanium nitride grains, wherein the atomic percentage of copper is in the range of 0.1 at.% to 2.0 at.% of the film.
[0043] Preferably, the cross-sectional morphology of the TiN grains is a dense columnar crystal structure.
[0044] Preferably, the titanium nitride grains have a (111) preferred orientation.
[0045] Preferably, the atomic percentage of copper is 0.54 at.% of the film. In this case, the size of the titanium nitride grains is in the range of 10 nm to 15 nm, the hardness of the film is 32 GPa, and the elastic modulus is 292 GPa; the radial crack length of the film is less than or equal to 1.6 µm in the Vickers indentation test.
[0046] The following will refer to Figures 3-5 Characterization of the structure and morphology of titanium nitride-copper composite films, and further reference to Figure 6 and Figure 7 Characterization of the properties of titanium nitride-copper composite films.
[0047] Figure 3 These are X-ray diffraction (XRD) patterns of thin films prepared according to embodiments and comparative examples of this disclosure. 0.54 at.% and 1.53 at.% are thin films prepared according to embodiments of this disclosure, while 0% and 8.49 at.% are comparative examples, showing the XRD patterns of the prepared thin films as the Cu content changes.
[0048] X-ray diffraction (XRD) analysis of the thin film prepared by the above method showed that the film had a typical face-centered cubic TiN structure. The titanium nitride grains had a (111) preferred orientation. The film had a strong (111) preferred orientation. No independent Cu or CuN diffraction peaks were observed in the spectrum, which preliminarily proved that Cu did not exist as an independent crystalline phase. According to the embodiments of this disclosure, since the Cu content is extremely low (e.g., less than 2 at.%), and Cu atoms do not have enough time and concentration to form their own crystal nuclei during magnetron sputtering deposition, it does not exist in the conventional form of "copper grains". Instead, these Cu atoms segregate to the grain boundaries of the growing TiN columnar crystals. Within this narrow space of the grain boundaries, Cu atoms eventually "fill" the spaces between TiN grains in an amorphous or nanocrystalline form.
[0049] According to materials growth theory, a strong (111) texture is a favorable crystallographic condition for the formation of growth twins in face-centered cubic materials (such as TiN). Adding extremely low amounts of Cu hinders the growth of some crystal planes in the film, while other crystal planes grow, resulting in a preferential orientation of the film. In other words, the addition of trace amounts of Cu can promote the dominant growth of (111) orientation by changing the surface energy of different crystal planes, thus creating the conditions for the formation of nanotwins.
[0050] like Figure 3 As shown, all samples exhibit a cubic TiN phase structure. With increasing Cu content, the TiN(220) diffraction intensity of the film continuously increases, but the preferred orientation remains TiN(111). As a comparative example, when the Cu content exceeds 2 at.%, for example, 8.49 at.%, no Cu phase appears. This is because the Cu grain size in the film is very fine, exceeding the limits of XRD measurement, or it is amorphous. When the Cu content is 8.49 at.%, the Cu in the film inhibits the growth of TiN grains, forming a fine spherical structure. The preferred orientation in the diffraction peaks is not obvious, and the average grain size also decreases.
[0051] Figure 4 This is a cross-sectional morphology image of the thin film prepared according to the embodiments and comparative examples of this disclosure. The cross-sectional morphology of the thin film was observed by transmission electron microscopy (TEM). Figure 5This is a transmission electron microscope image of the microstructure of the TiN-Cu composite film according to an embodiment of the present disclosure.
[0052] Reference Figure 4 The cross-sectional morphology of TiN-Cu composite films with different Cu contents is shown: (a) Cu content of 0 at.%, (b) Cu content of 0.54 at.%, (c) Cu content of 1.53 at.%, and (d) Cu content of 8.49 at.%. (b) and (c) are films prepared according to embodiments of this disclosure, while (a) and (d) are comparative examples showing the differences in cross-sectional morphology caused by variations in Cu content. To further analyze the microstructure of the TiN-Cu composite film, Figure 5 The TEM analysis of a thin film with a Cu content of 0.54 at.% is shown. (Refer to...) Figure 5 The following are surface samples of TiN-Cu composite films with a Cu content of 0.54 at.%: (a) TEM image; (b) selected area electron diffraction pattern; (c) HR-TEM image.
[0053] The cross-sectional morphology of the thin film was observed using transmission electron microscopy (TEM). Low-magnification image (see...) Figure 5 Image (a) shows that the thin film exhibits a dense columnar crystalline structure. High-resolution transmission electron microscopy (HRTEM) image (see image [link]). Figure 5 Further, (d) in the figure reveals the existence of amorphous regions between the clear TiN lattice fringes, proving that Cu is distributed in an amorphous form at the TiN grain boundaries. Simultaneously, within the TiN grains in the high-resolution image (see 5(d) in the figure), a straight, grain-penetrating layered structure can be observed, its characteristics highly consistent with nanotwin boundaries. Combined with the faint symmetrical spots appearing in the selected area electron diffraction pattern (see... Figure 5 (b) further confirms the existence of high-density nanotwins within the TiN grains. This indicates that the present invention successfully induced a nanotwin structure in TiN, a high-fault-energy material, through trace Cu doping.
[0054] Figure 4 The cross-sectional morphology of the film is shown. When the Cu content is less than 2 at.%, it exhibits a distinct columnar structure; when it exceeds 2 at.%, it exhibits a dense equiaxed crystal structure, indicating that the addition of too much Cu will block the propagation of the columns.
[0055] Reference Figure 5 , Figure 5 Image (a) is a low-magnification TEM image, showing that the grains in the thin film form encapsulated shells. Figure 5Measurements were made on the diffraction rings in the selected area electron diffraction pattern (b) in the image, revealing three distinct crystal plane indices, from the inside out: TiN(111), (200), and (220). The TEM image at low magnification (…) Figure 5 The black box area in (a) is enlarged to obtain Figure 5 In (c), HRTEM has a clear internal crystal structure and the grain size is in the range of 10~15nm. Figure 5 (d) in the middle is Figure 5 A magnified view of the area within the red box in (c) of the image, showing the Fourier transform (FFT) of the HRTEM. Figure 5 In (d) at the bottom right corner, no diffraction rings are shown. Instead, strong spots corresponding to the preferred orientation growth of the grains appear. These spots correspond to the TiN phase. Figure 5 In (d), the formed nanoparticles are shown to have random orientation, and an amorphous phase (white elliptical marker) is also faintly visible. By calculating the interplanar spacing of the diffraction fringes, three different diffraction fringes were found: d=2.44 Å, d=1.49 Å, and d=1.22 Å. By comparing with the standard PDF card, the first two different diffraction fringes correspond to TiN(111) and (220) respectively. Since TiN(311) and Cu(220) have very similar interplanar spacing, it is not possible to distinguish between these two substances by calculating the interplanar spacing.
[0056] According to the structured zone model (SZM) constructed by Barna and Adamik, impurities or additives provide a condensation surface for the growth of crystals and exist as a two-dimensional capping layer around the grown grains and grain boundaries. In this case, both grain growth and texture development are hindered by the presence of impurities or additives, resulting in a thin film composed of randomly oriented three-dimensional equiaxed crystals separated by impurity or additive phase layers. With increasing impurity or additive content, the impurities or additives inhibit grain growth and stimulate more nucleation, leading to the formation of a spherical microstructure. It can be considered that when Cu is co-deposited with TiN, Cu, acting as an additive, segregates to the grain boundaries, preventing the growth of TiN crystals. Initially, due to the low Cu content, columnar grains exist in films with a Cu content of less than 1 at.%, which is a typical characteristic of the I region of SZM single-phase films. When sufficient Cu is added (e.g., when the atomic percentage is 8.49 at.%), Cu grain precipitation inhibits the growth of TiN grains, leading to repeated nucleation of TiN grains (I2), and the film consists of dense equiaxed crystals (see...). Figure 4 (d)). Since Cu was not observed in either XRD or SAED, Cu in the film exists either in amorphous or nanocrystalline form.
[0057] During the deposition process, numerous defects typically exist around the columnar crystals in the thin film. For example, in conventional TiN thin film deposition, voids, dislocations, and other grain boundary defects inevitably form between the columnar crystals, resulting in poor film performance. These defects are weak points in the film and are highly susceptible to becoming crack initiation points under external forces. According to embodiments of this disclosure, the incorporated Cu is dispersed in the columnar crystal boundaries in an amorphous or nanocrystalline form, filling the inherent defects and reducing the density of defects (such as voids) along the columnar boundaries. The Cu atoms existing in amorphous / nanocrystalline form precisely fill these grain boundary defects, much like "cement" filling the gaps between "bricks," greatly improving the film density, reducing internal stress concentration sources, and suppressing crack initiation at the source.
[0058] Simultaneously, the coherent coordinated strain effect is used to explain that when crystalline and amorphous phases coexist in a thin film material, the amorphous phase (Cu) at a certain critical thickness will crystallize at the interface between the crystalline phase (TiN) and the amorphous phase (Cu), forming a coherent interface after crystallization. Figure 5 (d) In this context, when a coherent interface forms, the stress field in the film undergoes alternating action, causing distortion. Furthermore, the presence of the coherent interface increases the modulus difference in the film, leading to increased hardness and strengthening. When amorphous / nanocrystalline Cu fills the grain boundaries of crystalline TiN, two synergistic strengthening effects occur: the interface strengthening of the special coherent or semi-coherent interface formed between them can accommodate and dissipate stress through its own minute slip or deformation, thereby preventing cracks from propagating along the fragile grain boundaries, thus acting as crack deflection or termination. More importantly, the segregation of Cu atoms at the grain boundaries causes significant local lattice distortion and stress concentration. According to embodiments of this disclosure, this local high stress field caused by Cu doping, combined with the inherent high compressive stress during magnetron sputtering, provides the necessary driving force for the nucleation and growth of nanotwins within the TiN columnar crystals. These nanotwin boundaries formed within the grains, as a special type of planar defect, can effectively hinder dislocation movement, thereby further improving the film hardness. Simultaneously, the twin boundaries can also effectively deflect and pin microcracks, working together with the flexible Cu phase at the grain boundaries to significantly enhance the film toughness. Furthermore, since the hardness of the TiN matrix phase is not weakened and the overall film density is increased, the film hardness can be maintained at a very high level, and may even be improved due to increased modulus differences and interface strengthening effects.
[0059] Figure 6 It is a graph showing the hardness and elastic modulus of the films prepared according to the embodiments and comparative examples of this disclosure.
[0060] Reference Figure 6The hardness and elastic modulus of examples and comparative examples with different Cu contents are shown.
[0061] As a comparative example, the hardness of a Cu-free TiN film is 27 GPa. With increasing Cu content, the hardness initially increases and then decreases, reaching a maximum of 32 GPa at a Cu content of 0.54 at.%, with an elastic modulus of 292 GPa. Compared to a pure TiN film without Cu (hardness approximately 27 GPa, elastic modulus approximately 280 GPa), both hardness and elastic modulus are significantly improved. XRD results rule out Cu substitution of Ti or N atoms in the TiN lattice, as the interaction between Ti and N atoms is stronger than the interaction between these atoms and Cu. On the other hand, the radius of Cu atoms is large enough that Cu may exist as interstitial impurities between TiN grains, corresponding to the HRTEM results. At a Cu atomic percentage of 8.49 at.%, the hardness is only 24 GPa, even lower than the hardness of the TiN film itself. At this point, excessive Cu forms an intermediate layer or separates into independent phases between TiN grains, making the film easily deformable, resulting in a significant decrease in material hardness. That is, the introduction of a small amount of Cu will increase the hardness of the film, while the introduction of too much Cu will lead to a decrease in the overall load-bearing capacity and a decrease in the hardness of the film.
[0062] Figure 7 The image shows the indentation pattern of a film prepared according to the embodiments and comparative examples of this disclosure after testing with a Vickers hardness tester.
[0063] Reference Figure 7 The Vickers hardness of examples and comparative examples with different Cu contents is shown. (a) Cu content of 0 at.%; (b) Cu content of 0.54 at.%; (c) Cu content of 1.53 at.%; (d) Cu content of 8.49 at.%.
[0064] Indentation testing using a Vickers hardness tester is used to measure the toughness and adhesion of thin film materials. For example, if no cracks form around the indentation, the film generally has good toughness; if there is no crushing or peeling on the film surface, the adhesion between the film and the substrate is good. Figure 7 As shown, the indentation areas of all films were very clean. In particular, no cracks appeared when 0.54 at.% Cu was added, exhibiting the best performance. Furthermore, in the Vickers indentation test, no penetrating cracks appeared at the corners of the indentation, and the radial crack length was reduced to 1.6 µm, demonstrating excellent toughness.
[0065] As described above in the embodiments of this application, a breakthrough improvement in hardness and toughness is achieved by constructing a "grain boundary-twin" synergistic strengthening structure. This disclosure changes the traditional perception that "hard materials are inherently brittle, and tough materials are not hard." Through the dual mechanism of Cu filling grain boundaries and inducing nanotwins within the grains, the hardness is increased from 27 GPa to 32 GPa while significantly improving toughness, resulting in excellent comprehensive mechanical properties that combine high hardness and high toughness. This allows the film to adapt to more demanding working conditions, especially meeting the requirements of applications with extreme material performance, such as key components in nuclear power plants. On the other hand, the film structure is denser and more reliable. Through the effective filling of grain boundary defects by Cu, the density of internal defects (such as voids) in the prepared film is greatly reduced, resulting in a denser structure. This not only improves mechanical properties but also enhances the film's corrosion resistance and structural stability under high-temperature environments. Furthermore, this disclosure provides a clearer understanding of the strengthening and toughening mechanism, offering new ideas for the design of high-performance ceramic coatings. This disclosure reveals the toughening microstructure mechanism of the synergistic effect of trace metal doping-induced "grain boundary filling" and "nanotwins," providing clear theoretical guidance for the design of high-performance hard thin films. This discovery, achieving twinning toughening in high fault-energy ceramics, has significant scientific and technological value. Based on this, the proposed magnetron sputtering method can stably control the thin film composition and microstructure by precisely controlling the Cu target power—a key parameter. The process is simple, highly controllable, and reproducible, possessing the potential for large-scale industrial production.
Claims
1. A high-hardness, high-toughness TiN-Cu composite film, characterized in that, The TiN-Cu composite film has a nanocomposite structure, which includes: Titanium nitride grains containing nanotwin structures; and The copper, in an amorphous or nanocrystalline state, fills the grain boundaries of the titanium nitride grains, wherein the atomic percentage of the copper is in the range of 0.1 at.% to 2.0 at.% of the film.
2. The TiN-Cu composite film according to claim 1, characterized in that, The cross-sectional morphology of the titanium nitride grains is a dense columnar crystal structure.
3. The TiN-Cu composite film according to claim 1, characterized in that, The titanium nitride grains have a preferred orientation of (111).
4. The TiN-Cu composite film according to claim 1, characterized in that, The atomic percentage of copper is 0.54 at.% of the thin film.
5. The TiN-Cu composite film according to claim 1, characterized in that, The size of the titanium nitride grains is in the range of 10 nm to 15 nm.
6. The TiN-Cu composite film according to claim 5, characterized in that, The film has a hardness of 32 GPa and an elastic modulus of 292 GPa.
7. The TiN-Cu composite film according to claim 5, characterized in that, The radial crack length of the film is less than or equal to 1.6 µm in the Vickers indentation test.
8. A method for preparing a high-hardness, high-toughness TiN-Cu composite film, the method being used to manufacture a TiN-Cu composite film with a nanocomposite structure, the nanocomposite structure comprising: Titanium nitride grains containing nanotwin structures; The copper, in the form of amorphous or nanocrystalline copper filling the grain boundaries of the titanium nitride grains, wherein the atomic percentage content of copper is in the range of 0.1 at.% to 2.0 at.% of the thin film, is characterized in that the preparation method comprises: Prepare the substrate and place it in the processing chamber of the magnetron sputtering vacuum equipment; Prepare titanium and copper targets; A gaseous atmosphere including argon and nitrogen is formed in the processing chamber; and By supplying electrical energy to the titanium and copper targets, magnetron co-sputtering of the titanium and copper targets is induced and sputtered onto the substrate, thereby forming the TiN-Cu composite film on the surface of the substrate. In this process, DC power is applied to the titanium target and the copper target, and a substrate bias voltage is applied to the substrate. The DC power of the titanium target is 400W, the DC power of the copper target is greater than 15W and less than 45W, and the substrate bias voltage is -100V.
9. The preparation method according to claim 8, characterized in that, The process of forming a reaction atmosphere comprising argon and nitrogen in the processing chamber includes controlling the flow rate of argon in the gas atmosphere to be 20 sccm, the flow rate of nitrogen to be 7 sccm, and the working pressure to be 0.3 Pa.
10. The preparation method according to claim 8, characterized in that, After the step of preparing the substrate and before the step of preparing the titanium target and the copper target, the preparation method further includes: forming an argon atmosphere in a processing chamber, turning on the titanium target, and sputtering and depositing a pure titanium metal transition layer on the surface of the substrate, wherein the thickness of the transition layer is 10-100 nm.