A cemented carbide with a composite coating and a method of making the same

Abstract

The application provides a cemented carbide with a composite coating and a preparation method thereof, a magnesium alloy substrate and the composite coating, the composite coating comprising a CrTi transition layer, a TiCrAlN intermediate layer and a TiCrAlNC layer, the CrTi transition layer being arranged on the surface of the magnesium alloy substrate, the TiCrAlN intermediate layer being arranged on the side of the CrTi transition layer away from the magnesium alloy substrate, and the TiCrAlNC layer being arranged on the side of the TiCrAlN intermediate layer away from the magnesium alloy substrate. The cemented carbide with the composite coating provided by the application has the advantages that the three-layer composite coating structure is sequentially connected and cooperates, and the overall compactness, the bonding force and the stability of the mechanical properties of the coating are significantly improved.

Description

Technical Field

[0001] This invention relates to the field of alloy technology, and in particular to a cemented carbide with a composite coating and its preparation method. Background Technology

[0002] Physical vapor deposition (PVD) TiCrAl-based coatings possess excellent hardness, wear resistance, and corrosion resistance, making them key materials for surface strengthening of high-end mechanical components. Currently, the industry commonly uses conventional DC magnetron sputtering power to prepare TiCrAl-based coatings. This process suffers from problems such as low target ionization rate and insufficient film density. Furthermore, target poisoning easily occurs during reactive sputtering, resulting in poor coating composition uniformity, weak film-substrate adhesion, and unstable mechanical properties, making it difficult to meet the high density, high bonding strength, and long service life requirements of high-end operating conditions. In addition, traditional processes have limited precision in controlling element deposition rates and film composition, restricting further improvements in the overall performance of TiCrAl-based coatings. Summary of the Invention

[0003] To address the technical problem of unstable mechanical properties caused by poor film adhesion in the preparation of TiCrAl-based coatings in existing technologies, a cemented carbide with a composite coating and its preparation method are provided.

[0004] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows: On one hand, the present invention provides a cemented carbide with a composite coating, comprising a magnesium alloy substrate and a composite coating, wherein the composite coating comprises a CrTi transition layer, a TiCrAlN intermediate layer and a TiCrAlNC layer, the CrTi transition layer is disposed on the surface of the magnesium alloy substrate, the TiCrAlN intermediate layer is disposed on the side of the CrTi transition layer opposite to the magnesium alloy substrate, and the TiCrAlNC layer is disposed on the side of the TiCrAlN intermediate layer opposite to the magnesium alloy substrate.

[0005] Optionally, in the CrTi transition layer, the molar ratio of Ti to Cr is (6~8):(8~10).

[0006] Optionally, in the TiCrAlN interlayer, the molar ratio of Ti, Cr, and Al is (10~12):(10~12):(10~13); and / or, Along the direction away from the CrTi transition layer, the nitrogen content in the TiCrAlN intermediate layer gradually increases, and the nitrogen content in the TiCrAlN intermediate layer is 10%~25%.

[0007] Optionally, in the TiCrAlNC layer, the molar ratio of Ti, Cr, Al, N, and C is (10~12):(10~12):(10~13):(30~37):(10~72).

[0008] Optionally, the thickness of the CrTi transition layer is 0.3 μm to 0.5 μm, the thickness of the TiCrAlN intermediate layer is 0.6 μm to 1.4 μm, and the thickness of the TiCrAlNC layer is 1.3 μm to 2.1 μm.

[0009] Optionally, the method for preparing the cemented carbide with the composite coating includes the following steps: Magnesium alloy substrate pretreatment; Take the pretreated magnesium alloy substrate, introduce the first protective atmosphere into a vacuum environment, sputter the first titanium source and the first chromium source to form a CrTi transition layer, and obtain the first composite coating precursor. A second protective atmosphere and a first nitrogen source are introduced into the vacuum environment of the first composite coating precursor, and a second titanium source, a second chromium source and a first aluminum source are sputtered. The TiCrAlN intermediate layer is generated on the surface of the first composite coating precursor in situ to obtain the second composite coating precursor. A second protective atmosphere, a second nitrogen source, and a carbon source are introduced into the vacuum environment of the second composite coating precursor. A third titanium source, a third chromium source, and a second aluminum source are sputtered. The TiCrAlNC layer is generated in situ on the surface of the second composite coating precursor to obtain a cemented carbide with a composite coating.

[0010] Optionally, the voltage of the first titanium source is -80~-100V, the sputtering current is 60~80A, the voltage of the first chromium source is -80~-100V, the sputtering current is 80~100A, and the continuous sputtering time is 20~30min. The voltage of the second titanium source for sputtering is -60~-80V, the sputtering current is 100~120A, the voltage of the second chromium source for sputtering is -60~-80V, the sputtering current is 100~120A, the voltage of the first aluminum source for sputtering is -60~-80V, the sputtering current is 70~90A, and the sputtering time is 60~90min. The voltage of the third titanium source for sputtering is -60~-80V, the sputtering current is 100~120A, the voltage of the third chromium source for sputtering is -60~-80V, the sputtering current is 100~120A, the voltage of the second aluminum source for sputtering is -60~-80V, the sputtering current is 100~130A, and the sputtering time is 120~150min.

[0011] Optionally, the first nitrogen source is introduced in the form of nitrogen gas. During the sputtering of the second titanium source, the second chromium source and the first aluminum source, the nitrogen gas flow rate gradually increases. The initial nitrogen gas flow rate is 15~25 sccm, and the final nitrogen gas flow rate is 70~90 sccm.

[0012] Optionally, the "magnesium alloy substrate pretreatment" operation includes the following steps: The purified magnesium alloy substrate was placed in a 1.0×10 -5 Torr~2.0×10 -5 In a Torr vacuum environment, a fourth protective atmosphere is introduced for ion cleaning.

[0013] Optionally, the first protective atmosphere, the second protective atmosphere, the third protective atmosphere, and the fourth protective atmosphere are all argon gas, the gas flow rate of the first protective atmosphere is 30~50 sccm, the gas flow rate of the second protective atmosphere is 50~70 sccm, the gas flow rate of the third protective atmosphere is 50~70 sccm, and the gas flow rate of the fourth protective atmosphere is 30~50 sccm.

[0014] The beneficial effects of this application are as follows: The cemented carbide with a composite coating provided in this application includes a magnesium alloy substrate and a composite coating. The composite coating includes a CrTi transition layer, a TiCrAlN intermediate layer, and a TiCrAlNC layer. The CrTi transition layer is disposed on the surface of the magnesium alloy substrate, the TiCrAlN intermediate layer is disposed on the side of the CrTi transition layer facing away from the magnesium alloy substrate, and the TiCrAlNC layer is disposed on the side of the TiCrAlN intermediate layer facing away from the magnesium alloy substrate. The CrTi transition layer has good metallic ductility, which can match the difference in thermal expansion coefficients between the magnesium alloy substrate and the TiCrAlN intermediate layer, effectively releasing interfacial stress and improving the film-substrate bonding strength. The operation of placing the TiCrAlN intermediate layer adjacent to the magnesium alloy substrate and the CrTi transition layer can achieve a smooth transition in hardness, avoiding interfacial cracking and film peeling caused by abrupt changes in interlayer hardness. The TiCrAlNC layer, located on the outermost side of the composite coating, combines high hardness with excellent wear and corrosion resistance. In other words, the cemented carbide with a composite coating provided in this application, through the sequential connection and synergistic effect of the three-layer composite coating structure, significantly improves the overall density, bonding strength, and stability of mechanical properties of the coating. Detailed Implementation

[0015] To make the technical problems solved, the technical solutions, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0016] This invention provides a cemented carbide with a composite coating, comprising a magnesium alloy substrate and a composite coating. The composite coating comprises a CrTi transition layer, a TiCrAlN intermediate layer, and a TiCrAlNC layer. The CrTi transition layer is disposed on the surface of the magnesium alloy substrate, the TiCrAlN intermediate layer is disposed on the side of the CrTi transition layer opposite to the magnesium alloy substrate, and the TiCrAlNC layer is disposed on the side of the TiCrAlN intermediate layer opposite to the magnesium alloy substrate.

[0017] Specifically, the cemented carbide with a composite coating provided in this application includes a magnesium alloy substrate and a composite coating. The composite coating includes a CrTi transition layer, a TiCrAlN intermediate layer, and a TiCrAlNC layer. The CrTi transition layer is disposed on the surface of the magnesium alloy substrate, the TiCrAlN intermediate layer is disposed on the side of the CrTi transition layer facing away from the magnesium alloy substrate, and the TiCrAlNC layer is disposed on the side of the TiCrAlN intermediate layer facing away from the magnesium alloy substrate. The CrTi transition layer has good metallic ductility and can match the magnesium alloy substrate and the Ti... The difference in thermal expansion coefficients between the CrAlN intermediate layers effectively releases interfacial stress and enhances the film-substrate bonding strength. Placing the TiCrAlN intermediate layer adjacent to the magnesium alloy substrate between the CrTi transition layer allows for a smooth transition in hardness, avoiding interfacial cracking and film detachment caused by abrupt changes in interlayer hardness. The TiCrAlN layer, located on the outermost side of the composite coating, combines high hardness with excellent wear and corrosion resistance. In other words, the cemented carbide with a composite coating provided in this application significantly improves the overall density, bonding strength, and mechanical property stability of the coating through the sequential connection and synergistic effect of the three-layer composite coating structure.

[0018] In some embodiments, the molar ratio of Ti to Cr in the CrTi transition layer is (6~8):(8~10).

[0019] In the CrTi transition layer, the molar ratio of Ti to Cr is limited to the range of (3~4):(4~5). By adjusting the atomic ratio of Ti and Cr, the lattice constant, atomic packing density and metal bonding strength of the transition layer can be precisely controlled. Furthermore, a suitable Ti / Cr molar ratio can enable the CrTi alloy phase to form a solid solution structure with higher lattice compatibility with the magnesium alloy substrate, while ensuring the metal ductility and interface wettability of the transition layer itself. This avoids the formation of brittle intermetallic compounds or internal stress concentration in the transition layer due to component imbalance, thereby maintaining the transition layer's ability to release interface stress, ensuring the stability of the film-substrate bonding force, and preventing fluctuations in the mechanical properties of the coating caused by the instability of the transition layer components.

[0020] In some embodiments, the molar ratio of Ti, Cr, and Al in the TiCrAlN interlayer is (10~12):(10~12):(10~13); and / or, Along the direction away from the CrTi transition layer, the nitrogen content in the TiCrAlN intermediate layer gradually increases, and the nitrogen content in the TiCrAlN intermediate layer is 10%~25%.

[0021] Specifically, this application further defines the molar ratio of Ti, Cr, and Al in the TiCrAlN interlayer, as well as the gradient and range of nitrogen content. By controlling the ratio of Ti, Cr, and Al, the degree of lattice distortion and internal stress level of the interlayer can be optimized. The nitrogen content gradually increases away from the transition layer, which can achieve the transition of chemical bonding, hardness, and elastic modulus from the CrTi transition layer to the TiCrAlN interlayer. That is, by defining the molar ratio of Ti, Cr, and Al in the TiCrAlN interlayer, as well as the gradient and range of nitrogen content, it is beneficial to eliminate the interfacial energy difference and stress concentration caused by abrupt changes in elemental composition between layers. At the same time, the controllable change of nitrogen content can gradually strengthen the proportion and hardness of covalent bonds in the TiCrAlN phase, avoid interfacial cracking and film peeling caused by interlayer hardness differences, maintain the bonding stability between the interlayer, the transition layer, and the outer coating, and thus ensure the uniformity of overall mechanical properties.

[0022] In some embodiments, the magnesium alloy substrate includes magnesium, zinc, and zirconium. The mass ratio of the magnesium, zinc and zirconium elements is (88~92):(4~8):(3~5).

[0023] In some embodiments, the molar ratio of Ti, Cr, Al, N, and C in the TiCrAlNC layer is (10~12):(10~12):(10~13):(30~37):(10~72).

[0024] Specifically, in the TiCrAlNC layer, the molar ratio range of Ti, Cr, Al, N, and C is further defined. The introduction of C can form solid solution strengthening and grain refinement strengthening in the TiCrAlN lattice, while N is used to maintain its high hardness. The appropriate ratio of Ti, Cr, and Al helps to ensure the compatibility of the interface lattice between the coating and the intermediate layer. By defining the molar ratio of the above elements, this application enables the TiCrAlNC layer to have both high hardness, low internal stress, and good interfacial bonding, avoiding defects such as pores and cracks in the coating due to imbalance of element ratios. This improves the wear and corrosion resistance of the outermost layer while reducing the risk of interlayer delamination and ensuring the overall mechanical properties of the coating are stable.

[0025] In some embodiments, the thickness of the CrTi transition layer is 0.3 μm to 0.5 μm, the thickness of the TiCrAlN intermediate layer is 0.6 μm to 1.4 μm, and the thickness of the TiCrAlNC layer is 1.3 μm to 2.1 μm.

[0026] Specifically, by limiting the thickness of the CrTi transition layer, TiCrAlN intermediate layer, and TiCrAlNC layer, the bonding strength between each layer is improved, which is conducive to the function of each layer. Conversely, an excessively thin transition layer cannot effectively buffer the stress difference between the substrate and the functional layer, while an excessively thick layer is prone to generating its own internal stress. Appropriate thickness of the intermediate layer can ensure sufficient transition of hardness gradient, and appropriate thickness of the outer layer can achieve high protective performance while avoiding the accumulation of internal stress and peeling caused by excessive film thickness. The coordinated matching of the thickness of each layer within the above range can release the interfacial stress layer by layer, make the interlayer bonding tight, reduce the coating cracking and peeling problems caused by unreasonable thickness, and improve the bonding strength and mechanical property stability.

[0027] In some embodiments, the method for preparing the cemented carbide with a composite coating includes the following steps: Magnesium alloy substrate pretreatment; Take the pretreated magnesium alloy substrate, introduce the first protective atmosphere into a vacuum environment, sputter the first titanium source and the first chromium source to form a CrTi transition layer, and obtain the first composite coating precursor. A second protective atmosphere and a first nitrogen source are introduced into the vacuum environment of the first composite coating precursor, and a second titanium source, a second chromium source and a first aluminum source are sputtered. The TiCrAlN intermediate layer is generated on the surface of the first composite coating precursor in situ to obtain the second composite coating precursor. A second protective atmosphere, a second nitrogen source, and a carbon source (such as acetylene) are introduced into the vacuum environment of the second composite coating precursor. A third titanium source, a third chromium source, and a second aluminum source are sputtered. The TiCrAlNC layer is generated in situ on the surface of the second composite coating precursor to obtain a cemented carbide with a composite coating.

[0028] A stepwise sputtering deposition and in-situ reaction film formation method is used in a vacuum environment to sequentially deposit a CrTi transition layer, a TiCrAlN intermediate layer, and a TiCrAlNC layer, maintaining continuous vacuum deposition throughout the process. Specifically, the vacuum environment avoids high-temperature oxidation of the magnesium alloy substrate and film contamination, ensuring interface cleanliness; in-situ reaction film formation creates atomic-level interdiffusion interfaces between layers, enhancing interlayer chemical bonding; stepwise sputtering allows for precise control of film formation conditions and growth rates for each layer, avoiding component segregation and stress unevenness caused by simultaneous deposition of multiple elements. This reduces film defects and poor adhesion in the resulting composite coating from a process perspective, improving coating density and bonding strength.

[0029] In some embodiments, the voltage of the first titanium source sputtering is -80 to -100V, the sputtering current is 60 to 80A, the voltage of the first chromium source sputtering is -80 to -100V, the sputtering current is 80 to 100A, and the continuous sputtering time is 20 to 30 minutes. The voltage of the second titanium source for sputtering is -60~-80V, the sputtering current is 100~120A, the voltage of the second chromium source for sputtering is -60~-80V, the sputtering current is 100~120A, the voltage of the first aluminum source for sputtering is -60~-80V, the sputtering current is 70~90A, and the sputtering time is 60~90min. The voltage of the third titanium source for sputtering is -60~-80V, the sputtering current is 100~120A, the voltage of the third chromium source for sputtering is -60~-80V, the sputtering current is 100~120A, the voltage of the second aluminum source for sputtering is -60~-80V, the sputtering current is 100~130A, and the sputtering time is 120~150min.

[0030] This application limits the voltage, current, and time of sputtering for each layer. By adjusting the sputtering parameters, the particle incident energy, deposition rate, and film growth are controlled. Specifically, matching the sputtering voltage and current of the transition layer can form a low-stress, high-density metal transition layer, avoiding damage to the magnesium alloy substrate surface caused by high-energy particle bombardment. Matching the sputtering parameters of the intermediate and outer layers is beneficial for controlling atomic migration ability and grain growth orientation. The aforementioned sputtering time helps ensure uniform thickness and complete film formation for each layer. The aforementioned limited sputtering parameters can reduce internal stress in the film, improve interfacial bonding tightness, prevent film cracking and decreased bonding force caused by excessive particle energy or uneven deposition, and maintain stable mechanical properties.

[0031] In some embodiments, the first nitrogen source is introduced in the form of nitrogen gas. During the sputtering of the second titanium source, the second chromium source, and the first aluminum source, the nitrogen gas flow rate gradually increases. The initial nitrogen gas flow rate is 15~25 sccm, and the final nitrogen gas flow rate is 70~90 sccm.

[0032] Specifically, the nitrogen flow rate is gradually increased from an initial low flow rate, causing the nitrogen content in the TiCrAlN intermediate layer to gradually increase in the direction away from the CrTi transition layer, forming a hardened structure. This continuously improves the film hardness and reduces stress, while ensuring a strong bond with the CrTi transition layer, thus solving the problems of uneven composition and stress concentration caused by direct constant flow rate ventilation.

[0033] In some embodiments, the "magnesium alloy substrate pretreatment" operation includes the following steps: The purified magnesium alloy substrate was placed in a 1.0×10 -5 Torr~2.0×10 -5In a Torr vacuum environment, a fourth protective atmosphere is introduced for ion cleaning; The ion cleaning time is 15-30 minutes.

[0034] Specifically, ion cleaning pretreatment of magnesium alloy substrates can remove oxide films, oil stains, and adsorbed impurities from the substrate surface, while simultaneously producing a slight etching and activation effect on the substrate surface. This activated substrate surface also improves the interfacial wettability and atomic bonding between the substrate and the CrTi transition layer. Additionally, 1.0 × 10 -5 Torr~2.0×10 -5 Torr's vacuum level prevents secondary oxidation of the substrate during cleaning, optimizes the surface roughness of the substrate, and improves bonding strength.

[0035] In some embodiments, the first protective atmosphere, the second protective atmosphere, the third protective atmosphere, and the fourth protective atmosphere are all argon gas, the gas flow rate of the first protective atmosphere is 30~50 sccm, the gas flow rate of the second protective atmosphere is 50~70 sccm, the gas flow rate of the third protective atmosphere is 50~70 sccm, and the gas flow rate of the fourth protective atmosphere is 30~50 sccm.

[0036] It should be noted that argon, as an inert gas, can isolate reactive gases such as oxygen and water during the deposition process, preventing oxidation of the magnesium alloy substrate and coating. Argon is used as the protective and plasma gas source for the first, second, third, and fourth protective atmospheres. The first, second, third, and fourth protective atmospheres are matched with corresponding flow rates at different operation stages to further improve the adhesion and stability of the composite coating.

[0037] The present invention will be further illustrated by the following examples.

[0038] Example 1 This embodiment illustrates the cemented carbide with a composite coating and its preparation method disclosed in this invention, including the following steps: First, the magnesium alloy substrate (Mg:Zn:Zr=90:5:5) is placed on a cleaning rack. Then, the magnesium alloy substrate is subjected to ultrasonic degreasing, activation, surface conditioning, dehydration, and drying in sequence to remove oil and oxide scale from the substrate surface; 1.5×10 -5 Argon gas (flow rate 40 sccm) is introduced into a third protective atmosphere in a Torr vacuum environment. The negative bias voltage is adjusted to -450V to ionize the argon gas into high-energy ions. The surface of the magnesium alloy substrate is then bombarded and cleaned for 20 minutes to obtain the pretreated magnesium alloy substrate.

[0039] Take the pretreated magnesium alloy substrate, introduce the first protective atmosphere (argon 40 sccm) in a vacuum environment, and sputter the first titanium source (sputtering voltage -90V, sputtering current 70A) and the first chromium source (sputtering voltage -90V, sputtering current 90A) for 25 minutes to form a CrTi transition layer on the surface of the magnesium alloy substrate, and obtain the first composite coating precursor. The thickness of the CrTi transition layer is 0.4 μm; The molar ratio of Ti to Cr is 7:9.

[0040] A second protective atmosphere and a first nitrogen source (the nitrogen flow rate gradually increases, with an initial flow rate of 20 sccm and a final flow rate of 80 sccm) are introduced into the vacuum environment of the first composite coating precursor. A second titanium source (sputtering voltage of -70V and sputtering current of 110A), a second chromium source (sputtering voltage of -70V and sputtering current of 110A), and a first aluminum source (sputtering voltage of -70V and sputtering current of 90A) are sputtered continuously for 75 minutes. In situ reaction occurs on the surface of the first composite coating precursor to form a TiCrAlN intermediate layer, thus obtaining the second composite coating precursor. The thickness of the TiCrAlN intermediate layer is 0.9 μm; The molar ratio of Ti, Cr, and Al is 10:10:10.

[0041] A second protective atmosphere (50 sccm), a second nitrogen source (nitrogen flow rate of 80 sccm), and a carbon source (acetylene flow rate of 90 sccm) are introduced into the vacuum environment of the second composite coating precursor. A third titanium source (voltage of -70V, sputtering current of 110A), a third chromium source (voltage of -70V, sputtering current of 110A), and a second aluminum source (voltage of -70V, sputtering current of 115A) are sputtered continuously for 135 min. In situ reaction occurs to form a TiCrAlNC layer on the surface of the second composite coating precursor, resulting in a cemented carbide with a composite coating. The thickness of the TiCrAlNC layer is 1.6 μm; The molar ratio of Ti, Cr, Al, N, and C is 11:11:11.5:33.5:50.

[0042] Example 2 This embodiment illustrates the cemented carbide with a composite coating and its preparation method disclosed in this invention, including most of the operational steps in Example 1, with the following differences: A second protective atmosphere and a first nitrogen source are introduced into the vacuum environment of the first composite coating precursor (the nitrogen flow rate is gradually increased, with an initial nitrogen flow rate of 20 sccm and a final nitrogen flow rate of 70 sccm).

[0043] Example 3 This embodiment illustrates the cemented carbide with a composite coating and its preparation method disclosed in this invention, including most of the operational steps in Example 1, with the following differences: A second protective atmosphere and a first nitrogen source are introduced into the vacuum environment of the first composite coating precursor (the nitrogen flow rate is gradually increased, with an initial nitrogen flow rate of 20 sccm and a final nitrogen flow rate of 90 sccm).

[0044] Example 4 This embodiment illustrates the cemented carbide with a composite coating and its preparation method disclosed in this invention, including most of the operational steps in Example 1, with the following differences: The carbon source (acetylene flow rate of 80 sccm) and the TiCrAlNC layer thickness were 1.47 μm.

[0045] Example 5 This embodiment illustrates the cemented carbide with a composite coating and its preparation method disclosed in this invention, including most of the operational steps in Example 1, with the following differences: The carbon source (acetylene flow rate of 100 sccm) and the TiCrAlNC layer thickness were 1.62 μm.

[0046] Example 6 This embodiment illustrates the cemented carbide with a composite coating and its preparation method disclosed in this invention, including most of the operational steps in Example 1, with the following differences: A second protective atmosphere (50 sccm), a second nitrogen source (nitrogen flow rate of 80 sccm), and a carbon source (acetylene flow rate of 90 sccm) are introduced into the vacuum environment of the second composite coating precursor. A third titanium source (voltage of -70V, sputtering current of 110A), a third chromium source (voltage of -70V, sputtering current of 110A), and a second aluminum source (voltage of -70V, sputtering current of 115A) are sputtered continuously for 120 min. In situ reaction occurs to form a TiCrAlNC layer on the surface of the second composite coating precursor, resulting in a cemented carbide with a composite coating. The thickness of the TiCrAlNC layer is 1.43 μm.

[0047] Example 7 This embodiment illustrates the cemented carbide with a composite coating and its preparation method disclosed in this invention, including most of the operational steps in Example 1, with the following differences: A second protective atmosphere (50 sccm), a second nitrogen source (nitrogen flow rate of 80 sccm), and a carbon source (acetylene flow rate of 90 sccm) are introduced into the vacuum environment of the second composite coating precursor. A third titanium source (voltage of -70V, sputtering current of 110A), a third chromium source (voltage of -70V, sputtering current of 110A), and a second aluminum source (voltage of -70V, sputtering current of 115A) are sputtered continuously for 150 min. In situ reaction occurs to form a TiCrAlNC layer on the surface of the second composite coating precursor, resulting in a cemented carbide with a composite coating. The thickness of the TiCrAlNC layer is 1.79 μm.

[0048] Comparative Example 1 This comparative example is used to illustrate the cemented carbide with a composite coating and its preparation method disclosed in this invention. It includes most of the operation steps in Example 1, except that a CrTi transition layer is not provided in this comparative example. The specific operations include: First, the magnesium alloy substrate (Mg:Zn:Zr=90:5:5) is placed on a cleaning rack. Then, the magnesium alloy substrate is subjected to ultrasonic degreasing, activation, surface conditioning, dehydration, and drying in sequence to remove oil and oxide scale from the substrate surface; 1.5×10 -5 Argon gas (flow rate 40 sccm) is introduced into a third protective atmosphere in a Torr vacuum environment. The negative bias voltage is adjusted to -450V to ionize the argon gas into high-energy ions. The surface of the magnesium alloy substrate is then bombarded and cleaned for 20 minutes to obtain the pretreated magnesium alloy substrate.

[0049] A pretreated magnesium alloy substrate is taken, and an argon protective atmosphere and a first nitrogen source are introduced into a vacuum environment. A second titanium source, a second chromium source, and a first aluminum source are sputtered. An in-situ reaction is carried out on the surface of the magnesium alloy substrate to form a TiCrAlN intermediate layer, thus obtaining a composite coating precursor. Argon protective atmosphere is introduced into the vacuum environment of the composite coating precursor, and a third titanium source, a third chromium source and a second aluminum source are sputtered. The TiCrAlNC layer is generated on the surface of the composite coating precursor in situ, and a cemented carbide with composite coating is obtained.

[0050] Comparative Example 2 This comparative example is used to illustrate the cemented carbide with composite coating and its preparation method disclosed in this invention. It includes most of the operation steps in Example 1, except that the TiCrAlN intermediate layer is not set in this comparative example. The specific operation includes: First, the magnesium alloy substrate (Mg:Zn:Zr=90:5:5) is placed on a cleaning rack. Then, the magnesium alloy substrate is subjected to ultrasonic degreasing, activation, surface conditioning, dehydration, and drying in sequence to remove oil and oxide scale from the substrate surface; 1.5×10 -5Argon gas (flow rate 40 sccm) is introduced into a third protective atmosphere in a Torr vacuum environment. The negative bias voltage is adjusted to -450V to ionize the argon gas into high-energy ions. The surface of the magnesium alloy substrate is then bombarded and cleaned for 20 minutes to obtain the pretreated magnesium alloy substrate.

[0051] Take the pretreated magnesium alloy substrate, introduce argon gas into a vacuum environment to form a protective atmosphere, and sputter the first titanium source and the first chromium source to form a CrTi transition layer on the surface of the magnesium alloy substrate, thus obtaining the first composite coating precursor. Argon protective atmosphere, a second nitrogen source, and a carbon source are introduced into the vacuum environment of the first composite coating precursor. A third titanium source, a third chromium source, and a second aluminum source are sputtered, and an in-situ reaction is carried out on the surface of the first composite coating precursor to form a TiCrAlNC layer.

[0052] Comparative Example 3 This comparative example is used to illustrate the cemented carbide with a composite coating and its preparation method disclosed in this invention. It includes most of the operation steps in Example 1, except that the TiCrAlNC layer is not set in this comparative example. The specific operation includes: First, the magnesium alloy substrate (Mg:Zn:Zr=90:5:5) is placed on a cleaning rack. Then, the magnesium alloy substrate is subjected to ultrasonic degreasing, activation, surface conditioning, dehydration, and drying in sequence to remove oil and oxide scale from the substrate surface; 1.5×10 -5 Argon gas (flow rate 40 sccm) is introduced into a third protective atmosphere in a Torr vacuum environment. The negative bias voltage is adjusted to -450V to ionize the argon gas into high-energy ions. The surface of the magnesium alloy substrate is then bombarded and cleaned for 20 minutes to obtain the pretreated magnesium alloy substrate.

[0053] Take the pretreated magnesium alloy substrate, introduce argon gas into a vacuum environment for protective atmosphere, and sputter the first titanium source and the first chromium source to obtain the first composite coating precursor.

[0054] Argon protective atmosphere and a first nitrogen source are introduced into the vacuum environment of the first composite coating precursor, and a second titanium source, a second chromium source and a first aluminum source are sputtered. The TiCrAlN intermediate layer is generated in situ on the surface of the first composite coating precursor to obtain a cemented carbide with a composite coating.

[0055] Performance testing The following performance tests were performed on Examples 1-7 and Comparative Examples 1-3 prepared above: Adhesion strength: The Rockwell hardness tester indentation method is used to test the adhesion strength by applying 60 kg of pressure to the test piece. The adhesion strength level is determined by the amount of film peeling off around the indentation. HF1 (no film peeling), HF2 (film peeling at 3 or fewer locations), HF3 (film peeling at more than 3 locations, peeling area not exceeding 35% of the circumference), HF4 (peeling area exceeding 35% but not exceeding 50% of the circumference), HF5 (peeling area exceeding 50% of the circumference).

[0056] Film thickness: Measured using a scanning electron microscope (SEM).

[0057] Film hardness: Measured using a nano hardness tester.

[0058] The test results are entered into Table 1.

[0059] Table 1 As can be seen from the test results in Table 1, the overall performance of bonding force and film hardness of Examples 1-7 is better than that of Comparative Examples 1-3. However, the bonding force of Comparative Example 1, which lacks the CrTi transition layer, drops significantly to HF3 due to interfacial stress mismatch. The bonding force of Comparative Example 2, which lacks the TiCrAlN intermediate layer, deteriorates to HF2 due to the sudden change in interlayer hardness. Although the hardness of both examples does not decrease significantly due to the retention of the high-hardness TiCrAlNC layer, the reliability of film bonding is significantly reduced. This demonstrates that the cemented carbide with composite coating provided in this application significantly improves the overall density, bonding force, and mechanical property stability of the coating through the connection and synergistic effect of the three-layer composite coating structure.

[0060] Specifically, the alloy of Example 1 has the complete three-layer coating structure provided in this application, and the thicknesses of the CrTi transition layer, TiCrAlN intermediate layer, and TiCrAlNC layer are all within the range defined in this application. The bonding strength reaches the optimal level HF1, and the film hardness is 2870HV. The CrTi transition layer effectively buffers the difference in thermal expansion coefficients between the magnesium alloy substrate and the ceramic layer. The TiCrAlN intermediate layer achieves a smooth transition in hardness through a nitrogen content gradient. The TiCrAlNC surface layer provides high hardness and good interfacial bonding. The synergistic effect of the three-layer structure makes the coating density, bonding strength, and mechanical stability optimal. In Example 2, the nitrogen termination flow rate of the TiCrAlN interlayer was reduced to 70 sccm, and the bonding strength remained at HF1. ​​The film hardness was slightly reduced to 2800 HV. This was because the reduced nitrogen flow rate resulted in a lower nitrogen content in the interlayer, which weakened the covalent bond strengthening effect and caused a slight decrease in hardness. However, the stress buffering and gradient transition effects between the CrTi transition layer and the TiCrAlN interlayer were not affected, and the film-substrate bonding strength remained at the optimal level. In Example 3, the nitrogen termination flow rate of the TiCrAlN interlayer was increased to 90 sccm, the bonding strength remained at HF1, and the film hardness increased to 2875 HV. This was because the increased nitrogen flow rate resulted in a higher nitrogen content in the interlayer, an increased covalent bond ratio, a slight increase in coating hardness, and sufficient release of interlayer stress, without any interface cracking or decrease in bonding strength. In Example 4, the carbon source acetylene flow rate was reduced to 80 sccm, the thickness of the TiCrAlNC layer was slightly reduced, the bonding strength remained at HF1, and the hardness was 2830 HV. Due to the reduction in acetylene flow rate, the surface carbon content was reduced, and the hardness was slightly reduced, but the three-layer complete structure was not changed, and the stability of the film-substrate bonding and interlayer bonding was not affected. Example 5: Increasing the acetylene flow rate to 100 sccm slightly increased the thickness of the TiCrAlNC layer, maintained the bonding strength at HF1, and increased the hardness to 2870 HV. Increasing the carbon content can strengthen the TiCrAlNC lattice and improve the coating hardness, resulting in excellent bonding strength and hardness. Example 6 shortened the sputtering time of the TiCrAlNC layer to 120 min, the surface layer thickness was reduced to 1.43 μm, the bonding strength remained at HF1, and the hardness was 2864 HV. The shortened sputtering time reduced the surface layer deposition amount, and the thickness was slightly lower but still in the range of 1.3-2.1 μm. The strengthening effect of carbon and nitrogen elements was fully utilized, and the integrity of the three-layer structure ensured the stability of the bonding strength. Example 7 extended the sputtering time of the TiCrAlNC layer to 150 min, increasing the surface layer thickness to 1.79 μm, maintaining the adhesion at HF1, and achieving a hardness of 2872 HV. Extending the sputtering time resulted in a more complete and denser surface film, while maintaining both hardness and adhesion at a high level.

[0061] In Comparative Example 1, without setting a CrTi transition layer, a TiCrAlN intermediate layer and a TiCrAlNC layer were directly deposited on a magnesium alloy substrate. The adhesion dropped to HF3, while the hardness remained at 2870HV. This was because the lack of a metal transition layer buffer caused the mismatch in the thermal expansion coefficients of the magnesium alloy and the ceramic layer, resulting in stress concentration at the interface. Under the indentation test, the film layer was significantly peeled off. Since the hardness was exerted by the TiCrAlNC surface layer, there was no significant decrease. Comparative Example 2 does not have a TiCrAlN intermediate layer. The TiCrAlNC layer is directly connected by the CrTi transition layer. The bonding force is reduced to HF2, while the hardness remains at 2860HV. Due to the lack of a hardness gradient transition layer, the interlayer stress is concentrated, and local film peeling occurs under indentation. Comparative Example 3 did not prepare a TiCrAlNC layer, but only retained the CrTi transition layer and the TiCrAlN intermediate layer. Although its bonding strength can reach the HF1 level, the film hardness is only 2480HV, which is significantly lower than the 2870HV of Example 1. The reason is that there is no high-hardness and wear-resistant TiCrAlNC layer, the overall hardness of the coating is insufficient, and there is no stress constraint of the outer layer on the intermediate layer, resulting in poor interlayer bonding stability and failing to meet the requirements of high density and high mechanical properties.

[0062] Comparing the test results of the above embodiments and comparative examples, it can be seen that the cemented carbide with composite coating provided in this application includes a magnesium alloy substrate and a composite coating. The composite coating includes a CrTi transition layer, a TiCrAlN intermediate layer, and a TiCrAlNC layer. The CrTi transition layer is disposed on the surface of the magnesium alloy substrate, the TiCrAlN intermediate layer is disposed on the side of the CrTi transition layer facing away from the magnesium alloy substrate, and the TiCrAlNC layer is disposed on the side of the TiCrAlN intermediate layer facing away from the magnesium alloy substrate. The CrTi transition layer has good metallic ductility and can match the magnesium alloy substrate. The difference in thermal expansion coefficients between the alloy substrate and the TiCrAlN intermediate layer effectively releases interfacial stress and enhances the film-substrate bonding strength. Placing the TiCrAlN intermediate layer adjacent to the magnesium alloy substrate between the CrTi transition layer allows for a smooth transition in hardness, avoiding interfacial cracking and film detachment caused by abrupt changes in interlayer hardness. The TiCrAlN layer, located on the outermost side of the composite coating, combines high hardness with excellent wear and corrosion resistance. In other words, the cemented carbide with a composite coating provided in this application significantly improves the overall density, bonding strength, and mechanical property stability of the coating through the sequential connection and synergistic effect of the three-layer composite coating structure.

[0063] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A cemented carbide with a composite coating, characterized in that, The invention includes a magnesium alloy substrate and a composite coating. The composite coating includes a CrTi transition layer, a TiCrAlN intermediate layer, and a TiCrAlNC layer. The CrTi transition layer is disposed on the surface of the magnesium alloy substrate, the TiCrAlN intermediate layer is disposed on the side of the CrTi transition layer opposite to the magnesium alloy substrate, and the TiCrAlNC layer is disposed on the side of the TiCrAlN intermediate layer opposite to the magnesium alloy substrate.

2. The cemented carbide with a composite coating according to claim 1, characterized in that, In the CrTi transition layer, the molar ratio of Ti to Cr is (6~8):(8~10).

3. The cemented carbide with a composite coating according to claim 1, characterized in that, In the TiCrAlN interlayer, the molar ratio of Ti, Cr, and Al is (10~12):(10~12):(10~13); and / or, Along the direction away from the CrTi transition layer, the nitrogen content in the TiCrAlN intermediate layer gradually increases, and the nitrogen content in the TiCrAlN intermediate layer is 10%~25%.

4. The cemented carbide with a composite coating according to claim 1, characterized in that, In the TiCrAlNC layer, the molar ratio of Ti, Cr, Al, N and C is (10~12):(10~12):(10~13):(30~37):(10~72).

5. The cemented carbide with a composite coating according to claim 1, characterized in that, The thickness of the CrTi transition layer is 0.3μm~0.5μm, the thickness of the TiCrAlN intermediate layer is 0.6μm~1.4μm, and the thickness of the TiCrAlNC layer is 1.3μm~2.1μm.

6. The method for preparing a cemented carbide with a composite coating according to any one of claims 1 to 5, characterized in that, Includes the following steps: Magnesium alloy substrate pretreatment; Take the pretreated magnesium alloy substrate, introduce the first protective atmosphere into a vacuum environment, sputter the first titanium source and the first chromium source to form a CrTi transition layer, and obtain the first composite coating precursor. A second protective atmosphere and a first nitrogen source are introduced into the vacuum environment of the first composite coating precursor, and a second titanium source, a second chromium source and a first aluminum source are sputtered. The TiCrAlN intermediate layer is generated on the surface of the first composite coating precursor in situ to obtain the second composite coating precursor. A third protective atmosphere, a second nitrogen source, and a carbon source are introduced into the vacuum environment of the second composite coating precursor. A third titanium source, a third chromium source, and a second aluminum source are sputtered. The TiCrAlNC layer is generated in situ on the surface of the second composite coating precursor to obtain a cemented carbide with a composite coating.

7. The method for preparing a cemented carbide with a composite coating according to claim 6, characterized in that, The voltage of the first titanium source for sputtering is -80~-100V, the sputtering current is 60~80A, the voltage of the first chromium source for sputtering is -80~-100V, the sputtering current is 80~100A, and the continuous sputtering time is 20~30min. The voltage of the second titanium source for sputtering is -60~-80V, the sputtering current is 100~120A, the voltage of the second chromium source for sputtering is -60~-80V, the sputtering current is 100~120A, the voltage of the first aluminum source for sputtering is -60~-80V, the sputtering current is 70~90A, and the sputtering time is 60~90min. The voltage of the third titanium source for sputtering is -60~-80V, the sputtering current is 100~120A, the voltage of the third chromium source for sputtering is -60~-80V, the sputtering current is 100~120A, the voltage of the second aluminum source for sputtering is -60~-80V, the sputtering current is 100~130A, and the sputtering time is 120~150min.

8. The method for preparing a cemented carbide with a composite coating according to claim 6, characterized in that, The first nitrogen source is introduced in the form of nitrogen gas. During the sputtering of the second titanium source, the second chromium source and the first aluminum source, the nitrogen gas flow rate gradually increases. The initial nitrogen gas flow rate is 15~25 sccm, and the final nitrogen gas flow rate is 70~90 sccm.

9. The method for preparing a cemented carbide with a composite coating according to claim 6, characterized in that, The "pretreatment of magnesium alloy substrate" includes the following steps: The purified magnesium alloy substrate was placed in a 1.0×10 -5 Torr~2.0×10 -5 In a Torr vacuum environment, a fourth protective atmosphere is introduced for ion cleaning.

10. The method for preparing a cemented carbide with a composite coating according to claim 9, characterized in that, The first protective atmosphere, the second protective atmosphere, the third protective atmosphere, and the fourth protective atmosphere are all argon. The gas flow rate of the first protective atmosphere is 30-50 sccm, the gas flow rate of the second protective atmosphere is 50-70 sccm, the gas flow rate of the third protective atmosphere is 50-70 sccm, and the gas flow rate of the fourth protective atmosphere is 30-50 sccm.

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