A method for preparing a nano-ceramic film with sub-micron scale on a metal surface

Abstract

The present invention discloses a preparation method of a sub-micron level nano-ceramic film on a metal surface, belonging to the field of film preparation. A powder is coated on the surface of a metal substrate. In a nitrogen atmosphere, a large amount of plasma containing carbon, nitrogen, and metal elements is instantaneously generated on the surface of the metal substrate by the action of pulsed laser, and then the plasma is re-flushed onto the surface of the metal substrate. Due to the extremely cold effect on the surface of the substrate, the effect of refining the grains of the cladding surface layer is achieved, and finally a dense sub-micron level carbonitride nano-ceramic film is formed on the surface of the metal substrate. While not affecting the necessary mechanical properties of metal components, the surface film has high load-bearing capacity, high hardness, high bonding strength, good wettability, and maintains good smoothness, can significantly reduce the friction coefficient of the metal surface, and improve its wear resistance.

Description

Technical Field

[0001] The present invention relates to the field of thin film preparation, and particularly to a method for preparing a sub-micron scale nano-ceramic thin film on a metal surface. Background Art

[0002] The surface wear resistance of precision metal devices with high added value will greatly affect their reliability in engineering applications, such as precision bearings (steel) in aerospace or artificial joints and bones (titanium) in the medical field. Among them, as an important structural metal, titanium metal has been widely used in the fields of aerospace, medical and health, chemical machinery, sports goods, etc. since the 1950s due to its good corrosion resistance, low density, high specific strength, low thermal conductivity, non-toxic and non-magnetic properties, good biocompatibility, and easy surface functional modification. For example, because titanium is similar to human bones and has good biocompatibility and no toxic side effects on human tissues, the bones, joints, instruments, etc. made of titanium metal have good transplantation effects in the human body. To ensure that titanium structural parts meet the performance requirements in specific situations, it is usually necessary to prepare titanium alloys with corresponding properties. However, during the use of titanium components (titanium and titanium alloys), not only mechanical properties (high strength, high toughness, etc.) need to be considered, but also their surface physical and chemical properties in the environment, such as wear resistance. During the use of titanium joints, there is a problem of surface wear, and the wear debris can cause aseptic loosening, ultimately leading to the failure of the replacement joint. Therefore, how to prepare a dense nano-ceramic thin film with high bearing capacity, high hardness, high bonding strength, good wettability and good surface finish on the surface of titanium joints without affecting the necessary mechanical properties of titanium joints is a difficult point for further improving the long-term usability of artificial joints.

[0003] Based on this, the development of an efficient and universal metal surface nano-ceramic thin film preparation technology will greatly promote the application of high-value-added components such as precision bearings or artificial bones and joints in aerospace or medical and health. Currently, common coating methods include sputtering deposition, vacuum evaporation, ion implantation, electrochemical deposition, laser cladding and other technologies, and the characteristics of each technology are as follows:

[0004] Sputtering deposition technology utilizes the process where electrons are accelerated towards the substrate under the action of an electric field and collide with argon atoms during the flight, ionizing a large number of argon ions and electrons. The electrons fly towards the substrate. The argon ions are accelerated under the action of the electric field to bombard the target material, sputtering a large number of target atoms. The neutral target atoms (or molecules) are deposited on the substrate to form a film. The characteristics of this technology are high film formation rate, low substrate temperature, good film adhesion, and the ability to achieve large-area coating. By changing process parameters and target components, the composition and properties of the thin film can be flexibly controlled. The prepared alloy thin film has uniform composition, good density and properties, high deposition rate, good bonding strength with the substrate, and nitride thin films can be obtained by introducing reactive gases. However, the utilization rate of the target material is low and the cost is relatively high. In addition, there is an obvious delamination between the prepared alloy thin film and the substrate, and the bonding strength needs to be further considered, which limits its application to a certain extent.

[0005] The equipment used in vacuum evaporation technology is relatively simple and easy to operate; the prepared thin film has high purity and fast film formation speed; the thin film growth mechanism is simple and easy to control and simulate. However, it is not easy to obtain a thin film with a crystal structure; the adhesion of the deposited thin film to the substrate is poor.

[0006] The thin film prepared by ion implantation has good adhesion; high film density; high deposition rate; is conducive to the formation of composite films and can coat a variety of materials. However, the defect density in the thin film is higher, the transition zone between the thin film and the substrate is wider; the residual gas content in the thin film is higher.

[0007] The thin film prepared by electrochemical deposition can be evenly deposited on a substrate with a complex structure; by controlling process parameters, the thickness and composition of the thin film can be easily controlled; the process is simple, easy to operate, and has low economic cost. However, it is difficult to prepare ideal and complex composite thin films; parameters such as current and voltage are prone to fluctuations, resulting in poor uniformity of the deposited layer.

[0008] Laser cladding technology can quickly achieve surface alloying on the metal surface, but the thickness of the modified layer formed by this technology is about several hundred micrometers, and the surface topography roughness changes greatly after treatment, making it difficult to be widely applied to precision metal devices with high surface finish requirements.

[0009] In summary, coating technologies such as sputtering deposition, vacuum evaporation, ion implantation, electrochemical deposition, and laser cladding are difficult to efficiently and conveniently construct a dense sub-micron carbonitride nanoceramic thin film on the surface of titanium metal. Summary of the Invention

[0010] The object of the present invention is to provide an efficient and reliable technology for the preparation of sub-micron nano-ceramic films on the metal surface by constructing sub-micron nano-ceramic films on the metal surface. Without affecting the mechanical properties of the metal substrate and deteriorating the surface finish of the substrate, excellent anti-friction and wear resistance are imparted to the metal surface. For metal titanium, its lubrication and wear resistance state and biocompatibility can be improved; for steel devices such as precision bearings, its surface wear resistance is strengthened, and the engineering application range of metal materials is expanded.

[0011] The object of the present invention is achieved by the following technical solutions:

[0012] A method for preparing a sub-micron nano-ceramic film on a metal surface is provided, including the following steps:

[0013] S1. Uniformly coat carbon powder on the surface of the metal substrate to be modified;

[0014] S2. In a nitrogen atmosphere, scan the surface of the metal substrate with a first pulsed laser to form a first carbonitride nano-ceramic film on the surface of the metal substrate;

[0015] S3. Coat the carbon powder in step S1 on the first carbonitride nano-ceramic film, and scan the first carbonitride nano-ceramic film with a second pulsed laser to form an optimized carbonitride nano-ceramic film on the surface of the metal substrate.

[0016] Preferably, step S1 specifically includes:

[0017] Brush a small amount of solvent on the surface of the metal substrate to be modified, and then dry the surface with a non-woven fabric; then, weigh a certain amount of carbon material and rub it on the surface of the metal substrate.

[0018] Preferably, the coating amount of the carbon material is 1 mg / cm 2 ~15 mg / cm 2 .

[0019] Preferably, the solvent includes but is not limited to paraffin, glycerol or edible oil; the carbon material is graphene or carbon nanotube.

[0020] Preferably, the metal substrate includes but is not limited to metal titanium, steel, uranium, copper.

[0021] Preferably, the nitrogen atmosphere is 1 to 3 atmospheres.

[0022] Preferably, the nitrogen atmosphere is replaced with a nitrogen-containing solid material, and the nitrogen-containing solid material is loaded on the surface of the metal substrate by coating before the first pulsed laser scanning.

[0023] Preferably, the nitrogen-containing solid material includes but is not limited to boron nitride, silicon nitride.

[0024] Preferably, the first pulsed laser scanning parameters include:

[0025] Scanning step: 0.4 - 2.5 mm, scanning speed: 500 - 10000 mm / s, pulsed laser energy: 5 - 100 W, energy density: 5 - 20 J / cm 2 .

[0026] Preferably, the second pulsed laser scanning parameters include:

[0027] Scanning step: 0.4 - 1.0 mm, scanning speed: 1000 - 5000 mm / s, pulsed laser energy: 5 - 30 W, overlapping rate: 30% - 90%, energy density: 0.5 - 2 J / cm 2 .

[0028] It should be further noted that the technical features corresponding to the above options can be combined or replaced with each other to form a new technical solution without conflict.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0030] (1) It has almost no influence on the mechanical properties of the metal substrate: The present invention utilizes the rapid melting and extreme cooling effect generated by the pulsed laser on the metal surface to instantaneously generate a large amount of plasma, incorporating non-metallic elements such as carbon and nitrogen into the metal surface, refining the grains, and forming a nano-ceramic film with a sub-micron thickness that is metallurgically bonded to the metal surface. Compared with other surface modification technologies, the influence of the present invention on the mechanical properties of the substrate itself can be ignored (the thickness of the modified layers formed by traditional continuous laser cladding and thermal spraying and other technologies is in the order of hundreds of microns or millimeters, which has a greater impact on thinner metal substrates in terms of mechanical properties and surface microtopography); finally, by adjusting parameters such as laser energy density and scanning the metal surface after powder coating again, the prepared nano-ceramic film can be optimized, making the surface film have high bearing capacity, high hardness, high bonding strength, good wettability and maintain good smoothness, which can significantly reduce the friction coefficient of the metal surface and improve its wear resistance.

[0031] (2) The carbonitride nano-ceramic film is dense and has a strong bonding force with the substrate: The pulsed laser can achieve rapid melting and extreme cooling on the metal surface. The surface of the ceramic film is dense and continuous. During the extreme cooling process, the grains are refined to the nano-scale. The ceramic film and the substrate are metallurgically bonded without a boundary layer (the modified layers constructed on the metal surface by technologies such as magnetron sputtering, pulsed laser deposition, and vacuum evaporation have an obvious boundary layer with the substrate, and the compactness of the modified layer is poor. Usually, the thickness of the modified layer needs to be increased to improve the compactness).

[0032] (3) The composition of the ceramic thin film is simple and controllable: By adjusting the powder coating amount, type on the surface of the modified layer or the nitrogen atmosphere, the composition of the ceramic thin film can be regulated to design ceramic thin films with different element ratios. (Technologies such as electrochemical deposition and ion implantation have relatively strict requirements for the composition of added elements).

[0033] (4) Simple, efficient, and does not require high pressure and high temperature: During the entire preparation process of the nano-ceramic thin film, it can be carried out at room temperature and 1 - 3 atmospheric pressures, without the need for high temperature and high pressure. (Ion implantation technology usually requires a high temperature above 300°C). Description of the Drawings

[0034] Figure 1 It is a flowchart of a method for preparing a sub-micron nano-ceramic thin film on a metal surface shown in an embodiment of the present invention;

[0035] Figure 2 It is a practical flowchart of the method for preparing the nano-ceramic thin film shown in an embodiment of the present invention;

[0036] Figure 3 It is a diagram showing the wear morphology and the change of friction coefficient before and after the modification of the metal substrate surface shown in an embodiment of the present invention. Detailed Embodiments

[0037] The technical solutions of the present invention will be clearly and completely described below with reference to the drawings. Apparently, the described embodiments are some but not all of the embodiments of the present invention. The components of the embodiments of the present application described and illustrated herein can be arranged and designed in various different configurations. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0038] It should be noted that the defects existing in the above prior art solutions are all the results obtained by the inventor through practice and careful research. Therefore, the discovery process of the above problems and the solutions proposed by the embodiments of the present application below for the above problems should be the contributions made by the inventor to the present application during the invention creation process, and should not be understood as the technical content known to those skilled in the art.

[0039] In response to the technical problems pointed out in the background art, the embodiments provided by the present invention are as follows:

[0040] Embodiment 1

[0041] Refer to Figure 1 , in an exemplary embodiment, a method for preparing a sub-micron nano-ceramic thin film on a metal surface is provided, including the following steps:

[0042] S1. Uniformly coat carbon powder on the surface of the metal substrate to be modified;

[0043] S2. In a nitrogen atmosphere, scan the surface of the metal substrate with a first pulsed laser to form a first carbonitride nanoceramic film on the surface of the metal substrate;

[0044] S3. Apply the carbon powder in step S1 onto the first carbonitride nanoceramic film, and scan the first carbonitride nanoceramic film with a second pulsed laser to form an optimized carbonitride nanoceramic film on the surface of the metal substrate.

[0045] The principle of this method is:

[0046] When the pulsed laser acts on the surface of the metal substrate coated with carbon powder, a rapid melting and extremely cold effect is generated. The material on the surface of the metal substrate (micrometer-level depth) will absorb a large amount of energy within nanoseconds, instantaneously generating a large amount of plasma. At this time, the surface of the metal substrate is in a rapid melting state; compared with the high-temperature plasma, the surface temperature of the metal substrate and the ambient temperature of the atmosphere are at room temperature (tens of degrees Celsius), which is a cold body. When the plasma contacts the surface of the metal substrate, it will be instantly cooled and solidified on the surface of the metal substrate, incorporating non-metallic elements such as carbon and nitrogen into the metal surface, refining the grains, and forming a nanoceramic film with a sub-micrometer-level thickness that is metallurgically bonded to the surface of the metal substrate. Finally, adjust the parameters (laser energy density, etc.) of the second pulsed laser scanning, and scan the surface of the metal substrate after powder coating again to optimize the prepared nanoceramic film.

[0047] As Figure 2 shown, in step S1, powder coating is carried out. Specifically, first, brush a small amount of solvent (such as paraffin, glycerin, edible oil, etc.) on the surface of the metal substrate to be modified, and then dry the surface with a non-woven fabric. Then, weigh a certain amount of industrial graphite and rub it on the metal surface, and control the coating amount to be 1 mg / cm 2 ~15 mg / cm 2 . Among them, the main purpose of brushing the solvent on the surface of the metal substrate is to facilitate the dispersion and adhesion of the powder on the surface of the metal substrate. The specific implementation process depends on the surface roughness of the metal substrate. For a rough substrate surface, powder coating can also be directly carried out. The coating material is not limited to carbon powder, and the coating amount is adjusted adaptively according to the material and surface state of the metal substrate and the type of the coated material.

[0048] In step S2, the carbonitride nanoceramic film is prepared. First, place the metal substrate uniformly coated with carbon powder on the operating table under a nitrogen atmosphere (1 - 3 atmospheres); then control the pulsed laser scanning step size (0.4 - 2.5 mm), scanning speed (500 - 10000 mm / s), pulsed laser energy (5 - 100 W), and energy density (5 - 20 J / cm 2Parameters such as are used to prepare carbonitride nanoceramic films on the surface of a metal substrate. Among them, the sources of nitrogen and other non-metal elements include, but are not limited to, nitrogen gas, and can also be other solid materials containing nitrogen elements, such as boron nitride, silicon nitride, etc. These materials can also be loaded on the surface of the metal substrate by coating before the laser action to achieve the preparation of nanoceramic films containing other non-metal elements.

[0049] In step S3, the carbonitride nanoceramic film is optimized. Specifically, steps S1 and S2 are repeated, and the powder prepared in step S1 is coated on the surface of the metal substrate treated in step S2. Control the pulse laser scanning step size (0.4 - 1.0 mm), scanning speed (1000 - 5000 mm / s), pulse laser energy (5 - 30 W), overlap rate (30% - 90%), and regulate the laser energy density to 0.5 - 2 J / cm 2 , and optimize the first carbonitride nanoceramic film prepared in step S2. This can significantly reduce the friction coefficient of the metal surface and improve its wear resistance. It should be noted that in actual applications, the first carbonitride nanoceramic film can be optimized one or more times according to the actual situation until the friction coefficient of the metal surface is reduced to the target requirement.

[0050] Example 2

[0051] Based on the inventive concept of Example 1, this example presents a method for preparing submicron-scale nanoceramic films on the surface of titanium metal. It includes:

[0052] Step 1 (powder coating): First, brush a small amount of paraffin on the surface of titanium metal, and then dry the surface with a non-woven fabric. Then, weigh a certain amount of industrial graphite and rub it on the metal surface, and control the coating amount to 15 mg / cm 2 ;

[0053] Step 2 (nanoceramic film preparation): First, place the titanium metal substrate uniformly coated with carbon powder on the operating table under a nitrogen atmosphere (1 atmospheric pressure); then control the pulse laser scanning step size (0.4 mm), scanning speed (10000 mm / s), pulse laser energy (100 W), and energy density (round(20 J / cm 2 )) and other parameters to prepare a carbonitride nanoceramic film on the surface of titanium metal;

[0054] Step 3 (nanoceramic film friction reduction optimization): Repeat steps 1 and 2, and coat the powder prepared in step 1 on the surface of the titanium metal treated in step 2 (coating amount is 15 mg / cm 2 ), control the pulse laser scanning step size (1.0 mm), scanning speed (1000 mm / s), pulse laser energy (30 W), overlap rate (90%), and regulate the laser energy density to 2 J / cm 2, optimize the carbonitride nanoceramic film prepared in Step 2.

[0055] In this example, the data of the surface morphology and friction coefficient changes of the modified titanium surface after the wear test are as follows:

[0056] Figure 3 It is a diagram of the wear morphology and friction coefficient changes before and after the surface modification of titanium metal (reciprocating wear, the counter body is a Si3N4 ball, φ = 6 mm). As Figure 3 (a) and 3(d) show that for unmodified metallic titanium (Ti) under a 1 N load, severe wear occurs on the surface at the initial stage of wear, the friction coefficient fluctuates around 0.5, and after the wear ends, the width of the wear scar reaches 900 μm; as Figure 3 (b) and 3(d) show that after constructing a carbonitride nanoceramic film (TiN / C) on the surface of metallic titanium, its surface wear resistance has been improved to a certain extent, and it has a lower friction coefficient (0.15) at the initial stage of wear. However, as the wear progresses, its friction coefficient gradually increases. When the wear distance reaches 6 m, its friction coefficient rises above 0.6, indicating that the carbonitride ceramic layer on the surface has been worn, and the generated abrasive particles exacerbate the abrasive wear on the surface, resulting in a friction coefficient greater than that of unmodified metallic titanium. The color of the wear scar area is significantly different from that of the un-worn area, and the width of the wear scar reaches 500 μm; after optimizing the carbonitride ceramic layer (TiN / C-L), as Figure 3 (c) and 3(d) show that during the entire friction process, before the friction distance reaches 35 m, the optimized ceramic film has a stable and extremely low friction coefficient (0.15), and after the 50 m wear test ends, by observing the wear scar, it can be found that the wear scar area still retains the relatively good corrugated traces after laser modification, and the color is similar to that of the un-worn area. This indicates that the optimized nanoceramic layer has stable wear resistance, and compared with before optimization, the wear resistance has been improved by about 600%.

[0057] Example 3

[0058] Based on the inventive concept of Example 1, a method for preparing a sub-micron nanoceramic film on the surface of steel is given. It includes:

[0059] Step 1 (powder coating): First, brush a small amount of paraffin on the surface of 45# steel, and then dry the surface with a non-woven fabric. Then, weigh a certain amount of industrial graphite and rub it on the metal surface, and control the coating amount at 1 mg / cm 2 ;

[0060] Step 2 (Preparation of nano-ceramic thin film): First, place the metal substrate uniformly coated with carbon powder on the operating table under a nitrogen atmosphere (2 atmospheres); then control the pulse laser scanning step size (2.5 mm), scanning speed (500 mm / s), pulse laser energy (5 W), and energy density (5 J / cm 2 ) and other parameters to prepare a carbonitride nano-ceramic thin film on the surface of 45# steel;

[0061] Step 3 (Optimization of nano-ceramic thin film): Repeat Step 1 and Step 2, coat the powder prepared in Step 1 on the surface of the 45# steel processed in Step 2 (coating amount is 1 mg / cm 2 ), control the pulse laser scanning step size (0.4 mm), scanning speed (5000 mm / s), pulse laser energy (5 W), overlap rate (30%), and adjust the laser energy density to 0.5 J / cm 2 to optimize the carbonitride nano-ceramic thin film prepared in Step 2.

[0062] In this example, the change data of the surface morphology and friction coefficient of the modified steel surface after the wear test is similar to that of Example 2, and will not be elaborated here.

[0063] Example 4

[0064] Based on the inventive concept of Example 1, another method for preparing a sub-micron nano-ceramic thin film on the surface of titanium metal is given. It includes:

[0065] Step 1 (Preparation of carbon powder coating): First, brush a small amount of paraffin on the surface of titanium, and then dry the surface with a non-woven fabric. Then, weigh a certain amount of graphene and rub it on the metal surface, and control the coating amount at 8 mg / cm 2 ;

[0066] Step 2 (Preparation of sub-micron nano-ceramic thin film): First, place the metal substrate uniformly coated with carbon powder on the operating table under a nitrogen atmosphere (3 atmospheres); then control the pulse laser scanning step size (1.2 mm), scanning speed (5000 mm / s), pulse laser energy (60 W), and energy density (15 J / cm 2 ) and other parameters to prepare a carbonitride nano-ceramic thin film on the surface of metal titanium;

[0067] Step 3 (Optimization of nano-ceramic thin film): Repeat Step 1 and Step 2, coat the powder prepared in Step 1 on the surface of the metal titanium processed in Step 2 (coating amount is 5 mg / cm 2 ), control the pulse laser scanning step size (0.8 mm), scanning speed (2000 mm / s), pulse laser energy (18 W), overlap rate (50%), and adjust the laser energy density to 1 J / cm 2, optimize the carbonitride nanoceramic film prepared in Step 2.

[0068] In this example, the data of the changes in the surface morphology and friction coefficient of the modified titanium surface after the wear test are similar to those in Example 2, and will not be elaborated here.

[0069] In summary, the present invention constructs a sub-micron thick carbonitride nanoceramic film with an extremely low friction coefficient and metallurgical bonding with the substrate on the metal surface by successively performing powder coating, laser rapid melting and extreme cold cladding, and laser surface friction reduction optimization on the metal surface. It is a simple and efficient metal surface nanoceramic film preparation technology with great potential for engineering applications.

[0070] The above specific embodiments are detailed descriptions of the present invention. It cannot be determined that the specific embodiments of the present invention are only limited to these descriptions. For those of ordinary skill in the technical field to which the present invention pertains, without departing from the concept of the present invention, several simple deductions and substitutions can be made, which should all be regarded as belonging to the protection scope of the present invention.

Claims

1. A method for preparing a submicron nano-ceramic film on a metal surface, characterized in that: The following steps are involved: S1. Evenly coating carbon powder on the surface of the metal substrate to be modified; the step S1 specifically comprises: A small amount of solvent was brushed on the surface of the metal substrate to be modified, and then the surface was wiped dry with a non-woven fabric; then, a certain amount of carbon material was weighed and applied to the surface of the metal substrate; the coating amount of the carbon material was 1 mg / cm 2 ~ 15 mg / cm 2 ; The solvent is paraffin, glycerol or edible oil; the carbon material is graphene or carbon nanotubes; S2. In a nitrogen atmosphere, a first pulse laser is scanned on the surface of a metal substrate to produce a rapid melting extreme cold effect. The metal substrate surface absorbs a large amount of energy within nanoseconds, instantaneously generating a large amount of plasma. The metal substrate surface is in a rapid melting state. When the plasma contacts the metal substrate surface, it is instantly cooled and solidified on the metal substrate surface, incorporating carbon and nitrogen non-metallic elements into the metal substrate surface, refining the grains, and forming a first carbon-nitrogen nano-ceramic film metallurgically bonded to the metal substrate surface on the metal substrate surface. The nitrogen atmosphere is 1 to 3 atmospheres. The first pulse laser scanning parameters include: Scanning step: 0.4 ~ 2.5 mm, scanning speed: 500 ~ 10000 mm / s, pulse laser energy: 5 ~ 100 W, energy density: 5 ~ 20 J / cm 2 ; S3, coating the carbon powder in step S1 on the first carbon-nitrogen nano-ceramic film, scanning the first carbon-nitrogen nano-ceramic film with a second pulse laser to form an optimized carbon-nitrogen nano-ceramic film on the surface of the metal substrate; the second pulse laser scanning parameters include: Scanning step: 0.4 ~ 1.0 mm, scanning speed: 1000 ~ 5000 mm / s, pulse laser energy: 5 ~ 30 W, overlap rate: 30% ~ 90%, energy density: 0.5 ~ 2 J / cm 2 .

2. The method for preparing a submicron-scale nano-ceramic film on a metal surface according to claim 1, characterized in that: The metal substrate is titanium, steel, uranium or copper.

3. The method for preparing a submicron-scale nano-ceramic film on a metal surface according to claim 1, characterized in that: The nitrogen atmosphere is replaced by a solid material containing nitrogen, and the solid material containing nitrogen is loaded on the surface of the metal substrate by coating before the first pulse laser scanning is performed.

4. The method for preparing a submicron-scale nano-ceramic film on a metal surface according to claim 3, characterized in that: The solid material containing nitrogen is boron nitride or silicon nitride.

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