TaC coating modified M50NiL steel for unmanned aerial vehicle

Abstract

The invention discloses TaC coating modified M50NiL steel for an unmanned aerial vehicle, and belongs to the technical field of material modification. The method mainly comprises the following steps: preparing an M50NiL steel substrate and a TaC coating deposited on the surface of the substrate, wherein the chemical components of the M50NiL steel substrate comprise 0.13 wt% of C, 4.1 wt% of Cr, 4.2 wt% of Mo, 3.4 wt% of Ni, 1.2 wt% of V, 0.13 wt% of Mn, 0.18 wt% of Si and the balance of Fe; the TaC coating is prepared through an unbalanced magnetron sputtering physical vapor deposition technology and is of a coating structure which is compact in structure and uniform in component. By adopting the scheme of integrating an unbalanced magnetron sputtering physical vapor deposition technology and a matrix precise heat treatment process, the surface hardness and tribological performance of the M50NiL steel are remarkably improved, and the problems that under the extreme high-speed heavy-load dry friction working condition of an unmanned aerial vehicle, abrasion of a traditional material is aggravated, and the service life is limited are solved.

Description

A TaC-coated modified M50NiL steel for drones Technical Field

[0001] This invention relates to the field of material modification technology, and more particularly to a TaC-coated modified M50NiL steel for drones. Background Technology

[0002] M50NiL steel is a high-performance carburized bearing steel. It is widely used in high-speed, heavy-load bearings in aerospace and other fields due to its "hard outside and tough inside" characteristics. That is, a high-hardness, high-wear-resistant surface layer is obtained through the carburizing process, while maintaining good toughness and fatigue resistance in the core. However, under the extreme high-speed, heavy-load and dry friction conditions faced by equipment such as drones, its surface friction and wear performance is insufficient, which can easily lead to an increase in the coefficient of friction, accelerated wear and even failure, thus limiting its reliability and service life.

[0003] The prior art patent document with authorization announcement number CN117305679B discloses "an M50NiL bearing steel bar and its preparation method", which includes the following steps: first, preparing an electrode blank that meets the set requirements; wherein, the set requirements are as follows: TO≤8ppm, S≤0.002wt%, P≤0.006wt%, Ti≤0.0015wt% in the electrode blank; performing vacuum consumable remelting treatment on the electrode blank to obtain a consumable ingot; wherein, by controlling the parameters of the vacuum consumable remelting treatment, the consumable ingot meets the requirements. The required parameters are: TO≤7ppm, S≤0.002wt%, P≤0.006wt%, Ti≤0.0020wt%. The consumable ingot is subjected to high-temperature homogenization treatment to obtain a steel ingot with δ-ferrite content ≤3% and a maximum carbide size ≤3μm. The high-temperature homogenized steel ingot is then subjected to hot deformation treatment to obtain a hot-deformed bar with a grain size ≥5 and δ-ferrite content ≤1%. The hot-deformed bar undergoes a first annealing treatment to obtain M50NiL bearing steel bars.

[0004] The patent document with authorization announcement number CN108411244B discloses "a method for improving the tribological properties of M50NiL bearing steel surface", which uses vacuum pulse carburizing technology to carburize and temper the surface of M50NiL bearing steel substrate; then quenching and tempering are performed; the white bright layer on the surface of M50NiL bearing steel substrate is removed; and a bonding layer of chromium metal layer, Cr→GLC gradient layer and GLC-based solid lubricating film are deposited on the surface of M50NiL bearing steel substrate by multi-target non-magnetron sputtering technology.

[0005] While existing technologies can improve the purity, microstructure uniformity, and surface hardness of M50NiL steel through processes such as vacuum pulse carburizing and double vacuum purification smelting, and can also use multi-target sputtering coating technology to deposit multilayer films to enhance film-substrate adhesion and some tribological properties, meeting the usage requirements of some harsh conditions in the aerospace field, existing technologies are difficult to adapt to the extreme high-speed, heavy-load, and dry friction complex conditions faced by UAV bearings. The deposited coatings have limitations in structural density and compositional uniformity, and the conformal bonding effect between the film and substrate is poor, leading to coating peeling and delamination. Moreover, the overall improvement in tribological properties is limited, and the problem of increased friction coefficient and accelerated wear will still occur during long-term service, failing to fully meet the usage requirements of key UAV components for long life and high reliability. Summary of the Invention

[0006] Purpose of the invention: The purpose of this invention is to provide a TaC-coated modified M50NiL steel for drones to solve the problems mentioned in the background art.

[0007] Technical Solution: To solve the above-mentioned technical problems, according to one aspect of the present invention, more specifically, a TaC-coated modified M50NiL steel for unmanned aerial vehicles, comprising: an M50NiL steel substrate and a TaC coating deposited on the surface of the substrate, wherein the chemical composition of the M50NiL steel substrate comprises 0.13wt% C, 4.1wt% Cr, 4.2wt% Mo, 3.4wt% Ni, 1.2wt% V, 0.13wt% Mn, 0.18wt% Si, with Fe as the balance; the TaC coating is prepared by unbalanced magnetron sputtering physical vapor deposition technology and has a dense and uniform coating structure.

[0008] Preferably, the M50NiL steel matrix undergoes austenitization at 1100℃, oil quenching, and tempering heat treatment at 540℃. The matrix structure is mainly composed of cryptocrystalline martensite and fine lath martensite, with dispersed granular carbides and a small amount of retained austenite. The hardness is ≥55HRC, and the surface roughness Ra<0.1µm after grinding.

[0009] Preferably, the TaC coating deposition process uses argon as the working gas and acetylene as the reaction gas, the coating thickness is 0.1 mm, and the coating forms a conformal bond with the M50NiL steel substrate.

[0010] According to another aspect of the present invention, a method for preparing TaC-coated modified M50NiL steel for unmanned aerial vehicles (UAVs) is provided, comprising the following steps: S1, distributing and melting according to chemical composition to obtain M50NiL steel billet, and machining the steel billet into a base blank of the target shape for UAV bearings; S2, subjecting the base blank to heat treatment, first performing austenitization treatment at 1100℃ for 1 hour, then oil quenching for 10 minutes, and finally tempering heat treatment at 540℃ for 1 hour to obtain an M50NiL steel matrix with a hardness ≥55HRC and a microstructure mainly composed of cryptocrystalline martensite and fine lath martensite; S3, pretreating the surface of the heat-treated base by sequentially polishing with 280#, 800#, 1500#, and 2000# sandpaper until the surface roughness Ra <0.1µm, and then cleaning the surface with alcohol. Oil stains and impurities are removed and dried for later use; S4. Using an unbalanced magnetron sputtering physical vapor deposition system, with argon as the working gas and acetylene as the reactant gas, a TaC coating is deposited on the surface of an M50NiL steel substrate; during the deposition process, the substrate temperature is controlled at 200℃, an 800V bias voltage is applied, the deposition time is 12h, the argon flow rate is 300sccm, the acetylene flow rate is 600sccm, and the coating thickness is controlled at 0.1mm to form a conformal bonding structure between the coating and the substrate; S5. The workpiece after TaC coating deposition is characterized and tested. The microstructure of the coating is observed using a scanning electron microscope, the mechanical properties of the coating are tested using nanoindentation technology, and the tribological properties are verified using a pin-disc friction and wear experiment; S6. The workpiece that passes the characterization and testing is deburred, cleaned, and dried to obtain the TaC-coated modified M50NiL steel finished product for UAVs.

[0011] Preferably, in step S1, the ingredients are smelted using a combination of vacuum induction melting and vacuum arc remelting, with the vacuum level controlled to be ≤5×10⁻⁶ during the smelting process. -2 Pa, melting temperature 1550-1600℃, held for 2 hours and then cast; machining is carried out by a combination of CNC lathe and grinding machine to ensure that the dimensional tolerance of the base blank is ±0.02mm and the form and position tolerance is ≤0.01mm.

[0012] Preferably, in step S2, the heating rate of the austenitizing treatment is 5℃ / min, from room temperature to 1100℃; oil quenching is performed using N32 machine oil, with the oil temperature controlled at 80-100℃; after tempering heat treatment, air cooling is used to cool to room temperature, and direct contact between the substrate surface and cooling water is avoided during the cooling process.

[0013] Preferably, in step S3, the alcohol cleaning is performed using ultrasonic-assisted cleaning for 15 minutes with an alcohol concentration of 99.7%. After cleaning, the alcohol is dried in a drying oven at 60°C for 30 minutes, and the ambient humidity is controlled to be ≤30% during the drying process.

[0014] Preferably, in step S4, the target material of the unbalanced magnetron sputtering equipment is a TaC target with a purity ≥99.9%, and the distance between the target and the substrate is 80 mm; the initial vacuum degree of the vacuum chamber during the deposition process is ≤5×10⁻⁶. -3 Pa, the coating thickness is monitored in real time by a laser thickness gauge, and the thickness data is recorded every 30 minutes to ensure that the coating thickness deviation is ≤ ±0.005mm.

[0015] Preferably, in step S5, the accelerating voltage during scanning electron microscopy observation is 15kV, and the microstructure of the coating surface and cross-section are observed respectively; the Berkovich indenter is used for nanoindentation testing, with a loading rate of 5mN / s and a maximum load holding time of 10s, and 6 test points are randomly selected to take the average value; the pin-disc friction and wear test uses GCr15 steel as the mating part, and the experimental environment temperature is 25±2℃ and the relative humidity is 45±5%.

[0016] Beneficial effects: By adopting an integrated approach of non-equilibrium magnetron sputtering physical vapor deposition technology and precise substrate heat treatment, the surface hardness and tribological properties of M50NiL steel are significantly improved, solving the problems of accelerated wear and limited lifespan of traditional materials under extreme high-speed, heavy-load dry friction conditions of UAVs. Simultaneously, multi-stage gradient grinding pretreatment and precise process parameter control achieve conformal and tight bonding between the TaC coating and the substrate, effectively balancing the film-substrate adhesion and the density and uniformity of the coating. Furthermore, the dual-vacuum melting process ensures substrate purity, and strict control of temperature, vacuum, and gas flow reduces component segregation and coating defects. While enhancing the wear resistance and damage resistance of the material surface, the "hard on the outside, tough on the inside" characteristics of the substrate are retained, aligning with the high reliability development trend of UAV equipment and providing a stable and practical technical path for upgrading bearing materials under extreme conditions. Attached Figure Description

[0017] Figure 1 is a schematic diagram of the method flow of the present invention; Figure 2 is a schematic diagram of the friction coefficient test curve of M50NiL bearing steel under the same rotation speed of the present invention; Figure 3 is a schematic diagram of the friction coefficient test curve of M50NiL bearing steel under the same load of the present invention; Figure 4 is a schematic diagram of the microscopic wear mechanism of M50NiL bearing steel of the present invention; Figure 5 is a schematic diagram of the friction coefficient test curve of TaC coating under the same rotation speed of the present invention; Figure 6 is a schematic diagram of the friction coefficient test curve of TaC coating under the same load of the present invention; Figure 7 is a schematic diagram of the microscopic wear mechanism of TaC coating under different rotation speeds and loads of the present invention. Detailed Implementation

[0018] To make the technical solution of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0019] Example 1: A TaC-coated modified M50NiL steel for UAVs, comprising the following steps: raw materials are prepared according to the chemical composition (0.13wt% C, 4.1wt% Cr, 4.2wt% Mo, 3.4wt% Ni, 1.2wt% V, 0.13wt% Mn, 0.18wt% Si, with Fe as the balance), and smelted using a vacuum induction melting combined with vacuum arc remelting process, controlling the vacuum degree to 3×10⁻⁶. -2 Pa, melting temperature 1550℃, heat treatment for 2 hours and then casting to obtain M50NiL steel billet; using a combination of CNC lathe and grinding machine, the steel billet is machined into ring base blank for UAV bearing.

[0020] The base blank was heat-treated as follows: the temperature was increased from room temperature to 1100℃ at a heating rate of 5℃ / min for 1 hour for austenitization; then oil quenching was performed for 10 minutes using N32 machine oil, with the oil temperature controlled at 80℃; finally, tempering heat treatment was performed at 540℃ for 1 hour, and then air-cooled to room temperature. During the cooling process, direct contact between the base surface and the cooling water was avoided, resulting in an M50NiL steel base with a hardness of 56HRC and a microstructure mainly composed of cryptocrystalline martensite and fine lath martensite.

[0021] The surface of the heat-treated substrate was pretreated by successively polishing it with 280#, 800#, 1500# and 2000# sandpaper until the surface roughness Ra=0.08µm was finally controlled. Then, ultrasonic cleaning with 99.7% alcohol was performed for 15 minutes to remove surface oil and impurities. After cleaning, the substrate was placed in a 60℃ drying oven for 30 minutes with the humidity controlled at 28%. The substrate was then ready for use.

[0022] A Hauzer Flexicoat 1200 unbalanced magnetron sputtering physical vapor deposition system was used, with TaC of ≥99.9% purity as the target material and a target-substrate distance of 80 mm. Argon was used as the working gas and acetylene as the reactant gas to deposit a TaC coating on the surface of an M50NiL steel substrate. Before deposition, the initial vacuum level of the vacuum chamber was evacuated to 4 × 10⁻⁶. -3 During the deposition process, the substrate temperature was controlled at 200℃, an 800V bias voltage was applied, the deposition time was 12h, the argon flow rate was 300sccm, and the acetylene flow rate was 600sccm. The coating thickness was monitored in real time using a laser thickness gauge, and data was recorded every 30 minutes. The coating thickness was controlled at 0.1mm to form a conformal bonding structure between the coating and the substrate.

[0023] Characterization and testing were performed on the workpiece after TaC coating deposition: Scanning electron microscopy (accelerating voltage 15kV) was used to observe the microstructure of the coating surface and cross-section, showing a dense and uniform coating structure. Nanoindentation technology (Berkovich indenter, loading rate 5mN / s, maximum load holding time 10s) was used to test six randomly selected test points. The average nanohardness of the coating was 28GPa, and the elastic modulus was 3.38×10⁻⁶. 11 N / m 2 Under ambient temperature of 25℃ and relative humidity of 45%, pin-disc friction and wear test (the mating part is GCr15 steel) was carried out using MMW-1B multifunctional testing machine. Under the working conditions of 35N load and 200rpm speed, the friction coefficient was 0.29 and there was no coating peeling.

[0024] The workpieces that passed the characterization test were deburred, rinsed with water, and dried a second time to obtain the TaC-coated modified M50NiL steel for UAVs.

[0025] Example 2: A TaC-coated modified M50NiL steel for drones, comprising the following steps: mixing according to chemical composition (consistent with Example 1), and melting using a vacuum induction melting combined with a vacuum arc remelting process, controlling the vacuum degree to 4×10⁻⁶. -2 Pa, melting temperature 1580℃, held for 2 hours and then cast to obtain M50NiL steel billet; using a combination of CNC lathe and grinding machine, the steel billet is machined into cylindrical base blank for UAV bearing.

[0026] The base blank was heat-treated as follows: the temperature was increased from room temperature to 1100℃ at a heating rate of 5℃ / min for 1 hour for austenitization; then oil quenching was performed for 10 minutes using N32 machine oil, with the oil temperature controlled at 90℃; finally, tempering heat treatment was performed at 540℃ for 1 hour, and then air-cooled to room temperature. During the cooling process, direct contact between the base surface and the cooling water was avoided, resulting in an M50NiL steel base with a hardness of 57HRC and a microstructure mainly composed of cryptocrystalline martensite and fine lath martensite.

[0027] The surface of the heat-treated substrate was pretreated by successively polishing it with 280#, 800#, 1500# and 2000# sandpaper until the surface roughness Ra=0.09µm was finally controlled. Then, ultrasonic cleaning with 99.7% alcohol was performed for 15 minutes to remove surface oil and impurities. After cleaning, the substrate was placed in a 60℃ drying oven for 30 minutes with the humidity controlled at 25%. The substrate was then ready for use.

[0028] A Hauzer Flexicoat 1200 unbalanced magnetron sputtering physical vapor deposition system was used, with TaC of ≥99.9% purity as the target material and a target-substrate distance of 80 mm. Argon was used as the working gas and acetylene as the reactant gas to deposit a TaC coating on the surface of an M50NiL steel substrate. Before deposition, the initial vacuum level of the vacuum chamber was evacuated to 3×10⁻⁶. -3 During the deposition process, the substrate temperature was controlled at 200℃, an 800V bias voltage was applied, the deposition time was 12h, the argon flow rate was 300sccm, and the acetylene flow rate was 600sccm. The coating thickness was monitored in real time using a laser thickness gauge, and data was recorded every 30 minutes. The coating thickness was controlled at 0.1mm to form a conformal bonding structure between the coating and the substrate.

[0029] Characterization and testing were performed on the workpiece after TaC coating deposition: Scanning electron microscopy (accelerating voltage 15kV) was used to observe the microstructure of the coating surface and cross-section, showing that the coating was non-porous and had a uniform composition; nanoindentation testing revealed that the average nanohardness of the coating was 29 GPa and the elastic modulus was 3.40 × 10⁻⁶. 11 N / m 2 Under ambient temperature of 27℃ and relative humidity of 48%, pin-disc friction and wear test was conducted using MMW-1B multifunctional testing machine. Under a load of 40N and a speed of 250rpm, the friction coefficient was 0.30, and the wear volume was smaller than that of the uncoated sample.

[0030] The workpieces that passed the characterization test were deburred, rinsed with water, and dried a second time to obtain the TaC-coated modified M50NiL steel for UAVs.

[0031] Example 3: A TaC-coated modified M50NiL steel for UAVs, comprising the following steps: mixing according to chemical composition (consistent with Example 1), and melting using a vacuum induction melting combined with a vacuum arc remelting process, controlling the vacuum degree to 5×10⁻⁶. -2 Pa, melting temperature 1600℃, heat treatment for 2 hours and then casting to obtain M50NiL steel billet; using a combination of CNC lathe and grinding machine, the steel billet is machined into a square base blank for UAV bearing.

[0032] The base blank was heat-treated as follows: the temperature was increased from room temperature to 1100℃ at a heating rate of 5℃ / min for 1 hour for austenitization; then oil quenching was performed for 10 minutes using N32 machine oil, with the oil temperature controlled at 100℃; finally, tempering heat treatment was performed at 540℃ for 1 hour, and then air-cooled to room temperature. During the cooling process, direct contact between the base surface and the cooling water was avoided, resulting in an M50NiL steel base with a hardness of 58HRC and a microstructure mainly composed of cryptocrystalline martensite and fine lath martensite.

[0033] The surface of the heat-treated substrate was pretreated by successively polishing it with 280#, 800#, 1500# and 2000# sandpaper until the surface roughness Ra=0.07µm was finally controlled. Then, ultrasonic cleaning with 99.7% alcohol was performed for 15 minutes to remove surface oil and impurities. After cleaning, the substrate was placed in a 60℃ drying oven for 30 minutes with the humidity controlled at 22%. The substrate was then ready for use.

[0034] A Hauzer Flexicoat 1200 unbalanced magnetron sputtering physical vapor deposition system was used, with TaC of ≥99.9% purity as the target material and a target-substrate distance of 80 mm. Argon was used as the working gas and acetylene as the reactant gas to deposit a TaC coating on the surface of an M50NiL steel substrate. Before deposition, the initial vacuum level of the vacuum chamber was evacuated to 5 × 10⁻⁶. -3 During the deposition process, the substrate temperature was controlled at 200℃, an 800V bias voltage was applied, the deposition time was 12h, the argon flow rate was 300sccm, and the acetylene flow rate was 600sccm. The coating thickness was monitored in real time using a laser thickness gauge, and data was recorded every 30 minutes. The coating thickness was controlled at 0.1mm to form a conformal bonding structure between the coating and the substrate.

[0035] Characterization and testing were performed on the workpiece after TaC coating deposition: Scanning electron microscopy (accelerating voltage 15kV) was used to observe the microstructure of the coating surface and cross-section, showing excellent coating density and tight interfacial bonding; nanoindentation testing revealed an average nanohardness of 30GPa and an elastic modulus of 3.42×10⁻⁶. 11 N / m 2 Under ambient temperature of 23℃ and relative humidity of 42%, pin-disc friction and wear test was conducted using MMW-1B multifunctional testing machine. Under a load of 30N and a speed of 150rpm, the friction coefficient was 0.28, and the maximum friction temperature was lower than that of the uncoated sample.

[0036] The workpieces that passed the characterization test were deburred, rinsed with water, and dried a second time to obtain the TaC-coated modified M50NiL steel for UAVs.

[0037] Through Examples 1-3, we conducted the following analysis and research: Comparative analysis of the tribological behavior of TaC coating and substrate: To clarify the improving effect of TaC coating on the tribological properties of M50NiL bearing steel, a systematic comparison was carried out from three core dimensions—stress field, temperature field, and wear amount—through three-dimensional thermo-mechanical coupled finite element simulation and pin-disc friction and wear experiments. The inherent correlation and quantitative laws are as follows: In terms of stress field distribution, the augmented Lagrangian contact algorithm and the linear elastic material assumption were used to construct a simulation model. The results show that TaC coating has a significant mitigating effect on shear stress in the contact area. The statistical data of simulation under different loads are shown in Table 1 below: Table 1: Comparison of the influence of TaC coating on shear stress of M50NiL bearing steel Under constant speed conditions of 200 rpm, the maximum shear stress of uncoated M50NiL steel under loads of 30 N, 35 N, and 40 N are 8.59 MPa, 10.00 MPa, and 11.40 MPa, respectively. However, with the TaC coating, the maximum shear stress under the corresponding loads is only 0.85 MPa, 1.00 MPa, and 1.13 MPa, with stress reduction exceeding 90.0%. This difference stems from the higher elastic modulus of the TaC coating (3.40 × 10⁻⁶). 11 N / m 2 It can redistribute contact stress, avoid local stress concentration in the matrix, and thus reduce the risk of shear damage.

[0038] In the temperature field evolution comparison, based on Fourier's law of thermal conductivity and thermo-mechanical sequence coupling analysis, the TaC coating exhibits excellent frictional heat suppression effect. The temperature test results under different working conditions are shown in Table 2 below: Table 2: Comparison of the influence of TaC coating on the frictional temperature of M50NiL bearing steel The highest frictional temperature of the uncoated substrate under 250 rpm and 35 N conditions reached 76.5℃, while the highest temperature of the TaC coated sample under the same conditions was only 58.9℃, a reduction of 27.6%. Under 250 rpm and 35 N conditions, the highest temperature of the uncoated substrate was 70.7℃, while that of the coated sample dropped to 51.2℃, also a reduction of 27.6%. The low thermal conductivity of the coating (25 W / (m・K)) reduced the transfer of frictional heat to the substrate, while its good thermal stability suppressed the adverse effects of temperature on the material properties.

[0039] The wear comparison is based on the Archard wear model, the expression of which is shown below: In the formula, The wear coefficient is a dimensionless coefficient. For material volume loss, The sliding distance, The Brinell hardness of the material. The normal load on the contact surface is given by the Brinell hardness of the material. (It changes significantly with temperature, so a hardness-temperature relationship function can be introduced.) The original model Replace with ,Right now: In the formula, The wear coefficient is a function of Brinell hardness as a function of temperature. It changes significantly with temperature, which affects surface oxidation, adhesive wear, and abrasive hardness through mechanisms such as these. The wear coefficient-temperature relationship needs to be established. The model is corrected as follows: In the formula, The wear coefficient is a function of temperature. Increased temperature may cause thermal expansion of the material, altering the contact area and the distribution of normal load. The contact pressure distribution after thermal deformation should also be considered. The model is corrected as follows: In the formula It is a function of contact pressure as a function of temperature.

[0040] The effect of temperature on wear was quantified (see Tables 3 and 4 below): Table 3: Calculation results of the effect of temperature on the wear of TaC coating. Table 4: Results of temperature calculation on wear of M50NiL substrate The average wear mass of TaC-coated samples under different operating conditions ranged from 0.0471g to 0.1028g, while the wear mass of the uncoated substrate ranged from 0.0908g to 0.1259g. The wear mass of the coated samples was significantly reduced. At the same time, the temperature factor caused the predicted wear mass of the coating and the substrate to decrease by an average of about 10.5%. The absolute difference in wear mass of the TaC coating under the operating conditions of 30N and 200rpm was 0.0064260g, with a relative change percentage of 13.11%. This indicates that the moderating effect of frictional heat on the wear process cannot be ignored, and the TaC coating further slowed down the wear process by suppressing the temperature rise.

[0041] Wear Behavior Study of M50NiL Bearing Steel Matrix: The wear behavior of M50NiL bearing steel matrix is ​​closely related to operating parameters (speed and load). Through friction coefficient monitoring, wear morphology observation, and energy dispersive spectroscopy analysis, its wear law and internal mechanism are as follows: The evolution of friction coefficient shows a significant operating condition dependence. Under a constant load of 35N (as shown in Figure 2), the friction coefficient fluctuates greatly in the initial stage (0-300s), and tends to stabilize after 300s. The stable friction coefficients at speeds of 150rpm, 200rpm, and 250rpm are approximately 1.1, 1.35, and 1.2, respectively. Among them, the friction coefficient is the highest at 200rpm and the system stability is the worst. Under a constant speed of 200rpm (as shown in Figure 3), the friction coefficients corresponding to loads of 30N, 35N, and 40N in the stable stage are 1.15, 1.35, and 1.25, respectively. The overall trend is upward with the increase of load, indicating that the increase of contact pressure leads to the enhancement of friction resistance.

[0042] The wear morphology deteriorates progressively with increasing rotational speed. At a low speed of 150 rpm, only narrow and flat wear tracks are formed on the substrate surface. The three-dimensional profile shows that the wear tracks are shallow and smooth, and the wear mechanism is mainly mild abrasive wear, with the hard particles exerting a gentle scraping and cutting effect on the surface. At 200 rpm, the wear track width increases significantly, and obvious peeling and adhesion characteristics appear on the surface. The three-dimensional profile shows local convexity and depression, and the wear mechanism changes to a composite mode of abrasive wear and adhesive wear. At a high speed of 250 rpm, the surface wear traces are fine and scattered, with plastic deformation textures. The oxygen element is unevenly distributed, with local enrichment and deficiency coexisting. The wear mechanism is dominated by oxidative wear, accompanied by abrasive wear and adhesive wear, and the material damage is the most severe.

[0043] The influence of load on wear behavior is reflected in the degree of damage and the change in mechanism. Under a low load of 30N, the wear surface is mainly characterized by parallel furrows with a small amount of wear debris, and the adhesive wear characteristics are obvious. Under a medium load of 35N, the adhesive-stripping characteristics are more typical, with multiple discrete spalling blocks appearing, and the wear volume further increases. Under a high load of 40N, the surface is covered by a continuous adhesive wear layer, exhibiting large-area plastic deformation, extremely deep and irregularly contoured wear tracks, and the oxide film rapidly peels off due to mechanical damage. Abrasive wear and adhesive wear regain dominance.

[0044] The core of the wear mechanism is the synergy and transformation of multiple mechanisms (as shown in Figure 4). The mechanical interaction of the rough peaks at the contact interface is the initial damage source: the peaks adhere under high pressure and frictional heat, and are subsequently sheared and torn to form wear debris. The wear debris and the rough peaks together trigger ploughing, causing gradual material peeling. As the rotational speed increases, the accumulated frictional heat activates the oxidation reaction. The oxidation products, as hard abrasive particles, intensify the wear, forming an "oxidation-wear" cycle. As the load increases, the contact pressure strengthens the mechanical damage, the integrity of the oxide film is lost, and the wear mechanism transitions from stable ploughing to severe composite wear, ultimately leading to a large loss of matrix.

[0045] Wear Behavior Study of TaC Coating on M50NiL Substrate: The wear behavior of the TaC coating is regulated by rotational speed and load. Its tribological performance advantages and failure mechanism were clarified through systematic experiments and characterization, and the specific analysis is as follows: The friction coefficient shows a completely different pattern from that of the substrate. Under a constant load of 35N (as shown in Figure 5), as the rotational speed increases from 150rpm to 250rpm, the coating friction coefficient gradually increases from about 0.3 to close to 1.0, and the fluctuation is more significant at high speeds. The friction coefficient is lowest at 150rpm and stabilizes in the later stage, demonstrating excellent frictional stability. Under a constant rotational speed of 200rpm (as shown in Figure 6), the stable friction coefficients under loads of 30N and 35N are both about 0.4, with smaller fluctuations at 30N. Under a high load of 40N, the friction coefficient continues to rise to 1.25, close to the friction coefficient of the substrate, indicating that the coating has been almost completely worn away and has lost its protective function.

[0046] The evolution of wear morphology reflects the gradual process of coating damage. At a low speed of 150 rpm, the coating surface only has fine scratches, is generally flat, and has no obvious peeling. The three-dimensional profile shows shallow wear depth and small wear volume, with the wear mechanism mainly being slight abrasive wear. At a medium speed of 200 rpm, obvious wear grooves and local peeling areas appear on the surface, the integrity of the coating is damaged, and local high wear areas appear in the wear feature mapping. The wear mechanism is transitioning to a combined mode of abrasive wear and micro-peeling. At a high speed of 250 rpm, the coating shows large-scale peeling, deep and large wear tracks and wear product accumulation, locally exposing the substrate. The three-dimensional profile has extremely poor flatness, and the wear volume reaches its maximum value. The wear mechanism is a combination of abrasive wear, coating peeling and oxidative wear.

[0047] The effect of load on coating wear is reflected in the change of damage mode. Under a low load of 30N, the coating surface has only a few shallow scratches, mainly due to abrasive wear. EDS analysis shows that C is evenly distributed, O is sporadically distributed, and Fe content is extremely low, with good coating integrity. Under a medium load of 35N, wear grooves and local spalling intensify, C is locally absent, O density increases, and Fe content increases slightly. The wear mechanism changes to a combination of abrasive wear and local adhesive wear. Under a high load of 40N, the coating surface is covered by a continuous adhesive wear layer, resulting in large-area spalling. C is largely absent, O is densely distributed, and Fe content increases significantly. The wear mechanism is a coupled mode of severe adhesive wear, large-area spalling, and oxidative wear, and the coating's protective performance is completely lost.

[0048] The core of the coating wear mechanism is the synergistic effect of mechanical action and thermal effect (as shown in Figure 7). In the initial stage, the rough peak of the contact interface induces slight adhesion and abrasive wear, and the dense structure of the coating effectively resists damage. As the rotation speed increases, the accumulation of frictional heat leads to an increase in internal stress of the coating and a deterioration of the interfacial bonding force. The wear transitions from "micro-area damage" to "macro-scale failure". At 250 rpm, the high temperature and mechanical stress synergistically cause the coating to peel off in flakes. As the load increases, the contact pressure intensifies mechanical damage. At low loads, oxidative wear contributes little. At medium loads, frictional heat activates the oxidation reaction. At high loads, mechanical damage dominates, oxides peel off rapidly, and a large amount of coating matrix is ​​lost. The EDS elemental distribution characteristics further confirm this mechanism: as the rotation speed and load increase, C element changes from uniform coverage to significant absence, O element distribution density increases, and Fe element changes from trace transfer to significant enrichment, reflecting the process of intensified coating peeling, enhanced oxidation reaction, and strengthened interaction between the components.

[0049] In summary, the TaC-coated modified M50NiL steel for UAVs is prepared through vacuum melting, precise heat treatment, step-by-step grinding pretreatment, and non-equilibrium magnetron sputtering deposition. The coating has a dense structure, uniform composition, and conformal bonding with the substrate. Its coefficient of friction is significantly lower than that of the uncoated substrate, which can effectively reduce shear stress and frictional temperature rise in the contact area, and significantly reduce wear. The wear mechanism of the coating dynamically evolves with rotational speed and load. Under low load and low speed, it is mainly slight abrasive wear, while under high load and high speed, it transforms into a composite mode of abrasive, adhesive, and oxidative wear, and can always play a good protective role. At the same time, it retains the core characteristics of the substrate of "hard outside and tough inside", which can be adapted to the extreme high speed, heavy load and dry friction conditions of UAV bearings, significantly improving the reliability and service life of components.

[0050] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A TaC-coated modified M50NiL steel for unmanned aerial vehicles, characterized in that, include: An M50NiL steel substrate and a TaC coating deposited on the substrate surface. The chemical composition of the M50NiL steel substrate includes 0.13wt% C, 4.1wt% Cr, 4.2wt% Mo, 3.4wt% Ni, 1.2wt% V, 0.13wt% Mn, 0.18wt% Si, with Fe as the balance. The TaC coating is prepared by unbalanced magnetron sputtering physical vapor deposition and has a dense and uniform coating structure.

2. The TaC-coated modified M50NiL steel for UAVs according to claim 1, characterized in that: The M50NiL steel matrix undergoes austenitization at 1100℃, oil quenching, and tempering heat treatment at 540℃. The matrix structure is mainly composed of cryptocrystalline martensite and fine lath martensite, with dispersed granular carbides and a small amount of retained austenite. The hardness is ≥55HRC, and the surface roughness Ra<0.1µm after grinding.

3. The TaC-coated modified M50NiL steel for UAVs according to claim 1, characterized in that: The deposition process of the TaC coating uses argon as the working gas and acetylene as the reaction gas. The coating thickness is 0.1 mm, and the coating forms a conformal bond with the M50NiL steel substrate.

4. A method for preparing TaC-coated modified M50NiL steel for drones, comprising the TaC-coated modified M50NiL steel for drones as described in any one of claims 1-3, characterized in that, Includes the following steps: S1. Mix and smelt according to chemical composition to obtain M50NiL steel billet. Machin the steel billet into a base blank of the target shape for UAV bearings. S2. Heat treat the base blank: first, perform austenitization treatment at 1100℃ for 1 hour, then oil quench for 10 minutes, and finally temper at 540℃ for 1 hour to obtain an M50NiL steel matrix with a hardness ≥55HRC and a microstructure mainly composed of cryptocrystalline martensite and fine lath martensite. S3. Pre-treat the surface of the heat-treated matrix by successively polishing with 280#, 800#, 1500#, and 2000# sandpaper until the surface roughness Ra <0.1µm. Then, clean the surface with alcohol to remove oil and impurities, and dry for later use. S4. Use unbalanced magnetron sputtering... A vapor deposition (VCD) system was used, with argon as the working gas and acetylene as the reactant gas, to deposit a TaC coating on the surface of an M50NiL steel substrate. During deposition, the substrate temperature was controlled at 200℃, an 800V bias voltage was applied, the deposition time was 12 hours, the argon flow rate was 300 sccm, the acetylene flow rate was 600 sccm, and the coating thickness was controlled at 0.1 mm to ensure a conformal bonding structure between the coating and the substrate. S5: The workpiece after TaC coating deposition was characterized and tested. The microstructure of the coating was observed using a scanning electron microscope, the mechanical properties of the coating were tested using nanoindentation technology, and the tribological properties were verified using a pin-disc friction and wear experiment. S6: The workpiece that passed the characterization and testing was deburred, cleaned, and dried to obtain the TaC-modified M50NiL steel product for UAVs.

5. The method for preparing TaC-coated modified M50NiL steel for UAVs according to claim 4, characterized in that, In step S1, the ingredients are smelted using a combination of vacuum induction melting and vacuum arc remelting, with the vacuum level controlled to be ≤5×10⁻⁶ during the smelting process. -2 Pa, melting temperature 1550-1600℃, held for 2 hours and then cast; machining is carried out by a combination of CNC lathe and grinding machine to ensure that the dimensional tolerance of the base blank is ±0.02mm and the form and position tolerance is ≤0.01mm.

6. The method for preparing TaC-coated modified M50NiL steel for UAVs according to claim 4, characterized in that, In S2, the heating rate of the austenitizing treatment is 5℃ / min, from room temperature to 1100℃; oil quenching is performed using N32 machine oil, and the oil temperature is controlled at 80-100℃; after tempering heat treatment, air cooling is used to cool to room temperature, and direct contact between the substrate surface and cooling water is avoided during the cooling process.

7. The method for preparing TaC-coated modified M50NiL steel for UAVs according to claim 4, characterized in that, In step S3, the alcohol cleaning is performed using ultrasonic-assisted cleaning for 15 minutes with an alcohol concentration of 99.7%. After cleaning, the alcohol is dried in a drying oven at 60°C for 30 minutes, with the ambient humidity controlled to be ≤30% during the drying process.

8. The method for preparing TaC-coated modified M50NiL steel for UAVs according to claim 4, characterized in that, In step S4, the target material for the unbalanced magnetron sputtering equipment is a TaC target with a purity ≥99.9%, and the distance between the target and the substrate is 80 mm; the initial vacuum level of the vacuum chamber during deposition is ≤5×10⁻⁶. -3 Pa, the coating thickness is monitored in real time by a laser thickness gauge, and the thickness data is recorded every 30 minutes to ensure that the coating thickness deviation is ≤ ±0.005mm.

9. The method for preparing TaC-coated modified M50NiL steel for UAVs according to claim 4, characterized in that, In step S5, the accelerating voltage during scanning electron microscopy observation is 15kV, and the microstructure of the coating surface and cross-section are observed respectively; during nanoindentation testing, a Berkovich indenter is used, the loading rate is 5mN / s, the maximum load holding time is 10s, and 6 test points are randomly selected and the average value is taken. The pin-disc friction and wear test used GCr15 steel as the mating part, and the experimental environment was 25±2℃ and 45±5% relative humidity.

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