Brake disc surface wear resistant coating and method of manufacture

Abstract

This invention proposes a wear-resistant coating for brake discs and its preparation method, belonging to the field of surface modification technology. This invention prepares an Fe-Ti-C-B alloy coating on the working surface of a steel-based brake disc using laser cladding technology. Through precise alloy composition design, the high-temperature lubricating phase titanium boron compound and the hard phase titanium carbide are simultaneously precipitated in situ from the alloy during laser cladding, forming a eutectic network structure of titanium carbide and titanium boron compound. This achieves a seamless, all-metallurgical bond with the substrate. The titanium boron compound undergoes a tribochemical oxidation reaction under the coupling effect of high temperature and shear stress, generating a glassy lubricating film for self-lubrication, eliminating the need for external solid lubricants. This invention achieves a seamless, all-metallurgical bond between the coating and the substrate, with the hard phase and the high-temperature lubricating phase interlocking and coexisting at the nanoscale. It possesses a wide-temperature-range self-lubricating function, improving the coating's structural integrity, wear resistance, and lubrication synergy. It is suitable for steel-based brake discs in fields such as rail transportation, high-speed trains, and construction machinery.

Description

Technical Field

[0001] This invention relates to the field of surface modification technology, specifically to a wear-resistant coating for brake disc surface and its preparation method. Background Technology

[0002] With the development of transportation equipment towards high speed and heavy load, the wear resistance and thermal shock resistance of brake discs have become core research and development directions in the industry. Laser cladding technology, due to its ability to achieve strong metallurgical bonding between the coating and the substrate, has become the mainstream technology for surface modification of brake discs. However, current mainstream laser cladding coating solutions for brake discs generally suffer from core problems such as weak bonding between the ceramic phase and the substrate interface, easy peeling failure, insufficient microscopic synergy between the hard phase and the high-temperature lubricating phase, and large fluctuations in the coefficient of friction. These issues make it difficult to meet the requirements for long service life and high safety under harsh operating conditions.

[0003] To address the above issues, the industry is continuously improving laser cladding technology for brake disc surfaces. CN119040883A discloses a high-hardness, wear-resistant coating for automotive brake discs and its preparation method. Using NiCr-Cr3C2 composite powder as the matrix and adding AlN ceramic powder, a high-hardness, wear-resistant coating is prepared on the surface of automotive brake discs via laser cladding technology. Relying on the wear-resistant and oxidation-resistant properties of NiCr-Cr3C2 and the strengthening effect of AlN, a significant improvement in the surface hardness, wear resistance, and deformation resistance of the brake disc is achieved. However, its system design, which uses a purely external ceramic phase mechanical mixing, lacks any self-lubricating structure, failing to address the industry pain point of large fluctuations in the friction coefficient under braking conditions. Furthermore, the external ceramic phase and the metal matrix are only mechanically encapsulated, leading to interface stress concentration and easy debonding and peeling under alternating loads. Additionally, there is no wide-temperature-range high-temperature lubricating phase suitable for the transient high-temperature environment of braking, resulting in insufficient tribological stability under high-temperature conditions. CN120666330A discloses a high-hardness, wear-resistant coating for automotive brake disc surfaces. The method for preparing wear-resistant coatings of iron-based alloys by laser cladding utilizes iron-based alloy powders of the Fe-Cr-Mo-VWC system. By optimizing the laser cladding process parameters, wear-resistant coatings of iron-based alloys can be directly prepared on the surface of brake discs. However, this method is based on a single iron-based alloy system design and lacks a dedicated hard reinforcing phase and high-temperature lubricating phase design. The improvement in coating hardness and wear resistance is limited, making it unsuitable for the harsh braking conditions of high-frequency heavy loads and high-temperature impacts. Furthermore, the lack of a multi-phase synergistic microstructure design fails to address the challenges of the braking process. The problem of insufficient thermal shock resistance and anti-stripping performance exists. CN120230972A discloses a laser cladding iron-based corrosion-resistant and wear-resistant coating and its preparation method. By first laser cladding a 316 transition layer on the surface of H13 steel, and then cladding a layer of iron-based alloy coating containing elements such as boron, chromium, and titanium, aluminum liquid corrosion resistance and wear resistance are obtained. However, the borides in the coating prepared by this process are hard and brittle, and are prone to cracking due to thermal stress. Moreover, the coating only relies on the hard phase to improve wear resistance and lacks self-lubricating function, resulting in a high coefficient of friction.

[0004] In summary, in order to address some of the defects in current brake disc coatings, it is urgent to develop a novel, green, environmentally friendly, self-lubricating, and wear-resistant composite coating system that can completely eliminate the mechanical mixing interface from a physical and chemical perspective, achieve self-assembly and synergistic distribution of the hard phase and the high-temperature lubricating phase at the microscopic scale, exhibit excellent self-lubricating properties, and possess a fully metallurgical continuous structure. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention proposes a wear-resistant coating for brake disc surfaces and its preparation method. This invention utilizes laser cladding technology to prepare an Fe-Ti-CB alloy coating on the working surface of a steel-based brake disc. Through precise alloy composition design, the high-temperature lubricating phase titanium boron compound and the hard phase titanium carbide are simultaneously precipitated in situ from the alloy during the laser cladding process, forming a eutectic network structure of titanium carbide and titanium boron compound. This achieves a seamless, all-metallurgical bond with the substrate. The titanium boron compound undergoes a tribochemical oxidation reaction under the coupling effect of high temperature and shear stress, generating a glassy lubricating film for self-lubrication. This eliminates the need for external solid lubricants and avoids problems such as uneven dispersion, burn-off, and peeling.

[0006] This invention proposes a wear-resistant coating for the surface of a brake disc. The coating contains an iron-based solid solution, a hard phase TiC, and a high-temperature lubricating phase TiB2. The proportions of each component are 70%-92% iron-based solid solution, 5%-18% hard phase TiC, and 3%-15% high-temperature lubricating phase TiB2.

[0007] This invention also proposes a method for preparing a wear-resistant coating on the surface of a brake disc, the specific technical solution of which is as follows: Step 1: Sodium carboxymethyl cellulose is heated and stirred in deionized water to form a base liquid. Then, polyvinyl alcohol aqueous solution is added to the base liquid and stirring is continued to obtain an aqueous binder. Iron-based alloy powder, titanium powder, boron carbide powder and graphite powder are wet-milled in a ball mill and then vacuum dried.

[0008] Step 2: Add the dried mixed powder to the water-based binder and shear and stir it under vacuum using a disperser to obtain the alloy fluid pre-slurry.

[0009] Step 3: The working surface of the low alloy steel brake disc is roughened by sandblasting, then ultrasonically cleaned and blown dry. The alloy slurry is coated on the working surface of the brake disc and placed in a blower drying oven for step drying to obtain a solid dried preform layer.

[0010] Step 4: Fix the brake disc covered with the preform layer onto the laser equipment, first continuously purge with inert gas and then scan the preform layer with a laser beam, and then cool the brake disc to room temperature to obtain a wear-resistant coating on the surface of the low alloy steel brake disc.

[0011] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. All wear-resistant and lubricating functional phases undergo a process of liquid-phase dissolution followed by in-situ reaction and crystallization, eliminating the sharp stress concentration caused by added ceramic particles and the microscopic mechanical weak interface caused by the mismatch of thermal expansion coefficients. The tough iron-based solid solution firmly encapsulates and locks the nano-scale titanium carbide and titanium boron compound eutectic network system, achieving a high-strength all-metallurgical continuous bond and eliminating the blocky peeling failure problem that traditional coatings are prone to under the large shear force of emergency braking.

[0012] 2. Under high temperature and high shear conditions during braking, the titanium boron compounds precipitated in situ generate a glassy lubricating film with low shear strength through tribochemical oxidation reaction. This film plays a role in boundary lubrication and microcrack filling, enabling the coating to achieve a stable and low friction coefficient and effectively suppress wear of mating parts throughout its entire life cycle without the need for external lubricants.

[0013] 3. The elemental composition, microhardness and crystal structure of the material all exhibit a smooth and continuous gradient transition. Under the extreme transient high temperature thermal shock and high frequency alternating mechanical stress coupling generated during braking, it can effectively dissipate heat and mechanical stress, avoid stress concentration and accumulation at a certain interface, and enable the coating to maintain a stable service state of integrity, density, no cracks and no peeling under heavy load emergency braking conditions. Attached Figure Description

[0014] Figure 1 This is a TEM transmission electron microscope image of the sample from Example 1; Figure 2 The image shows the XPS scan spectrum of the sample from Example 1 after high-temperature friction. Detailed Implementation

[0015] This invention proposes a method for preparing a wear-resistant coating on the surface of a brake disc, the specific technical solution of which is as follows: 1. Premixing water-based binder with alloy powder A water-based binder is formed by compounding sodium carboxymethyl cellulose (CCC) and polyvinyl alcohol (PVA). Simultaneously, alloy powder, titanium powder, boron carbide powder, and graphite powder are wet-milled and then vacuum-dried. The CCC molecular chain contains carboxymethyl hydrophilic groups. When heated and stirred in deionized water, the chain segments extend and form a hydrogen bond network with water, becoming a shear-thinned non-Newtonian fluid. During coating, the shear force reduces viscosity, facilitating flow and spreading to form a uniform wet film. After coating, the viscosity recovers, allowing the slurry to stably adhere to the vertical or inclined surface of the brake disc without flowing or piling up. Subsequently, an aqueous solution of PVA is added to introduce a high-molecular-weight film-forming component. The hydroxyl groups on the PVA molecular chain crosslink with the carboxyl groups of CCC during drying, forming a three-dimensional network. After step drying, the powder particles are anchored, giving the preform sufficient mechanical strength.

[0016] Due to the significant differences in density, particle size, and morphology of multi-element alloy composite powders composed of iron-based alloys, titanium, boron carbide, and graphite, wet ball milling is required to avoid segregation. Anhydrous ethanol is used as the medium, and the powders are forcibly mixed to a near-atomic scale homogeneous state through ball collision and shearing. The addition of ethanol reduces the powder surface energy, eliminates air films, and promotes sufficient contact between different powders. During wet mixing, it also breaks up soft agglomerates, allowing lightweight graphite to be uniformly dispersed and embedded in the metal powder, preventing floating and agglomeration in the laser molten pool due to density differences.

[0017] 2. Preparation of alloy slurry The dried mixed powder is added in batches to an aqueous binder and then subjected to high-speed vacuum shearing to obtain a pre-formed alloy fluid slurry. Because adding a large amount at once easily leads to agglomeration on the liquid surface, and the particles are encased in an air film, preventing liquid penetration and effective wetting of the powder, the dried mixed powder needs to be added to the aqueous binder in batches, rather than all at once. By slowly adding the powder in batches and stirring, it is fully wetted upon falling onto the liquid surface. The liquid penetrates into the interparticle spaces through capillary action, achieving good solid-liquid wetting. Simultaneously, the carboxyl groups on the sodium carboxymethyl cellulose molecular chains in the aqueous binder are adsorbed onto the metal powder surface through hydrogen bonds and electrostatic adsorption, forming a steric hindrance layer that prevents particle agglomeration and sedimentation, avoiding compositional unevenness caused by the sedimentation of high-density iron-based and titanium powders.

[0018] To obtain a uniformly dispersed slurry, a high-shear disperser is used to break up residual micron-sized agglomerates using high-frequency, high-shear forces. This allows the binder macromolecular chains to fully spread on the particle surface and form a stable steric hindrance layer. Simultaneously, turbulence and cavitation effects promote macroscopically uniform mixing of the solid and liquid phases. However, during atmospheric pressure stirring, air is entrained into the slurry, forming microbubbles. Some of this air comes from eddy entrainment, and the other from the release of gases adsorbed on the powder surface. If this air remains in the slurry, it will form pores after drying, becoming points of thermal stress concentration during laser cladding, causing the coating to crack and splatter. Therefore, it is necessary to simultaneously apply a vacuum during the high-shear process to expand the bubble volume, increase buoyancy, and make it easier for the bubble to float and escape. At the same time, dissolved gases are released and removed, thereby eliminating the risk of porosity defects.

[0019] 3. Pre-treatment of brake disc and precast blank layer After pretreatment of the working surface of the low-alloy steel brake disc, an alloy slurry is coated and dried in a stepped heating process to obtain a solid-state dried preform. The pretreatment of the brake disc working surface includes sandblasting and ultrasonic cleaning. First, high-pressure abrasive particles impact the substrate, thoroughly removing oxide scale, rust, and work-hardened layers through micro-cutting and plastic deformation, exposing a fresh, highly active metal surface. This simultaneously forms a micro-uneven structure, increasing the contact area between the coating and the substrate, and providing anchoring points for the molten metal to form a mechanical bond after solidification, enhancing interfacial strength through metallurgical bonding. Ultrasonic cleaning ensures surface chemical cleanliness by utilizing cavitation to generate micro-jet streams and shock waves from collapsing microbubbles in the cleaning solution, thoroughly removing oil and particles deep within the pits. Finally, purging and drying evaporate residual moisture in the micropores to prevent vaporization and explosion during laser heating.

[0020] The thickness of the wet film of the coated alloy slurry is controlled according to the laser parameters, ensuring that the laser energy penetrates the entire thickness without causing excessive melting of the substrate, which would prevent the in-situ reaction from proceeding fully and resulting in insufficient formation of TiC and TiB2. Furthermore, to prevent cracking of the preform layer, stepped drying is used to allow the moisture in the coating layer to slowly migrate and evaporate in a liquid state, avoiding premature hardening of the surface layer. Heating is then applied after most of the free moisture has been removed, causing the deep-bound water to desorb and promoting thermal cross-linking of polyvinyl alcohol to form a water-resistant three-dimensional network, thereby enhancing its strength.

[0021] 4. Laser cladding in-situ reactive coating The brake disc covered with a precast blank is first purged with inert gas, then irradiated with a laser beam and cooled to obtain a self-lubricating and wear-resistant coating. Before laser irradiation, the brake disc is continuously purged with inert gas, which forms a local protective shield above the molten pool, isolating oxygen and nitrogen in the air and preventing titanium from preferentially reacting with oxygen to form brittle titanium oxide. During the laser cladding process, the high-energy laser raises the precast layer to thousands of degrees Celsius within milliseconds, causing the binder to instantly vaporize and decompose without residual carbon. The alloy powder and the substrate surface melt simultaneously to form a micro-molten pool. The interior of the molten pool is dominated by Marangoni convection, and the surface tension gradient drives the melt to form a circulation, uniformly mixing elements such as boron, carbon, titanium, and iron at the atomic level.

[0022] After the laser is removed, the molten pool solidifies rapidly at a rate of hundreds of thousands of Kelvin per second, inhibiting grain growth and allowing TiC and TiB2 grains to reach submicron to nanometer scale. Because TiB2 has a more negative Gibbs free energy at high temperatures, it preferentially nucleates and grows into hexagonal lamellar or short rod-shaped crystals. After its precipitation, the boron concentration in the liquid phase decreases while the carbon concentration relatively increases. TiC undergoes heterogeneous nucleation on its surface. At the same time, due to the extremely low lattice mismatch between the two, TiC grows coherently epitaxially along TiB2, tightly intertwining at the nanoscale to form a thermodynamically driven self-assembled eutectic network.

[0023] During the rapid solidification process after laser removal, TiB2 preferentially nucleates due to its more negative Gibbs free energy, growing into hexagonal lamellar or short rod-shaped crystals. Subsequently, TiC is heteroepitaxially grown on its surface and tightly intertwined at the nanoscale, forming a thermodynamically driven self-assembled eutectic network. TiC, as a hard phase, constructs a high-rigidity, wear-resistant skeleton, bearing normal loads and resisting abrasive cutting. TiB2, as a lubricating phase, undergoes a tribochemical oxidation reaction under the coupling effect of high temperature and shear stress generated by braking, generating an in-situ glassy, ​​softened, viscous lubricating film with boron oxide and titanium dioxide as its core. This low-shear-strength rheological film plays a boundary lubrication role at the friction interface, while filling microcracks, suppressing friction coefficient fluctuations, and reducing wear on mating parts. This allows the coating to achieve a synergistic effect of wide-temperature-range self-lubrication and high wear resistance without the need for external traditional easily burnable lubricants.

[0024] The preferred embodiments of the present invention are described in detail below; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combining the various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

[0025] Table 1 Raw Material Information Table for Example 1

[0026] Example 1 S1: Heat 1000g of deionized water to 40℃, and slowly add 25g of sodium carboxymethyl cellulose while stirring at 300rpm. Continue stirring for 2h to form a homogeneous and transparent solution. Then, add 30g of 3% polyvinyl alcohol aqueous solution dropwise and continue stirring for 30min to obtain an aqueous binder. Weigh the mixed powder according to the mass ratio of iron-based self-fluxing alloy powder: pure titanium powder: boron carbide powder: spheroidized graphite powder = 80:15:3.5:1.5. Place the mixed powder in a planetary ball mill, use anhydrous ethanol as the wet grinding medium, the ball-to-material ratio is 5:1, set the ball mill speed to 150r / min, and ball mill for 4h. Then, transfer the mixed slurry to a vacuum drying oven and dry it at 80℃ and -0.09MPa for 8h to obtain a homogeneous multi-element alloy powder.

[0027] S2: Take 420g of dried multi-element alloy powder and slowly add it to 60g of water-based binder in 3 batches. Then transfer it to a vacuum high-shear emulsification disperser and shear and stir at 1200rpm for 40min at -0.08MPa to obtain alloy fluid pre-slurry.

[0028] S3: The working surface of the low-alloy steel brake disc is roughened by sandblasting using 60-mesh brown corundum abrasive, with a sandblasting pressure of 0.6 MPa, a distance of 200 mm, and a sandblasting angle of 90°. The sandblasted brake disc is then placed in an ultrasonic cleaning tank using anhydrous ethanol as the cleaning solution. The ultrasonic frequency is set to 40 kHz, the power to 500 W, and the cleaning is continued for 15 minutes. After cleaning, the disc is removed and dried by blowing with cold air. The alloy slurry prepared in S2 is then uniformly coated onto the working surface of the brake disc using an automatic scraper coating device with a scraper gap of 0.7 mm and a coating speed of 30 mm / s. The coated brake disc is then placed horizontally in a programmed temperature rise constant temperature forced-air drying oven. In the first stage, the disc is heated to 65°C at a heating rate of 1°C / min and held for 2 hours. In the second stage, the disc is heated to 130°C at a heating rate of 1.5°C / min and held for 2.5 hours. After cooling to room temperature, the disc is removed to obtain a solid-state dried preform.

[0029] S4: Fix the brake disc covered with the preform layer on the rotary table of the six-axis CNC laser additive manufacturing equipment. Adjust the position of the laser processing head to make the defocusing amount 0. Use a 1070nm wavelength fiber laser, set the laser power to 2000W, the spot diameter to 3mm, the scanning speed to 6mm / s, and the overlap rate to 45%. At the same time, use argon gas for continuous purging at a gas flow rate of 12L / min. After 8s of purging, start the laser and perform cladding processing on the working surface of the brake disc according to the spiral scanning path from the inside to the outside. Keep argon gas purging throughout the scanning process. After cladding is completed, continue purging for 60s. Then, transfer the entire brake disc to an insulated sand box and bury it in dry sand to cool for 8 hours. After taking it out, use a 46-mesh grinding wheel to grind the coating surface to remove the surface oxide layer. The grinding depth is 0.05mm / time to obtain a wear-resistant coating on the surface of the low alloy steel brake disc.

[0030] Example 2 The preparation method according to Example 1 differs in that: S1: Iron-based self-fluxing alloy powder: pure titanium powder: boron carbide powder: spheroidized graphite powder = 70:22:5:3, and the remaining steps are the same.

[0031] Example 3 The preparation method according to Example 1 differs in that: S1: Iron-based self-fluxing alloy powder: pure titanium powder: boron carbide powder: spheroidized graphite powder = 92:6:1.5:0.5, and the remaining steps are the same.

[0032] Example 4 The preparation method according to Example 1 differs in that: S1: Iron-based self-fluxing alloy powder: pure titanium powder: boron carbide powder: spheroidized graphite powder = 85:10:2:3, and the remaining steps are the same.

[0033] Example 5 The preparation method according to Example 1 differs in that: S1: Iron-based self-fluxing alloy powder is replaced with Fe316L type alloy powder; S3: Use white corundum abrasive during sandblasting; S4: Helium is used for purging; the other steps are the same.

[0034] Example 6 The preparation method according to Example 1 differs in that: S1: Iron-based self-fluxing alloy powder is replaced with Fe1060 type alloy powder; S3: Use quartz sand for sandblasting; S4: Use a mixture of 60% argon and 40% helium for purging; the other steps are the same.

[0035] Example 7 The preparation method according to Example 1 differs in that: S1: The concentration of carboxymethyl cellulose solution is 1.5%, the ball milling time is 2 hours, the vacuum drying temperature is 60℃, and the vacuum drying time is 12 hours; S2: The solid-liquid ratio of alloy powder and binder is 6:1, the shearing speed is 800 rpm, and the shearing time is 20 min; S3: Doctor blade gap 0.5mm, coating speed 20mm / s; S4: Laser power 1500W, scanning rate 4mm / s, overlap rate 40%, all other steps are the same.

[0036] Example 8 The preparation method according to Example 1 differs in that: S1: The concentration of carboxymethyl cellulose solution is 3.5%, the ball milling time is 6 hours, the vacuum drying temperature is 90℃, and the vacuum drying time is 6 hours; S2: The solid-liquid ratio of alloy powder and binder is 9:1, the shearing speed is 1500 rpm, and the shearing time is 60 min; S3: Squeegee gap 1.0mm, coating speed 50mm / s; S4: Laser power 2500W, scanning rate 8mm / s, overlap rate 55%, all other steps are the same.

[0037] Comparative Example 1 The preparation method according to Example 1 differs in that: S1: Replace pure titanium powder, boron carbide powder, and spheroidized graphite powder with equal proportions of titanium carbide powder, molybdenum disulfide powder, and flake graphite powder. All other steps remain the same.

[0038] The powders prepared in this comparative example are all externally applied rather than in-situ grown coatings.

[0039] Comparative Example 2 The preparation method according to Example 1 differs in that: S1: Without adding boron carbide powder and spheroidized graphite powder, weigh the mixed powder according to the mass ratio of iron-based self-fluxing alloy powder: pure titanium powder = 82:18. The remaining steps are the same.

[0040] This comparative example prepared a coating lacking the TiB2 high-temperature self-lubricating phase.

[0041] Comparative Example 3 The preparation method according to Example 1 differs in that: S4: Place the brake disc covered with the precast blank into a vacuum heat treatment furnace and hold it at 1050℃ for 30 minutes under argon protection. Then cool it down to room temperature with the furnace. The remaining steps are the same.

[0042] This comparative example shows the preparation of a coating lacking a gradient transition structure.

[0043] Comparative Example 4 The preparation method according to Example 1 differs in that: S1: Without adding sodium carboxymethyl cellulose, directly add 30g of a 3.0% polyvinyl alcohol aqueous solution to deionized water to obtain an adhesive solution containing only polyvinyl alcohol. The remaining steps are the same.

[0044] This comparative example prepares a coating with a binder free from steric hindrance.

[0045] Comparative Example 5 The preparation method according to Example 1 differs in that: S3: Eliminate the stepped drying method and directly place the coated brake disc into a constant temperature drying oven at 130℃ for 3.5 hours, followed by natural cooling. All other steps are the same.

[0046] This comparative example prepares a coating that releases thermal stress gradually without step drying.

[0047] Experimental Example 1 The surface coatings of the samples prepared in Examples 1-8 and Comparative Examples 1-5 were peeled off. 10-15 mg of the sample was placed in an alumina crucible and heated from room temperature to 1000 °C in air at a heating rate of 10 °C / min. Thermogravimetric-differential scanning calorimetry (TG-DSC) analysis was performed on the samples using a simultaneous thermal analyzer. The TG and DSC curves of the samples were recorded. The temperature at which the coating began to show severe oxidation or phase transition was taken as the highest high temperature resistance temperature of the sample.

[0048] The coated brake disc samples prepared in Examples 1-8 and Comparative Examples 1-5 were processed into block-shaped samples of 30mm×30mm×5mm as disc samples. They were tested using a high-temperature pin-disc friction and wear testing machine. The mating part was a pin sample with the same material as the actual friction pair of the brake disc. The pin sample had a diameter of 6mm and a flat end face. The normal load was set to 50N, the rotation speed to 500r / min, the wear trajectory radius to 15mm, the sliding linear velocity to 0.8m / s, the test time to 30min, and the relative humidity to 55%. When testing the friction coefficient at room temperature, the test was conducted directly at room temperature. When testing the friction coefficient at 600℃, the sample was placed in a high-temperature furnace chamber and heated to 600℃ at a heating rate of 10℃ / min. After holding at this temperature for 30min, the test was started and maintained at a constant temperature of 600℃ throughout the test. The friction coefficient curves were recorded in real time by the sensor of the testing machine for both tests. The average value of the last 20min of the test process was taken as the friction coefficient value of the coating.

[0049] The test results are shown in Table 2.

[0050] Table 2. High-temperature tribological performance data of the examples and comparative samples.

[0051] As shown in Table 2, the sample in the examples generated a TiC / TiB2 nano-eutectic network using an in-situ reaction system. The TiB2 layered structure activated the self-lubricating function at high temperatures, reducing the friction coefficient at 600℃. Comparative Example 1 was an external particle system, where the particles and the matrix were only physically and mechanically bonded, resulting in a weakened interface. Molybdenum disulfide and graphite suffered severe burn-off under high-temperature laser conditions, leading to poor thermal stability and a high friction coefficient. Comparative Example 2 lacked a boron source and could not generate a high-temperature lubricating phase of TiB2, only a hard TiC phase was present, completely lacking self-lubricating function, resulting in the highest friction coefficient and a small decrease in high-temperature performance. Comparative Example 3 used a slow heating and cooling process, leading to grain coarsening, loss of gradient structure, and concentration of interfacial stress, resulting in a decrease in both thermal stability and self-lubricating performance. Comparative Example 4 only used PVA binder and lacked the steric hindrance effect of CMC, causing powder sedimentation and component segregation, resulting in incomplete reaction and uneven structure. Comparative Example 5 used a one-stage drying process, causing the pre-coated layer to bubble and crack, leading to the formation of pores and microcracks in the coating, thus reducing performance.

[0052] Experiment Example 2 Dry friction tests were conducted using a pin-disc friction and wear testing machine. The coated brake disc sample was processed into a block sample with dimensions of 30mm×30mm×5mm as the disc sample. The mating part was a pin sample with the same material as the actual friction pair of the brake disc. The pin sample had a diameter of 6mm and a spherical end face. The normal load was set to 50N, the rotation speed to 500r / min, the wear trajectory radius to 15mm, the sliding linear velocity to 0.8mm / s, the test time to 60min, the ambient temperature to 25℃, and the relative humidity to 55%. A three-dimensional white light interferometer was used to scan the wear area. The wear volume loss was calculated by the wear width and depth. The wear rate was evaluated according to the formula: wear rate = wear volume / (normal load × sliding distance).

[0053] The coated brake disc sample was processed into a block sample with dimensions of 30mm×30mm×5mm, ensuring that the coating surface was intact and free of defects. The sample was heated to 600℃ in a box-type resistance furnace and held at that temperature for 10 minutes to ensure uniform temperature distribution. The sample was then quickly removed and immersed in circulating cooling water at 25℃ for rapid cooling. After cooling for 10 seconds, the sample was removed and the surface moisture was dried with compressed air. This was one heating-quenching cycle. The cycle was repeated, and the coating surface condition was recorded after every 5 cycles until the coating showed cracks with a length of not less than 1mm or the peeling area exceeded 5% of the total area. The number of thermal cycles at this point was used as the evaluation index for thermal shock resistance.

[0054] The test data above are shown in Table 3.

[0055] Table 3. Durability data of the examples and comparative examples

[0056] As can be seen from Table 3, the TiC / TiB2 nano-eutectic network was generated in situ in the embodiment. The hard phase provides an anti-wear skeleton, and the high-temperature lubricating phase reduces the friction coefficient, thereby resulting in a low wear rate. In addition, the combined effect with the gradient transition structure enables the coating to effectively dissipate stress under thermal shock, avoiding crack initiation and propagation, thus resulting in a high number of thermal cycles. Comparative Example 1: Particles easily detach and become abrasive particles, exacerbating wear. Simultaneously, interface defects become sources of thermal crack initiation, resulting in a high wear rate and low thermal cycle count. Comparative Example 2: Lacking self-lubricating function, it has the highest friction coefficient, leading to the most severe wear. Furthermore, without a lubricating film protection, it is prone to cracking under thermal shock. Comparative Example 3: Lacking grain coarsening and gradient transition structures leads to interface stress concentration, significantly reducing wear resistance and thermal shock resistance. Comparative Example 4: Lacking CMC steric hindrance, powder sedimentation causes component segregation, incomplete reaction, and uneven structure. Defects preferentially lead to wear and cracking, resulting in a high wear rate and low thermal cycle count. Comparative Example 5: Pre-coated layer blistering and cracking defects are inherited by the coating, forming pores and microcracks, becoming the starting point for wear and crack propagation, thus resulting in poor durability.

[0057] Experimental Example 3 The laser-clad brake disc sample prepared in Example 1 was cut into small pieces, and the cross-section was mechanically polished. These pieces were then placed in the vacuum chamber of an FIB (Film Injection Block) device. A 2 μm thick Pt protective band was deposited on the surface of the micro-region rich in the reinforcing phase in the upper part of the coating using electron and ion beam induction. Ga... + The ion beam performs a stepped pitting cut on both sides of the protective layer to form a 1.5 μm thick sheet. This sheet is then welded securely, the bottom is cut off, and the vacuum chamber is extracted. The extracted sheet is transferred onto micropillars of a specially designed copper mesh and firmly welded by Pt deposition, thus adding Ga. + The accelerating voltage of the ion beam was gradually reduced to 2 kV for double-sided ion thinning of the sheet until the thickness of the observation area was less than 50 nm. Finally, the amorphous damage layer on the surface was cleaned using a voltage of 500 V. The cleaned sample was then sent to a field emission high-resolution transmission electron microscope for observation at an accelerating voltage of 200 kV. The observation results are as follows: Figure 1 As shown.

[0058] Figure 1 (a) is a low-magnification TEM bright-field image, mainly showing the nano-complex structure caused by laser rapid cooling. As can be seen from the image, the needle-like or hexagonal lamellar material with a very high aspect ratio in dark black or dark gray is the primary TiB2 phase. Due to its extremely low Gibbs free energy and high melting point, it first nucleates in the molten pool and actively grows along specific crystal planes, forming the first hard skeleton of the coating. The large number of light gray particles with a size of tens of nanometers are the TiC phase. They are not suspended independently, but are densely adsorbed on the edge of TiB2. The bright background without obvious geometric boundaries is the α-Fe solid solution matrix that provides toughness. Figure 1 (b) in the figure shows the lattice stripe pattern of the sample. It can be seen that the left side is the (0001) plane lattice stripe of TiB2 with a spacing of about 0.32 nm, while the right side is the (111) plane stripe of TiC with a spacing of about 0.25 nm. The lattice stripes of the two phases achieve large-area parallel docking and continuous transition. This extremely low lattice mismatch greatly reduces the interfacial energy barrier of TiC heteronucleation on the TiB2 surface, allowing epitaxial growth to occur naturally and giving the coating extremely strong shear resistance and peeling resistance. Figure 1 The regularly arranged bright spots in (c) are the superposition of two sets of diffraction spots, TiB2 and TiC, indicating that the (0001) diffraction vector direction of TiB2 and the (111) diffraction vector direction of TiC are completely collinear and parallel, confirming the epitaxial growth orientation relationship between the two phases.

[0059] Experiment Example 4 After completing the 600℃ high-temperature dry friction test, the Sample 1 from Example 1 was cut from the working surface of the brake disc using a wire cutting device. The cut sample contained the core area of ​​the complete wear track and the surrounding original surface area of ​​the wear track. The sample size was 10mm × 10mm × 3mm. The sample was ultrasonically cleaned in anhydrous ethanol for 5 minutes, then dried with cold air. The dried sample was then fixed to an XPS sample holder using conductive adhesive. The sample was scanned using a high-resolution scanning mode. The fitted scanning results are shown below. Figure 2 As shown.

[0060] Figure 2 Images (a) and (b) show the B 1s energy level spectra. It can be seen that the main B 1s peak on the original surface surrounding the wear track is concentrated in the lower binding energy range, with the central peak at 187.2 eV-187.8 eV. This reflects the three-center, two-electron-deficient, multi-center covalent bonds and Ti-B metallic hybrid state of boron in the TiB2 lattice, indicating that the coating maintained its initial high-hardness crystal physical characteristics in this region. However, after being subjected to 600℃ high temperature and mechanical shear force, the characteristic boride peak, originally located near 187.5 eV, experienced a sharp decay, while a broadened and stronger characteristic diffraction peak appeared in the high binding energy range of 192.5 eV-193.6 eV. This binding energy shift corresponds to the oxidation of boron from a low-valence state to B. 3+ The high valence state confirms that a large amount of B2O3 oxidation products are generated in situ at the friction interface.

[0061] Figure 2 (c) and (d) are Ti 2p energy level diagrams, which show the Ti 2p energy level of the original surface. 3 / 2 The main peak is located in the low binding energy range of 454.8 eV-455.3 eV, corresponding to the bonding environment of the intermetallic compounds in TiB2 and TiC, indicating that Ti has not undergone significant oxidation and maintains a stable structure in its elemental and low-valence states. However, after friction at 600℃, the Ti 2p spectrum shows a significant chemical shift and peak broadening, indicating that Ti 2p... 3 / 2 The main peak is located at 458.6 eV-458.8 eV, corresponding to Ti 2p. 1 / 2 The companion peak is located at 464.3 eV-464.5 eV, and the spin-orbit splitting energy is stable at 5.7 eV, which perfectly matches the standard XPS characteristic peaks of rutile / anatase TiO2, proving that a large amount of Ti is generated at the interface. 4+ Oxidized titanium dioxide.

Claims

1. A wear-resistant coating for a brake disc surface, prepared by laser cladding on the working surface of a low-alloy steel brake disc, characterized in that: The coating is an Fe-Ti-CB self-lubricating wear-resistant composite coating grown in situ on the working surface of the brake disc; the composite coating contains an iron-based solid solution, a hard phase TiC, and a high-temperature lubricating phase TiB2, wherein the iron-based solid solution is 70%-92%, the hard phase TiC is 5%-18%, and the high-temperature lubricating phase TiB2 is 3%-15%; the iron-based solid solution is derived from iron-based self-fluxing alloy powder; the iron-based self-fluxing alloy powder is one or more of Fe60, Fe316L, and Fe1060 type alloy powders.

2. The wear-resistant coating on the surface of a brake disc according to claim 1, characterized in that: All phases in the composite coating are generated in situ in the laser melting pool, achieving atomic-level metallurgical bonding with the iron-based solid solution within the coating. At the same time, the coating as a whole also forms a gradient transition structure with continuous metallurgical bonding with the brake disc steel substrate. The hard phase and the high-temperature lubricating phase form a nanoscale three-dimensional dense eutectic interlocking network framework structure inside the coating. The iron-based solid solution provides toughness support for the hard phase and the high-temperature lubricating phase.

3. A method for preparing a wear-resistant coating on the surface of a brake disc according to any one of claims 1-2, characterized in that: It is prepared according to the following method: S1: Sodium carboxymethyl cellulose is heated and stirred in deionized water to form a base liquid. Then, polyvinyl alcohol aqueous solution is added to the base liquid and stirring is continued to obtain an aqueous binder. Iron-based alloy powder, titanium powder, boron carbide powder and graphite powder are wet-milled in a ball mill and then vacuum dried. S2: Add the dried mixed powder to the water-based binder and shear and stir it in a vacuum environment using a disperser to obtain the alloy fluid pre-slurry; S3: The working surface of the low alloy steel brake disc is roughened by sandblasting, then ultrasonically cleaned and blown dry. The alloy slurry is coated on the working surface of the brake disc and placed in a blower drying oven for step drying to obtain a solid dried preform layer. S4: Fix the brake disc covered with the preform layer onto the laser equipment, first continuously purge with inert gas and then scan the preform layer with a laser beam, and then cool the brake disc to room temperature to obtain a wear-resistant coating on the surface of the low alloy steel brake disc.

4. The method for preparing a wear-resistant coating on the surface of a brake disc according to claim 3, characterized in that: The mass ratio of the iron-based alloy powder, titanium powder, boron carbide powder and graphite powder in S1 is (70%-92%):(6%-22%):(1.5%-5.0%):(0.5%-3.0%).

5. The method for preparing a wear-resistant coating on the surface of a brake disc according to claim 3, characterized in that: The mass fraction of sodium carboxymethyl cellulose in the base liquid of S1 is 1.5%-3.5%; the wet milling time is 2-6 hours; the vacuum drying temperature is 60-90℃ and the time is 6-12 hours.

6. The method for preparing a wear-resistant coating on the surface of a brake disc according to claim 3, characterized in that: The solid-liquid ratio of the mixed powder and the binder in S2 is (6:1)-(9:1); the shearing and stirring speed is 800-1500 rpm, and the time is 20-60 min.

7. The method for preparing a wear-resistant coating on the surface of a brake disc according to claim 3, characterized in that: The sand used for sandblasting roughening described in S3 is one or more of brown fused alumina sand, white fused alumina sand, and quartz sand.

8. The method for preparing a wear-resistant coating on the surface of a brake disc according to claim 3, characterized in that: The blade gap during coating, as described in S3, is 0.5-1.0 mm; the coating rate is 20-50 mm / s.

9. The method for preparing a wear-resistant coating on the surface of a brake disc according to claim 3, characterized in that: The inert gas is one or more of argon or helium.

10. The method for preparing a wear-resistant coating on the surface of a brake disc according to claim 3, characterized in that: The laser beam power of S4 is 1500-2500W; the scanning speed is 4-8mm / s, and the overlap rate is 40%-55%.

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