High-speed laser cladding metal ceramic coating, cast iron brake disc and preparation method and application of cast iron brake disc

Abstract

The invention provides a high-speed laser cladding metal ceramic coating, a cast iron brake disc and a preparation method and application of the cast iron brake disc. The high-speed laser cladding metal ceramic coating comprises the following preparation raw materials in percentage by mass: 40%-60% of stainless steel, 10%-20% of SiC, 10%-30% of ZrO2, 5%-10% of Ti and 1%-2% of CeO2. According to the coating, the hardness, the wear resistance, the friction coefficient and the toughness of a cast iron matrix can be remarkably improved, and the braking requirement of a motor vehicle under the extreme working condition can be well met. The invention further provides the cast iron brake disc and a preparation method and application thereof.

Description

Technical Field

[0001] This application relates to the field of metal-ceramic coating technology, specifically to a high-speed laser cladding metal-ceramic coating, a cast iron brake disc, its preparation method, and its application. Background Technology

[0002] Currently, brake discs made of gray cast iron are widely used in passenger and commercial vehicles due to their advantages such as low cost, good thermal conductivity, excellent wear resistance, and self-lubricating properties. However, with the rapid development of electric vehicles, the inherent performance defects of gray cast iron brake discs have gradually become apparent, especially under extreme operating conditions, where their performance is insufficient to meet the high braking requirements of modern vehicles.

[0003] Specifically, gray cast iron brake discs have the following main problems: (1) Under continuous or frequent braking conditions, the brake disc temperature rises rapidly, and the friction coefficient of ordinary cast iron continues to decrease under high temperature friction, which can easily lead to brake failure; (2) Under emergency braking conditions, abrasive wear mainly occurs between the brake disc and the brake pad, which leads to rapid wear of parts and shortens the life of the brake disc; (3) Gray cast iron has poor corrosion resistance, the brake disc is prone to rust, and dust is generated during braking, which cannot meet the National VII emission standards.

[0004] To address these issues, current research primarily focuses on modifying the surface properties of brake disc materials to improve their overall performance while maintaining the advantages of the gray cast iron matrix. Currently, the most common type of coating on the market is a metal-ceramic coating with titanium carbide (TiC) as the hard phase. However, when the temperature exceeds 800℃, TiC is prone to oxidation in atmospheric conditions (TiC + 2O2 → TiO2 + CO2). This reaction intensifies above 1000℃, resulting in TiO2 with a rutile structure and strong oxygen diffusion capabilities. Furthermore, the significant difference in thermal expansion coefficients between TiO2 and TiC easily leads to voids, cracks, and localized spalling within the coating, making it difficult to meet the comprehensive requirements of safety, reliability, and long lifespan for brake discs under high-load vehicles and high-speed emergency braking conditions.

[0005] Therefore, there is an urgent need to develop a new type of coating material that can maintain excellent thermal and frictional stability in high-temperature environments to meet braking requirements under extreme conditions. Summary of the Invention

[0006] This application provides a high-speed laser cladding metal-ceramic coating that significantly improves the hardness, wear resistance, coefficient of friction, and toughness of the cast iron substrate, meeting the braking requirements of high-load vehicles or extreme conditions such as emergency braking.

[0007] This application also provides a cast iron brake disc.

[0008] This application also provides a method for preparing the cast iron brake disc.

[0009] This application also provides the application of the high-speed laser cladding metal-ceramic coating or the cast iron brake disc.

[0010] A first aspect of the present invention relates to a high-speed laser cladding metal-ceramic coating, comprising the following raw materials by mass percentage: Stainless steel 40%~60%, SiC 10%~20%, ZrO2 10%~30%, Ti5%~10%, CeO2 1%~2%.

[0011] The high-speed laser cladding metal-ceramic coating according to the first aspect of the present invention has at least the following beneficial effects: The high-speed laser cladding metal-ceramic coating of this invention achieves in-situ composite of the metal matrix and the ceramic reinforcing phase under the ultra-high temperature and rapid solidification molten pool conditions formed by laser cladding through the synergistic ratio design of stainless steel, SiC, ZrO2, Ti and CeO2, which significantly improves the braking performance under high temperature and high load conditions.

[0012] Stainless steel, as the metallic matrix phase in the coating, can fully mix with the gray cast iron base material and other components during laser cladding to form a continuous and stable metallic phase. On the one hand, stainless steel imparts good impact toughness and corrosion resistance to the coating, making it less prone to brittle cracking under high-temperature braking and alternating load conditions. On the other hand, it is not a hard phase-forming element, and can form a buffer zone with moderate hardness between hard ceramic phases, preventing the overall coating from becoming brittle. While maintaining the reliability of the coating structure, a coating thickness of more than 1 mm can be achieved. By controlling the stainless steel content within the range of 40% to 60%, problems such as decreased coating hardness due to excessive content or increased cracking and difficulty in achieving thick coatings due to insufficient content can be avoided.

[0013] Under the high-temperature conditions of laser cladding (usually using an inert gas as a protective atmosphere, with argon being the preferred and more economical option), when the molten pool temperature exceeds 2850℃, SiC undergoes a decomposition reaction (SiC→Si+C). Most of the Si escapes in gaseous form, while a small amount remains in the molten pool as atoms or incompletely decomposed particles. The carbon atoms produced by decomposition react in situ with ZrO2 within the molten pool (ZrO2+3C→ZrC+2CO), generating a fine and uniformly distributed ZrC ceramic phase, achieving in-situ synthesis of hard particles. The trace amounts of undecomposed SiC coexist with the generated ZrC in the same system, forming a dense composite structure; the remaining atomic Si is mainly distributed at grain boundaries, effectively bonding and bridging the various phases.

[0014] If the SiC content is too high, the proportion of brittle phases in the system increases, which can easily lead to overall embrittlement of the coating and significantly increase the risk of cracking. If the ZrO2 content is too high, its particle morphology is difficult to be effectively controlled and transformed in the molten pool, which can easily weaken the strengthening effect of the ceramic phase; if the ZrO2 content is too low, the TiC hard phase will be mainly generated.

[0015] The addition of rare earth oxide CeO2 enhances grain boundary stability. Even a small amount of residual Si forming SiO2 at high temperatures significantly increases coating brittleness. CeO2 reacts with SiO2 to form stable rare earth silicates, purifying grain boundaries, reducing grain boundary defects and the formation of brittle phases, and further improving the overall density, crack resistance, and long-term service stability of the coating. Controlling the CeO2 content within the range of 1% to 2% effectively strengthens the grain boundaries while avoiding excessive introduction that could become a crack initiation point.

[0016] Compared to traditional wear-resistant coatings with TiC as the main reinforcing phase, this invention significantly improves the thermal stability of the coating in high-temperature atmospheric environments by generating ZrC in situ as the main hard reinforcing phase. In atmospheric conditions below 1000℃, the ZrO2 formed by the reaction of ZrC with oxygen (2ZrC + 3O2 → 2ZrO2 + 2CO) has a dense fluorite structure. Its ability to block oxygen diffusion is significantly stronger than that of rutile TiO2 formed after TiC oxidation. This mechanistically inhibits the inward diffusion of oxygen and the occurrence of continuous oxidation reactions, thus avoiding the voids, cracks, and peeling problems common in traditional TiC coatings. This results in higher safety and reliability of the coating under high-load braking conditions.

[0017] When using ZrC as a hard-particle reinforcing phase, simply adding ZrC particles requires the addition of a metal binder. This binder softens or melts at high temperatures, causing the hard particles to lose their reinforcing effect. Therefore, this invention generates ZrC through in-situ reaction in a molten pool, forming chemical bonds between the components, which significantly improves bonding strength, structural stability, and impact strength.

[0018] Ti plays multiple roles in the system: 1) Ti can form a solid solution with Fe and, together with elements such as Ni and Cr, strengthens the iron-based structure through solid solution, improving the overall strength of the coating; 2) Ti can form intermetallic compounds with Fe, further improving the mechanical properties of the coating; 3) In the molten pool, Ti wets ZrC and SiC, enhancing the bonding strength between hard particles and the metal matrix and reducing stress concentration at the interface of the hard phase. In a molten pool environment exceeding 2800℃, the Zr–Ti–C coexistence system preferentially forms ZrC, while simultaneously forming a small amount of Zr-rich (Ti, Zr)C solid solution, enabling the ceramic phase to maintain high hardness while possessing better interfacial compatibility and crack resistance. If the Ti content is too high, a TiC hard phase is easily formed; if the content is too low, the coating becomes brittle.

[0019] Based on the aforementioned component design and in-situ reaction mechanism, a cermet coating can be formed on the surface of cast iron using laser cladding. The laser beam possesses extremely high energy density, enabling the formation of a high-temperature molten pool in a very short time, fully completing the in-situ generation of the ceramic phase and densification of the microstructure. Simultaneously, the heat-affected zone is minimal, effectively preventing thermal deformation and decarburization of the gray cast iron matrix. Combined with the high-linear-velocity cladding characteristics, a uniform and firmly bonded coating structure can be obtained while ensuring processing efficiency.

[0020] During actual braking, the coefficient of friction of this metal-ceramic coating slowly increases with the number of braking cycles and temperature rise, exhibiting a distinct red-hard characteristic. It demonstrates excellent wear resistance at high temperatures, with minimal wear when rubbing against the brake pads. The wear mechanism shifts from abrasive wear to adhesive wear, and braking dust generation under emergency braking conditions is negligible. Furthermore, the coating showed no rust after 20 days of neutral salt spray testing, exhibiting excellent corrosion resistance. This allows the brake disc to maintain stable braking performance even after long-term parking, solving the problem of dust generation during braking caused by rust on cast iron brake discs. This fully meets the safety, reliability, and environmental protection requirements for braking under high-load vehicles or emergency braking conditions.

[0021] According to some embodiments of the present invention, the SiC is in the α-crystal form, which decomposes more completely at high temperatures.

[0022] According to some embodiments of the present invention, the mass percentage of SiC is 15% to 20%.

[0023] According to some embodiments of the present invention, the stainless steel is selected from at least one of 304 stainless steel, 304L stainless steel, 316 stainless steel, or 316L stainless steel. Among them, 304L is the cheapest and has the lowest oxygen content; 304 stainless steel has an austenitic structure and high impact toughness.

[0024] According to some embodiments of the present invention, the stainless steel has a mass percentage of 45% to 50%.

[0025] According to some embodiments of the present invention, the ZrO2 has a mass percentage of 20% to 30%, more specifically 22% to 28%.

[0026] According to some embodiments of the present invention, the mass percentage of Ti is 6% to 8%.

[0027] According to some embodiments of the present invention, the stainless steel, SiC, ZrO2, Ti and CeO2 are all powders with a particle size of not less than 320 mesh.

[0028] A second aspect of the present invention relates to a cast iron brake disc, comprising a cast iron substrate and a metal-ceramic coating loaded on the surface of the cast iron substrate, wherein the metal-ceramic coating is prepared by a high-speed laser cladding process from the raw materials for preparing the high-speed laser cladding metal-ceramic coating.

[0029] According to some embodiments of the present invention, the thickness of the metal-ceramic coating is 0.5~1.8 mm, more specifically 0.8~1.6 mm, and even more specifically 1~1.5 mm.

[0030] According to some embodiments of the present invention, the cast iron matrix is ​​a gray cast iron matrix.

[0031] A third aspect of the present invention relates to a method for preparing the cast iron brake disc, comprising the following steps: The raw materials for preparing the high-speed laser cladding metal-ceramic coating are slurried, granulated, and made into a mixed powder; The metal-ceramic coating is formed on the surface of the cast iron substrate using the mixed powder through a high-speed laser cladding process.

[0032] Specifically, the raw materials can be pre-granulated, dried, and sieved by mixing powder with water to form a slurry, ready for use. This method ensures the uniformity and particle size of the powder, facilitating subsequent laser cladding processing.

[0033] Under laser cladding conditions, the formation time of the molten pool is extremely short, but the temperature is very high. By controlling the reaction conditions, the desired phase (such as ZrC) can be effectively formed based on the thermodynamic stability and crystallographic properties of the material, thereby ensuring the hardness, wear resistance, and thermal stability of the coating.

[0034] According to some embodiments of the present invention, the particle size of the mixed powder is 100-300 mesh, more specifically 100-270 mesh.

[0035] According to some embodiments of the present invention, the granulation is carried out by centrifugal spray drying.

[0036] According to some embodiments of the present invention, the high-speed laser cladding process satisfies at least one of the following conditions: (1) The powder feeding rate is 70~160g / min, further 70~120g / min, and even further 70~100g / min; (2) The linear velocity is 50~150mm / s, further to 60~100mm / s, and even further to 70~100mm / s; (3) The step size is 1.2~2.2mm, and further 1.2~1.5mm; (4) The power is 3~6kW, and further 4~5.5kW.

[0037] Excessive powder feed can hinder powder melting and potentially cause coating flaking; insufficient powder feed results in low deposition efficiency and a thin, difficult-to-thicken coating. Excessive linear velocity limits the molten pool temperature, potentially leading to a thin coating and discontinuous melt flow; insufficient linear velocity necessitates a lower powder feed, resulting in low efficiency. Excessive step size leads to a thin coating with high dilution, reducing coating hardness; insufficient step size requires sufficient overlap to maintain coating continuity, otherwise the coating may become brittle. By appropriately matching laser power and powder feed, cladding efficiency can be improved while ensuring coating performance.

[0038] The fourth aspect of the present invention relates to the application of the high-speed laser cladding metal-ceramic coating, or the cast iron brake disc, or the cast iron brake disc prepared by the preparation method, in the manufacture of vehicles.

[0039] According to some embodiments of the present invention, the vehicle includes a passenger car or a commercial vehicle.

[0040] Specifically, the passenger vehicles include sedans, SUVs, and MPVs; the commercial vehicles include buses, trucks, or special-purpose vehicles, wherein the buses include vans and public buses, and the trucks include light trucks, medium trucks, heavy trucks, and trailer trucks. Special-purpose vehicles refer to vehicles equipped with special devices or structures for performing specific operational tasks, in addition to general passenger and cargo transport purposes. These typically include engineering and municipal operation vehicles (such as sweeping and watering vehicles, road maintenance vehicles), crane and aerial work platforms, rescue and emergency vehicles, hazardous materials and special-purpose transport vehicles (such as oil tankers and refrigerated trucks), and special-purpose support vehicles such as police and security vehicles. Vehicles can be new energy vehicles (including hybrid or pure electric vehicles) or fuel-powered vehicles.

[0041] The terms “above,” “below,” and “not less than” all include the numerical value itself.

[0042] "Room temperature" refers to 23±2℃.

[0043] In this article, the numerical ranges mentioned all include the endpoint values ​​and cover any subranges within that range, such as the ranges obtained by arbitrarily combining the specifically listed numerical values. Attached Figure Description

[0044] Figure 1 This is the microstructure of the coating in Example 4 of the present invention.

[0045] Figure 2 This shows the interface bonding between the coating and the base material in Embodiment 6 of the present invention. Detailed Implementation

[0046] The following are specific embodiments of the present invention, and the technical solutions of the present invention will be further described in conjunction with the embodiments, but the present invention is not limited to these embodiments.

[0047] Unless otherwise specified in the examples, the procedures should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0048] Examples 1-6 and Comparative Examples 1-8 Take the corresponding powder (all with a particle size of -320 mesh) according to the formula shown in Table 1, add water to make a slurry, centrifuge and spray dry it, and pass it through a 100-mesh sieve to make a mixed powder with a particle size of no less than 100 mesh. The mixed powder was used to form a coating on gray cast iron base material using a high-speed laser cladding process, which was carried out under an argon protective atmosphere. The process parameters for high-speed laser cladding are shown in Table 2.

[0049] Table 1

[0050] In Table 1, WC-Co8 refers to an alloy powder composed of tungsten carbide and 8 wt% cobalt, with a particle size range mainly of 10~50 μm; TiC has a particle size range mainly of 5~50 μm; and Ni60 has a particle size range mainly of 10~50 μm.

[0051] Table 2

[0052] In Table 2, the coating thickness refers to the newly added coating thickness on the surface of the base material after laser cladding, excluding the metallurgical bonding interface layer formed with the base material.

[0053] The test results of each embodiment and comparative example are shown in Table 2. Among them, comparative examples 3, 5 and 6 were not tested because the coating cracked during the preparation process.

[0054] The wear test instrument was the Zhongke Kaihua GF-1 high-speed reciprocating friction and wear tester. The wear material was a ceramic ball with a diameter of 4mm. The load was 50kg, the motor frequency was 300Hz, the friction radius was 5mm, the test temperature was 600℃, and the test time was 30min.

[0055] Impact performance testing method: The coating surface is manually struck with a 19mm diameter cutting tip by the same tester at maximum force until cracks appear in the coating. The number of impacts is recorded. Because the coating has good toughness, it is difficult to assess differences in the coating under conventional testing conditions. Therefore, a destructive testing method is used to more effectively reflect the relative toughness of the coating.

[0056] Based on the above results, the coating material in the embodiments can effectively balance hardness and toughness, exhibiting low wear at 600℃ and a friction coefficient that is not significantly different from that at room temperature, thus ensuring efficient braking performance and better meeting the braking requirements under extreme conditions. Furthermore, the coating in the embodiments showed no rust after 20 days of neutral salt spray testing, demonstrating excellent corrosion resistance and fully meeting the braking requirements for safety, reliability, and environmental protection under high-load vehicles or emergency braking conditions.

[0057] A comparison of the results from Examples 1-6 shows that when the proportion of 304 stainless steel is higher and the proportion of hard phase is lower, the coating has better toughness but relatively lower hardness, leading to increased wear. A comparison between Comparative Example 1 and Example 4 shows that the lack of cerium oxide significantly reduces toughness and increases wear. Comparative Examples 2-8 show that adding other hard phase powders makes the coating too hard and brittle, significantly increasing wear and even causing cracking.

[0058] Figure 1 The image shows the microstructure of the coating in Example 4. It can be seen that the hard phase in the coating of Example 4 is fine and uniformly dispersed, resulting in a dense microstructure. Figure 2 The figure shows the interface bonding between the coating and the base material in Example 6. The thickness D1 indicated in the figure is the characteristic thickness of the coating material, which is 2.35 mm. The actual coating thickness is increased by 1.6 mm, indicating that a penetration layer is formed and a tight metallurgical bonding interface is formed between the coating and the base material.

[0059] The present invention has been described in detail above with reference to the embodiments. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A high velocity laser cladded cermet coating, characterized in that, The preparation raw materials include the following by mass percentage: stainless steel 40%~60%, SiC 10%~20%, ZrO2 10%~30%, Ti 5%~10%, CeO2 1%~2%.

2. The high velocity laser cladded cermet coating according to claim 1, characterized in that, The SiC is in alpha crystal form; and / or, the mass percentage of the SiC is 15%~20%; and / or, the stainless steel is selected from at least one of 304 stainless steel, 304L stainless steel, 316 stainless steel or 316L stainless steel; and / or, the mass percentage of the stainless steel is 45%~50%.

3. The high velocity laser cladded cermet coating of claim 1, wherein, The mass percentage of the ZrO2 is 20%~30%; and / or, the mass percentage of the Ti is 6%~8%.

4. The high velocity laser cladded cermet coating of claim 1, wherein, The stainless steel, SiC, ZrO2, Ti and CeO2 all use powders with particle size not coarser than 320 mesh.

5. A cast iron brake disc characterised in that, The cast iron base body and the cermet coating loaded on the surface of the cast iron base body, the cermet coating is prepared from the preparation raw materials of the high-speed laser cladding cermet coating according to any one of claims 1-4 by high-speed laser cladding process.

6. The cast iron brake disc according to claim 5, characterized in that The thickness of the cermet coating is 0.5~1.8mm; and / or, the cast iron base body is gray cast iron base body.

7. The method of producing a cast iron brake disc according to claim 5 or 6, characterized in that, The method includes the following steps: Slurry the preparation raw materials of the high-speed laser cladding cermet coating, granulate, and make mixed powders; Use the mixed powders to form the cermet coating on the surface of the cast iron base body by high-speed laser cladding process.

8. The preparation method according to claim 7, characterized in that, The particle size of the mixed powders is 100~300 mesh; and / or, the granulation uses centrifugal spray drying.

9. The preparation method according to claim 7, characterized in that, The high-speed laser cladding process meets at least one of the following conditions: (1) powder feeding amount is 70~160g / min; (2) linear velocity is 50~150mm / s; (3) step distance is 1.2~2.2mm; (4) power is 3~6kW.

10. The use of the high-speed laser cladding cermet coating according to any one of claims 1-4, or the cast iron brake disc according to claim 5 or 6, or the cast iron brake disc prepared by the method according to any one of claims 7-9 in the preparation of a vehicle; optionally, the vehicle includes a passenger car or a commercial vehicle.

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