Method for preparing gradient transition layer connected to powder metallurgy guillotine pads using cold spraying technology

Abstract

This invention relates to the field of powder metallurgy thimble fabrication technology, specifically to a method for preparing a gradient transition layer connecting powder metallurgy thimbles using cold spraying technology. The method includes: setting powder supply ratio adjustment parameters for a dual-channel powder supply system; setting spraying parameters for the spray gun; using the powder supply ratio adjustment parameters and the spraying parameters, sequentially depositing powders of different composition ratios onto the substrate surface to form a gradient layer with a continuous transition from a metal-bonded phase to a ceramic-reinforcing phase; and welding the substrate with the gradient layer to the powder metallurgy thimble to obtain the finished thimble. This invention, by adjusting the dual-channel powder supply ratio and spraying parameters, can precisely control the composition distribution and thickness of the gradient layer, ensuring gradient continuity and controllable performance transition, achieving a high-strength connection between the powder metallurgy thimble and the substrate, and extending the thimble's service life.

Description

Technical Field

[0001] This invention relates to the field of powder metallurgy thimble fabrication technology, specifically to a method for preparing a gradient transition layer connected to a powder metallurgy thimble using cold spraying technology. Background Technology

[0002] Powder metallurgy brake pads are widely used in high-speed railways, rail transit, and industrial braking systems due to their excellent wear resistance, superior thermal shock performance, and high frictional stability, making them ideal for high-speed operation and high-frequency braking environments. Powder metallurgy brake pads typically consist of a metallic bonding phase and a ceramic reinforcing phase, forming a dense and uniform composite material structure through powder metallurgy processes. This allows them to maintain good frictional performance and structural integrity even under high temperature and high stress loads. However, in practical applications, when powder metallurgy brake pads are directly bonded to the metal matrix, stress concentration and microcracks easily occur at the interface. Especially under high temperature, strong friction, or impact loads, interface delamination and localized damage become more prominent, leading to a decrease in the overall service life of the brake pad.

[0003] Traditional connection methods mainly include welding and bonding. During welding, excessively high temperatures may cause local melting or grain coarsening of the internal structure of the powder metallurgy brake pads. Although the interface bonding is strong, it is difficult to form a gradient structure. The bonding method has limited bonding strength and cannot meet the load requirements under high-speed operation. Especially under high temperature and high impact conditions, these traditional methods are difficult to balance interface bonding strength and gradient performance at the same time, causing the brake pads to experience performance degradation or failure during long-term use. Summary of the Invention

[0004] (a) Purpose of the invention The purpose of this invention is to provide a method for preparing a gradient transition layer connected to a powder metallurgy thimble using cold spraying technology. By adjusting the dual-path powder supply ratio and spraying parameters, the composition distribution and thickness of the gradient layer can be precisely controlled, achieving a change of 2-20 vol% in the volume fraction of the metal bonding phase per 100 μm. This ensures the continuity of the gradient and the controllability of the performance transition, realizing a high-strength connection between the powder metallurgy thimble and the substrate, and extending the service life of the thimble.

[0005] (II) Technical Solution To address the above problems, this invention provides a method for preparing a gradient transition layer connecting powder metallurgy gate plates using cold spraying technology, comprising: The powder supply ratio adjustment parameters of the dual powder supply channels are set, wherein the dual powder supply channels respectively transport metal-bound phase powder and ceramic-reinforced phase powder; Set the spraying parameters of the spray gun, including the jet pressure, spraying gas temperature and spray gun movement speed, and the spray gun is connected to a dual powder supply channel; Using the powder supply ratio adjustment parameters and spraying parameters, powders with different component ratios are sequentially deposited on the substrate surface to form a gradient layer that continuously transitions from the metal-bonded phase to the ceramic-reinforcing phase. The substrate forming the gradient layer is welded to the powder metallurgy gate piece to obtain the finished gate piece; The gradient layer has a metal-bound phase volume fraction that varies by 2 to 20 vol% per 100 μm in the thickness direction, and the volume proportion of the metal-bound phase powder on the side of the gradient layer closest to the powder metallurgy gate is greater than 50%.

[0006] In another aspect, preferably, the invention further includes: sandblasting and degreasing the substrate surface before spraying to obtain an active surface with a surface roughness Ra of 3 to 8 μm.

[0007] In another aspect of the present invention, preferably, a mixing chamber is provided in front of the dual-path powder supply channel and the spray gun for gas-solid mixing of the metal-bonded phase powder and the ceramic-reinforcing phase powder before spraying.

[0008] In another aspect of the present invention, preferably, the mixing chamber has a length of 50 to 150 mm and an inner diameter of 1.2 to 2 times the diameter of the spray gun.

[0009] In another aspect of the present invention, preferably, the metal bonding phase powder is copper, iron, nickel or an alloy of the present invention, and the ceramic reinforcing phase powder is Al2O3, SiC or TiC powder. The particle size range of the metal-bonded phase powder and the ceramic-reinforced phase powder is 10–60 μm.

[0010] In another aspect of the present invention, preferably, the powder supply ratio adjustment parameter changes linearly or piecewise linearly during the spraying process, and the volume fraction ratio of the metal bonding phase to the ceramic reinforcing phase is between 1:9 and 9:1.

[0011] In another aspect of the present invention, preferably, the jet pressure is 1.5 to 3.5 MPa, the spray gas temperature is 200 to 600°C, and the spray gun moving speed is 200 to 600 mm / s.

[0012] In another aspect of the present invention, preferably, the spraying gas is nitrogen, helium, or a mixture thereof.

[0013] In another aspect of the present invention, preferably, the thickness of the gradient layer is 0.1 to 1.0 mm.

[0014] In another aspect of the present invention, preferably, the welding is vacuum diffusion welding or hot-press diffusion welding, the welding temperature is 400-600°C, and the holding time is 10-60 min.

[0015] (III) Beneficial Effects The above-described technical solution of the present invention has the following beneficial technical effects: This invention achieves a high-strength bond between powder metallurgy brake pads and the substrate by employing cold spraying technology to prepare a gradient layer with a continuous transition between the metal bonding phase and the ceramic reinforcing phase on the surface of a metal substrate. By adjusting the dual-path powder supply ratio and spraying parameters, the composition distribution and thickness of the gradient layer can be precisely controlled, achieving a 2-20 vol% variation in the volume fraction of the metal bonding phase per 100 μm, ensuring gradient continuity and controllable performance transition. Compared to traditional welding processes, this avoids problems such as high-temperature melting, grain coarsening, or interface delamination, enabling solid-state deposition and metallurgical bonding of particles at low temperatures, maintaining the original microstructure and properties of the powder metallurgy brake pads. Furthermore, the cold spraying process is flexible and can be programmed to deposit different material systems and complex geometries, adapting to the high-stress, high-thermal-shock operating environments of high-speed railways and industrial braking systems, thereby significantly extending the service life of the brake pads and improving the reliability and safety of the braking system. Attached Figure Description

[0016] Figure 1 This is an overall flowchart of one embodiment of the present invention. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments and the accompanying drawings. It should be understood that these descriptions are merely exemplary and not intended to limit the scope of the invention. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0018] Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0019] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0020] The invention will now be described in more detail with reference to the accompanying drawings. In the various drawings, the same elements are indicated by similar reference numerals. For clarity, the various parts in the drawings are not drawn to scale.

[0021] Example A method for preparing gradient transition layer-connected powder metallurgy guillotine plates using cold spraying technology. Figure 1 An overall flowchart of one embodiment of the present invention is shown, as follows: Figure 1 As shown, it includes: A powder supply ratio adjustment parameter is set for a dual-channel powder supply system, whereby the dual channels respectively supply metal-bound phase powder and ceramic-reinforcing phase powder. The powder supply ratio adjustment parameter can be precisely controlled according to the required compositional distribution of the gradient layer, achieving a continuous transition between the metal and ceramic phase powders. This step ensures that powders of different compositions are mixed and deposited in a predetermined ratio during spraying, thereby forming a compositionally controllable gradient structure. In this embodiment, the powder supply ratio adjustment parameter changes linearly or piecewise linearly during spraying, with the volume fraction ratio of the metal-bound phase to the ceramic-reinforcing phase ranging from 1:9 to 9:1. For example, along the thickness direction of the gradient layer, the volume fraction of the metal-bound phase powder gradually increases from its initial value, while the volume fraction of the ceramic-reinforcing phase powder gradually decreases accordingly, achieving a smooth compositional transition. Specifically, the volume fraction ratio of the metal bonding phase to the ceramic reinforcing phase powder can be in the range of 1:9 to 9:1, and can be 1:9, 2:8, 3:7, 4:6, 5:5, 6:4, 7:3, 8:2, or 9:1, etc. Linear variations can be 1:9–9:1, 2:8–8:2, 3:7–7:3, or 4:6–4:6, etc. The volume proportion of the metal bonding phase powder on the side of the gradient layer closest to the powder metallurgy gate is greater than 50%, which enables the formation of a more continuous metal phase network on the side close to the powder metallurgy gate, thereby improving the bonding ability between the gradient layer and the powder metallurgy gate and reducing the risk of brittle failure at the interface due to excessive ceramic phase. The region with a higher metal phase content has good plasticity and toughness, while the region with a higher ceramic reinforcing phase content provides high hardness and wear resistance, thus achieving optimized matching of interface properties, reducing the risk of residual stress concentration and cracking at the interface caused by differences in thermal expansion coefficients and abrupt changes in elastic modulus, and improving connection strength and service life. The powder supply ratio adjustment method in this embodiment not only creates a gradient layer with a smooth composition transition in the thickness direction, but also allows for the determination of the distribution of metal and ceramic components according to actual working conditions, thus achieving a gradient structure with adjustable performance.

[0022] Furthermore, in this embodiment, the metal-binding phase powder is copper, iron, nickel, or their alloy powder, and the ceramic reinforcing phase powder is Al2O3, SiC, or TiC powder. The particle size range of the metal-binding phase powder and the ceramic reinforcing phase powder is 10–60 μm, specifically 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, or 60 μm. Copper powder has good thermal conductivity and plasticity, iron powder has certain strength and hardness, and nickel powder and its alloy powder can balance corrosion resistance and high-temperature performance. The ceramic reinforcing phase powder can be selected from Al2O3, SiC, or TiC powder, wherein Al2O3 powder has high hardness and wear resistance, SiC powder has excellent thermal shock resistance and wear resistance, while TiC powder has both hardness and high-temperature stability, which can significantly improve the wear resistance and heat resistance of the gradient layer. The particle size range can balance the powder flowability, deposition efficiency, and adhesion performance during the spraying process. Smaller particle sizes, around 10 μm, can improve the uniformity of powder filling and interfacial bonding during spraying, while larger particle sizes, around 60 μm, can increase the deposition rate and mechanical strength of the gradient layer, while reducing the risk of excessive powder vaporization or decomposition during spraying. By using the above powder types and particle size ranges, combined with the proportional adjustment method of dual-channel powder supply, a smooth transition between the metallic phase and the ceramic reinforcing phase can be achieved in the gradient layer, enabling the gradient layer to possess toughness, strength, and wear resistance in the thickness direction.

[0023] The spraying parameters of the spray gun are set, including jet pressure, spray gas temperature, and spray gun movement speed. The spray gun is connected to a dual-channel powder supply system. The spraying parameters can be optimized based on the morphology, density, and required deposition rate of the powder particles to ensure that the powder gains sufficient kinetic energy and adheres to the substrate surface during high-speed spraying, while avoiding powder melting or decomposition. During spraying, the spray gun moves along a predetermined path and speed, causing powders of different compositions to be deposited layer by layer on the substrate surface, forming a gradient layer in the thickness direction where the metal-bonded phase continuously transitions to the ceramic reinforcing phase. In this embodiment, the jet pressure is 1.5–3.5 MPa, specifically 1.5 MPa, 2.0 MPa, 2.5 MPa, 3.0 MPa, or 3.5 MPa; the spray gas temperature is 200–600°C, specifically 200°C, 300°C, 400°C, 500°C, or 600°C; and the spray gun moving speed is 200–600 mm / s, specifically 200 mm / s, 300 mm / s, 400 mm / s, 500 mm / s, or 600 mm / s. The spray gas is nitrogen, helium, or a mixture thereof. This ensures that the powder gains sufficient kinetic energy during high-speed spraying, stably adhering to the substrate surface, while preventing the melting of metal powder or the decomposition of ceramic powder, thus ensuring the density and continuity of the gradient layer.

[0024] A mixing chamber is provided in front of the dual-path powder supply channel and the spray gun to perform gas-solid mixing of the metal-bound phase powder and the ceramic-reinforcing phase powder before spraying. The length of the mixing chamber is 50-150 mm, specifically 50 mm, 70 mm, 90 mm, 110 mm, 130 mm, or 150 mm, etc., and the inner diameter is 1.2-2 times the diameter of the spray gun, specifically 1.2 times, 1.4 times, 1.6 times, 1.8 times, or 2 times, etc. The mixing chamber ensures that the two powders form a uniformly mixed powder flow before entering the spray gun nozzle, thereby improving the compositional uniformity and deposition stability of the gradient layer. The length of the mixing chamber within the above-mentioned structural dimensions provides sufficient mixing time while ensuring smooth powder flow, so that the powder maintains a stable proportional distribution during spraying and avoids powder separation or agglomeration.

[0025] Before spraying, the substrate surface is roughened by sandblasting and degreased. Sandblasting creates a micro-uneven structure on the substrate surface, significantly increasing surface roughness and enhancing the mechanical bonding force of the powder during spraying. Degreasing removes surface grease, dust, and other impurities, resulting in a clean surface that improves powder adhesion and gradient layer bonding strength. A surface roughness Ra of 3–8 μm is obtained, specifically 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, or 8 μm. This ensures uniform powder deposition while avoiding localized stress concentration or deposition defects caused by excessive surface roughness.

[0026] Using the powder supply ratio adjustment parameters and spraying parameters, powders with different composition ratios are sequentially deposited on the substrate surface to form a gradient layer with a continuous transition from the metal-bonded phase to the ceramic reinforcing phase. The thickness of the gradient layer is 0.1–1.0 mm, specifically 0.1 mm, 0.2 mm, 0.4 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, or 1.0 mm. By linearly or piecewise linearly controlling the powder supply ratio and optimizing the settings of the spray gun movement speed, jet pressure, and spray gas temperature, a continuous transition from the metal-bonded phase to the ceramic reinforcing phase can be achieved in the thickness direction, resulting in a smooth and uniform composition distribution in the gradient layer and avoiding abrupt interface changes or local compositional inhomogeneities. The thickness can be combined with the gradient composition distribution, allowing areas with a higher metal-bonded phase content to provide good toughness and thermal shock resistance, while areas with a higher ceramic reinforcing phase content provide excellent hardness and wear resistance, thereby achieving functional optimization of the gradient layer.

[0027] The substrate forming the gradient layer is welded to the powder metallurgy thimble to obtain the finished thimble. The welding is performed using vacuum diffusion welding or hot-press diffusion welding at a temperature of 400–600℃ (specifically 400℃, 450℃, 500℃, 550℃, or 600℃), with a holding time of 10–60 min (specifically 10 min, 20 min, 30 min, 40 min, 50 min, or 60 min). This ensures sufficient interfacial diffusion and bonding between the metallic bonding phase and the ceramic reinforcing phase, while avoiding excessively high temperatures that could adversely affect the microstructure of the gradient layer and the performance of the powder metallurgy thimble. Appropriate pressure is applied during welding, controlled within the range of 5–20 MPa (specifically 5 MPa, 8 MPa, 10 MPa, 12 MPa, 14 MPa, 16 MPa, 18 MPa, or 20 MPa), and pressure is held during the temperature holding phase to ensure sufficient interfacial contact and atomic diffusion, thereby obtaining a dense and robust bonding interface.

[0028] The gradient layer varies in volume fraction of metal bonding phase by 2 to 20 vol% per 100 μm in the thickness direction, specifically 2 vol%, 4 vol%, 8 vol%, 12 vol%, 15 vol%, 18 vol%, or 20 vol%. This effectively alleviates the difference in thermal expansion coefficients and stress concentration between the matrix and the powder metallurgy gate, and improves the interfacial bonding strength and the thermal shock resistance of the overall structure.

[0029] This embodiment utilizes cold spraying technology to prepare a gradient layer with a continuous transition between the metal bonding phase and the ceramic reinforcing phase on the surface of a metal substrate, achieving a high-strength bond between the powder metallurgy brake pad and the substrate. By adjusting the dual-path powder supply ratio and spraying parameters, the composition distribution and thickness of the gradient layer can be precisely controlled, achieving a 2-20 vol% variation in the volume fraction of the metal bonding phase per 100 μm, ensuring the continuity of the gradient and the controllability of the performance transition. Compared to traditional welding processes, this avoids problems such as high-temperature melting, grain coarsening, or interface delamination, enabling solid-state deposition and metallurgical bonding of particles at low temperatures, maintaining the original microstructure and properties of the powder metallurgy brake pad. Furthermore, the cold spraying process is flexible and can be programmed to deposit different material systems and complex geometries, adapting to the high-stress, high-thermal-shock operating environments of high-speed railways and industrial braking systems, thereby significantly extending the service life of the brake pad and improving the reliability and safety of the braking system.

[0030] Example 1 The substrate surface was roughened by sandblasting and degreased to achieve a surface roughness Ra=3μm. Dual powder supply channels transported copper powder (10μm particle size) and Al2O3 powder (10μm particle size) respectively. The mixing chamber was 50mm long with an inner diameter 1.2 times the spray gun diameter. Spraying parameters were: jet pressure 1.5MPa, spray gas temperature 200℃, spray gun movement speed 200mm / s, and nitrogen as the spray gas. The volume fraction ratio of the metal bonding phase to the ceramic reinforcing phase linearly varied from 4:6 to 6:4, with a gradient layer thickness of 0.1mm. Vacuum diffusion welding was performed at 400℃ for 10min, with a variation of 20 vol per 100μm.

[0031] Example 2 The substrate surface was roughened by sandblasting and degreased, with a Ra=5μm. Dual powder supply channels provided iron powder (30μm particle size) and SiC powder (30μm particle size). The mixing chamber was 100mm long, with an inner diameter 1.5 times the spray gun diameter. Spraying parameters were: jet pressure 2.5MPa, spray gas temperature 400℃, spray gun movement speed 400mm / s, and a nitrogen-helium mixture. The volume fraction ratio of the metal bonding phase to the ceramic reinforcing phase changed linearly from 3:7 to 7:3, with a gradient layer thickness of 0.5mm. Hot-press diffusion welding was performed at 500℃ for 30min, with a variation of 8 vol per 100μm.

[0032] Example 3 The substrate surface was roughened by sandblasting and degreased, with a Ra=8μm. Dual powder supply channels provided nickel powder (60μm particle size) and TiC powder (60μm particle size). The mixing chamber was 150mm long, with an inner diameter twice the spray gun diameter. Spraying parameters included a jet pressure of 3.5MPa, a spray gas temperature of 600℃, a spray gun movement speed of 600mm / s, and helium as the spray gas. The volume fraction ratio of the metal bonding phase to the ceramic reinforcing phase linearly changed from 1:9 to 9:1, with a gradient layer thickness of 1.0mm. Vacuum diffusion welding was performed at 600℃ for 60min. The change was 8 vol% per 100μm.

[0033] Example 4 The substrate surface was roughened by sandblasting and degreased, with a Ra=4μm. Dual powder supply channels provided copper powder (20μm particle size) and SiC powder (50μm particle size). The mixing chamber was 75mm long, with an inner diameter 1.5 times the spray gun diameter. Spraying parameters included a jet pressure of 3.0MPa, a spray gas temperature of 500℃, a spray gun movement speed of 300mm / s, and nitrogen as the spray gas. The volume fraction ratio of the metal bonding phase to the ceramic reinforcing phase changed linearly from 2:8 to 8:2, with a gradient layer thickness of 1.0mm. Hot-press diffusion welding was performed at 550℃ for 40min, with a variation of 6 vol per 100μm.

[0034] Example 5 The substrate surface was roughened by sandblasting and degreased, with a Ra=6μm. Dual powder supply channels provided iron powder (15μm particle size) and Al2O3 powder (25μm particle size). The mixing chamber was 125mm long, with an inner diameter 1.8 times the spray gun diameter. Spraying parameters included a jet pressure of 2.0MPa, a spray gas temperature of 300℃, a spray gun movement speed of 500mm / s, and a nitrogen-helium mixture. The volume fraction ratio of the metal bonding phase to the ceramic reinforcing phase linearly changed from 4:6 to 6:4, with a gradient layer thickness of 1.0mm. Vacuum diffusion welding was performed at 450℃ for 20 minutes. The thickness varied by 2 vol% per 100μm.

[0035] Comparative Example 1 The volume fraction ratio of the metal bonding phase to the ceramic reinforcing phase remains constant at 5:5 in the thickness direction, without forming a gradient distribution structure, and the bonding layer thickness is 1.0 mm. The spray gun parameters are: jet pressure 2.0 MPa, spray gas temperature 300℃, spray gun moving speed 500 mm / s, and the spray gas is a mixture of nitrogen and helium.

[0036] Comparative Example 2 The difference from Example 3 is that the volume fraction ratio of the metal-bonded phase to the ceramic reinforcing phase changes linearly from 8:2 to 2:8. Other parameters include substrate surface roughening by sandblasting, degreasing and cleaning, and Ra=8μm. Dual powder supply channels are used: nickel powder (60μm particle size) and TiC powder (60μm particle size). The mixing chamber length is 150mm, and the inner diameter is twice the spray gun diameter. Spraying parameters include a jet pressure of 3.5MPa, a spray gas temperature of 600℃, a spray gun movement speed of 600mm / s, and a gradient layer thickness of 1.0mm. Vacuum diffusion welding is performed at 600℃ for 60min. The variation is 8 vol% per 100μm.

[0037] Comparative Example 3 The difference from Example 3 is that the gradient layer thickness varies by 40 vol% per 100 μm, and the remaining parameters are as follows: the substrate surface is roughened by sandblasting, degreased and cleaned, and Ra=8 μm. Dual powder supply channels are used, one for nickel powder (60 μm particle size) and the other for TiC powder (60 μm particle size). The mixing chamber is 150 mm long, with an inner diameter twice the diameter of the spray gun. The spraying parameters are: jet pressure 3.5 MPa, spraying gas temperature 600 °C, spray gun movement speed 600 mm / s, and helium as the spraying gas. The volume fraction ratio of the metal bonding phase to the ceramic reinforcing phase changes linearly from 1:9 to 9:1. Vacuum diffusion welding is used at 600 °C for 60 min.

[0038] Table 1 shows the performance parameters of Examples 1-5 and Comparative Examples 1-3. The interfacial bonding strength was obtained by shear bonding strength test; the impact life was the number of cycles before the sample developed interfacial cracks or peeled off under high temperature, strong friction and impact load cycles.

[0039] As shown in Table 1, the interfacial bonding strength is significantly improved and the impact life is significantly extended as the volume fraction of the metal bonding phase in the gradient layer approaches the size of the powder metallurgy gate.

[0040] Table 1 Performance parameters of Examples 1-5 and Comparative Examples This invention effectively alleviates the stress concentration problem caused by the mismatch of the interfacial thermal expansion coefficients by constructing a continuous gradient transition structure of the metal bonding phase / ceramic reinforcing phase between the powder metallurgy gate and the ceramic reinforcing layer, thereby significantly improving the interfacial bonding performance and thermal shock stability.

[0041] The interfacial bonding strength of Examples 1-5 reached 110-142 MPa, significantly higher than the 85 MPa of Comparative Example 1 without a gradient structure, indicating that the gradient transition layer can enhance the metallurgical bonding ability of the interface and improve the load transfer stability. Among them, Example 3 formed a large-range continuous gradient distribution of 1:9 to 9:1, with the highest interfacial bonding strength reaching 142 MPa, indicating that the wider gradient range and the synergistic effect of high-temperature diffusion welding are conducive to the formation of a denser and more stable interfacial structure. The impact life of Examples 1-5 reached 800-1100 cycles, all superior to the 720 cycles of Comparative Example 1, indicating that the gradient structure can effectively disperse the thermal stress generated during thermal cycling and reduce the risk of interfacial crack initiation and propagation. Among them, Example 3 had an impact life of 1100 cycles, demonstrating the significant improvement in thermal fatigue resistance due to the large-range continuous gradient distribution.

[0042] In Comparative Example 2, the volume fraction ratio of the metal bonding phase to the ceramic reinforcing phase changed from 8:2 to 2:8, indicating a higher ceramic content near the powder metallurgy gate plate. This led to increased interfacial brittleness, resulting in a decrease in interfacial bonding strength to 76 MPa and an impact life of 680 cycles. This demonstrates that an improper gradient direction weakens the interfacial buffering effect. In Comparative Example 3, the gradient changed by 40 vol% per 100 μm, which was too steep, causing abrupt changes in local composition. Stress concentration still easily formed at the interface, resulting in an interfacial bonding strength of 120 MPa and an impact life of 962 cycles, both lower than in Example 3 where the gradient change was gentler. This shows that controlling the gradient change rate is beneficial for forming a more stable stress transition region, thereby further improving interfacial performance.

[0043] In summary, this embodiment achieves simultaneous improvement in interfacial bonding strength and impact life by controlling the gradient distribution direction, gradient change rate, and diffusion welding process parameters of the metal bonding phase and the ceramic reinforcing phase, exhibiting excellent interfacial stability and long-term service performance.

[0044] It should be understood that the specific embodiments described above are merely illustrative or explanatory of the principles of the invention and do not constitute a limitation thereof. Therefore, any modifications, equivalent substitutions, improvements, etc., made without departing from the spirit and scope of the invention should be included within the protection scope of the invention. Furthermore, the appended claims are intended to cover all variations and modifications falling within the scope and boundaries of the appended claims, or equivalent forms of such scope and boundaries.

[0045] The present invention has been described above with reference to embodiments thereof. However, these embodiments are merely illustrative and not intended to limit the scope of the invention. The scope of the invention is defined by the appended claims and their equivalents. Various substitutions and modifications can be made by those skilled in the art without departing from the scope of the invention, and all such substitutions and modifications should fall within the scope of the invention.

[0046] Although embodiments of the present invention have been described in detail, it should be understood that various changes, substitutions, and modifications can be made to the embodiments of the present invention without departing from the spirit and scope of the invention.

[0047] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for producing a gradient transition layer for connecting a powder metallurgical brake pad by cold spraying, characterized in that include: The powder supply ratio adjustment parameters of the dual powder supply channels are set, wherein the dual powder supply channels respectively transport metal-bound phase powder and ceramic-reinforced phase powder; Set the spraying parameters of the spray gun, including the jet pressure, spraying gas temperature and spray gun movement speed, and the spray gun is connected to a dual powder supply channel; Using the powder supply ratio adjustment parameters and spraying parameters, powders with different component ratios are sequentially deposited on the substrate surface to form a gradient layer that continuously transitions from the metal-bonded phase to the ceramic-reinforcing phase. The substrate forming the gradient layer is welded to the powder metallurgy gate piece to obtain the finished gate piece; The gradient layer has a metal-bound phase volume fraction that varies by 2-20 vol% per 100 μm in the thickness direction, and the volume proportion of the metal-bound phase powder on the side of the gradient layer closest to the powder metallurgy gate is greater than 50%. The dual-path powder supply channel and the mixing chamber in front of the spray gun are used to perform gas-solid mixing of metal-bonded phase powder and ceramic-reinforced phase powder before spraying. The mixing chamber has a length of 50-150 mm and an inner diameter of 1.2-2 times the diameter of the spray gun. It also includes: sandblasting and degreasing cleaning of the substrate surface before spraying to obtain an active surface with a surface roughness Ra of 3 to 8 μm; The metal bonding phase powder is copper, iron, nickel or their alloy powder, and the ceramic reinforcing phase powder is Al2O3, SiC or TiC powder; The particle size range of the metal-bonded phase powder and the ceramic-reinforced phase powder is 10–60 μm; The powder supply ratio adjustment parameter changes linearly or piecewise linearly during the spraying process, and the volume fraction ratio of the metal bonding phase to the ceramic reinforcing phase is between 1:9 and 9:

1. The jet pressure is 1.5–3.5 MPa, the spray gas temperature is 200–600°C, and the spray gun moving speed is 200–600 mm / s; The thickness of the gradient layer is 0.1 to 1.0 mm.

2. The method for preparing gradient transition layer connected powder metallurgy gate plates using cold spraying technology according to claim 1, characterized in that, The spraying gas is nitrogen, helium, or a mixture thereof.

3. The method for preparing gradient transition layer connected powder metallurgy gate plates using cold spraying technology according to claim 1, characterized in that, The welding is vacuum diffusion welding or hot-press diffusion welding, with a welding temperature of 400-600℃ and a holding time of 10-60 minutes.

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