A powder metallurgy bushing alloy layer and a method of making the same

Abstract

This invention relates to a powder metallurgy bearing alloy layer and its preparation method, belonging to the field of metal-based nanocomposite materials and advanced powder metallurgy forming technology. The powder metallurgy bearing alloy layer comprises a matrix layer and a surface layer from the inside out. The matrix layer contains 0.01wt%~0.03wt% nickel-plated carbon nanotubes, and the surface layer contains 0.05wt%~0.08wt% nickel-plated carbon nanotubes. The preparation method of the powder metallurgy bearing alloy layer includes the following steps: sequentially depositing matrix layer powder and surface layer powder on a steel backing plate, applying an axial magnetic field, and performing cold isostatic pressing; followed by spark plasma sintering and surface laser remelting to obtain the powder metallurgy bearing alloy layer. This invention, through a carbon nanotube gradient structure and dual interface modification, breaks through the upper limit of fatigue strength of aluminum-based bearings and simultaneously solves the problem of ammonia corrosion.

Description

Technical Field

[0001] This invention belongs to the field of metal-based nanocomposite materials and advanced powder metallurgy forming technology, specifically relating to a powder metallurgy bearing alloy layer and its preparation method. Background Technology

[0002] As a key friction pair component in internal combustion engines, the performance of bearings directly affects the engine's reliability, efficiency, and service life. With the increasing urgency of energy conservation and emission reduction, ammonia-blended fuel engines have gradually gained attention as a new low-carbon power solution. However, the combustion products of ammonia fuel contain nitrogen oxides and unburned ammonia molecules, making the engine lubrication environment more corrosive and complex. This places more stringent requirements on the wear resistance, corrosion resistance, and fatigue strength of bearing materials.

[0003] To address the bearing failure problem of high-horsepower engines (≥400kW) in commercial vehicles under high load (≥75MPa alternating load) and frequent start-stop conditions, existing technologies typically employ aluminum-based or copper-based bearings. Aluminum-based bearings (Al-Si system) are prone to interface delamination and fretting wear (wear rate >0.05mm / 1000 hours) due to their fatigue strength ≤80MPa and thermal fatigue life <3000 hours. While copper-based bearings meet strength requirements, they face the corrosive environment of NH3 / H2O / sulfides generated by the combustion of diesel-ammonia mixed fuels, leading to [Cu(NH3)4] corrosion. 2+ Complexation reaction occurs, corrosion rate > 0.4 mm / a, and lifespan is significantly shortened.

[0004] Currently, there are numerous aluminum-based modification technologies that utilize carbon nanotubes (CNTs) for reinforcement, but the following major technical problems still exist: 1. The conflict between uniform phase distribution and performance: Traditional powder metallurgy processes typically disperse carbon nanotubes uniformly within an aluminum matrix. However, in actual operating conditions, the surface layer of a bearing primarily bears frictional wear, requiring high hardness and good self-lubricating properties; while the matrix primarily bears alternating loads, requiring high toughness to resist fatigue fracture. A uniformly distributed structure cannot simultaneously meet the differentiated performance requirements of high wear resistance in the surface layer and high toughness in the matrix, often resulting in a trade-off between the two. Under high loads, the surface layer may become brittle and spall off, or the matrix may become too soft, leading to plastic deformation.

[0005] 2. Weakened Interfacial Bonding and Formation of Brittle Phases: During high-temperature fabrication, carbon nanotubes readily undergo interfacial reactions with the aluminum matrix, generating a brittle Al4C3 phase. This phase not only weakens the interfacial bonding strength, becoming a crack initiation source, but also easily forms corrosion microcells at the interface under the corrosive environment of ammonia-doped fuels, accelerating material failure. While existing technologies attempt to modify the interface through simple surface nickel plating or the addition of titanium powder, under extreme conditions, single modification methods are insufficient to completely suppress the formation of brittle phases and provide a sufficient interfacial barrier, resulting in inadequate interfacial stability.

[0006] 3. Uncontrollable Reinforcing Phase Orientation Leads to Wasted Performance: Carbon nanotubes exhibit significant anisotropy, and their reinforcement and lubrication effects are best when arranged in a regular pattern. Existing powder metallurgy forming processes (such as conventional molding and hot pressing) struggle to effectively orient carbon nanotubes in solid powders, resulting in a random and disordered distribution of the reinforcing phase within the matrix. This not only fails to fully utilize the low axial friction coefficient of carbon nanotubes but may also lead to mediocre material properties in all directions, preventing the optimization of tribological performance.

[0007] Therefore, there is an urgent need to develop a powder metallurgy bearing alloy layer with excellent fatigue performance, wear resistance, and ammonia corrosion resistance, as well as its preparation method. Summary of the Invention

[0008] In view of the deficiencies in the existing technology, the purpose of this invention is to provide a powder metallurgy bearing alloy layer and its preparation method, so as to solve the technical problem that it is difficult to achieve excellent fatigue performance, wear resistance and ammonia corrosion resistance in the existing aluminum-based modification technology.

[0009] To achieve the above objectives, the first aspect of the present invention provides a powder metallurgy bearing alloy layer, which comprises a substrate layer and a surface layer from the inside out, wherein the content of nickel-plated carbon nanotubes in the substrate layer is 0.01wt%~0.03wt%, and the content of nickel-plated carbon nanotubes in the surface layer is 0.05wt%~0.08wt%.

[0010] In some embodiments, the nickel-plated carbon nanotubes in the substrate layer are randomly distributed, while the nickel-plated carbon nanotubes in the surface layer are oriented circumferentially.

[0011] A second aspect of the present invention provides a method for preparing a powder metallurgy bearing alloy layer as described in the first aspect of the present invention, comprising the following steps: A base layer powder and a surface layer powder are sequentially laid on a steel back plate, an axial magnetic field is applied, and cold isostatic pressing is performed; then, the powder metallurgy bearing alloy layer is obtained by spark plasma sintering and surface laser remelting.

[0012] In some embodiments, the preparation methods of the matrix powder and the surface powder are the same, both including the following steps: Nickel-plated carbon nanotubes and aluminum powder were ball-milled in a solvent for the first time, and then pre-alloyed powder was added for a second ball milling.

[0013] In some embodiments, the first ball milling is performed at a speed of 200-300 rpm for 20-40 min, with a ball-to-material ratio of (3-10):1. The second ball milling process involves a rotation speed of 400-600 rpm and a time of 0.5-1.5 hours.

[0014] In some embodiments, the preparation method of the nickel-plated carbon nanotubes includes the following steps: Carbon nanotubes are placed in a chemical nickel plating solution and stirred and dispersed, then washed and dried to obtain nickel-plated carbon nanotubes. The thickness of the nickel layer in the nickel-plated carbon nanotubes is 50~100nm.

[0015] In some embodiments, the pre-alloyed powder comprises the following components: Sn 5.0wt%~10.0wt% Si 2.0wt%~5.0wt% Cr 0.1wt%~0.5wt% Zr 0.1wt%~0.5wt% TiH2 0.5wt%~0.8wt%; and Al is the margin.

[0016] In some embodiments, the strength of the magnetic field is 1.0~1.5T; the pressure of the cold isostatic pressing is 250~350MPa.

[0017] In some embodiments, the spark plasma sintering process includes the following steps: Under a vacuum of 1~10Pa, the temperature is raised to 500~600℃ at a heating rate of 50~150℃ / min, and sintered for 5~15min under a sintering pressure of 35~50MPa.

[0018] In some embodiments, the laser power of the surface laser remelting process is 1.0~2.0kW, and the scanning speed is 3~8mm / s.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: The powder metallurgy bearing alloy layer provided by this invention achieves a compositional and orientational gradient of nickel-plated carbon nanotubes (CNTs) along the thickness direction of the bearing. In terms of composition, the content of nickel-plated carbon nanotubes decreases from the surface layer to the substrate layer along the bearing thickness direction. Specifically, the content of nickel-plated carbon nanotubes in the surface layer is 0.05wt%~0.08wt%, and the content in the substrate layer is 0.01wt%~0.03wt%, forming a "high-strength surface layer-tough substrate" composite structure to inhibit crack propagation. In terms of orientation, along the bearing thickness direction, the nickel-plated carbon nanotubes in the surface layer are circumferentially oriented to reduce the coefficient of friction, while the nickel-plated carbon nanotubes in the substrate layer are randomly distributed to improve overall toughness.

[0020] The method for preparing the powder metallurgy bearing alloy layer provided by this invention first involves preparing surface powder and matrix powder with different nickel-plated carbon nanotube contents through a staged ball milling process. This allows the nickel-plated carbon nanotubes to be embedded into the surface of aluminum particles through plastic deformation, forming a mechanical interlocking interface. Subsequently, the surface powder and matrix powder are layered and deposited onto a steel backing plate. Under the influence of a magnetic field, cold isostatic pressing and spark plasma sintering are performed, causing the interlayer interfaces to fuse together through diffusion and metallurgical bonding, ultimately forming a gradient structure with composition and orientation along the thickness direction. Finally, surface laser remelting is performed to further improve density.

[0021] Therefore, this invention, through a dual-gradient design of composition and orientation, takes into account both the high load-bearing and wear-resistant properties of the bearing surface and the high toughness and fatigue resistance of the matrix, breaking through the upper limit of fatigue strength of aluminum-based bearings, while solving the problem of ammonia corrosion. It achieves fatigue strength > 100MPa, ammonia environment corrosion rate ≤ 0.015mm / a, and a significant improvement in thermal fatigue life, meeting the durability requirements of diesel-ammonia mixed combustion engines (NH3 content 5wt%~15wt%) under China VI emission standards. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 A schematic diagram of the orientation gradient structure of the powder metallurgy bearing alloy layer provided by the present invention is shown; in the figure, 1-steel back plate; 2-substrate layer; 3-surface layer; the arrow indicates the circumferential direction. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments and accompanying drawings. 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 creative effort are within the scope of protection of the present invention.

[0025] Given the technical challenge of existing aluminum-based modification technologies in achieving optimal fatigue performance, wear resistance, and ammonia corrosion resistance simultaneously, this invention provides a powder metallurgy bearing alloy layer and its preparation method. Through carbon nanotube gradient structure and dual-interface modification, it breaks through the upper limit of fatigue strength of aluminum-based bearings while simultaneously solving the ammonia corrosion problem. This results in fatigue strength >100MPa, ammonia corrosion rate ≤0.015mm / a, and a significant improvement in thermal fatigue life, meeting the durability requirements of diesel-ammonia mixed combustion engines (NH3 content 5wt%~15wt%) under China VI emission standards.

[0026] In a first aspect, embodiments of the present invention provide a powder metallurgy bearing alloy layer, such as... Figure 1 As shown, it comprises a substrate layer 2 and a surface layer 3 disposed on a steel back plate 1 from the inside out. The content of nickel-plated carbon nanotubes in the substrate layer 2 is 0.01wt%~0.03wt%, and the content of nickel-plated carbon nanotubes in the surface layer 3 is 0.05wt%~0.08wt%.

[0027] Whether it is a traditional aluminum-based bearing or a conventional carbon nanotube reinforced composite material, the structure is usually uniformly distributed, which makes it difficult to balance "strength" and "toughness". That is, the performance of the surface layer and the matrix layer must be consistent. Either the surface layer is not hard enough and is easy to wear, or the matrix layer is too brittle and easy to crack.

[0028] The powder metallurgy bearing alloy layer provided by this invention introduces a composition gradient design. Along the thickness direction of the bearing, the content of nickel-plated carbon nanotubes decreases from the surface layer to the substrate layer, forming a "high-strength surface layer-tough substrate" composite structure to inhibit crack propagation.

[0029] In some preferred embodiments, the nickel-plated carbon nanotubes in the substrate layer are randomly distributed, and the nickel-plated carbon nanotubes in the surface layer are oriented circumferentially.

[0030] The powder metallurgy bearing alloy layer provided by this invention also incorporates an orientation gradient design. Along the thickness direction of the bearing, the nickel-plated carbon nanotubes in the surface layer are oriented circumferentially with the assistance of a magnetic field to reduce the coefficient of friction, while the nickel-plated carbon nanotubes in the matrix layer are randomly distributed to improve overall toughness.

[0031] The powder metallurgy bearing alloy layer provided by this invention improves the fatigue strength of the bearing alloy layer through a dual gradient structure design in terms of composition and orientation, while also enhancing its wear resistance and ammonia corrosion resistance.

[0032] Secondly, embodiments of the present invention also provide a method for preparing a powder metallurgy bearing alloy layer as described in the first aspect of the present invention, comprising the following steps: A base layer powder and a surface layer powder are sequentially laid on a steel back plate, an axial magnetic field is applied, and cold isostatic pressing is performed; then, the powder metallurgy bearing alloy layer is obtained by spark plasma sintering and surface laser remelting.

[0033] In the powder metallurgy bearing alloy layer preparation method provided by the present invention, the preparation methods of the substrate powder and the surface powder are the same, both including the following steps: Nickel-plated carbon nanotubes and aluminum powder are ball-milled in a solvent for the first time, then pre-alloyed powder is added and ball-milled a second time. After drying, a matrix layer powder or a surface layer powder is obtained. The content of nickel-plated carbon nanotubes in the matrix layer powder is 0.01wt%~0.03wt%, and the content of nickel-plated carbon nanotubes in the surface layer powder is 0.05wt%~0.08wt%.

[0034] Existing technologies typically employ long-duration, single-stage high-energy ball milling to disperse carbon nanotubes. While this can mix the powder, prolonged impact can easily damage the structure of the carbon nanotubes (Raman ID / IG>1.5), and may even generate a brittle Al4C3 phase, weakening the interfacial bonding.

[0035] This invention employs a staged ball milling process. The first stage involves low-speed ball milling with pre-dispersion in a solvent (surfactant) to reduce van der Waals forces and prevent carbon nanotube entanglement. The second stage involves high-speed ball milling, adding pre-alloyed powder, and cold welding to embed the carbon nanotubes into the surface of aluminum particles through plastic deformation, forming a mechanical interlock. This staged ball milling process not only protects the structure of the carbon nanotubes, preventing structural damage, and ensures dispersibility, but also avoids sintering porosity caused by surfactant residue, and is compatible with powder metallurgy production lines.

[0036] In some specific embodiments, the first ball milling is performed at a speed of 200-300 rpm for 20-40 min, with a ball-to-material ratio of (3-10):1; the second ball milling is performed at a speed of 400-600 rpm for 0.5-1.5 h.

[0037] In some preferred embodiments, the solvent (surfactant) is selected from one or more of hexadecyltrimethylammonium bromide (CTAB), sodium dodecyl sulfate (SDS), sodium dodecylbenzene sulfonate (SDBS), polyethylene glycol octylphenyl ether (Triton X-100), disodium nonylphenol ether sulfosuccinate monoester (HT A-103), and octylphenol polyoxyethylene ether (OP-10).

[0038] In some preferred embodiments, the concentration of the solvent is 0.6~1.0 g / L.

[0039] In some preferred embodiments, the pre-alloyed powder comprises the following components: Sn 5.0wt%~10.0wt% Si 2.0wt%~5.0wt% Cr 0.1wt%~0.5wt% Zr 0.1wt%~0.5wt% TiH2 0.5wt%~0.8wt%; and Al is the margin.

[0040] The pre-alloyed powder used in this invention is prepared by gas atomization and has a particle size of 10~45μm. Limiting this particle size range ensures that the powder has good flowability and filling properties, which is conducive to layering and coating. At the same time, it improves sintering activity, promotes densification and uniform composition, thereby obtaining a high-density, high-performance bearing alloy layer.

[0041] In some preferred embodiments, the aluminum powder is atomized aluminum powder with a particle size of 20~50μm and a purity of ≥99.5%.

[0042] In this invention, the high purity of the aluminum powder results in a low impurity content (<0.5wt%), ensuring the stable performance of the composite material. The aluminum powder particle size of 20-50μm contributes to achieving good green density and sintering activity during pressing and sintering. The atomized powder is mostly spherical or near-spherical, exhibiting good flowability, which facilitates uniform powder coating and filling. Furthermore, the atomized powder diffuses sufficiently during sintering, contributing to higher density.

[0043] In this invention, a staged ball milling process is used to disperse nickel-plated carbon nanotubes, while controlling the rotation speed, time and ball-to-material ratio of each stage of ball milling to improve the dispersion uniformity and structural integrity of the nickel-plated carbon nanotubes and avoid agglomeration and damage.

[0044] In some preferred embodiments, when preparing the matrix powder or surface powder, the amount of nickel-plated carbon nanotubes added is controlled according to the desired content of nickel-plated carbon nanotubes in the matrix or surface layer. For example, when the required content of nickel-plated carbon nanotubes in the surface powder is 0.06 wt%, and the total mass of nickel-plated carbon nanotubes, aluminum powder, and pre-alloyed powder equals the mass of the final surface powder (100 wt%), the amount of nickel-plated carbon nanotubes added is 0.06 wt% of the total mass of these components. Furthermore, the amount of pre-alloyed powder added is 75 wt% to 85 wt% of the total mass of the nickel-plated carbon nanotubes, aluminum powder, and pre-alloyed powder to prevent excessive dilution of effective elements such as Sn and Si in the alloy layer, thus ensuring the wear resistance of the alloy layer. Additionally, the amount of solvent added is sufficient to submerge the solid powder.

[0045] The method for preparing the powder metallurgy bearing alloy layer provided by this invention includes the following steps: Carbon nanotubes are placed in a chemical nickel plating solution and stirred and dispersed, then washed and dried to obtain nickel-plated carbon nanotubes. The thickness of the nickel layer in the nickel-plated carbon nanotubes is 50~100nm.

[0046] In this invention, it is necessary to control the thickness of the nickel layer in the nickel-plated carbon nanotube to be 50~100nm, so as to satisfy the magnetic responsiveness of the carbon nanotube, ensure its wettability with the aluminum substrate, and suppress the harmful phase Al4C3.

[0047] The carbon nanotubes (CNTs) used in this invention are multi-walled carbon nanotubes with an outer diameter of 10~20nm, a length of 5~15μm, and a purity of ≥95%.

[0048] Carbon nanotubes (CNTs) with an outer diameter of 10–20 nm are beneficial for uniform dispersion in aluminum matrices and effectively fill microscopic defects. Their large specific surface area also contributes to good interfacial bonding with the matrix. A length of 5–15 μm gives CNTs a high aspect ratio (length to diameter), which more effectively improves the elastic modulus and yield strength of the composite material. Under stress, CNTs with a high aspect ratio can more effectively transfer loads. Using high-purity CNTs is fundamental to obtaining high-performance, high-reliability composite materials.

[0049] In some preferred embodiments, the electroless nickel plating solution comprises: 20-35 g / L nickel sulfate, 20-45 g / L sodium hypophosphite, and 10-45 g / L sodium citrate, and the pH value of the electroless nickel plating solution is 4.0-5.5.

[0050] In this invention, the nickel-plated carbon nanotubes exhibit ferromagnetism and can align themselves in a magnetic field. Chemical nickel plating of the carbon nanotubes improves their interfacial bonding properties.

[0051] In the method for preparing the powder metallurgy bearing alloy layer provided by the present invention, after obtaining the surface powder and the substrate powder respectively, the substrate powder and the surface powder are sequentially layered and coated on a steel backing plate. The thickness of the substrate powder is 1.5~2.5 mm, and the thickness of the surface powder is 0.3~0.8 mm.

[0052] In this invention, the thickness of the matrix powder and the surface powder is controlled so that the surface layer provides high load-bearing capacity and low friction, while the matrix layer provides overall toughness and prevents fatigue crack propagation.

[0053] In the powder metallurgy bearing alloy layer preparation method provided by the present invention, after the matrix powder and the surface powder are layered and coated, the mold is placed in a cold isostatic press and an axial magnetic field (the direction is consistent with the circumferential direction of the bearing) is applied to perform cold isostatic pressing forming process.

[0054] In some preferred embodiments, the strength of the magnetic field is 1.0~1.5T; the pressure of the cold isostatic pressing is 250~350MPa, and the time is 3~7min.

[0055] In this invention, based on layered deposition, a magnetic field is used to assist pressing. Utilizing the magnetic responsiveness of nickel-plated carbon nanotubes, combined with the shielding effect of the powder layer within the mold on the magnetic field, the surface nickel-plated carbon nanotubes are oriented under magnetic torque, while the substrate nickel-plated carbon nanotubes are randomly distributed. This solves the problem of excessive anisotropy and reduced toughness in the matrix that may result from a uniformly oriented structure throughout the entire thickness. By controlling the pressure and time of cold isostatic pressing, the density and strength of the preform are improved.

[0056] In the powder metallurgy bearing alloy layer preparation method provided by the present invention, spark plasma sintering is performed after cold isostatic pressing.

[0057] In some preferred embodiments, the spark plasma sintering process includes the following steps: Under a vacuum of 1~10Pa, the temperature is raised to 500~600℃ at a heating rate of 50~150℃ / min, and sintered for 5~15min under a sintering pressure of 35~50MPa.

[0058] In this invention, during the spark plasma sintering process, Ti produced from the decomposition of TiH2 reacts with CNTs to form a TiC transition layer, further improving the interfacial bonding performance. By controlling the spark plasma sintering treatment conditions, the density and microstructure of the product are further improved.

[0059] Existing technologies either employ simple "chemical nickel plating" or simple "TiC in-situ reaction" techniques to improve interfacial bonding performance. However, simple nickel plating may result in weak interfacial bonding due to incomplete reaction, while simply adding TiH2 may make it difficult to control the degree of reaction or may not be suitable for powder metallurgy processes.

[0060] In this invention, a dual interfacial modification is achieved using both electroless nickel plating and in-situ TiC reaction. First, a nickel plating layer (50-100 nm) enhances wettability and inhibits Al4C3 formation. Then, during sintering, Ti generated from the decomposition of TiH2 reacts with CNTs to form a TiC transition layer. This dual-layer transition structure of "nickel + TiC" provides a greater improvement in interfacial shear strength (target ≥150 MPa) compared to single modification.

[0061] In the powder metallurgy bearing alloy layer preparation method provided by the present invention, surface laser remelting is performed after spark plasma sintering treatment.

[0062] In some preferred embodiments, the laser power for the surface laser remelting treatment is 1.0~2.0kW, the scanning speed is 3~8mm / s, and the spot diameter is 2~4mm. This treatment is performed under argon protection. Surface laser remelting further refines the surface grains, resulting in a further increase in product density.

[0063] The method for preparing the powder metallurgy bearing alloy layer provided by this invention first involves preparing surface powder and matrix powder with different nickel-plated carbon nanotube contents through a staged ball milling process. This allows the nickel-plated carbon nanotubes to be embedded into the surface of aluminum particles through plastic deformation, forming a mechanical interlocking interface. Subsequently, the surface powder and matrix powder are layered and deposited onto a steel backing plate. Under the influence of a magnetic field, cold isostatic pressing and spark plasma sintering are performed, causing the interlayer interfaces to fuse together through diffusion and metallurgical bonding, ultimately forming a gradient structure with composition and orientation along the thickness direction. Finally, surface laser remelting is performed to further improve the product density.

[0064] Thirdly, embodiments of the present invention also provide an application of the powder metallurgy bearing alloy layer as described in the first aspect of the present invention or the powder metallurgy bearing alloy layer prepared by the method described in the second aspect of the present invention in the connecting rod bearing of a commercial vehicle diesel engine using ammonia-blended fuel.

[0065] This invention, through a dual-gradient design of composition and orientation, balances the high load-bearing and wear-resistant properties of the bearing surface with the high toughness and fatigue resistance of the matrix, breaking through the upper limit of fatigue strength of aluminum-based bearings. At the same time, it solves the problem of ammonia corrosion, achieving fatigue strength >100MPa, ammonia environment corrosion rate ≤0.015mm / a, and a significant improvement in thermal fatigue life, meeting the durability requirements of diesel-ammonia mixed combustion engines (NH3 content 5wt%~15wt%) under China VI emission standards.

[0066] Example The raw materials used in the following examples are as follows: Carbon nanotubes: Multi-walled carbon nanotubes with an outer diameter of 15 nm, a length of 10 μm, and a purity of 98%.

[0067] Aluminum powder: Atomized aluminum powder with a particle size of 30μm and a purity of 99.5%.

[0068] Pre-alloyed powder: Sn 8.0wt%, Si 3.0wt%, Cr 0.3wt%, Zr 0.3wt%, TiH2 0.6wt%, and the balance Al; prepared by gas atomization, with a particle size of 10~45μm.

[0069] Electroless nickel plating solution: nickel sulfate 25g / L, sodium hypophosphite 30g / L, sodium citrate 15g / L, pH=4.5.

[0070] Unless otherwise specified, all raw materials used in the embodiments of the present invention are commercially available, all instruments and equipment used are conventional instruments and equipment in the art, and all operating methods used are conventional methods in the art.

[0071] Example 1 The method for preparing the powder metallurgy bearing alloy layer provided in this embodiment includes the following steps: (1) Electroless nickel plating of CNTs The CNTs were placed in a chemical nickel plating solution and stirred for 30 minutes in a 60°C water bath. After washing and drying, nickel-plated CNTs were obtained with a nickel layer thickness of 70 nm.

[0072] (2) Preparation of surface powder and matrix powder 0.06 g of nickel-plated CNTs and 19.94 g of aluminum powder were added to 150 mL of 0.8 g / L CTAB aqueous solution at a ball-to-particle ratio of 5:1 and ball-milled at 250 rpm for 30 min for pre-dispersion. Then, 80 g of pre-alloyed powder (accounting for 80 wt% of the total mass) was added and ball-milled at 500 rpm for 1 h. After drying, a surface powder with a nickel-plated CNT content of 0.06 wt% was obtained.

[0073] The preparation method of the matrix powder is the same as that of the surface powder. The amount of nickel-plated CNTs added is 0.02g, the amount of aluminum powder added is 19.98g, and the content of nickel-plated CNTs in the matrix powder is 0.02wt%.

[0074] (3) Layered laying Place a 1.5mm thick low-carbon steel backing plate at the bottom of a cylindrical mold with an inner diameter of 120mm. First, lay a 2.0mm thick base layer powder on it, then lay a 0.5mm thick surface layer powder, and level it.

[0075] (4) Magnetic field-assisted cold isostatic pressing process The mold is placed in a cold isostatic press, and an axial magnetic field of 1.2T (in the same direction as the circumferential direction of the bearing) is applied. The mold is held under a pressure of 300MPa for 5 minutes to obtain the blank.

[0076] (5) Spark plasma sintering (SPS) treatment Under a vacuum of 5 Pa, the temperature was increased to 550 °C at a heating rate of 100 °C / min, and the green body was sintered for 10 min under a sintering pressure of 40 MPa.

[0077] (6) Surface laser remelting treatment Under argon protection, with a laser power of 1.5kW, a scanning speed of 5mm / s, and a spot diameter of 3mm, the sintered green body is subjected to surface laser remelting treatment to refine the surface grains to ≤5μm, thereby further improving the product density.

[0078] Example 2 The preparation method of the powder metallurgy bearing alloy layer provided in this embodiment is basically the same as that in Example 1, except that the content of nickel-plated carbon nanotubes in the surface powder and the substrate powder is different. Specifically: (2) Preparation of surface powder and matrix powder 0.08 g of nickel-plated CNTs and 19.92 g of aluminum powder were added to 150 mL of 0.8 g / L CTAB aqueous solution at a ball-to-particle ratio of 5:1 and ball-milled at 250 rpm for 30 min for pre-dispersion. Then, 80 g of pre-alloyed powder (accounting for 80 wt% of the total mass) was added and ball-milled at 500 rpm for 1 h. After drying, a surface powder with a nickel-plated CNT content of 0.08 wt% was obtained.

[0079] The preparation method of the matrix powder is the same as that of the surface powder. The amount of nickel-plated CNTs added is 0.01g, the amount of aluminum powder added is 19.99g, and the content of nickel-plated CNTs in the matrix powder is 0.01wt%.

[0080] Example 3 The preparation method of the powder metallurgy bearing alloy layer provided in this embodiment is basically the same as that in Example 1, except that the thickness of the nickel layer is different in the electroless nickel plating process. Specifically: (1) Electroless nickel plating of CNTs CNTs were placed in a chemical nickel plating solution and stirred for 15 minutes in a 60°C water bath. After washing and drying, nickel-plated CNTs with a nickel layer thickness of 50 nm were obtained.

[0081] Example 4 The preparation method of the powder metallurgy bearing alloy layer provided in this embodiment is basically the same as that in Embodiment 1, except that the rotation speed and time of the two ball milling processes are different in the preparation of the surface powder and the matrix powder. Specifically: (2) Preparation of surface powder and matrix powder 0.06 g of nickel-plated CNTs and 19.94 g of aluminum powder were added to 150 mL of 0.8 g / L CTAB aqueous solution at a ball-to-powder ratio of 5:1 and ball-milled at 200 rpm for 40 min for pre-dispersion. Then, 80 g of pre-alloyed powder (accounting for 80 wt% of the total mass) was added and ball-milled at 400 rpm for 1.5 h. After drying, a surface powder with a nickel-plated CNT content of 0.06 wt% was obtained.

[0082] The preparation method of the matrix powder is the same as that of the surface powder. The amount of nickel-plated CNTs added is 0.02g, the amount of aluminum powder added is 19.98g, and the content of nickel-plated CNTs in the matrix powder is 0.02wt%.

[0083] Example 5 The preparation method of the powder metallurgy bearing alloy layer provided in this embodiment is basically the same as that in Embodiment 1, except that the thickness of each layer is different during the layering process. Specifically: (3) Layered laying Place a 1.5mm thick low-carbon steel backing plate at the bottom of a cylindrical mold with an inner diameter of 120mm. First, lay a 2.5mm thick base layer powder on it, then lay a 0.3mm thick surface layer powder, and level it.

[0084] Example 6 The preparation method of the powder metallurgy bearing alloy layer provided in this embodiment is basically the same as that in Embodiment 1, except that the magnetic field strength, pressing pressure, and holding time are different during the magnetic field-assisted cold isostatic pressing process. Specifically: (4) Magnetic field-assisted cold isostatic pressing process The mold is placed in a cold isostatic press, and an axial magnetic field of 1.0T (with the direction consistent with the circumferential direction of the bearing) is applied. The mold is held under a pressure of 250MPa for 7 minutes to obtain the blank.

[0085] Example 7 The preparation method of the powder metallurgy bearing alloy layer provided in this embodiment is basically the same as that in Example 1, except that the conditions for the spark plasma sintering (SPS) treatment are different. Specifically: (5) Spark plasma sintering (SPS) treatment Under a vacuum of 5 Pa, the temperature was increased to 500 °C at a heating rate of 50 °C / min, and the green body was sintered for 15 min under a sintering pressure of 35 MPa.

[0086] Example 8 The preparation method of the powder metallurgy bearing alloy layer provided in this embodiment is basically the same as that in Example 1, except that the surface laser remelting treatment conditions are different. Specifically: (6) Surface laser remelting treatment Under argon protection, with a laser power of 1.0kW, a scanning speed of 3mm / s, and a spot diameter of 4mm, the sintered green body was subjected to surface laser remelting treatment.

[0087] The performance of the bearing alloy layers prepared in Examples 1-8 was tested. The specific test methods are as follows: 1. Surface CNT orientation factor Test Principle: Based on scanning electron microscope (SEM) images, the orientation of carbon nanotubes (CNTs) in the SEM images is quantitatively analyzed using two-dimensional Fourier transform (2D-FFT) or topological data analysis methods. The orientation factor f value is calculated using the Herman orientation factor formula. The closer the value is to 1, the higher the degree of orientation of CNTs along a specific direction.

[0088] The specific testing steps are as follows: Samples were cut circumferentially from the surface of the bearing alloy layer, and then metallographically prepared and polished. Secondary electron images of the surface cross-section were acquired using field emission scanning electron microscopy (FE-SEM) at magnifications of 5000–50000. Perform a two-dimensional fast Fourier transform (2D-FFT) on the SEM image to convert the spatial domain image into a frequency domain image; The orientation distribution function is determined by integrating the spectral intensity along the azimuth direction. According to the Hermann orientation factor calculation formula: f = (3 cos²θ 1) / 2, where θ is the angle between the major axis of the CNT and the reference direction (circumferential direction of the bearing bush). cos²θ The cosine square mean of all measurements; The orientation factor f value of the surface CNTs was calculated.

[0089] 2. Dynamic load-bearing capacity (fatigue strength) Test standard: Refer to ASTM E466, "Standard Specification for Force-Controlled Axial Fatigue Testing of Metallic Materials".

[0090] Test principle: A high-frequency fatigue testing machine is used to apply an alternating cyclic load controlled by axial force to the specimen, and the maximum stress amplitude at which the material does not fail due to fatigue after a specified number of cycles is determined.

[0091] The specific testing steps are as follows: A smooth axial fatigue specimen was cut from the bearing alloy layer along the circumferential direction. The specimen dimensions were machined according to ASTM E466 standard. The specimen is mounted on a high-frequency fatigue testing machine (test frequency 80~150Hz); In a room temperature air environment, a constant amplitude sinusoidal cyclic load is applied using a force control mode, with a stress ratio R=0.1; Set the target loop base to 1×10 7 The fatigue strength was determined using either the lifting method or the group method. Record the sample at 1×10 7 The maximum stress amplitude that prevents fracture under multiple cycles is the fatigue strength (MPa) of the material.

[0092] 3. Coefficient of friction Test standard: Refer to ASTM G99, "Standard method for testing sliding wear and friction of pin-disc or ball-disc assemblies".

[0093] Test principle: The pin-disc friction and wear tester is used, with the bearing alloy layer sample as the disc sample and the bearing steel ball or pin as the grinding object, to determine the coefficient of friction under boundary lubrication conditions.

[0094] The specific testing steps are as follows: A disc sample with a size of not less than Φ30mm×5mm was cut from the surface of the bearing alloy layer and the surface was polished to a roughness Ra≤0.8μm; The sample was mounted on the rotating platform of the friction and wear testing machine, and Φ6mm GCr15 bearing steel balls were selected for the abrasive. Install the test specimen to ensure that the perpendicularity error between the pin and the disc is ≤1°; The calibrated load was 10N, and the sliding speed was set to 0.1m / s; The test was started, and the cumulative sliding distance was 1000m; During the test, friction force data was continuously recorded by a friction force sensor (sampling frequency ≥ 200Hz). The friction coefficient μ = friction force F / normal load P, and the average value during the steady-state phase is taken as the final result.

[0095] 4. Density Test standard: Refer to ASTM B311, "Standard test method for density of powder metallurgy materials with porosity less than 2%".

[0096] Test principle: The Archimedes displacement method (water displacement method) is used. The actual density of the sample is calculated by measuring the mass of the sample in air and water, and then compared with the theoretical density to calculate the density.

[0097] The specific testing steps are as follows: Take a sample of the sintered bearing alloy layer, remove surface oil, and dry it in a vacuum drying oven. Weigh the sample in air, m1, on an analytical balance (accuracy 0.1 mg); Suspend the sample in deionized water (water temperature 20±2℃), remove surface air bubbles, and weigh the sample in water as m2. Calculate the actual density: ρ_actual = m1 × ρ_water / (m1) m2), where ρ_water is the density of water at the test temperature; Calculate the theoretical density ρ_theoretical based on the mass fraction of each component and its theoretical density; Packing density (%) = (ρ_actual / ρ_theoretical) × 100%.

[0098] 5. Corrosion rate in ammonia environments Test standard: Refer to ASTM G31, "Standard Guide for Laboratory Immersion Corrosion Testing of Metallic Materials".

[0099] Test principle: The static plate mass loss method is used to expose the sample to a simulated ammonia-blended fuel engine corrosion environment. The corrosion rate is calculated by measuring the mass loss of the sample before and after exposure.

[0100] The specific testing steps are as follows: A 20mm×20mm×3mm sample was cut from the bearing alloy layer and the surface was ground to Ra≤0.8μm; Clean the sample according to ASTM G1 standard, dry it, and weigh the initial mass m0 (accuracy 0.1 mg). The sample was suspended and immersed in a simulated corrosion solution: a mixed solution containing 10% NH3·H2O and 90% deionized water; Test conditions: Temperature 80±1℃ (constant temperature water bath), continuous exposure time 500h; After the test, the sample was removed, the corrosion products were removed according to ASTM G1 standard, and after cleaning and drying, the mass m1 after corrosion was measured. The corrosion rate CR was calculated to be 8.76 × 10⁻⁶. 4 ×(m0 m1) / (A×T×D), where CR is the corrosion rate (mm / a) and A is the sample surface area (cm²). 2 T is the exposure time (h), and D is the material density (g / cm³). 3 ).

[0101] 6. Thermal fatigue life Test standard: Refer to GB / T 19055 "Test Methods for Reliability of Automobile Engines".

[0102] The bearing bushes are assembled on a multi-cylinder diesel engine test bench according to actual engine requirements. Through the actual operation of the engine, the alternating mechanical loads, thermal cycles and frequent start-stop impacts that the bearing bushes will experience during service are simulated to evaluate the bearing bushes' resistance to fatigue, delamination and fretting wear under simulated real working conditions.

[0103] Record bearing temperature, oil pressure, and vibration signals in real time. If obvious high-frequency impact pulses appear in the vibration signal (indicating oil film rupture between the bearing and journal or increased fretting wear), an alarm will be triggered and the machine will be stopped for inspection.

[0104] Every 500 hours of operation, the machine is stopped and the bearing shells are disassembled for visual inspection (observing whether there are signs of delamination and peeling at the interface between the alloy layer and the steel backing, and whether there are micro-wear marks on the working surface of the bearing shells). If everything is normal after the inspection, the machine is reassembled and the test continues.

[0105] Final disassembly and inspection: After a cumulative operation of 9200 hours, the bearing shell was disassembled.

[0106] Interface delamination inspection: Use a stereomicroscope (10~50x) or ultrasonic scanning microscope (SAM) to observe the interface between the alloy layer and the steel backing to confirm whether there is interface peeling, opening or obvious transverse cracks. Fretting wear inspection: Use a surface profilometer to measure the wear depth on the working surface of the bearing (especially near the bearing mating surface) and calculate the wear rate. If the wear depth is ≤5μm and there is no obvious adhesion transfer or abrasive scratches on the surface, it is judged as "no fretting wear".

[0107] Result determination: If no engine power reduction, abnormal noise or bearing seizure occurs due to bearing failure during 9200 hours of continuous operation, and the final disassembly and inspection confirms no interface delamination or fretting wear, then the bearing is deemed to have qualified thermal fatigue life.

[0108] See Table 1 for specific test results.

[0109] Table 1

[0110] As shown in Table 1, the powder metallurgy bearing alloy layers prepared in Examples 1-8 of this invention are significantly superior to traditional aluminum-based bearings and traditional copper-based bearings in terms of fatigue strength, friction coefficient, density, corrosion resistance and thermal fatigue life.

[0111] Therefore, this invention, through a dual-gradient design of composition and orientation, takes into account both the high load-bearing and wear-resistant properties of the bearing surface and the high toughness and fatigue resistance of the matrix, breaking through the upper limit of fatigue strength of aluminum-based bearings, while solving the problem of ammonia corrosion. It achieves fatigue strength >100MPa, corrosion rate ≤0.015mm / a, and a significant improvement in thermal fatigue life, meeting the durability requirements of diesel-ammonia mixed combustion (NH3 content 5wt%~15wt%) engines under China VI emission standards.

[0112] In the description of this specification, the references to terms such as "one embodiment / mode," "some embodiments / modes," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment / mode or example is included in at least one embodiment / mode or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment / mode or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments / modes or examples. Furthermore, without contradiction, those skilled in the art can combine and integrate the different embodiments / modes or examples described in this specification, as well as the features of different embodiments / modes or examples.

[0113] It should be noted that in this application, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element. In this application, "a plurality of" means at least two, such as two, three, etc., unless otherwise expressly specified.

[0114] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A powder metallurgy bushing alloy layer characterized by, It comprises a substrate layer and a surface layer from the inside out, wherein the content of nickel-plated carbon nanotubes in the substrate layer is 0.01wt%~0.03wt%, and the content of nickel-plated carbon nanotubes in the surface layer is 0.05wt%~0.08wt%.

2. The powder metallurgy bushing alloy layer of claim 1, wherein, The nickel-plated carbon nanotubes in the substrate layer are randomly distributed, while the nickel-plated carbon nanotubes in the surface layer are oriented circumferentially.

3. A method of producing a layer of a powder metallurgical bearing alloy according to claim 1 or 2, characterized in that Includes the following steps: A base layer powder and a surface layer powder are sequentially laid on a steel back plate, an axial magnetic field is applied, and cold isostatic pressing is performed; then, the powder metallurgy bearing alloy layer is obtained by spark plasma sintering and surface laser remelting.

4. The method of claim 3, wherein the powder metallurgy bearing alloy layer is prepared by a method comprising: The preparation methods for the matrix powder and the surface powder are the same, both including the following steps: ​ Nickel-plated carbon nanotubes and aluminum powder were ball-milled in a solvent for the first time, and then pre-alloyed powder was added for a second ball milling.

5. The method of claim 4, wherein the powder metallurgy bearing alloy layer is prepared by a process comprising: The first ball milling operation was performed at a speed of 200-300 rpm for 20-40 minutes, with a ball-to-material ratio of (3-10):

1. The second ball milling process involves a rotation speed of 400-600 rpm and a time of 0.5-1.5 h.

6. The method of claim 4, wherein the powder metallurgy bearing alloy layer is prepared by a process comprising: The preparation method of the nickel-plated carbon nanotubes includes the following steps: Carbon nanotubes are placed in a chemical nickel plating solution and stirred and dispersed, then washed and dried to obtain nickel-plated carbon nanotubes. The thickness of the nickel layer in the nickel-plated carbon nanotubes is 50~100nm.

7. The method of claim 4, wherein the powder metallurgy bearing alloy layer is prepared by a process comprising: The pre-alloyed powder comprises the following components: Sn 5.0wt%~10.0wt% Si 2.0wt%~5.0wt% Cr 0.1wt%~0.5wt% Zr 0.1wt%~0.5wt% TiH2 0.5wt%~0.8wt%; and The remaining amount of Al.

8. The method for preparing the powder metallurgy bearing alloy layer according to claim 3, characterized in that, The strength of the magnetic field is 1.0~1.5T; the pressure of the cold isostatic pressing is 250~350MPa.

9. The method for preparing the powder metallurgy bearing alloy layer according to claim 3, characterized in that, The spark plasma sintering process includes the following steps: Under a vacuum of 1~10Pa, the temperature is raised to 500~600℃ at a heating rate of 50~150℃ / min, and sintered for 5~15min under a sintering pressure of 35~50MPa.

10. The method of claim 3 wherein the powder metallurgy bearing alloy layer is prepared by the steps of: The laser power for the surface laser remelting process is 1.0~2.0kW, and the scanning speed is 3~8mm / s.

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