A surface composite layer of a powder metallurgical component and a method for producing and using it

Abstract

This invention belongs to the field of surface engineering of metallic materials and powder metallurgy technology, specifically relating to a surface composite layer for powder metallurgy components, its preparation method, and its application. The preparation method of the surface composite layer includes the following steps: uniformly mixing a base metal powder, pressing it into shape to obtain a powder metallurgy preform blank; mixing a reinforcing phase material, a binder, a dispersant, and an organic carrier to prepare a composite reinforcing slurry; coating the composite reinforcing slurry onto the surface area of ​​the preform blank requiring reinforcement; and heat-treating the coated preform blank to obtain the surface composite layer for the powder metallurgy component. The base metal powder includes iron-based, nickel-based, or cobalt-based alloy powders. The powder metallurgy component surface reinforcing layer prepared in this application combines the high hardness and high wear resistance of the reinforcing phase with the toughness and corrosion resistance of the metallic binder phase, making it suitable for surface reinforcement of large, heavy-duty, and complex-shaped powder metallurgy components with extremely high requirements for reliability and durability.

Description

Technical Field

[0001] This invention belongs to the field of surface engineering of metallic materials and powder metallurgy technology, specifically relating to a composite layer on the surface of powder metallurgy components, its preparation method and application. Background Technology

[0002] The manufacturing and surface strengthening of large and complex metal components (such as heavy machinery gears, hydroelectric blades, and aerospace structural parts) face severe challenges. Powder metallurgy technology has become an important choice for manufacturing such components due to its advantages such as near-net-shape forming, high material utilization, and ability to produce complex parts. However, conventional powder metallurgy parts usually have residual porosity, and their surface hardness, wear resistance, and corrosion resistance are often insufficient to meet the requirements of extreme working conditions. Therefore, surface strengthening treatment of powder metallurgy parts is necessary.

[0003] In the prior art, patent application CN114523111A discloses a method for surface strengthening of copper-based powder metallurgy components using arc remelting. The specific steps are as follows: preparing alloy powder; preparing powder metallurgy components; performing arc remelting on the surface of the powder metallurgy components; performing solution treatment and aging heat treatment on the remelted components; and surface treatment. Patent application CN113828779A discloses a laser repair method for surface defects of high-entropy alloys prepared by powder metallurgy. The specific method is as follows: grinding the high-entropy alloy sample and performing pretreatment by cleaning and drying; placing the pretreated high-entropy alloy sample on a sample stage and pre-supplying argon gas using a coaxial gas delivery method; irradiating the surface of the high-entropy alloy using a continuous laser; and repairing the surface defects of the powder metallurgy high-entropy alloy by adjusting the laser process parameters.

[0004] Surface strengthening technologies, such as thermal spraying, electroplating, and laser cladding, are typically applied after the component has been fully densified. The coatings formed by these methods are mostly mechanically bonded to the substrate or have limited metallurgical bonding, resulting in a distinct interface. Under high contact stress, thermal cycling, or corrosive media, the interface easily becomes a source of crack initiation and propagation, leading to coating peeling and failure. Furthermore, abrupt performance changes at the interface can easily cause stress concentration. Current technologies lack the ability to organically integrate surface coating technology with the densification process of powder metallurgy, utilizing the thermal conditions during densification to drive the directional migration of the strengthening phase into the porous matrix, thereby constructing a gradient functional material on the surface. Therefore, developing a method that can be seamlessly integrated with the powder metallurgy process to form a wear-resistant and corrosion-resistant layer on the component surface with strong metallurgical bonding, no sharp interfaces, and a gradient performance transition is of great significance for improving the service reliability and lifespan of large powder metallurgy components. Summary of the Invention

[0005] To address the aforementioned deficiencies or improvement needs of existing technologies, this application provides a method for preparing a high-performance wear-resistant and corrosion-resistant gradient functional layer on the surface of powder metallurgy (PM) components. Specifically, this invention utilizes the inherent controllable pores of the powder metallurgy preform as penetration channels, allowing the surface-pre-coated reinforcing composite material to in-situ melt-infiltrate into the matrix during the final densification process, thereby forming a surface composite layer with metallurgical bonding and a continuous transition in composition and properties.

[0006] Specifically, this is achieved through the following technical solutions: In a first aspect, this application provides a method for preparing a gradient composite layer on the surface of a powder metallurgy component based on in-situ melting infiltration, comprising the following steps: S1. Preparation of porous preform: The matrix metal powder is uniformly mixed and pressed into shape to obtain a powder metallurgy preform blank; Furthermore, the matrix metal powder includes iron-based, nickel-based, or cobalt-based alloy powder; Furthermore, the pressing pressure is 200~500 MPa; Furthermore, the relative density of the preform blank is 70%~90%; Furthermore, the porosity of the preform blank is 10%~30%, providing channels for subsequent melting and infiltration.

[0007] S2. Preparation and coating of composite reinforcing slurry: The reinforcing phase material, binder, dispersant and organic carrier are mixed to form a slurry; the slurry is coated on the surface area of ​​the preform blank that needs to be reinforced; Further, based on the mass percentage of the total slurry mass, the slurry comprises the following components: 2-15 wt% reinforcing phase material, 20-60 wt% binder, and 2-5 wt% dispersant, with the balance being an organic carrier; Furthermore, the slurry also contains 1-5 wt% of an organic temporary binder, which is selected from at least one of polyvinyl butyral (PVB), ethyl cellulose or acrylic resin, and is used to fix the slurry composition before melting and infiltration. The lower limit of the reinforcing phase is not less than 2% to ensure the formation of a continuous reinforcing network, which significantly improves performance. The upper limit is not more than 15%, which is limited by the stability and coatability of the slurry. If the content is too high, it will easily lead to excessive slurry viscosity, particle agglomeration, uneven coating, and blockage of pore channels during melting and infiltration. The lower limit of the binder should not be less than 20% to ensure that a sufficient liquid phase is formed to fully wet and carry the reinforcing phase, achieving effective penetration and bonding. The upper limit should not be more than 60% to avoid excessive liquid phase leading to surface buildup or composition deviation from the design, while also considering economic efficiency.

[0008] A dispersant range of 2-5 wt% is a common and effective addition amount to ensure uniform dispersion of nano / micro-scale reinforcing phases (such as graphene) in the slurry and prevent sedimentation.

[0009] Furthermore, the reinforcing phase material is selected from one or more of graphene, carbon nanotubes, and ceramic particles, and the ceramic particles are selected from at least one of silicon carbide, boron carbide, tungsten carbide, or boron nitride. Furthermore, the binder is a metal powder selected from at least one of chromium, manganese, nickel, copper or cobalt, and the melting point or eutectic point of the binder is lower than the sintering temperature of the base metal powder; Furthermore, the eutectic point is the eutectic point where a low-melting-point eutectic phase is formed at the interface between the binder and the matrix. In this case, the eutectic point of the binder is required to be lower than the sintering temperature of the matrix metal powder.

[0010] Further, the dispersant is selected from at least one of polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), polyethylene glycol (PEG), sodium polyacrylate, sodium dodecyl sulfate (SDS), or hexadecyltrimethylammonium bromide (CTAB); Furthermore, the organic carrier is selected from at least one of ethanol, terpineol, ethylene glycol, propylene glycol, butyl carbitol (ethylene glycol butyl ether), or terpineol; Furthermore, the prepared slurry is mixed and dispersed by ball milling; Furthermore, the coating method is selected from one of spraying, brushing, or dipping.

[0011] S3. In-situ melting and synchronous densification: The coated preform blank is heat-treated to obtain a densified component, which is a powder metallurgy component with a surface composite layer. Furthermore, the heat treatment temperature is 50-200°C higher than the melting point or eutectic point of the binder and lower than the solidus temperature of the base metal powder; it needs to be able to melt the binder or form a eutectic liquid phase while keeping the base metal powder solid. Furthermore, the heat treatment method is sintering or hot isostatic pressing, and the heat treatment is carried out under a protective atmosphere or vacuum. Furthermore, the hot isostatic pressing is performed at a pressure range of 50~150 MPa, with a holding time of 1~4 hours.

[0012] Furthermore, in step S3, under the combined action of capillary force, gravity and external pressure, the molten binder carries the reinforcing phase to penetrate into the porous preform, while the matrix powder particles undergo diffusion sintering, thereby achieving the synchronous formation of the overall densification of the component and the surface gradient composite layer. Furthermore, depending on performance requirements, the densified components may undergo one or more post-treatments, such as quenching, tempering, machining, or surface finishing.

[0013] Secondly, this application provides a composite layer on the surface of a powder metallurgy component, which is prepared by the above-described preparation method.

[0014] Thirdly, this application provides the application of the above-mentioned powder metallurgy component surface composite layer in large and complex metal components in the fields of aerospace, energy and power, and heavy machinery.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The surface reinforcement layer of the powder metallurgy component prepared in this application forms a strong metallurgical bond and element interdiffusion with the substrate through the melting-sintering process, which ingeniously transforms the porosity characteristics of powder metallurgy into a process advantage and fundamentally avoids the risk of peeling off traditional coatings.

[0016] 2. The composition, microstructure, and properties (such as hardness and elastic modulus) of the surface strengthening layer of this application change continuously from the surface to the interior, realizing a high-strength metallurgical bond between the strengthening layer and the substrate and a continuous transition of properties, eliminating the interface of abrupt performance changes, optimizing stress distribution, and effectively inhibiting crack propagation.

[0017] 3. The surface strengthening layer of this application combines the high hardness and high wear resistance of the reinforcing phase with the toughness and corrosion resistance of the metal binder phase. It is suitable for surface strengthening of large, heavy-duty, and complex-shaped powder metallurgy components with extremely high requirements for reliability and durability, and has broad prospects for industrial application. Detailed Implementation

[0018] It should be noted that the implementation steps in the examples may be further adjusted according to the specific experimental environment. Implementation steps not specified are generally conditions used in routine experiments. All compounds involved in the following examples are commercially available pharmaceutical products.

[0019] Example 1 This embodiment provides a method for gradient strengthening of the tooth surface of large, heavy-duty iron-based alloy gears.

[0020] S1. Preparation of porous preform Water-atomized Fe-2Cu-0.8C (wt%) alloy powder was pressed into shape at 500 MPa to obtain a gear blank with a relative density of about 85% (porosity of about 15%).

[0021] S2. Preparation and Coating of Composite Slurry Slurry composition: By total mass of slurry, it contains sheet graphene (2 wt%) and boron carbide micro powder (B4C, 5 wt%) as reinforcing phase materials, electrolytic nickel powder (60 wt%, particle size ~10 μm) as metal binder, polyvinyl butyral (PVB, 5 wt%) as organic temporary binder, polyvinylpyrrolidone (5 wt%) as dispersant, and ethanol solvent (balance) as organic carrier.

[0022] The above components were ball-milled and mixed for 24 hours to form a uniform slurry. The non-reinforced areas were protected by a special fixture, and the slurry was evenly sprayed onto all tooth surfaces of the gear using a spray gun to form a wet film of about 300 μm thickness.

[0023] S3, In-situ melting and simultaneous densification The coated gear blank was placed in a vacuum sintering furnace. Under hydrogen protection, the temperature was increased to 1130℃ at a rate of 10℃ / min (higher than the melting point of nickel at 1455℃, but far below the solidus of the iron matrix), and held for 2 hours. During this process, the nickel powder melted, and the resulting molten nickel carried graphene and B4C particles into the porous iron matrix through capillary action. Simultaneously, the iron-based powder particles underwent diffusion sintering at high temperature, achieving densification. The furnace was then cooled.

[0024] Subsequent processing: The gears undergo oil quenching at 860℃ and low-temperature tempering at 200℃ to improve the strength of the base material. Finally, the gear teeth are precision ground.

[0025] Example 2 This embodiment provides a method for strengthening the sealing cone surface of a corrosion-resistant nickel-based alloy valve body.

[0026] S1. Preparation of porous preform Inconel 625 nickel-based alloy powder was atomized and pressed into valve body blanks at 200 MPa, with a relative density of about 80% (porosity of about 30%).

[0027] S2. Preparation and Coating of Composite Slurry Slurry composition: By total mass of slurry, it contains tungsten carbide (WC, 15 wt%) as reinforcing phase material, chromium powder (Cr, 20 wt%) as metal binder and corrosion-resistant alloying element, ethyl cellulose (1 wt%) as organic temporary binder, hexadecyltrimethylammonium bromide (CTAB) 2 wt% as dispersant, and terpineol (balance) as organic carrier.

[0028] The above components are ball-milled and mixed until homogeneous to form a slurry suitable for brushing. The slurry is then precisely coated onto the sealing cone surface of the valve body using a brushing method.

[0029] S3, In-situ melting and densification The valve body blank was encapsulated in a vacuum-sealed glass sleeve and placed in a hot isostatic pressing (HIP) machine. It was then treated at 1200℃ and 100MPa for 3 hours. At this temperature, the chromium powder did not melt, but it could form a low-melting-point eutectic liquid phase with the nickel matrix, achieving melting and densification.

[0030] Post-processing: Remove the sleeve and polish the sealing surface.

[0031] Comparative Example 1 (Contrast with Traditional Coating) Using the same Fe-Cu-C powder and pressing process as in Example 1 (i.e., step S1), but without the composite slurry provided in this application, the gear blank was first conventionally sintered at 1120°C to a relative density >95%. Then, a Ni60 alloy coating (containing tungsten carbide) was sprayed onto the gear surface using high-velocity vapor deposition (HVOF) technology, with a coating thickness of approximately 300 μm. Finally, the same quenching and tempering treatment as in Example 1 was performed.

[0032] Comparative Example 2 (Comparison without added reinforcing phase melt infiltration) The same preform and process as in Example 1 were used, but no graphene and boron carbide micro powder were added to the composite slurry. Only an ethanol solution of nickel powder and PVB was used for spraying and subsequent melt infiltration sintering.

[0033] Experimental Example The performance of the reinforcing layers of the samples obtained in the above embodiments and comparative examples was tested: Surface hardness testing was performed according to ASTM B933-20; interfacial bond strength testing was performed using the pull-off test, in which the clamps bonded to the coating surface were pulled vertically apart, and the failure load was measured according to ASTM D4541; wear rate testing was performed according to ASTM G99; corrosion rate testing was performed using the general method of weight loss; reinforcement layer thickness testing was performed according to ASTM E2522; and microstructure characteristics were observed using scanning electron microscopy (SEM) combined with energy dispersive spectroscopy (EDS).

[0034] Key test data are shown in Table 1: Table 1

[0035] Based on the test results in the table above, the bonding strength of the gradient layers in Examples 1 and 2 achieved metallurgical bonding with the substrate, with a bonding strength higher than that of the substrate itself; both fractured at the substrate during testing. In contrast, the HVOF coating in Comparative Example 1 exhibited typical mechanical bonding, with the lowest bonding strength.

[0036] Furthermore, the scanning electron microscopy (EDS) line scanning analysis of the reinforcement layers in Examples 1 and 2 confirmed that the nickel and carbon content decreased continuously from the surface to the interior, and the distribution density of the reinforcing phase, the matrix grain size, and the phase composition all changed continuously. In terms of performance, the microhardness and elastic modulus decreased smoothly from the surface to the core. Because the embodiment contains a hard reinforcing phase and is firmly bonded, the wear rate is much lower than that of the comparative example. Although the comparative example 2 has a good bond, it lacks a hard phase, has low surface hardness, and poor wear resistance. Example 1 uses reasonable parameters, resulting in a gradient layer of considerable thickness and uniformity.

Claims

1. A method of producing a surface composite layer of a powder metallurgical component, characterized in that Including the following steps: The base metal powder is uniformly mixed and pressed into shape to obtain a powder metallurgy preform blank. The reinforcing phase material, binder, dispersant and organic carrier are mixed to form a composite reinforcing slurry, and the composite reinforcing slurry is coated on the surface area of ​​the preform blank that needs to be reinforced. The coated preform blank is heat-treated to prepare a composite layer on the surface of the powder metallurgy component.

2. The production method according to claim 1, characterized by, The matrix metal powder includes iron-based, nickel-based, or cobalt-based alloy powders.

3. The production method according to claim 1 or 2, characterized by, The pressure for compression molding is 200~500MPa.

4. The production method according to claim 1 or 2, characterized by, The relative density of the preform blank is 70%~90%, and the porosity is 10%~30%.

5. The production method according to claim 1 or 2, characterized by, The slurry comprises, by mass percentage of the total mass of the slurry, 7-15 wt.% reinforcing phase material, 20-60 wt.% binder, and 2-5 wt.% dispersant, with the balance being an organic carrier.

6. The production method according to claim 5, wherein The slurry also contains 1-5 wt% of an organic temporary binder, which is selected from at least one of polyvinyl butyral (PVB), ethyl cellulose, and acrylic resin.

7. The production method according to claim 1 or 2, characterized by, The reinforcing phase material is selected from at least one of graphene, carbon nanotubes, and ceramic particles, wherein the ceramic particles are selected from at least one of silicon carbide, boron carbide, tungsten carbide, and boron nitride.

8. The production method according to claim 1 or 2, characterized by, The binder is a metal powder selected from at least one of chromium, manganese, nickel, copper and cobalt.

9. The production method according to claim 1 or 2, characterized by, The melting point or eutectic point of the binder is lower than the sintering temperature of the matrix metal powder.

10. The preparation method according to claim 1 or 2, characterized in that, The dispersant is selected from at least one of polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), polyethylene glycol (PEG), sodium polyacrylate, sodium dodecyl sulfate (SDS), and hexadecyltrimethylammonium bromide (CTAB).

11. The preparation method according to claim 1 or 2, characterized in that, The organic carrier is selected from at least one of ethanol, terpineol, ethylene glycol, propylene glycol, butyl carbitol (ethylene glycol butyl ether), and terpineol.

12. The preparation method according to claim 1 or 2, characterized in that, The coating method is selected from one of spraying, brushing or dipping, and the wet film thickness of the coating is 100~500 μm.

13. The preparation method according to claim 1 or 2, characterized in that, The heat treatment temperature is 50-200°C higher than the melting point or eutectic point of the binder, and lower than the solidus temperature of the base metal powder.

14. The preparation method according to claim 1 or 2, characterized in that, The heat treatment method is sintering or hot isostatic pressing, carried out under a protective atmosphere or vacuum.

15. A composite layer on the surface of a powder metallurgy component, characterized in that, It is prepared by the preparation method according to any one of claims 1-14.

16. The application of a preparation method as described in any one of claims 1-14 or a surface composite layer as described in claim 15 in large and complex metal components in the fields of aerospace, energy and power, and heavy machinery.

Images