A method for enhancing the bond strength of cold sprayed coatings to substrates based on aluminothermic reactions and applications thereof

Abstract

This invention discloses a method and its application for enhancing the bonding strength between a cold-sprayed coating and a substrate based on aluminothermic reaction, belonging to the fields of surface engineering and additive manufacturing technology. The method includes the following steps: using metal powder with an oxide layer on its surface as the cold-spraying raw material, the oxide layer thickness of the metal powder surface being ≤2 μm; using a metal workpiece or a workpiece with a metal surface as the substrate, wherein the metal is selected from elemental aluminum, aluminum alloy, or magnesium alloy; and performing cold spraying on the substrate surface using the metal powder with an oxide layer, causing the oxide layer on the metal powder surface to collide at high speed with the substrate metal, resulting in an aluminothermic reaction that releases the heat of reaction and enhances the bonding strength between the cold-sprayed coating and the substrate. This invention achieves a significant improvement in the bonding strength between the coating and the substrate through in-situ aluminothermic reaction exothermics, while maintaining the low-temperature solid-state deposition advantages of cold spraying technology, broadening the application range of the material, and possessing good industrial application prospects and economic benefits.

Description

Technical Field

[0001] This invention relates to the fields of surface engineering and additive manufacturing technology, specifically to a method and its application for enhancing the bonding strength between a cold spray coating and a substrate based on aluminothermic reaction. Background Technology

[0002] Cold spraying is an emerging solid-state material deposition technology. Its basic principle is to use high-pressure gas (such as nitrogen, helium, or air) to accelerate metal powder particles to supersonic speeds, allowing them to impact the substrate under completely solid conditions. The particles undergo intense plastic deformation, resulting in deposition and coating formation. Compared to traditional thermal spraying techniques (such as plasma spraying and flame spraying), the heating temperature of particles in cold spraying is much lower than their melting point. Therefore, it effectively avoids thermal damage problems such as phase transformation and grain growth, making it particularly suitable for preparing temperature-sensitive metal coatings and composite material coatings.

[0003] In cold spraying, the bonding quality between the coating and the substrate is a key factor determining its application performance. Currently, it is believed that the bonding mechanism of cold spray coatings mainly relies on the adiabatic shear instability and localized plastic flow generated by particle impact at high speeds, resulting in mechanical interlocking and limited metallurgical bonding. However, this bonding method is quite sensitive to the intrinsic properties of the material. For high-hardness, high-strength metal powders, due to their poor plastic deformation capacity, sufficient deformation and effective bonding are often difficult to achieve during cold spraying, leading to insufficient coating bonding strength.

[0004] To improve the bonding performance between cold-sprayed coatings and substrates, existing technologies typically employ methods such as introducing external heat sources or post-heating treatments of the workpiece. For example, Chinese patent document CN114032537A discloses a method for enhancing the bonding strength between cold-sprayed coatings and substrates. This invention uses a point heat source to scan the substrate surface to reduce its surface hardness until no precipitated phases are observed, and / or ages the cold-sprayed powder until a second phase precipitates to increase its hardness. Finally, cold spraying is performed, increasing the embedding depth of powder particles when impacting the substrate surface and improving the consistency of plastic strain at the powder-substrate interface. Another example is Chinese patent document CN116445904A, which discloses a method for improving the bonding strength of cold-sprayed additive manufacturing. This invention involves multi-stage heat treatment of the cold-sprayed additive component to improve the bonding strength between the coating and the substrate. For example, Chinese patent document CN118272801A discloses a method for strengthening cold spray coatings on copper and copper alloy substrates. This invention utilizes high-frequency induction heating to achieve rapid strengthening of the metal coating on the surface of copper and its alloys, enabling the coating to achieve metallurgical bonding with the substrate. Bottom water cooling reduces the thermal impact of the high-frequency induction heating process on the substrate, and heats the coating as much as possible while ensuring the excellent performance of the substrate.

[0005] However, the aforementioned methods of introducing external heat sources or post-heating the workpiece may not only cause the entire substrate to be heated, leading to changes in the microstructure (such as coarsening of grains, softening of phase transformation, etc.), but may even introduce thermal stress, causing workpiece deformation or microcracks, which is particularly detrimental to precision components or heat-sensitive substrates. At the same time, these methods often require additional process equipment (such as laser heating devices, induction heating equipment, etc.), which not only increases equipment costs and process complexity, but also places higher demands on operating space and working environment. In addition, the method of post-heating the workpiece as a whole or in part is limited by the cavity size or heating range of the heating equipment, making it difficult or even unsuitable for ultra-large workpieces (such as large structural parts, long pipes, ship components, etc.), which seriously restricts its application in large-scale industrial production.

[0006] Therefore, how to introduce additional heat energy in situ and in a controllable manner during the cold spray deposition process to promote the bonding between metal powder and substrate, while maintaining the advantages of low-temperature solid-state deposition of cold spray, has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0007] To overcome the shortcomings of the existing technology, this invention provides a method for enhancing the bonding strength between cold spray coating and substrate based on aluminothermic reaction. By releasing heat through in-situ aluminothermic reaction, the bonding strength between the coating and substrate is significantly improved, while maintaining the low-temperature solid deposition advantage of cold spray technology. This broadens the application range of the material and has good industrial application prospects and economic benefits.

[0008] The specific technical solution adopted is as follows: A method for enhancing the bonding strength between a cold-sprayed coating and a substrate based on aluminothermic reaction includes the following steps: (1) Metal powder with an oxide layer on its surface is used as the raw material for cold spraying, and the thickness of the oxide layer on the surface of the metal powder is ≤2 μm; (2) The metal workpiece or the workpiece with a metal surface is used as the base material, wherein the metal is selected from elemental aluminum, aluminum alloy or magnesium alloy; (3) Using metal powder with an oxide layer on the surface of the substrate, cold spraying is performed, so that the oxide layer on the surface of the metal powder collides with the substrate metal at high speed to produce an aluminothermic reaction, releasing the reaction heat to strengthen the bonding strength between the cold spray coating and the substrate.

[0009] This invention achieves in-situ, instantaneous interfacial exothermic reaction by cleverly utilizing the aluminothermic reaction that occurs between the oxide layer on the surface of metal powder and the substrate metal under high-speed collision conditions. This heat of reaction can: generate high temperatures locally at the collision interface, promoting atomic diffusion and metallurgical bonding between the metal powder and the substrate; soften the surfaces of the metal powder and the substrate, enhancing plastic deformation capacity and improving mechanical interlocking effects.

[0010] In step (1), the metal powder is selected from at least one of the following: chromium powder, iron powder, cobalt powder, nickel powder, copper powder, zinc powder, cadmium powder, tin powder, lead powder, chromium alloy powder, iron alloy powder, cobalt alloy powder, nickel alloy powder, copper alloy powder, zinc alloy powder, cadmium alloy powder, tin alloy powder, and lead alloy powder; more preferably, copper powder, N06625 nickel alloy powder, or cupronickel powder.

[0011] Furthermore, the average particle size of the metal powder ranges from 5 to 100 μm, and the shape is spherical, near-spherical, or irregular.

[0012] In step (1), the oxide layer on the surface of the metal powder originates from any of the following: An oxide layer that forms naturally during the production and preparation of metal powder; An oxide layer is introduced by post-processing metal powder.

[0013] Furthermore, an oxide layer can be introduced by post-processing the metal powder, specifically using any of the following methods: Heating oxidation method: Heating metal powder in an air or oxygen atmosphere to form an oxide layer; Chemical oxidation method: Metal powder is immersed in a solution containing an oxidizing agent, and an oxide layer is formed by the chemical reaction between the oxidizing substances in the solution and the metal powder. Anodizing method: Using metal powder as the anode and an inert material as the cathode, an electric current is passed through an electrolyte to treat the metal surface, so that oxygen ions in the electrolyte combine with the metal surface to form an oxide layer; Hydrothermal or solvothermal methods: Metal powder is placed in a sealed container and oxidized in a high-temperature and high-pressure water or solvent environment to form an oxide layer.

[0014] Furthermore, the process parameters for cold spraying include: inert gas (more specifically nitrogen) as the process gas, gas pressure of 2–8 MPa, gas temperature of 500–750℃, spraying distance of 10–50 mm, powder feeding rate of 10–100 g / min, and spray gun moving speed of 100–500 mm / s.

[0015] Furthermore, in the workpiece with coating obtained after the cold spraying process, the coating thickness is 100 μm to 2 mm.

[0016] The present invention also provides a workpiece with a coating, which is prepared by the method described above for strengthening the bonding strength between the cold spray coating and the substrate based on the aluminothermic reaction.

[0017] The present invention also provides the application of the method for enhancing the bonding strength between the cold spray coating and the substrate based on the aluminothermic reaction in the field of surface protection.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The present invention is based on the aluminothermic reaction to enhance the bonding strength between the cold spray coating and the substrate. While the aluminothermic reaction releases heat, it does not change the nature of the cold spray process. During the spraying process, the gas temperature in the spray gun chamber can still be controlled within a low temperature range. The metal powder remains solid during flight, avoiding thermal damage such as phase change and grain growth caused by melting.

[0019] (2) Traditional cold spraying technology often fails to achieve ideal deposition results for high-hardness, high-strength metal powders. This invention utilizes the exothermic aluminothermic reaction to assist bonding, achieving efficient deposition and strong bonding for elemental metal powders and their alloys, including chromium, iron, cobalt, nickel, copper, zinc, cadmium, tin, and lead. It is particularly suitable for aluminum and magnesium-based substrates, which exhibit high aluminothermic reactivity with transition metal oxides. Therefore, this invention broadens the application scope of cold spraying technology in the preparation of high-performance metal coatings.

[0020] (3) The method of the present invention achieves a significant improvement in the bonding strength between the coating and the substrate by exothermic reaction in situ, with the bonding strength increased by 30-70%. At the same time, it maintains the low-temperature solid deposition advantage of cold spraying technology, broadens the application range of the material, and has good industrial application prospects and economic benefits. Attached Figure Description

[0021] Figure 1 The results are the transmission electron microscope and X-ray energy dispersive spectroscopy characterization results of the prepared coating at the interface between the coating and the substrate in Example 1. Detailed Implementation

[0022] To make the objectives, features, and advantages of this invention more apparent and understandable, a detailed description is provided below through specific embodiments. Many specific details are set forth in the following description to provide a thorough understanding of the invention. However, the invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below. Technical features in various embodiments of the invention can be combined appropriately without mutual conflict.

[0023] Unless otherwise specified, the operating methods in the following examples are generally performed under conventional conditions or as recommended by the manufacturer. Contents not described in detail in this specification are prior art known to those skilled in the art. Unless otherwise specified, the experimental materials used in the examples below can be purchased from conventional biochemical reagent companies.

[0024] Example 1 In this embodiment, a stainless steel workpiece with a pure aluminum layer (1060 aluminum, Al content >99.6%, containing a small amount of Si about 0.25%) is selected as the substrate.

[0025] Pure copper powder with an average particle size of 20 μm was placed in air at 80°C for 60 hours to form an oxide layer with a thickness of approximately 1 μm on its surface. Using the oxidized copper powder as a cold spraying raw material, a coating was prepared on the substrate surface using a cold spraying process. The cold spraying process parameters included: nitrogen as the process gas, a gas pressure of 5 MPa, a gas temperature of 500°C, a spraying distance of 30 mm, a powder feed rate of 25 g / min, and a spray gun moving speed of 500 mm / s. After the cold spraying process, the coating thickness on the workpiece was approximately 2 mm.

[0026] The interface between the coating and the substrate was characterized using transmission electron microscopy and corresponding X-ray energy dispersive spectroscopy. The results are as follows: Figure 1 As shown in the figure, analysis reveals that the oxides on the surface of the original copper particles were almost completely consumed after an aluminothermic reaction with the aluminum in the substrate, achieving complete atomic-scale bonding between the coating and the substrate. Notably, a small amount of Si enrichment was also found at the interface. The Si originated from the 1060 aluminum layer of the substrate (Si content approximately 0.25%). Due to the aluminothermic reaction at the interface, some of the Al at the interface underwent melting and transient solidification, leading to the segregation and enrichment of Si at the interface.

[0027] To verify the strengthening effect of the method in this embodiment, coating samples were prepared using copper powder that had not undergone oxidation treatment and that had undergone oxidation treatment, respectively, and the adhesion strength was tested by pull-out method. The results showed that the coating prepared with oxidized copper powder had an adhesion strength to the substrate that was 167% of that of the untreated sample (the adhesion strength of the oxidized sample was 72.1 MPa, and the adhesion strength of the unoxidized sample was 43.2 MPa), significantly improving the adhesion performance of the coating.

[0028] Example 2 In this embodiment, ZK61M magnesium alloy is selected as the base material.

[0029] N06625 nickel alloy powder with an average particle size of 25 μm was taken and calcined in an oxygen atmosphere at 400℃ for 30 minutes to form an oxide layer with a thickness of approximately 0.5 μm. Using the oxidized nickel alloy powder as the coating material, a coating was prepared on the substrate surface using a cold spraying process. The cold spraying process parameters included: nitrogen as the process gas, a gas pressure of 6 MPa, a gas temperature of 600℃, a spraying distance of 15 mm, a powder feed rate of 45 g / min, and a spray gun moving speed of 200 mm / s. After the cold spraying process, the coating thickness of the workpiece was approximately 480 μm.

[0030] To verify the strengthening effect of the method in this embodiment, coating samples were prepared using nickel alloy powders that were neither oxidized nor unoxidized, and the bond strength was tested by pull-out method. The results showed that the coating prepared using oxidized nickel alloy powder had a bond strength to the substrate that was 131% of that of the untreated sample (the bond strength of the oxidized sample was 39.8 MPa, and the bond strength of the unoxidized sample was 30.4 MPa), significantly improving the bonding performance of the coating.

[0031] Example 3 In this embodiment, AZ91D magnesium-aluminum alloy is selected as the base material.

[0032] White copper powder (Cu-18Ni-18Zn alloy) with an average particle size of 15 μm was calcined in air at 300℃ for 15 minutes to form an oxide layer with a thickness of approximately 1.5 μm. Using the oxidized white copper powder as the coating material, a cold spraying process was employed to prepare a coating on the substrate surface. The cold spraying process parameters included: nitrogen as the process gas, a gas pressure of 6 MPa, a gas temperature of 500℃, a spraying distance of 45 mm, a powder feed rate of 60 g / min, and a spray gun moving speed of 250 mm / s. After the cold spraying process, the coating thickness on the workpiece was approximately 1 mm.

[0033] To verify the strengthening effect of the method in this embodiment, coating samples were prepared using untreated and oxidized white copper powder, respectively, and the bond strength was tested by pull-out method. The results showed that the coating prepared with oxidized white copper powder had a bond strength to the substrate that was 156% of that of the untreated sample (the bond strength of the oxidized sample was 59.0 MPa, and the bond strength of the untreated sample was 37.9 MPa), significantly improving the bonding performance of the coating.

[0034] The embodiments described above provide a detailed explanation of the technical solutions of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, additions, or similar substitutions made within the scope of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for enhancing the bonding strength between a cold-sprayed coating and a substrate based on aluminothermic reaction, characterized in that, Includes the following steps: (1) Metal powder with an oxide layer on its surface is used as the raw material for cold spraying, and the thickness of the oxide layer on the surface of the metal powder is ≤2 μm; (2) The metal workpiece or the workpiece with a metal surface is used as the base material, wherein the metal is selected from elemental aluminum, aluminum alloy or magnesium alloy; (3) Using metal powder with an oxide layer on the surface of the substrate, cold spraying is performed, so that the oxide layer on the surface of the metal powder collides with the substrate metal at high speed to produce an aluminothermic reaction, releasing the reaction heat to strengthen the bonding strength between the cold spray coating and the substrate.

2. The method for enhancing the bonding strength between the cold spray coating and the substrate based on the aluminothermic reaction according to claim 1, characterized in that, In step (1), the metal powder is selected from at least one of the following: chromium powder, iron powder, cobalt powder, nickel powder, copper powder, zinc powder, cadmium powder, tin powder, lead powder, chromium alloy powder, iron alloy powder, cobalt alloy powder, nickel alloy powder, copper alloy powder, zinc alloy powder, cadmium alloy powder, tin alloy powder, and lead alloy powder.

3. The method for enhancing the bonding strength between the cold spray coating and the substrate based on the aluminothermic reaction according to claim 1, characterized in that, In step (1), the metal powder is selected from copper powder, N06625 nickel alloy powder or cupronickel powder.

4. The method for enhancing the bonding strength between a cold-sprayed coating and the substrate based on aluminothermic reaction according to claim 1, characterized in that, In step (1), the average particle size of the metal powder ranges from 5 to 100 μm.

5. The method for enhancing the bonding strength between the cold spray coating and the substrate based on the aluminothermic reaction according to claim 1, characterized in that, The oxide layer on the surface of metal powder originates from any of the following: An oxide layer that forms naturally during the production and preparation of metal powder; An oxide layer is introduced by post-processing metal powder.

6. The method for enhancing the bonding strength between a cold-sprayed coating and the substrate based on aluminothermic reaction according to claim 1, characterized in that, The process parameters for cold spraying include: inert gas as the process gas, gas pressure of 2-8 MPa, gas temperature of 500-750℃, spraying distance of 10-50 mm, powder feeding rate of 10-100 g / min, and spray gun moving speed of 100-500 mm / s.

7. The method for enhancing the bonding strength between the cold spray coating and the substrate based on the aluminothermic reaction according to claim 6, characterized in that, The inert gas mentioned is nitrogen.

8. The method for enhancing the bonding strength between a cold-sprayed coating and the substrate based on aluminothermic reaction according to claim 1, characterized in that, The coating thickness of the workpiece obtained after the cold spraying process is 100 μm to 2 mm.

9. A workpiece with a coating, characterized in that, The coating is prepared according to any one of claims 1-8 by the method of enhancing the bonding strength between the cold spray coating and the substrate based on the aluminothermic reaction.

10. The application of the method for enhancing the bonding strength between cold spray coating and substrate based on aluminothermic reaction as described in any one of claims 1-8 in the field of surface protection.

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