Method for strengthening cold spraying of metal deposits through in-situ densification

Abstract

The invention discloses a method for strengthening cold spraying of a metal sedimentary body through in-situ densification. The method comprises the following steps that (1) metal powder with wide particle size distribution is selected as a spraying raw material; and (2) metal powder with wide particle size distribution is deposited on the surface of a base body under the low-temperature condition under the action of accelerating gas through a cold spraying method, and a high-density metal coating or block is formed. The powder with the small particle size can be accelerated to the critical speed or above, and therefore the powder is deposited on the surface of a base body. The powder with the large particle size rebounds and cannot be deposited after being impacted, so that the compaction effect of the large particles in the process can be utilized to reduce the particle interface gaps in the deposition coating or the block, the bonding state among the particles is improved, and the cold spraying metal deposition body with higher compactness and mechanical property is prepared. According to the method, the use of high-temperature gas or expensive and non-renewable helium which has potential heat influence on the deposits can be avoided to improve the performance of the cold spraying deposits.

Description

Technical Field

[0001] The invention relates to a method for preparing a plated metal, in particular to a method for in-situ densification and strengthening of a cold-sprayed metal deposition body. Background Art

[0002] Cold spraying (CS) is an emerging solid-state material deposition technology. This technology uses compressed gas (nitrogen, helium or compressed air) as an accelerating gas flow to accelerate the micron metal powder fed into the nozzle to 300-1200 m / s. The powder particles collide with the substrate or the deposited metal surface in a fully solid state below the melting point of the material, and the deposition is achieved through strong plastic deformation between the particle / substrate or particle / particle interface. The cold spray process does not require a high-energy beam heat source. The material is deposited on the substrate surface by high strain and high strain rate plastic deformation in a fully solid state. The deposited body retains the microstructure and various properties of the original powder to the greatest extent, and can avoid problems such as component oxidation, thermal stress accumulation, and phase structure changes to the greatest extent. In addition, the cold spray deposition rate can reach 30kg / h, the work efficiency is high, and it has the ability to prepare large-size components. It has broad application prospects in the fields of functional coating preparation, damaged parts repair, and additive manufacturing.

[0003] The performance of cold spray deposits is closely related to their microstructure. Due to incomplete bonding between particles, there are gaps or even micropores at the interface. These microstructural defects have a serious impact on the physical properties, mechanical properties, wear resistance and corrosion resistance of the deposits. Although the speed and temperature of the particles can be increased by increasing the gas pressure and gas temperature, or using helium as an accelerating gas, the bonding state between the particles can be improved to a certain extent. However, this improvement has certain limitations. On the one hand, there is an upper limit to the gas pressure in cold spraying, which cannot be increased all the time. On the other hand, for metal powders with low melting points, increasing the gas temperature will cause the particles to partially or completely melt in the nozzle, resulting in nozzle blockage. Although the use of helium can avoid these problems, helium is expensive and is a non-renewable energy source, which is not suitable for use in industrial production. Therefore, it is of great significance to improve the performance of cold spray deposits by exploring new processes, new technologies, and new methods. Summary of the invention

[0004] Purpose of the invention: The purpose of the present invention is to provide a method for in-situ densification strengthening of cold sprayed metal deposits, which can obtain metal deposits with high density and excellent mechanical properties.

[0005] Technical solution: The method of in-situ densification strengthening of cold sprayed metal deposits of the present invention comprises the following steps:

[0006] (1) Selecting metal powder with a wide particle size distribution as the spraying raw material;

[0007] (2) Cold spraying is a method of depositing metal powder with a wide particle size distribution onto the substrate surface under the action of accelerating gas and at low temperature to form a high-density metal coating or block.

[0008] Wherein, the particle size range of the metal powder with wide particle size distribution is 5 to 200 μm.

[0009] Wherein, in step (1), the spraying raw material comprises small-particle metal powder and large-particle metal powder, wherein the particle size range of the small-particle metal powder is 5 to 80 μm, and the particle size range of the large-particle metal powder is 80 to 200 μm.

[0010] Wherein, in step (2), the gas pressure during the cold spraying process is 0-6 MPa. As the pressure increases, the flying speed of the powder particles and the deposition efficiency of the obtained coating increase.

[0011] Wherein, in step (2), the temperature range of the low temperature condition is 100-600° C. As the temperature increases, the flying speed of the powder particles and the deposition efficiency of the obtained coating increase.

[0012] The metal powder with a wide particle size distribution can be obtained by directly screening or by mixing metal powders of the same raw material but with different particle size distributions.

[0013] Wherein, the metal powder with wide particle size distribution is spherical, nearly spherical or irregular in shape; the metal powder is pure metal or alloy powder.

[0014] Beneficial effects: Compared with the prior art, the present invention has achieved the following significant effects: (1) The method provided by the present invention enables powders with smaller particle sizes to be accelerated to above the critical speed under low spraying parameters, so that they are deposited on the substrate surface; while powders with larger particle sizes cannot obtain sufficient impact speed, and cannot be deposited after rebounding after impact. By utilizing the compaction effect of large particles in this process, the interfacial gaps between particles in the deposited coating or block can be reduced, and the bonding state between particles can be improved, thereby preparing a cold-sprayed metal deposit with higher density and mechanical properties. (2) This method can avoid the use of high-temperature gases or expensive, non-renewable helium that have potential thermal effects on the deposited body to improve the performance of the cold-sprayed deposited body. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a schematic diagram of the in-situ densification principle proposed by the present invention;

[0016] Figure 2 This is the SEM image of the gas atomized pure aluminum powder with a wide particle size distribution in Example 1;

[0017] Figure 3 This is the SEM image of the gas atomized pure aluminum powder with conventional particle size distribution in Comparative Example 1;

[0018] Figure 4 The cross-sectional microstructure of the deposit prepared in Example 1;

[0019] Figure 5 The cross-sectional microstructure of the deposit prepared in Comparative Example 1;

[0020] Figure 6 The cross-sectional microstructure of the deposit prepared in Comparative Example 2;

[0021] Figure 7 The SEM image of the gas atomized FeCoNiCr high entropy alloy powder with a wide particle size distribution in Example 2;

[0022] Figure 8 The SEM image of the gas atomized FeCoNiCr high entropy alloy powder with medium particle size distribution of Comparative Example 3;

[0023] Fig. 9 The SEM image of the gas atomized FeCoNiCr high entropy alloy powder with conventional particle size distribution of Comparative Example 4;

[0024] Fig.10 The cross-sectional microstructure of the deposit prepared in Example 2;

[0025] Fig.11 The cross-sectional microstructure of the deposit prepared in Comparative Example 3;

[0026] Fig.12 This is the cross-sectional microstructure of the deposit prepared in Comparative Example 4. DETAILED DESCRIPTION

[0027] The present invention is described in further detail below.

[0028] Example 1

[0029] Step 1: Before spraying, place the pure aluminum powder raw material with a particle size range of 10 to 140 μm in a vacuum drying oven and dry it for 1 hour at a drying temperature of 60° C. wherein the pure aluminum powder in this particle size range is obtained by directly sieving pure aluminum.

[0030] Step 2: Use dried pure aluminum powder with a particle size range of 10 to 140 μm (see Figure 2 ) was used as the spraying raw material, and nitrogen was used as the accelerating gas. The block was prepared by cold spraying at a gas pressure of 3.0 MPa and a gas temperature of 300 °C. Its cross-sectional morphology is shown in Figure 4 The principle diagram of the in-situ densification proposed by the present invention is shown in Figure 1 shown.

[0031] Comparative Example 1

[0032] On the basis of Example 1, the difference from Example 1 is that the cold spray block is prepared by using pure aluminum powder with a conventional particle size distribution covering a particle size range of 20 to 50 μm, see Figure 3 Its cross-sectional morphology is as follows Figure 5 shown.

[0033] Comparative Example 2

[0034] On the basis of Example 1, the difference from Example 1 is that the more expensive helium is used as the accelerating gas, the gas temperature is 20°C, and the cross-sectional morphology is as follows Figure 6 shown.

[0035] By comparison, it can be found that the block density prepared by Example 1 using wide particle size pure aluminum powder under low spraying parameters is about 99.9%, which is equivalent to the block density prepared by Comparative Example 2 using helium, see Figure 6 , while the bulk particles of comparative example 1 prepared by using pure aluminum powder with conventional particle size distribution under low parameter conditions show obvious micropores between particles, see Figure 5 . The tensile properties of the cold sprayed deposits prepared in Example 1 and Comparative Example 2 were evaluated, and the ultimate tensile strengths were ~266.75MPa and ~237.93MPa, respectively. It can be seen that the density of the deposit prepared by Example 1 using wide particle size powder under low spraying parameter conditions is better than that of the deposit prepared by Comparative Example 1 using narrow particle size powder, and the tensile strength of the deposit in Example 1 is better than that of the deposit prepared under helium conditions in Comparative Example 2. Due to the rebound of large particle size particles after impact under low parameter conditions, the compaction effect caused by this process significantly improves the density of the cold sprayed deposit and enhances the tensile strength.

[0036] Table 1 Process parameters and density data of cold spray blocks prepared by pure aluminum powder with different particle sizes

[0037] Powder particle size / μm Gas pressure / MPa Gas temperature / ℃ Density Example 1 10～140 Nitrogen, 3.0 300 99.9％ Comparative Example 1 20～50 Nitrogen, 3.0 300 98％ Comparative Example 2 10～140 Helium, 3.0 20 99.5％

[0038] Example 2

[0039] Step 1: Before spraying, place the FeCoNiCr high entropy alloy powder raw material with a particle size range of 15 to 200 μm in a vacuum drying oven and dry it for 1 hour at a drying temperature of 60° C. wherein the high entropy alloy powder in this particle size range is obtained by mixing FeCoNiCr high entropy alloys with different particle size distributions.

[0040] Step 2: Use the dried FeCoNiCr high entropy alloy powder with a particle size range of 15 to 200 μm as the spraying raw material, see Figure 7The block was prepared by cold spraying with nitrogen as the accelerating gas at a gas pressure of 3.0 MPa and a gas temperature of 500 °C. The cross-sectional morphology is shown in Fig.10 shown.

[0041] Comparative Example 3

[0042] On the basis of Example 2, the difference from Example 2 is that FeCoNiCr high entropy alloy powder with a particle size range of 15 to 105 μm (see Figure 8 ) was used as the spraying raw material, and nitrogen was used as the accelerating gas. The block was prepared by cold spraying at a gas pressure of 5.0 MPa and a gas temperature of 500 °C. Its cross-sectional morphology is shown in Fig.11 shown.

[0043] Comparative Example 4

[0044] On the basis of Example 2, the difference from Example 2 is that FeCoNiCr high entropy alloy powder with a particle size range of 15 to 53 μm is used as the spraying raw material, see Fig. 9 The block was prepared by cold spraying with nitrogen as the accelerating gas at a gas pressure of 5.0 MPa and a gas temperature of 900 °C. The cross-sectional morphology is shown in Fig.12 shown.

[0045] By comparison, it can be found that the block density prepared by Example 2 using wide-particle FeCoNiCr powder under low spraying parameters (N2, 3.0MPa, 500°C) is about 96.50%, which is higher than the block density of 89.90% prepared by Comparative Example 3 using medium-particle FeCoNiCr powder under higher gas pressure conditions (N2, 5.0MPa, 500°C), and is close to the block density of 98.60% prepared by Comparative Example 4 using conventional particle FeCoNiCr powder under the highest spraying parameters (N2, 5.0MPa, 900°C). This is because the processing height of Comparative Example 4 is higher, so the cost is very high, and the present invention can achieve results comparable to those of Comparative Example 4 at lower costs and parameters. The hardness of the cold-sprayed high-entropy alloy deposits prepared in Example 2, Comparative Example 3, and Comparative Example 4 was tested, and the results were 329HV and 329HV, respectively. 0.5 , 270HV 0.5 and 380HV 0.5. The hardness of the deposited body prepared by wide particle size powder under low spraying parameters in Example 2 is higher than that of the block prepared by medium particle size powder under medium spraying parameters in Comparative Example 3, and is 86.58% of the hardness of the block prepared by conventional particle size FeCoNiCr powder under high spraying parameters in Comparative Example 4. This shows that the present invention can achieve a hardness result basically equivalent to that of Comparative Example 4 at a lower cost and parameters. It can be seen from Example 2, Comparative Example 3 and Comparative Example 4 that the present invention can achieve in-situ densification of cold sprayed blocks by using a combination of wide powder particle size and low spraying parameters.

[0046] Table 2 Process parameters and properties of cold spray blocks prepared from FeCoNiCr high entropy alloy powders with different particle sizes

[0047] Powder particle size / μm Gas pressure / MPa Gas temperature / ℃ Block density / % Example 2 15～200 3.0 500 96.50 Comparative Example 3 15～105 5.0 500 89.90 Comparative Example 4 15～53 5.0 900 98.60

Claims

1. A method for strengthening a cold sprayed metal deposit by in-situ densification, characterized in that: The following steps are involved: (1) Selecting metal powder with a wide particle size distribution as the spraying raw material; (2) Cold spraying is a method of depositing metal powder with a wide particle size distribution onto the substrate surface under the action of accelerating gas and at low temperature to form a high-density metal coating or block.

2. The method for strengthening a cold sprayed metal deposit by in-situ densification according to claim 1, characterized in that: The particle size of the metal powder with a wide particle size distribution ranges from 5 to 200 μm.

3. The method for strengthening a cold sprayed metal deposit by in-situ densification according to claim 1, characterized in that: In step (1), the spraying raw material comprises small-particle metal powder and large-particle metal powder, wherein the particle size range of the small-particle metal powder is 5 to 80 μm, and the particle size range of the large-particle metal powder is 80 to 200 μm.

4. The method of strengthening a cold sprayed metal deposit by in-situ densification according to claim 1, characterized in that: In step (2), the gas pressure during the cold spraying process is 0 to 6 MPa.

5. The method for strengthening a cold sprayed metal deposit by in-situ densification according to claim 1, characterized in that: In step (2), the temperature of the low temperature condition is 100 to 600°C.

6. The method for strengthening a cold sprayed metal deposit by in-situ densification according to claim 1, characterized in that: The method for obtaining the metal powder with a wide particle size distribution is to directly sieve or mix metal powders of the same material but with different particle size distributions.

7. The method for strengthening a cold sprayed metal deposit by in-situ densification according to claim 1, characterized in that: The metal powder with a wide particle size distribution is spherical, nearly spherical or irregular in shape.

8. The method of strengthening a cold sprayed metal deposit by in-situ densification according to claim 1, characterized in that: The metal powder is pure metal or alloy powder.

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