Preparation method of B4C reinforced CoCrFeNiTi high-entropy alloy composite coating

Abstract

This invention discloses a method for preparing a B4C-reinforced CoCrFeNiTi high-entropy alloy composite coating. The method includes the following steps: spraying and remelting unmixed B4C CoCrFeNiTi powder onto a 45 steel substrate; adjusting the argon flow rate and power during laser cladding and remelting until no black material accumulation areas are found at the edge and bottom of the molten pool, and simultaneously achieving a pot-bottom shaped interface between the coating and the substrate with a melting depth of 380-400 μm, thus obtaining laser cladding and remelting parameters; preparing a mixed powder by proportionally configuring Ni-B4C powder and CoCrFeNiTi powder, wherein B4C powder accounts for 4-8% of the mixed powder mass; plasma spraying the mixed powder onto the pretreated 45 steel substrate; and remelting the mixture according to the aforementioned laser cladding and remelting parameters to obtain the B4C-reinforced CoCrFeNiTi high-entropy alloy composite coating. In this invention, the hardness of the remelted layer is not less than 751 HV, and the wear volume is not greater than 0.874 × 10⁻⁶. 6 μm 3 .

Description

Technical Field

[0001] This invention relates to the field of high-entropy alloy coating preparation technology, and in particular to a method for preparing a B4C-reinforced CoCrFeNiTi high-entropy alloy composite coating. Background Technology

[0002] High-entropy alloys, due to their unique structure and elemental composition, exhibit superior mechanical properties compared to traditional alloys, such as high hardness and high strength, making them a widely used coating material. Some high-entropy alloys with excellent wear resistance, when used as coating materials, can improve the wear resistance, corrosion resistance, and high-temperature performance of components, thereby providing a longer service life and higher working efficiency.

[0003] CoCrFeNiTi-based high-entropy alloy-ceramic composite coatings inherit the excellent mechanical properties of CoCrFeNiTi-based high-entropy alloys. The ceramic phase effectively inhibits grain boundary expansion and dislocation movement, improving the coating's mechanical properties and thus enhancing its wear resistance, resulting in high hardness and good wear resistance. In the preparation of wear-resistant coatings, atmospheric plasma spraying is a commonly used coating technology, characterized by high-temperature spraying, rapid coating, strong adhesion, diverse material selection, and high adjustability. For example, CN202310238454.1 discloses a high-entropy alloy coating material and a method for preparing wear-resistant coatings by plasma cladding. This method involves spraying a mixture of FeCoCrNiAl and yttrium powder onto a substrate via plasma cladding to obtain a coating with a single BCC structure. However, the wear resistance of coatings prepared by plasma spraying is limited due to the potential presence of a small number of pores and microcracks. Remelting sprayed coatings can effectively improve their structure. Common remelting methods include laser remelting, induction remelting, electron beam remelting, and flame remelting. Laser remelting, with its advantages of high energy density and rapid cooling, is frequently used for remelting sprayed coatings. However, some problems exist in the actual laser remelting process of CoCrFeNiTi coatings. At high temperatures, Ti and oxygen readily react to form oxides with low Gibbs free energy, such as TiO and TiO2. These oxides are not easily dissolved upon cooling and typically precipitate near the coating-matrix interface, forming black aggregates that degrade the material's mechanical properties, thereby reducing the coating's wear resistance.

[0004] Therefore, exploring suitable laser remelting process parameters, reducing defects such as microcracks and pores in the coating, solving the oxidation problem of titanium, and obtaining a CoCrFeNiTi-B4C high-entropy alloy composite coating with dense structure, uniform composition, good bonding with the substrate, and excellent wear resistance is a problem that needs to be solved in the field of high-entropy alloy wear-resistant coating preparation. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing a B4C-reinforced CoCrFeNiTi high-entropy alloy composite coating (represented as CoCrFeNiTi-B4C). B4C ceramic particles are added to CoCrFeNiTi powder, and the CoCrFeNiTi-B4C high-entropy alloy composite coating is prepared using a combination of atmospheric plasma spraying and laser remelting to improve the performance of the high-entropy alloy coating. The high-entropy alloy composite coating prepared by this method exhibits excellent wear resistance and hardness. The coating has uniform thickness, a dense structure, good adhesion to the substrate, and excellent wear resistance.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] In a first aspect, the present invention provides a method for preparing a B4C-reinforced CoCrFeNiTi high-entropy alloy composite coating, comprising the following steps:

[0008] The first step is to prepare CoCrFeNiTi-B4C composite powder for plasma spraying;

[0009] CoCrFeNiTi powder and Ni-B4C powder were mixed to form a mixed powder, and then CoCrFeNiTi-B4C composite powder was obtained by ordinary stirring in a three-dimensional mixer for 60 minutes.

[0010] The CoCrFeNiTi powder has a particle size of 51–105 μm, and the Ni-B4C powder has a particle size of 34–98 μm. In the mixed powder, B4C accounts for 4–8% of the mass of the mixed powder. In the CoCrFeNiTi powder, the atomic percentages of various elements are Co 22%, Cr 21.08%, Fe 21.09%, Ni 19.07%, and Ti 16.55%.

[0011] The second step is the pretreatment of the metal substrate, which involves sandblasting the metal substrate.

[0012] The sandblasting process uses cast steel sand with a size of 0.8-1.2mm; the Vickers hardness of the substrate after sandblasting is 194-208 HV.

[0013] The metal matrix is ​​made of No. 45 steel.

[0014] The third step is to prepare a CoCrFeNiTi-B4C composite coating.

[0015] Plasma spraying was used to spray the CoCrFeNiTi-B4C composite powder obtained in the first step onto the surface of the pretreated metal substrate in the second step, resulting in a coating with a thickness of 500 μm. The spraying parameters were: current 540A, voltage 69.3V, power 37.5kw, argon flow rate 50L / min, hydrogen flow rate 9L / min, spraying distance 120mm, spray gun moving speed 600mm / s, and powder delivery argon flow rate 3.5L / min.

[0016] Laser cladding technology was used to remelt the sprayed coating to obtain a B4C-reinforced CoCrFeNiTi composite coating. The parameters for the remelting process were: defocusing amount 7 mm, scanning speed 12 mm / s, overlap rate 50%, argon gas flow rate 12 L / min, and power 930 W.

[0017] Remelting equipment model: YLS-4000-KC.

[0018] In the preparation method of the CoCrFeNiTi-B4C composite coating, the raw material powders involved are all working materials or commercially available.

[0019] Secondly, the present invention provides a method for preparing a B4C-reinforced CoCrFeNiTi high-entropy alloy composite coating, the method comprising the following steps:

[0020] Unmixed B4C CoCrFeNiTi powder was sprayed and remelted on the surface of 45 steel substrate. The argon flow rate and power in the laser cladding and remelting process were adjusted until there were no black material accumulation areas at the edge and bottom of the molten pool, and the interface between the coating and the substrate was made to have a pot-bottom shaped melting depth of 380-400μm. The laser cladding and remelting parameters were obtained.

[0021] A mixed powder was obtained by mixing Ni-B4C powder and CoCrFeNiTi powder in a certain proportion, wherein B4C powder accounted for 6% of the mass of the mixed powder;

[0022] Plasma spraying with mixed powder was performed on the pretreated 45 steel substrate. After plasma spraying, remelting was carried out according to the laser cladding and remelting parameters determined above, resulting in a remelted layer with a hardness of not less than 751 HV and a wear volume not greater than 0.874 × 10⁻⁶. 6 μm 3 B4C-reinforced CoCrFeNiTi high-entropy alloy composite coating.

[0023] The beneficial effects of this invention are as follows:

[0024] Compared with the prior art, the outstanding substantive feature of this invention is that the method of this invention utilizes plasma spraying and laser remelting technology to obtain a CoCrFeNiTi-B4C composite coating with high hardness and high wear resistance under specific remelting conditions, which has low porosity, high hardness and good wear resistance.

[0025] The significant advancement of this invention compared to existing technologies lies in:

[0026] This invention addresses the problem of decreased mechanical properties caused by titanium oxidation by adding B4C ceramic particles to a CoCrFeNiTi high-entropy alloy and determining suitable laser remelting process parameters for the hybrid system. Through second-phase strengthening, solid solution strengthening, and grain refinement, the final coating exhibits excellent wear resistance, expanding the application of high-entropy alloy coatings under high strength and high wear resistance requirements.

[0027] The preparation method of this invention requires precise control of the laser remelting process, because a large laser power may cause the substrate to overmelt, which dilutes the coating, while a small laser power may cause incomplete remelting, which prevents the coating from forming a metallurgical bond with the substrate. Both of these situations will lead to a decrease in the wear resistance of the coating. The preparation method of this application can obtain a coating with high hardness and high wear resistance. Attached Figure Description

[0028] The invention will be further described below with reference to the accompanying drawings.

[0029] Figure 1 This is a SEM image of the CoCrFeNiTi powder used in this invention.

[0030] Figure 2 This is a SEM image of the Ni-B4C powder used in this invention.

[0031] Figure 3(a) is a cross-sectional SEM image of the CoCrFeNiTi coating in Group A of Example 1;

[0032] Figure 3(b) is a magnified view of a portion of Figure 3(a).

[0033] Figure 4(a) is a cross-sectional SEM image of the CoCrFeNiTi coating in Group B of Example 1.

[0034] Figure 4(b) is a cross-sectional SEM image of the CoCrFeNiTi coating in Group C of Example 1.

[0035] Figure 5(a) is a SEM image of the sprayed coating surface in the CoCrFeNiTi-B4C composite coating of Example 2 of the present invention;

[0036] Figure 5(b) SEM image of the remelted layer surface in the CoCrFeNiTi-B4C composite coating of Example 2 of the present invention.

[0037] Figure 6 This is a hardness comparison diagram of the substrate and the sprayed and remelted layers of the CoCrFeNiTi-B4C composite coating in Example 2 of the present invention.

[0038] Figure 7 This is a comparison diagram of the wear volume of the sprayed layer and the remelted layer of the CoCrFeNiTi-B4C composite coating in Example 2 of the present invention.

[0039] Table 1 shows the energy spectrum analysis results of the black clustered area in Figure 3(b). Detailed Implementation

[0040] The present invention will be further described below with reference to specific embodiments.

[0041] Example 1

[0042] We explored suitable remelting process parameters by spraying and remelting unmixed B4C CoCrFeNiTi powder.

[0043] CoCrFeNiTi powder was sprayed onto the pretreated 45 steel substrate using plasma spraying to obtain a CoCrFeNiT coating with a thickness of 500 μm. The spraying parameters were: current: 540 A; voltage: 69.3 V; power: 37.5 kW; argon flow rate: 50 L / min; hydrogen flow rate: 9 L / min; spraying distance: 120 mm; spray gun moving speed: 600 mm / s; powder feed gas: argon; powder feed gas flow rate: 3.5 L / min.

[0044] The plasma spraying equipment uses a PT3X IPS-800 plasma arc spraying power supply and a MECO F4 spray gun.

[0045] Laser cladding technology was used to remelt the prepared coating to eliminate defects such as porosity and microcracks, improve the coating density, and give the coating structure higher hardness and wear resistance. The remelting parameters were: defocusing amount: 7mm; scanning speed: 12mm / s; overlap rate: 50%; argon gas flow rate: 10L / min; power: 900W (Group A).

[0046] Remelting equipment model: YLS-4000-KC.

[0047] The SEM morphology of the single-pass remelting weld bead of the CoCrFeNiTi coating is shown in Figures 3(a) and 3(b).

[0048] As can be seen from Figures 3(a) and 3(b), the molten pool is shallow, and no metallurgical bond is formed between the coating and the substrate. Furthermore, black material accumulation areas appear at the edge and bottom of the molten pool, which reduces the wear resistance of the coating. In Figure 3(b), 1, 2, and 3 represent the three detection points, respectively. According to the energy dispersive spectroscopy analysis results (see Table 1), the black accumulation areas are mainly titanium oxides, indicating that oxygen has invaded the coating. It is necessary to enhance the protective gas to isolate oxygen, and further adjust the laser power.

[0049] Table 1. Element content (wt.%) of the black area in Figure 3(b).

[0050]

[0051] Based on the above, the remelting parameters were optimized by adjusting the argon gas flow rate to 12 L / min and the power to 960 W (Group B) and the argon gas flow rate to 14 L / min and the power to 930 W (Group C), while keeping other experimental conditions unchanged.

[0052] As can be seen from Figures 4(a) and 4(b), no obvious black oxides appeared in the coatings under the parameters of groups B and C, indicating that oxygen intrusion was controlled after the enhancement gas protection. The melting depth in group B was 660.5 μm and the melting depth in group C was 398.5 μm. However, the melting depth of the coating in group B was too large, which led to over-melting of the substrate, dilution of the coating, and reduced the beneficial effect of the coating.

[0053] The final selected argon gas flow rate was 12L / min, and the power was 930W. Under these conditions, the interface between the substrate and the coating was pot-shaped, and the sides and middle of the interface were relatively uniform and flat.

[0054] Example 2

[0055] Prepare a B4C-reinforced CoCrFeNiTi high-entropy alloy composite coating.

[0056] Step 1: Prepare CoCrFeNiTi-B4C composite powder for plasma spraying;

[0057] CoCrFeNiTi powder with a particle size range of 51μm to 105μm and Ni-B4C powder with a particle size range of 34μm to 98μm were uniformly mixed to form a mixed powder, wherein Ni-B4C powder accounted for 6% of the mass of the mixed powder. The mixture was stirred by three-dimensional mechanical mixing for 60 minutes to prepare CoCrFeNiTi-B4C composite powder for plasma spraying.

[0058] Step 2: Matrix pretreatment;

[0059] The 45 steel substrate was sandblasted using cast steel sand doped with a small amount of silicon nitride, with a particle size of 0.8-1.2 mm. After sandblasting, the Vickers hardness of the substrate was 194-208 HV.

[0060] Step 3: Preparation of CoCrFeNiTi-B4C composite coating;

[0061] Plasma spraying was used to spray the CoCrFeNiTi-B4C composite powder obtained in the first step onto the surface of the pretreated 45 steel substrate in the second step, resulting in a coating with a thickness of 500 μm. The spraying parameters were as follows: current: 540A; voltage: 69.3V; power: 37.5kW; process gas: argon flow rate: 50L / min; hydrogen flow rate: 9L / min; spraying distance: 120mm; spray gun moving speed: 600mm / s; powder feed gas: argon; powder feed gas flow rate: 3.5L / min.

[0062] The plasma spraying equipment uses a PT3X IPS-800 plasma arc spraying power supply and a MECO F4 spray gun;

[0063] Laser cladding technology was used to remelt the sprayed coating to eliminate defects such as pores and microcracks, improve the coating's density, and give the coating structure higher hardness and wear resistance. The remelting parameters were: defocusing amount: 7mm; scanning speed: 12mm / s; overlap rate: 50%; argon gas flow rate: 12L / min; power: 930W.

[0064] Remelting equipment model: YLS-4000-KC.

[0065] The SEM morphology of the CoCrFeNiTi-B4C high-entropy alloy spray coating prepared in this embodiment is shown in Figure 5(a). The figure shows obvious pores and gaps on the surface of the spray coating.

[0066] The SEM morphology of the CoCrFeNiTi-B4C high-entropy alloy remelted layer prepared in this embodiment is shown in Figure 5(b). Compared with the morphology of the sprayed layer, the porosity and cracks of the remelted layer are significantly reduced, and the surface becomes smoother.

[0067] The hardness of the B4C-reinforced CoCrFeNiTi high-entropy alloy composite coating prepared in this embodiment is as follows: Figure 6As shown, compared to the 45 steel substrate, the hardness of both the sprayed and remelted layers of the B4C-reinforced CoCrFeNiTi high-entropy alloy composite coating is significantly improved. Specifically, the hardness of the remelted layer is 751 HV, which is 11.41% higher than the 674 HV of the sprayed layer. This is mainly because the remelting process increases the density of the coating, making its microstructure more compact. B4C can form reinforcing phases in high-entropy alloy coatings, such as cobalt boride (CoB) or iron boride (FeB), and the presence of these reinforcing phases can increase the hardness and strength of the coating.

[0068] The wear volume of the B4C-reinforced CoCrFeNiTi high-entropy alloy composite coating prepared in Example 2 is as follows: Figure 7 As shown in the figure, the wear volume of the remelted layer is approximately 1 / 5 that of the sprayed layer, exhibiting superior wear resistance. After remelting, B4C is more uniformly distributed in the coating, and the second-phase strengthening effect is more pronounced, thus improving the wear resistance of the coating.

[0069] The B4C-reinforced CoCrFeNiTi high-entropy alloy composite coating of the present invention is composed of elements Co, Cr, Ni, Fe, Ti, B and C. The prepared B4C-reinforced CoCrFeNiTi high-entropy alloy composite coating has a uniform and orderly structure, a smooth surface, no obvious defects, and exhibits excellent wear resistance.

[0070] In summary, this invention solves the oxidation problem of Ti in CoCrFeNiT high-entropy alloy coatings by exploring suitable laser remelting processes, resulting in a CoCrFeNiTi-B4C high-entropy alloy composite coating with excellent wear resistance. It should be noted that the scope of this invention should include the specific embodiments in Example 2, but is not limited thereto, and can be varied according to specific applications.

[0071] All matters not covered in this invention are common knowledge.

Claims

1. A method for preparing a B4C-reinforced CoCrFeNiTi high-entropy alloy composite coating, characterized in that: The preparation method described above solves the problem of decreased mechanical properties caused by the oxidation of titanium. Includes the following steps: The first step is to prepare CoCrFeNiTi-B4C composite powder for plasma spraying; CoCrFeNiTi powder and Ni-B4C powder were mixed to form a mixed powder, and then CoCrFeNiTi-B4C composite powder was obtained by ordinary stirring in a three-dimensional mixer for 60 minutes. The CoCrFeNiTi powder has a particle size of 51~105μm, and the Ni-B4C powder has a particle size of 34~98μm; in the mixed powder, B4C accounts for 4-8% of the mass of the mixed powder; in the CoCrFeNiTi powder, the atomic percentages of various elements are Co 22%, Cr 21.08%, Fe 21.09%, Ni 19.07%, and Ti 16.55%; The second step is the pretreatment of the metal substrate, which involves sandblasting the metal substrate. The sandblasting process uses cast steel grit with a size of 0.8-1.2mm; the Vickers hardness of the substrate after sandblasting is 194~208 HV. The metal matrix is ​​made of No. 45 steel; The third step is to prepare a CoCrFeNiTi-B4C composite coating. Plasma spraying was used to spray the CoCrFeNiTi-B4C composite powder obtained in the first step onto the surface of the pretreated metal substrate in the second step, resulting in a coating with a thickness of 500 μm. The spraying parameters were: current 540A, voltage 69.3V, power 37.5kw, argon flow rate 50L / min, hydrogen flow rate 9L / min, spraying distance 120mm, spray gun moving speed 600mm / s, and powder delivery argon flow rate 3.5L / min. Laser cladding technology was used to remelt the sprayed coating to obtain a B4C-reinforced CoCrFeNiTi composite coating. The parameters for the remelting process were: defocusing amount 7 mm, scanning speed 12 mm / s, overlap rate 50%, argon gas flow rate 12 L / min, and power 930 W.

2. The preparation method according to claim 1, characterized in that, The B4C-reinforced CoCrFeNiTi composite coating has a hardness of not less than 751 HV and a wear volume of not more than 0.874 × 10⁻⁶. 6 μm 3 .

3. A method for preparing a B4C-reinforced CoCrFeNiTi high-entropy alloy composite coating, characterized by: The preparation method solves the problem of decreased mechanical properties caused by the oxidation of titanium, and includes the following steps: Unmixed B4C CoCrFeNiTi powder was sprayed and remelted on the surface of 45 steel substrate. The argon flow rate and power in the laser cladding and remelting process were adjusted until there were no black material accumulation areas at the edge and bottom of the molten pool, and the interface between the coating and the substrate was made to have a pot-bottom shaped melting depth of 380-400μm. The laser cladding and remelting parameters were obtained. A mixed powder is obtained by mixing Ni-B4C powder and CoCrFeNiTi powder in a certain proportion, wherein B4C powder accounts for 4-8% of the mass of the mixed powder; Plasma spraying with mixed powder was performed on the pretreated 45 steel substrate. After plasma spraying, remelting was carried out according to the laser cladding and remelting parameters determined above, resulting in a remelted layer with a hardness of not less than 751 HV and a wear volume not greater than 0.874 × 10⁻⁶. 6 μm 3 B4C-reinforced CoCrFeNiTi high-entropy alloy composite coating.

4. The preparation method according to claim 3, characterized in that, The CoCrFeNiTi powder has a particle size of 51~105μm, and the Ni-B4C powder has a particle size of 34~98μm; in the mixed powder, B4C accounts for 6% of the mass of the mixed powder.

5. The preparation method according to claim 3, characterized in that, Remelting equipment model: YLS-4000-KC; Plasma spraying equipment uses PT3X IPS-800 plasma arc spraying power supply and MICO F4 spray gun.

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