A corrosion and wear resistant coating for screw rotor shafts and a method of making screw rotor shafts

Abstract

The application provides a kind of corrosion and wear resistant screw rotor shaft coating and the manufacturing method of screw rotor shaft, specifically relates to surface coating field.The coating is used to cladding in the surface of screw rotor shaft matrix, including transition coating and wear-resistant coating;Transition coating uses one of cobalt-based alloy powder or nickel-based alloy powder;Wear-resistant coating uses high-entropy alloy powder.The surface of screw rotor shaft provided by the application is divided into transition coating and wear-resistant coating by laser cladding, which can realize the gradient change between coatings, so that the obtained composite coating has good strength and toughness and good corrosion resistance in neutral and acidic environments, thereby improving the corrosion and wear resistance of screw rotor shaft;At the same time, full coverage coating cladding is carried out by using multiple spiral paths, which avoids the problem of uneven wear caused by material difference during the use of non-full coverage coating.

Description

Technical Field

[0001] This invention patent relates to the field of surface coating technology, specifically to a corrosion-resistant and wear-resistant screw rotor shaft coating and a method for manufacturing the screw rotor shaft. Background Technology

[0002] Screw vacuum pumps are widely used in semiconductor, machinery, chemical, pharmaceutical, and other manufacturing industries due to their compact structure, stable operation, and high vacuum levels. However, long-term operation in environments containing water vapor, acidic gases, and dust can easily lead to wear and corrosion on the surfaces of working parts, negatively impacting their service life. The rotor shaft, a key component of screw vacuum pumps, is typically made of QT500-7 material. During operation, water vapor may enter the pump through the inlet and come into contact with the rotor shaft surface. This water vapor forms a lubricant through friction, which accelerates friction and wear under prolonged high-speed operation, especially when the water vapor contains acidic components, leading to corrosion of the rotor shaft. Some working environments may contain acidic gases such as sulfuric acid vapor and hydrochloric acid gas. When these acidic gases come into contact with the rotor shaft surface, a chemical reaction occurs, causing corrosion. Corrosion weakens the strength and stability of the shaft material, ultimately leading to wear. Furthermore, dust particles may often be suspended in the working environment and enter the vacuum pump through the inlet. When these particles come into contact with the surface of the screw rotor shaft, they increase friction and cause wear; the wear is particularly pronounced when hard metal particles are present in the dust. When metal powder is deposited on the surface of ductile iron, the large amount of brittle carbides formed in the bonding area will directly cause the coating to crack due to residual stress.

[0003] Currently, chromium plating technology is mainly used to improve the quality and service life of screw rotor shafts. Preparing a chromium plating coating on the surface of traditional screw rotor shaft materials has become a way to improve corrosion and wear resistance. However, since most of it is done by electrochemical methods, the bonding strength between the chromium plating coating and the screw rotor shaft is not high. When operating in a working environment containing water vapor, acidic gases and dust for a long time, the chromium plating coating is prone to peeling off, causing the screw rotor shaft to be directly exposed to the outside, and the anti-corrosion and anti-wear effect is still not good.

[0004] The corrosion-resistant and wear-resistant coating provided by this invention can significantly improve the surface properties of ductile iron and ensure the reliability of screw vacuum pumps under extreme operating conditions. Summary of the Invention

[0005] To overcome the shortcomings of the existing technology and solve the problem of short service life of ordinary screw rotor shafts under long-term operation in working environments containing water vapor, acidic gases, and dust, this invention provides a corrosion-resistant and wear-resistant screw rotor shaft coating and a method for manufacturing the screw rotor shaft. The specific technical solution is as follows:

[0006] A corrosion-resistant and wear-resistant screw rotor shaft coating is used to clad the surface of a screw rotor shaft, comprising a transition coating and a wear-resistant coating; the transition coating is made of cobalt-based alloy powder or nickel-based alloy powder; the wear-resistant coating is made of high-entropy alloy powder.

[0007] Preferably, the components in the cobalt-based alloy powder are as follows by mass percentage: C 0.1-1.5%, Cr 18-21%, Si 0.3-1.5%, W 13-15%, Fe 0.5-3.0%, Mo ≤ 5.5%, Ni 9-12%, Mn 1.0-1.5%, and the balance is Co.

[0008] Preferably, the nickel-based alloy powder contains the following components by mass percentage: C 0.02-0.5%, Cr 2.0-5.0%, Fe 5.0-10%, Mo 0.1-5.0%, B 1.0-3.5%, and the balance being Ni.

[0009] Preferably, the components in the high-entropy alloy powder are as follows by mass percentage: Fe 21.60%, Co 11.39%, Cr 20.10%, Ni 34.04%, B 2.09%, and Nb 10.78%.

[0010] Preferably, the hardness of the transition coating is 250–400 HV. 0.2 The wear-resistant coating has a hardness of 500–650 HV. 0.2 .

[0011] More preferably, the total thickness of the transition coating and the wear-resistant coating is 2.1 to 2.4 mm.

[0012] More preferably, the cobalt-based alloy powder or nickel-based alloy powder used in the transition coating and the high-entropy alloy powder used in the wear-resistant coating both have a particle size of 50-120 μm.

[0013] A method for manufacturing a screw rotor shaft, wherein the surface of the screw rotor shaft is coated with the aforementioned corrosion-resistant and wear-resistant screw rotor shaft coating, specifically including the following steps:

[0014] S1. The dimensions of the screw rotor shaft base are reduced according to the thickness of the transition coating and the wear-resistant coating to be clad;

[0015] S2. Remove the surface oxide layer by grinding the cut screw rotor shaft base with an angle grinder, and polish it smooth with 360, 500 and 1000 grit sandpaper in sequence; then clean the contaminants on the surface of the screw rotor shaft base with anhydrous ethanol, and then put the cleaned screw rotor shaft base into a constant temperature drying oven at 60℃ to dry for later use.

[0016] S3. The screw rotor shaft base is pre-scanned using a fiber semiconductor laser with a laser power of 1500w and a scanning speed of 500mm / s;

[0017] S4. Prepare the alloy powder required for the transition coating and wear-resistant coating, and use laser cladding technology to sequentially clad the transition coating and wear-resistant coating on the surface of the screw rotor shaft substrate;

[0018] S5. Place the screw rotor shaft with the transition coating and wear-resistant coating prepared in step S4 into a furnace for annealing.

[0019] S6. After the annealing process in step S5, the surface of the screw rotor shaft is machined, ground, and polished to obtain a corrosion-resistant and wear-resistant screw rotor shaft with the required dimensions and roughness.

[0020] Preferably, the thickness of the transition coating and the wear-resistant coating in step S4 is adjusted according to the actual needs by the number of cladding cycles; and the thickness of the transition coating in a single cladding cycle is 0.7 to 0.8 mm, and the thickness of the wear-resistant coating in a single cladding cycle is 0.7 to 0.8 mm.

[0021] More preferably, the annealing process in step S5 includes the following sub-steps:

[0022] S5.1. Raise the furnace temperature to 800-1000℃;

[0023] S5.2. Maintain a constant temperature inside the furnace for 4–8 hours;

[0024] S5.3. Cool the furnace to 300-400℃;

[0025] S5.4. Remove the screw rotor shaft and air cool it outside the furnace.

[0026] The beneficial effects of this invention are:

[0027] (1) The corrosion-resistant and wear-resistant screw rotor shaft provided by the present invention has a transition coating and a wear-resistant coating on its surface by laser cladding, which can achieve a gradient change in the coating. The transition coating can be selected according to the material and service requirements of the screw rotor shaft. By designing a composite coating with gradient changes, the difference in expansion coefficient and thermal conductivity caused by abrupt changes in composition is reduced. At the same time, the wear-resistant coating on the surface is composed of FCC phase, Laves phase, NbC phase and NbB2 phase, so that the resulting composite coating has good toughness and wear resistance, and also has good corrosion resistance in neutral and acidic environments, which improves the corrosion and wear resistance of the screw rotor shaft. The service life of the screw rotor shaft made with the coating provided by the present invention can reach more than 5 times that of ordinary screw rotor shafts.

[0028] (2) In the process of cladding the transition coating and the wear-resistant coating, the present invention adopts a multi-spiral path for full-coverage cladding, which avoids the problem of slow feed speed in the axial direction of the single spiral path, heat accumulation and uneven distribution after cladding, which leads to thermal expansion and cracking of the coating; at the same time, full-coverage cladding also avoids the problem of uneven wear caused by material differences in the non-full-coverage coating during use. Attached Figure Description

[0029] The accompanying drawings constituting this application are provided to further understand this application and do not constitute an undue limitation of this application.

[0030] Figure 1 This is a graph showing the change in cross-sectional hardness of the corrosion-resistant and wear-resistant coating of the present invention.

[0031] Figure 2 The image shows a comparison of the electrochemical tafel values ​​of the wear-resistant coating in Example 1 and the ordinary screw rotor shaft material in a 3.5 wt% NaCl solution.

[0032] Figure 3 The image shows a comparison of the electrochemical Tafel values ​​of the wear-resistant coating in Example 2 and the ordinary screw rotor shaft material in 0.5 mol / L HCl solution.

[0033] Figure 4 This is a comparison chart showing the wear amount detection of the wear-resistant coating portion and the surface wear of the ordinary screw rotor shaft material in Example 1;

[0034] Figure 5 This is a comparison chart showing the wear amount detection of the wear-resistant coating portion and the surface wear of the ordinary screw rotor shaft material in Example 2;

[0035] Figure 6 This is a schematic diagram of the laser cladding method for the corrosion-resistant and wear-resistant coating on the surface of the screw rotor shaft in this invention. Detailed Implementation

[0036] Combined with appendix Figure 1-6 The embodiments further illustrate the specific implementation of the corrosion-resistant and wear-resistant screw rotor shaft coating and the manufacturing method of the screw rotor shaft provided by the present invention.

[0037] A corrosion-resistant and wear-resistant screw rotor shaft coating is used to clad the substrate surface of the screw rotor shaft, comprising a transition coating and a wear-resistant coating.

[0038] The transition coating is made of either cobalt-based alloy powder or nickel-based alloy powder. Preferably, the cobalt-based alloy powder contains the following components by mass percentage: C 0.1–1.5%, Cr 18–21%, Si 0.3–1.5%, W 13–15%, Fe 0.5–3.0%, Mo ≤ 5.5%, Ni 9–12%, Mn 1.0–1.5%, with the remainder being Co; the nickel-based alloy powder contains the following components by mass percentage: C 0.02–0.5%, Cr 2.0–5.0%, Fe 5.0–10%, Mo 0.1–5.0%, B 1.0–3.5%, with the remainder being Ni.

[0039] Commonly used cobalt-based alloys include the Stellite series (Stellite 6, Stellite 12, etc.) and the Triballoy series (Triballoy T-400, Triballoy T-800, etc.); commonly used nickel-based alloys include the Inconel series (Inconel 625, Inconel 718, etc.) and the Hastelloy series (Hastelloy C-276, Hastelloy X, etc.).

[0040] The wear-resistant coating is made of high-entropy alloy powder; preferably, the components of the high-entropy alloy powder are as follows by mass percentage: Fe 21.60%, Co 11.39%, Cr 20.10%, Ni 34.04%, B 2.09%, and Nb 10.78%; thus, the chemical formula of the high-entropy alloy powder is FeCo. 0.5 CrNi 1.5 B 0.5 Nb 0.3 .

[0041] Preferably, the hardness of the transition coating is 250–400 HV. 0.2 The wear-resistant coating has a hardness of 500–650 HV. 0.2 The total thickness of the transition coating and the wear-resistant coating is 2.1 to 2.4 mm.

[0042] More preferably, the cobalt-based alloy powder or nickel-based alloy powder used in the transition coating and the high-entropy alloy powder used in the wear-resistant coating both have a particle size of 50-120 μm.

[0043] A method for manufacturing a screw rotor shaft, wherein the surface of the screw rotor shaft is coated with the aforementioned corrosion-resistant and wear-resistant screw rotor shaft coating, specifically including the following steps:

[0044] S1. The dimensions of the screw rotor shaft base are reduced according to the thickness of the transition coating and the wear-resistant coating to be clad;

[0045] S2. Remove the oxide layer from the cut screw rotor shaft base surface by grinding with an angle grinder, and then polish it smooth with 360, 500 and 1000 grit sandpaper in sequence; then clean the contaminants on the surface of the screw rotor shaft base with anhydrous ethanol, and then put the cleaned screw rotor shaft base into a constant temperature drying oven at 60℃ to dry for later use.

[0046] S3. The screw rotor shaft base is pre-scanned using a fiber semiconductor laser with a laser power of 1500w and a scanning speed of 500mm / s;

[0047] S4. Prepare the alloy powder required for the transition coating and wear-resistant coating, and use laser cladding technology to sequentially clad the transition coating and wear-resistant coating on the surface of the screw rotor shaft substrate; the thickness of the transition coating and wear-resistant coating can be adjusted according to actual needs by the number of cladding times, and the required coating thickness can be obtained by multiple stacking; wherein, the thickness of the transition coating in a single cladding is 0.7-0.8 mm, and the thickness of the wear-resistant coating in a single cladding is 0.7-0.8 mm.

[0048] S5. The screw rotor shaft coated with the transition coating and wear-resistant coating obtained in step S4 is placed in a furnace for annealing; wherein the annealing process includes the following sub-steps: S5.1. The furnace temperature is raised to 800-1000℃; S5.2. The furnace temperature is maintained for 4-8 hours; S5.3. The furnace is cooled to 300-400℃; S5.4. The screw rotor shaft is removed from the furnace and air-cooled.

[0049] S6. After the annealing process in step S5, the surface of the screw rotor shaft is machined, ground, and polished to obtain a corrosion-resistant and wear-resistant screw rotor shaft with the required dimensions and roughness.

[0050] The performance advantages of the corrosion-resistant and wear-resistant coating provided by the present invention will be explained below with reference to Examples 1-2:

[0051] First, cast iron plate, which is made of the same material as ordinary screw rotor shaft, was selected as the test substrate and cut into a cuboid of 150mm×50mm×10mm using an EDM machine; the total thickness of the transition coating and wear-resistant coating to be clad was set to 2.2mm, and the size of the test substrate was reduced according to the thickness of the transition coating and wear-resistant coating.

[0052] Secondly, the surface oxide layer of the cut test substrate was removed by grinding with an angle grinder, and then smoothed with 360, 500 and 1000 grit sandpaper in sequence; then the contaminants on the surface of the test substrate were cleaned with anhydrous ethanol, and then the cleaned test substrate was placed in a constant temperature drying oven at 60°C to dry for later use.

[0053] Then, the test substrate was removed and pre-scanned using a fiber semiconductor laser with a laser power of 1500w and a scanning speed of 500mm / s.

[0054] Subsequently, alloy powders required for the transition coating and wear-resistant coating were prepared according to the above component ratio. The transition coating and wear-resistant coating were sequentially clad onto the surface of the test substrate using laser cladding technology. Here, the transition coating was set to be clad once with a thickness of 0.8 mm, and the wear-resistant coating was clad twice with a thickness of 1.4 mm. Preferably, the specific process parameters of the laser cladding process are as follows: a fiber semiconductor laser (LSJG-BGQ-2000) is used for pre-set laser cladding, with a power of 1700-1900 W, a spot diameter of 3-4 mm, an overlap rate of 40%-50%, a scanning speed of 350 mm / min-450 mm / min, a powder feed rate of 30-45 g / min, a protective gas flow rate of 12-14 L / min, and the laser cladding path is along an S-shaped path on the surface of the test substrate. The laser cladding path of the transition coating is opposite to that of the wear-resistant coating. The laser cladding process adopts a full-coverage cladding form.

[0055] Next, the prepared test substrate coated with the transition coating and the wear-resistant coating was placed in a furnace for annealing.

[0056] Subsequently, the surface of the test substrate after annealing is machined, ground, and polished until the surface roughness Ra of the wear-resistant coating of the test substrate is no greater than 0.1 μm and the coefficient of friction is 0.43 to 0.45, thereby obtaining a corrosion-resistant and wear-resistant test substrate with the required dimensions and roughness.

[0057] Finally, the machined, ground, and polished test substrates were subjected to corrosion resistance tests, placed in 3.5wt% NaCl solution and 0.5mol / L HCl solution respectively, to obtain the relevant corrosion resistance parameters of the corrosion-resistant coating surface. These parameters were then compared with those obtained from ordinary screw rotor shaft material QT500-7 under the same test conditions, as detailed below:

[0058] Example 1:

[0059] The test solvent used was 3.5 wt% NaCl, a neutral environmental corrosion test solvent. The transition coating used cobalt-based alloy powder, with the following composition by mass percentage: C 0.1%, Cr 19%, Si 0.5%, W 14%, Fe 2.0%, Mo 5.5%, Ni 10%, Mn 1.0%, and Co 47.9%. The wear-resistant coating used high-entropy alloy powder, with the following composition by mass percentage: Fe 21.60%, Co 11.39%, Cr 20.10%, Ni 34.04%, B 2.09%, and Nb 10.78%. The test duration was 2 hours.

[0060] The corrosion-resistant and wear-resistant screw rotor shaft coating provided by this invention exhibits a self-corrosion potential of -395 mV and a self-corrosion current density of 0.21 μA / cm² in a 3.5 wt% NaCl solution. 2 The self-corrosion potential of the common screw rotor shaft material QT500-7 in a 3.5wt% NaCl solution is -856mV, and the self-corrosion current density is 8.19μA / cm. 2 .

[0061] Example 2:

[0062] The test solvent used was 0.5 mol / L HCl, an acidic environment corrosion test solvent; the transition coating used nickel-based alloy powder, with the following components by mass percentage: C 0.5%, Cr 3.5%, Fe 7.0%, Mo 3.5%, B 2.5%, Ni 83%; the wear-resistant coating used high-entropy alloy powder, with the following components by mass percentage: Fe 21.60%, Co 11.39%, Cr 20.10%, Ni 34.04%, B 2.09%, Nb 10.78%; the test duration was 2 hours.

[0063] The corrosion-resistant and wear-resistant screw rotor shaft coating provided by this invention exhibits a self-corrosion potential of -337 mV and a self-corrosion current density of 1.10 μA / cm² in 0.5 mol / L HCl solution. 2 The self-corrosion potential of the ordinary screw rotor shaft material QT500-7 in 0.5 mol / L HCl solution is -451 mV, and the self-corrosion current density is 875 μA / cm. 2 .

[0064] Combination Figure 2-3 It is evident that, compared to the ordinary screw rotor shaft material QT500-7, the composite coating prepared by this invention has a higher self-corrosion potential and a lower self-corrosion current density. Furthermore, compared to the ordinary screw rotor shaft material QT500-7, the wear-resistant coating portion of the composite coating prepared by this invention shows a significant reduction in wear. Figure 4-5As shown, it can be concluded that the composite coating of the present invention is more suitable for the working requirements of screw vacuum pumps in neutral and acidic environments compared with ordinary screw rotor shaft materials.

[0065] Based on the characteristics of high-carbon substrates, this invention develops a HEA powder with excellent adhesion. By adjusting the proportions of various elements and adding metal additives, a high-performance coating without passivation defects is obtained. The combination of a transition coating and a wear-resistant coating in this invention achieves a gradient change in the coating. Compared to a single high-entropy alloy powder coating, this gradient change significantly reduces the differences in expansion coefficient and thermal conductivity caused by abrupt changes in composition, which often lead to obvious cracks and various defects in the coating. Furthermore, the total thickness of the corrosion-resistant and wear-resistant coating provided by this invention is only about 2.1–2.4 mm, requiring less alloy powder and resulting in lower production costs.

[0066] It is worth noting that the screw rotor shaft surface coating provided in this invention adopts a multi-helix path for full-coverage coating cladding along the screw helix direction. This avoids the problem of slow feed speed in the axial direction of a single helix path, which leads to heat accumulation and uneven distribution after cladding, resulting in thermal expansion and cracking of the coating. Simultaneously, the full-coverage cladding also avoids the problem of uneven wear caused by material differences during use in non-full-coverage coatings, such as… Figure 6 As shown.

[0067] In this invention, terms such as "upper," "lower," "bottom," and "top" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. These terms are merely used to facilitate the description of the structural relationships of the various components or elements of this invention and do not specifically refer to any particular component or element in this invention, nor should they be construed as limiting the invention. Terms such as "connected" and "linked" should be interpreted broadly, indicating a fixed connection, an integral connection, or a detachable connection; a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can determine the specific meaning of the above terms in this invention based on the specific circumstances, and they should not be construed as limiting the invention.

[0068] Of course, the above description is not intended to limit the present invention, and the present invention is not limited to the examples given above. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A corrosion and wear resistant coating for a screw rotor shaft, characterized in that, The application relates to a transition coating and wear-resistant coating for cladding on the surface of a screw rotor shaft. The transition coating is made of cobalt-based alloy powder or nickel-based alloy powder by laser cladding; The wear-resistant coating is made of high-entropy alloy powder by laser cladding; The cobalt-based alloy powder comprises the following components in percentage by mass: C is 0.1-1.5%, Cr is 18-21%, Si is 0.3-1.5%, W is 13-15%, Fe is 0.5-3.0%, Mo is less than or equal to 5.5%, Ni is 9-12%, Mn is 1.0-1.5%, and the balance is Co; The nickel-based alloy powder comprises the following components in percentage by mass: C is 0.02-0.5%, Cr is 2.0-5.0%, Fe is 5.0-10%, Mo is 0.1-5.0%, B is 1.0-3.5%, and the balance is Ni; The high-entropy alloy powder comprises the following components in percentage by mass: Fe is 21.60%, Co is 11.39%, Cr is 20.10%, Ni is 34.04%, B is 2.09%, and Nb is 10.78%.

2. The corrosion and wear resistant coated screw rotor shaft of claim 1, wherein, The hardness of the transition coating is 250-400 HV 0.2 ; the hardness of the wear-resistant coating is 500-650 HV 0.2 .

3. The corrosion and wear resistant coated screw rotor shaft of claim 1 wherein, The total thickness of the transition coating and the wear-resistant coating is 2.1-2.4 mm.

4. The corrosion and wear resistant coated screw rotor shaft of claim 1 wherein, The particle size of the cobalt-based alloy powder or the nickel-based alloy powder used in the transition coating and the high-entropy alloy powder used in the wear-resistant coating is 50-120 mu m.

5. A method of manufacturing a screw rotor shaft, the screw rotor shaft surface being cladding with the corrosion and wear resistant screw rotor shaft coating according to claim 4, characterized in that, Specifically comprises the following steps: S1. According to the thickness of the transition coating and the wear-resistant coating to be cladded, the size of the screw rotor shaft substrate is reduced; S2. The reduced screw rotor shaft substrate is polished by an angle grinder to remove the surface oxidation layer, and is polished smooth by using sandpaper with a mesh of 360, 500 and 1000 in sequence; then the screw rotor shaft substrate is cleaned by using anhydrous ethanol to remove the contaminants on the surface, and is dried in a constant-temperature drying box at 60 DEG C for standby; S3. The screw rotor shaft substrate is pre-scanned by a fiber semiconductor laser, the laser power is 1500 w, and the scanning speed is 500 mm / s; S4. Alloy powder required by the transition coating and the wear-resistant coating is prepared, and the transition coating and the wear-resistant coating are cladded on the surface of the screw rotor shaft substrate by using a laser cladding technology; S5. The screw rotor shaft with the transition coating and the wear-resistant coating prepared in the step S4 is placed in a furnace for annealing process treatment; S6. The surface of the screw rotor shaft after the annealing process treatment in the step S5 is machined, polished and polished to obtain a corrosion-resistant and wear-resistant screw rotor shaft with required size and roughness.

6. The method of manufacturing a screw rotor shaft according to claim 5, wherein, The thickness of the transition coating and the wear-resistant coating in the step S4 is adjusted according to the actual requirement, the single cladding thickness of the transition coating is 0.7-0.8 mm, and the single cladding thickness of the wear-resistant coating is 0.7-0.8 mm.

7. The method of manufacturing a screw rotor shaft according to claim 5, wherein The annealing process treatment in the step S5 comprises the following sub-steps: S5.

1. The temperature in the furnace is raised to 800-1000 DEG C; S5.

2. The temperature in the furnace is kept constant for 4-8 h; S5.

3. The furnace is cooled to 300-400 DEG C; S5.

4. The screw rotor shaft is taken out of the furnace for air cooling.

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