Preparation method of wear-resistant heterogeneous pure chromium coating

Abstract

The invention relates to the technical field of chromium plating layers, in particular to a preparation method of a wear-resistant heterogeneous pure chromium plating layer. The method comprises the following steps: performing surface treatment on a workpiece and pure chromium powder; dispersing the treated pure chromium powder in the electroplating solution by adopting an ultrasonic method to form an electroplating solution colloid; the workpiece is connected with a cathode of a direct-current power supply to serve as an electroplating cathode plate, the lead-tin alloy plate is connected with an anode of the direct-current power supply to serve as an electroplating anode plate, and the electroplating cathode plate and the electroplating anode plate are arranged in the electroplating liquid colloid to form an electroplating loop; starting a direct-current power supply, and preparing an isomerous pure chromium plating layer by utilizing deposition; and hydrogen removal treatment is conducted on the deposited workpiece. According to the method, the heterogeneous pure chromium plating layer is prepared through deposition, chromium atoms are continuously deposited, a freely-growing chromium matrix is in a low-energy state, the defect density of grown chromium crystals is very low, meanwhile, chromium particles are consistent with the plating layer in component, have affinity and wettability with the chromium matrix, and can form colloidal suspension in a plating solution, so that the chromium particles are not prone to falling off. And the obtained heterogeneous pure chromium plating layer has relatively high wear resistance.

Description

Technical Field

[0001] The invention relates to the technical field of chromium plating layers, and in particular to a method for preparing a wear-resistant heterogeneous pure chromium plating layer. Background Art

[0002] Due to its excellent properties, chrome plating is widely used as the outer layer and functional coating of protective and decorative coating systems, and has always occupied an important position in the electroplating industry. Hard chrome (wear-resistant chrome) plating has extremely high hardness (800-1200 HV) and wear resistance, which can extend the service life of workpieces such as cutting and drawing tools, various materials pressing and casting molds, bearings, shafts, gauges, gears, etc., and can also be used to repair the dimensional tolerances of worn parts. The thickness of hard chrome is generally 5-50 μm, but can be adjusted according to needs, and some can reach as high as 200-800 μm.

[0003] Traditional hard chrome electroplating processes often result in numerous apparent cracks due to internal stresses and crystal transformations during the deposition process. On the one hand, these cracked areas create stress concentrations, making them susceptible to greater wear during friction. Stress concentration at the crack edges accelerates localized wear, impacting overall performance. On the other hand, these cracks can gradually expand and connect, ultimately leading to coating delamination. The abrasive particles that fall off during frictional contact can further exacerbate wear and increase the wear rate. Furthermore, the presence of cracks can affect surface smoothness and topography, altering the coefficient of friction and causing unstable workpiece operation.

[0004] In order to improve the wear resistance of traditional hard chrome coatings, new processes such as microcrack and microporous chrome, black chrome, loose-porous chrome, and trivalent chrome plating have been developed. Although the friction and wear performance of these new processes has been improved, they still have their own technical difficulties: (1) Microcrack, microporous, and loose-porous chrome coatings still have cracks of a certain density, which does not fundamentally solve the problem of surface cracks; (2) Although black chrome has a uniform gloss, good decorative properties, and good matting properties, its hardness is only 150-350HV. Therefore, it is currently mainly used as decorative chrome; (3) Although the trivalent chromium electroplating process is more environmentally friendly, the coating can often only reach a few microns and the efficiency is very low, which limits its application in the field of friction and wear.

[0005] Furthermore, the commonality among these new processes is that the chromium coating is microscopically uniform, which does not address the problem of localized stress concentration during friction. A study [Chen, X. et al. Lowering Coefficient of Friction in Cu Alloys with Stable Gradient Nanostructures, Science Advances, 2016, 2:e1601942] on the friction and wear behavior of gradient nanocrystalline copper found that the mixed soft and hard structures can effectively coordinate internal stresses, resulting in a stable low coefficient of friction and wear rate.

[0006] The paper [Zhu, YT and Wu XL, Heterostructured materials, Progress in Materials Science, 2022, 131: 101019] proposes the concept of heterogeneous materials and points out that due to the structural diversity and synergistic effects of components, these metal materials can break through the performance limits of single materials through precise design of interfaces, phase distribution, and scale effects, meeting the needs of cutting-edge fields for multifunctionality and high reliability. Currently, the main methods for preparing heterogeneous metal materials are powder metallurgy and severe plastic deformation combined with heat treatment. Due to voids and interface issues, the plasticity of heterogeneous metal materials obtained by powder metallurgy is generally poor. The strategy of achieving heterogeneity through severe plastic deformation combined with heat treatment is to first obtain a nano / ultrafine grain structure through mechanical deformation, then recrystallize some of the nanocrystals into larger grains through heat treatment, ultimately obtaining a heterogeneous metal material with excellent performance. However, due to the thermal instability, residual stress and size effect of nano-grains, the heterogeneous materials obtained after heat treatment generally have the problem of structural inhomogeneity (volume fraction of soft and hard structures, recrystallization unit size, recrystallized grain size and recrystallized grain distribution, etc.) which is difficult to precisely control. Summary of the Invention

[0007] In response to the problems existing in the background technology, a method for preparing a wear-resistant heterogeneous pure chromium coating is proposed. The heterogeneous pure chromium coating is prepared by deposition. Through the continuous deposition of chromium atoms, the freely growing chromium matrix moves towards a low-energy state. The defect density of the grown chromium crystals is very low. At the same time, the chromium particles have the same composition as the coating, have affinity and wettability with the chromium matrix, and can form a colloidal suspension in the plating solution. The obtained heterogeneous pure chromium coating has strong wear resistance. The specific steps include:

[0008] S1. Surface treatment of the workpiece and pure chromium powder;

[0009] S2, dispersing the treated pure chromium powder in the electroplating solution by ultrasonic method to form an electroplating solution colloid;

[0010] S3, connecting the workpiece to the negative pole of a DC power supply as an electroplating cathode plate, and connecting the lead-tin alloy plate to the positive pole of a DC power supply as an electroplating anode plate, and placing both in the electroplating solution colloid to form an electroplating circuit;

[0011] S4, turning on the DC power supply to prepare a heterogeneous pure chromium coating by deposition;

[0012] S5. Dehydrogenate the deposited workpiece.

[0013] Preferably, the average particle size of the pure chromium powder in S1 is 0.8-10 μm.

[0014] Preferably, the surface treatment process in S1 includes pickling, rinsing with pure water for 2-4 minutes, chemical degreasing, rinsing with pure water for 2-4 minutes, and vacuum drying.

[0015] Preferably, the ultrasonic frequency of the ultrasonic method in S2 is 15-55 kHz, and the ultrasonic time is 30-60 min.

[0016] Preferably, the amount of pure chromium powder added to each 1L of electroplating solution in S2 is 0.5-30g.

[0017] Preferably, the tin content of the lead-tin alloy plate in S3 is 0-5%.

[0018] Preferably, S4 needs to stir the plating solution colloid during the electroplating process, the electroplating temperature is 50-70°C, and the electroplating current density is 30-70A / dm 2 The electroplating voltage is controlled by the current density, and the electroplating time is 20min-4h.

[0019] Preferably, the dehydrogenation conditions in S5 are 170-200° C. and heating for 2-12 h.

[0020] The present invention also proposes a heterogeneous pure chromium coating prepared by the above-mentioned preparation method of wear-resistant heterogeneous pure chromium coating. The friction coefficient of the heterogeneous pure chromium coating is 0.4, and the wear loss is 0.02mm. 3 N -1 m -1 .

[0021] Compared with the existing technology, the present invention has the following beneficial technical effects: the present invention utilizes deposition to prepare heterogeneous pure chromium coatings. On the one hand, through the continuous deposition of chromium atoms, the freely growing chromium matrix moves toward a low-energy state, and the defect density of the grown chromium crystals is very low. On the other hand, since the composition of the chromium particles is consistent with that of the coating, they have good affinity and wettability with the chromium matrix, and can form a colloidal suspension in the plating solution. Under the action of stirring, they interact with the workpiece along with the water flow and are easily deposited on the surface of the workpiece. As chromium atoms continue to accumulate, the chromium particles are gradually immersed in the chromium matrix, and the interface can be seamlessly combined. The pure chromium particles are evenly dispersed in the aggregate as the second phase, and can also connect to the matrix, release the residual stress of the matrix, and reduce the apparent crack density of the coating. The obtained heterogeneous pure chromium coating has a friction coefficient of 0.4 and a wear amount of 0.02 mm. 3 N -1 m -1 , and has strong wear resistance. Furthermore, the electroplating process involved in the present invention is relatively mature and free of technical difficulties. It features simple equipment, low cost, and strong operability. The pure chromium powder particle size and electroplating parameters can be adjusted according to actual needs to produce heterogeneous coatings that meet different performance requirements. In other words, both material preparation parameters and material properties can be controlled within a certain range. The present invention offers a simple process, low investment, a high safety factor, and high production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 A diagram of an apparatus for implementing a method for preparing a wear-resistant heterogeneous pure chromium coating;

[0023] Figure 2 This is an enlarged view of the surface morphology of the heterogeneous pure chromium coating prepared in the present invention.

[0024] Figure numerals: 1. electroplating cathode plate; 2. electroplating anode plate; 3. electroplating liquid colloid; 4. DC power supply;. DETAILED DESCRIPTION

[0025] The following is a detailed description of the specific embodiments of the present invention. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention and are not intended to limit the present invention.

[0026] Example 1

[0027] The present invention provides a method for preparing a wear-resistant heterogeneous pure chromium coating, comprising the following steps:

[0028] 1) Surface treatment of pure chromium powder with an average particle size of 5 μm and a stainless steel workpiece to obtain a workpiece with a clean surface and pure chromium powder;

[0029] The specific process of surface treatment is as follows: pickling (nitric acid 50ml / L, hydrofluoric acid 20ml / L, corrosion inhibitor Lan-8262.5g / L, temperature control 25℃, immersion time 30s), pure water cleaning for 4min, chemical degreasing (sodium hydroxide 50g / L, industrial detergent 1ml / L, pure water 1L; temperature control 55℃, immersion time 10min), pure water cleaning for 4min, vacuum drying;

[0030] 2) 30 g of pure chromium powder was dispersed in 2 L of electroplating solution using an ultrasonic method (ultrasonic frequency of 40 kHz, ultrasonic time of 40 min) to form electroplating solution colloid 3;

[0031] The electroplating solution contains the following components, with the concentrations of each component being: 250 g / L chromic acid, 20 g / L sulfuric acid, 5 g / L brightener, and 5 g / L buffer; the brightener is sodium methane disulfonate, and the buffer is sodium dihydrogen phosphate;

[0032] 3) If Figure 1 As shown, a stainless steel plate workpiece is connected to the negative pole of a DC power supply 4 as an electroplating cathode plate 1, and a lead-tin alloy (tin content 4%) plate is connected to the positive pole of a DC power supply 4 as an electroplating anode plate 2, and placed in an electroplating liquid colloid 3 to form an electroplating circuit;

[0033] 4) Stir the electroplating solution colloid 3, turn on the DC power supply 4, the electroplating temperature is 60℃, and the electroplating current density is 40A / dm 2 , the electroplating voltage is driven, and the heterogeneous pure chromium coating is deposited and prepared. The electroplating time is 4 hours, and the preparation of the heterogeneous pure chromium coating is completed;

[0034] 5) The workpiece having the heterogeneous pure chromium coating is placed in a blast drying oven for dehydrogenation treatment at a temperature of 200° C. for 12 h.

[0035] Example 2

[0036] 1) Surface treatment of pure chromium powder with an average particle size of 10 μm and a stainless steel workpiece to obtain a workpiece with a clean surface and pure chromium powder;

[0037] The specific process of surface treatment is as follows: pickling (nitric acid 50ml / L, hydrofluoric acid 60ml / L, corrosion inhibitor Lan-8263g / L, temperature control 30℃, immersion time 20s), pure water cleaning for 3min, chemical degreasing (sodium hydroxide 45g / L, industrial detergent 2ml / L, pure water 1L; temperature control 60℃, immersion time 5min), pure water cleaning for 3min, vacuum drying;

[0038] 2) 10 g of pure chromium powder was dispersed in 2 L of electroplating solution using an ultrasonic method (ultrasonic frequency of 40 kHz, ultrasonic time of 30 min) to form electroplating solution colloid 3;

[0039] The electroplating solution contains the following components, with the concentrations of each component being: 500 g / L chromium, 15 g / L sulfuric acid, 8 g / L brightener, and 10 g / L buffer; the brightener is a mixture of sodium methane disulfonate and polyvinyl pyrrolidone in a ratio of 1:1, and the buffer is sodium acetate;

[0040] 3) If Figure 1 As shown, a stainless steel plate workpiece is connected to the negative pole of a DC power supply 4 as an electroplating cathode plate 1, and a lead-tin alloy (tin content 4%) plate is connected to the positive pole of a DC power supply 4 as an electroplating anode plate 2, and placed in an electroplating liquid colloid 3 to form an electroplating circuit;

[0041] 4) Stir the electroplating solution colloid 3, turn on the DC power supply 4, the electroplating temperature is 55°C, and the electroplating current density is 55A / dm 2 , the electroplating voltage is driven, and the heterogeneous pure chromium coating is deposited and prepared. The electroplating time is 4 hours, and the preparation of the heterogeneous pure chromium coating is completed;

[0042] 5) The workpiece having the heterogeneous pure chromium coating is placed in a blast drying oven for dehydrogenation treatment at a temperature of 200° C. for 5 h.

[0043] Example 3

[0044] 1) Surface treatment of pure chromium powder with an average particle size of 0.8 μm and a stainless steel workpiece to obtain a workpiece with a clean surface and pure chromium powder;

[0045] The specific process of surface treatment is as follows: pickling (nitric acid 70ml / L, hydrofluoric acid 50ml / L, corrosion inhibitor Lan-8263g / L, temperature control 30℃, immersion time 25s), pure water cleaning for 3min, chemical degreasing (sodium hydroxide 55g / L, industrial detergent 2ml / L, pure water 1L; temperature control 60℃, immersion time 8min), pure water cleaning for 2min, vacuum drying;

[0046] 2) 60 g of pure chromium powder was dispersed in 2 L of electroplating solution using an ultrasonic method (ultrasonic frequency of 30 kHz, ultrasonic time of 60 min) to form electroplating solution colloid 3;

[0047] The electroplating solution contains the following components, with the concentrations of each component being: 300 g / L chromic acid, 20 g / L sulfuric acid, 5 g / L brightener, and 10 g / L buffer; the brightener is sodium lauryl sulfate, and the buffer is a 1:1 mixture of sodium carbonate and sodium acetate;

[0048] 3) If Figure 1 As shown, a stainless steel plate workpiece is connected to the negative pole of a DC power supply 4 as an electroplating cathode plate 1, and a lead-tin alloy (tin content 4%) plate is connected to the positive pole of a DC power supply 4 as an electroplating anode plate 2, and placed in an electroplating liquid colloid 3 to form an electroplating circuit;

[0049] 4) Stir the electroplating solution colloid 3, turn on the DC power supply 4, the electroplating temperature is 60°C, and the electroplating current density is 45A / dm 2 , the electroplating voltage is driven, and the heterogeneous pure chromium coating is deposited and prepared. The electroplating time is 2h, and the preparation of the heterogeneous pure chromium coating is completed;

[0050] 5) The workpiece having the heterogeneous pure chromium coating is placed in a blast drying oven for dehydrogenation treatment at a temperature of 180° C. for 12 h.

[0051] Example 4

[0052] The present invention provides a method for preparing a wear-resistant heterogeneous pure chromium coating, comprising the following steps:

[0053] 1) Surface treatment of pure chromium powder with an average particle size of 0.2 μm and a stainless steel workpiece to obtain a workpiece with a clean surface and pure chromium powder;

[0054] The specific process of surface treatment is as follows: pickling (nitric acid 50ml / L, hydrofluoric acid 20ml / L, corrosion inhibitor Lan-8262.5g / L, temperature control 25℃, immersion time 30s), pure water cleaning for 4min, chemical degreasing (sodium hydroxide 50g / L, industrial detergent 1ml / L, pure water 1L; temperature control 55℃, immersion time 10min), pure water cleaning for 4min, vacuum drying;

[0055] 2) 30 g of pure chromium powder was dispersed in 2 L of electroplating solution using an ultrasonic method (ultrasonic frequency of 40 kHz, ultrasonic time of 40 min) to form electroplating solution colloid 3;

[0056] The electroplating solution contains the following components, with the concentrations of each component being: 250 g / L chromic acid, 20 g / L sulfuric acid, 5 g / L brightener, and 5 g / L buffer; the brightener is sodium methane disulfonate, and the buffer is sodium dihydrogen phosphate;

[0057] 3) If Figure 1 As shown, a stainless steel plate workpiece is connected to the negative pole of a DC power supply 4 as an electroplating cathode plate 1, and a lead-tin alloy (tin content 4%) plate is connected to the positive pole of a DC power supply 4 as an electroplating anode plate 2, and placed in an electroplating liquid colloid 3 to form an electroplating circuit;

[0058] 4) Stir the electroplating solution colloid 3, turn on the DC power supply 4, the electroplating temperature is 60℃, and the electroplating current density is 40A / dm 2 , the electroplating voltage is driven, and the heterogeneous pure chromium coating is deposited and prepared. The electroplating time is 4 hours, and the preparation of the heterogeneous pure chromium coating is completed;

[0059] 5) The workpiece having the heterogeneous pure chromium coating is placed in a blast drying oven for dehydrogenation treatment at a temperature of 200° C. for 12 h.

[0060] Example 5

[0061] The present invention provides a method for preparing a wear-resistant heterogeneous pure chromium coating, comprising the following steps:

[0062] 1) Surface treatment of pure chromium powder with an average particle size of 12 μm and a stainless steel workpiece to obtain a workpiece with a clean surface and pure chromium powder;

[0063] The specific process of surface treatment is as follows: pickling (nitric acid 50ml / L, hydrofluoric acid 20ml / L, corrosion inhibitor Lan-8262.5g / L, temperature control 25℃, immersion time 30s), pure water cleaning for 4min, chemical degreasing (sodium hydroxide 50g / L, industrial detergent 1ml / L, pure water 1L; temperature control 55℃, immersion time 10min), pure water cleaning for 4min, vacuum drying;

[0064] 2) 30 g of pure chromium powder was dispersed in 2 L of electroplating solution using an ultrasonic method (ultrasonic frequency of 40 kHz, ultrasonic time of 40 min) to form electroplating solution colloid 3;

[0065] The electroplating solution contains the following components, with the concentrations of each component being: 250 g / L chromic acid, 20 g / L sulfuric acid, 5 g / L brightener, and 5 g / L buffer; the brightener is sodium methane disulfonate, and the buffer is sodium dihydrogen phosphate;

[0066] 3) If Figure 1 As shown, a stainless steel plate workpiece is connected to the negative pole of a DC power supply 4 as an electroplating cathode plate 1, and a lead-tin alloy (tin content 4%) plate is connected to the positive pole of a DC power supply 4 as an electroplating anode plate 2, and placed in an electroplating liquid colloid 3 to form an electroplating circuit;

[0067] 4) Stir the electroplating solution colloid 3, turn on the DC power supply 4, the electroplating temperature is 60℃, and the electroplating current density is 40A / dm 2 , the electroplating voltage is driven, and the heterogeneous pure chromium coating is deposited and prepared. The electroplating time is 4 hours, and the preparation of the heterogeneous pure chromium coating is completed;

[0068] 5) The workpiece having the heterogeneous pure chromium coating is placed in a blast drying oven for dehydrogenation treatment at a temperature of 200° C. for 12 h.

[0069] Comparative Example 1

[0070] The heterogeneous pure chromium coating was prepared according to the method of Example 1, except that in step (1), the surface of the pure chromium powder was not subjected to chemical degreasing treatment.

[0071] Test Example 1

[0072] 1) The surface of the heterogeneous pure chromium coating prepared in Example 1 was observed using a Quanta250 scanning electron microscope (FEI). The specific results are shown in Figure 2 .Depend on Figure 2 It can be seen that the pure chromium particles are uniformly embedded in the chromium matrix, and the surface of the pure chromium particles has good bonding with the chromium matrix. No obvious pores or cracks were found under a scanning electron microscope. In addition, electroplating is a process of continuous atomic deposition. The freely growing chromium matrix moves towards a low-energy state, and the chromium particles can effectively coordinate and release internal stress. This is the fundamental reason why the heterogeneous pure chromium coating prepared by the present invention has good friction and wear properties.

[0073] The tests were performed using the same method, and the test results of Examples 1 and 3 were basically consistent with those of Example 2. However, the test results of Examples 4-5 were slightly worse. Specifically, when the pure chromium particle size was less than 0.8 μm, some chromium particles easily agglomerated in the plating solution. The aggregated particles introduced voids into the matrix, reducing the density. When the chromium particle size was greater than 10 μm, sedimentation was likely to occur, reducing the probability of chromium particles being deposited on the workpiece. The test result of Comparative Example 1 was the worst. Specifically, after electroplating, the chromium particles had poor bonding with the matrix, with many cracks and gaps at the interface between the two, and the wear rate was excessively high.

[0074] 2) The friction and wear properties of the heterogeneous pure chromium coating prepared above were tested using an MMW-1 vertical universal wear tester (Jinan Quanli Testing Technology Co., Ltd.). The test results are shown in Table 1. The friction coefficient is 0.4-0.43, and the wear volume is 0.02-0.05 mm. 3 N -1 m -1 , wherein Example 1 is the optimal implementation scheme.

[0075] Table 1

[0076]

[0077] The embodiments of the present invention are described in detail above with reference to the accompanying drawings, but the present invention is not limited thereto. Various changes can be made within the scope of knowledge possessed by those skilled in the art without departing from the spirit of the present invention.

Claims

1. A method for preparing a wear-resistant heterogeneous pure chromium coating, characterized in that the steps include: S1. Surface treatment of the workpiece and pure chromium powder; S2, dispersing the treated pure chromium powder in the electroplating solution by ultrasonic method to form an electroplating solution colloid (3); S3, connecting the workpiece to the negative electrode of a DC power supply (4) as an electroplating cathode plate (1), and connecting the lead-tin alloy plate to the positive electrode of the DC power supply (4) as an electroplating anode plate (2), and placing both in an electroplating liquid colloid (3) to form an electroplating circuit; S4, turning on the DC power supply (4) to prepare a heterogeneous pure chromium coating by deposition; S5. Dehydrogenate the deposited workpiece.

2. The method for preparing the wear-resistant heterogeneous pure chromium coating according to claim 1, characterized in that: The average particle size of the pure chromium powder in S1 is 0.8-10 μm.

3. The method for preparing the wear-resistant heterogeneous pure chromium coating according to claim 1, characterized in that: The surface treatment process in S1 includes pickling, rinsing with pure water for 2-4 minutes, chemical degreasing, rinsing with pure water for 2-4 minutes, and vacuum drying.

4. The method for preparing the wear-resistant heterogeneous pure chromium coating according to claim 1, characterized in that: The ultrasonic frequency of the ultrasonic method in S2 is 15-55 kHz, and the ultrasonic time is 30-60 min.

5. The method for preparing the wear-resistant heterogeneous pure chromium coating according to claim 1, characterized in that: The amount of pure chromium powder added to each 1L of electroplating solution in S2 is 0.5-30g.

6. The method for preparing the wear-resistant heterogeneous pure chromium coating according to claim 1, characterized in that: The tin content of the lead-tin alloy plate in S3 is 0-5%.

7. The method for preparing the wear-resistant heterogeneous pure chromium coating according to claim 1, characterized in that: S4 needs to stir the plating solution colloid (3) during the electroplating process, the electroplating temperature is 50-70℃, and the electroplating current density is 30-70A / dm 2 The electroplating voltage is controlled by the current density, and the electroplating time is 20min-4h.

8. The method for preparing the wear-resistant heterogeneous pure chromium coating according to claim 1, characterized in that: The dehydrogenation conditions in S5 are 170-200°C and heating for 2-12h.

9. A heterogeneous pure chromium coating prepared by the method for preparing a wear-resistant heterogeneous pure chromium coating according to claims 1 to 8.

10. The heterogeneous pure chromium coating according to claim 9, characterized in that: The friction coefficient of the heterogeneous pure chromium coating is 0.4 and the wear loss is 0.02mm 3 N -1 m -1 .

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