CN111876801A - Crack-free Ni-Cr alloy coating and preparation method and application thereof - Google Patents

Abstract

The invention provides a crack-free Ni-Cr alloy coating and a preparation method and application thereof. In the Ni-Cr alloy coating, Ni and Cr are calculated by mass percentage, the content of Cr is 15-25%, and the balance is Ni . The preparation method is as follows: putting a platinum-plated titanium plate into an electroplating solution as an anode, placing a metal workpiece with poor corrosion resistance or no resistance to high temperature oxidation into the electroplating solution as a cathode; connecting a power supply to control the current density to be 8-15A/dm ^2. The temperature of the electroplating solution is 20~30℃, the pH is 2.0~3.0, the mechanical stirring speed is 200~300r/min, and the electroplating time is 15~35min. The Ni-Cr alloy coating prepared by the invention can be used as a protective coating for metal materials with poor corrosion resistance or high temperature oxidation resistance, and can be used for protection of metal materials in thermal power generation, petrochemical, energy transmission pipelines, and offshore oil exploitation platforms.

Description

A kind of crack-free Ni-Cr alloy coating and its preparation method and application

technical field

The invention relates to the technical field of alloy electrodeposition, in particular to a crack-free Ni-Cr alloy coating and a preparation method and application thereof.

Background technique

It is well known that Ni-Cr alloy has corrosion resistance in corrosive liquid medium, and its corrosion resistance increases with the increase of Cr co-precipitation; when the Cr content reaches 20% (mass percentage), the alloy can be thermally grown below 1000 ℃ Continuous protective Cr ₂ O ₃ oxide film, that is, with high temperature oxidation resistance. Ni-Cr protective coatings have also been reported. However, high-quality corrosion-resistant and high-temperature oxidation-resistant Ni-Cr alloy coatings have not been prepared by Ni and Cr co-electrodeposition. The key to the problem is that with the increase of Cr content, the coatings cannot be Avoid microcracks and through cracks, resulting in poor corrosion resistance and high temperature oxidation resistance.

SUMMARY OF THE INVENTION

In order to solve the above-mentioned technical problems, the first aspect of the present invention provides a crack-free Ni-Cr alloy coating. The amount is Ni.

The second aspect of the present invention provides a method for preparing a crack-free Ni-Cr alloy coating. The titanium platinized plate is placed in an electroplating solution as an anode, and a metal workpiece with poor corrosion resistance or high temperature oxidation resistance is placed in the electroplating solution. As the cathode; connect the power supply, control the current density to be 8~15A/dm ² , the temperature of the electroplating solution to be 20~30°C, the pH to be 2.0~3.0, the mechanical stirring speed to be 200~300r/min, and the electroplating time to be 15~35min.

Wherein, the metal workpiece may be Ni-based alloy, Fe-based alloy, carbon steel or alloy steel.

Wherein, the components and concentrations of the electroplating solution are: 0.3~0.4mol/LCrCl ₃ ·6H ₂ O, 0.03~0.05mol/LNiCl ₂ ·6H ₂ O, 0.25~0.35mol/L Na ₃ C ₆ H ₅ O ₇ , 0.85~0.9mol/L HCOONa, 0.9~1.1mol/L CH ₄ ON ₂ , 0.8~0.9mol/L NH ₄ Cl, 0.14~0.16mol/L NaB, 0.65~0.8 mol/LH ₃ BO ₃ , 0.1~ 0.2g/L sodium lauryl sulfate, 0.75~1.5g/L saccharin.

Wherein, the basic formula of the electroplating solution is a chloride salt system.

Wherein, in the electroplating solution, the mass percentage concentration of NaCl is 3.0-4.0%.

Wherein, the metal workpiece is pretreated before electroplating, and the specific process is: mechanical polishing → flowing water washing → chemical degreasing → flowing water washing → deionized water washing → pickling → flowing water washing → deionized water washing.

Wherein, the metal workpiece is chemically degreased with an alkaline washing solution, and the alkaline washing solution components and concentrations are: 15g/L NaOH, 30g/L Na ₂ CO ₃ , 10 g/L Na ₃ PO ₄ .12H ₂ O.

Wherein, the metal workpiece is pickled with a pickling solution, and the formula of the pickling solution by volume is: HF: _HNO3 : _H2SO4 : _H2O = ₁ :1:1:7, pickling The time is 15 minutes.

Wherein, the metal workpiece containing the Ni-Cr alloy coating on the surface after electroplating is placed below 1000° C., and a continuous protective Cr ₂ O ₃ oxide film is thermally grown on the surface of the Ni-Cr alloy coating.

The third aspect of the present invention provides an application of a crack-free Ni-Cr alloy coating, the Ni-Cr alloy coating can be used as a protective coating for metal materials with poor corrosion resistance or high temperature oxidation resistance, and can be used in thermal power generation, petrochemical , energy transmission pipelines, protection of metal materials for offshore oil exploration platforms.

Beneficial effects of the present invention:

The invention takes the commonly used environment-friendly Cr ³⁺ chloride salt system as the basic plating solution, and through the improvement and optimization of its composition, breaks through the technical bottleneck of the preparation of the crack-free Ni-Cr alloy coating with a Cr content of up to 25%. The alloy coating not only has excellent corrosion resistance in corrosive solution, but also has ideal high temperature oxidation resistance in high temperature oxidizing atmosphere because it can form a continuous protective Cr ₂ O ₃ oxide film.

The Ni-Cr alloy coating prepared by the present invention has the following advantages:

1. The coating has no cracks;

2. The distribution of Cr in the coating is uniform, the content is continuously controllable, and the Cr content can reach up to 25%;

3. Used as a protective coating for Ni-based alloys, Fe-based alloys, carbon steel and alloy steel, etc., which can greatly improve their corrosion resistance in corrosive solutions;

4. Used as a high temperature protective coating for Ni-based alloys, Fe-based alloys, carbon steel and alloy steel, etc., it can thermally grow Cr ₂ O ₃ protective oxide film in a high temperature (<1000 ^o C) environment, so that they are not resistant to oxidation. converted to antioxidants;

5. The coating does not need to be processed by vacuum diffusion and can be used directly;

6. The coating has a bright color and can be used as a corrosion-resistant decorative coating;

7. The coating can be used for the protection of metal materials such as thermal power generation, petrochemical, energy transmission pipelines, and offshore oil exploration platforms;

8. The coating preparation process is simple, the cost is low, the preparation is easy, and the application range is wide.

Detailed ways

The following are the preferred embodiments of the present invention. It should be pointed out that for those skilled in the art, some improvements and modifications can be made without departing from the principles of the present invention, and these improvements and modifications are also regarded as the present invention. the scope of protection of the invention.

The invention provides a method for preparing a crack-free Ni-Cr alloy coating, comprising the following steps:

S1. First, pre-process the nickel sheet of the metal workpiece. The pre-processing includes: mechanical grinding → flowing water washing → chemical degreasing → flowing water washing → deionized water washing → pickling → flowing water washing → deionized water washing;

Mechanical grinding is to use 600#, 800#, 1000#, 1200#, 1500#, 2000# sandpaper in turn to polish the nickel sheet until it is bright without scratches;

The chemical degreasing is to place the nickel sheet in an alkaline washing solution, and the components and concentrations of the alkaline washing solution are: 15g/L NaOH, 30g/L Na ₂ CO ₃ , 10 g/L Na ₃ PO ₄ ·12H ₂ O;

Pickling is to place the nickel sheet in a pickling solution, and the formula of the pickling solution by volume is: HF:HNO ₃ :H ₂ SO ₄ :H ₂ O=1:1:1:7, and the pickling time is 15min;

S2, put the platinized titanium plate into the electroplating solution as the anode, and put the nickel sheet pretreated in step S1 into the electroplating solution as the cathode; connect the power supply, control the current density to be 12A/dm ² , and the temperature of the electroplating solution to be 25 ℃, pH is 2.5, mechanical stirring speed is 250r/min, electroplating is 20min;

S3. The nickel sheet containing the Ni-Cr alloy coating on the surface after electroplating in step S2 is placed below 950°C, and a continuous protective Cr ₂ O ₃ oxide film is thermally grown on the surface of the Ni-Cr alloy coating.

The electroplating solution components and concentrations adopted in this embodiment are:

0.35mol/LCrCl ₃ ·6H ₂ O, 0.04mol/L NiCl ₂ ·6H ₂ O, 0.3mol/L Na ₃ C ₆ H ₅ O ₇ , 0.87mol/LHCOONa, 1.0mol/L CH ₄ ON ₂ , 0.85mol /L NH ₄ Cl, 0.15 mol/L NaB, 0.7 mol/L H ₃ BO ₃ , 0.15 g/L sodium dodecyl sulfate, 1 g/L saccharin.

In the coating prepared by using the conventional Ni-Cr alloy electroplating solution formula in the prior art, the mass percentage of Cr content is 12%, and there are many microcracks in the coating, and the SEM surface morphology is shown in Figure 1.

In the coating prepared by using the electroplating solution formula and the electroplating method provided in the embodiment of the present invention, the mass percentage of Cr content is 20%, and the coating is finely crystallized, eliminating the microcracks of the coating, and the SEM surface morphology is shown in Figure 2.

In order to verify the influence of the current density on the Cr content in the Ni-Cr alloy coating, the following will take the above example as a reference, control other process parameters to remain unchanged, and set the current density to 6A/dm ² , 8A/dm ² , 10A/ dm ² , 12A/dm ² , 14A/dm ² , 16A/dm ² , test the Cr content in the coating. Figure 3 is a graph showing the change of the Cr content in the coating with the current density. It can be seen from Figure 3 that when the current density is small, the Cr content in the coating increases with the increase of the current density, and when the current density is 12A/dm ² When , reaches the maximum value, but then with the increase of current density, the Cr content in the coating decreases instead. This is because the deposition potential of Cr ³⁺ is relatively negative. When the current density is small, Ni ²⁺ is mainly deposited on the cathode, and Cr ³⁺ is difficult to be deposited. However, as the current density increases, the cathode polarization increases, so that Cr ^{3 +} The reduction reaction at the cathode proceeds smoothly; but when the cathode current density is too large, a large amount of hydrogen evolves on the cathode surface, which competes with the cathode metal reduction deposition, which is not conducive to the precipitation of Cr ³⁺ , and the surface of the coating is scorched and blackened. The edges are loose and peeling, and the bonding force of the coating becomes poor. Therefore, in order to obtain a qualified coating with high Cr content, the cathode current density is preferably 10-14 A/dm ² .

Figure 4 is a comparison diagram of the polarization curves of Ni substrate and Ni-20Cr (Cr content is 20%) alloy coating in NaCl solution with a mass concentration of 3.5%. It can be seen from Figure 4 that the self-corrosion current of Ni-Cr alloy coating is It is obviously smaller than the self-corrosion current of the Ni substrate, so the corrosion resistance of the Ni-Cr alloy coating in the NaCl solution with a mass concentration of 3.5% is significantly improved.

In order to verify the effect of Cr content on the oxidation rate of Ni-Cr alloy coating in Ni-Cr alloy coating, the oxidation characteristics and properties of Cr ₂ O ₃ film grown when Ni-20Cr alloy coating was oxidized at 900 ^o C were controlled. The oxidation characteristics of Ni substrate without Cr and Ni-15Cr (15% Cr content) alloy coating are compared.

Figure 5 is the oxidation kinetics curve of Ni substrate, Ni-15Cr alloy coating and Ni-20Cr alloy coating at 900℃ for 20h. It can be seen from Figure 5 that the oxidation rate of Ni-20Cr alloy coating decreases sharply, starting from the 15th hour , the coating almost no longer increases in weight, indicating that a dense protective film is formed on the surface of the coating to protect the inner metal from further oxidation, and the oxidation rate of the Ni-15Cr alloy coating is also lower than that of the Ni substrate, but higher than that of the Ni-20Cr alloy. Plating, indicating that a part of the oxide layer protective film is formed on the surface of the plating.

Figure 6 is the SEM surface topography of the oxide layer of the Ni substrate. It can be seen from Figure 6 that the NiO grains grown on the Ni substrate are coarse; while the oxide grown on the Ni-15Cr alloy coating and the Ni-20Cr alloy coating The oxide grains are fine. Figure 7 shows the SEM surface topography of the oxide layer of the Ni-20Cr alloy coating. It can be seen from Figure 7 that the oxide grains on the Ni-20Cr alloy coating are more obvious. From this, it can be seen that the decrease of the crystal grain size is related to the decrease of the oxidation growth rate, which is due to the formation of a Cr ₂ O ₃ rich oxide layer.

The above results can also be verified from the corresponding XRD analysis. Figure 8 is the XRD analysis result of the Ni-20Cr alloy coating. It can be seen from Figure 8 that there are very few NiO and NiCr ₂ O ₄ in the oxide layer of the Ni-20Cr alloy coating. , mainly Cr ₂ O ₃ , indicating that a continuous protective Cr ₂ O ₃ film can be formed rapidly. The corresponding cross-sectional morphologies of Ni substrate, Ni-15Cr alloy coating, and Ni-20Cr alloy coating oxidized at 900 °C for 20 h are shown in Figure 9, Figure 10, and Figure 11, respectively. It can be seen that thick non-dense NiO oxides grow on Ni substrate. The Ni-15Cr alloy coating is obviously thinner because it can grow Cr ₂ O ₃ , but the thickness of the oxide layer is uneven due to the different growth rates of Cr ₂ O ₃ in different places, while the Ni-20Cr alloy coating is continuous The Cr ₂ O ₃ film can be formed quickly, resulting in a very thin oxide film, indicating that the Ni-20Cr alloy coating has ideal high temperature oxidation resistance.

The Ni-Cr alloy coating prepared by the method provided by the present invention can be used as a passivation film rich in Cr ₂ O ₃ in a corrosive solution and a protective Cr ₂ O ₃ film can be thermally grown in a high temperature environment. Protective coatings for metal materials such as Ni-based alloys, Fe-based alloys, carbon steels and alloy steels with poor resistance to room temperature corrosion or high temperature oxidation. Due to the simple process and low preparation cost, it is easy to popularize for thermal power generation, petrochemical, energy Normal temperature/high temperature corrosion protection of metal structural materials such as pipelines and offshore oil drilling platforms.

The above examples only represent specific embodiments of the present invention, and the descriptions thereof are specific and detailed, but should not be construed as a limitation on the scope of the patent of the present invention. It should be pointed out that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can also be made, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention should be subject to the appended claims.

Claims (10)

1. A crack-free Ni-Cr alloy coating is characterized in that: in the Ni-Cr alloy plating layer, the content of Cr is 15-25% by mass percent, and the balance is Ni.

2. A preparation method of a crack-free Ni-Cr alloy coating is characterized by comprising the following steps: putting a titanium platinized plate into the electroplating solution to be used as an anode, and putting a metal workpiece with poor corrosion resistance or poor high-temperature oxidation resistance into the electroplating solution to be used as a cathode; the power supply is switched on, and the current density is controlled to be 8-15A/dm²The temperature of the electroplating solution is 20-30 ℃, the pH value is 2.0-3.0, the mechanical stirring speed is 200-300 r/min, and the electroplating time is 15-35 min.

3. The method of claim 2, wherein the plating solution comprises the following components in concentration: 0.3 to 0.4mol/LCrCl₃·6H₂O，0.03~0.05mol/L NiCl₂·6H₂O，0.25~0.35mol/L Na₃C₆H₅O₇，0.85~0.9mol/L HCOONa，0.9~1.1mol/L CH₄ON₂，0.8~0.9mol/LNH₄Cl，0.14~0.16mol/L NaB，0.65~0.8 mol/L H₃BO₃0.1-0.2 g/L sodium dodecyl sulfate and 0.75-1.5 g/L saccharin.

4. The method for producing a crack-free Ni — Cr alloy plating layer according to claim 3, wherein: the basic formula of the electroplating solution is a chloride system.

5. The method for producing a crack-free Ni — Cr alloy plating layer according to claim 4, wherein: in the electroplating solution, the mass percentage concentration of NaCl is 3.0-4.0%.

6. The method of claim 2, wherein the Ni-Cr alloy plating layer is formed by: the metal workpiece is pretreated before electroplating, and the specific process comprises the following steps: mechanical polishing → flow water washing → chemical degreasing → flow water washing → deionized water washing → acid washing → flow water washing → deionized water washing.

7. The method of claim 6, wherein the Ni-Cr alloy plating layer is formed by: and chemically removing oil from the metal workpiece by using alkaline wash, wherein the alkaline wash comprises the following components in concentration: 15g/L NaOH, 30g/LNa₂CO₃，10 g/L Na₃PO₄·12H₂O。

8. The method of claim 6, wherein the Ni-Cr alloy plating layer is formed by: adopting a pickling solution to pickle the metal workpiece, wherein the formula of the pickling solution comprises the following components in percentage by volume: HF: HNO₃:H₂SO₄:H₂O =1:1:1:7, and the pickling time is 15 min.

9. The method for producing a crack-free Ni — Cr alloy plating layer according to any one of claims 2 to 8, wherein: placing the metal workpiece with the electroplated Ni-Cr alloy coating on the surface below 1000 ℃, and thermally growing continuous protective Cr on the surface of the Ni-Cr alloy coating₂O₃And (5) oxidizing the film.

10. The application of the crack-free Ni-Cr alloy coating is characterized in that: the Ni-Cr alloy coating can be used as a protective coating of a metal material with poor corrosion resistance or no high-temperature oxidation resistance, and can be used for protecting metal materials of thermal power generation, petrifaction, energy transmission pipelines and offshore oil exploitation platforms.

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