An aluminizing slurry for dip coating, its preparation method and use

Abstract

The application discloses a kind of impregnation aluminizing slurry and its preparation method and application, preparation raw material includes: alkali metal hydroxide, silicic acid, polyol, aluminum powder, alkali swelling thickening agent and alkyne diol surfactant.The application proposes a kind of impregnation aluminizing slurry, when using this slurry to impregnate turbine blade, can form the wet state coating with uniform thickness, good surface on the inside passage of blade, and form the uniform protective permeation layer after heat treatment diffusion, and additional protection is not needed during aluminizing process Unpermeated surface, and the quality of permeation layer is not affected.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of coating, and particularly relates to an impregnation coating aluminizing slurry as well as a preparation method and application thereof. BACKGROUND

[0002] Nickel-based superalloy is the most commonly used material for manufacturing gas turbine components. Gas turbine turbine blades are subjected to high-temperature gas corrosion during use, and there is high-temperature oxidation corrosion on the surface under working conditions. In order to improve the temperature resistance of turbine blades, complex cooling channels are used in the turbine blade cavity to achieve film cooling, and protective coatings are applied to the outer surface of the turbine blade. Gas turbine blades are usually cast with hollow internal channels for delivering cooling air. The cross section of the cooling channel is generally circular, and its length is much larger than its diameter. The channel can be straight or curved, and can have a complex profile or a serpentine channel. Proper design of the blade cavity and corresponding cooling technology can enable the high-temperature alloy to withstand higher gas temperatures. However, the temperature in the blade cavity cooling channel still reaches more than 900℃, and the cooling air temperature is sufficient to oxidize the internal channel without protective infiltration. In aviation gas turbine blades, the cooling cavity opening is narrow, and it is difficult to prepare a protective infiltration layer on the internal surface. The corrosion and oxidation of the internal channel of the blade have become a technical problem for engine design. Therefore, for hollow blades, both the surface and the cavity need to be prepared with high-temperature oxidation-resistant coatings to improve the oxidation resistance and high-temperature corrosion resistance of the blade. There are many techniques for preparing high-temperature oxidation-resistant coatings on the outer surface of the blade, mainly including: embedding method, chemical vapor deposition (CVD), gas phase method, hot dipping method, slurry method. At present, the main techniques for preparing high-temperature oxidation-resistant coatings in the cavity are chemical vapor deposition (CVD), gas phase method, and slurry injection method, among which the chemical vapor deposition equipment is not widely used due to its high price. In the production of blade manufacturers in China, the most widely used high-temperature oxidation-resistant coatings for the cavity are solid powder filling method, gas phase method, chemical vapor deposition (CVD), and slurry injection method. Solid powder filling method: uses aluminizing powder by embedding method, which contains alumina, aluminum and alloy powder, halide activator, etc. The aluminizing process similar to the embedding method is not suitable for filling small-diameter (less than 1 cm) channels in the blade cavity, and embedding method generally requires a large amount of powder to produce active gas to deposit the infiltration layer. At the same time, the powder lacks fluidity, limiting its application in curved channels, and the sintered residue is also difficult to remove from the narrow cooling channel. Gas method and chemical vapor deposition method: use gas method to prepare coating, first prepare gaseous compounds containing saturated elements, then deliver them to the part, and through thermal decomposition reaction, reduction reaction, disproportionation reaction or other gas delivery reactions to deposit saturated element atoms to form coating. Gas method and chemical vapor deposition method are consistent in principle, but gas method is uncontrollable and the depth of the infiltration layer is shallower. The latest research of chemical vapor deposition (CVD) is to directly introduce the reaction gas into the equipment, and through diffusion and convection, the reaction gas enters the gas-cooled channel and small holes in the inner cavity of the part and reacts with the hot inner surface of the part to generate a deposition or diffusion type protective coating. Gas method and chemical vapor deposition method require high-temperature resistant materials to protect the un-infiltrated surface, as the active gas will deposit the infiltration layer at the location where it contacts.Meanwhile, the CVD equipment is expensive, difficult to purchase, long in procurement cycle, complicated in operation and small in production capacity, and thus difficult to meet the manufacturing of large batches of blades. The slurry injection method: generally, the slurry composition is injected into the blade cavity and channel, and then sintered at high temperature. According to the principle of forming the infiltration layer, the slurry infiltration aluminum can be divided into diffusion type and melting type. The diffusion type slurry needs an activating agent or a catalyst infiltration agent, such as ammonium chloride, ammonium hydrogen fluoride, etc. The activating agent forms a gas phase compound at high temperature to catalyze the infiltration, and thus a sufficient amount of slurry needs to be filled into the blade hole to generate sufficient gas phase compounds. Generally, an amount of more than 1000 microns is needed to obtain an infiltration layer of 20-50 microns. For small hole diameter (hole diameter less than 1 cm) channels, the active substance is less likely to produce an infiltration layer, and the gas phase compound at high temperature will also be deposited in the non-infiltration part to produce an infiltration layer, which needs a high-temperature protective coating to protect the non-infiltration part and prevent the formation of the infiltration layer. The melting type slurry only uses aluminum powder as the infiltrant without adding an activating agent. The melting type is to make a slurry by adding a binder to the metal or alloy powder, then uniformly apply the slurry on the surface of the workpiece, dry it, and then heat and sinter it in an inert gas or vacuum environment at a temperature slightly higher than the melting point of the slurry. An alloy layer is formed by liquid-solid interface diffusion. The melting method generally only needs to adhere a wet coating layer of several tens of microns on the metal surface, and the thickness of the infiltration layer is proportional to the amount of slurry adhesion. The viscosity of the slurry needs to be controlled, and the sintering residue needs to be easily removed without blocking the hole.

[0003] Therefore, it is urgent to provide a stable slurry suitable for dip coating process. SUMMARY

[0004] The present application aims to at least solve one of the above technical problems in the prior art. To this end, the present application provides a dip coating infiltration aluminum slurry. When the turbine blade is dip coated using the slurry, a wet coating layer with uniform thickness and good surface can be formed on the internal channel of the blade, and a uniform protective infiltration layer can be formed after heat treatment and diffusion. In the process of infiltration aluminum, no additional protection is needed for the non-infiltration surface, and the quality of the infiltration layer is not affected.

[0005] The second aspect of the present application provides a preparation method of the dip coating infiltration aluminum slurry.

[0006] The third aspect of the present application provides an infiltration aluminum protective coating, and the preparation raw material of the infiltration aluminum protective coating comprises the dip coating infiltration aluminum slurry.

[0007] The fourth aspect of the present application provides an application of the infiltration aluminum protective coating in the channel of the nickel-based alloy blade.

[0008] According to the first aspect of the present application, an impregnation slurry for dip coating is provided, and the preparation raw materials include: alkali metal hydroxide, silicic acid, polyol, aluminum powder, alkali swelling thickening agent, and acetylenic diol surfactant.

[0009] According to the first aspect of the present application, at least the following beneficial effects are achieved:

[0010] The present application provides an impregnation slurry for dip coating, the modulus and pH of silicate are controlled by the reaction of silicic acid and alkali metal hydroxide, and then the alcohol compound is compounded, so that the aluminum powder is in a stable state in the slurry, the alkali swelling thickening agent maintains the dispersion effect of the aluminum powder in the slurry and the high viscosity of the slurry, and the acetylenic diol surfactant can form a wet coating with uniform thickness and good appearance on the internal passage of the turbine blade when the turbine blade is dip coated in the above-mentioned slurry. After the wet coating is dried by solvent, the un-impregnated surface does not need to be protected, and then diffusion and heat treatment are performed to obtain a protective impregnated layer on the internal passage, and the residual slurry after diffusion and fusion is automatically peeled off, the surface roughness of the impregnated layer is not affected, and the preparation requirements of the aluminum impregnated layer for the internal cavity and air cooling hole of the blade are met. The problems of the existing technology, such as the great environmental hazard of chromate system impregnation slurry, the low and unadjustable viscosity of the chromate system impregnation slurry, the poor dispersion effect, the unsuitability for dip coating process, and the large amount of catalytic impregnation slurry and the need for protection of the un-impregnated surface, are solved. At the same time, the compounding of the acetylenic diol surfactant with the alkali swelling thickening agent and the silicate has a synergistic effect. In the system, the acetylenic diol surfactant and the thickening agent jointly maintain the high viscosity of the slurry and effectively prevent the sedimentation of the aluminum powder. Not only the adhesion of the coating is improved, but also the dispersion stability of the aluminum powder in the slurry is enhanced, and the influence of the aluminum powder on the dip coating effect due to sedimentation or agglomeration is avoided.

[0011] On the one hand, the traditional impregnation slurry generally has low viscosity and cannot be adjusted, and it is difficult to form a wet coating with a certain thickness on the surface of the blade. The impregnation slurry system provided by the present application does not have strong oxidizing agents, and the alkali swelling thickening agent has high viscosity and good wetting and leveling properties, so it is easy to form a wet coating on the metal surface.

[0012] According to some embodiments of the present application, the alkali metal hydroxide includes at least one of sodium hydroxide, potassium hydroxide, and lithium hydroxide.

[0013] According to some embodiments of the present application, the acetylenic diol surfactant includes at least one of dimethyl octyne diol and tetramethyl decyne diol.

[0014] According to some embodiments of the present application, the alkali-swellable thickener comprises a polyacrylate thickener.

[0015] In a conventional aluminizing slurry, a silicate system is used, generally directly using a silicate with a fixed modulus. High-modulus silicates have poor high-temperature adhesion, and low-modulus silicates are strongly alkaline, making it difficult to maintain the stability of aluminum powder in the slurry for a long time. The modulus needs to be adjusted according to the slurry system. In an alkaline environment, aluminum reacts with the solution to produce a certain amount of high-valence ions. If the system does not have more high-valence polymers to stabilize, it is easy to precipitate with silicates, affecting the dispersion effect of the system. The silicate modulus of the aluminizing slurry system provided by the present application is controllable, and is further compounded with an alcohol compound. The polyacrylate is a high-charge polyelectrolyte, which provides dispersion stability for the system and is not easy to settle. Specifically, the compounding of polyacrylate and silicate plays a synergistic effect. Through compounding with polyacrylate, polyacrylate can effectively neutralize the instability caused by silicates, enhance the overall dispersibility of the slurry, and make the aluminum powder disperse in a more stable system, preventing the problems of aluminum powder settlement and reduced reactivity. At the same time, the introduction of polyacrylate not only stabilizes the dispersibility of silicates and reduces the side effects caused by alkaline environment, but also inhibits the precipitation of high-valence ions by forming a polymer stabilizer, further improving the dispersion stability and uniformity of the system.

[0016] According to some embodiments of the present application, the polyhydric alcohol comprises at least one of dihydric alcohol and trihydric alcohol.

[0017] According to some embodiments of the present application, the polyhydric alcohol has a general formula of CnH2n+2-x(OH)x (x≥2).

[0018] According to some embodiments of the present application, the polyhydric alcohol comprises at least one of oil and ethylene glycol.

[0019] According to some embodiments of the present application, the polyhydric alcohol has a boiling point of not higher than 320℃.

[0020] The alcohol has a corrosion inhibition effect on aluminum powder in the system. The carbon atom is high, the boiling point is high, the curing temperature is too high, the solvent cannot be volatilized, and a dry film cannot be formed. If the boiling point is too low, the solvent will boil at 320℃, resulting in coating defects.

[0021] According to some embodiments of the present application, the preparation raw materials comprise, by weight parts, 1-6 parts of alkali metal hydroxide, 2-10 parts of silicic acid, 6-12 parts of polyhydric alcohol, 30-50 parts of aluminum powder, 0.1-2.0% parts of alkali-swellable thickener, and 0.01-0.2 parts of acetylenic diol surfactant.

[0022] The traditional slurry mainly passivates the surface of aluminum particles by using chromate to form a protective film. In the absence of chromate, the aluminum powder cannot exist in the slurry system for a long time, and the aluminum particles react with water, acid and alkali in the slurry system in a few hours (or even a few minutes), producing hydrogen gas, and finally the aluminum powder loses activity and cannot be applied to the preparation of aluminum infiltration layer. The infiltration slurry provided by the present application is long-term stable and does not contain chromate, and has better environmental protection.

[0023] According to some embodiments of the present application, the preparation raw material of the dip coating aluminum infiltration slurry further comprises water by weight.

[0024] According to some embodiments of the present application, the dip coating aluminum infiltration slurry is composed of 1-6wt% alkali metal hydroxide, 2-10wt% silicic acid, 6-12wt% polyol, 30-50wt% aluminum powder, 0.1-2.0wt% alkali swelling thickening agent and 0.01-0.2wt% acetylenic diol surfactant, and the balance is deionized water.

[0025] According to some embodiments of the present application, the molar ratio of the silicic acid to the alkali metal hydroxide is 1-4.

[0026] The above molar ratio range helps to control the dispersibility of the slurry. Too much silicic acid may cause gelation or agglomeration, which is not conducive to the stability of the slurry. By controlling the ratio of silicic acid and hydroxide, the appropriate viscosity and fluidity of the slurry can be maintained.

[0027] According to some embodiments of the present application, the pH value of the dip coating aluminum infiltration slurry is 11-13.

[0028] By controlling the pH value in the above range, a suitable alkaline environment is provided for the reaction, which helps the aluminum powder to react with metal ions in the solution to form a coating with good adhesion, while avoiding the adverse effects of excessive acidic environment on the quality of the coating. High alkaline conditions also help to maintain the dispersibility of the aluminum powder and avoid particle agglomeration.

[0029] According to some embodiments of the present application, the D50 of the aluminum powder is 4-6μm.

[0030] According to some embodiments of the present application, the mesh number of the aluminum powder is -1000 mesh.

[0031] According to some embodiments of the present application, the aluminum powder is uncoated nitrogen atomized aluminum powder.

[0032] According to a second aspect of the present application, a preparation method of a dip coating aluminum infiltration slurry is provided, comprising:

[0033] S1. dispersing and mixing the alkali metal hydroxide and the silicic acid to obtain a mixed solution 1;

[0034] S2. mixing the alkali swelled thickener, the polyol, the acetylenic diol surfactant and the mixed solution 1 to obtain a mixed solution 2;

[0035] S3. mixing and dispersing the aluminum powder and the mixed solution 2.

[0036] The viscosity property of the slurry is determined according to the national standard GB / T1723-1993 viscosity determination method of paint, and the flow-out time in a coating-4 cup at 25 DEG C is 15s-35s.

[0037] According to some embodiments of the present application, in step S3, the dispersing is performed in a disperser with blades.

[0038] According to some embodiments of the present application, in step S3, the rotating speed of the dispersing is 1000-2000r / min, and the stirring time is 30-40min.

[0039] According to some embodiments of the present application, in step S3, the dispersing further comprises standing after the dispersing.

[0040] After the standing, the slurry is not stratified, and the dip-coating aluminizing slurry is obtained.

[0041] According to a third aspect of the present application, a dip-coating aluminizing slurry is provided.

[0042] According to a fourth aspect of the present application, a dip-coating aluminizing slurry is applied to a nickel-based alloy blade channel.

[0043] According to some embodiments of the present application, the nickel-based alloy blade channel comprises a channel with a pore diameter less than 1cm.

[0044] The present application uses the dip-coating aluminizing slurry to prepare a nickel-based high-temperature alloy blade aluminizing layer, and the preparation method specifically comprises the following steps:

[0045] A1. slurry stirring: stirring with a disperser with blades, rotating speed 1000-2000r / min, stirring for at least 30min;

[0046] A2. viscosity test: using a coating-4 cup to measure the viscosity of the slurry, and the viscosity suitable for dip-coating is 15s-35s;

[0047] A3. blade treatment: using abrasive flow to treat the inner cavity and channel of the turbine blade, and removing the surface oxide layer;

[0048] A4. Dip coating process: the blade with channel is weighed and the blade channel size is measured, and the dip coating area is calculated; the weighed blade is immersed in the slurry at room temperature, the immersion rate is 1-3 mm / s, to prevent too fast immersion rate from causing the slurry to fail to completely wet the inner cavity and channel surface of the blade, first in the immersed state, stand for 3-5 min, then slowly lift away from the dip coating slurry at a speed of 1-3 mm / s; the single dip coating amount needs to meet 15-30 mg / cm 2 For small aperture blades, slow lifting cannot remove the excess slurry in the channel, a gas flow can be used to remove it from the channel, leaving a wet coating layer on the inner wall, if the single dip coating amount is less than 15 mg / cm 2 , add alkali swelling thickener to improve viscosity, if the single dip coating amount is greater than 30 mg / cm 2 , add deionized water to reduce viscosity, measure the slurry viscosity with coating-4 cup, the suitable viscosity for dip coating is 15 s-35 s;

[0049] A5. Air drying treatment: use a rotary drying fan to dry the blade with channel; re-weigh the blade after drying, calculate the thickness of the wet coating after the first dip coating according to the weight, complete the first dip coating; return to step 3 and dip again until the dip coating amount is 15-30 mg / cm 2 ;

[0050] A6. Wet coating drying and curing treatment: dry at 80±5℃ for at least 15 min, remove the water in the wet coating, then cure the coating at 340℃±20℃ for at least 30 min to remove the organic solvent in the coating and cure the silicate.

[0051] If the water is not removed first and the coating is cured directly, the water in the wet coating will directly vaporize, causing bubbles on the surface of the coating.

[0052] A7. Prepare aluminum infiltration layer: put the blade into a tank, put the tank into an argon furnace, heat the furnace to 885℃-900℃, and keep the temperature for 2h; cool down, stop the argon flow when the temperature cools down to ≤100℃;

[0053] A8. Cleaning: after diffusion treatment, when the temperature in the furnace cools down to room temperature, take out the test piece, and when the part cools down, use high-pressure gas flow to remove the residual slurry in the inner cavity and channel of the blade, until the surface of the blade is uniform in color.

[0054] Use metallographic method to check the cross section of the blade after diffusion, the dip coating amount is 20 mg / cm 2The aluminum infiltration layer depth of the vane is 0.065mm-0.070mm, the inner cavity and the vane surface infiltration layer depth is close, and the infiltration layer depth is mainly related to the immersion coating amount. The infiltration layer is divided into two layers, the surface aluminum concentration of the outer layer can reach 28.5wt%, and the surface aluminum concentration of the diffusion layer is 8.5wt%.

[0055] The aluminum infiltration slurry principle of the present application is a melting type aluminum infiltration slurry, mainly through high-temperature aluminum melting, active aluminum elements infiltrate into the vane. Generally, only 50-100 microns of wet coating is needed on the surface of the vane, and the immersion coating amount is 15-30mg / cm 2 After baking and high-temperature diffusion, the vane can obtain 30-100 microns of infiltration layer, and the non-coating part does not need protection. The traditional aluminum infiltration slurry uses gas phase aluminum powder to add solvent to prepare slurry, fills the vane hole, and then diffuses aluminum at high temperature, the principle mainly relies on the gas phase compounds formed by halides such as ammonium chloride at high temperature to catalyze infiltration, therefore, in order to generate enough gas phase compounds, enough slurry needs to be filled into the vane hole, generally more than 1000 microns, to obtain 30-100 microns of infiltration layer, and the gas phase compounds at high temperature will also deposit in the non-infiltration part to produce an infiltration layer, which needs high-temperature protective coating to protect the non-infiltration part and prevent the infiltration layer from being produced. The amount of the aluminum infiltration slurry of the present application is one tenth of the amount of the traditional gas phase slurry to prepare the same thickness of the infiltration layer. DETAILED DESCRIPTION

[0056] The concept and technical effects of the present application will be described below in combination with examples, so as to fully understand the purpose, features and effects of the present application. Obviously, the described examples are only part of the examples of the present application, not all examples, and other examples obtained by those skilled in the art without creative labor based on the examples of the present application are within the scope of protection of the present application.

[0057] Example 1

[0058] A kind of immersion coating aluminum infiltration slurry is prepared in this example, the specific components are shown in Table 1, and the specific process is as follows:

[0059] S1. Preparation of liquid A: mix the alkali hydroxide, silicic acid and deionized water according to the proportion, stir and mix until the solution is clear and transparent;

[0060] S2. Preparation of liquid B: mix the alkali swelling thickening agent, polyol and alkyne diol surfactant according to the proportion with liquid A, stir and mix until the solution is clear and transparent;

[0061] S3. Preparation of the slurry: the aluminum powder and liquid B were mixed in proportion, and stirred with a dispersing machine with blades at a speed of 1000-2000 r / min for at least 30 min, and then left for 30 min. The slurry did not separate, and was ready for use.

[0062] Viscosity test: the viscosity of the slurry was tested according to the national standard GB / T1723-1993, and the results were as follows: the flow-out time in a No. 4 cup was 15-35 s at 25°C.

[0063] The pH value of the slurry in step S3 was 11.

[0064] The specific proportions of the raw materials used in this example are shown in Table 1.

[0065] Examples 2-11

[0066] Examples 2-11 were prepared by using the slurry for aluminum infiltration coating, and the specific components are shown in Table 1. The specific process was the same as that of Example 1.

[0067] Comparative Examples 1-4

[0068] Comparative Examples 1-4 were prepared by using the slurry for aluminum infiltration coating, and the specific components are shown in Table 1. The specific process was the same as that of Example 1.

[0069] Comparative Example 5

[0070] Comparative Example 5 was prepared by using the slurry for aluminum infiltration coating, and the difference from Example 1 was that hydroxyethyl cellulose was used instead of the alkali-swellable thickener in Example 1, and the other conditions were the same.

[0071] Comparative Example 6

[0072] Comparative Example 6 was prepared by using the slurry for aluminum infiltration coating, and the difference from Example 1 was that polyethylene glycol was used instead of the acetylenic diol surfactant in Example 1, and the other conditions were the same.

[0073] Comparative Examples 1-4 were prepared by using the slurry for aluminum infiltration coating, and the specific components are shown in Table 1. The specific process was the same as that of Example 1.

[0074] Table 1. Weight percentage of raw materials for preparing the slurry for aluminum infiltration coating in Examples and Comparative Examples

[0075]

[0076]

[0077] Test Example 1

[0078] In this test example, the slurry for aluminum infiltration coating in Examples and Comparative Examples was used to prepare an aluminum infiltrated layer on a nickel-based superalloy blade. The diameter of the nickel-based superalloy blade workpiece was 0.5 cm. The preparation method was as follows:

[0079] 1. Slurry stirring: stirring with a disperser, rotation speed 1000-2000 r / min, stirring for at least 30 min;

[0080] 2. Viscosity test: measuring the viscosity of the slurry with a Brookfield DV-4 cup;

[0081] 3. Blade treatment: treating the inner cavity and hole of the turbine blade with abrasive grain flow to remove the surface oxide layer;

[0082] 4. Dip coating process: weighing the blade with holes and measuring the size of the blade hole, calculating the dip coating area; immersing the weighed blade into the slurry at room temperature, the immersion rate is 1 mm / s, to prevent the fast immersion rate from failing to completely wet the surface of the inner cavity and hole of the blade, first standing for 3 min in the immersed state, and then slowly lifting away from the dip coating slurry at a speed of 1 mm / s;

[0083] 5. Air drying treatment: air drying the blade with holes with a rotary drying fan;

[0084] 6. Wet coating drying and curing treatment:

[0085] 80±5℃ temperature drying for 15 min to remove the water in the wet coating. Then, the coating is cured at 340℃±20℃ for 30 min.

[0086] 7. Preparing aluminum infiltration layer: loading the blade into a can, loading the can into an argon furnace, heating the furnace to 885℃-900℃, and keeping the temperature for 2 h; cooling, and stopping the argon flow when the temperature cools to ≤100℃;

[0087] 8. Cleaning: after the diffusion treatment, taking out the test piece when the temperature in the furnace cools to room temperature, and removing the residual slurry in the inner cavity and hole of the blade with high-pressure air flow after the part cools, until the color of the blade surface is uniform.

[0088] The aluminum infiltration layer in the experimental examples and the comparative examples is subjected to metallographic examination according to the metallographic examination method for the aluminum infiltration layer of the turbine blade of the aircraft engine in HB 20113-2012.

[0089] Comparative Example 7 uses the process powder embedding aluminum infiltration process and quality inspection standard for steel components in JB / T 10448-2005, in which the aluminum powder (mass fraction) is 30%, the diluent alumina (mass fraction) is 69%, and the catalyst (mass fraction) is 1% for powder embedding aluminum infiltration. The workpiece pipe diameter is 2 cm.

[0090] Comparative Example 8 used the process powder embedding aluminizing in JB / T 10448-2005 Steel Member Solid Aluminizing Process and Quality Inspection Standard, in which the aluminum powder (mass fraction) 30%, diluent alumina (mass fraction) 69% and catalytic agent (mass fraction) 1% were used for powder embedding aluminizing. The workpiece pipe diameter was 0.5 cm. The test results are shown in Table 2.

[0091] Table 2 Metallurgical test results of aluminized layer

[0092]

[0093] The metallurgical test results of the aluminized layer of the examples and comparative examples show that the immersion coating aluminizing slurry of the examples, the aluminized layer depth is positively correlated with the slurry viscosity, and the aluminized layer depth can be controlled by controlling the slurry viscosity. Comparative Examples 5 and 6 show that powder embedding aluminizing is not suitable for small pipe diameter aluminizing, mainly because the pipe diameter is too small, the powder is difficult to enter and fill, or the filling amount is too small, and enough atmosphere cannot be generated in the pipe, resulting in no coating in some areas. While the immersion coating aluminizing slurry mainly relies on the penetration of molten aluminum powder, it does not require sufficient atmosphere. Generally, only a few tens of microns of wet coating on the metal surface is needed, and the aluminized layer thickness is positively correlated with the amount of slurry adhesion. The slurry viscosity needs to be controlled, and the sintering residue should be easily removed without blocking the hole.

[0094] The above has made a detailed description of the embodiments of the present application, but the present application is not limited to the above embodiments, and various changes can be made within the knowledge of those skilled in the art without departing from the spirit of the present application. In addition, the embodiments of the present application and the features in the embodiments can be combined with each other without conflict.

Claims

1. An aluminizing dip coating slurry characterized by, The preparation raw materials include, by weight parts, 1-6 parts of alkali metal hydroxide, 2-10 parts of silicic acid, 6-12 parts of polyhydric alcohol, 30-50 parts of aluminum powder, 0.1-2.0 parts of alkali swelling thickening agent and 0.01-0.2 parts of acetylenic diol surfactant; The pH value of the dip-coating aluminizing slurry is 11-13; The polyhydric alcohol includes at least one of ethylene glycol and glycerol; The acetylenic diol surfactant includes at least one of dimethyl octyne diol and tetramethyl decyne diol; The molar ratio of the silicic acid to the alkali metal hydroxide is 1-4.

2. The dip-coating aluminizing slurry according to claim 1, characterized in that, The alkali metal hydroxide includes at least one of sodium hydroxide, potassium hydroxide and lithium hydroxide.

3. The dip-coating aluminizing slurry according to claim 1, wherein The D50 of the aluminum powder is 4-6 μm.

4. A method for preparing the impregnation slurry for dip-coating aluminizing according to any one of claims 1 to 3, characterized in that, The preparation raw materials include, by weight parts, 1-6 parts of alkali metal hydroxide, 2-10 parts of silicic acid, 6-12 parts of polyhydric alcohol, 30-50 parts of aluminum powder, 0.1-2.0 parts of alkali swelling thickening agent and 0.01-0.2 parts of acetylenic diol surfactant; The preparation raw materials include, by weight parts, 1-6 parts of alkali metal hydroxide, 2-10 parts of silicic acid, 6-12 parts of polyhydric alcohol, 30-50 parts of aluminum powder, 0.1-2.0 parts of alkali swelling thickening agent and 0.01-0.2 parts of acetylenic diol surfactant; 6. Use of the aluminizing protective coating of claim 5 in a nickel-based alloy blade passage. ​ 5. An aluminide barrier coating characterized by, ​ ​

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