Dip-coating aluminizing slurry as well as preparation method and application thereof

Abstract

The invention discloses dip-coating aluminizing slurry as well as a preparation method and application thereof. The dip-coating aluminizing slurry is prepared from the following raw materials: alkali metal hydroxide, silicic acid, polyol, aluminum powder, an alkali swelling thickener and an alkynediol surfactant. According to the dip-coating aluminizing slurry provided by the invention, when the slurry is used for dip-coating a turbine blade, a wet-state coating which is consistent in thickness and good in surface can be formed on an internal channel of the blade, a uniform protective infiltrated layer is formed after heat treatment diffusion, an un-infiltrated surface does not need to be additionally protected in the aluminizing process, and the quality of the infiltrated layer is not influenced.

Description

Technical Field

[0001] The invention belongs to the technical field of coatings, and in particular relates to a dip-coating aluminizing slurry and a preparation method and application thereof. Background Art

[0002] Nickel-based high-temperature alloys are the most commonly used materials for manufacturing gas turbine components. Gas turbine blades are corroded by high-temperature gas during use, and high-temperature oxidation corrosion occurs on their surfaces under working conditions. In order to improve the temperature bearing capacity of turbine blades, complex cooling channels are used in the inner cavity of turbine blades to achieve air film cooling, and protective coatings are applied to their outer surfaces. Gas turbine blades are usually cast with hollow internal channels for conveying cooling air. The cross-section of the cooling channel is generally circular, and its length is many times larger than its diameter. The channel can be straight or curved, and may have complex contours or serpentine channels. Reasonable design of the blade cavity and corresponding cooling technology can enable high-temperature alloys to withstand higher gas temperatures. However, the temperature in the cooling channel of the blade cavity still reaches above 900°C, and the cooling air temperature is sufficient to oxidize the internal channel without a protective carbide layer. In aviation gas turbine blades, the cooling cavity opening is narrow, and it is difficult to prepare a protective carbide layer on the inner surface. Corrosion and oxidation of the internal channel of the blade has become a technical problem in engine design. Therefore, for hollow blades, both the surface and the inner cavity need to be prepared with a high-temperature anti-oxidation coating to improve the oxidation resistance and high-temperature corrosion resistance of the blade. There are many preparation technologies for high-temperature anti-oxidation coatings on the outer surface of blades, mainly including: embedding method, chemical vapor deposition (CVD), gas phase method, hot dip method, and slurry method. At present, there are three main preparation technologies for high-temperature anti-oxidation coatings in the inner cavity: chemical vapor deposition (CVD), gas phase method, and slurry method. Among them, chemical vapor deposition equipment has not been widely used due to its high price. In the production of domestic blade manufacturers, the most widely used high-temperature anti-oxidation coatings in the inner cavity are solid powder filling method, gas phase method, chemical vapor deposition (CVD) and slurry injection method. Solid powder filling method: Aluminized powder using embedding method, which contains alumina, aluminum and alloy powder, halide activator, etc. The application of the embedding method aluminizing process in the blade cavity is not suitable for filling channels with small apertures (apertures less than 1 cm). At the same time, the embedding method generally requires a large amount of powder to generate active gas to deposit the aluminized layer. At the same time, the lack of fluidity of the powder limits its application in aluminizing in curved channels, and the sintered residue is also difficult to remove from narrow cooling channels. Gas method and chemical vapor deposition method: the coating is prepared by the gas method. First, a gaseous compound containing saturated elements is made, and then it is transported to the parts. After thermal decomposition reaction, reduction reaction, disproportionation reaction or other gas transmission reaction, the atoms of the saturated elements are precipitated to form a coating. The gas method and chemical vapor deposition method are consistent in principle, but the gas method is uncontrollable and the depth of the infiltration layer is shallow. The latest research on chemical vapor deposition (CVD) is to directly introduce the reaction gas into the equipment, and the reaction gas that enters the air cooling channel and small holes in the inner cavity of the part by diffusion and convection reacts chemically with the hot inner surface of the part to form a deposited or diffused protective coating on the inner cavity surface. The gas method and chemical vapor deposition method require high temperature resistant materials to protect the uninfiltrated surface, because the active gas will deposit the infiltration layer at the position where it contacts.At the same time, CVD equipment is expensive, difficult to purchase, has a long cycle, is complex to operate, and has a small production volume, which makes it difficult to meet the needs of large-scale blade manufacturing. 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 the formation of the infiltration layer, slurry aluminization can be divided into two types: diffusion type and melting type. Diffusion type slurry The diffusion type aluminizing agent requires an activator or a catalyst, such as ammonium chloride, ammonium bifluoride, etc. The gas phase compound formed by the activator at high temperature is used for infiltration. Therefore, in order to produce enough gas phase compounds, it is necessary to fill the blade channel with enough slurry. Generally, more than 1000 microns are required to obtain a 20-50 micron infiltration layer. For small aperture channels (apertures less than 1 cm), due to the small amount of active substances produced, the infiltration layer may not be produced, and the gas phase compounds at high temperature will also deposit in the non-infiltration parts to produce the infiltration layer. High temperature protective coatings are required to protect the non-infiltration parts and prevent the formation of infiltration layers. The sintering type slurry only uses aluminum powder as a penetrant without adding an activator. The sintering type is to add a binder to the infiltrated metal or alloy powder to make a slurry, and then evenly apply the slurry on the surface of the workpiece. After drying, it is heated and sintered in an inert gas or vacuum environment at a temperature slightly higher than the melting point of the slurry. The alloy layer is formed by diffusion at the liquid-solid interface. The sintering method generally only requires a few tens of microns of wet coating to adhere to the metal surface. 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 should be easy to remove and not block the channels. Conventional slurries are generally chromate systems, and the viscosity is uncontrollable. It is impossible to control the amount of slurry adhesion in the channels. If too much slurry is injected, the channels are easily blocked after sintering. Chromates have great environmental hazards, which limits their application in aluminum infiltration in channels.

[0003] Therefore, it is urgent to provide a stable slurry suitable for dip coating process. Summary of the invention

[0004] The present invention aims to solve at least one of the technical problems existing in the above-mentioned prior art. To this end, the present invention proposes a dip-coating aluminizing slurry, which can form a wet coating with uniform thickness and good surface on the internal channel of the blade when the slurry is used for dip-coating the turbine blade, and a uniform protective aluminizing layer is formed after heat treatment and diffusion, and no additional protection of the non-aluminized surface is required during the aluminizing process, and the quality of the aluminizing layer is not affected.

[0005] A second aspect of the present invention provides a method for preparing a dip-coating aluminizing slurry.

[0006] The third aspect of the present invention provides an aluminized protective coating, wherein the raw materials for preparing the aluminized protective coating include the aforementioned dip-coating aluminized slurry.

[0007] A fourth aspect of the present invention provides the use of an aluminized protective coating in a nickel-based alloy blade passage.

[0008] According to a first aspect of the present invention, a dip-coating aluminizing slurry is provided, wherein the raw materials for preparing the slurry include: alkali metal hydroxide, silicic acid, polyol, aluminum powder, alkali swelling thickener and acetylene glycol surfactant.

[0009] The first aspect of the present invention has at least the following beneficial effects:

[0010] The present invention proposes a dip-coating aluminizing slurry, wherein the modulus and pH value of silicate are controlled by reacting silicic acid with alkali metal hydroxide, and then the slurry is compounded with an alcohol compound so that the aluminum powder is in a stable state in the slurry, and the alkali swelling thickener maintains the dispersion effect of the aluminum powder in the slurry and the high viscosity of the slurry. When the acetylene glycol surfactant is used to dip-coat the turbine blade in the above slurry, a wet coating with uniform thickness and good appearance can be formed on the internal channel of the turbine blade, and after the wet coating solvent is subsequently dried, there is no need to protect the un-infiltrated surface, and then the internal channel is diffused by heat treatment to obtain a protective infiltration layer, and the residual slurry after diffusion and melting will automatically peel off, and the surface roughness of the infiltration layer is not affected, thereby meeting the requirements for preparing the aluminum infiltration layer in the blade cavity and the air-cooling channel, and is used to solve the problems of the chromate system aluminizing slurry in the prior art, great environmental hazards, low viscosity of the chromate system aluminizing slurry and non-adjustable viscosity, poor dispersion effect, unsuitable for dip-coating process, large amount of catalytic aluminizing slurry, and need to protect the un-infiltrated surface. At the same time, the compounding of acetylene glycol surfactant with alkali swelling thickener, silicate and other ingredients has a synergistic effect. In the system, acetylene glycol surfactant and thickener work together to maintain the high viscosity of the slurry and effectively prevent the sedimentation of aluminum powder. It not only improves the adhesion of the coating, but also enhances the dispersion stability of aluminum powder in the slurry, avoiding the influence of aluminum powder sedimentation or agglomeration on the dip coating effect.

[0011] On the one hand, most of the traditional aluminizing slurries adopt chromate systems, which have strong oxidizing properties. Organic thickeners and wetting and leveling agents are not compatible with the system, so they do not have high viscosity and good wetting and leveling effects. Therefore, the traditional aluminizing slurry generally has a low viscosity and cannot be adjusted. The low-viscosity traditional aluminizing slurry is difficult to dip-coat, and it is difficult to form a certain thickness of wet coating on the blade surface. The aluminizing slurry system provided by the present invention has no strong oxidant, uses an alkali swelling thickener, has high viscosity, good wetting and leveling properties, and is easy to dip-coat on the metal surface to form a wet coating.

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

[0013] According to some embodiments of the invention, the acetylene glycol surfactant includes at least one of dimethyloctyne glycol and tetramethyldecyne glycol.

[0014] According to some embodiments of the present invention, the alkali swelling thickener includes: a polyacrylate thickener.

[0015] In the traditional aluminizing slurry, the silicate system is generally directly using silicates with fixed modulus. High modulus silicates have poor high temperature adhesion, and low modulus silicates have strong alkalinity. It is difficult to maintain the stability of aluminum powder in the slurry for a long time. It is necessary to adjust the appropriate modulus according to the slurry system. In an alkaline environment, aluminum reacts with the solution to produce a certain amount of high-valent ions. If the system does not have more high-valent 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 invention is controllable, and then compounded with alcohol compounds. Polyacrylate is a highly negatively charged polyelectrolyte, which provides dispersion stability for the system and is not easy to settle. Specifically: the compounding of polyacrylate and silicate exerts a synergistic effect. By compounding with polyacrylate, polyacrylate can effectively neutralize the instability brought by silicate, enhance the overall dispersibility of the slurry, and enable aluminum powder to be dispersed in a more stable system, preventing the problem of aluminum powder sedimentation and reduced reactivity. At the same time, the introduction of polyacrylate can not only stabilize the dispersion of silicate and reduce the side effects caused by the alkaline environment, but also inhibit the precipitation of high-valent ions by forming polymer stabilizers, thereby further improving the dispersion stability and uniformity of the system.

[0016] According to some embodiments of the present invention, the polyol includes at least one of a diol and a triol.

[0017] According to some embodiments of the present invention, the general formula of the polyol is CnH2n+2-x(OH)x (x≥2).

[0018] According to some embodiments of the invention, the polyol comprises at least one of oil and ethylene glycol.

[0019] According to some embodiments of the invention, the boiling point of the polyol is no higher than 320°C.

[0020] Alcohol has a corrosion inhibition effect on aluminum powder in the system. It has a high carbon atom and a high boiling point. The curing temperature will be too high, the solvent cannot evaporate, and a dry film cannot be formed. If it is too low, the boiling point is low, and it will boil over when baked at 320°C, resulting in coating defects.

[0021] According to some embodiments of the present invention, the preparation raw materials include, by weight: 1 to 6 parts of alkali metal hydroxide, 2 to 10 parts of silicic acid, 6 to 12 parts of polyol, 30 to 50 parts of aluminum powder, 0.1 to 2.0% of alkali swelling thickener and 0.01 to 0.2 parts of acetylene glycol surfactant.

[0022] Traditional slurries mainly rely on chromates to passivate the surface of aluminum particles to form a protective film. In the absence of chromates, aluminum powder cannot exist stably in the slurry system for a long time. Over the course of several hours (or even minutes), the aluminum particles react violently with water, acid, and alkali in the slurry to produce hydrogen. Eventually, the aluminum powder loses its activity and cannot be used in the preparation of aluminum diffusion layers. The aluminizing slurry provided by the present invention is stable in the long term, does not contain chromates, and is more environmentally friendly.

[0023] According to some embodiments of the present invention, the raw materials for preparing the dip-coating aluminizing slurry further include water, in parts by weight.

[0024] According to some embodiments of the present invention, the dip-coating aluminizing slurry is composed of the following components: 1-6wt% alkali metal hydroxide, 2-10wt% silicic acid, 6-12wt% polyol, 30-50wt% aluminum powder, 0.1-2.0wt% alkali swelling thickener and 0.01-0.2wt% acetylene glycol surfactant, and the balance is deionized water.

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

[0026] The above molar ratio is helpful to control the dispersibility of the slurry, while too much silicate may cause gelation or coagulation, which is not conducive to the stability of the slurry. By controlling the ratio of silicate to hydroxide, the appropriate viscosity and fluidity of the slurry can be maintained.

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

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

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

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

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

[0032] According to a second aspect of the present invention, a method for preparing a dip-coating aluminizing 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. The alkali-swellable thickener, the polyol, the acetylene glycol surfactant and the mixed solution 1 are mixed to obtain a mixed solution 2;

[0035] S3. Mix and disperse the aluminum powder and the mixed solution 2.

[0036] The viscosity characteristics of the slurry were measured according to the national standard GB / T1723-1993 coating viscosity measurement method: the flow time in the coating-4 cup at 25°C was 15s to 35s.

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

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

[0039] According to some embodiments of the present invention, in step S3, the step of dispersing further includes standing.

[0040] After standing, the slurry is not separated into layers, and the aluminizing slurry is obtained.

[0041] According to a third aspect of the present invention, an aluminized protective coating is provided, wherein the raw materials for preparing the aluminized protective coating include the dip-coating aluminized slurry.

[0042] According to a fourth aspect of the present invention, an application of an aluminized protective coating in a nickel-based alloy blade channel is proposed.

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

[0044] The present invention uses aluminizing slurry for dip coating to prepare an aluminizing layer of a nickel-based high-temperature alloy blade, and the specific preparation method is as follows:

[0045] A1. Slurry stirring: Use a disperser with blades to stir at a speed of 1000-2000r / min for at least 30 minutes;

[0046] A2. Viscosity test: Use a coating-4 cup to measure the slurry viscosity. The viscosity suitable for dipping is 15s to 35s.

[0047] A3. Blade treatment: Use abrasive flow to treat the inner cavity and pores of turbine blades to remove the surface oxide layer;

[0048] A4. Dipping process: Weigh the blades with holes and measure the hole size, and calculate the dipping area; immerse the weighed blades in the slurry at room temperature at a rate of 1-3mm / s to prevent the slurry from not completely wetting the inner cavity and the hole surface of the blade due to too fast an immersion rate. First, let it stand for 3-5 minutes in the immersed state, and then slowly lift it out of the immersion slurry at a speed of 1-3mm / s; the single dipping amount needs to be 15-30mg / cm 2 For blades with small apertures, if the excess slurry in the channel cannot be discharged by slowly lifting it away, it can be discharged through the channel by introducing air flow. The remaining slurry will form a wet coating on the inner wall. If the dipping amount does not meet the standard, clean the slurry in the pipeline with deionized water, dry it, and then dip it again. If the single dipping amount is less than 15mg / cm 2 , then add alkali swelling thickener to increase viscosity. If the single dipping amount is greater than 30mg / cm 2 , then add deionized water to reduce the viscosity, and use a coating-4 cup to measure the slurry viscosity. The viscosity suitable for dip coating is 15s to 35s;

[0049] A5. Air drying: Use a rotary dryer to air dry the blades with holes; re-weigh the air-dried blades, calculate the thickness of the wet coating after the first dip coating based on the weight, and complete the first dip coating; return to step 3 and dip coating again until the dip coating amount reaches 15-30mg / cm 2 ;

[0050] A6. Drying and curing of wet coating: Dry at 80±5℃ for at least 15 minutes to remove moisture from the wet coating, and then cure the coating at 340℃±20℃ for at least 30 minutes to remove organic solvents from the coating and cure the silicate at the same time.

[0051] Direct curing without first removing the moisture will cause the moisture in the wet coating to vaporize directly, resulting in blistering on the coating surface.

[0052] A7. Preparation of aluminum infiltration layer: Put the blade into a can, put the can into an argon furnace, heat the furnace to 885℃-900℃, keep warm for 2h; cool, stop passing argon when the temperature cools to ≤100℃;

[0053] A8. Cleaning: After diffusion treatment, wait for the temperature in the furnace to cool to room temperature, take out the test piece, and when the part is cooled, use high-pressure airflow to gently blast to remove the residue of thick slurry in the blade cavity and pores until the color of the blade surface is uniform.

[0054] Metallographic examination of the blade cross section after diffusion, with a coating amount of 20 mg / cm 2The depth of the aluminized layer of the blade is 0.065mm-0.070mm, and the depth of the inner cavity and the blade surface is close. The depth of the aluminized layer is mainly related to the dipping amount. The aluminized layer is divided into two layers, the aluminum concentration of the outer layer can reach 28.5wt%, and the aluminum concentration of the diffusion layer surface is 8.5wt%.

[0055] The aluminizing slurry of the present invention is a molten aluminizing slurry, which mainly uses high-temperature aluminum to melt and then infiltrate active aluminum elements into the blade. Generally, only 50-100 microns of wet coating are needed on the blade surface, and the dipping amount is 15-30 mg / cm 2 After baking and high-temperature diffusion, the blades can obtain a 30-100 micron infiltration layer, and the non-coating parts do not need protection. In the traditional aluminizing slurry, vapor-phase aluminizing powder is added to a solvent to form a slurry, which is then filled into the blade pores and then diffused into aluminizing at high temperature. The principle is mainly to catalyze the infiltration by vapor-phase compounds formed by halides such as ammonium chloride at high temperatures. Therefore, in order to produce enough vapor-phase compounds, it is necessary to fill the blade pores with enough slurry, generally more than 1000 microns are required to obtain a 30-100 micron infiltration layer, and the vapor-phase compounds at high temperatures will also deposit in the non-infiltration parts to produce an infiltration layer. A high-temperature protective coating is required to protect the non-infiltration parts and prevent the formation of an infiltration layer. To prepare an infiltration layer of the same thickness, the amount of aluminizing slurry used in the present invention is one-tenth of the amount used in the traditional vapor-phase slurry. DETAILED DESCRIPTION

[0056] The following will be combined with the embodiments to clearly and completely describe the concept of the present invention and the technical effects produced, so as to fully understand the purpose, characteristics and effects of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative work are all within the scope of protection of the present invention.

[0057] Example 1

[0058] This embodiment prepares a dip-coating aluminizing slurry, the specific components are shown in Table 1, and the specific process is as follows:

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

[0060] S2. Preparation of liquid B: mixing the alkali-swellable thickener, polyol, acetylenic diol surfactant with liquid A in proportion, stirring and mixing until the solution is clear and transparent;

[0061] S3. Preparation of slurry: Mix aluminum powder and liquid B according to the proportion, stir with a disperser with blades at a speed of 1000-2000r / min, stir for at least 30 minutes, and then let it stand for 30 minutes until the slurry is not stratified.

[0062] Viscosity test: The viscosity characteristics of the slurry were measured according to the national standard GB / T1723-1993 coating viscosity determination method: the flow time in the coating-4 cup at 25°C was 15s to 35s.

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

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

[0065] Embodiments 2 to 11

[0066] Examples 2 to 11 prepared aluminizing slurries for dip coating, the specific components of which are shown in Table 1, and the specific process was the same as that of Example 1.

[0067] Comparative Examples 1 to 4

[0068] Comparative Examples 1 to 4 prepared dip-coating aluminizing slurries, the specific components of which are shown in Table 1, and the specific processes are the same as those of Example 1.

[0069] Comparative Example 5

[0070] Comparative Example 5 prepared a dip-coating aluminizing slurry, which differed from Example 1 in that hydroxyethyl cellulose was used to replace the alkali swelling thickener in Example 1, and the other conditions were the same.

[0071] Comparative Example 6

[0072] Comparative Example 6 prepared a dip-coating aluminizing slurry, which differed from Example 1 in that polyethylene glycol was used to replace the acetylene glycol surfactant in Example 1, and the other conditions were the same.

[0073] Comparative Examples 1 to 4 prepared dip-coating aluminizing slurries, the specific components of which are shown in Table 1, and the specific processes are the same as those of Example 1.

[0074] Table 1. Weight percentage of raw materials for preparing the dip-coating aluminizing slurry of the examples and comparative examples

[0075]

[0076]

[0077] Test Example 1

[0078] In this test example, the aluminized layer of the nickel-based high-temperature alloy blade was prepared using the dip-coating aluminized slurry of the embodiment and the comparative example. The diameter of the nickel-based high-temperature alloy blade workpiece was 0.5 cm. The preparation method is specifically as follows:

[0079] 1. Slurry stirring: Use a disperser to stir at a speed of 1000-2000r / min for at least 30 minutes;

[0080] 2. Viscosity test: Use a Tu-4 cup to measure the viscosity of the slurry;

[0081] 3. Blade treatment: Use abrasive flow to treat the inner cavity and pores of turbine blades to remove the surface oxide layer;

[0082] 4. Dipping process: Weigh the blades with holes and measure the hole size of the blades to calculate the dipping area; immerse the weighed blades in the slurry at room temperature at a rate of 1mm / s to prevent the slurry from failing to completely wet the inner cavity and hole surface of the blades due to too fast an immersion rate. First, let it stand for 3 minutes in the immersed state, and then slowly lift it out of the dipping slurry at a speed of 1mm / s;

[0083] 5. Air drying: Use a rotary drying fan to air dry the leaves with holes;

[0084] 6. Drying and curing of wet coating:

[0085] Dry at 80±5℃ for 15min to remove moisture from the wet coating. Then, cure the coating at 340℃±20℃ for 30min.

[0086] 7. Prepare aluminum infiltration layer: put the blade into the can, put the can into the argon furnace, heat the furnace to 885℃-900℃, keep it warm for 2h; cool, stop passing argon when the temperature cools to ≤100℃;

[0087] 8. Cleaning: After diffusion treatment, wait for the temperature in the furnace to cool to room temperature, take out the test piece, and when the part is cooled, use high-pressure airflow to lightly blast to remove the residue of thick slurry in the blade cavity and pores until the color of the blade surface is uniform.

[0088] The aluminized layers in the experimental examples and comparative examples were subjected to metallographic inspection according to the metallographic inspection method for aero-engine blade aluminized layers in HB 20113-2012.

[0089] Comparative Example 7 adopts the process of powder embedding aluminizing in accordance with JB / T 10448-2005 Solid Aluminizing Process and Quality Inspection Standard for Steel Components, wherein aluminum powder (mass fraction) is 30%, diluent alumina (mass fraction) is 69%, and accelerator (mass fraction) is 1% for powder embedding aluminizing. The diameter of the workpiece is 2 cm.

[0090] Comparative Example 8 adopts the process of powder embedding aluminizing in accordance with JB / T 10448-2005 Solid Aluminizing Process and Quality Inspection Standard for Steel Components, wherein aluminum powder (mass fraction) is 30%, diluent alumina (mass fraction) is 69%, and accelerator (mass fraction) is 1% for powder embedding aluminizing. The diameter of the workpiece is 0.5 cm. The test results are shown in Table 2.

[0091] Table 2 Metallographic inspection results of aluminized layer

[0092]

[0093] The metallographic inspection results of the aluminizing layers of the embodiments and comparative examples show that the depth of the aluminizing layer of the dip-coated aluminizing slurry of the embodiments is positively correlated with the viscosity of the slurry, and the depth of the aluminizing layer can be controlled by controlling the viscosity of the slurry. Comparative Examples 5 and 6 show that powder-embedded aluminizing is not suitable for small-diameter aluminizing, mainly because the diameter of the tube is too small, making it difficult for the powder to enter and fill, or the filling amount is too small to generate enough atmosphere in the tube, resulting in no coating in some areas. The dip-coated aluminizing slurry mainly relies on the infiltration of the aluminum powder after melting, and does not require sufficient atmosphere. Generally, only a few tens of microns of wet coating need to be adhered to the metal surface. The thickness of the aluminizing layer is proportional to the amount of slurry adhesion. The viscosity of the slurry needs to be controlled, and at the same time, the sintering residue should be easy to remove and not block the pores.

[0094] The above is a detailed description of the embodiments of the present invention, but the present invention is not limited to the above embodiments. Various changes can be made within the knowledge of ordinary technicians in the relevant technical field without departing from the purpose of the present invention. In addition, the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

Claims

1. A dip-coating aluminizing slurry, characterized in that: The preparation raw materials include: alkali metal hydroxide, silicic acid, polyol, aluminum powder, alkali swelling thickener and acetylene glycol surfactant.

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, characterized in that: The acetylene glycol surfactant includes at least one of dimethyloctyne glycol and tetramethyldecyne glycol.

4. The dip-coating aluminizing slurry according to claim 1, characterized in that: The polyol comprises at least one of a diol and a triol; and / or the boiling point of the polyol is not higher than 320°C.

5. The dip-coating aluminizing slurry according to claim 1, characterized in that: The raw materials include, by weight: 1 to 6 parts of alkali metal hydroxide, 2 to 10 parts of silicic acid, 6 to 12 parts of polyol, 30 to 50 parts of aluminum powder, 0.1 to 2.0 parts of alkali swelling thickener and 0.01 to 0.2 parts of acetylene glycol surfactant.

6. The dip-coating aluminizing slurry according to claim 1, characterized in that: The pH value of the dipping aluminizing slurry is 11-13.

7. The dip-coating aluminizing slurry according to claim 1, characterized in that: The D50 of the aluminum powder is 4 to 6 μm.

8. A method for preparing a dip-coating aluminizing slurry according to any one of claims 1 to 7, characterized in that: include: S1. dispersing and mixing the alkali metal hydroxide and the silicic acid to obtain a mixed solution 1; S2. The alkali-swellable thickener, the polyol, the acetylene glycol surfactant and the mixed solution 1 are mixed to obtain a mixed solution 2; S3. Mix and disperse the aluminum powder and the mixed solution 2.

9. An aluminized protective coating, characterized in that: The raw material for preparing the aluminized protective coating comprises the dip-coating aluminized slurry according to any one of claims 1 to 7.

10. Use of the aluminized protective coating as claimed in claim 9 in a nickel-based alloy blade channel.

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