CN109182951B - A method for preparing chromium-aluminum-carbon composite coating by plasma spraying - Google Patents

Abstract

The present invention is a method for preparing chromium-aluminum-carbon composite coating by plasma spraying. The method includes the following steps: adding deionized water, gel and dispersant to Cr powder, Al powder and graphite powder to obtain a mixed slurry; then spraying and drying to obtain plasma spraying feeding powder; spraying in a plasma spraying device On the bonding layer, an initial coating is obtained, and then heat preservation treatment is carried out in a vacuum or argon atmosphere at a temperature of 550-900° C., and the temperature is kept for 1-4 hours to obtain a chromium-aluminum-carbon composite coating. The invention forms the ternary Cr2AlC compound in situ, achieves the purpose of reducing the brittleness of the coating, improving the hardness and wear resistance, and overcomes the problems of high preparation cost, low deposition efficiency and thin thickness of the existing Cr2AlC-containing coating.

Description

A method for preparing chromium-aluminum-carbon composite coating by plasma spraying

technical field

The invention relates to a method for preparing a spray coating and optimizing the coating quality, in particular to a plasma spray coating with high hardness and high wear resistance and a preparation method thereof.

Background technique

In major national defense technical equipment such as aerospace, iron and steel metallurgy and petrochemical industry, key components are in extremely complex and harsh working environments (high temperature, heavy load, corrosion, etc.), and they are objectively required to have excellent strength, toughness, resistance to Abrasion resistance and high temperature oxidation resistance, obviously a single material cannot meet the above requirements, and the use of surface coating technology to prepare wear and oxidation resistance coatings on metal surfaces is economical and effective.

Chromium carbide ceramics (Cr7C3 and Cr23C6) have the advantages of high hardness, good oxidation resistance and excellent wear resistance. 900 ℃) environment, the most widely used coating material, widely used in metallurgy, aviation, electric power, nuclear energy and other industries. Chromium carbide ceramics are inherently brittle, and material workers reduce the brittleness by adding transition metals (Fe, Ni, NiCr, Co, etc.), but this leads to an increase in coating density and an increase in cost . Plasma spraying is a common preparation method for chromium carbide coatings. Generally, nickel-chromium-chromium carbide sintered composite powder is used as the spraying feed. The preparation of the feed requires pre-sintering treatment, which increases the process complexity and production cost. Although the hardness of the chromium carbide composite layer is high, the brittleness is still large, and cracks are easily generated during the spraying process, which affects the performance of the coating. Therefore, the second phase toughness ceramics are added to the chromium carbide coating to prepare the composite coating. Coating toughness is important.

The ternary chromium-aluminum-carbon compound Cr2AlC is a layered structure ceramic, which has the high toughness of metal and the high strength and hardness of ceramics, and has good high temperature oxidation resistance. The thermal expansion coefficient of Cr2AlC is (13.3×10 ^{- 6} K ^-1 ), which can form a good thermal match with most metal alloys. On the other hand, the layered structure of Cr2AlC also has a certain self-lubricating effect and toughening effect, which is beneficial to improve material toughness and reduce friction coefficient. Therefore, it has great application prospects in the field of coating protection. At present, Cr2AlC coatings are mainly prepared by methods such as magnetron sputtering and multi-arc ion plating. Magnetron sputtering requires a high temperature stage to heat the substrate, which increases the preparation cost, and in addition, the deposition efficiency is low, and the obtained coating thickness is low; Multi-arc ion plating uses alloy targets, which increases the cost and the thickness of the deposited coating is also thin, which is not conducive to the wide application of Cr2AlC coatings. Plasma spraying has the advantages of high deposition rate, high coating thickness and easy operation, but there is no report on the preparation of Cr2AlC-containing coatings by plasma spraying.

SUMMARY OF THE INVENTION

Aiming at the deficiencies of the existing plasma spraying chromium carbide coating technology, the present invention provides a plasma spraying preparation and optimization method of a high-hard wear-resistant chromium-aluminum-carbon composite coating. The present invention adopts a two-step method, that is, the method of preparing the initial coating by plasma spraying and the subsequent vacuum or atmosphere protection annealing treatment. Under the appropriate material ratio and operating parameters, the ultra-high temperature Cr of three different particle sizes by plasma spraying is used. Powder, Al powder and graphite powder react and deposit on the substrate to form coating material, and then annealing treatment is carried out to further optimize the coating quality. The invention forms the ternary Cr2AlC compound in situ, achieves the purpose of reducing the brittleness of the coating, improving the hardness and wear resistance, and overcomes the problems of high preparation cost, low deposition efficiency and thin thickness of the existing Cr2AlC-containing coating.

The technical scheme of the present invention is:

A method for preparing a chromium-aluminum-carbon composite coating by plasma spraying, comprising the following steps:

Step 1: Weigh the raw material powder by mass percentage; wherein, the proportion of each component in the raw material powder is: 60%-82% is Cr powder, 10%-30% is Al powder, 7%-10% is graphite powder;

Step 2, adding deionized water, gel and dispersant to the weighed raw material powder, and mechanically stirring for 3 to 5 hours to obtain a mixed slurry;

Among them, the gel is prepared by mixing deionized water and sodium carboxymethylcellulose, and the mass ratio is deionized water: sodium carboxymethylcellulose = 80-120:1; the mass ratio is raw material powder: deionized water: gelling Glue=2:1.5～2.5:1, the mass of added dispersant PVP is 0.5～2.5% of the total mass of raw material powder;

Step 3, preparing the agglomerated composite powder by spray drying the mixed slurry; wherein, the inlet temperature of the spray granulator is 230-280°C, and the outlet temperature is 110-130°C;

Step 4: Dry and sieve the agglomerated composite powder to obtain 100-mesh-300-mesh agglomerated particles, which are used as the feed powder for plasma spraying;

Step 5, roughening the surface of the substrate;

Step 6. Pre-spray Ni-10wt% Al self-fluxing alloy powder on the surface of the roughened substrate to obtain a bonding layer with a thickness of 50-120 μm;

Step 7. Add the spraying feed powder obtained in the fourth step into the plasma spraying device, and spray it on the adhesive layer to obtain an initial coating with a thickness of 200-300 μm;

Step 8: The initial coating obtained in Step 7 is subjected to heat preservation treatment in a vacuum or argon atmosphere, the temperature is 550-900° C., and the heat preservation time is 1-4 h to obtain a chromium-aluminum-carbon composite coating.

In the first step, the particle size of the Cr powder is 325-500 mesh, the particle size of the Al powder is 300-500 mesh, and the particle size of the graphite powder is 8000-15000 mesh.

The roughening treatment of the substrate in the step 5 is specifically: first sanding with sandpaper, and then sandblasting the surface.

The substrate is specifically carbon steel, titanium alloy, high temperature alloy or ceramic.

In the step 7, the agglomerated powder screened in the step 4 is used as the spraying feed, and the initial coating is prepared on the surface of the substrate by plasma spraying, wherein the plasma spraying process parameters are: the working voltage is 60-75V, the working current is 450-500A, The flow rate of argon gas is 20-40L/min, the flow rate of hydrogen gas is 20-30L/min, the powder feeding speed is 2-5L/min, and the spraying distance is 70-130mm, in which argon gas is used as both powder feeding gas and protective gas.

The essential features of the present invention are:

The invention adopts a two-step method, that is, the scheme of preparing the initial coating by plasma spraying + subsequent atmosphere protection annealing treatment, and utilizing the ultra-high temperature of plasma spraying to react and deposit the three raw materials on the substrate to form coating materials as protective materials. The present invention is obviously different from the previous patent spraying (such as Ti-C-N, Ti-N, etc.). The three raw materials of Cr, Al, and graphite in the reaction, as well as the subsequent heat treatment steps or parameters, all determine the success or failure of the reaction. The invention forms the ternary Cr2AlC compound in situ, achieves the purpose of reducing the brittleness of the coating, improving the hardness and wear resistance, and overcomes the problems of high preparation cost, low deposition efficiency and thin thickness of the existing Cr2AlC-containing coating.

The advantages of the present invention relative to the prior art are:

(1) The Cr-Al-graphite agglomeration powder feed is prepared by spray drying. The operation is simple, the obtained feed has good fluidity, and is suitable for spraying. During the spraying process, the reaction between Cr and graphite is more complete, and finer carbonization can be formed. Chrome grains.

(2) The two-step treatment of plasma spraying and annealing is adopted, and Al reacts with chromium carbide inside the initial coating to generate in situ a ternary chromium-aluminum-carbon compound Cr2AlC, which is a layered ceramic phase with a small thermal expansion coefficient and The advantages of high fracture toughness help reduce the brittleness of the composite coating and improve the wear resistance of the coating; and the coating not only generates a Cr2AlC layered ceramic phase in situ, but also greatly improves the hardness; because Cr2AlC itself is not high in hardness , it is not suitable as a single component material alone, the present invention generates Cr2AlC as a toughening phase in-situ in the coating through the annealing process, and the annealing process can also strengthen the matrix phase at the same time, so that the hardness and toughness of the coating are improved at the same time.

(3) Using Al powder as the raw material, in the process of plasma spraying, aluminum can play the role of wetting the interface and bonding the chromium carbide coating, which can effectively improve the density of the initial spray coating, and the initial coating is coated in Al Heat preservation treatment above the melting point temperature can also reduce the internal stress of the coating.

(4) The coating preparation technology of the present invention has simple operation, high deposition efficiency, and easy control of coating thickness and phase volume fraction.

Description of drawings

Fig. 1 is the SEM image of Cr-Al-graphite agglomeration powder after spray granulation in Example 1 of the present invention;

2 is the XRD pattern of the initial coating (a) sprayed on the surface of the 45# steel substrate and the chromium-aluminum-carbon composite coating (b) after annealing in Example 1 of the present invention;

Fig. 3 is the SEM picture of chromium-aluminum-carbon composite coating after plasma spraying and annealing treatment on the surface of 45# steel substrate in Example 1 of the present invention;

4 is a hardness diagram of the initial coating on the surface of the 45# steel substrate and the chromium-aluminum-carbon composite coating after annealing in Example 1 of the present invention.

Detailed ways

The present invention will be described in further detail below with reference to the embodiments of the accompanying drawings. It should be pointed out that the following embodiments are intended to facilitate the understanding of the present invention and do not have any limiting effect on it.

Example 1:

The present embodiment utilizes reactive plasma spraying to prepare a Cr-Al-C metal-ceramic composite coating method based on agglomerated powder modification, including the following steps:

Step 1: Weigh the raw materials according to 72.7wt% of Cr powder, 18.8wt% of Al powder, and 8.5wt% of graphite powder; wherein, the particle sizes of the materials are respectively: the particle size of the Cr powder is 500 mesh, and the particle size of the Al powder is 500 mesh , the particle size of the graphite powder is 10000 mesh (the same in the following examples);

Step 2: In addition, according to the total mass of the original powder and the mass of deionized water, the gel mass ratio is 2:2:1, 1% PVP of the total mass of the raw powder is added as a dispersant, mixed, and mechanically stirred for 3 hours to obtain a mixed slurry; The gel is prepared by mixing water and sodium carboxymethyl cellulose in a ratio of 100:1 (the same as in the following examples);

Step 3, spray drying: spray the mixed slurry into the drying chamber for atomization, and quickly dry to form agglomerated particles, wherein the inlet temperature of the spray dryer is 230°C, and the outlet temperature is 110°C;

Step 4: Screen out the agglomerated particles with a size of 100 mesh to 300 using the standard as the spraying feed;

Step 5. Clean the No. 45 steel substrate with sandpaper, and then carry out sandblasting and roughening treatment;

Step 6, using plasma spraying to spray Ni-10wt% Al on the roughened No. 45 steel substrate as a bonding layer, and the thickness is controlled at 50-120 μm;

Step 7. Spray the screened agglomerated composite powder feed on the bonding layer to obtain an initial coating with a thickness of 200-300 μm. The plasma spraying parameters adopted are: working voltage is 70V, working current is 450A, argon gas The flow rate is 30L/min, the hydrogen flow rate is 25L/min, the powder feeding speed is 2L/min, and the spraying distance is 110mm, in which argon is used as both the powder feeding gas and the protective gas.

Step 8: Under the protection of argon atmosphere, the initial coating obtained in step (7) is kept at 800° C. for 1 hour to obtain a chromium-aluminum-carbon ceramic composite coating.

SEM observation was carried out on the powder obtained after spray granulation. As shown in Figure 1, Cr powder and Al powder were wrapped by graphite powder to form spherical or ellipsoidal agglomerated particles, and a small amount of spherical Al particles were distributed in the agglomerated particles. In between, the powder has good fluidity and is very suitable for plasma spraying.

Phase detection and analysis were carried out on the initial coating and composite coating on the surface of the 45# steel substrate prepared above, as shown in the XRD pattern of FIG. 2 . It can be seen from Figure 2(a) that the initial coating is mainly composed of Cr23C6, Cr7C3 and unreacted Al elements. It can be seen from Figure 2(b) that after the annealing treatment, a diffusion reaction occurs between the phases, forming three Elemental chromium-aluminum-carbon compound Cr2AlC, and Al-Cr intermetallic compounds are formed, and the carbides are mainly Cr23C6 and Cr7C3, which indicates that the three raw material powders undergo a compound reaction during the plasma spraying process, mainly forming chromium carbide and aluminum powder. There are residues, but after high temperature and long-term heat preservation, the reaction continues to form a new phase Cr2AlC.

For the composite coating obtained in step 8, the surface SEM image is shown in Figure 3. It can be seen that the surface of the coating is relatively dense and there are a few holes.

The hardness of the Cr-Al-C composite coating on the surface of the 45# steel substrate prepared above was tested with a microhardness tester. The average value of the coating surface hardness measured by the microhardness test is shown in Figure 4. It can be seen from the figure that the initial coating hardness value obtained in this example is 544HV, and the hardness is increased to 544HV after annealing at 800℃. 874HV.

Example 2:

Step 1: Weigh the raw materials according to 64.5wt% of Cr powder, 25wt% of Al powder, and 10.5wt% of graphite powder;

Step 2: In addition, according to the total mass of the original powder and the mass of deionized water, the gel mass ratio is 2:2:1, adding 1% PVP of the total mass of the raw powder as a dispersant, mixing, and mechanically stirring for 3 hours to obtain a slurry;

Step 3, spray drying: spray the mixed slurry into the drying chamber for atomization, and quickly dry to form agglomerated particles, wherein the inlet temperature of the spray dryer is 260°C, and the outlet temperature is 110°C;

Step 4: Screen out the agglomerated particles with a size of 100 mesh to 300 using the standard as the spraying feed;

Step 5. Clean the No. 45 steel substrate with sandpaper, and then carry out sandblasting and roughening treatment;

Step 6, using plasma spraying to spray Ni-10wt% Al on the roughened No. 45 steel substrate as a bonding layer, and the thickness is controlled at 50-120 μm;

Step 7. Spray the screened agglomerated composite powder feed on the bonding layer to obtain a coating with a thickness of 200-300 μm. The plasma spraying parameters adopted are: the working voltage is 75V, the working current is 400A, and the argon gas flow rate It is 30L/min, the hydrogen flow rate is 25L/min, the powder feeding speed is 2.5L/min, and the spraying distance is 110mm, in which argon is used as both the powder feeding gas and the protective gas.

Step 8: Under the protection of argon atmosphere, the coating obtained in step (7) is kept at 700° C. for 1 hour to obtain a Cr-Al-C ceramic composite coating.

SEM observation was carried out on the powder after spray granulation prepared above, and the morphology similar to that shown in Figure 1 was obtained. The Cr powder and the Al powder were wrapped by the graphite powder to form spherical or ellipsoidal agglomerated particles, and there were a small amount of spherical Al particles. Distributed among the agglomerated particles, the powder has good fluidity and is very suitable for plasma spraying.

Phase detection and analysis were carried out on the initial coating and composite coating on the surface of the 45# steel substrate prepared above, and the XRD pattern similar to that shown in Figure 2 was obtained. The composition of the reacted Al element, compared with the initial coating obtained in Example 1, the diffraction peak of the Al element is enhanced. After annealing, a composite coating similar to Figure 2(b) is obtained. The main phases are Cr2AlC, Cr7C3 and Cr23C6, the diffraction peaks of Al-Cr intermetallic compounds decreased.

For the composite coating obtained in step 8, the surface SEM image is similar to that shown in Figure 3. It can be seen that the surface of the coating is relatively dense and there are a few holes.

The hardness of the Cr-Al-C composite coating on the surface of the 45# steel substrate prepared above was tested with a microhardness tester. The average value of the coating surface hardness measured by the microhardness test is shown in Figure 4, from which it can be seen that the coating hardness value obtained in this example is 710HV, which is greatly improved compared to the initial coating hardness.

Example 3:

Step 1: Weigh the raw materials according to 80wt% of Cr powder, 10.5wt% of Al powder, and 9.5wt% of graphite powder;

Step 2: According to the total mass of the original powder and the mass of deionized water, the gel mass ratio is 2:2:1, and 1% PVP of the total mass of the raw powder is added as a dispersant, mixed, and mechanically stirred for 3 hours to obtain a slurry;

Step 3, spray drying: spray the mixed slurry into the drying chamber for atomization, and quickly dry to form agglomerated particles, wherein the inlet temperature of the spray dryer is 260°C, and the outlet temperature is 110°C;

Step 4. Use a sieve to select the agglomerated particles with a size of 100 mesh to 300 as the spraying feed;

Step 5. Clean the No. 45 steel substrate with sandpaper, and then carry out sandblasting and roughening treatment;

Step 6, using plasma spraying to spray Ni-10wt% Al on the roughened No. 45 steel substrate as a bonding layer, and the thickness is controlled at 50-120 μm;

Step 7. Spray the screened agglomerated composite powder feed on the bonding layer to obtain a coating with a thickness of 200-300 μm. The plasma spraying parameters adopted are: the working voltage is 65V, the working current is 500A, and the argon gas flow rate It is 35L/min, the hydrogen flow rate is 25L/min, the powder feeding speed is 3L/min, the spraying distance is 90mm, and argon gas is used as both the powder feeding gas and the protective gas.

Step 8: Under the protection of argon atmosphere, the coating obtained in step (7) is kept at 700° C. for 2 hours to obtain a Cr-Al-C ceramic composite coating.

SEM observation was carried out on the powder after spray granulation prepared above, and the morphology similar to that shown in Figure 1 was obtained. The Cr powder and the Al powder were wrapped by the graphite powder to form spherical or ellipsoidal agglomerated particles, and there were a small amount of spherical Al particles. Distributed among the agglomerated particles, the powder has good fluidity and is very suitable for plasma spraying.

Phase detection and analysis were carried out on the initial coating and composite coating on the surface of the 45# steel substrate prepared above, and the XRD pattern similar to that shown in Figure 2 was obtained. The composition of the reacted Al element, compared with the initial coating obtained in Example 1, the diffraction peak of the Al element is weakened. After annealing, a composite coating similar to Figure 2(b) is obtained. The main phases are Cr2AlC, Cr7C3 and Cr23C6, the diffraction peaks of Al-Cr intermetallic compounds decreased.

For the composite coating obtained in step 8, the surface SEM image is similar to that shown in Figure 3. It can be seen that the surface of the coating is relatively dense and there are a few holes.

The hardness of the Cr-Al-C composite coating on the surface of the 45# steel substrate prepared above was tested with a microhardness tester. The average value of the coating surface hardness measured by the microhardness test is shown in Figure 4, from which it can be seen that the hardness value of the coating obtained in this example is 860HV, which is greatly improved compared to the initial coating hardness.

The above embodiments describe the technical solutions of the present invention in detail. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Anything done within the scope of the principles of the present invention Any modifications, additions or substitutions in similar manners, etc., shall be included within the protection scope of the present invention.

Matters not addressed in the present invention are known in the art.

Claims (4)

1. A method for preparing a chromium-aluminum-carbon composite coating by plasma spraying is characterized by comprising the following steps:

step one, weighing raw material powder according to mass percentage; wherein the raw material powder comprises the following components in proportion: 60-82% of Cr powder, 10-30% of Al powder and 7-10% of graphite powder;

step two, adding deionized water, gel and a dispersing agent into the weighed raw material powder, and mechanically stirring for 3-5 hours to obtain mixed slurry;

the gel is prepared by mixing deionized water and sodium carboxymethylcellulose, and the mass ratio of the deionized water to the sodium carboxymethylcellulose is as follows: 80-120: 1 of sodium carboxymethylcellulose; the mass ratio of the raw material powder is as follows: deionized water: gel 2: 1.5-2.5: 1, adding 0.5-2.5% of dispersant PVP (polyvinyl pyrrolidone) by mass based on the total mass of the raw material powder;

step three, preparing the agglomerated composite powder from the mixed slurry by a spray drying method; wherein the inlet temperature of the spray granulator is 230-280 ℃, and the outlet temperature is 110-130 ℃;

drying and screening the agglomerated composite powder to obtain 100-300-mesh agglomerated particles serving as plasma spraying feeding powder;

step five, roughening the surface of the matrix;

step six, spraying Ni-10 wt% Al self-fluxing alloy powder on the roughened surface of the substrate in advance to obtain a bonding layer with the thickness of 50-120 mu m;

step seven, adding the spraying feeding powder obtained in the step four into a plasma spraying device, and spraying the powder on the bonding layer to obtain an initial coating with the thickness of 200-300 mu m;

step eight, performing heat preservation treatment on the initial coating obtained in the step seven in vacuum or argon atmosphere at the temperature of 550-900 ℃ for 1-4h to obtain a chromium-aluminum-carbon composite coating;

in the seventh step, the agglomerated powder screened in the fourth step is used as spraying feed, and the initial coating is prepared on the surface of the substrate by plasma spraying, wherein the plasma spraying process parameters are as follows: the working voltage is 60-75V, the working current is 450-500A, the argon flow is 20-40L/min, the hydrogen flow is 20-30L/min, the powder feeding speed is 2-5L/min, and the spraying distance is 70-130mm, wherein the argon is simultaneously used as the powder feeding gas and the protective gas;

the dispersant is PVP.

2. The method for preparing a chromium-aluminum-carbon composite coating by plasma spraying as claimed in claim 1, wherein the particle size of the Cr powder in the first step is 325-500 mesh, the particle size of the Al powder is 300-500 mesh, and the particle size of the graphite powder is 8000-15000 mesh.

3. The method for preparing the chromium-aluminum-carbon composite coating by plasma spraying as claimed in claim 1, wherein the substrate roughening treatment in the fifth step is specifically: sanding with sand paper and then surface blasting.

4. The method for preparing a chromium-aluminum-carbon composite coating by plasma spraying as claimed in claim 1, wherein the substrate is carbon steel, titanium alloy, high temperature alloy or ceramic.

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