JPS6155589B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention turns open pores in a sprayed ceramic layer as a metal-ceramic composite used in an adiabatic engine into closed pores, and also strengthens the ceramic structure to increase the durability of parts. This relates to a method for increasing lifespan. Conventionally, engines have been mainly constructed of metal materials such as cast iron and aluminum. However, recently, from the perspective of energy conservation, research has been actively conducted to reduce the large heat loss caused by engine exhaust and cooling, and to increase the thermal efficiency of the engine. Many proposals have been made for composite structures with metals. The ceramics of these composites are made by shrink-fitting ceramics sintered at high temperatures into metal parts.
Many types of combinations have been prototyped, including casting, bolting, brazing, and ceramic spray joining to metal parts. All of these ceramics, except for ceramic spray bonding, require advanced manufacturing techniques, have complicated manufacturing processes, and are sintered at extremely high temperatures, which has the disadvantage of significantly increasing manufacturing costs. . On the other hand, ceramic thermal spray coating technology has recently been developed into an automatic system of thermal spray equipment, making it possible to form a relatively homogeneous ceramic layer on metal parts, making it relatively easy to manufacture, and compared to the above-mentioned parts bonded with high-temperature sintered ceramics. However, the manufacturing cost is extremely low. In addition, ceramic sprayed layers are generally porous, and the pores in the structure absorb the difference in thermal expansion with the metal substrate and strain caused by mechanical stress, alleviate thermal expansion and deformation, and form a relatively thin layer. It has the advantage of providing a large heat insulating effect. However, open pores on the other side allow gas and oil to enter the tissue from the outside. For example, ceramic sprayed layers applied to metal substrates such as engine liners, piston tops, and exhaust ports penetrate into the tissue through the open pores of the ceramic due to decomposition and polymerization reactions at high temperatures of combustion gas, fuel, lubricating oil, etc. during engine operation.・Diffuses and carbon and impurities precipitate and accumulate. For this reason, it has drawbacks such as causing damage due to cracking and peeling of the ceramic. The present invention eliminates such conventional drawbacks, changes the open pores of the ceramic sprayed layer as a metal-ceramic composite used in adiabatic engines into closed pores, and strengthens the ceramic structure to improve the durability of parts. The aim is to provide a method for increasing the lifespan of the battery and increasing its lifespan. That is, the present invention provides a heat-resistant nonmetallic inorganic fine powder having a particle size distribution corresponding to the size of the open pores of the ceramic sprayed onto a metal substrate in a composite with a metal/ceramic sprayed layer as an insulating engine part. A concentrated solution of a soluble chromium compound containing is used as a first solution, and this is applied to the ceramic surface and heat treated, and a separately prepared solution of a soluble chromium compound is applied to this treated product as a second solution, Heat treat again. Furthermore, by repeating the coating and heat treatment with this second liquid at least once, the open pores of the ceramic layer are turned into closed pores, thereby forming a durable ceramic without impairing the thermal insulation properties of the sprayed ceramic layer. It is. This method is a simple treatment process, and the heat treatment temperature is relatively low, so the manufacturing cost is low. Therefore, it is very advantageous as a method for improving the properties of metal-ceramic thermal sprayed composite parts such as cylinder liners, piston tops, and exhaust ports in adiabatic gasoline engines, diesel engines, and other fuel-powered internal combustion engines. To explain the present invention in more detail, the metal base material used in the present invention is mainly steel, such as cast iron and stainless steel. The ceramics sprayed onto these base materials are mainly heat-resistant oxides, such as Y ₂ O ₃ , CaO, and
Partially stabilized or stabilized by MgO etc.
Examples include ZrO ₂ , TiO ₂ +Al ₂ O ₃ , Al ₂ O ₃ and Cr ₂ O ₃ . In addition, thermal spray raw materials are melted by high-temperature plasma,
The droplets collide with the substrate surface at high speed, turn into flat particles, adhere to the substrate, and sequentially overlap and bond to form a ceramic layer. For this reason, thermal sprayed ceramics are essentially porous, and the structure of ceramics varies considerably depending on the type of raw material, particle size distribution, thermal spraying conditions, etc. For example, ceramics formed by plasma spraying a powder of ZrO ₂ or Al ₂ O ₃ stabilized with Y ₂ O ₃ or CaO with a particle size distribution of 44 to 10 μm onto a metal substrate under favorable conditions usually have a particle size of 7 to 13 μm. % of pores. Pores in the ceramic structure absorb stress caused by temperature changes and mechanical vibrations, so
It has the characteristics that thermal shock and deformation are alleviated, and a large heat insulating effect can be obtained even by forming a relatively thin layer. However, since most of the pores in ceramics are open, combustion gas, fuel, lubricating oil, etc. can come into contact with and invade the pores of high-temperature ceramics, and carbon and impurities in reaction products can be used as engine parts. Precipitation, adhesion, and accumulation occur, which causes damage such as cracks and spalling. Therefore, the present invention aims to perform a treatment that closes only the pores exposed on the surface without reducing the pores of the ceramic coating layer as much as possible, and further strengthens the bond between the ceramic and the base and the bond between the ceramic tissues. This is what I did. That is, depending on the spraying conditions, the surface of the thermally sprayed ceramic coating is quite rough due to its adhesion mechanism. Therefore, thermally sprayed ceramic surfaces are usually polished to a smooth surface using diamond or CBN tools. In the present invention, first, in order to investigate the size and shape of open pores in ceramics, a ceramic specimen is separately prepared under the same conditions as the thermal spraying, and its surface and cut surface are observed under a microscope using a replica method or the like. The stomata seen with a speculum are usually of various shapes and sizes, such as cocoon-shaped, human-shaped, lizard-shaped,
They come in various sizes and shapes, such as semi-molten particles of thin plate glass. For example, in the pores formed in a ceramic coating layer that has been plasma sprayed under optimal conditions with ZrO ₂ powder with a particle size distribution of 40 to 10 μm stabilized by 10% by weight of Y ₂ O ₃ , most of the pores are open pores. The closed pores are small, accounting for less than 20% of the total pores and are mostly less than 2 μm in size. The largest open pore is 20×30
×5μm, 25×6×3μm, 17×7×5μm, 16
Oblate pores such as ×14 × 8 μm and 15 × 13 × 7 μm are found here and there. The first liquid for converting the open pores of this ceramic layer into closed pores has a particle size distribution close to the short diameter of the largest pore group, for example, when the pore group is the one described above, based on the above microscopic results. A concentrated solution of a soluble chromium compound containing powder having the same composition as the thermal spray material prepared to a thickness of about 5 to 10 μm is prepared as the first solution. For example, when the ceramic is the above-mentioned stabilized zirconia, the first liquid has the same composition as this.
ZrO ₂ 20-1μ stabilized by 10% by weight of Y ₂ O ₃
This is a solution in which powder having a particle size distribution of m is contained in a concentrated solution of a soluble chromium compound. Solutions of soluble chromium compounds are, for example, concentrated aqueous solutions of H ₂ CrO ₄ in which CrO ₃ is dissolved in water;
It can be made by dissolving 700g of CrO ₃ in 500g of water. Good results can also be obtained by using a solution in which MgO or ZnO is further dissolved in this solution. The dissolved amount is 0.1 MgO or ZnO per 1 mole of H ₂ CrO ₄
~0.4 mol % and water is added to adjust the specific gravity to 1.6 to 1.8. The heat-resistant nonmetallic inorganic material to be contained in the chromium compound solution is preferably a powder having the same composition as that of the ceramic layer, but in addition to this, other materials may be used for the purpose of improving heat resistance, wear resistance, or high-temperature lubricity. For example, when the ceramic is zirconia, ZrO ₂ is combined with SiC, Si ₃ N ₄ ,
Favorable results can also be obtained by selectively mixing powders such as MoS ₂ and BN. The powder to be contained in the first liquid is prepared to have a particle size similar to the maximum pore size of ceramics, and the amount added is preferably 5 to 20% by weight based on the solution. Using a ball mill, approx.
It was prepared in the form of a slurry that was mixed for 8 hours. The first liquid is first sprayed or brushed onto the ceramic sprayed surface, or the ceramic is applied by dipping it in the first liquid, and after being left for 5 to 10 minutes, the member is heat treated in a furnace. The heating rate is not constant depending on the size of the object to be treated, but preferably 3 to 4 degrees C/min up to 300 degrees Celsius, and 6 to 8 degrees C/min above that.
The maximum temperature is 500-700℃, and the holding time is 20
~40min is appropriate. The atmosphere for heat treatment is not particularly limited. As mentioned above, the first liquid is a high viscosity (2000 to 4000 cP) slurry that contains powder with a particle size distribution similar to the pore size of the ceramic, so when this is applied, the pores on the ceramic surface are The pores penetrated to a depth of about 20 μm from the surface of the ceramic, and by heat treatment, most of the pores exposed on the ceramic surface were found to be Cr ₂ O ₃ generated from the solution and present in the solution. Only the pores on the surface are filled and blocked by the fine particles. On the surface of heat-treated ceramics, there is a surplus that does not bond with the ceramics (precipitated from the liquid).
There is a light amount of powder attached to it, so wipe it off. The second liquid is a solution of a soluble chromium compound, e.g.
Dissolve CrO ₃ in water and add MgO or ZnO to an aqueous solution with a specific gravity of 1.4 to 1.6 or 0.1 to H ₂ CrO ₄ to this solution.
~0.3 mol% dissolved, preferably by adding water to specific gravity
This is a solution prepared at 1.5-1.6. For treatment with the second liquid, the object coated and heat-treated with the first liquid is dipped approximately 20 mm into the second liquid, and after being left for approximately 10 minutes, the adhered liquid on the ceramic surface is lightly wiped off, and the ceramic is heated to approximately 180°C. Insert it into a heated oven to quickly dry and dehydrate it, then
4℃/min between 180 and 350℃, 6 to 8 above 350℃
The temperature is increased at a rate of 0.degree. C./min and maintained at a maximum of 550 to 750.degree. C. for 0 to 40 minutes to complete the heat treatment. Since the second liquid has a considerably lower viscosity than the first liquid, at 400 to 1000 cP, it penetrates into the ceramic through the fine pores left on the ceramic surface during the first liquid treatment. In this state, the ceramic is inserted into a 180℃ furnace and heated rapidly, so that most of the liquid in the pores is discharged to the surface and dehydrated, and in the next heating step, the crystal water is separated and _Cr Due to the conversion reaction to ₂ O ₃ , the pores on the ceramic surface are almost closed. In addition, in this treatment, the liquid adhering to the pore walls inside the ceramic, that is, the particles, bonds and strengthens the base material, the ceramic, and the intergranular structure in the same manner as described above. By painting and heat-treating thermally sprayed ceramics with two types of solutions in this way, the pores in the ceramics are hardly reduced, so the heat insulating properties of the ceramics are not impaired. In addition, by performing immersion and heat treatment with the second liquid once, most pinholes are removed, but in order to ensure even more completeness, and to increase the hardness and smoothness of the surface, polishing is performed. As necessary, coating with the second liquid and heat treatment are repeated at least once. Through this operation, a pore-free coating is formed on the thermally sprayed ceramic to a desired thickness, and by polishing it, it is possible to impart excellent properties as a heat-insulating engine part. Next, the present invention will be explained in more detail with reference to Examples. Example 1 (1) Plasma-sprayed metal member An alloy of Ni50:Cr50 (weight ratio) was plasma-sprayed to a thickness of about 0.1 mm on one side of a 70 x 70 mm stainless steel plate to a thickness of about 0.1 mm. Rough and Y ₂ O ₃ 8 on it
A ceramic layer was formed by plasma spraying a 44-10 μm powder of ZrO ₂ stabilized by weight % to a thickness of 1 mm. In order to investigate the pore size of this layer, a thermally sprayed ceramic layer was formed on a separately prepared specimen under the same conditions as above, and it was observed under a microscope.
18×14×6μm, 17×15×3μm and 15×13×7
The size of about μm was examined using a microscope. (2) Preparation of the first liquid Dissolve 250 g of CrO ₃ in 200 g of water, and add ZrO ₂ powder stabilized with 8% by weight of Y ₂ O ₃ with an average particle size of 5 μm.
50 g was added and mixed for 8 hours using a porcelain ball mill to prepare a slurry-like first liquid. (3) Preparation of the second liquid The second liquid is prepared by dissolving 350g of CrO ₃ in 250g of water.
Water was added to adjust the specific gravity to 1.45, which was used as a second liquid. (4) Treatment process for thermal sprayed ceramic layer First, a polystyrene resin paint is applied to the surface of the component except for the thermal sprayed ceramic surface to mask it, then it is dipped in the first liquid and painted, and left for about 10 minutes. , using an electric furnace, 3.5 between room temperature and 300℃
The temperature was raised at a rate of 0.degree. C./min, then heated to a maximum of 700.degree. C. at a rate of 6.degree. C./min, held for 20 minutes, cooled outside the furnace, and excess adhered powder that did not bond to the treated surface was wiped off. Next, mask the unnecessary parts with paint in the same way as above, immerse the part in the second liquid for about 20 minutes, paint it, leave it for about 10 minutes, then lightly wipe off the liquid attached to the surface of the part. was placed in a furnace heated to 180°C for rapid drying for about 20 minutes, and then
Heat at 4°C/min up to 350°C, then increase the temperature at 7°C/min above 350°C, and at 700°C.
It was held for 20min. Dipping and painting with this second liquid and heat treatment were repeated three more times to strengthen the sprayed ceramic layer. Example 2 (1) Plasma sprayed metal parts Gray cast iron (JIS FC-35 equivalent), 70×70×4
On one side of a 70 x 70 mm plate, the surface was roughened by plasma spraying Ni to a thickness of about 0.1 mm, and then Y ₂ O ₃ 8
A ceramic layer with a thickness of 1.0 mm was formed by plasma spraying a mixed powder of ZrO ₂ stabilized by weight%, 44-10 μm powder, and 10 wt% of 20-5 μm powder of 99% purity Al ₂ O ₃ . did. The size of the largest pore group was examined using the same method as in Example-1, and the sizes were 14 x 7 x 3 μm, 16 x 8 x 5 μm, and 15 x 9.
×4μm etc. were examined using a microscope. (2) Preparation of the first liquid Dissolve 16 g of MgO in a concentrated aqueous solution of 200 g of CrO ₃ dissolved in 140 g of water, add water to make a solution with a specific gravity of 1.5, and add 99% purity Al ₂ O ₃ and average particle size to this liquid. 5μ
Using a ball mill, add 17 g each of ZrO ₂ powder of 10 μm or less stabilized with m and Y ₂ O ₃ 8%.
The mixture was mixed for 8 hours to prepare a slurry, which was used as the first liquid. (3) Preparation of second liquid Dissolve 400g of CrO ₄ in 250g of water, and then add
35 g of ZnO was dissolved and water was added to adjust the specific gravity to 1.6 to obtain a second solution. (4) Treatment process of thermal sprayed ceramic layer The coating and heat treatment of the ceramic layer with the first and second liquids were carried out in the same manner as in Example 1, except that the heat treatment temperature was set at a maximum of 560°C. I went there. A comparison of the properties of the reinforced thermal sprayed ceramic layer and the unstrengthened ceramic layer for the samples of Examples 1 and 2 above is as shown in Table 1 below. The layer could be improved to a ceramic coating layer without open pores without deteriorating its heat insulating properties, making it suitable for use as a heat insulating engine component. 【table】

Claims (1)

[Claims] 1. A concentrated solution of a soluble chromium compound containing fine non-metallic inorganic powder having a particle size approximating the short diameter of the ceramic layer that is thermally sprayed onto a metal member in order to close the open pores exposed on the surface of the ceramic layer. is used as the first solution, and after coating this on the ceramic surface, heat treatment is performed, then a solution of a soluble chromium compound is applied to the treated product as the second solution, heat treatment is performed again, and further painting with this second solution. and heat treatment at least once or more.