JP6065388B2 - Thermal insulation film structure and manufacturing method thereof - Google Patents

Description

  The present invention relates to a heat insulating coating structure provided with a thermal spray coating formed on a substrate surface and a method for manufacturing the same.

As for the heat insulating structure formed on the substrate surface, in the 1980s, as a method for increasing the thermal efficiency of the engine, it was proposed to provide a heat insulating layer on the part facing the engine combustion chamber (for example, Patent Document 1). A heat insulating layer made of a ceramic sintered body and a heat insulating layer made of a thermal spray layer containing ZrO ₂ particles having low thermal conductivity have been proposed.

  However, ceramic sintered bodies faced problems such as generation of cracks due to thermal stress and thermal shock, and generation of cracks. For this reason, in particular, a structure in which a heat insulating layer made of a ceramic sintered body is applied to portions having a relatively large area such as the top surface of the piston, the inner peripheral surface of the cylinder liner, and the lower surface of the cylinder head has not been put into practical use.

On the other hand, the sprayed layer itself has been used for trochoidal surfaces of cylinder liners and rotary engines, but this is intended to improve wear resistance and not to improve heat insulation. Absent. Thus, in order to make the thermal spray layer a heat insulating layer, it is preferable to spray a low thermal conductive material mainly composed of ZrO ₂ (zirconia) as described above, but the zirconia-based layer is more preferable than the cermet-based layer. However, the adhesion between the particles is inferior, and there is a problem that cracks are likely to occur due to fatigue due to thermal stress or repeated stress.

  In order to solve such a problem, for example, Patent Document 2 proposes a structure in which particles and reinforcing fiber materials are included in a heat insulating thin film.

International Publication No. 89/03930 Pamphlet JP 2009-243352 A

  The above-mentioned Patent Document 2 does not describe in detail the method for obtaining the heat insulating thin film only by the description of coating or bonding, but for the purpose of containing particles and ensuring heat insulating properties. In view of this, it can be considered that the heat insulating thin film is somewhat porous (porous). And although the thin film for heat insulation of patent document 2 contains the reinforcing fiber material, since it is not the form which couple | bonds particles, it is difficult to suppress effectively that a crack arises in the thin film for heat insulation. Conceivable.

  The present invention has been made in view of the above points, and the object of the present invention is to increase the heat insulating property of the base material in the heat insulating film structure provided with the thermal spray coating formed on the surface of the base material and the manufacturing method thereof. On the other hand, it is to provide a technique for suppressing the occurrence of cracks in the sprayed coating.

In order to achieve the above object, in the heat insulating coating structure and the manufacturing method thereof according to the present invention, ZrO ₂ -containing particles having low thermal conductivity and at least a part of the surface of which are covered with a metal component are sprayed onto the surface of the substrate. I am doing so.

  Specifically, the first invention is directed to a heat insulating coating structure provided with a thermal spray coating formed on the surface of a substrate.

The thermal spray coating has an oxide layer containing hollow ZrO ₂ -containing particles that are sprayed and flattened on the base material, and at least a part of the ZrO ₂ -containing particles contained in the oxide layer is present. Further, it is characterized by being bonded by a metal component covering at least a part of the surface of each ZrO ₂ -containing particle as a spraying raw material.

According to the first invention, the thermal spray coating has an oxide layer containing ZrO ₂ -containing particles having a flat and hollow low thermal conductivity, and the oxide layer has a large amount of air having a low thermal conductivity. Since it will be contained, the heat insulation of a base material can be improved.

In addition, since at least a part of the surface of each ZrO ₂ -containing particle as a spraying raw material is covered with a metal component, when the ZrO ₂ -containing particle is sprayed, the metal component is softened or melted by the thermal spraying heat. However, the ZrO ₂ -containing particles are deposited on the surface of the base material, whereby the ZrO ₂ -containing particles are firmly bonded to each other by the metal component. Therefore, it can suppress effectively that the particle | grains contained in a thermal spray coating are couple | bonded firmly, and a crack generate | occur | produces in a heat insulation layer.

  According to a second invention, in the first invention, the oxide layer has pores, and at least the pores exposed on the surface of the oxide layer contain Si and O. It is characterized by containing an oxide.

  According to the second invention, at least the pores exposed on the surface of the oxide layer are filled or substantially filled with a dense SiO-based oxide. When applied to the inner peripheral surface of the cylinder liner, the lower surface of the cylinder head, etc., it is possible to prevent the sprayed fuel from entering the oxide layer (taken into the pores).

The third invention is directed to a method for manufacturing a heat insulating coating structure provided with a thermal spray coating formed on a substrate surface.

Then, at least part of its surface by the metal component is covered, a preparation step of preparing a hollow ZrO ₂ containing particles as the sprayed material, the ZrO ₂ containing particles, by spraying against the substrate And forming a flat oxide layer including the hollow ZrO ₂ -containing particles, and bonding the ZrO ₂ -containing particles to each other by a metal component covering at least a part of the surface of each ZrO ₂ -containing particle And a process.

According to the third aspect , the same effect as in the first aspect can be obtained.

According to a fourth invention, in the third invention, the surface of the oxide layer reacts with a solution of perhydropolysilazane or moisture in the air to form -Si-O-Si-O- as a main chain. The method further includes a coating step of applying a solution containing an alkoxysilane compound as a main component, which is an inorganic polymer, and impregnating the pores exposed on the surface of the oxide layer.

According to the fourth invention, the perhydropolysilazane impregnated in the pores or the solution containing the alkoxysilane compound as a main component reacts with moisture in the air to form dense silica (SiO2), or , -Si-O-Si-O- is converted into an inorganic polymer having a main chain, in other words, it is converted into a SiO-based oxide containing Si and O, so that it is the same as the second invention. The effect of can be obtained.

According to the heat insulating film structure and the manufacturing method thereof according to the present invention, since the oxide layer containing ZrO ₂ -containing particles having flat and low thermal conductivity is formed, the heat insulating property of the base material is improved. be able to. In addition, since at least a part of the surface of each ZrO ₂ -containing particle as a spraying raw material is covered with a metal component, the ZrO ₂ -containing particle becomes a surface of the base material while the metal component is softened or melted by thermal spraying. As a result, the ZrO ₂ -containing particles are firmly bonded to each other by the metal component, so that the occurrence of cracks in the sprayed coating can be effectively suppressed.

1 is a cross-sectional view showing an engine structure according to Embodiment 1. FIG. It is a graph which shows the relationship between the geometric compression ratio of the engine from which specifications differ, and an illustration thermal efficiency. It is a graph which shows the relationship between the excess air ratio (lambda) of the engine from which a specification differs, and illustration thermal efficiency. It is sectional drawing which shows the heat insulation film structure of an aluminum alloy piston. It is an expanded sectional view which shows typically the thermal spray coating of the piston. It is a figure which illustrates typically reaction of permeate and water. It is an expanded sectional view which shows typically the thermal spray coating of the piston. It is a flowchart which shows the manufacturing method of a heat insulation film structure. It is a figure which shows the illustration thermal efficiency (%) of an Example and the comparative example 1 and the comparative example 2. FIG.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  In the present embodiment, the heat insulating film structure according to the present invention is employed in the piston of the engine shown in FIG.

<Engine features>
This engine is an in-line four-cylinder 2L gasoline engine. Reference numeral 3 in FIG. 1 is a cylinder block, reference numeral 5 is a cylinder head, reference numeral 7 is an intake valve for opening and closing the intake port 9, and reference numeral 11 is an exhaust port 13. Reference numeral 15 denotes an exhaust valve that opens and closes the fuel injection valve. The combustion chamber of the engine is formed by the top surface of the piston 1, the inner peripheral surface of the cylinder block 3, the lower surface of the cylinder head 5, and front surfaces of the umbrella portions of the intake and exhaust valves 7 and 11 (surfaces facing the combustion chamber). A cavity 17 is formed on the top surface of the piston 1. In FIG. 1, the ignition plug is not shown.

  By the way, it is known that the thermal efficiency of the engine theoretically increases as the geometric compression ratio increases and the excess air ratio of the working gas increases. As the excess air ratio is increased and the excess air ratio is increased, the cooling loss, which is the energy taken away as heat to the outside, increases. Therefore, the improvement of the thermal efficiency due to the increase in the compression ratio and the excess air ratio reaches its peak.

  That is, the cooling loss depends on the heat transfer rate from the working gas to the engine combustion chamber wall, its heat transfer area, and the temperature difference between the gas temperature and the wall temperature, and the heat transfer rate depends on the gas pressure and temperature. Therefore, if the gas pressure and temperature increase due to the increase in the compression ratio and excess air ratio, the heat transfer rate increases and the temperature difference between the wall temperature and the gas temperature increases, resulting in a large cooling loss. Become. For this reason, at present, it is not possible to achieve an ultra-high compression ratio of 20 or more due to cooling loss.

  In turn, the engine of the present embodiment is a lean burn engine that has a geometric compression ratio ε = 20 to 50 and is operated at an excess air ratio λ = 2.5 to 6.0 at least in a partial load region. . Therefore, in order to obtain the desired thermal efficiency commensurate with the compression ratio ε and excess air ratio λ, the engine heat loss must be increased unless the engine cooling loss is significantly reduced. In order to explain this point on the basis of the thermal efficiency shown in the model calculation, when the compression ratio ε is increased, whether the combustion chamber has a heat insulating structure or not, and whether the excess air ratio λ is large or small, A model calculation was performed to see how it is affected.

  FIG. 2 shows the result. In the figure, “without heat insulation” means a conventional engine that does not employ a heat insulation structure in the combustion chamber, and “with heat insulation” means that the combustion chamber is more than a conventional engine that does not employ a heat insulation structure in the combustion chamber. This means an engine with a 50% higher heat insulation rate. “200 kPa” and “500 kPa” represent the magnitude of the engine load.

  First, in the case of “no heat insulation 200 kPa λ = 1”, the indicated thermal efficiency increases as the compression ratio ε increases. However, even if the compression ratio ε = 50 is exceeded, the indicated thermal efficiency does not greatly improve, and the compression ratio ε Since the theoretical efficiency at = 50 is about 80%, the indicated thermal efficiency of the engine is considerably low. Most of this difference is cooling loss and exhaust loss.

  In the case of “without heat insulation 200 kPa λ = 2”, the specific heat ratio decreases due to an increase in the excess air ratio, so that the illustrated thermal efficiency is high, but it is still low in terms of theoretical efficiency. Looking at “without heat insulation 200 kPa λ = 4” and “without heat insulation 200 kPa λ = 6”, when the compression ratio ε exceeds 15 or 25, the indicated thermal efficiency decreases as the compression ratio ε increases. This is because the excess air ratio λ is large (the air density of the air-fuel mixture is high), so when the compression ratio is high, the gas pressure during combustion becomes very high, and the heat transfer coefficient as a function of the gas pressure and temperature is high. This is because the cooling loss increases. That is, the cooling loss becomes larger than the increase in thermal efficiency due to the increase in excess air ratio λ (increase in specific heat ratio).

  On the other hand, in the case of “with heat insulation 200 kPa λ = 2.5”, the indicated thermal efficiency increases as the compression ratio ε increases. In the case of “with heat insulation 200 kPa λ = 6” in which the excess air ratio λ is increased, when the compression ratio ε exceeds 40, the illustrated thermal efficiency slightly decreases, but the illustrated thermal efficiency is very high at the compression ratio ε = 20 to 50 It is a value. Even in the case of “with heat insulation 500 kPa λ = 2.5” in which the engine load is increased, the indicated thermal efficiency is high at the compression ratio ε = 20-50.

  FIG. 3 is a graph showing the relationship between the excess air ratio λ and the indicated thermal efficiency. In the case of “no heat insulation 200 kPa ε = 15”, the illustrated thermal efficiency peaks near the excess air ratio λ = 4.5, and the illustrated thermal efficiency decreases as the excess air ratio λ increases. On the other hand, in the case of “with heat insulation 200 kPa ε = 40”, the illustrated thermal efficiency peaks in the vicinity of the excess air ratio λ = 6.0. This is because the compression ratio ε is high and the cooling loss is suppressed by heat insulation.

  In the case of the lean burn engine, it operates at an excess air ratio λ = 2.5 or more at least in the partial load region, which is advantageous for suppressing NOx generation. As the compression ratio ε increases, the combustion temperature increases. However, by controlling the excess air ratio λ so as to increase as the engine load increases, NOx generation is prevented so that the maximum combustion temperature does not exceed 1800 (K). Can be suppressed.

  Although not shown, an intercooler that cools the intake air is provided in the intake system of the engine. As a result, the in-cylinder gas temperature at the start of compression is lowered, the increase in gas pressure and temperature during combustion is suppressed, and this is advantageous in reducing cooling loss (improving the indicated thermal efficiency).

<Insulation coating structure>
Therefore, in the following, in order to reduce the cooling loss necessary for increasing the indicated thermal efficiency in the engine operated at the above-described ultra-high compression ratio ε = 20 to 50 and high excess air ratio λ = 2.5 to 6.0. The heat insulating film structure will be described. FIG. 4 is a cross-sectional view showing the heat insulating film structure of the piston. The piston 1 includes a thermal spray coating 21 on a top surface forming a combustion chamber of the engine. The thermal spray coating 21 includes an undercoat 23 formed over the entire top surface of the piston base material 19 and the undercoat 23. And an oxide layer 25 covering the coat 23.

The piston base material 19 can be formed by, for example, an aluminum alloy AC8A for casting (thermal conductivity: 141.7 (W / (m · K)), specific heat capacity: 2300 (kJ / (m ³ · K))). it can. The piston base material 19 may be formed of other aluminum alloy or a cast iron piston.

The undercoat 23 serves to improve the adhesion of the oxide layer 25 to the piston base material 19 and to reduce the difference in thermal expansion between the oxide layer 25 and the piston base material 19. The alloy is formed with a thickness of about 100 (μm) by plasma spraying the top surface of the piston base material 19. As the Ni—Cr alloy, for example, a Ni-20Cr alloy (thermal conductivity: 12.6 (W / (m · K)), volume specific heat: 3660 (kJ / (m ³ · K))) is employed. be able to.

As shown in FIG. 5, the oxide layer 25 includes a large number of zirconia particles (ZrO ₂ -containing particles) 27 sprayed on the top surface of the piston base material 19, and a bonding metal 35 that bonds the zirconia particles 27 to each other. And a pore portion 29 (void) formed from the surface to the inside of the oxide layer 25, and the pore portion 29 is a SiO-based oxide 31 containing Si and O in the present invention. An inorganic polymer or silica glass having —Si—O—Si—O— as the main chain is filled or substantially filled (included).

As a material of the zirconia particles 27, for example, partially stabilized zirconia (ZrO ₂ —Y ₂ O ₃ ) using yttria as a stabilizer can be used, and the zirconia particles 27 as the thermal spray raw material have a particle size distribution range. Is formed into a substantially hollow sphere having a diameter of 45 to 125 μm. Thus, the oxide layer 25 is formed by spraying the zirconia particles 27 on the top surface of the piston base material 19 that has been subjected to the undercoat treatment using a plasma spraying device (not shown), and softening by the thermal spraying heat. Is collided with the piston base material 19 and deformed and accumulated in a flat shape to form a porous material having a thickness of about 900 (μm) and a porosity of 13 (vol%). The porosity of the oxide layer 25 can be adjusted by adjusting the particle size and spraying speed of the zirconia particles 27, preferably 5 to 40 (vol%), more preferably 10 to 25 (vol%). . Moreover, the size of each pore portion 29 is preferably 1 to 100 (μm).

  As the binding metal (metal component) 35, for example, Ni, Cu, or Fe can be employed. Here, when the bonding metal 35 is plasma sprayed separately from the zirconia particles 27, the sprayed coating 21 is divided into an oxide layer 25 containing the zirconia particles 27 and a layer of the bonding metal 35, and bonds the zirconia particles 27 together. Since the shape cannot be formed and it is difficult to effectively suppress the occurrence of cracks, in the heat insulating coating structure of the present embodiment, prior to thermal spraying the zirconia particles 27 on the top surface of the piston base material 19, The binding metal 35 covers at least a part of the zirconia particles 27. In other words, in the heat insulating coating structure of the present embodiment, at least a part of the zirconia particles 27 included in the oxide layer 25 by the bonding metal 35 covering at least a part of the surface of each zirconia particle 27 as the thermal spraying raw material. Are to be combined. The thickness of the bonding metal 35 covering the surface of the zirconia particles 27 is preferably 0.5 to 2 (μm).

  Examples of the method of covering the zirconia particles 27 formed in a substantially hollow sphere with the binding metal 35 (for example, Ni) include the following two methods.

  First, in order to attach Ni to the zirconia particles 27 having poor wettability, first, the zirconia particles 27 formed in a substantially hollow spherical shape are immersed in nickel nitrate, and then taken out and fired at about 300 (° C.). Only the Ni component is supported on the surface of the zirconia particles 27. Then, the zirconia particles 27 having Ni supported on the surface are put into an electroless nickel plating bath, and nickel plating is provided on the surface of the zirconia particles 27 using the supported Ni components as nuclei. The other is a method in which after the surface of the zirconia particles 27 is etched, this is put into an electroless nickel plating bath to provide nickel plating on the surfaces of the zirconia particles 27.

  When the zirconia particles 27 having the surface covered with the bonding metal 35 manufactured in this way are subjected to plasma spraying on the top surface of the piston base material 19 subjected to the undercoat treatment using a plasma spraying device, The zirconia particles 27 softened by the thermal spray heat are deformed and accumulated in a flat shape by colliding with the piston base material 19, and at the same time, the bonded metal 35 softened or melted by the thermal spray heat is uniformly formed on the oxide layer 25. As shown in FIG. 5, the zirconia particles 27 are bonded to each other to form the thermal spray coating 21 in which cracks are unlikely to occur.

  Furthermore, in the heat insulating coating structure of the present embodiment, when the mixture of gasoline (fuel) and air is sprayed into the combustion chamber, the gasoline penetrates into the thermal spray coating 21 (taken into the pores 29), and thus is not In order to suppress the increase in the fuel loss ratio, the surface of the oxide layer 25 is mainly composed of an alkoxysilane compound that reacts with moisture in the air to become an inorganic polymer having —Si—O—Si—O— as the main chain. Applying a solution as a component or a solution of perhydropolysilazane, and filling the pores 29 with a dense inorganic polymer or silica glass having —Si—O—Si—O— as the main chain as described above, or By being substantially filled (included), the sprayed gasoline is prevented from entering the thermal spray coating 21.

As a solution containing an alkoxysilane compound as a main component for forming an inorganic polymer having —Si—O—Si—O— as the main chain, for example, a permeate manufactured by D & D Corporation can be used. This permeate is a solventless one-pack type sealant mainly composed of an alkoxylane compound that is a raw material of a silicone resin, and includes a partially hydrolyzed condensate (oligomer) and a curing catalyst in addition to the alkoxylane compound. As shown in FIG. 6, it reacts with moisture in the air, becomes an inorganic polymer, cures, and forms a SiO-based oxide 31 in which Si and O are continuously bonded to form an oxide layer 25. The existing pores 29 are blocked. Incidentally, R in FIG. 6 refers to a hydrocarbon group such as CH _3.

Further, as a solution of perhydropolysilazane forming silica glass, Aquamica manufactured by AZ Electronic Materials can be used. This aquamica is a sealing agent mainly composed of perhydropolysilazane and contains organic solvent and catalyst in addition to perhydropolysilazane, which reacts with moisture in the air and is converted to silica glass (SiO ₂ ). Thus, the pores 29 existing in the oxide layer 25 are blocked.

  In FIG. 5, the pores 29 existing in the oxide layer 25 are almost completely blocked by the SiO-based oxide 31. However, in order to positively leave air with extremely low thermal conductivity, FIG. As shown in FIG. 5, for example, only in the pores 29 exposed on the surface of the oxide layer 25 or in the pores 29 having a depth of ½ or less from the surface of the oxide layer 25 toward the inside, The oxide 31 may be filled or substantially filled. Thus, in order to suppress the range in which the SiO-based oxide 31 containing Si and O is formed, for example, a thickener is added to increase the viscosity of permeate or aquamica and then applied to the surface of the oxide layer 25. In this case, the viscosity of permeate or aquamica at room temperature is preferably 10 to 10,000 (mPa · s), and more preferably 500 to 5000 (mPa · s).

  In addition, as shown in FIG. 7, hollow particles 33 may be included in the SiO-based oxide 31 containing Si and O in order to further improve the heat insulation. As the hollow particles 33, ceramic hollow particles such as alumina bubbles, fly ash balloons, shirasu balloons, silica balloons, airgel balloons, and other inorganic hollow particles can be used. Each material and particle size are as shown in Table 1.

For example, the chemical composition of the fly _{ash, SiO 2; 40.1~74.4%, Al} 2 O 3; 15.7~35.2%, Fe 2 O 3; 1.4~17.5%, MgO 0.2 to 7.4%, CaO; 0.3 to 10.1% (the above is mass%). The chemical composition of the Shirasu _{balloon, SiO 2; 75~77%, Al} 2 O 3; 12~14%, Fe 2 O 3; 1~2%, Na 2 O; 3~4%, K 2 O; 2~ 4%, IgLoss; 2 to 5% (the above is mass%).

The oxide layer 25 containing one of these hollow particles 33 can be easily obtained by simply applying a permeate or aquamica mixed with the hollow particles 33 on the surface of the oxide layer 25. In the case of the hollow particles 33 exemplified above, the thermal conductivity is about 0.03 to 0.3 W / (m · K), and the volume specific heat is about 200 to 1900 kJ / (m ³ · K). Become.

<Method of manufacturing heat insulating film structure>
Next, based on the flowchart shown in FIG. 8, the manufacturing method of the heat insulation film structure which concerns on Embodiment 1 is demonstrated.

  First, in step S1, zirconia particles formed in a substantially hollow sphere are immersed in nickel nitrate, and then taken out and fired at about 300 (° C.). Thereafter, the zirconia particles having Ni supported on the surface are put into an electroless nickel plating bath, and nickel plating is provided on the surface of the zirconia particles using the supported Ni component as a nucleus (preparation step).

  In the next step S2, a Ni-20Cr alloy is plasma sprayed on the top surface of the piston base material 19 using a plasma spray gun to form an undercoat 23 having a thickness of about 100 (μm).

Next, in step S3, similarly using a plasma spray gun, the output is 25-50 (kW), the Ar gas flow rate is 35-50 (L / min), the H ₂ gas flow rate is 10-20 (L / min), and the spray distance is 50 Zirconia particles having nickel plating on the top surface of the piston base material 19 that has been subjected to undercoat treatment under a spraying condition of ˜150 (mm) and a sprayed particle supply amount of 20 to 50 (g / min) (ZrO ₂ —Y ₂ O ₃ ) is plasma sprayed to form an oxide layer 25 having a thickness of about 900 (μm) and a porosity of 13 (vol%) (spraying process). As the plasma spray gun, for example, an F4 type plasma spray gun manufactured by Sulzer Metco can be used.

  In the next step S4, the surface of the oxide layer 25 formed in step S3 is coated with, for example, a liquid sealant permeate mixed with a shirasu balloon, and at least the surface of the oxide layer 25 is applied. The exposed pores 29 are impregnated (application process).

  Next, in step S5, of the permeate applied in step S4, excess permeate blown to the surface of the oxide layer 25 without impregnating the pores 29 is wiped off with a cloth.

  In the next step S6, as preliminary drying, the piston 1 from which the permeate on the surface of the oxide layer 25 has been wiped off is cured by touching at room temperature (touch-curing is a change in the cured film even when touched by the finger). It means a state of being hardened to the extent that it cannot be done.)

  Next, in step S7, the pre-dried piston 1 is heat-treated at 40 to 150 ° C. for a predetermined time as a curing process. In addition, also when using aquamica as a sealing agent, after carrying out finger touch hardening at room temperature, it heat-processes for 40 hours at 150-150 degreeC.

<Improvement of heat insulation and durability>
In order to confirm the improvement effect of the heat insulation and fuel penetration suppression by the heat insulating film structure according to the present embodiment, the illustrated thermal efficiency (%) is obtained for each of the examples and comparative examples under predetermined evaluation conditions, The presence or absence of cracks on the surface of the sprayed coating was examined, and these results were compared.

More specifically, a piston made of aluminum alloy AC8A for casting was used as Comparative Example 1. Further, using the F4 type plasma spray gun on the top surface of the piston of Comparative Example 1, output 35 (kW), Ar gas flow rate 40 (L / min), H ₂ gas flow rate 15 (L / min), spraying distance Under spraying conditions of 100 (mm) and sprayed particle supply rate 40 (g / min), Ni-20Cr alloy is sprayed to form an undercoat with a thickness of 100 (μm), and partial stabilization using yttria Comparative Example 2 was obtained by spraying zirconia particles (ZrO ₂ —Y ₂ O ₃ ) to form an oxide layer having a porosity of 13 (vol%) and a thickness of 900 (μm).

On the other hand, a Ni-20Cr alloy is sprayed on the top surface of the piston of Comparative Example 1 under the same thermal spraying conditions as in Comparative Example 2 to form an undercoat 23 having a thickness of 100 (μm), and the surface is plated with nickel. After spraying the provided partially stabilized zirconia particles (ZrO ₂ —Y ₂ O ₃ ) to form an oxide layer having a porosity of 13 (vol%) and a thickness of 900 (μm), the pores of the oxide layer The part was sealed with permeate as an example.

  Then, these three types of pistons are subjected to the same evaluation conditions, that is, a displacement of 198.8 (CC), four cylinders, a compression ratio of 20, an excess air ratio of 2.5, and a rotational speed of 2000 (rpm). Each indicated thermal efficiency (%) was determined.

  FIG. 9 is a graph showing the indicated thermal efficiency (%) of the examples and Comparative Examples 1 and 2. As shown in FIG. 9, in the example in which the thermal spray coating is formed, the thermal efficiency shown in the figure is greatly improved as compared with the comparative example 1 in which the thermal spray coating is not formed and the comparative example 2 in which the sealing treatment is not performed. . Thus, it was confirmed that by forming an oxide layer containing zirconia particles having low thermal conductivity, the engine cooling loss is reduced, in other words, the heat insulation of the engine is improved. In addition, although the thermal efficiency (%) shown in the comparative example 2 is lower than the comparative example 1 in which the thermal spray coating is not formed, this is the unburned loss ratio in the comparative example 2 in which the sealing treatment is not performed. It is considered that the decrease in the illustrated thermal efficiency due to the deterioration exceeds the increase in the illustrated thermal efficiency due to the improvement of the heat insulating property by the thermal spray coating.

  In addition, as for the two types of pistons of Comparative Example 2 and Example, as a result of carrying out an endurance test with an actual machine for 200 hours respectively, the occurrence of cracks in the thermal spray coating was observed in the piston of Comparative Example 2, In the examples, no abnormality was observed. Thus, it was confirmed that by forming the oxide layer by spraying the zirconia particles whose surfaces are covered with the binding metal, the zirconia particles can be bonded to each other to suppress the occurrence of cracks.

-Effect-
According to the present embodiment, since the thermal spray coating 21 has the oxide layer 25 including the zirconia particles 27 having low thermal conductivity, the heat insulating property of the piston base material 19 can be improved.

  Further, since at least a part of the surface of each zirconia particle 27 as a spraying raw material is covered with the bonding metal 35, when the zirconia particle 27 is sprayed, the bonding metal 35 is softened or melted by the thermal spraying heat. However, the zirconia particles 27 are deposited on the surface of the piston base material 19, whereby the zirconia particles 27 are firmly bonded by the bonding metal 35. Therefore, it is possible to effectively suppress the occurrence of cracks in the heat insulating layer by firmly bonding particles contained in the thermal spray coating 21.

  In addition, the pores 29 formed from the surface to the inside of the oxide layer 25 are filled or substantially filled with the dense SiO-based oxide 31, so that the heat insulating film structure is formed, for example, on the top surface of the piston 1, When applied to the inner peripheral surface of the cylinder liner, the lower surface of the cylinder head, etc., it is possible to prevent the sprayed fuel from entering the oxide layer 25.

  Furthermore, since the thermal spray coating 21 is formed by using the zirconia particles 27 made of hollow particles as a raw material, the oxide layer 25 contains a large amount of air having low thermal conductivity. The heat insulation in can be further improved.

(Other embodiments)
The present invention is not limited to the embodiments, and can be implemented in various other forms without departing from the spirit or main features thereof.

  In the above embodiment, the heat insulating film structure according to the present invention is applied to the top surface of the piston 1, but is not limited thereto, and may be applied to, for example, the inner peripheral surface of the cylinder block 3 and the lower surface of the cylinder head 5. . Moreover, you may apply the heat insulation film structure which concerns on this invention not only to an engine but the other thing in which heat insulation is requested | required.

  Moreover, in the said embodiment, although the Ni-Cr alloy was used as the undercoat 23, it is not restricted to this, For example, you may use a Ni-Al alloy.

  Furthermore, in the above embodiment, the layer thickness of the undercoat 23 is about 100 (μm) and the layer thickness of the oxide layer 25 is about 900 (μm). Is not particularly limited.

  As described above, the above-described embodiment is merely an example in all respects and should not be interpreted in a limited manner. Further, all modifications and changes belonging to the equivalent scope of the claims are within the scope of the present invention.

  As described above, the present invention is useful for a heat insulating coating structure including a thermal spray coating formed on the surface of a substrate, a manufacturing method thereof, and the like.

19 Piston substrate 21 Thermal spray coating 25 Oxide layer 27 Zirconia particles (ZrO ₂ -containing particles)
29 Pore 31 SiO-based oxide 35 Bonded metal (metal component)
S1 preparation process S3 spraying process S4 coating process

Claims (4)

A heat insulating coating structure provided with a thermal spray coating formed on a substrate surface,
The thermal spray coating has an oxide layer containing hollow ZrO ₂ -containing particles sprayed and flattened on the base material,
A heat insulating film characterized in that at least a part of the ZrO ₂ -containing particles contained in the oxide layer is bonded by a metal component covering at least a part of the surface of each ZrO ₂ -containing particle as a thermal spraying raw material Construction. In the heat insulating coating structure according to claim 1,
The oxide layer has pores, and at least the pores exposed on the surface of the oxide layer contain a SiO-based oxide containing Si and O. Film structure. A method of manufacturing a heat insulating coating structure provided with a thermal spray coating formed on a substrate surface,
A preparation step of preparing hollow ZrO ₂ containing particles as a thermal spraying raw material, at least part of the surface of which is covered with a metal component;
By spraying the ZrO ₂ -containing particles onto the substrate, an oxide layer containing the flattened hollow ZrO ₂ -containing particles is formed, and the ZrO ₂ -containing particles are contained in each ZrO ₂ -containing particle. A thermal spraying step of bonding with a metal component covering at least a part of the surface of the particles ;
The manufacturing method of the heat insulation film structure characterized by including. In the manufacturing method of the heat insulation film structure of Claim 3 ,
The main component is an alkoxysilane compound that reacts with a solution of perhydropolysilazane or moisture in the air to form an inorganic polymer having —Si—O—Si—O— as the main chain on the surface of the oxide layer. A method for producing a heat insulating coating structure, further comprising an application step of applying the solution to impregnate the pores exposed on the surface of the oxide layer.

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