Thermal spray powder material and thermal spray coating formation method

Abstract

To provide a technology capable of acquiring a thermal spray film that is precise and excellent in high-temperature corrosion resistance and suitable for coating a boiler furnace wall panel of a refuse incinerator.SOLUTION: A thermal spray powder material for coating a boiler furnace wall panel of a refuse incinerator includes, by mass, 2.0-4.0% B, 3.5-5.5% Si and the balance Ni with inevitable impurities.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a thermal spray powder material and a method for forming a thermal spray coating. [Background technology]

[0002] Boiler tubes in waste incinerators are exposed to a high-temperature, corrosive atmosphere, and for this reason, the surfaces of the heat transfer tubes of the boiler tubes are coated and protected with a thermally sprayed coating of a Ni-Cr alloy to enhance their resistance to high-temperature corrosion (see, for example, Patent Document 1).

[0003] Ni-Cr alloys are materials with excellent high-temperature corrosion resistance, but when thermal spray coatings are formed using Ni-Cr alloy powders, the thermal spray coatings contain pores. The pores may constitute through-pores that penetrate from the surface of the thermal spray coating to the substrate. When such through-pores are present in the thermal spray coating, corrosive components may penetrate through the through-pores, causing corrosion at the interface between the thermal spray coating and the substrate, which may result in early peeling of the thermal spray coating.

[0004] For this reason, a thermal spray coating is formed using an alloy powder containing Ni-Cr alloys to which elements that lower the melting point, such as B and Si, have been added. The thermal spray coating is then remelted by a heat treatment called fusing, which densifies the coating and further enhances corrosion resistance (see, for example, Patent Documents 2 to 4). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 4-335997 [Patent Document 2] Japanese Patent Application Publication No. 8-13119 [Patent Document 3] Japanese Patent Application Publication No. 10-46315 [Patent Document 4] Japanese Patent Application Laid-Open No. 2007-169733 Summary of the Invention [Problem to be solved by the invention]

[0006] Thermal spray coatings using Ni-Cr alloy powder are useful materials for improving high-temperature corrosion resistance. However, the Cr contained in the thermal spray coating can be corroded by chlorides and other substances in waste incinerators, creating an entry path for corrosive components inside the thermal spray coating, which could reduce the corrosion resistance of the thermal spray coating.

[0007] Therefore, there is a demand for a thermal spray coating with excellent high-temperature corrosion resistance that can suitably cover and protect boiler furnace wall panels of waste incinerators, which are exposed to environments where corrosion by chlorides occurs. [Means for solving the problem]

[0008] The boiler wall panels of waste incinerators are exposed to combustion gases of over 850°C, but the furnace wall panels have furnace wall tubes through which saturated water passes, and the surface temperature of the furnace wall panels remains below 500°C, which is lower than the temperature of the combustion gases. Therefore, the inventors of the present application thought that although Cr is often used for heat resistance in high-temperature atmospheres, at low temperatures of 500°C or less, the necessary heat resistance can be maintained even if the thermal spray powder formed on the surface of the furnace wall panel does not contain Cr. In other words, it was thought that if a thermal spray coating was formed using a thermal spray powder that does not contain Cr, which is easily corroded by chlorides, it would be possible to improve resistance to chloride corrosion while maintaining the necessary heat resistance, so a thermal spray coating was formed using pure Ni material and its high-temperature corrosion resistance was examined.

[0009] However, thermal spray coatings made from pure Ni materials contain a large amount of Ni oxides, which are formed when the spray powder material is oxidized during thermal spraying. These Ni oxides impair the density of the thermal spray coating, making it impossible to improve high-temperature corrosion resistance. Based on the above findings, the inventors of the present invention conducted further studies and completed the present invention.

[0010] (1) That is, the present invention is a thermal spray powder material for coating boiler furnace wall panels of a waste incinerator, which contains 2.0 to 4.0 mass% B, 3.5 to 5.5% Si, and the remainder being Ni and unavoidable impurities.

[0011] The surface of a boiler furnace wall panel having a furnace wall tube through which saturated water passes is at a temperature of 500° C. In contrast, the thermal spray powder material having the above configuration does not contain Cr but contains Ni as a main component, and therefore, a thermal spray coating having sufficient heat resistance can be obtained within the temperature range on the surface of the boiler furnace wall panel. Furthermore, since this thermal spray powder material does not contain Cr as a component, it is possible to obtain a thermal spray coating with excellent corrosion resistance, which does not produce Cr oxides that can cause corrosion due to chlorides. Furthermore, because the thermal spray powder material contains appropriate amounts of B and Si, during thermal spraying, the B and Si in the thermal spray powder material are oxidized preferentially over Ni, suppressing Ni oxidation, thereby reducing the amount of Ni oxide contained in the thermal spray coating. Furthermore, by suppressing the generation of Ni oxides, it is possible to suppress the presence of Ni oxides between the particles that are layered during thermal spraying. In addition, the oxides of B and Si that are generated during thermal spraying are present between the particles of the formed thermal spray coating, increasing their mutual wettability and further increasing the bonding strength between the particles. As a result, by using the above-mentioned thermal spray powder material, it is possible to obtain a thermal spray coating that is dense and has excellent resistance to high-temperature corrosion, and can suitably coat and protect the boiler furnace wall panels of waste incinerators, which are exposed to environments where corrosion by chlorides occurs.

[0012] (2) In the above thermal spray powder material, The average particle size is preferably 10 to 100 μm. If the average particle size is smaller than 10 μm, the surface area per unit weight increases, and there is a risk that the oxidation of B and Si will proceed more than necessary. If the average particle size is greater than 100 μm, the density of the thermal spray coating formed using this thermal spray powder material may decrease. By setting the average particle size to 10 to 100 μm, B and Si can be oxidized appropriately, and a dense thermal spray coating can be obtained.

[0013] (3) From another viewpoint, the present invention provides a method for forming a thermal spray coating on the surface of a boiler furnace wall panel of a refuse incinerator by thermal spraying using the above-mentioned thermal spray powder material. This configuration makes it possible to obtain a thermal spray coating that has excellent high-temperature corrosion resistance and is suitable for covering boiler furnace wall panels in waste incinerators.

[0014] (4) In the above thermal spray coating forming method, The thermal spraying is preferably atmospheric pressure plasma spraying. Atmospheric pressure plasma spraying can reduce the burden on workers during thermal spraying compared to, for example, high velocity flame spraying, which burns a flammable gas. Furthermore, with atmospheric pressure plasma spraying, the surfaces of sprayed particles are more likely to oxidize than with high velocity flame spraying, making it easier to form oxides of B and Si.

[0015] (5) In the above thermal spray coating forming method, The fusing process may not be performed after the formation of the thermal spray coating. In this case, by not performing the fusing process of burning a flammable gas to remelt the thermal spray coating, the number of steps required to form the thermal spray coating can be reduced and the burden on the worker can be reduced.

[0016] (6) In the above thermal spray coating forming method, The thermal spray coating preferably contains a Ni matrix, an oxide of B, and an oxide of Si. In this case, the formation of through pores in the thermal spray coating is suppressed by the oxides of B and Si, resulting in a dense thermal spray coating.

[0017] (7) In the above thermal spray coating forming method, The oxygen content of the thermal spray coating is preferably 0.1 to 1.0 mass %. By setting the oxygen content of the thermal spray coating within the above range, the thermal spray coating contains an appropriate amount of B oxide and Si oxide, while suppressing oxidation of Ni.

[0018] (8) In the above thermal spray coating forming method, The porosity of the thermal spray coating is preferably 0 to 2%, which results in a sufficiently dense thermal spray coating with reduced pore formation.

[0019] (9) In the above thermal spray coating forming method, The thickness of the thermal spray coating is preferably 50 μm to 1.0 mm, and in this case, it can be the thickness required for covering the boiler furnace wall panel of a waste incinerator. [Effects of the Invention]

[0020] According to the present invention, a thermal spray coating that is dense and has excellent high-temperature corrosion resistance can be obtained. [Brief explanation of the drawings]

[0021] [Figure 1] FIG. 1 is a schematic diagram showing an example of a waste incinerator. [Figure 2] FIG. 2 is a diagram showing a part of a boiler furnace wall panel. [Figure 3] FIG. 3 is a cross-sectional view showing an example of a thermal sprayed coating obtained by the above-described method for forming a thermal sprayed coating. [Figure 4] FIG. 4(a) is an electron microscope photograph (×200) of a cross section of the thermal spray coating according to Example 1, and FIG. 4(b) is an electron microscope photograph (×3000) of a cross section of the thermal spray coating according to Example 1. [Figure 5] FIG. 5(a) is an electron microscope photograph of a cross section of the thermal spray coating according to Comparative Example 1, and FIG. 5(b) is an electron microscope photograph of a cross section of the thermal spray coating according to Comparative Example 2. [Figure 6] FIG. 6(a) is an electron microscope photograph of a cross section of a thermal sprayed coating according to Comparative Example 3, FIG. 6(b) is an electron microscope photograph of a cross section of a thermal sprayed coating according to Comparative Example 4, and FIG. 6(c) is an electron microscope photograph of a cross section of a thermal sprayed coating according to Comparative Example 5. [Figure 7]FIG. 7(a) is an electron microscope photograph of a cross section of the thermal spray coating of Example 1 after the high-temperature corrosion test, and FIG. 7(b) is an electron microscope photograph of a cross section of the thermal spray coating of Comparative Example 2 after the high-temperature corrosion test. DETAILED DESCRIPTION OF THE INVENTION

[0022] [About thermal spray powder materials] A thermal spray powder material according to an embodiment of the present invention will be described below. The thermal spray powder material of this embodiment is a thermal spray powder material for coating boiler furnace wall panels of a waste incinerator, and contains 2.0 to 4.0 mass% B, 3.5 to 5.5 mass% Si, and the remainder being Ni and unavoidable impurities.

[0023] Ni is an element that constitutes the matrix of the thermal spray coating formed using the thermal spray powder material of this embodiment. Ni also has excellent corrosion resistance against chlorides in waste incinerators.

[0024] B functions as a flux that lowers the melting point of the thermal spray powder material. Furthermore, B is oxidized preferentially to Ni, thereby suppressing the generation of Ni oxides during thermal spraying. The thermal spray powder material is exposed to high temperatures during thermal spraying, and at that time, B on the surface of the thermal spray powder material is oxidized preferentially to Ni, suppressing the oxidation of Ni. In addition, B is oxidized during thermal spraying to form oxides that reside at the boundaries between the spray particles that are layered during thermal spraying, increasing their mutual wettability and lowering the melting point of the spray powder material, thereby suppressing the occurrence of through pores in the thermal spray coating.

[0025] The content of B is 2.0 mass % or more and 4.0 mass % or less. If the B content is less than 2.0 mass%, the effect of suppressing the generation of Ni oxides during the formation of the thermal spray coating cannot be sufficiently obtained.If the B content exceeds 4.0 mass%, the B content becomes excessive, and the strength of the resulting thermal spray coating may decrease. The content of B is more preferably 2.5% by mass or more and 3.5% by mass or less.

[0026] Like B, Si functions as a flux that lowers the melting point of the thermal spray powder material. Furthermore, like B, Si is oxidized preferentially over Ni, and can therefore suppress the oxidation of Ni during thermal spraying. In addition, Si is oxidized during thermal spraying to form oxides that are present at the boundaries between the spray particles that are layered during thermal spraying, increasing their mutual wettability and lowering the melting point of the spray powder material, thereby suppressing the occurrence of through pores in the thermal spray coating.

[0027] The Si content is 3.5 mass % or more and 5.5 mass % or less. If the Si content is less than 3.5 mass%, the effect of suppressing the generation of Ni oxides during the formation of the thermal spray coating cannot be sufficiently obtained, and if the Si content exceeds 5.5 mass%, the Si content becomes too high, which may reduce the strength of the resulting thermal spray coating. The Si content is more preferably 4.0 mass % or more and 5.0 mass % or less.

[0028] The average particle size of the thermal spray powder material is preferably 10 μm or more and 100 μm or less. In this specification, the average particle size of the thermal spray powder material is defined as the particle size (median diameter) at which the cumulative value is 50% when particle size distribution is measured by the laser diffraction / scattering method (microtrack method). If the average particle size is smaller than 10 μm, the surface area per unit weight of the thermal spray powder material increases, which may cause the oxidation of B and Si to proceed more than necessary. If the average particle size is greater than 100 μm, the density of the thermal spray coating formed using this thermal spray powder material will decrease. By setting the average particle size to 10 to 100 μm, B and Si can be oxidized appropriately, and a dense thermal spray coating can be obtained.

[0029] [Method of forming thermal spray coating] Next, a thermal spray coating forming method according to an embodiment of the present invention will be described. In the thermal spray coating forming method according to this embodiment, a thermal spray coating is formed on the surface of a boiler furnace wall panel of a waste incinerator by thermal spraying using the above-mentioned thermal spray powder material.

[0030] FIG. 1 is a schematic diagram showing an example of a waste incinerator. The waste incinerator 1 is configured to recover the heat of the combustion gas generated when waste is burned, and is equipped with a hopper 2 into which the waste is fed, a combustion chamber 3 in which the fed waste is burned, a re-burning chamber 4 to which the combustion gas generated in the combustion chamber 3 is guided, and a boiler 5. The reburning chamber 4 is defined by a boiler furnace wall panel 6 . The boiler furnace wall panel 6 is provided with furnace wall tubes 5a of the boiler 5 laid all over it. The boiler 5 includes a boiler drum 5b and a furnace wall tube 5a. The furnace wall tube 5a is connected to the boiler drum 5b. The boiler drum 5b passes saturated water through the furnace wall tube 5a. When the combustion gas from the combustion chamber 3 passes through the re-burning chamber 4, the heat of the combustion gas is recovered by the saturated water passing through the furnace wall tube 5a. The heat recovered by the saturated water is converted into electricity or the like by a steam turbine (not shown).

[0031] FIG. 2 is a diagram showing a part of the boiler furnace wall panel 6. As shown in FIG. As shown in FIG. 2, the boiler furnace wall panel 6 includes a plurality of furnace wall tubes 5a arranged in parallel, and a wall portion 7 provided between the plurality of furnace wall tubes 5a. An inner surface 6 a of the boiler furnace wall panel 6 facing the inside of the re-burning chamber 4 is exposed to the combustion gas from the combustion chamber 3 . The temperature of the combustion gas is, for example, about 850°C to 1000°C. On the other hand, the temperature of the saturated water passing through the furnace wall tube 5a is about 200 to 300°C. The inner surface 6a of the boiler furnace wall panel 6 is exposed to combustion gases at 850°C or higher, but is cooled by saturated water passing through the furnace wall tubes 5a. Therefore, the surface temperature of the inner surface 6a becomes 500°C or lower. The thermal spray coating of this embodiment is formed on the inner surface 6 a , which is the surface of the boiler furnace wall panel 6 .

[0032] The thermal spraying onto the inner surface 6a is carried out by atmospheric pressure plasma spraying. The thermal spray coating can be formed on the boiler furnace wall panel 6 before it is installed in the waste incinerator 1. It can also be formed on the boiler furnace wall panel 6 after the waste incinerator 1 has been constructed and installed in the waste incinerator 1. The thermal spray coating is formed after the waste incinerator 1 is constructed by a worker entering the re-burning chamber 4 and operating a thermal spraying device inside the re-burning chamber 4. The thermal spray coating is formed after the waste incinerator 1 has been constructed mainly for the purpose of repairs after it has been in operation for a certain period of time. The inside of the re-burning chamber 4 is not a particularly large space. For this reason, for example, if a thermal spray coating is formed by high-velocity flame spraying, which burns a flammable gas, the temperature inside the re-burning chamber 4 rises, which is not a good working environment. In this regard, atmospheric plasma spraying generates less heat than high-velocity flame spraying, which burns a combustible gas. Therefore, forming a thermal spray coating by atmospheric plasma spraying can improve the working environment during coating formation, especially during repair work, compared to high-velocity flame spraying. Furthermore, with atmospheric pressure plasma spraying, the surfaces of sprayed particles are more likely to oxidize than with high velocity flame spraying, making it easier for oxides of B and Si to form.

[0033] Furthermore, in the method for forming a thermal spray coating according to this embodiment, it is not necessary to perform a fusing process after forming the thermal spray coating. Fusing is a process in which a flammable gas is burned to remelt the thermal spray coating. By eliminating this fusing process, the number of steps required to form the thermal spray coating can be reduced. Furthermore, in this case too, the working environment during repairs can be improved.

[0034] FIG. 3 is a cross-sectional view showing an example of a thermal sprayed coating obtained by the above-described method for forming a thermal sprayed coating. The thermal spray coating 10 obtained by the above-described method for forming a thermal spray coating contains a Ni matrix 11, an oxide of B, and an oxide of Si. The oxide of B and the oxide of Si are dispersed in the Ni matrix 11. The Ni matrix 11 is composed of an alloy mainly containing Ni with small amounts of B and Si. Furthermore, the thermal spray coating 10 has an extremely low content of Ni oxide.

[0035] Because the thermal spray powder material contains appropriate amounts of B and Si, during thermal spraying, the B and Si in the thermal spray powder material are oxidized preferentially over Ni, thereby suppressing Ni oxidation. As a result, as described above, the thermal spray coating 10 has an extremely low Ni oxide content, and the amount of Ni oxide contained in the thermal spray coating 10 can be reduced. Furthermore, by suppressing the oxidation of Ni, it is possible to prevent Ni oxides from being present between particles that are layered during thermal spraying, thereby increasing the bonding strength between the particles. In addition, as described above, the oxides of B and Si produced during thermal spraying are present between particles in the thermal spray coating 10, increasing their mutual wettability and further increasing the bonding strength between the particles. As a result, the oxides of B and Si suppress the generation of through pores that form in the thermal spray coating during thermal spraying, and a dense thermal spray coating 10 is obtained.

[0036] As described above, the temperature of the inner surface 6a, which is the surface of the boiler furnace wall panel 6 having the furnace wall tubes 5a through which saturated water passes, is 500°C or lower. In contrast, the thermal spray powder material used in this thermal spray coating formation method does not contain Cr, but does contain Ni as a main component. Therefore, the thermal spray coating 10 obtained by this method has a Ni matrix 11 and has sufficient heat resistance within the temperature range of the inner surface 6a of the boiler furnace wall panel 6. Furthermore, because the thermal spray powder material does not contain Cr as a component, the thermal spray coating 10 does not produce Cr oxides that can cause corrosion by chlorides, and therefore the thermal spray coating 10 exhibits excellent resistance to corrosion by chlorides.

[0037] In this way, the thermal spray coating 10 obtained by using the above-mentioned thermal spray powder material is dense and has excellent resistance to high-temperature corrosion, and can suitably coat and protect the boiler furnace wall panel 6 of the waste incinerator 1, which is exposed to an environment where corrosion by chlorides occurs.

[0038] Here, the oxygen content of the thermal spray coating 10 is preferably 0.1 mass % or more and 1.0 mass % or less. The oxygen content of the thermal spray coating 10 is a value determined by quantitatively analyzing oxygen on a cross section of the thermal spray coating 10 using EDS (Energy Dispersive X-ray Spectroscopy).

[0039] If the oxygen content of the thermal spray coating 10 is less than 0.1 mass %, the content of B oxides and Si oxides in the thermal spray coating 10 will be low, and the effect of B oxides and Si oxides in suppressing the generation of through pores may be reduced. If the oxygen content of thermal spray coating 10 is greater than 1.0 mass %, thermal spray coating 10 will contain a relatively large amount of Ni oxide, which may impair the denseness of thermal spray coating 10. By setting the oxygen content of thermal spray coating 10 to 0.1 mass % or more and 1.0 mass % or less, a dense thermal spray coating 10 in which the generation of through pores is suppressed can be obtained.

[0040] The porosity of the thermal spray coating 10 is preferably 2% or less. The porosity of the thermal spray coating 10 is a value obtained by identifying pores in a photograph of the cross section of the thermal spray coating and determining the proportion of the pores to the entire coating by image processing (binarization processing). If the porosity of the thermal spray coating 10 is greater than 2%, through pores will be formed, allowing corrosive components of the combustion gas to penetrate into the thermal spray coating 10, which may cause the thermal spray coating 10 to peel off early. By setting the porosity of thermal spray coating 10 to 2% or less, the generation of through pores in thermal spray coating 10 can be suppressed, and early peeling of thermal spray coating 10 can be suppressed.

[0041] The thickness of the thermal spray coating 10 is preferably 50 μm to 1.0 mm. Thermal spray coating 10 is exposed to combustion gases, and if the thickness of thermal spray coating 10 is less than 50 μm, through-pores are likely to form in parts of thermal spray coating 10, and corrosive components may reach the substrate through the through-pores. Furthermore, if the thickness of the thermal spray coating 10 is greater than 1.0 mm, the thickness will be greater than necessary and the internal stress of the thermal spray coating 10 will be large, which may cause peeling. By setting the thickness of the thermal spray coating 10 to 50 μm to 1.0 mm, it is possible to ensure the thickness necessary for covering the boiler furnace wall panel 6 of the waste incinerator 1.

[0042] Although the thermal spray coating of this embodiment is sufficiently dense and has a low porosity, the thermal spray coating may be subjected to a sealing treatment to further improve corrosion resistance. The sealing treatment can be carried out by applying a sealing agent with a brush or by spraying. The sealing agent is preferably a heat-resistant agent such as a silica-based or silicone-based agent. [Example]

[0043] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples. Example 1 An SS400 steel substrate (15 mm × 20 mm × 5 mm thick) was prepared, and a metal powder (average particle size 80 μm) with the composition shown in Table 1, consisting of 3.0 mass% Si, 4.5 mass% B, and the remainder Ni and unavoidable impurities, was used as the thermal spray powder material. This was sprayed onto the substrate surface by atmospheric plasma spraying to form a thermal spray coating with a thickness of 450 μm, and a test specimen was obtained.

[0044] (Comparative Example 1) As shown in Table 1, a thermal spray coating was formed on the surface of a substrate in the same manner as in Example 1, except that Ni powder (average particle size 30 μm) was used as the thermal spray powder material, to obtain a test piece.

[0045] (Comparative Example 2) As shown in Table 1, a thermal spray coating was formed on the surface of the substrate in the same manner as in Example 1, except that a powder (average particle size: 80 μm) of Inconel 625 (registered trademark) (58.0Ni-21.5Cr-9.0Mo-5.0Fe-3.7(Nb+Ta)-1.0Co-0.5Si-0.5Mn-0.4Al-0.4Ti) was used as the thermal spray powder material.

[0046] (Comparative Example 3) As shown in Table 1, a thermal spray coating was formed on the surface of the substrate in the same manner as in Example 1, except that Inconel 622 (registered trademark) (Ni-21Cr-14Mo-3Fe-2.3Co-3.2W-0.3V) powder (average particle diameter: 80 μm) was used as the thermal spray powder material, and test specimens were obtained.

[0047] Comparative Example 4 As shown in Table 1, a thermal spray coating was formed on the surface of the substrate in the same manner as in Example 1, except that a powder of Ni-Cr-Si alloy (90.7Ni-8.5Cr-0.8Si) (average particle size 80 μm) was used as the thermal spray powder material, and test specimens were obtained.

[0048] (Comparative Example 5) As shown in Table 1, a thermal spray coating was formed on the surface of the substrate in the same manner as in Example 1, except that a powder (average particle size: 80 μm) of Inconel 625 self-fluxing alloy (Ni-22.3Cr-9.3Mo-3.9Nb-3.0Cu-3.1B-2.9Si-0.9C-0.5Fe-0.4Mn-0.3Ti-0.2Al) was used as the thermal spray powder material.

[0049] [Table 1]

[0050] (Evaluation test) (1) Cross-sectional observation of thermal spray coating Each test piece from each of Example 1 and Comparative Examples 1 to 5 was cut using a high-speed cutter, and the resulting cut pieces were embedded in resin and mirror-polished. The cross section of the thermal spray coating was observed using an SEM device (JSM-6390LA manufactured by JEOL Ltd.).

[0051] Fig. 4(a) is an electron microscope photograph (x200) of the cross section of the thermal sprayed coating according to Example 1, and Fig. 4(b) is an electron microscope photograph (x3000) of the cross section of the thermal sprayed coating according to Example 1. Fig. 5(a) is an electron microscope photograph of the cross section of the thermal sprayed coating according to Comparative Example 1, and Fig. 5(b) is an electron microscope photograph of the cross section of the thermal sprayed coating according to Comparative Example 2. 6(a) is an electron microscope photograph of a cross section of the thermal spray coating according to Comparative Example 3, FIG. 6(b) is an electron microscope photograph of a cross section of the thermal spray coating according to Comparative Example 4, and FIG. 6(c) is an electron microscope photograph of a cross section of the thermal spray coating according to Comparative Example 5.

[0052] In Figure 5(a), the numerous black linear areas seen in the thermal spray coating are pores or Ni oxides. The remaining white areas are Ni. As such, in Comparative Example 1, which used Ni powder, numerous pores and Ni oxides are seen in the thermal spray coating. On the other hand, in FIG. 4(a) showing the thermal spray coating of Example 1, the black line-like portions seen in FIG. 5(a) are hardly visible.

[0053] Table 2 below shows the results of qualitative (quantitative) analysis performed at the positions indicated by the rectangular marks f1 to f8 in FIG. 4(b).

[0054] [Table 2]

[0055] As shown in Table 2 above, no oxides are present in the matrix portions (rectangles f5 to f8), and oxides are present only in the particle boundaries (rectangles f1 to f4). This clearly shows that the thermal spray coating of Example 1 has significantly fewer pores and Ni oxides than Comparative Example 1. The comparison results between Example 1 and Comparative Example 1 show that by using a thermal spray powder material containing Ni with appropriate amounts of B and Si, oxidation of Ni during thermal spraying can be suppressed, and the occurrence of pores can also be suppressed.

[0056] Similar to Fig. 5(a), numerous black linear areas, which are pores or oxides, can be seen in Fig. 5(b), which shows the thermal spray coating of Comparative Example 2. Note that in Comparative Example 2, the thermal spray powder material contains 20 mass% or more of Cr, so the oxide areas are mainly oxides of Ni and Cr.

[0057] 6(a), 6(b), and 6(c) are similar to FIG. 5(b), and show numerous black linear areas that are pores or oxides of Ni or Cr. In particular, Figure 5(c) shows the thermal spray coating of Comparative Example 5. The thermal spray powder material used in Comparative Example 5 is Inconel 625 self-fluxing alloy, which contains certain amounts of Si and B. Despite this, numerous pores and oxides of Ni and Cr are observed in the thermal spray coating. The comparison results between Example 1 and Comparative Example 5 show that by using a thermal spray powder material containing appropriate amounts of B and Si without adding Cr to Ni, the generation of oxides of Ni and Cr during thermal spraying can be suppressed, and the generation of pores can also be suppressed.

[0058] (2) Measurement of porosity and oxygen content As described above, the porosity was determined based on an electron microscope photograph of the cross section of the thermal spray coating. The oxygen content was determined by quantitatively analyzing oxygen within a certain area of ​​the cross section of the thermal spray coating using an EDS device attached to the above-mentioned SEM device.

[0059] As shown in Table 3, the porosity of Comparative Examples 1 to 5 was 1 to 5%, whereas the porosity of Example 1 was 0.58%, indicating that the generation of pores was suppressed. Moreover, the oxygen content in Comparative Examples 1 to 5 was 1 to 3 mass %, while the oxygen content in Example 1 was 0.73 mass %, and it can be seen that the oxygen content was also kept low compared to Comparative Examples 1 to 5. In particular, the comparison between Example 1 and Comparative Example 1 shows that the generation of Ni oxides during thermal spraying can be suppressed by using a thermal spray powder material containing Ni with appropriate amounts of B and Si, as can be seen from the cross-sectional observation as well as the oxygen content measurement results.

[0060] [Table 3]

[0061] (3) High-temperature corrosion test Ash was applied to the thermal spray coating of each test piece of Example 1 and Comparative Examples 1 to 5, and the test pieces were placed in a tubular furnace whose atmosphere had been adjusted to be the same as that in the re-burning chamber of the waste incinerator 1, heated, and maintained for a certain period of time. The ash applied to the thermal spray coating is a simulated version of the furnace ash that adheres to the boiler furnace wall panel 6 during operation. The test conditions are as follows: Test temperature: 450℃ Test duration: 100 hours Furnace atmosphere: CO2: 10%, O2: 8%, HCl: 1000ppm, SO2: 50ppm, N2: balance Pseudo ash: NaCl: 21.4%, KCl: 14.7%, Na2SO4: 37.1%, K2SO4: 21.3%, ZnCl: 2.5%

[0062] Thereafter, each test piece was taken out, and the cross section of the thermal spray coating of each test piece was observed and qualitatively analyzed. As a result, in the thermal spray coating of Example 1, no corrosive components were found in the thermal spray coating, and the corrosive components had not penetrated into the thermal spray coating. On the other hand, in Comparative Examples 1 to 5, corrosive components were found in the thermal spray coating, and the corrosive components had permeated into the thermal spray coating. This confirms that the thermal spray coating of Example 1 inhibits the penetration of corrosive components into the coating, and is superior in high-temperature corrosion resistance to Comparative Examples 1-5.

[0063] FIG. 7(a) is an electron microscope photograph of a cross section of the thermal spray coating of Example 1 after the high-temperature corrosion test, and FIG. 7(b) is an electron microscope photograph of a cross section of the thermal spray coating of Comparative Example 2 after the high-temperature corrosion test. The rectangular marks e1 to e8 in Figure 7(a) indicate the positions where qualitative (quantitative) analysis was performed within the observation range. The results are shown in Table 4. Similarly, rectangular marks c1 to c8 in Figure 7(b) indicate the locations where qualitative (quantitative) analysis was performed within the observation range. The results are shown in Table 5.

[0064] [Table 4]

[0065] [Table 5]

[0066] As shown in Figures 7(a) and 7(b), it can be seen that the surfaces of both thermal spray coatings are covered with oxides (the areas shown in dark gray).

[0067] In addition, in FIG. 7(a), rectangular marks e1, e2, and e3 indicating the vicinity of the surface of the thermal spray coating have almost no corrosive components related to corrosion by chlorides such as Na, Cl, and K. On the other hand, in FIG. 7(b), the rectangular marks c3 and c4 indicating the inside of the thermal spray coating show the presence of corrosion components related to corrosion by chlorides, such as Na, Cl, and K.

[0068] From these results, it can be seen that the rectangular marks c3 and c4 are areas of Ni and Cr oxides that are formed during thermal spraying, and that corrosive components penetrate into the thermal spray coating along the Ni and Cr oxides that are formed during thermal spraying. Furthermore, in the thermal spray coating of Example 1, oxidation of Ni during thermal spraying is suppressed, so the thermal spray coating contains almost no Ni oxide, and it has been revealed that the penetration of corrosive components into the coating is suppressed. [Explanation of symbols]

[0069] 1. Incinerator 2 Hopper 3 Combustion chamber 4 Reburning chamber 5. Boiler 5a Furnace wall tube 5b Boiler drum 6. Boiler furnace wall panel 6a Inside surface 7 Wall 10 Thermal spray coating 11 Ni matrix

Claims

1. A thermal spray powder material for coating boiler furnace wall panels of a waste incinerator, consisting solely of alloy powder, The alloy powder is a thermal spray powder material for coating boiler wall panels of a waste incinerator, containing 2.0 to 4.0 mass % of B, 3.5 to 5.5 mass % of Si, and the remainder consisting of only Ni and unavoidable impurities.

2. 2. The thermal spray powder material according to claim 1, wherein the average particle size is 10 to 100 μm.

3. A method for forming a thermal spray coating on the surface of a boiler wall panel of a waste incinerator by thermal spraying using a thermal spray powder material consisting solely of alloy powder, said alloy powder containing 2.0 to 4.0 mass % B, 3.5 to 5.5 mass % Si, and the remainder consisting solely of Ni and unavoidable impurities.

4. The thermal spraying is atmospheric pressure plasma spraying. The method for forming a thermal spray coating according to claim 3.

5. No fusing treatment is performed after the thermal spray coating is formed. The method for forming a thermal spray coating according to claim 3 or 4.

6. The thermal spray coating is It includes a Ni matrix, an oxide of B, and an oxide of Si. The method for forming a thermal spray coating according to any one of claims 3 to 5.

7. The oxygen content of the thermal spray coating is 0.1 to 1.0 mass%. The method for forming a thermal spray coating according to any one of claims 3 to 6.

8. The porosity of the thermal spray coating is 0 to 2%. The method for forming a thermal spray coating according to any one of claims 3 to 7.

9. The thickness of the thermal spray coating is 50 μm to 1.0 mm. The method for forming a thermal spray coating according to any one of claims 3 to 8.

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