JPS6362858A - Formation of thermally sprayed ceramic layer - Google Patents

Abstract

PURPOSE:To surely prevent the exfoliation and dislodgment of a thermally sprayed ceramic layer by uniformly forming a 1st underlying thermally sprayed layer to the required section of a base metal, then forming the 2nd underlying thermally sprayed layer having ruggedness of specific roughness thereon, and thermally spraying ceramics onto said layer. CONSTITUTION:The 1st underlying material (Ni-Ci-Al alloy, etc.) is thermally sprayed perpendicularly from a thermally spraying gun 3 to the surface of the required part of the base material 1 (Al alloy, etc.) where a heat insulating characteristic and heat resistance are required to form the 1st underlying sprayed layer 2 uniformly to about 0.05-0.1mm thickness. The gun 3 is then inclined by an angle theta within 40-70 deg. from the perpendicular O and the thermally spraying material equiv. to the 1st thermally spraying material is sprayed onto the 1st underlying layer 2 to form the 2nd underlying sprayed layer 4 having the ruggedness of >=0.1mm ten-point average roughness Rz. Ceramics (ZrO2, Si3N4, etc.) are then thermally sprayed perpendicularly from the gun 3 onto the 2nd layer 4 to form the thermally sprayed ceramic layer 5 to about 0.1-1.0mm thickness. The exfoliation and dislodgment of the ceramic layer 5 by a difference in thermal expansion are thereby effectively and surely prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a method for forming a ceramic sprayed layer with excellent heat resistance and heat insulation properties on the surface of a base material made of aluminum alloy, etc. The present invention relates to a method for forming a ceramic sprayed layer on the surface of a portion where excellent heat insulation and/or heat resistance is required, such as the bore surface of a motor.

2. Description of the Related Art Conventionally, parts such as automobile engine screws that have parts that are heated to high temperatures, especially parts whose base material is aluminum alloy, have a surface that has low thermal conductivity and low heat resistance. Ceramic sprayed members with improved heat insulation and heat resistance are being used by spraying a superior ceramic to form a ceramic sprayed layer.

Such a conventional ceramic sprayed member will be described in detail below using a piston for an automobile engine as an example.

In recent years, as pistons used in engines, pistons cast from aluminum alloy have been increasingly used, with a focus on weight reduction in order to reduce the inertia of reciprocating parts in the engine. However, since aluminum alloy is a material with high thermal conductivity, in engines using aluminum alloy pistons, the combustion heat generated by combustion of fuel in the combustion chamber is transferred to the outside of the combustion chamber through the piston, and the engine There was a tendency to deteriorate the thermal efficiency of the engine, lowering the engine's output and fuel efficiency. Therefore, in order to reduce the heat loss transferred to the outside of the combustion chamber via the aluminum alloy piston, a ceramic material with low thermal conductivity such as zirconia or alumina is sprayed on the top surface (piston head) of the piston. Attempts have been made to apply ceramic sprayed pistons with improved thermal insulation properties (e.g. [Cumm1ns/TACO
HA Advanced Adiabatic Engine,
JR, Kamo et al, SAE Pape
rNα840428 etc.).

However, in ceramic sprayed pistons in which a ceramic sprayed layer is formed using an aluminum alloy as a base material, there is a large difference between the coefficient of thermal expansion of the aluminum alloy that is the base material and the thermal expansion coefficient of the ceramic material. During repeated heating and cooling associated with engine operation, cracks occur at the interface due to the difference in thermal expansion between the surface of the aluminum alloy base material and the ceramic sprayed layer.
In the end, the ceramic sprayed layer sometimes peeled off or fell off from the base material surface, and as a result, the durability was still not sufficient.

Therefore, as a conventional method to prevent the peeling of the ceramic sprayed layer due to the difference in thermal expansion coefficient between the aluminum alloy base material and the ceramic sprayed layer, the thermal expansion coefficient is set on the surface of the base material in advance so that the thermal expansion coefficient is intermediate between that of the base material and the ceramic. Moreover, metals that have good adhesion to ceramics, such as Ni-Cr-A1 alloy,
Ni-0r-Al-Y alloy, Ni-Co-Cr-A
A method is known in which a base sprayed layer called a pond layer or an intermediate layer is formed by spraying a thin layer of l-Y alloy, and then a ceramic is sprayed on top of the base sprayed layer (for example, as described in the above publication). thing).

Problems to be Solved by the Invention As mentioned above, as a conventional solution to the problem of cracking or peeling of the ceramic sprayed layer due to the difference in the thermal expansion coefficient between the aluminum alloy base material and the ceramic sprayed layer, A method is known in which a base thermal sprayed layer made of a metal intermediate between the base material and ceramic is previously formed on the surface of the base material, but even when the base melted tJA layer is formed in this way,
It has not yet been sufficient to prevent cracking or peeling of the ceramic sprayed layer due to differences in thermal expansion.

This invention was made against the background of the above-mentioned circumstances, and in ceramic sprayed parts such as pistons that are repeatedly heated and cooled, ceramic spraying occurs due to the difference in thermal expansion between the base material made of aluminum alloy etc. and the ceramic sprayed layer. The object of the present invention is to provide a method for forming a ceramic sprayed layer that can effectively and reliably prevent the occurrence of situations that lead to peeling or falling off of the layer.

Means for Solving the Problems This invention provides a ceramic material made of a ceramic material having a lower thermal conductivity and a smaller coefficient of thermal expansion than the base material in a region where heat insulation and/or heat resistance is required on the surface of the base material. Melt!
In the method of forming 11@, after uniformly forming a first base sprayed layer on the surface of the portion of the base material, a spray gun is placed on the first base sprayed layer at an angle of 40° to a perpendicular line.
A second base sprayed layer having an unevenness with a ten-point average roughness Rz of 0.1M or more is formed by thermally spraying the base thermal sprayed material in an inclined state within a range of 70', and the second base sprayed layer is This method is characterized by spraying ceramic onto the soil.

Function: In the method of the present invention, the first step is applied to the surface of the base material made of aluminum alloy, etc., at a portion where heat insulation and heat resistance are required.
After uniformly forming the base sprayed layer, the base spray material is sprayed by tilting the spray gun within the range of 40° to 70' relative to the perpendicular line to form a second base sprayed layer. As mentioned above, if you spray with the spray gun tilted, the shielding phenomenon of spray particles,
That is, a phenomenon occurs in which the sprayed particles are not attached to the shadowed portion of the minute convex portion of the surface to be sprayed when viewed from the spraying direction. Therefore, when viewed from the spraying direction, the sprayed particles adhere one after another to the front side of the minute convexities on the surface to be thermally sprayed, and the convexities grow, while in the shadowed areas, almost no sprayed particles adhere, so they remain as concavities. As a result, as the spraying progresses, the unevenness of the sprayed surface gradually becomes larger, and the final ten-point average roughness R2 becomes 0.1. It is possible to form a second base sprayed layer having large irregularities as described above.

As described above, a ceramic sprayed layer is formed by spraying a ceramic to obtain the desired heat insulation and heat resistance on the second base sprayed layer having irregularities of Rzo of 1 m or more. This ceramic sprayed layer is formed by biting into the coarse irregularities of the second base sprayed layer, so that the ceramic sprayed layer is firmly held to the base sprayed layer by a mechanical anchoring effect.

Therefore, the above-mentioned mechanical anchoring effect can effectively cope with the thermal stress caused by repeated heating and cooling during use, and can prevent the ceramic molten tJJ layer from peeling off. In addition, as mentioned above, since the second base sprayed layer has irregularities, the contact area between the ceramic layer and the base sprayed layer per unit surface area of the ceramic layer is extremely large, which also helps to firmly hold the ceramic layer. It is working effectively.

Note that the first base sprayed layer formed on the surface of the base material and the second base sprayed layer thereon can be integrated by using the same thermal spraying material or a similar thermal spraying material,
Therefore, the adhesion strength between the first thermal sprayed layer and the second base sprayed layer can be ensured sufficiently, and the adhesion strength between these base sprayed layers and the base material will also be described later as the base sprayed material. A sufficient amount can be obtained by appropriately selecting a Ni-based alloy or the like, and forming irregularities on the surface of the base material by shot blasting or the like, if necessary.

Therefore, as mentioned above, RZo, 1
By forming irregularities of m or more and firmly holding the ceramic sprayed layer to the base sprayed layer, it becomes possible to effectively prevent peeling in any part of the entire sprayed layer.

Detailed Description for Carrying Out the Invention The base material to be used in the method of the present invention is typically an aluminum alloy, but it is needless to say that the base material is not limited thereto.

In the method of the present invention, first, as shown in FIG. 1(A), a first base sprayed layer 2 is uniformly formed on the surface of a portion of the base material 1 where heat insulation and/or heat resistance is required. .

In forming this first base thermal spray B2, the usual)
The base thermal spray material may be thermally sprayed by holding the thermal spray gun 3 substantially perpendicular to the surface to be thermally sprayed according to the 8-spraying method. Also the first
The thermal spraying material for the base thermal sprayed layer 2 is a metal whose coefficient of thermal expansion is intermediate between that of the base material and the ceramic material to be finally sprayed, and which has good adhesion to the base material and the ceramic material, such as N1-Cr- Ni-based alloys such as Affi alloy, N1-Cr-Al-Y alloy, and Ni-Go-Cr-Al-Y alloy are optimal. Note that the thickness of the first base sprayed layer 2 is not particularly limited, but is usually about 0.05 - o.is. Furthermore, in forming the first base thermal spray layer 2, it is desirable to subject the surface of the base material to shot blasting in advance in order to improve the adhesion to the base material 1.

Next, as shown in FIG. 1(B), the thermal spray gun 3 is moved at an angle of 40° to 70° with respect to the perpendicular O to the surface to be thermally sprayed.
It is installed in a state where it is tilted by an angle θ within the range of 2
A second base thermal sprayed layer 4 having RZo and irregularities of 1M or more is formed by thermal spraying on top. The process of forming an uneven thermal sprayed layer by tilting the thermal spraying gun in this way is schematically shown in FIGS. However, when viewed microscopically, there are minute irregularities on the surface as shown in Figure 2 (A>).Therefore, at an angle θ of 40' or more, the first substrate with the minute irregularities is When thermal spraying is performed on the thermal spray layer 2, as shown in FIG. Thermal spray particles 7 are difficult to adhere to, whereas the spray particles 7 easily adhere to the portion 6a facing the thermal spray direction. Thermal spray particles will adhere to the top.Then, as the thermal spraying progresses, it will appear as shown in Figure 2 (C).
), the irregularities become even larger, and finally, as shown in FIG. 2(D), a second base melt IJA layer 4 having large irregularities of 1 m or more is formed.

The second base sprayed layer 4 is integrally combined with the first base sprayed layer 2 by using the same base sprayed material as the first base sprayed layer 2 or a similar base sprayed material. .

As described above, Rlo, the second thermal sprayed layer 4 with a thickness of 1 mm or more
After forming, as shown in FIG. 1(C), the thermal spraying gun 3 is set vertically and ceramic is thermally sprayed to form a ceramic thermal sprayed layer 5. During this thermal spraying, the ceramic spraying material penetrates to the bottom of the recess of the second base thermal spray layer 4 and is sprayed, so that the ceramic spray @ 5 has largely penetrated into the recess of the second base thermal spray layer 4. formed,
It is firmly held by the base sprayed layer 4 due to the anchoring effect as described above.

The ceramic used for this ceramic sprayed layer 5 may be selected from oxide-based ceramics such as ZrO2 (including Y2O2, Cab, and M stabilized with 10, etc.), Af'203, etc., depending on the application and heat resistance temperature. , M (70
, or nitride ceramics such as 5t3N4, BN, and AIN, carbide ceramics such as SiC T i B2
, a boride ceramic such as Cr'82, or a mixture thereof can be used as desired. Further, the ceramic sprayed layer 5 has a total thickness of 0.1 to 1.0 mm, including a portion that bites into the base sprayed layer. It is desirable to spray until it reaches about O#.

After the ceramic sprayed layer 5 is formed as described above, the surface of the ceramic sprayed layer 5 is finished into a smooth surface by performing surface processing such as polishing as shown in FIG. 1 (D>), if necessary.

In some cases, as shown in FIG. 3, the surface of the ceramic sprayed layer 5 may be processed until the convex portions of the base sprayed layer 4 are exposed on the surface after the ceramic spraying. In this case, the ceramic sprayed layer 5 is divided by the convex portions of the base sprayed layer 4, and independent ceramic sprayed layer cells 5a are formed for each small region. In this way, each ceramic sprayed layer cell 5a is independently surrounded by the surrounding base sprayed layer convex portions, so that even if the ceramic sprayed layer is repeatedly heated and cooled, the ceramic sprayed layer due to the difference in thermal expansion movement in the two-dimensional direction is prevented for each cell, and the thermal stress is
Since accumulation in the dimensional direction is prevented, peeling of the ceramic sprayed layer can be more reliably prevented.

In the above description, it is necessary that the unevenness of the second base sprayed layer 4 has a ten-point average Rz of not less than O,ts. If it is less than O11νMRZ, the mechanical anchoring effect on the ceramic sprayed layer 5 cannot be sufficiently exerted,
Therefore, peeling of the ceramic sprayed layer 5 cannot be sufficiently prevented.

Further, the angle θ of the thermal spray gun 3 when forming the second base thermal spray layer 4 needs to be 40° or more and 70' or less, and the reason is as follows. That is, the formation of unevenness due to the shielding phenomenon of sprayed particles during thermal spraying becomes more pronounced as the angle θ becomes larger. According to experiments conducted by the inventors, the spraying angle θ
Regarding the relationship between RZo and the surface roughness RZ of the sprayed layer, as shown by the solid line in FIG. 4, it has been found that when the angle θ is 40° or more, a surface roughness of about RZo, 1# or more can be obtained. Angle θ
If the angle θ is less than 40', it is not possible to ensure a roughness of 0.1 sRz or more, and therefore the mechanical anchoring effect of the ceramic molten gA layer cannot be sufficiently obtained. Therefore, the angle θ was limited to 40' or more. On the other hand, if the angle θ is too large, the second base melt
) The porosity in one layer increases, leading to a risk of corrosion when used at high temperatures, and also decreasing mechanical strength. According to experiments conducted by the present inventors, it has been found that, as shown by the broken line in FIG. 4, when the angle θ exceeds 70', the porosity increases rapidly.

Furthermore, if the angle θ is too large, the sprayed material at the upper end of the convex portion of the second sprayed layer 4 will protrude like an eaves in the opposite direction to the spraying direction, as shown in FIG. Due to the presence of the ceramic spraying material in the next ceramic spraying step, the ceramic spraying material does not penetrate to the bottom of the recess in the base thermal spray layer 4 as shown in FIG. 5(B), and a gap G is created at the bottom of the recess. If the angle θ is 70° or less, the above-mentioned eaves-like portion can be prevented from occurring.For these reasons, the upper limit of the angle θ was set to 70°.

Example After subjecting the surface of a base material made of Z-SR alloy to shot blasting, N1-17-Or-Y alloy was sprayed onto the surface of base material 1 as shown in FIG. 1(A). 203. It was formed with a thickness of fil+. At this time, the thermal spray gun 3 was held vertically. Next, as shown in FIG. 1(B), the thermal spray gun 3 was tilted at an angle of θ = 60°, and the same Ni-Ai' Cr-Y alloy as described above was sprayed, and a second layer having irregularities of RZo and 2 mm was formed. A base sprayed layer 4 was formed.

Subsequently, as shown in FIG. 2(C), with the thermal spraying gun 3 held vertically, ZrO2.8Y203 was thermally sprayed as a ceramic to a total thickness of 0.5 m to form a ceramic thermal sprayed layer 5. Thereafter, the surface of the ceramic sprayed layer 5 is polished and finished, resulting in a ceramic sprayed member 1q as shown in Fig. 1 (D>).The cross-sectional state of the sprayed layer of the ceramic sprayed member thus obtained is shown in Fig. 6. .

In addition, a portion of the surface of the ceramic sprayed layer 5 formed as described above was removed by polishing until the convex portions of the base sprayed layer were formed as shown in FIG.

On the other hand, for comparison, as shown in FIG. 8, a base thermal spraying material made of the same material as described above is applied to the surface of the same base material 1 at a zero rate while the thermal spraying gun is held vertically according to the conventional conventional method.
A base sprayed layer 1Q with a uniform thickness and few irregularities was formed by thermal spraying to a thickness of 1 mm, and a ceramic sprayed layer 5 made of the same material as described above was formed on the base sprayed layer 10 to a total thickness of 0.5mm. .

FIG. 7 shows the cross-sectional state of the sprayed layer of the ceramic sprayed member that has been lifted up in this way.

The above three types of ceramic sprayed members, namely the first
The member obtained by the method of the present invention shown in Figure (D) (Fig. 6), the member obtained by the method of the present invention shown in Fig. 3, and the conventional member shown in Fig. 8 (Fig. 7). The members obtained by this method were subjected to a heating/cooling cycle test to examine the peeling status of the ceramic layer. In addition, in this heating/cooling cycle test, from 50'C to 15°C/S
A cycle of heating with a burner flame to 500°C at a heating rate of aC, then cooling again to 50°C at a cooling rate of 10°C/SeC was repeated, and the number of cycles until the ceramic layer peeled off was investigated. The results are shown in FIG.

As is clear from FIG. 9, in the ceramic sprayed member obtained by the conventional method, the ceramic layer peeled off and fell off after less than 4000 cycles of heating and cooling, whereas the ceramic sprayed member obtained by the method of the present invention So, 1ooo
Even after o cycles, no peeling or falling off of the ceramic layer was observed.

Effects of the Invention As is clear from the above explanation, according to the method of the present invention, the solvent gun is tilted at an angle of 40° to 70' to form the second base sprayed layer on the first base sprayed layer. This forms a second base thermal sprayed layer having an unevenness of 0.1 m or more in ten-point average roughness RZ, and by applying ceramic molten steel on top of it, the ceramic) sprayed layer is formed on the base thermal sprayed layer. It is formed by biting into the irregularities, and as a result, the ceramic sprayed layer is firmly held to the base sprayed layer, so even after repeated heating and cooling, the ceramic sprayed layer will not peel or fall off due to thermal stress due to the difference in thermal expansion. Such a situation can be effectively prevented, and therefore, the durability of a member coated with a ceramic sprayed layer can be significantly extended compared to the conventional method when the member is used particularly in applications where repeated heating and cooling are required.

[Brief explanation of the drawing]

FIGS. 1A to 1D are schematic cross-sectional views showing step-by-step an example of the process of forming a sprayed layer by the method of the present invention;
Figures 2 (A) to (D> are schematic diagrams for step-by-step explanation of the action of forming a second base spray layer by tilting the spray can, and Figure 3 is a diagram showing the process obtained by the method of the present invention. A sectional view showing another example of a ceramic sprayed member, FIG. 4 shows the angle (spraying angle) θ of the spray gun when forming the second base sprayed layer,
A graph showing the relationship between the 10-point average roughness Rz and the porosity of the thermal sprayed layer that is generated. Figures 5 (A> and (B)) are schematic diagrams showing the thermal spraying situation when the angle θ of the thermal spray gun is too large. 6 is a cross-sectional structure micrograph (magnification: 50x) of a sprayed layer of a sprayed member obtained by an example of the present invention, and FIG. 7 is a sprayed member obtained by a conventional method (comparative example). Figure 8 is a cross-sectional view schematically showing the sprayed layer of a sprayed member obtained by the conventional method (comparative example), and Figure 9 is an example of the present invention. It is a graph showing the heating/cooling cycle test results of the thermal sprayed members obtained in Comparative Examples using the conventional method. 1... Base material, 2... First base sprayed layer, 3...
- Thermal spray gun, 4... Second base thermal spray layer, 5...
Ceramic sprayed layer.

Claims (1)

[Claims] A method of forming a ceramic sprayed layer made of a ceramic material having a lower thermal conductivity and a smaller coefficient of thermal expansion than the base material at a location on the surface of the base material that requires heat insulation and/or heat resistance. After uniformly forming a first base sprayed layer on the surface of the portion of the base material, a thermal spray gun is tilted within a range of 40° to 70° with respect to the perpendicular on the first base sprayed layer. The base thermal spraying material was sprayed in this state, and the ten-point average roughness Rz was 0.1.
A method for forming a ceramic sprayed layer, comprising forming a second base sprayed layer having irregularities of mm or more, and spraying a ceramic onto the second base sprayed layer.