JPH01184261A - Ceramic heat-insulating member - Google Patents

Abstract

PURPOSE:To improve the thermal shock resistance and durability of a ceramic surface layer by providing a primary transition layer consisting of Ni-Cr-Al alloy and ZrO2.8Y2O3 on an Al-alloy base material via an undercoat layer and further providing a secondary transition layer in which ceramics with low coefficient of thermal expansion is blended on the above via an intermediate layer. CONSTITUTION:An undercoat layer 11 of Ni-Cr-Al alloy is formed on the surface of a base material 10 made of Al alloy, on which a primary transition layer 12 where Ni-Cr-Al alloy and ZrO2.8Y2O3 are mixed and the proportion of Ni-Cr-Al alloy is decreased with the approach to the outside is continuously formed. Subsequently, an intermediate layer 13 composed essentially of ZrO2.8Y2 O3 is formed, and then, a secondary transition layer 14 in which ceramics of <=9X10<-6>/ deg.C coefficient of thermal expansion and ZrO2.8Y2O3 are mixed and the proportion of ZrO2.8Y2O3 is decreased with the approach to the outside is continuously formed. By this method, thermal stress is reduced when heat cycle is applied, and thermal shock resistance is improved and, as a result, this surface layer has no possibility of causing peeling and falling.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to parts used in parts that are heated to high temperatures, such as the pistons of automobile engines, and in particular, parts made of an aluminum alloy as a base material and having a ceramic layer on the surface for heat insulation. The present invention relates to a formed ceramic heat insulating member.

BACKGROUND ART Conventionally, members having parts that are heated at high temperatures, such as pistons or cylinder pores for automobile engines, especially members whose base material is aluminum alloy,
Ceramics with low thermal conductivity and excellent heat resistance are thermally sprayed onto the surface of a base material to form a thermal sprayed coating with excellent heat insulation and heat resistance.

Such a conventional ceramic thermally sprayed heat insulating member will be described in more detail below, taking a piston for a diesel engine as an example.

In recent years, pistons used in diesel engines are made of aluminum alloy J: with the main purpose of reducing the inertia of the reciprocating parts of the engine.
Increasingly, pistons are cast and molded. On the other hand, recent diesel engines have high supercharging,
There is a strong trend toward higher output, and as a result, the heat load placed on the piston is also increasing. However, since aluminum alloy is a material with high thermal conductivity, in a piston made of aluminum alloy, heat from the top surface of the piston is transmitted to the piston ring groove, and the piston ring groove tends to become hot. However, if the temperature of the piston ring groove becomes too high, oil will burn, causing problems such as seizure of the piston ring.

Therefore, attempts have been made to spray a ceramic material with low thermal conductivity on the top surface of the piston to improve its heat shielding properties so that the heat on the top surface of the piston is not transferred to the piston ring groove. In this case, in order to improve the adhesion between the ceramic spray coating and the aluminum alloy base material, N
i-Ajl' alloy, Ni-Cr-A1 alloy, N1-C
r-Al-Y alloy or N 1-Co-Cr-Af-
Attempts have been made to spray a base thermal spray coating of Y alloy or the like without applying ceramic thermal spraying on top of it (for example, lCum1ns/TACOHA Advanced Ad
iabatic EngineJR, Kamo et
at; SAE Paper No. 84
No. 0428).

However, in pistons that are made of aluminum alloy as a base material and subjected to ceramic spraying after base thermal spraying, due to the difference in thermal expansion coefficient between the aluminum alloy base material and the ceramic sprayed coating, there is a problem with engine operation. During repeated heating and cooling, cracks may develop near the interface between the ceramic sprayed coating and the base sprayed coating, which may eventually lead to the ceramic sprayed coating peeling off or falling off.

One method for solving such problems is as shown in Japanese Patent Application Laid-open No. 197861/1986,
A method has also been proposed in which the porosity of the ceramic sprayed coating formed on the base sprayed coating (undercoat layer) made of Ni Cr A2 alloy is controlled in the thickness direction, and such a method can also prevent peeling to some extent. However, the reality is that it is still not sufficient.

Problems to be Solved by the Invention As mentioned above, the piston base material 1 made of aluminum alloy
A base film 2 is formed by thermal spraying on the base film 2, and the base film W is
Figure 3 shows the results of an investigation conducted by the present inventors regarding the temperature distribution during use when a piston with a ceramic coating 3 formed on A2 by thermal spraying is used in an actual engine. Figure 4 shows the results of examining the internal elongation (=thermal expansion coefficient x temperature). Here, a Ni-Cr-Aβ alloy is used as the base thermal spray coating 2, and ZrO2.8Y, which has a coefficient of thermal expansion close to that of metal, is used as the ceramic spray coating 3.
2O3 was used.

As shown in FIG. 3, the temperature near the surface of the ceramic coating 3, which corresponds to the top surface of the piston, that is, the contact point facing the combustion chamber, is <To. ) is extremely high at 700 to 800°C, and since the ceramic coating 3 itself has high heat insulation properties, the temperature gradient in the thickness direction within the ceramic coating 3 is extremely large. As a result, as shown in FIG. 4, there is a large difference in the elongation of the ceramic film 3 between the elongation near the surface (!) and the elongation (1o1) in the portion in contact with the base film 2. Furthermore, due to the difference in thermal expansion coefficient between the ceramic material, the base thermal spray material, and the base material/M alloy, the elongation (β...) of the portion of the ceramic film 3 in contact with the base film 2 and the elongation of the base film 2 (β..., 1b1 ) and elongation on the surface of base material 1 (βII
l. ) There are also large differences.

The causes of the ceramic film peeling and falling off include thermal stress due to the difference in elongation in the thickness direction within the ceramic film layer as described above, and the difference in elongation between the ceramic film, the base film, and the base material. Peeling of ceramic film,
In order to prevent it from falling off, β and β in Figure 4 must be changed!
. . 〜l□. It turns out that it is better to get closer to co cl .

Here, increase the value of β! circle. ~! □. Various methods have been considered in the past to bring the value closer to . For example, a mixed layer of ceramic and metal such as Ni or GO as an intermediate layer between a ceramic film and a base film;
In other words, a cermet layer is provided, or the ceramic film itself is a mixed layer of ceramic and metal, and the ratio of ceramic and metal gradually changes to form a part that contacts the base film (if no base film is provided, the part that contacts the base film) Methods such as grated thermal spraying are being considered so that the metal is 100% on the parts that come into contact with the material. However, like this! . It is difficult to sufficiently prevent peeling only by increasing the value of 1, and breakage often occurs inside the mixed layer of ceramic and metal, resulting in peeling.

This invention was made against the background of the above-mentioned circumstances, and it is possible to significantly reduce the thermal stress inside the ceramic film when heated to high temperatures compared to the conventional technology, thereby increasing the thermal shock resistance of the ceramic film. Peeling of ceramic film,
An object of the present invention is to provide a ceramic heat insulating member that can reliably prevent falling off and has significantly improved durability under usage conditions subject to thermal cycles compared to conventional ceramic heat insulating members.

Means for Solving the Problems In the ceramic heat insulating member of the present invention, a base layer made of a Ni-Cr-A& series alloy is formed on the surface of a base material made of an A1 alloy. - A first transition layer in which an Al-based alloy and ZrO2/8Y2O3 are mixed and the Ni-Cr-A & gold alloy mixing ratio decreases toward the outside is formed continuously and integrally with the base layer, and a first transition layer is formed on the first transition layer. In this method, an intermediate layer consisting essentially only of ZrO2.8Y2Oa is formed continuously and integrally with the first transition layer, and furthermore, a low thermal expansion coefficient ceramic with a thermal expansion coefficient of 9x10-6x°C or less and ZrO2 are formed on the intermediate layer. - A second transition layer in which ZrO2 and 8Y2O3 are mixed and the mixing ratio of ZrO2 and 8Y2O3 decreases toward the outside is formed continuously and integrally with the intermediate layer.

Operation FIG. 1 schematically shows the cross-sectional structure of the ceramic heat insulating member of the present invention, and FIG. 2 schematically shows an example of the distribution of constituent materials in each layer.

In the ceramic heat insulating member of the present invention, the main ceramic constituent material for heat insulation etc. is partially stabilized zirconia, which has a high melting point, good corrosion resistance, low thermal conductivity, high strength, and high fracture toughness. Seed Zr
O2・8Y2O3 is used, and this Zr
O2.8Y2O3 is used to ensure heat insulation and heat shielding functions as well as the necessary strength. The most important point in the heat insulating member of this invention is that the above-mentioned ZrO2.
The outermost surface layer is not exposed to the Z'
r02 ・8Y2Oa and coefficient of thermal expansion is 9x 104 /
The transition layer is made of a mixture with a ceramic having a low thermal expansion coefficient of less than
14 (second transition layer) 14.

Is ZrO2/8Y2O3 a hot film? ,% rate (0~100
The average coefficient of thermal expansion at 0°C (same below) is 11X10-6
The temperature is relatively large at 7°C, so it is effective in reducing the difference in thermal expansion between the base layer metal and the base metal. However, due to its low thermal conductivity and high heat insulating properties, when the surface of a piston is exposed to temperatures as high as 700 to 800°C, the Z
In a film made of rO2.8Y2O3 alone, the temperature gradient in the thickness direction within the film becomes extremely steep, the difference in elongation within the film in the thickness direction becomes extremely large, and thermal stress within the film becomes large.

However, in the heat insulating member of the present invention, the outermost surface layer is made of ZrO2.8Y2O with a coefficient of thermal expansion of 11X 10-6/°C.
3 and a low thermal expansion coefficient ceramic having a thermal expansion coefficient of 9x10-6x℃ or less, and ZrO2 toward the surface.
- Transition layer where the proportion of 8Y2O3 decreases (second transition layer)
14, the coefficient of thermal expansion gradually decreases in the thickness direction toward the surface within the second transition layer 14, so the elongation due to thermal expansion at the surface where the highest temperature is
It is smaller than when 2.8Y2O3 is used alone, and the temperature decreases as it goes inward in the thickness direction from the surface, but the coefficient of thermal expansion increases, so the change in elongation due to thermal expansion in the thickness direction becomes smaller. Therefore, the difference in elongation in the thickness direction within the second transition layer 14 is small, and the thermal stress generated inside is also small.

Further, in the part where the second transition @14 transitions to the intermediate layer 13 made of ZrO2.8Y2O3 alone, the proportion of ZrO2.8Y2O3 only changes from less than 100% to 100%, and no particularly clear boundary is formed. Therefore, no particularly large thermal stress occurs in that part either.

Further, the heat insulating member of the present invention includes an intermediate layer 13 made of ZrO2.8Y2O3 and Ni-C.
Intermediate layer 1 is interposed between base layer 11 made of r-Af alloy.
3 and the Ni-Cr-/M alloy forming the underlayer 11.
A transition layer (first transition layer) 12 is formed in which the mixing ratio of the -Aff alloy decreases. This first transition layer 12 corresponds to a cermet layer formed by conventional graded thermal spraying, and within this first transition layer 12, an intermediate layer 13 is formed.
The thermal expansion coefficient from ZrO2 to the base layer 11 is ZrO2.8Y2O
The coefficient of thermal expansion changes gradually from the coefficient of thermal expansion of 3 to that of the N i -Qr-Ajl' alloy. Therefore, the elongation due to thermal expansion does not change suddenly in the portion from the intermediate layer 13 to the base layer 11, and therefore no large thermal stress occurs.

If the above is taken together, the outermost surface (the surface of the second transition layer 14)
Even when exposed to high temperatures of 700 to 800°C, there is no significant change or difference in elongation due to thermal expansion across the entire thickness from the outermost surface to the underlying layer, so there is no overall thermal stress. becomes small, and peeling and falling off from the base material 10 can be sufficiently prevented.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the heat insulating member of the present invention, the low thermal expansion ceramic having a coefficient of thermal expansion of 9x10-6/°C or less used for the second transition layer may be, for example, a ceramic having a coefficient of thermal expansion of 8x10-6/°C. 6/°C
Al2O2,4,5x 10-8 / °C ZrO
2.SiO2,2,5x 10-6 / 2M of °Q
q0・2A! 2O3, 5SiO2, etc. can be used, but of course the material is not limited to these.

In addition, the Ni-Cr-Al2 alloy used for the underlayer is
Any material that has been conventionally used as a base for ceramic thermal spraying may be used, and its composition is not particularly limited, but it is usually about 10 to 30 wt% Cr, A & 5 to 10 Xv.
t% and the remainder is substantially Ni, or if necessary, Y is 0.3
~1. It is also possible to add about 20 to 60 wt% of GO.

Further, the base layer, first transition layer, intermediate layer, and second transition layer can all be formed using a solvent, but in this case, the first transition layer and the second transition layer must be formed using a so-called graded solvent. Of course. When thermal spraying is carried out, the spray powder particles preferably have a particle size of about 30 to 105 for Ni-Cr-A and base layer alloys, and 10 to 105 for ZrO2.8Y2Oa and low thermal expansion coefficient ceramics. It is preferably about 74 IJln.

In addition, the first transition layer is made of Ni-
It is most preferable that the mixing ratio of the Cr-A&-based alloy decreases continuously, but it may be decreased stepwise in some cases. In the second transition layer as well, it is most preferable that the mixing ratio of ZrO2.8Y2O3 decreases continuously from the intermediate layer toward the outermost surface, but it may decrease stepwise in some cases.

13 One Example Below, an example of the heat insulating part I of the present invention and a comparative example consisting of a conventional heat insulating member are shown, and each member of the example and comparative example was subjected to a heat resistance cycle test and an actual machine durability test as a piston. Show the results.

[Example 1] Diameter 50 mm x thickness i made of JIS AC8A alloy
After shot blasting the surface of the base material in the shape of a .
1 alloy, specifically 94 sv t% (Ni-2Ow
Grated thermal spraying of t%Cr)-6wt%Aβ alloy and ZrO2.
．． This was done at 3mm. At this time, on the base metal side, Ni-Cr
-A & series alloy is 100% pure, and the top part of the caster is 100% ZrO2/8Y2O3.
Then, a base layer, a first transition layer, and an intermediate layer were successively formed. Furthermore, graded thermal spraying of ZrO2.8Y2O3, a low thermal expansion coefficient ceramic, and 1 layer of AL2O3 was carried out to a thickness of 0.2 mm to form a second transition layer, thereby obtaining the ceramic heat insulating member of the present invention. At this point, ZrO2.8Y2O3 is 100% on the side of the second transition layer that is in contact with the intermediate layer, and Al2O2 and ZrO2.
Thermal spraying was carried out so that 8Y2Oa was 50% of each.

Example 2] Ajh in Example 1 as a low thermal expansion coefficient ceramic
A ceramic heat insulating member was produced in the same manner as in Example 1 except that ZrO2.5iO2 was used instead of O3.

[Example 31 Ajl in Example 1 as a low thermal expansion coefficient ceramic
! 2M go・2A12O3・5Si instead of 2Oa
A ceramic heat insulating member was produced in the same manner as in Example 1 except that O2 was used.

Comparative Example 1] JIS AC8AC3b diameter 50mm x thickness 1
After shot blasting the surface of the 0mm disc-shaped base material, Ni-Qr-A1! An alloy (specific composition is the same as in Example 1) was thermally sprayed to a thickness of 0.1 mm to form a base layer. Then ZrO2・8Y2O3 on top
was thermally sprayed to a thickness of 0.4 mtn to create a conventional ceramic heat insulating member.

[Comparative Example 2] Made of JIS AC8AC3b, diameter 50 mm x thickness 1
After shot blasting the surface of the base I in the shape of a 0 mm disk, graded thermal spraying of Ni-Cr-A1 alloy (specific composition is the same as in Example 1) and ZrO2. This was done with a thickness of 3 mm. At this time, the lowest part in contact with the base material is made of 100% Ni-Cr-A & gold alloy.
And at the top, ZrO2・8Y2O3 is 100
%. Furthermore, on top of that, ZrO2・
8Y2O3 was thermally sprayed to a thickness of 0.2 mm to create a conventional ceramic heat insulating member.

[Thermal Cycle Test 1 The ceramic heat insulating members of Examples 1 to 3 and Comparative Examples 1 and 2 described above were subjected to a heat cycle test in which a heating-cooling cycle was applied as follows.

In other words, the surface of the film was heated to 1 with a 02 N2-02 burner.
Heat for 2 seconds to bring the temperature of the base material directly under the coating to 400°C, then stop heating and heat the base material at 30°C from the back side of the base material.
Second cooling fJ] A heating-cooling cycle was repeated 3000 times to bring the temperature of the base material directly below the film to 70°C. At this time, the state of peeling of the film was examined every 100 cycles. The results are shown in Table 1.

1 Table 1 Example/'4] As the base material, φ80m made of JIS AC8AC3b
EXAMPLE 1 A ceramic heat-insulating piston was prepared by using a diesel engine piston of No. m and subjecting its top surface to the same treatment as in Example 1.

"Comparative Example 31 Base material is 980m made of JIS AC8AC3b"
A ceramic heat-insulating piston was prepared by using a diesel engine piston of 1.0 m and subjecting its top surface to the same treatment as in Comparative Example 2.

[Actual Machine Durability Test] The ceramic heat-insulating pistons of Example 4 and Comparative Example 3 were each incorporated into a 2200cc easel engine with a turbocharger, and a continuous operation test was conducted. The operating conditions are supercharging pressure 550mmH (1,42OOrpm, 9
The test was conducted for a total of 300 hours, with a power output of 5 horsepower, and the operation was stopped every 50 hours to check the status of the heat insulating coating on the piston. The results are shown in Table 2.

Table 2 From the thermal cycle test results shown in Table 1 and the actual machine durability test results as a heat insulating piston shown in Table 2, the example product of this invention is superior to the conventional two-layer thermal sprayed product (comparative example 1). It is clear that the thermal shock resistance is much better than that of the graded solvent amount (Comparative Example 2.3), and that the film is less likely to peel off. This is thought to be because by mixing a ceramic with a low coefficient of thermal expansion in the upper part of the film, the elongation of the upper part of the film, which is at the highest temperature, can be suppressed to a lower level than before, and the thermal stress within the film can be reduced. That is, β shown in FIG. 4 is O'bo~β□. This is thought to be due to the fact that it could be brought closer to .

Effects of the Invention The ceramic heat insulating member of the present invention has a second layer in which the upper part of the film is a mixture of ZrO2.8Y2O3, which is the main constituent material of the heat insulating reservoir, and a ceramic with a low coefficient of thermal expansion, and the proportion of ZrO2.8Y2O3 decreases toward the outside. Because of the structure of the transition layer, even when the outermost surface of the film is exposed to high temperatures, the difference in elongation inside the film in the second transition layer is small;
・ In the part from the intermediate layer made of 8Y2O3 to the base layer, Cr-Aβ alloy and Z are added to the Ni-C of the base layer.
rO2.8Y2O3 is mixed and N flows toward the intermediate layer.
Since the first transition layer in which the proportion of i-Cr-Aβ alloy decreases is formed, the difference in elongation inside the film is small in that part as well, and therefore the difference in elongation inside the film as a whole is small, so it is difficult to heat. The thermal stress when cycles are applied is small, and therefore the thermal shock resistance is extremely excellent, so there is little risk of the film peeling or falling off, and it is possible to obtain much superior durability performance than conventional products.

[Brief explanation of the drawing]

FIG. 1 is a vertical cross-sectional view schematically showing an example of the structure of the ceramic heat-insulating member of the present invention, and FIG. 2 is a line showing an example of the distribution in the thickness direction of the constituent materials of each layer in the ceramic heat-insulating member of FIG. It is a diagram. Figure 3 is a schematic diagram showing the temperature distribution in the thickness direction when a conventional ceramic heat insulating member is used as a piston, and Figure 4 is a schematic diagram showing the amount of elongation of each layer based on the temperature distribution in Figure 3. . 10... Base material, 11... Base layer, 12... First
Transition layer, 13... Intermediate layer, 12... Second transition layer. Applicant Toyota Motor Corporation Agent Attorney Funeral 1) Takehisa (and 1 other person) > Disgrace

Claims (1)

[Claims] A base layer made of a Ni-C and Cr-Al alloy is formed on the surface of a base material made of an Al alloy.
A first transition layer in which an i-Cr-Al alloy and ZrO_2.8Y_2O_3 are mixed and the mixing ratio of the Ni-Cr-Al alloy decreases toward the outside is formed continuously and integrally with the base layer, and the first transition layer is formed continuously and integrally with the underlayer. On the layer, substantially ZrO_2.
An intermediate layer consisting only of 8Y_2O_3 is formed continuously and integrally with the first transition layer, and further on the intermediate layer, a low thermal expansion coefficient ceramic having a thermal expansion coefficient of 9×10^-^6/℃ or less and ZrO_2.8Y_2O_3 and ZrO_2.8Y_2O_3 are formed. A ceramic heat insulating member characterized in that a second transition layer in which ZrO_2.8Y_2O_3 is mixed and the mixing ratio of ZrO_2.8Y_2O_3 decreases toward the outside is formed continuously and integrally with the intermediate layer.