JPH07122126B2 - Ceramic heat insulating material - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a member used at a high temperature heated portion such as a piston of an automobile engine, and particularly to a member made of an aluminum alloy as a base material and a ceramic layer for heat insulation on the surface thereof. The present invention relates to the formed ceramic heat insulating member.

2. Description of the Related Art Conventionally, a member having a portion that is heated to a high temperature such as a piston or a cylinder bore portion for an automobile engine, particularly a portion having an aluminum alloy as a base material, has a low thermal conductivity and heat resistance on the surface of the base material. BACKGROUND ART Ceramics having excellent properties are sprayed to form a sprayed coating having excellent heat insulation and heat resistance.

Such a conventional ceramic thermal spraying heat insulating member will be described in more detail below by taking a piston for a diesel engine as an example.

2. Description of the Related Art In recent years, as a piston used in a diesel engine, a piston molded by an aluminum alloy has been often used mainly for the purpose of weight reduction for reducing the inertial force of the reciprocating part of the engine. On the other hand, in recent diesel engines, there is a strong tendency toward high supercharging and high output, and therefore the heat load applied to the piston is also large. However, since the aluminum alloy is a material having a high thermal conductivity, the heat of the piston top surface is transferred to the piston ring groove portion in the aluminum alloy piston, and the piston ring groove portion is likely to have a high temperature. However, if the temperature of the piston ring groove becomes too high, oil combustion will occur, causing problems such as seizure of the piston ring. Therefore, in order to prevent the heat of the piston top surface from being transferred to the piston ring groove, an attempt has been made to improve the heat shielding property by spraying a ceramic material having a low thermal conductivity on the piston top surface. In this case, in order to improve the adhesion between the ceramic sprayed coating and the aluminum alloy base material, Ni-Al alloy, Ni-Cr-Al alloy, Ni-Cr-Al are prepared in advance.
-Y alloys or Ni-Co-Cr-Al-Y alloys have been spray-formed on a base spray coating, and then ceramic spraying has been attempted (for example, "Cumins / TACOM Adv.
anded Adiabatic Engin '' R. Kamo et al .; SAE Paper No.
No. 840428).

However, in a piston that has been subjected to ceramic spraying after base metal spraying using an aluminum alloy as a base material in this manner, due to the difference in the coefficient of thermal expansion between the aluminum alloy base material and the ceramic sprayed coating, During repeated heating-cooling, cracks may occur in the vicinity of the interface between the ceramic sprayed coating and the base sprayed coating, and eventually the ceramic sprayed coating may come off or fall off.

One way to solve this problem is
As shown in JP-A-60-197861, Ni-Cr-Al
A method of controlling the porosity of the ceramic sprayed coating formed on the undercoating spray coating (undercoat layer) made of an alloy in the thickness direction has also been proposed, and such method can also prevent peeling to some extent. However, the reality is that it is not enough.

Problems to be Solved by the Invention As described above, the piston base material 1 made of an aluminum alloy
The results of the present inventors' investigation of the temperature distribution during use when the piston having the undercoat film 2 formed by thermal spraying and the ceramic film 3 formed by thermal spraying on the undercoat film 2 is used in an actual engine FIG. 3 shows the results of examining the elongation (= coefficient of thermal expansion × temperature) in each coating layer based on the temperature distribution, and FIG. Here, a Ni—Cr—Al alloy was used as the base thermal spray coating 2, and ZrO ₂ · 8Y ₂ O ₃ having a thermal expansion coefficient close to that of a metal was used as the ceramic spray coating 3.

As shown in FIG. 3, the temperature (T _co ) in the vicinity of the surface of the ceramic coating 3 corresponding to the piston top surface, that is, the ignition portion facing the combustion chamber is extremely high at 700 to 800 ° C., and the ceramic coating 3 itself is Due to the high heat insulating property, the temperature gradient in the thickness direction in the ceramic film 3 is remarkably large. As a result, the elongation of the ceramic film 3 as shown in FIG.
There is a large difference between the elongation near the surface (l _co ) and the elongation in contact with the undercoat 2 (l _c1 ). Also, due to the difference in the coefficient of thermal expansion between the ceramic material, the thermal sprayed base material, and the base material Al alloy, the elongation of the portion of the ceramic coating 3 in contact with the primary coating 2 (l _co ) and the elongation of the _primary coating 2 (l _bo , l _b1 ) Also, there is a large difference in the elongation (l _mo ) on the surface of the base material 1.

The reasons why the ceramic film peels off or falls include the thermal stress due to the difference in the elongation in the thickness direction of the ceramic film layer as described above, and the difference in the elongation between the ceramic film, the base film, and the base material. Peeling of the ceramic film,
In order to prevent the falling off, _lco and _lc1 in Fig. 4 are changed to _lbo
~ It turns out that it's better to get closer to l _mo .

Here, as a method for increasing the value of l _c1 to approach l _bo to l _mo , various means have been conventionally considered. For example, a mixed layer of ceramic and a metal such as Ni or Co, that is, a cermet layer may be provided as an intermediate layer between the ceramic film and the base film, or the ceramic film itself may be a mixed layer of the ceramic and the metal. It is considered to be a method of graded thermal spraying so that the metal content becomes 100% at the part that contacts the underlying film (the part that contacts the base metal when the underlying film is not provided) by gradually changing the ratio of . However, it is difficult to sufficiently prevent peeling only by the method of increasing the value of l _c1 as described above, and in many cases, fracture occurs inside the mixed layer of ceramic and metal and peels off.

This invention has been made against the background of the above circumstances, the thermal stress inside the ceramic coating generated when heated to a high temperature is significantly smaller than before, thereby increasing the thermal shock resistance of the ceramic coating, Peeling of the ceramic film,
It is intended to provide a ceramic heat insulating member which can be surely prevented from falling off and whose durability under a use condition to which a heat cycle is applied is remarkably improved as compared with the conventional case.

Means for Solving Problems The ceramic heat insulating member of the present invention has a base layer made of a Ni—Cr—Al alloy formed on the surface of a base material made of an Al alloy,
On this underlayer, a first transition layer in which the Ni-Cr-Al-based alloy and ZrO ₂ · 8Y ₂ O ₃ are mixed and the mixing ratio of the Ni-Cr-Al alloy decreases toward the outside is the underlayer. Is formed integrally with
An intermediate layer consisting essentially of ZrO ₂ · 8Y ₂ O ₃ is continuously and integrally formed on the first transition layer, and a thermal expansion coefficient of 9 × is formed on the intermediate layer. 10 ^-6 / ° C. or lower thermal expansion ceramic and a ZrO ₂ · 8Y ₂ O ₃ are mixed and continuously second transition layer the mixing ratio of ZrO ₂ · 8Y ₂ O ₃ decreases toward the outside as an intermediate layer It is characterized by being integrally formed.

Action 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 constituent material of each layer.

In the ceramic heat insulating member of the present invention, as a main ceramic constituent material for heat insulation and the like, a partially stabilized zirconia having a high melting point, good corrosion resistance, low thermal conductivity, high strength, and high fracture toughness is used. One type of ZrO ₂
· 8Y and using ₂ O _3, mainly by the ZrO ₂ · 8Y ₂ O _3, thereby achieving thermal insulation, the securing features and required strength of the thermal barrier. And the most important point of the heat insulating member of the present invention is that the above ZrO ₂ · 8Y ₂ O ₃ is not exposed as it is on the member surface (that is, the part exposed to the highest temperature), but the outermost surface. The layer has a coefficient of thermal expansion of 9 × 10 ⁻⁶ / ZrO ₂ · 8Y ₂ O ₃ described above.
The point is that the transition layer (second transition layer) 14 is made of a mixture with a ceramic having a low coefficient of thermal expansion of ℃ or less and the mixing ratio of ZrO ₂ .8Y ₂ O ₃ decreases toward the outside.

ZrO ₂ · 8Y ₂ O ₃ has a relatively large coefficient of thermal expansion (average coefficient of thermal expansion at 0 to 1000 ° C, the same applies below) of 11 × 10 ^-6 / ° C. It is effective in reducing the difference in thermal expansion. However, for there is a high thermal insulation has low thermal conductivity, when the surface as the piston is exposed to a high temperature 700 to 800 ° C. stuff, ZrO already to Figure 3, the surface as shown in Figure 4 ₂・ In the case of 8Y ₂ O ₃ film alone, the temperature gradient in the film thickness direction becomes extremely sharp, the difference in elongation in the film thickness direction becomes extremely large, and the thermal stress inside the film increases.

However, in the heat insulating member of the present invention, the outermost surface layer has a coefficient of thermal expansion of 11 × 10 ⁻⁶ / ° C. and ZrO ₂ · 8Y ₂ O ₃ and a coefficient of thermal expansion of 9 × 10 ⁻⁶ /
Since the transition layer (second transition layer) 14 is made of a mixture with a low thermal expansion coefficient ceramic of ℃ or less and the ratio of ZrO ₂ · 8Y ₂ O ₃ decreases toward the surface, the inside of the second transition layer 14 is Since the coefficient of thermal expansion gradually decreases toward the surface in the thickness direction, the expansion due to thermal expansion on the surface with the highest temperature
ZrO ₂・ 8Y ₂ O ₃ is smaller than the case of using it alone, and the temperature decreases as it goes inward from the surface in the thickness direction, but the coefficient of thermal expansion increases, so there is less change in elongation in the thickness direction due to thermal expansion. . Therefore, the difference in the elongation in the thickness direction in the second transition layer 14 is small, and the thermal stress generated inside is also small. Also, from the second transition layer 14 to the intermediate layer 13 of ZrO ₂ · 8Y ₂ O ₃ alone.
The ratio of ZrO ₂ · 8Y ₂ O ₃ is less than 100%
Only the change to 100% does not result in the formation of a particularly clear boundary, so that no particularly large thermal stress occurs in that part.

Further, the heat insulating member of the present invention, between the intermediate layer 13 made of ZrO ₂ · 8Y ₂ O ₃ and the base layer 11 made of Ni-Cr-Al alloy,
ZrO ₂ , 8Y ₂ O ₃ forming the intermediate layer 13 and N forming the underlayer 11
A transition layer (first transition layer) 12 is formed which is composed of a mixture with the i-Cr-Al-based alloy and which is reduced outward (that is, toward the intermediate layer) in which the mixing ratio of the Ni-Cr-Al-based alloy is reduced. ing. This first transition layer 12 is equivalent to a conventional cermet layer formed by graded spraying, and the first transition layer 12
Within 12, the thermal expansion coefficient gradually changes from the intermediate layer 13 to the underlayer 11 from the thermal expansion coefficient of ZrO ₂ · 8Y ₂ O _{3 to} the thermal expansion coefficient of the Ni—Cr—Al alloy. Therefore, the intermediate layer 13 to the underlying layer
Even in the area up to 11, the expansion due to thermal expansion does not change rapidly, so that large thermal stress does not occur.

Summarizing the above, the outermost surface (the surface of the second transition layer 14) is
Even when exposed to a high temperature of 700 to 800 ° C, there is no significant change or difference in elongation due to thermal expansion due to the problem of the total thickness from the outermost surface to the underlying layer, so that the thermal stress as a whole is It becomes smaller and can be prevented from peeling off from the base material 10.

Specific Description for Carrying Out the Invention In the heat insulating member of the present invention, as the low thermal expansion ceramic having a thermal expansion coefficient of 9 × 10 ⁻⁶ / ° C. or less used for the second transition layer, for example, a thermal expansion coefficient of 8 × 10 6 is used. ^-6 / ℃ Al ₂ O ₃ , 4.5 × 10 ^-6 /
℃ ZrO ₂ · SiO ₂ , 2.5 × 10 ^-6 / ℃ 2MgO · 2Al ₂ O ₃ , · 5SiO
_{2 and the} like can be used, but the present invention is not limited to these.

The Ni-Cr-Al-based alloy used in the underlayer may be one that has been conventionally used for the undercoat of ceramic spraying, and its component composition is not particularly limited, but usually Cr10-30
wt%, Al 5-10 wt%, with the balance being substantially N
It may have a component composition of i, or may further contain Y of about 0.3 to 1.0 wt% and Co of about 20 to 60 wt% as required.

Further, the underlayer, the first transition layer, the intermediate layer, and the second transition layer can all be formed by thermal spraying, but in this case, the first transition layer and the second transition layer are so-called graded thermal spraying. Of course. When the thermal spraying is performed as described above, the particle size of the Ni-Cr-Al-based alloy of the underlayer is preferably about 30 to 105 μm, and ZrO ₂ · 8Y ₂ O ₃ is desirable.
As the low thermal expansion coefficient ceramic, a particle size of about 10 to 74 μm is preferable.

The first transition layer is Ni-Cr from the underlayer side to the intermediate layer.
It is most preferable that the mixing ratio of the -Al alloy is continuously reduced, but it may be gradually reduced in some cases. Also in the second transition layer, it is most preferable that the mixing ratio of ZrO ₂ .8Y ₂ O ₃ continuously decreases from the intermediate layer toward the outermost surface, but it may decrease stepwise in some cases.

Examples Examples of heat insulating members of the present invention and comparative examples consisting of conventional heat insulating members are shown below, and the results of the heat cycle test and the actual machine durability test as pistons for each member of Examples and Comparative Examples are shown. Show.

[Example 1] A surface of a disk-shaped base material made of JIS AC8A alloy having a diameter of 50 mm and a thickness of 10 mm was shot-blasted, and then Ni-Cr-Al alloy as an underlayer material, specifically, 94wt%
And (Ni-20wt% Cr) -6wt % Al alloy, a graded thermal spray of ZrO ₂ · 8Y ₂ O ₃ as the intermediate layer material was performed to a thickness 0.3 mm. At this time, the Ni-Cr-Al alloy is 100% on the base metal side.
And the uppermost layer was sprayed so that ZrO ₂ .8Y ₂ O ₃ was 100% to continuously form an underlayer, a first transition layer, and an intermediate layer. Furthermore, a graded thermal spray of ZrO ₂ · 8Y ₂ O ₃ and Al ₂ O ₃ as a low coefficient of thermal expansion ceramic was performed thereon with a thickness of 0.2 mm to form a second transition layer, and the ceramic heat insulating member of the present invention was formed. Obtained. At this time, ZrO ₂ · 8Y ₂ O ₃ is 100% on the side of the second transition layer in contact with the intermediate layer, and Al ₂ O ₃ and ZrO ₂ · 8Y ₂ O ₃ are 50% on the outermost surface portion. Sprayed.

Example 2 As a low coefficient of thermal expansion ceramic, Al ₂ O ₃ in Example 1 was used.
A ceramic heat insulating member was prepared in the same manner as in Example 1 except that ZrO ₂ .SiO ₂ was used instead of.

Example 3 As a low coefficient of thermal expansion ceramic, Al ₂ O ₃ in Example 1 was used.
A ceramic heat insulating member was prepared in the same manner as in Example 1 except that 2MgO.2Al ₂ O ₃ .5SiO ₂ was used instead of.

[Comparative Example 1] After the surface of a disc-shaped base material made of JIS AC8A alloy with a diameter of 50 mm and a thickness of 10 mm was shot-blasted, Ni was used.
-Cr-Al alloy (specific composition is the same as in the case of Example 1)
An underlayer was formed by thermal spraying with a thickness of 0.1 mm. Then Z on it
A conventional ceramic heat insulating member was created by spraying rO ₂ · 8Y ₂ O ₃ with a thickness of 0.4 mm.

[Comparative Example 2] A surface of a disk-shaped base material having a diameter of 50 mm and a thickness of 10 mm made of JIS AC8A alloy was subjected to shot blasting, and then Ni
-Cr-Al alloy (specific composition is the same as in Example 1)
Greater thermal spraying with ZrO ₂ · 8Y ₂ O ₃ was performed with a thickness of 0.3 mm. At this time, thermal spraying was performed so that the Ni-Cr-Al alloy was 100% at the lowermost part in contact with the base material and the ZrO ₂ .8Y ₂ O ₃ was 100% at the uppermost part. On top of that, add ZrO ₂ , 8Y ₂ O ₃ 0.2 mm.
A conventional ceramic heat insulating member was prepared by thermal spraying with a thick thickness.

[Heat Cycle Test] The above-described ceramic heat insulating members of Examples 1 to 3 and Comparative Examples 1 and 2 were subjected to a heat cycle test for giving a heating-cooling cycle as follows.

That is, the film surface C ₂ H ₂ -O ₂ the temperature of the preform immediately below the film was heated for 12 seconds by the burner and 400 ° C., followed by heating and cooled for 30 seconds from the back surface side of the base material to stop film A heating-cooling cycle in which the temperature of the base metal immediately below is 70 ° C
3000 cycles were repeated. At this time, the peeling state of the coating was examined every 100 cycles. The results are shown in Table 1.

[Example 4] A φ80 mm diesel engine piston made of JIS AC8A alloy was used as a base material, and the top surface thereof was treated in the same manner as in Example 1 to prepare a ceramic heat insulating piston.

[Comparative Example 3] A φ80 mm diesel engine piston made of JIS AC8A alloy was used as a base material, and the top surface thereof was subjected to the same treatment as in Comparative Example 2 to prepare a ceramic heat insulating piston.

[Actual Machine Durability Test] The ceramic heat insulating pistons of Example 4 and Comparative Example 3 were each incorporated into a 2200cc diesel engine with a turbocharger, and a continuous operation test was performed. The operating conditions are supercharging pressure of 550 mmHg, 4200 rpm, 95 horsepower, and the operation is stopped every 50 hours to check the condition of the heat insulating film on the piston.
Time tested. The results are shown in Table 2.

From the heat cycle test result shown in Table 1 and the actual machine durability test result as the heat insulating piston shown in Table 2, in the example product of the present invention, the conventional two-layer thermal spray product (comparative example 1) and the graded product were obtained. It is clear that the thermal shock resistance is remarkably superior to that of the thermal sprayed products (Comparative Examples 2 and 3), and peeling of the coating hardly occurs. It is considered that this is because by mixing a ceramic having a low coefficient of thermal expansion in the upper part of the film, the elongation of the upper part of the film, which has the highest temperature, can be suppressed to be smaller than in the conventional case, and the thermal stress in the film can be reduced. That is probably because that could close a l _co shown in Figure 4 to l _bo to l _mo.

Ceramic insulating member of Effect of the Invention The present invention, coating top, main constituent material ZrO ₂ · 8Y ₂ O ₃ is mixed with low thermal expansion ceramic and toward the outer ZrO ₂ · 8Y ₂ O for thermal insulation _Since it is the second transition layer in which the ratio of ₃ is reduced, even if the outermost surface of the film becomes high temperature by being exposed to high temperature, the difference in elongation inside the film in the second transition layer is small, Moreover, Zr
O ₂ · 8Y ₂ O from an intermediate layer consisting of ₃ also ground layer in portion ranging underlayer Ni-Cr-Al alloy and ZrO ₂ · 8Y ₂ O ₃ and are mixed and toward the intermediate layer Ni-Cr -Since the first transition layer in which the proportion of -Al-based alloy decreases is formed, the difference in elongation inside the film is small even at that portion, and therefore the difference in elongation inside the film as a whole is also small, so thermal cycling is added. Since the thermal stress at that time is also small, and therefore the thermal shock resistance is remarkably excellent, there is little risk of peeling or falling of the film, and it is possible to obtain significantly superior durability performance than before.

[Brief description of drawings]

FIG. 1 is a longitudinal 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 distribution in the thickness direction of constituent materials of each layer in the ceramic heat insulating member of FIG. It is a figure. FIG. 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 FIG. 4 is a schematic diagram showing the amount of expansion of each layer based on the temperature distribution of FIG. . 10 …… Base material, 11 …… Underlayer, 12 …… First transition layer, 13 ……
Middle layer, 14 ... Second transition layer.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-60-197861 (JP, A) JP-A-61-250159 (JP, A) JP-A-62-103368 (JP, A) JP-A-61- 143576 (JP, A) JP 61-250161 (JP, A) JP 53-54214 (JP, A)

Claims (1)

[Claims] 1. A base layer made of a Ni—Cr—Al alloy is formed on the surface of a base material made of an Al alloy, and a Ni layer is formed on the base layer.
A first transition layer in which the --Cr--Al alloy and ZrO ₂ .8Y ₂ O ₃ are mixed and the mixing ratio of the Ni--Cr--Al alloy decreases toward the outside is formed continuously and integrally with the underlayer. On the first transition layer, an intermediate layer consisting essentially of ZrO ₂ · 8Y ₂ O ₃ is formed continuously and integrally with the first transition layer, and further on the intermediate layer,
Low coefficient of thermal expansion ceramics with a coefficient of thermal expansion of less than 9 × 10 ^-6 / ℃ and Z
When mixed with rO ₂・ 8Y ₂ O ₃ and directed outward, ZrO ₂・ 8Y ₂ O ₃
A ceramic heat insulating member, characterized in that the second transition layer in which the mixing ratio of is reduced is formed continuously and integrally with the intermediate layer.