JPH0673522A - Heat insulating thermal spraying material - Google Patents

Abstract

PURPOSE:To produce a thermal spraying material having superior heat insulating property and high coefficient of expansion by preparing a thermal spraying material having a composition consisting of specific amounts of one or more kinds among FeO, Fe2O3, and Fe3O4 and the balance ceramics other than these oxides. CONSTITUTION:The thermal spraying material which has a composition consisting of, by weight, >=25%, preferably >= about 28%, in total, of at least one or more kinds among FeO, Fe2O3, and Fe3O4 and the balance ceramics Al2O3, ZrO2-8wt.% Y2O3, 3Al2O3.2SiO2, SiO2, CeO2, Cr2O3, etc.) other than FeO, Fe2O3, and Fe3O4 and is used for thermal spraying onto a member made of metal is prepared. When this thermal spraying material is thermally sprayed onto the member made of metal, a film practically free from peeling from a base material can be formed and thermal spraying cost can be reduced to half or less.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal spray material having excellent heat insulating properties and a high expansion coefficient, which is sprayed to impart heat resistance to a metal member.

[0002]

2. Description of the Related Art For example, internal combustion engine members such as pistons and piston heads are required to have heat resistance because they are continuously used at high temperatures. Therefore, although the use of a ceramic material having a low thermal conductivity for a member for an internal combustion engine has been studied, it has not yet been put into practical use. Therefore, at present, on the surface of members for internal combustion engines made of metal members such as aluminum-based alloys, steel materials, cast iron, nickel-based alloys,
Thermal resistance is imparted to the metal member by spraying a ceramic having a low thermal conductivity. When a member having a ceramic sprayed coating is used under conditions of repeated heating-cooling, for example, when the coefficient of thermal expansion of the member is much larger than the coefficient of thermal expansion of the coating, the coating cannot follow the thermal expansion of the member, It peels off from the member. Therefore, it is necessary to consider not only the heat transfer coefficient but also the thermal expansion coefficient of the ceramic material to be sprayed.

Japanese Unexamined Patent Publication No. 3-223455 discloses Zr.
Although a thermal spray material composed of O ₂ -8 wt% Y ₂ O ₃ is disclosed, this ZrO ₂ -8 wt% Y ₂ O ₃ exhibits a relatively high coefficient of thermal expansion among ceramics and has a thermal conductivity. It is widely used as a thermal spray material due to its small size and excellent heat insulation. Used as heat resistant thermal spray material in Table 1,
ZrO ₂ -8 wt% Y ₂ O ₃ and, as a reference, other ceramics used as a heat-resistant thermal spray material, Al ₂ O ₃ , 3
The coefficient of thermal expansion of Al ₂ O ₃ .2SiO ₂ is shown as ZrO ₂
-8wt% Y ₂ thermal expansion coefficient of the O ₃ it can be seen that the highest.

[0004]

[Table 1]

[0005]

However, as shown in Table 1, various kinds of metals for sprayed materials (aluminum-based materials,
ZrO ₂ and thermal expansion coefficient of steel materials, cast iron, nickel-based heat resistant materials)
The difference in the coefficient of thermal expansion of −8 wt% Y ₂ O ₃ is still open. Therefore, when various metals to be sprayed having ZrO ₂ -8 wt% Y ₂ O ₃ as a thermal spray coating are used under conditions in which heating and cooling are repeated, ZrO ₂ -8 wt% Y ₂ O _{3 is used.}
The thermal spray coating of can not follow the thermal expansion of the metal for thermal spray material,
It peels off from the material to be sprayed. Therefore, it is an object of the present invention to reduce the difference in the coefficient of thermal expansion between the base material and the thermal spray material so that peeling of the coating film from the base material caused by repeated heating and cooling is less likely to occur.

[0006]

A heat-resistant thermal spray material for thermal spraying a metallic member of the present invention is FeO, Fe ₂ O ₃ ,
Fe consists ₃ O ₄ of at least one or more, or, FeO, Fe include ₂ O _3, Fe ₃ O ₄ at least one or more, and the total content as 25 wt% or more, the balance being the FeO, Fe ₂ O ₃ , characterized by being made of ceramics other than Fe ₃ O ₄ .

FeO, Fe₂O₃, Fe₃O_FourOther than
For Lamic, for example, Al₂O₃, ZrO₂-8 wt
% Y₂O₃3 Al₂O₃・ 2SiO₂, SiO₂, C
eO ₂, Cr₂O₃Etc.

If the total content of FeO, Fe ₂ O ₃ and Fe ₃ O ₄ is less than 20 wt%, a large coefficient of thermal expansion cannot be obtained, and if it is 16 wt% or more and less than 25 wt%, a strong film strength can be obtained. FeO, Fe ₂ O ₃ , Fe ₃ O
The total content of ₄ is 25 wt% or more, more preferably 28 w.
t% or more.

[0009]

[Function] Iron oxide (FeO, Fe ₂ O) obtained by thermal spraying
₃ , Fe ₃ O ₄ ) film contains many pores. Since the pores have a low thermal conductivity, the iron oxide sprayed coating has a heat insulating property. Further, the thermal expansion coefficient of the thermal sprayed coating of iron oxide is small, and the difference in thermal expansion coefficient between the thermal sprayed member made of a metallic member is small. It can follow the coefficient of thermal expansion.

[0010]

EXAMPLES The present invention will be described below with reference to Examples and Comparative Examples. Example 1 Two test pieces made of cast iron (coefficient of thermal expansion, 6 × 10 ⁻⁶ m / ° C.) and having a diameter of 30 mm and a height of 20 mm were manufactured, and the top surface of each test piece was shot blasted. . Blast material has a diameter of 1200-1400
μm calcined alumina was used. Next, Fe on this treated surface
₃ O ₄ powder (particle size 10 to 74 μm, purity 99%) was plasma sprayed to form a film having a thickness of 0.5 mm.

Observation of the outside of the film of one of the test pieces revealed no defects such as cracks, and confirmed that the film was good. Further, when the test piece was vertically cut and the structure in the film was observed, no crack was observed at the interface of the film and in the film, and it was confirmed that the film was good. When the pores in the film were measured with a porosimeter, a large amount of pores of about 13 vol% was measured.

Next, using the other test piece,
A heat cycle test was conducted. In the test, the coating surface was heated to 800 ° C. with a gas burner and then cooled in water as one cycle, the number of cycles until peeling was measured, and the heating and cooling were repeated. The durability was evaluated. The result is shown in FIG. The evaluation was completed with the maximum being 500 cycles. (Comparative Example 1) ZrO ₂ -8w instead of Fe ₃ O ₄ powder
Under the same conditions as in Example 1 except that t% Y ₂ O ₃ powder was used, a ZrO ₂ -8 wt% Y ₂ O ₃ film was formed on each of the top surfaces of the two cast iron test pieces. When the outside and inside of the film of one of the test pieces was observed in the same manner as in Example 1, defects such as cracks were not observed, and it was confirmed that the film was good. When the pores in the film were measured with a porosimeter, a large amount of pores of about 8 vol% were measured. Then, under the same conditions as in Example 1, a heat cycle test was performed using the other test piece. The result is shown in FIG.

As can be seen from FIG. 1, the coating on the test piece of Example 1 did not peel off even after 500 cycles, whereas the coating of Comparative Example 1 peeled off after 50 cycles. Therefore, ZrO ₂ -8, which has been conventionally used,
It was confirmed that the coating film formed by spraying Fe ₃ O ₄ rather than wt% Y ₂ O ₃ exhibits superior adhesive strength to cast iron under the condition of repeated heating and cooling. Example 2 An FeO film was formed on each of the surfaces of two cast iron test pieces under the same conditions as in Example 1 except that FeO was used instead of the Fe ₃ O ₄ powder. When the outside and inside of the film of one of the test pieces was observed in the same manner as in Example 1, defects such as cracks were not observed, and it was confirmed that the film was good. The porosity in the film was measured with a porosimeter and found to be about 13 vol%
A large number of stomata were measured. Then, under the same conditions as in Example 1, a heat cycle test was performed using the other test piece. As a result, as in Example 1, the coating on the test piece did not peel off even after 500 cycles, and the thermal spray coating formed by the thermal sprayed material of FeO also had good adhesion to cast iron under the condition of repeated heating and cooling. It was confirmed that But using (Example _{3) Fe 3 O 4 Fe 2} O 3 instead of the powder, under the same conditions as in Example 1, the Fe ₂ O ₃ in each of the two cast iron test piece surface A film was formed. When the outside and inside of the film of one of the test pieces was observed in the same manner as in Example 1, defects such as cracks were not observed, and it was confirmed that the film was good. The porosity in the film was measured with a porosimeter, and it was about 13
A large amount of pores of vol% was measured. And Example 1
A thermal cycle test was performed using the other test piece under the same conditions as in. As a result, as in Example 1, the film on the test piece did not peel off even after 500 cycles, and
e ₂ O ₃ thermal spray coating formed by thermal spray material-
It was confirmed that a good adhesive force was exhibited under the condition of repeated cooling.

In order to measure the coefficient of thermal expansion of the sprayed coatings of Examples 1 to 3, samples of φ10 mm × 20 mm were cut out from each. The coefficient of thermal expansion rises at a rate of 2 ° C / min,
The elongation of the sample was measured and calculated from this. The results are shown in Table 2.

[0015]

[Table 2]

Comparing Table 1 and Table 2, Examples 1 to 1
It can be seen that the film of No. 3 has a larger coefficient of thermal expansion. (Example 4) Ni-based alloy (Ni-14 wt% Cr-6w
Two test pieces made of t% Fe) having a diameter of 30 mm and a height of 20 mm were manufactured, and the top surface of each test piece was shot blasted. Blast material has a diameter of 120
A calcined alumina of 0 to 1400 μm was used. Next, ZrO ₂ -8 wt% Y ₂ O ₃ powder (particle size 10 to 10
A powder obtained by mixing 40 wt% of 74 μm, purity 99%) and 60 wt% of Fe ₃ O ₄ powder (particle size: 10 to 74 μm, purity 99%) was plasma sprayed to form a film having a thickness of 0.5 mm.

The thermal expansion coefficient of the thermal spray material formed by mixing two or more kinds of thermal spray materials is determined by the sum of the products of the thermal expansion coefficient of each and the content ratio of each. Therefore, as described above, ZrO ₂ -8w having a coefficient of thermal expansion of 10 × 10 ^-6 ° C ^-1
t% Y ₂ O ₃ is 40 wt% and the thermal expansion coefficient is 16.6 × 1.
The thermal expansion coefficient of the thermal spray material obtained by mixing 60 wt% of Fe ₃ O ₄ at 0 ^-6 ° C ^-1 is 13.96 × 10 ^-6 ° C ^-1 . The coefficient of thermal expansion of the Ni-based alloy used in this example is 1
It was 4.0 × 10 ^-6 ° C ^-1 , and the difference in the coefficient of thermal expansion between the thermal spray material and the Ni-based alloy could be made considerably small.

The mixed powder material is not limited to this embodiment, but Fe₃O_Four
By mixing 50 wt% of FeO and 50 wt% of FeO
However, the coefficient of thermal expansion of the Ni-based alloy is 14.0 × 10^-6℃^-1Close to
A thermal spray material having a high value can be obtained. In addition, in this embodiment
Is Fe₃O_FourTo ZrO₂-8wt% Y₂O₃Mixed with
However, it is not limited to this, it has heat resistance and is mixed with iron oxide.
By doing so, it is possible to approximate the thermal expansion coefficient of the material to be sprayed.
Any ceramic may be used, for example, Al₂O₃,
SiO₂3 Al₂O₃・ 2SiO₂, CeO₂, Cr
₂O₃Etc. Outside the film on one test piece
When the portion and the inside were observed in the same manner as in Example 1, cracks were found.
It was confirmed that there was no problem such as
Was done. Then, under the same conditions as in Example 1, the other
A heat cycle test was conducted using the test piece. That conclusion
The results are shown in FIG. (Comparative Example 2) ZrO₂-8wt% Y₂O₃Powder and Fe₃
O_FourInstead of powder mixture, ZrO ₂-8wt% Y₂O
₃Two as in Example 1 except that powder is used
ZrO on each of the top surfaces of the Ni alloy test pieces of
₂-8wt% Y₂O₃Was formed. One test
Observation of the exterior and interior of the film of the piece as in Example 1.
However, no defects such as cracks were found, and a good film
Was confirmed. Then, the same conditions as in Example 1
Then, perform the thermal cycle test using the other test piece.
went. The result is shown in FIG.

As can be seen from FIG. 1, the coating on the test piece of Example 4 did not peel off even after 500 cycles, whereas the coating of Comparative Example 2 peeled off after 90 cycles. Therefore, ZrO ₂ -8, which has been conventionally used,
than _{wt% Y 2 O 3, Fe} 3 O 4 to 60 wt%, the balance is towards the film formed by spraying a spray material comprising a _{ZrO 2 -8wt% Y 2 O 3} , heating - under conditions repeating cooling , It was confirmed that it exhibits excellent adhesion with Ni-based alloys. (Example 5) Aluminum alloy (Al-12 wt% S
In i), a piston having a shape of 80 mm in diameter was manufactured, and the top surface was shot blasted. As the blast material, calcined alumina having a diameter of 1200 to 1400 μm was used. Next, Ni-Cr-Al (Ni-20 wt%
Cr-5.0 wt% Al) powder was plasma sprayed to form a film having a thickness of 0.1 mm. Next, on this, Fe ₃ O
_{The 4} powders were plasma sprayed to form a film having a thickness of 0.5 mm. The coefficient of thermal expansion of Ni-Cr-Al is 15.0 x 10 ^-6.
The thermal expansion coefficients of ℃ ^-1 and Fe ₃ O ₄ are 16.6 × 10 ^-6 ℃ ^-1, which are similar to each other, so that the thermal spraying material does not mix with 100 wt% Fe ₃ O 4. ₄ powders were used.

The piston thus manufactured was incorporated into a 4-cylinder diesel engine having a displacement of 2200 cc, and [supercharging pressure 650 mmHg, 400 rpm: 6 minutes] →
[Idle: 1 minute] → [Stop: 1 minute] → [Idle: 1 minute]
Minutes] as one cycle, and this cycle was repeated to evaluate the durability of the actual machine. The results are shown in Table 3. In this example, an aluminum alloy and Fe ₃ O _{4 were used.}
Although by spraying Ni-Cr-Al powder during the thermal spray coating, which is for alleviating the difference in the thermal expansion coefficient of the thermal spray coating of aluminum alloy and Fe ₃ O _4, commonly used Others include Ni-Cr and Ni-A.
1, Co-Cr, etc.

[0021]

[Table 3]

Comparative Example 3 A piston was manufactured in the same manner as in Example 5 except that ZrO ₂ -8 wt% Y ₂ O ₃ powder was used instead of Fe ₃ O ₄ powder.

The produced piston was evaluated for durability in the actual machine under the same conditions as in Example 5, and the results are shown in Table 3. As is clear from Table 3, the coating of the piston of Comparative Example 3 was peeled off during the evaluation, whereas the piston of Example 5 was in a good state even after 700 hours.

Fe ₃ O ₄ and ZrO ₂ -8 wt% Y ₂ O ₃
The thermal conductivity of Fe ₃ O ₄ is about 10 W / mK,
With ZrO ₂ -8 wt% Y ₂ O ₃ being about 1 W / mK, ZrO ₂ -8 wt% Y ₂ O ₃ is far superior in heat insulation. However, after the endurance evaluation of the actual machine, the coating was forcibly peeled off from each piston to expose the aluminum alloy, and the highest temperature reached on the upper surface of the exposed aluminum alloy was measured. All of the 3 pistons had a temperature of 250 ° C. ± 30 ° C., and no difference was observed. This is because the thermal spray coating of Fe ₃ O ₄ has many pores, and the thermal conductivity of these pores is small, as is known by measuring in Examples 1 to 3.
ZrO is not affected by the high thermal conductivity of Fe ₃ O ₄ itself.
_It is considered to have a low thermal conductivity equivalent to 2-8 wt% Y ₂ O ₃ . Not only Fe ₃ O ₄ but also FeO and F
It has been confirmed that similar results can be obtained with e ₂ O ₃ . (Example 6) Set the Fe ₃ O ₄ powder mixing ratio of Al ₂ O ₃ in various, Figure 2 shows the results of investigating the relationship between film strength. The spraying conditions are plasma spraying (70 k
w) was used and the spraying distance was 130 mm. From Figure 2, F
It was clarified that the film strength was changed by changing the mixing ratio of e ₃ O ₄ . The film strength is generally 20M
Although it is required that the pressure is not less than Pa, from FIG.
_{2 when} the mixing ratio of ₃ O ₄ is 16 wt% or more and less than 25 wt%
It can be seen that the film strength of 0 MPa or more cannot be obtained.

Iron oxide (FeO, Fe ₂ O ₃ , Fe
₃ O ₄ ) is very excellent in reactivity with other ceramics, but has a feature that reactivity between particles of the same material is inferior to reactivity between particles of the same material of other ceramics. .

Al₂O₃Fe in₃O_Four25 wt% or less
When spraying the thermal spray material consisting of the above ceramic,
As mentioned above, Fe that is iron oxide₃O_FourIs the reaction between particles
Due to its poor property, particles with a size of several microns are
There will be racks and unbonded parts. But this
They do not have any adverse effect on the film strength.
The good effect of adjusting the amount of deformation when the film expands
Bring fruit. And Al₂O₃Fe in contact with₃
O_FourIs Al₂O₃Reacts with Fe₃O_FourAnd Al₂O₃
On the interface of FeAl₂O_FourTo generate. This, Fe₃O_Four
And Al ₂O₃Has a different crystal structure from FeAl₂O_FourRaw
As the volume changes due to growth, FeAl₂O_FourIs the base point
Then, a crack occurs. But this crack
Is Fe₃O_FourA few Miku that are seen in the adjacent areas
Ron cracks and unbonded parts
It will be stopped. Therefore, Al₂O₃Fe in₃O_Four
A thermal spray material made of ceramic containing 25 wt% or more of
The film obtained by irradiation has a strong film strength
It is thought to be.

[0027] When spraying the thermal spraying material consisting of a ceramic containing less than Fe ₃ O ₄ to 16 wt% or more 25 wt% in Al ₂ O _3, the periphery of the Fe ₃ O ₄ particles Al ₂ O ₃ particles covers, Fe ₃ O FeAl ₂ O ₄ between ₄ and Al ₂ O ₃
Is produced by the reaction. This Fe ₃ O ₄ and Al ₂ O
₃ A with the formation of different crystal structures FeAl ₂ O _4, the interface to the volume change of the Fe ₃ O ₄ and Al ₂ O ₃ is generated,
It is considered that the film strength is lowered because large cracks are generated in the Al ₂ O ₃ particles which are adhered in a good state.

When a thermal spraying material consisting of ceramic containing Fe ₃ O ₄ in an amount of less than 16 wt% in Al ₂ O ₃ is sprayed, most of the inside of the coating is Al ₂ O ₃ which is a ceramic excellent in reactivity between the same material particles. It is considered that the film has excellent adhesion between particles and has strong film strength. However, the original high thermal expansion coefficient cannot be expected only by containing Fe ₃ O ₄ in an amount of less than 20 wt% in the thermal spray material. Therefore, Fe ₃ O ₄ needs to be included in the coating in an amount of 20 wt% or more. . Of course, not only Fe ₃ O ₄
The same can be said for other FeO and Fe ₂ O ₃ having a high coefficient of thermal expansion.

In this embodiment, Fe₃O_Four-Al₂O₃system
However, not limited to this, other iron oxides
(FeO, Fe₂O₃) Or FeO, Fe
₂O₃, Fe ₃O_FourVarious mixtures of other ceramics
It was confirmed that similar results can be obtained for
ing. From the above, with a high coefficient of thermal expansion, and
In order to obtain a coating strength of 20 MPa or more,
, FeO, Fe₂O₃, Fe₃O_FourIncluding one or more of
It is necessary to make the total content 25 wt% or more.
Become. More preferably, the content is 28 wt% or more.
By, the film strength of 30 MPa or more can be obtained.
It

The thermal spray material of the present invention can be sprayed on any metal member which requires heat insulation, but especially on the piston top surface obtained by spraying on the piston top surface of the combustion chamber of an internal combustion engine. The effect of improving heat insulation is great.

[0031]

Since the thermal spray material of the present invention has a small difference in coefficient of thermal expansion from the base material, peeling of the thermal spray coating from the base material does not easily occur even under repeated heating and cooling conditions. Also,
In the case of thermal spraying, the ratio of material cost to product cost is high.
ZrO ₂ powder is generally 1000 yen to 2000 yen / kg, which is extremely expensive as compared with general thermal spray powder. On the other hand, iron oxide such as Fe ₃ O ₄ is inexpensive and costs 100 yen /
Some kg are also present. From these things, the present invention can reduce the cost required for thermal spraying to half or less.

[Brief description of drawings]

FIG. 1 is a graph showing the number of cycles until a coating is peeled off from a member to be sprayed as a result of a heat cycle test.

FIG. 2 is a graph showing the film strength when the amount of Fe ₃ O ₄ contained in Al ₂ O ₃ is variously changed.

Claims (2)

[Claims] 1. An adiabatic thermal spray material for thermal spraying on a metal member, which is composed of at least one of FeO, Fe ₂ O ₃ and Fe ₃ O ₄ . 2. FeO, Fe₂O₃, Fe₃O_FourA little
Contains at least one kind, and its total content is 25 wt% or more
And the balance is FeO, Fe₂O₃, Fe ₃O_FourOther than
Melts into metal parts characterized by
Insulating thermal spray material for spraying.