JPH11278921A - Engine part and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide both an engine part having a low thermal conductivity and a high strength at high temperatures and a method for producing the engine part. SOLUTION: This engine part is formed from ceramics obtained by sintering a molded product prepared by compounding 80-95.5 wt.% of a cordierite powder having <=5 μm average particle diameter, 0.5-20 wt.% of a rare earth element oxide having <=2 μm average particle diameter and further <=30 wt.% of at least one kind selected from silicon nitride, silicon carbide and silicon oxynitride at a temperature within the range of 1,200-1,500 deg.C and then cooling the sintered molded product to 1,000 deg.C at <=10 deg.C/min rate. The ceramics contain cordierite crystal grains having <=10 μm average grain diameter, have <=5% porosity of open pores, further contain a compound oxide crystal phase of the rare earth element oxide and silicon oxide deposited on the grain boundary of cordierite crystal grains and have <=5 W/m.K thermal conductivity at ambient temperature and >=80 MPa strength at 800 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an engine component suitable as a component requiring heat insulation, such as a piston, a cylinder, a chamber, and the like, and a method of manufacturing the same.

[0002]

2. Description of the Related Art Cordierite-based sintered bodies are conventionally known as ceramics having a low thermal expansion, and include filters,
It is applied to honeycombs and refractories. This cordierite-based sintered body is mixed with cordierite powder or MgO, Al ₂ O ₃ , and SiO ₂ powder that forms cordierite, and as a sintering aid, a rare earth element oxide or SiO ₂ , CaO, MgO, etc., molded into a predetermined shape, and fired at a temperature of 1000 to 1400 ° C. (JP-B-57-3629, JP-A-2-229760).

[0003] In recent years, high-temperature combustion of automobile engines has been progressing along with high output. For this reason, the temperature around the combustion chamber is increasing, and its heat insulating property is becoming important. It is also important to prevent heat dissipation from the viewpoint of energy saving and high efficiency. Therefore, conventionally, low thermal conductive ceramics such as aluminum titanate and cordierite have been used for engine parts.

[0004]

However, since these ceramics have excellent heat insulation properties and low thermal expansion,
Although it is excellent in thermal shock resistance to some extent, it is difficult to obtain a dense body, and its strength is as low as about 40 MPa, and the range and conditions that can be used as a structural member are limited.

On the other hand, ceramics such as silicon nitride are known as a high-temperature high-strength material. However, silicon nitride ceramics have a high thermal conductivity of 30 W / m · K and poor heat insulating properties. A material having strength properties has not been obtained so far.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an engine part having low thermal conductivity itself and high strength, and a method of manufacturing an engine part capable of stably manufacturing the same. is there.

[0007]

Means for Solving the Problems As a result of intensive studies on the above problems, the present inventors have added an appropriate amount of a rare earth element oxide to cordierite, and controlled the particle size of the sintered body. It has been found that by precipitating a specific crystal phase at the cordierite crystal grain boundaries, densification can be promoted while maintaining low thermal conductivity, and the strength can be greatly increased, and the present invention has been achieved.

That is, the engine part of the present invention contains 80 to 95.5% by weight of cordierite and 0.5 to 20% by weight of a rare earth element (RE) in terms of oxide, and contains cordierite crystal particles. It has an average particle diameter of 10 μm or less, a porosity of 5% or less, and a composite oxide crystal phase of a rare earth element oxide and silicon oxide precipitates at the grain boundaries of the cordierite crystal particles, and has a thermal conductivity at room temperature. Rate is 5W /
m · K or less,
A flexural strength from room temperature to 800 ° C. is 80 MPa or more, and at least one selected from silicon nitride, silicon carbide, and silicon oxynitride is contained in a proportion of 30% by weight or less. Things.

Further, according to the method for manufacturing an engine part of the present invention, a cordierite powder having an average particle size of 5 μm or less is used
A molded article containing 95.5% by weight of a rare earth element oxide having an average particle diameter of 2 μm or less at a ratio of 0.5 to 20% by weight was prepared as 1
After sintering in the temperature range of 200 to 1500 ° C, 1000
Cooling to 10 ° C. at a rate of 10 ° C./min or less. Further, at least one selected from silicon nitride, silicon carbide and silicon oxynitride is cooled to 3 ° C.
It is characterized in that it is added in a proportion of 0% by weight or less.

[0010]

Engine parts of the embodiment of the present invention, the composition on the cordierite complex oxide represented by _{2MgO · 2Al 2 O 3 · 5SiO} 2 80~99.5 % by weight, in particular 85 to 95 weight %, And it is important that the cordierite crystal phase exists as fine crystal particles having an average particle size of 1 to 10 μm, preferably 1 to 5 μm. The strength can be improved without deteriorating the low thermal conductivity.

The sintered body contains a rare earth element as a sintering aid component in an amount of 0.5 to 20% by weight, especially 5 to 15% by weight in terms of oxide. These react with a part of cordierite in the sintering process, act as a sintering aid, enable sintering at a low temperature, reduce the size of the structure, and promote densification. Examples of the rare earth element include Y, Yb, Er, and Sm.

The reason why the amount of the cordierite and the rare earth element is limited to the above ratio is that the amount of the cordierite is more than 99.5% by weight, in other words, the amount of the rare earth element is less than 0.5% by weight. In this case, densification is hindered, and the sintering temperature must be increased. As a result, the crystal grain size of cordierite increases, and low thermal conductivity and high strength cannot be achieved. In addition, the amount of cordierite is 80% by weight.
If the amount is less than that, in other words, if the amount of the rare earth element is more than 20% by weight, grain growth is promoted and the grain boundary phase is increased, so that low thermal conductivity and high strength at high temperatures cannot be achieved.

The ceramic has an open porosity of 5%.
% Or less, particularly 3% or less is important. If the open porosity is more than 5%, the pores serve as a fracture source and the strength is reduced.

In this ceramic, it is also important that a composite oxide crystal phase of a rare earth oxide and silicon oxide precipitates at the grain boundaries of the cordierite crystal phase.

As described above, the high-temperature strength can be increased by the precipitation of the crystal phase at the grain boundaries. As a composite oxide crystal phase of a rare earth element oxide (RE ₂ O ₃ ) and silicon oxide (SiO ₂ ), monosilicate (RE ₂ Si)
O ₅ ) and disilicate (RE ₂ Si ₂ O ₇ ).

According to the present invention, according to the above-described structure, the JIS-R-1601 can be obtained at room temperature to 800 ° C. with low thermal conductivity of 5 W / m · K or less, particularly 3 W / m · K or less at room temperature. In the four-point bending buckling strength based on the above, high strength of 80 MPa or more, particularly 100 MPa or more can be achieved.

According to the present invention, in order to further increase the strength, at least one selected from the group consisting of silicon nitride, silicon carbide and silicon oxynitride is contained in the ceramics.
It is desirable that the content is not more than 10% by weight, preferably 10 to 20% by weight.

However, if the content exceeds 30% by weight, low thermal conductivity is lost, which is not desirable.

Such ceramics are used as engine parts. Thus, a schematic sectional view of the engine of FIG. 1 is shown. In FIG. 1, the ceramic according to the present invention is suitably used for a piston crown 1, a cylinder liner 2, a piston ring 3, a cylinder head liner 4, a chamber 5, and an exhaust port liner 6. In particular, it is most suitable as a piston crown.

In order to prepare the above ceramics, first, cordierite powder having an average particle size of 5 μm or less, preferably 3 μm or less is 80 to 95.5% by weight, preferably 85 to 95% by weight, and the average particle size is 2 μm or less, especially 1
A rare earth element oxide having a size of not more than μm is added and mixed at a ratio of 0.5 to 20% by weight, preferably 5 to 15% by weight. Also,
In order to improve the strength, at least one of silicon nitride, silicon carbide, and silicon oxynitride is not more than 30% by weight, especially
Add and mix at a ratio of 20% by weight.

After the components are blended in the above ratio, they are sufficiently mixed by a ball mill or the like, and are optionally formed into a predetermined shape by a desired molding means, for example, a die press, a cold isostatic press, an extrusion molding or the like. After forming into a shape, it is fired.

The firing is performed in the air or in vacuum, Ar, N
1200 to 1500 ° C in an inert gas atmosphere such as ₂ ,
It is preferably 1 to 10 in a temperature range of 1250 to 1400 ° C.
By sintering for about an hour, the relative density can be increased to 95% or more.

If the firing temperature at this time is lower than 1200 ° C., densification cannot be achieved, and if it exceeds 1500 ° C., the molded body is melted or accompanied by grain growth, which impairs the properties of low thermal conductivity and high strength.

In order for the composite oxide crystal phase of the rare earth element oxide and silicon oxide to precipitate at the grain boundaries of the ceramic, the temperature must be increased from the maximum firing temperature to 100 ° C. during the cooling process after firing.
The temperature range up to 0 ° C. is 10 ° C./min or less, especially 5 ° C./min.
What is necessary is just to cool at a speed of min or less. If the cooling rate in this temperature range is higher than 10 ° C./min, it is difficult to precipitate a composite oxide crystal phase of a rare earth element oxide and silicon oxide at a grain boundary. Note that the annealing temperature range may be expanded from the maximum firing temperature to a range of 1000 ° C. or less.

[0025]

EXAMPLE Cordierite powder having an average particle size of 1 to 6 μm, rare earth element oxide powder having an average particle size of 0.5 to 3 μm, and silicon nitride, silicon carbide and silicon oxynitride having an average particle size of 1 μm or less After mixing each powder to obtain the composition shown in Table 1, mixing with a ball mill for 24 hours,
Molding was performed at a pressure of t / cm ² . Then, the molded body is placed in an alumina sagger, and the one containing silicon nitride, silicon carbide, and silicon oxynitride is fired under the conditions shown in Table 1 in the air or in a nitrogen atmosphere. It cooled at the cooling rate of Table 1.

The obtained ceramic is polished and 10 mm
Grind to a size of φ × 3mm, 3 × 4 × 15mm,
The four-point bending strength of this sample at room temperature and 800 ° C. based on JISR1601 was measured. Further, the thermal conductivity at room temperature was measured by a laser flash method (sample thickness: 3 mm). The sintered body was mirror-finished, and the average particle size of the cordierite crystal phase was measured from a scanning electron micrograph based on the intercept method. Further, the crystal phase in the ceramic was identified by X-ray diffraction measurement. The results are shown in Table 1.

[0027]

[Table 1]

[0028]

[Table 2]

As is clear from the results shown in Tables 1 and 2, Sample No. 1 which is a conventional cordierite sintered body has a low thermal conductivity of 3 W / m · K, Is as low as 30 MPa.

On the other hand, according to the present invention, by adding a rare earth element oxide at a predetermined ratio and controlling the average grain size, open porosity, and grain boundary crystal phase of cordierite crystals, the thermal conductivity is increased. While achieving 5W / m · K
The strength at 00 ° C. could be increased to 80 MPa or more.

However, the amount of the rare earth element is 20 in terms of oxide.
In Sample No. 8 having a weight percentage higher than 8% and Sample No. 9 having a weight percentage lower than 0.5% by weight, the crystal grain size exceeded 10 μm, the strength at 800 ° C. was lower than 80 MPa, and the thermal conductivity was 5 W /
m · K.

A sample No. 1 using a cordierite powder or a rare earth oxide powder having a large particle diameter as a raw material powder.
Even in Nos. 2 and 15, the cordierite crystal grain size exceeded 10 μm, the strength at 800 ° C. was lower than 80 MPa, and the thermal conductivity was 5 W / m · K or more.

Further, by adding silicon nitride, silicon carbide, and silicon oxynitride to a system containing an appropriate amount of the additive component, an improvement in strength was observed. However, in Sample No. 26 whose amount exceeded 30% by weight, the thermal conductivity exceeded 5 W / m · K, which was not suitable for the purpose.

Regarding the sintering temperature, the sample No. 22 lower than 1200 ° C. cannot be densified and the open porosity is large, and the sample No. 23 higher than 1500 ° C. An improvement in conductivity was observed.

Further, in Sample No. 29, in which the cooling rate was higher than 10 ° C./min, no crystal phase of the rare earth element oxide and silicon oxide was precipitated at the grain boundaries, and as a result, it had low thermal conductivity. However, the strength at 800 ° C. was insufficient.

[0036]

As described in detail above, the engine component of the present invention can increase the strength at a high temperature of 800 ° C. while maintaining the excellent low thermal conductivity of cordierite. As a result, the reliability of the engine can be improved by using it as an engine component such as a piston or a cylinder that requires excellent heat insulation and high strength.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of an engine.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Piston crown 2 Cylinder liner 3 Piston wear ring 4 Cylinder head liner 5 Chamber 6 Exhaust port liner

Claims (5)

[Claims] 1. A cordierite comprising 80 to 95.5% by weight,
0.5 to 20% by weight of rare earth element (RE) as oxide
And the average particle size of the cordierite crystal particles is 1
0 μm or less, the open porosity is 5% or less, and a composite oxide crystal phase of a rare earth element oxide and silicon oxide precipitates at the grain boundaries of the cordierite crystal particles, and the thermal conductivity at room temperature is 5 W / M · K or less of ceramics. 2. The engine part according to claim 1, wherein the flexural strength of the ceramic from room temperature to 800 ° C. is 80 MPa or more. 3. The ceramic according to claim 1, wherein the ceramic contains at least one kind selected from silicon nitride, silicon carbide and silicon oxynitride in a proportion of 30% by weight or less.
Engine parts as described. 4. A compact comprising 80 to 95.5% by weight of cordierite powder having an average particle diameter of 5 μm or less and 0.5 to 20% by weight of a rare earth element oxide having an average particle diameter of 2 μm or less, After sintering in the temperature range of 1200 to 1500 ° C,
A method for manufacturing an engine component, comprising cooling to 1000 ° C. at a rate of 10 ° C./min or less. 5. The method according to claim 4, wherein at least one selected from silicon nitride, silicon carbide and silicon oxynitride is added in a proportion of 30% by weight or less.