JP2002348177A - Static member for heat engine and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a static member for heat engine, which is hard to break at the time of contact, does not cause great deterioration of oxidation resistance of a precise object and mechanical property, and has excellent grinding property, and also to provide its manufacturing method. SOLUTION: This static member for heat engine is characterized in that it includes a silicon nitride as its main crystal phase, an excess oxygen, a 3a group element in the periodic table, and comprises a sintered compact with 0.05-1.5 wt.% total amount of Al, Ca and Fe, has 0.01-0.5 μm central pore size, 1-5 μm mean pore size, <=30 μm maximum pore size by mercury penetration method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stationary member for a heat engine such as a turbine shroud facing a tip of a turbine blade in a gas turbine, a jet engine, or the like, which is made of a silicon nitride-based sintered body having improved grinding performance. It relates to a manufacturing method.

[0002]

2. Description of the Related Art Conventionally, sintered bodies containing silicon nitride as a main component are excellent in heat resistance and thermal shock resistance, and therefore have been actively applied to engineering ceramics, particularly for heat engines such as parts for turbo rotors and gas turbine engines. Is being advanced.

In order to produce a sintered body containing silicon nitride as a main component, an oxide of a Group 3a element in the periodic table such as Y ₂ O ₃ ,
Aluminum oxide (Al ₂ O ₃ ), aluminum nitride (A
aluminum compound such as 1N), silica (SiO ₂ )
And the like are added as a sintering aid, followed by firing in a normal pressure or nitrogen pressurized atmosphere, whereby a dense sintered body is obtained.

[0004] For example, for a sintered body containing silicon nitride as a main component, an auxiliary agent to be added is selected depending on its use. For example, SiO ₂ and an oxide of a Group 3a element of the periodic table are essential, and when Al ₂ O ₃ or MgO is added thereto, a liquid phase is formed at a low temperature. It can be densified by sintering under pressure, and according to this method, a sintered body having high room temperature strength can be obtained.

Further, from the advantage that firing shrinkage can be reduced, a molded body of metallic silicon and a sintering aid such as MgO, Y ₂ O ₃ , CeO ₂ is heated in nitrogen at a temperature of 1500 ° C. or less. After nitriding silicon to silicon nitride, 1500 ° C
Is used to obtain a dense body.

Although the silicon nitride-based sintered body produced by such a method has many dense bodies, a conventional high-strength, high-toughness silicon nitride-based sintered body is replaced with a stationary member for a heat engine, specifically, a turbine shroud. Used during the rotation of the turbine rotor,
There is a problem that the turbine rotor and the shroud are broken when the tip of the rotor and the shroud slide.

In addition, there is a problem that consumable parts for processing these members are greatly consumed, and the processing cost is high.
As described above, in the heat engine stationary member, the strength and toughness characteristics are not so important. Rather, since these components have a large and complicated shape, good grindability is strongly required from the viewpoint of cost. .

Therefore, as a method of adjusting the gap between two members that are relatively driven at a predetermined interval, such as a combination of a gas turbine rotor and a shroud, a seal member is provided between the rotor and the shroud. Japanese Patent Application Laid-Open No. H11-310465 proposes a method in which the gap between the rotor and the seal member is adjusted to a minimum by bringing the rotor and the seal member into contact with each other so that the seal member is worn by the rotor.

[0009]

However, since the sealing member described in Japanese Patent Application Laid-Open No. H11-310465 uses a low-density, low-strength sintered body, it is kept at a high temperature for a long time like a gas turbine or the like. Then, there is a problem in that the member is oxidized, the life of the member is significantly shortened, and the member itself is damaged.

Further, when such a seal member is used, it takes time to join the seal member and the shroud, the processing cost is high, and the yield is low, which causes an increase in product cost. I was

[0011] Therefore, for the shroud facing the tip of the turbine rotor, the characteristics of high strength, high hardness and high toughness are not so important, but rather excellent in free cutting properties so that the gap between the two members can be adjusted. In addition, characteristics that are excellent in oxidation resistance are required in order to withstand long-time operation, but there has been no member having such characteristics so far.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a stationary member for a heat engine, which is hardly broken even upon contact and has excellent grinding properties without significantly deteriorating the oxidation resistance and mechanical properties of the dense body, and its production. It is to provide a method.

[0013]

SUMMARY OF THE INVENTION According to the present invention, a structure in which fine pores are uniformly distributed can be produced by shrinking a silicon nitride molded body containing a metal to a predetermined range at the time of nitriding and then firing. As a result, while maintaining the mechanical properties and oxidation resistance of the dense body almost,
The grindability of the sintered body can be enhanced, and the sintered body can be hardly damaged during contact.

That is, from a sintered body containing silicon nitride as a main crystal phase, containing excess oxygen, a Group 3a element of the periodic table, and containing a total of 0.05 to 1.5% by weight of Al, Ca and Fe. And the central pore diameter in the mercury intrusion method is 0.01 to 0.5.
μm, average pore diameter is 1-5 μm, maximum pore diameter is 30 μm
It is characterized by the following. This allows
Because it has free cutting properties and small pores in the sintered body,
Material destruction can be reduced.

In particular, the sintered body has a Vickers hardness of 10
It is preferably from 13 to 13 GPa. Thereby, the grindability can be further improved, and the reliability as a heat-resistant member can be further improved.

The Group 3a element of the periodic table is 1 to 10 mol% in terms of oxide, and excess oxygen is converted to silica (SiO ₂ ).
It is contained in a converted amount of 25 mol% or less, and has a molar ratio of SiO ₂ / SiO _{2 in} terms of excess oxygen in terms of silica (SiO ₂ ) to oxides in terms of the Group 3a element of the periodic table (RE ₂ O ₃ )
Preferably, RE ₂ O ₃ is 2-3. This allows
The melting point of the grain boundary component of the sintered body can be increased, and the deterioration of the strength characteristics can be reduced even when the sintered body is kept in a high-temperature atmosphere for a long time, thereby improving the long-term reliability as a stationary part for a heat engine.

Further, a method of manufacturing a stationary member for a heat engine of the present invention includes a silicon nitride powder, a silicon powder and a sintering aid,
A molded body containing Al, Ca, and Fe in a total amount of 0.05 to 1.5% by weight is prepared, and the molded body is heat-treated in an atmosphere containing nitrogen gas to reduce the shrinkage of the molded body to 92 to 99%. %, And the silicon is nitrided.
It is characterized by firing at a temperature of 1700 to 1900 ° C.

[0018] This makes it possible to cause shrinkage at a low temperature due to the impurity metal uniformly dispersed in the compact, and to reduce the pores after firing by shrinking a certain amount during the nitriding treatment. And can be uniformly dispersed. As a result, a stationary member for a heat engine excellent in grindability can be realized without significantly deteriorating mechanical properties and oxidation resistance.

In particular, it is preferable that the molded body has a weight ratio Si / Si ₃ N ₄ of silicon (Si) to silicon nitride (Si ₃ N ₄ ) contained in the molded body of 0.3 or more. Thereby, sintering during the nitriding treatment can be further promoted, and finer pores can be obtained.

Further, the heat treatment is performed between 1100 and 1500
It is preferably carried out at a temperature of 0 ° C. Thereby, the nitriding reaction can be surely advanced to the inside of the sintered body, and the silicon nitride crystal can be made more uniform.

Furthermore, it is preferable that the calcination is performed at a pressure of 2 atm or less. This facilitates sintering while leaving fine pores, thereby improving grindability.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION The stationary member for a heat engine of the present invention contains silicon nitride as a main crystal phase, contains excess oxygen, a Group 3a element of the periodic table, and contains Al, Ca, and Fe in a total amount of 0.05 to 0.05%. 1.5
It is important that the sintered body contains about 10% by weight. A
By setting the contents of l, Ca and Fe in the above range in total, small pores can be uniformly distributed in the sintered body. In particular, Al, Ca, and Fe form uniformly distributed pores, so that 0.08 to 1 in total.
% By weight, more preferably 0.1 to 0.8% by weight. Further, a sintered body having excellent oxidation resistance can be obtained by including a Group 3a element of the periodic table.

The element of Group 3a of the periodic table is 1 to 10 mol%, especially 3 to 7 mol% in terms of oxide, and excess oxygen is 25 mol% or less, particularly 20 mol% in terms of silica (SiO ₂ ). Hereafter, it is preferable that the content is further contained at a ratio of 15 mol% or less. The molar ratio SiO ₂ / RE ₂ O _{3 of the} amount of excess oxygen in terms of silica (SiO ₂ ) to the amount in terms of oxide of the Group 3a element of the periodic table (RE ₂ O ₃ ) is preferably 2-3. . With such a composition, the deterioration of the strength characteristics in a high-temperature atmosphere can be reduced while suppressing the precipitation of a crystal phase containing nitrogen having poor oxidation resistance and increasing the oxidation resistance.

According to the present invention, it is important that the central pore diameter in the mercury intrusion method is 0.01 to 0.5 μm, and particularly preferably 0.1 to 0.3 μm. If the central pore diameter is smaller than 0.01 μm, the free-cutting property deteriorates, and if the central pore diameter is larger than 0.5 μm, although the free-cutting property is obtained, the mechanical properties are reduced due to the large pores.

It is important that the average pore diameter is 1 to 5 μm, and particularly preferably 1.5 to 3 μm.
If the average pore diameter is smaller than 1 μm, the free-cutting property is deteriorated, and if the average pore diameter is larger than 5 μm, the sintered body is broken at the time of contact.

Further, it is important that the maximum pore diameter is 30 μm or less, particularly preferably 15 μm or less, more preferably 10 μm or less. If the maximum pore diameter is larger than 30 μm, the material breaks down with the large pores as a starting point, and the reliability of the member is reduced.

The Vickers hardness of the sintered body in the stationary member for a heat engine is 10 to 13 GPa, particularly 11
It is preferably from 12 to 12 GPa. Hardness is 10 GPa
If the diameter is smaller than the above, there is a possibility that the wall thickness may be reduced by gas during operation of the engine.
If it exceeds 3 GPa, the grindability tends to deteriorate.

The stationary member for a heat engine as described above can improve the grindability without significantly impairing the mechanical characteristics, and can realize a low-cost and highly reliable stationary member for a heat engine.

The heat engine stationary member of the present invention has excellent oxidation resistance because it is exposed to a high temperature atmosphere for a long time.
1500 ° C., oxidation weight gain after 100 hour hold in the atmosphere is 1.00 mg / cm ² or less, particularly 0.8 mg / cm ²
Below, it is necessary that it is 0.60 mg / cm ² or less. If the oxidation weight increase is more than 1.00 mg / cm ² , stability in long-time operation is exerted, and reliability for use as a stationary member for a heat engine is lacking.

Next, a method for manufacturing a stationary member for a heat engine according to the present invention will be described.

First, silicon nitride powder, silicon powder and sintering aid powder are prepared as raw material powders. Silicon nitride powder is α
-Si ₃ N ₄ or β-Si ₃ N ₄ in any state, having a particle size of 0.4 to 1.2 μm and oxygen of 0.5 to 0.5 μm.
It is preferable to use one containing 1.5% by weight.

A silicon powder having a particle size of 1 to 10 μm and containing oxygen in a range of 0.1 to 1.2% by weight is added.

Further, as a sintering aid, Periodic Table No. 3a
An oxide such as a group _III compound (RE ₂ O ₃ ) or SiO ₂ is added and mixed. The elements of Group 3a of the periodic table include Sc, Y, and L.
a, Ce, Sm, Gd, Ho, Eu, Er, Yb and Lu.

As the composition, a known composition for producing a silicon nitride sintered body can be used. In particular, silicon nitride powder is 10 to 70% by weight, silicon powder is 20 to 80% by weight,
The rest are sintering aids as elements of Group 3 of the periodic table and Al and C
a and Fe are preferred. By using this composition, high characteristics as a stationary member for a heat engine, such as high-temperature mechanical characteristics and oxidation resistance characteristics, can be exhibited.

If the weight ratio Si / Si ₃ N ₄ is smaller than 0.3, the amount of pores during the nitriding treatment tends to decrease, and it tends to be difficult to obtain free-cutting properties. The weight ratio is preferably 0.3 or more, particularly 0.8 or more, and more preferably 1.3 or more.

These raw material powders are mixed and molded into a desired shape by a known molding method. The molding is performed into a desired shape by press molding, extrusion molding, injection molding, casting molding, cold isostatic molding, or the like.

It is important that Al, Ca, and Fe be contained in the compact in a total amount of 0.05 to 1.5% by weight. When Al, Ca, and Fe are added in a total amount of 0.05% by weight or more, the temperature is lower than the melting point of silicon, particularly, 1100 to 1500.
Since it has a function of accelerating the nitridation reaction at ℃ and accelerating the sintering of silicon nitride, the compact can be shrunk to prevent large pores from remaining, and fine and uniform pores can be formed.

By limiting the content to 1.5% by weight or less, it is possible to prevent excessive shrinkage and prevent deterioration of the high-temperature characteristics of the obtained sintered body. In particular, Al, C
It is preferable that the total of a and Fe is 0.08 to 1.0% by weight, more preferably 0.1 to 0.8% by weight.

It should be noted that Al, Ca and Fe may be added to the raw material as metal powder and / or compound powder,
Further, it may be contained as an impurity component of silicon nitride powder, silicon powder and a sintering aid. As the metal compound powder, A
_{l 2 O 3, AlN, CaO} , and CaCO _3, Fe ₂ O ₃ or the like can be exemplified.

Next, the above compact is heat-treated in an atmosphere containing nitrogen gas. Silicon in the compact is nitrided into silicon nitride. Also, Al, Ca and Fe are contained in the compact.
Is contained in a total of 0.05 to 1.5% by weight.
At a nitriding temperature of 0 ° C. or lower, the nitriding reaction can be promoted, and the compact can be shrunk. By this heat treatment, it is important that the compact is shrunk to a size of 92 to 99% as compared with before the heat treatment, whereby uniform and fine pores can be produced.

Due to this shrinkage, the molded body was 92%
If the diameter is smaller than the above range, the densification proceeds too much by firing, and the porosity becomes small, and it becomes difficult to uniformly distribute fine pores. Therefore, a sintered body having high grindability cannot be obtained. On the other hand, if the size of the molded body after the heat treatment is larger than 99% of the dimension before the treatment, the pore diameter after the firing becomes large, and the mechanical properties deteriorate. The shrinkage is particularly preferably 93 to 98%, and more preferably 94 to 97%.

The above heat treatment is performed at 1100 to 1500.
° C, especially 1150-1450 ° C, further 1200-1400
It is preferably performed at a temperature of 00 ° C. A sufficient reaction rate can be obtained at a heat treatment temperature of 1100 ° C. or higher, and 1500 ° C.
The following makes it easy to prevent precipitation of unreacted silicon due to progress of sintering. The nitriding temperature may be appropriately adjusted so that the shrinkage ratio falls within the above range.

The calcination is preferably performed at a pressure of 2 atm or less, particularly at normal pressure. When the pressure is higher than 2 atm, the pores are easily crushed at the time of firing, and the grindability decreases.

Then, the molded body subjected to the heat treatment is
It is important to fire at a temperature of 700 to 1900 ° C. In particular, 1750 to 1850C is preferable. Thus, by firing at a relatively low temperature, it is possible to form fine and uniformly distributed pores, and to produce a stationary member for a heat engine with improved grindability without significantly impairing mechanical characteristics. Can be.

The sintered body thus obtained has good free-cutting properties and excellent oxidation resistance and mechanical properties. Therefore, when it is used for a stationary member for a heat engine such as a turbine shroud, the sintered body may not be compatible with a turbine rotor. It is possible to enhance stability during long-time operation without damaging the turbine rotor during contact sliding.

[0046]

EXAMPLE A silicon nitride powder having an average particle size of 0.5 μm and an α conversion of 90% or more, and a silicon powder having an average particle size of 5 μm were used as sintering aids. An oxide powder of an element of the group III was added, and each was prepared so that the composition of the molded body became the composition shown in Table 1.

Next, the powder mixed, ground and dried in a rotary mill for 72 hours was molded by a mold press at 100 MPa, and the obtained molded body was heat-treated under the conditions shown in Table 1 under a normal pressure of nitrogen under nitrogen. The dimensions of the treated body before and after the nitriding treatment were measured with a vernier caliper, and the shrinkage (= size after firing / dimension before firing × 100) was calculated and then fired.

The pore distribution of the obtained sintered body was measured by a mercury intrusion method. Also, the surface of the sintered body was mirror-finished, and the processed surface was observed by SEM to measure the pore diameter within a range of 110 μm × 90 μm from the photograph,
The average pore diameter and the maximum pore diameter were determined.

The main crystal phase of the sintered body was identified by X-ray diffraction, and the Vickers hardness ( _Hv ) at room temperature was measured. Also, the obtained sintered body was 5 mm × 5 mm × 4
A sample was prepared by processing the sample to 0 mm, and the oxidation increase was measured by holding the sample in the air at 1500 ° C. for 100 hours.
Less than 1.00 mg / cm ² was regarded as good.

Further, a turbine shroud opposed to a turbine rotor made of a silicon nitride sintered body having a room temperature strength of 1000 MPa and a hardness of 15 GPa was manufactured using the sintered body. Then, it was tested whether or not the turbine blade was damaged by rotating the turbine rotor at 40,000 rpm. The results are shown in Tables 1 and 2.

[0051]

[Table 1]

[0052]

[Table 2]

In the sample No. of the present invention, 3 to 10, 12, 1
3, 16-18, 20, 21, 24, 25, 28 and 2
9 has a total content of Al, Ca and Fe of 0.08 to
1.2% by weight, and the central pore diameter is 0.07 to 0.4μ
m, average pore size is 1.1 to 4.4 μm, maximum pore size is 2
At 8 μm or less and the weight gain of oxidation was 0.9 mg / cm ² or less, no blade damage was observed.

On the other hand, the total content of Al, Ca and Fe was as small as 0.01% by weight, and the shrinkage during the heat treatment was small. 19 had no wing damage,
The oxidation weight gain was as large as 1.3 mg / cm ² .

In addition, the total content of Al, Ca, and Fe was as large as 2% by weight, and the sample No. which was out of the range of the present invention and had a large shrinkage during heat treatment. 22 has an oxidation weight increase of 2.3 mg / cm ²
The wing was damaged.

Further, Sample No. having a central pore diameter of 0.008 μm or less and an average pore diameter of 0.9 μm or less, which is outside the range of the present invention. In 1, 2, 14 and 30, the wing was damaged.

Further, Sample No. having a maximum pore diameter of 35 μm or more was used. In Nos. 11 and 27, there was no blade damage, but the weight gain by oxidation was as large as 1.2 mg / cm ² or more.

The sample No. having a center pore diameter of 0.008 μm and an average pore diameter of 7 μm, which is outside the range of the present invention. 15 is
Wings were damaged.

The sample No. having a heat treatment temperature as high as 1600 ° C. In No. 26, Si was melted during the heat treatment. Further, Sample No. having a low heat treatment temperature of 1050 ° C. 23 is
Since Si was not nitrided by the heat treatment, Si was melted during firing.

[0060]

The stationary member for a heat engine of the present invention is made of a sintered body containing silicon nitride as a main component, and has a central pore diameter of 0.01 to 0.5 μm and an average pore diameter of 1 to 1 in a mercury intrusion method. 5
μm, the maximum pore diameter is 30 μm or less, and by uniformly dispersing small pores in the sintered body, the free cutting property is improved without greatly deteriorating the mechanical properties and oxidation resistance of the dense body, and It is possible to adjust the gap between the members or reduce the processing cost, and it is possible to realize a highly reliable product that is hardly damaged even if there is contact between the members.

Claims (7)

[Claims] 1. A sintered body containing silicon nitride as a main crystal phase, containing excess oxygen, a Group 3a element of the periodic table, and containing a total of 0.05 to 1.5% by weight of Al, Ca and Fe. The central pore diameter in the mercury intrusion method is 0.01 to 0.5 μm,
A stationary member for a heat engine, having an average pore diameter of 1 to 5 μm and a maximum pore diameter of 30 μm or less. 2. The sintered body has a Vickers hardness of 10 to 13.
The stationary member for a heat engine according to claim 1, wherein the stationary member is GPa. 3. The periodic table contains a Group 3a element in an amount of 1 to 10 mol% in terms of oxide, and excess oxygen in a proportion of 25 mol% or less in terms of silica (SiO ₂ ). terms of oxide amount of the group 3a element (RE ₂ O ₃₎ in terms of silica of excess oxygen to the molar ratio of _{(SiO 2) SiO 2 / RE} 2
Claim 1 or 2 heat engine for still member, wherein the O ₃ is 2-3. 4. A silicon nitride powder, a silicon powder and a sintering aid, wherein Al, Ca and Fe are contained in a total amount of 0.05 to 1.5% by weight.
A molded body containing the molded body is prepared, and the molded body is heat-treated in an atmosphere containing nitrogen gas to nitride the silicon and to reduce the shrinkage of the molded body to 92 to 99%. A method for producing a stationary member for a heat engine, characterized by firing at a temperature of: 5. The silicon nitride (Si) contained in said compact.
₃ N The process of claim 4 thermal engine for a stationary member according to the weight ratio Si / Si ₃ N ₄ is equal to or less than 0.3 silicon (Si) for _4). 6. The method for manufacturing a stationary member for a heat engine according to claim 4, wherein the heat treatment is performed at 1100 to 1500 ° C. 7. The method for manufacturing a stationary member for a heat engine according to claim 4, wherein the firing is performed at a pressure of 2 atm or less.