JPH10218674A - Forming method of silicon nitride ceramics - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a proper structure suitable for functions of which each part takes charge in each part of silicon nitride-based ceramic. SOLUTION: Silicon nitride-based raw material powder is prepared by mixing (a1), the mixed powder is packed into a mold jig and hot-pressed (a2), the hot- pressed sintered compact is subjected to first hot working and crystal grain is orientated in a fixed direction (a3). A part of the sintered compact subjected to the first hot-working is subjected to second hot-working to form an oriented structure of crystal grain in a given direction different from that of the first hot working. Consequently, since each part is provided with a crystal grain orientated structure in which the crystal grain is oriented in the fixed direction, mechanical properties are improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a silicon nitride-based ceramic, and more particularly to a multi-step forming method for forming a predetermined crystal grain orientation structure in each portion of a silicon nitride-based ceramic sintered body.

[0002]

2. Description of the Related Art In recent years, silicon nitride ceramics (including sialon ceramics) have excellent properties such as high strength, high heat resistance, low specific gravity, high corrosion resistance and high thermal shock resistance. It is attracting attention as a material for use. 2. Description of the Related Art Conventionally, mechanical parts made of silicon nitride-based ceramics have been manufactured by a method of sintering after molding raw material powder by die molding or the like. However, since such a method involves shrinkage due to sintering, parts requiring high precision require further machining such as cutting, grinding, and polishing, and problems remain in terms of productivity and cost. .
Therefore, development of a molding method that can solve these problems is desired. On the other hand, recently, a molding method utilizing superplasticity has been proposed for silicon nitride ceramics. For example, JP-A-8-104571 discloses that a silicon nitride-based ceramics sintered body can be formed by superplasticity under controlled temperature and strain rate. According to the plastic working utilizing such superplasticity, the silicon nitride-based ceramics can be accurately formed into a predetermined shape without going through a conventional machining process, and therefore, it is made of silicon nitride-based ceramics. The productivity of machine parts can be improved.

[0003]

As described above, since silicon nitride ceramics can be formed by superplasticity, machining after sintering can be omitted, and problems associated with machining can be solved. can do. However, mechanical parts produced by superplastic working have a problem of so-called anisotropy in which mechanical properties vary depending on the direction, because crystal grains are oriented in the direction of plastic flow by forming. As a result, the applicable range of the mechanical component is limited. The present inventors have conducted detailed studies on the above problem, and as a result, performed multi-stage superplastic forming on the silicon nitride-based ceramics sintered body, and obtained a crystal grain of each portion of the sintered body at each forming stage. It has been found that the above problem can be solved by orienting the particles in a predetermined direction.

The present invention has been completed based on the above findings, and an object of the present invention is to provide a silicon nitride-based ceramic sintered body with a crystal grain oriented structure suitable for each part in accordance with its function. It is intended to provide a method for forming a silicon nitride-based ceramic which can form a ceramic.

[0005]

According to the present invention, a silicon nitride-based raw material powder is formed and sintered to form a temporary sintered body or a sintered body. A molding process is performed, and a plastic flow is generated in at least a part of the pre-sintered body or the sintered body at each forming step so that the orientation direction of crystal grains in each part of the pre-sintered body or the sintered body is set in a predetermined direction. A method for forming a silicon nitride ceramic. According to the present invention, the preliminary sintered body or the sintered body is sequentially subjected to a multi-stage molding process, so that at least a portion of the temporary sintered body or the sintered body undergoes plastic deformation at each molding stage. Occurs. Therefore, by controlling the plastic flow direction of each portion of the temporary sintered body or the sintered body, the orientation direction of the crystal grains of each portion can be oriented in a predetermined direction. Normally, the tensile strength of a crystal in silicon nitride ceramics in a direction parallel to the orientation direction and the bending strength and toughness in a direction perpendicular to the orientation direction are the tensile strength and the bending strength in other directions. And higher strength than toughness, and high toughness,
By forming the oriented structure in a predetermined portion, strength and toughness in a plurality of predetermined directions can be improved. As a result, it is possible to impart, to each portion of the silicon nitride-based ceramic, a characteristic according to the function of each portion.

Further, the silicon nitride-based raw material powder of the present invention comprises one or a combination of α silicon nitride powder, α sialon powder, β silicon nitride powder, β sialon powder and sintering aid powder. Features. According to the present invention, a plurality of types of the silicon nitride-based raw material powder can be used, and the applicable range of the raw material powder is wide. Therefore, an appropriate raw material powder is selected and used according to the required characteristics of the silicon nitride-based ceramic. can do.

[0007] Further, the present invention provides that the relative density of the sintered body is 9
It is not less than 5%. According to the present invention, the relative density can be further increased by performing, for example, superplastic working on the high-density sintered body having a relative density of 95% or more before the multi-step forming. . Further, by performing the superplastic working, fine defects inside the sintered body can be eliminated. as a result,
The strength and toughness of silicon nitride-based ceramics can be greatly improved.

Further, the present invention is characterized in that the relative density of the temporary sintered body is 70 to 95%. According to the present invention, the relative density of the pre-sintered body before the multi-stage forming is 70%.
Since the density is as low as ~ 95%, the deformability at the time of multi-stage molding is increased. Therefore, for example, by performing superplastic working, the degree of orientation of the crystal grains of the temporary sintered body can be greatly increased. In addition, the relative density can be improved at the same time as the degree of orientation of the crystal grains is improved.

The forming process of the pre-sintered body or the sintered body of the present invention is selected from hot compression working, hot rolling working, hot extrusion working and hot stretching working at each forming stage. And one or more processing methods. According to the present invention, the multi-stage molding of the temporary sintered body or the sintered body is performed by one or a plurality of processing methods selected for each molding step from a plurality of processing methods. Therefore, all of the molding steps may be performed by hot compression processing, the first step is performed by hot extrusion processing, the second step is performed by hot compression processing, and the third step is performed by hot tension processing. You may. As described above, the multi-stage molding of the temporary sintered body or the sintered body can be performed by using a processing method selected from a plurality of processing methods for each molding step. Alternatively, the sintered body can be formed into various shapes. As a result, the applicable range as a machine part can be greatly expanded.

[0010]

FIG. 1 is a flow chart showing a method for forming a silicon nitride-based ceramic according to a first embodiment of the present invention. FIG. FIG. 3 is a schematic diagram showing the direction of plastic flow. In the present embodiment, the silicon nitride-based ceramic is formed as follows. In step a1, a raw material powder is prepared, and a silicon nitride-based powder and a sintering aid are mixed. In step a2, the mixed powder is filled in a mold jig, and hot pressing is performed.
In step a3, the first-stage hot working is performed on the hot-pressed silicon nitride-based ceramic sintered body (hereinafter, may be simply referred to as a “sintered body”) by hot compression superplastic working, The crystal grains of the sintered body are oriented in a predetermined direction by plastic flow. In step a4, a second stage of hot working is performed on a part of the sintered body by hot compression superplastic working, and a crystal in a predetermined direction different from that of the first stage of hot working is formed on a part of the sintered body. An oriented texture of the grains is formed.

The silicon nitride raw material powder comprises one or a combination of α silicon nitride powder, α sialon powder, β silicon nitride powder, β sialon powder and sintering aid powder. Alpha silicon nitride usually contains a small amount of oxygen,
The composition is expressed as Si ₃ N _{4 to} Si _11.5 N ₁₅ O _0.5 .
The grains of α silicon nitride are equiaxed,
At a temperature of 00 ° C. or more, phase transition to β silicon nitride occurs. β-silicon nitride is stable at high temperatures and low oxygen partial pressures, and is compositionally represented as Si ₃ N ₄ . The crystal grains of β silicon nitride are rod-shaped or columnar. Note that α silicon nitride and β silicon nitride are mixed and synthesized at the time of powder synthesis.
The content of silicon nitride is 90% or more. Sialon is a material in which Si and N in Si ₃ N ₄ are partially substituted with Al and O, and has two types of crystal types, α-type and β-type. The sintering aid is a sintering accelerator, such as Mg, Al, Y, Sc, L
It consists of one or more combinations of oxides or nitrides of a, Ce, Be, Zr. As described above, a plurality of types of silicon nitride-based raw material powders can be used, and the applicable range of the raw material powders is wide, so that it is possible to select and use an appropriate raw material powder according to the required characteristics of the silicon nitride-based ceramics. it can. Next, the processing content of each step will be described more specifically.

The raw material powder used in the step a1 is composed of, for example, α silicon nitride powder and β silicon nitride powder which are silicon nitride-based powders, and Y ₂ O ₃ powder and Al ₂ O ₃ powder which are sintering aids. Become. The α and β silicon nitride powders are synthesized by nitriding metal silicon powder in ammonia gas. The content ratio of α silicon nitride in the synthetic powder is, for example, 95%. Further, in preparing the silicon nitride-based raw material powder in step a1, 5 wt% of Y ₂ O ₃ and 3 wt% of Al ₂ O ₃ are added to the synthetic powder as a sintering aid, and the resulting mixture is subjected to ball milling in methanol at 750 rpm. This is done by mixing for 3 hours.

In the hot pressing in the step a2, after filling the mixed powder into a carbon mold, a temperature: 1600 ° C., a time: 2 hours, and a molding pressure: 30 MPa
a, Atmosphere: It is performed under the condition of atmospheric pressure nitrogen. During hot pressing, the sintering aid reacts with SiO ₂ present on the surface of the silicon nitride particles to generate a liquid phase by heating, α
The silicon nitride particles dissolve in the liquid phase, precipitate on undissolved β silicon nitride particles, and grow. The α-silicon nitride particles undergo a phase transition to β-silicon nitride during the dissolution, precipitation, and grain growth processes, and the generated β-silicon nitride particles grow in a rod shape, form an entangled structure, and provide mechanical properties of the sintered body. Improve. The sintering aid is added to the raw material powder,
This is for promoting the liquid phase sintering.

Usually, when there are many α particles, sintering proceeds rapidly through the phase transformation from α to β. In addition, by controlling the amount and shape of the β silicon nitride particles serving as nuclei for grain growth, it is possible to control the structure formation after sintering. By controlling the ratio and shape of the α and β particles in this manner, it is possible to manufacture a temporary sintered body that is an appropriate sintered body or a low-density sintered body.

The sintered body 1 is formed by the hot pressing. The shape of the sintered body 1 is, for example, a cube as shown in FIG.
1: 100 mm, width W1: 100 mm, length L1: 10
0 mm. For convenience of explanation, the height direction is indicated by an arrow 2,
The width direction is indicated by an arrow 6 and the length direction is indicated by an arrow 4.
The relative density of the sintered body 1 is, for example, 97%. The relative density of the sintered body 1 is preferably 95% or more, as described later. The sintered body 1 may be formed by molding a green compact instead of the hot press and subsequently sintering the compact.

The first stage hot working in step a3 is as follows:
The sintered body 1 is inserted into the mold jig 3 and hot-compressed in the height direction 2 under superplastic working conditions in a state where the deformation in the width direction 6 is restrained as shown by oblique lines in FIG. This is done by processing. 2 (2) and FIG. 2 (4) to be described later show a front view, and a right view shows a side view. The superplastic working conditions are preferably a forming temperature of 1300 to 2300 ° C. and a strain rate of 10 ⁻¹ / sec or less. 180
At 0 ° C. or higher, molding is performed in a nitrogen gas pressurized atmosphere to prevent sublimation decomposition of silicon nitride. This is because if the molding temperature is lower than 1300 ° C., the molding speed becomes slow, and the molding efficiency is reduced.
This is because sublimation decomposition of silicon nitride may occur.
Further, the reason why the strain rate is set to 10 ^-1 / sec or less is that if the strain rate exceeds that, a cavity is generated in the sintered body 1 during molding,
This is because superplastic deformation cannot be performed up to a predetermined strain amount. The preferable molding temperature range is 1350 to 200
The range is 0 ° C., and the preferred strain rate is 10 ⁻² / sec or less.

The molding pressure is appropriately controlled within the range of 2 to 100 MPa so that the strain rate is 10 ^-1 / sec or less depending on the molding temperature. The molding atmosphere is preferably a non-oxidizing atmosphere, preferably a nitrogen gas atmosphere. Molding in an oxidizing atmosphere is not preferred because oxidation of silicon nitride occurs. The material of the mold jig is preferably ceramics, graphite or the like. As an example of the present embodiment, the superplastic working conditions are as follows: atmosphere: atmospheric pressure nitrogen, forming temperature: 1750 ° C., strain amount: 50%, working time: 1.5 hr, and the mold jig used is made of SiC. It is.

By the first-stage hot working, plastic flow is generated in the sintered body 1 in the longitudinal direction 4 as shown in FIG. 2 (2), and as a result, the overall shape of the sintered body 1 is changed. As shown in FIG. 2 (3), it is formed in a substantially rectangular parallelepiped. The dimensions of the sintered body 1 after the forming are, for example, a height H2: 50 mm and a width W1: 1.
00 mm, length L2: 200 mm, and its relative density is 98%. Further, the crystal grains of the sintered body 1 are oriented in the plastic flow direction by the plastic flow. As described above, since the crystal phase of the sintered body 1 has undergone a phase transition to β silicon nitride,
In the sintered body 1, a crystal grain oriented structure is formed in which the longitudinal direction of the rod-like crystal grains of β silicon nitride is oriented in the direction of an arrow 5 parallel to the length direction 4 of the sintered body 1.

The second stage of hot working in step a4 is as follows:
The sintered body 1 after the first-stage hot working is inserted into the mold jig 3, and the sintered body 1 is partially hot-pressed under superplastic working conditions as shown in FIG. This is done by: That is, in the second-stage hot compression working, the sintered body 1 is divided into a multi-stage molded portion 1a and a one-stage molded portion 1b, and the one-stage molded portion 1b is hatched in FIG. The entire outer peripheral surface is restrained by the mold jig 3. The multi-stage molded portion 1a is restrained in the height direction 2 and is hot-compressed in the length direction 4. As a result, plastic flow occurs in the width direction 6 in the multi-stage formed portion 1a of the sintered body 1 as shown in FIG. 2 (4), and as a result, the overall shape of the sintered body 1 becomes as shown in FIG. As shown, it is formed in a substantially T-shape.

The dimensions of the sintered body 1 after the second-stage hot compression working are, for example, a height H2: 50 mm and a width W1: 100 m.
m, width W2: 200 mm, length L3: 100 mm, and length L4: 50 mm, and the relative density of the multi-stage formed part 1a after the second-stage hot compression working is 99%. Further, a crystal grain oriented structure in which the longitudinal direction of the rod-shaped crystal grains is oriented in the direction of an arrow 7 parallel to the width direction 6 of the sintered body 1 is formed in the multi-stage formed portion 1a of the sintered body 1 by the plastic flow. You. On the other hand, since the grain forming structure in which the longitudinal direction of the rod-like crystal grains is oriented in the direction indicated by the arrow 5 has already been formed in the single-stage formed portion 1b, the multi-stage formed portion 1a and the single-stage formed portion 1b have already been formed. As shown in FIG. 2 (5), a grain-oriented structure in a curved arrow 8 direction is formed at a boundary portion with the formed portion 1b.

As described above, in the present embodiment, since the sintered body 1 is subjected to multi-stage molding, plastic deformation occurs in the whole or a part of the sintered body at each molding stage. Therefore, if the plastic flow direction of each part of the sintered body 1 is controlled in a predetermined direction in each molding step, the crystal in which the crystal grains are oriented in a predetermined direction is formed in each part of the sintered body 1. A grain-oriented structure is formed. Further, the tensile strength for the force in the direction parallel to the orientation direction of the crystal grains, and the bending strength and toughness for the force in the direction perpendicular to the orientation direction are more than the tensile strength, the bending strength and the toughness for the force in the other direction. Since it has high strength and high toughness, the strength and toughness of the sintered body in a plurality of predetermined directions can be improved by forming the crystal grain oriented structure in a predetermined portion of the sintered body. In addition, even if a crack that progresses in the direction perpendicular to the crystal grain orientation direction occurs due to the formation of the crystal grain orientation structure, the crack progress direction changes in the direction along the crystal grain orientation direction. Straight traveling is hindered, and the crack penetration depth is reduced. Further, as described above, the relative density of the sintered body 1 after hot pressing is 95%.
% Or more, the relative density of the sintered body 1 is further increased by the subsequent multi-stage molding. As a result, the overall strength level of the sintered body 1 is greatly improved.

FIG. 3 is a schematic view showing the arrangement of turbine blades made of silicon nitride ceramics according to the present invention, and FIG. 4 is a schematic view showing the state of attachment of the turbine blade shown in FIG. Referring to FIG. 3 and FIG.
A specific application example of the silicon nitride ceramics subjected to the multi-stage forming process shown in FIG. 1 will be described. The turbine blade 13 is made of silicon nitride-based ceramics, and is equally spaced in the circumferential direction on the outer peripheral surface of the turbine disk 14.
In addition, they are radially mounted so as to protrude radially outward from the outer peripheral surface. The turbine blade 13 is composed of a base 15 extending in the circumferential direction of the turbine disk 14 and a blade 16 extending in the radial direction of the turbine disk 14. This is the same as the sintered body 1 shown in 2 (5). That is, the base 15 of the turbine blade 13 corresponds to the multi-stage formed portion 1a shown in FIG. 2 (5), and the wing portion 16 of the turbine blade 13 corresponds to the single-stage formed portion 1b shown in FIG. 2 (5). Therefore, a crystal grain oriented structure extending in the circumferential direction of the turbine disk 14 is formed at the base 15 of the turbine blade 13, and the blade 1 of the turbine blade 13 is formed.
6, a crystal grain oriented structure extending in the radial direction of the turbine disk 14 is formed. The base 15 and the wing 1
At the boundary 17 with the surface 6, a curved crystal grain oriented structure is formed.

As described above, the tensile strength with respect to the force in the direction parallel to the grain structure and the bending strength and toughness with respect to the force in the direction perpendicular to the texture are defined as the tensile strength and the bending strength with respect to the force in other directions. Since the strength and toughness are higher than the strength and toughness, the wing portion 16 can overcome the centrifugal force generated in the radial direction during rotation. Further, for the same reason, the base portion and the boundary portion 17 can overcome a run-out that occurs in the circumferential direction during rotation. Further, as described above, the formation of the crystal grain oriented structure reduces the crack penetration depth in the direction perpendicular to the crystal grain orientation direction, so that the durability of the turbine blade 13 can be improved. As described above, the turbine blade 13 has extremely excellent mechanical properties, and thus can be suitably used as a high-performance turbine component.

As described above, since silicon nitride ceramics can freely form a predetermined crystal grain orientation structure in each portion by multi-stage molding, the characteristics according to the function of each portion can be obtained. It can be given every time. As a result, it can be applied to a wide range of uses as a mechanical part.

FIG. 5 is a flowchart showing a method of forming a silicon nitride ceramic according to a second embodiment of the present invention, and FIG. 6 shows the shape transition and the plastic flow direction of the silicon nitride ceramic by forming. FIG. In the present embodiment, the silicon nitride ceramic is formed as follows. In step b1, a raw material powder is prepared. The processing contents of step b1 are exactly the same as the processing contents of step a1 shown in FIG. In step b2, hot pressing is performed. The processing content of step b2 is exactly the same as the processing content of step a2 shown in FIG. 1 except for the shape of the sintered body. The shape of the sintered body 21 after hot pressing is shown in FIG.
It is cylindrical as shown in (1). In step b3,
Hot extrusion processing is performed on the sintered body 21 by superplastic processing. The hot extrusion causes plastic flow in the sintered body 21 in the longitudinal direction 23, and as a result, the sintered body 21
Is formed in a rod shape as shown in FIG. 6 (2). Further, since the crystal grains of the sintered body 21 are oriented in the plastic flow direction by the plastic flow, a crystal grain oriented structure in which the longitudinal direction of the crystal grains is oriented in the length direction 23 is formed in the sintered body 21. .

In step b4, a part of the sintered body 21 is subjected to hot compression working by superplastic working. In the compression processing in step b4, the sintered body 21 is divided into a multi-stage molded portion 21a and a one-stage molded portion 21b, and the one-stage molded portion 21b is inserted into the mold jig 24, and is hatched in FIG. The entire outer peripheral surface is restrained by the mold jig 24 as shown by. On the other hand, the multi-stage molded portion 21a is hot-compressed in the length direction 23 in a free state without any restraint. Thereby, the multi-stage molded portion 2 of the sintered body 21 is formed.
6A, plastic flow occurs in the radial direction 26 and the circumferential direction 27 as shown in FIG. 6D, and as a result, the entire shape of the sintered body 21 is substantially flat rivet-shaped as shown in FIG. Formed. Further, since the crystal grains of the multi-stage formed portion 21a of the sintered body 21 are oriented in the plastic flow direction by the plastic flow, the longitudinal direction of the crystal grain is formed in the multi-stage formed portion 21a,
A crystal grain oriented structure oriented in the radial direction 26 and the circumferential direction 27 is formed. On the other hand, the crystal grain oriented structure formed by the extrusion process remains in the first-stage formed portion 21b. Thus, the sintered body 2
In the first multi-stage forming process, even if hot extrusion is performed as the first-stage forming process, crystal grains are oriented in a predetermined direction in each part of the sintered body as in the first embodiment. An oriented grain oriented structure is formed.

As is apparent from the first and second embodiments, the multi-stage forming of the sintered body of the present invention is performed by a plurality of working methods, for example, hot compression, hot rolling, hot rolling, and the like. It can be carried out by one or a plurality of working methods selected for each molding step from among inter-extrusion processing, hot tension processing and the like. Therefore, the multi-stage molding may be performed by hot compression at each stage as in the first embodiment, and the first stage may be performed by hot extrusion as in the second embodiment, The second step may be performed by hot pressing. Further, as a third step, hot stretching or hot rolling may be performed as necessary. As described above, since the multi-stage molding of the sintered body can be performed using a processing method selected from a plurality of molding methods for each molding step, the sintered body is molded into various shapes. be able to. As a result, the applicable range as a machine part can be greatly expanded.

Next, as a third embodiment of the present invention, a multi-stage molding process may be performed using a temporary sintered body that is a low density sintered body. In the present embodiment, it is preferable that the relative density of the temporary sintered body is selected in a range of 70 to 95%. Since the provisional sintered body having the relative density has a large deformability during the subsequent multi-stage molding, the degree of orientation of the crystal grain orientation structure of the sintered body formed by the multi-stage molding is significantly increased. Can be enhanced. Further, the relative density can be improved at the same time as the degree of orientation of the crystal grain oriented structure is improved. Furthermore, the provisional sintered body having the above-mentioned relative density has a low relative density, so that it is easy to manufacture, and the productivity and cost can be greatly improved.

The relative density of the pre-sintered body was selected to be in the range of 70 to 95%, because if the relative density exceeds 95%, productivity and cost advantages are lost.
If the relative density is less than 70%, it is difficult to sufficiently increase the relative density in the subsequent multi-stage molding. The provisional sintered body having the relative density is produced by filling a silicon jig-based raw material powder into a mold jig, press-molding, and sintering the molded body under normal pressure.
The sintering temperature of the normal pressure sintering is 1450 to 1800 ° C,
The relative density of the temporary sintered body is adjusted by the sintering temperature and the sintering time. In addition, sintering may be performed under a pressurized atmosphere of nitrogen gas in order to prevent decomposition of silicon nitride and the sintering aid during sintering. Further, the multi-stage molding of the present embodiment may be performed by the same method as in the first embodiment, or may be performed by the same method as in the second embodiment.

In the first to third embodiments, whiskers or particles are added to the raw material powder to form the temporary sintered body or the sintered body, and the temporary sintered body is formed while suppressing the growth of crystal grains. The sintered body or the sintered body may be subjected to a multi-stage forming process. In this case, a silicon nitride whisker or a silicon carbide whisker can be used as the whisker, and fine particles of silicon carbide can be used as the particles.

Next, as a fourth embodiment of the present invention, a pre-sintered body or a sintered body (hereinafter abbreviated as "oriented structure sintered body") having a crystal grain oriented structure already formed is used. Multi-stage molding may be performed. The oriented texture sintered body is manufactured by adding the particles or whiskers to a silicon nitride-based raw material powder, performing sheet molding or injection molding to form a molded body, and sintering the molded body. Alternatively, it may be manufactured by performing sintering forging. In the present embodiment, the multi-stage forming process is further performed on the oriented structure sintered body to form a silicon nitride-based ceramic. As a result, the crystal grain orientation structure of the silicon nitride-based ceramics is further variously formed, so that characteristics corresponding to the functions of the respective portions of the silicon nitride-based ceramics can be imparted more finely to each portion. As a result, applications of the silicon nitride-based ceramics are further expanded. In addition, since the multi-stage forming process can be performed as a finishing process, the crystal grain orientation structure of the silicon nitride-based ceramic can be controlled with high precision so as to match the desired orientation structure.

[0032]

As described above, according to the present invention, the orientation direction of the crystal grains of each portion of the silicon nitride ceramics can be oriented in a predetermined direction.
Characteristics according to the function assigned to each part can be provided. As a result, the applicable range of the silicon nitride-based ceramics as a mechanical part can be greatly expanded.

According to the present invention, a plurality of types of silicon nitride-based raw material powders can be used, and the applicable range of the raw material powders is wide. Therefore, an appropriate raw material powder can be selected according to the required characteristics of the silicon nitride-based ceramics. Can be used.

Further, according to the present invention, it is possible to further increase the relative density by subjecting a high density sintered body having a relative density of 95% or more before the multi-stage forming to superplastic working during the multi-stage forming. it can. As a result, the strength and toughness of the silicon nitride-based ceramic can be significantly improved.

Further, according to the present invention, since the relative density of the pre-sintered body before the multi-stage forming is a low density of 70 to 95%, the deformability during the multi-stage forming is increased. Therefore, by performing the superplastic working, the degree of orientation of the crystal grains of the temporary sintered body can be greatly increased. In addition, the relative density can be improved at the same time as the degree of orientation of the crystal grains is improved.

Further, according to the present invention, the multi-stage molding of the pre-sintered body or the sintered body is performed by hot-pressing,
Since it can be performed by using a processing method selected from hot rolling, hot extrusion, and hot tensioning, the pre-sintered body or the sintered body can be formed into various shapes. . As a result, the applicable range as a machine part can be greatly expanded.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a method for forming a silicon nitride-based ceramic according to a first embodiment of the present invention.

FIG. 2 is a schematic diagram showing a shape transition of silicon nitride-based ceramics by hot compression and its plastic flow direction.

FIG. 3 is a schematic diagram showing an arrangement of turbine blades made of a silicon nitride-based ceramic according to the present invention.

FIG. 4 is a schematic view showing a mounting state of the turbine blade shown in FIG. 3;

FIG. 5 is a flowchart showing a method for forming a silicon nitride-based ceramic according to a second embodiment of the present invention.

FIG. 6 is a schematic diagram showing a shape transition of a silicon nitride-based ceramic by a forming process and its plastic flow direction.

[Explanation of symbols]

 1, 21 Sintered body 1a, 21a Multi-stage molded part 1b, 21b Single-stage molded part 3, 24 Mold jig 13 Turbine blade 14 Turbine disk 15 Base 16 Blade part 17 Boundary part

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Naoki Kondo 2-219 Mataho-cho, Nishi-ku, Nagoya-shi, Aichi Prefecture 2-219 Mataho 2-72 (72) Inventor Fumihiro Wakai 2--20 Konocho, Gifu-shi, Gifu ( 72) Inventor Mamoru Imuta 1 Kawasaki-cho, Kakamigahara-shi, Gifu Prefecture Inside the Kawasaki Heavy Industries Gifu Plant (72) Inventor Jun Goto 1 Kawasaki-cho, Kakamigahara City, Gifu Prefecture Inside the Gifu Plant Kawasaki Heavy Industries, Ltd.

Claims (5)

[Claims] 1. Forming and sintering a silicon nitride-based raw material powder to form a pre-sintered body or a sintered body, and subjecting the pre-sintered body or the sintered body to a multi-stage forming process, Each time, a plastic flow is caused in at least a part of the temporary sintered body or the sintered body to control the orientation direction of crystal grains in each part of the temporary sintered body or the sintered body in a predetermined direction. A method for forming silicon nitride ceramics. 2. The silicon nitride-based raw material powder comprises one or a combination of α silicon nitride powder, α sialon powder, β silicon nitride powder, β sialon powder, and a sintering aid powder. The method for forming a silicon nitride-based ceramic according to claim 1. 3. The method according to claim 1, wherein a relative density of the sintered body is 95% or more. 4. The relative density of the temporary sintered body is 70 to 95%.
The method for forming a silicon nitride-based ceramic according to claim 1, wherein: 5. The forming process of the pre-sintered body or the sintered body is selected from hot compression working, hot rolling working, hot extrusion working and hot stretching working at each forming step.
The method for forming a silicon nitride-based ceramic according to any one of claims 1 to 4, wherein the method is performed by a plurality of processing methods.