JPH0274571A - High strength/high toughness sintered body and its manufacturing method - Google Patents

Abstract

PURPOSE:To produce a sintered material having high strength and toughness by forming a crystal aggregate maintaining the form of fiber composed of crystals of SiC and Ti carbide. CONSTITUTION:Inorganic fibers composed of inorganic substances consisting of (A) an amorphous substance essentially composed of Si, M (Ti or Zr), C and O and/or (B) essentially beta-SiC, MC or solid solution of beta-SiC and MC having particle diameter of <=500Angstrom and/or (C) aggregate of crystalline fine particles of formula MC1-x (0<=x<1) and amorphous SiO2 and MO2 are laminated and formed to a prescribed form. Simultaneous to or after the forming, the material is heated and sintered at 1700-2200 deg.C in at least one kind of atmosphere selected from vacuum, inert gas, reducing gas and hydrocarbon. A sintered material composed of a crystal aggregate maintaining the form of fiber composed of the crystals of Si and MC1-x can be produced by this process.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a high-strength, high-toughness sintered body and a method for producing the same. It is used for engine parts such as piston rings, sub-combustion chambers, and Roken 1 engine parts such as nose cones and nozzles.

[Problems to be solved by conventional techniques and inventions] Conventionally,
Examples of ceramics with excellent heat resistance include AltO
Oxide-based such as J, B2O, MgO1ZrOz, 5t02, carbide-based such as S i C, T + C, W C, BaC, nitride-based such as 5IINa, BN, AfN, etc.
Boride-based materials such as TiBz and ZrBz, MoS
Silicide-based ceramics such as iZ, WSiz, and Cr5iz are known. These ceramic molded bodies have been manufactured at extremely high temperatures, but recently, sintering aids have been actively investigated with the aim of lowering the sintering temperature and sintering pressure. Sintering aids improve the sinterability of ceramics, suppress grain growth in sintered bodies, prevent pores from remaining between grains, and also play the role of densely filling grain boundaries. have.

Examples of additives conventionally used as sintering aids include M g O, N i O, C; i 0,'r
102,Δ! 203, Y2O3, [3, C, +3. C
The reason why these additives are selected is to assist in the sintering of ceramics that have poor self-sintering properties.
This is because sintering progresses more easily because a phase reaction occurs between the base ceramic and the additive, or because the additive becomes a plasticized liquid phase at high temperatures. Further, B and C have the function of lowering the surface energy of the SiC crystal and improving sinterability.

However, when a sintering aid is present as mentioned above,
It is thought that the second and third phases appear due to the reaction between the base ceramic and the auxiliary agent, and these exist mainly at the grain boundaries, and when the temperature rises, they are likely to be plastically deformed from these grain boundary constituents. In many cases, it is not possible to obtain a sintered body with high strength at high temperatures. For example, when MgO is added to Si, N,
A glassy phase of S i M g Oy is formed as the second phase, and high density is achieved by filling the grain boundaries, but the mechanical strength of this sintered body at high temperatures is due to the softening of the glassy phase. Therefore, the temperature decreases rapidly at about 1,000'C.

In order to prevent such a decrease in strength at high temperatures, it is best to choose an auxiliary agent that does not become vitrified, but such auxiliary agents generally have low sintering properties and cannot be used to produce a satisfactory molded product. can't get it.

As a method to eliminate the above-mentioned disadvantages, a specific organometallic nail combination is used as a binder for ceramic and cus i5) powder, and the mixture of both is heated and sintered to create a ceramic sintered material with less strength loss at high temperatures. A method of producing the aggregates has been proposed.

For example, Japanese Patent Publication No. 59-40786, No. 59-40
Publication No. 789 discloses a method for producing a sintered body by heating and sintering a mixture of metallocarbosilane and ceramic powder after or simultaneously with shaping. A similar method is
It is also described in Publications No. 6 and No. 60-9982.

The polymetallocarbosilane used as a binder for the ceramic powder in the method described in the above publication is converted into an inorganic substance when the mixture is heated and sintered, and since this inorganic substance has a high melting point, The sintered body produced has relatively high strength even at high temperatures. The reason is,
The sintered bodies obtained by the methods described in these publications were
As described in Publication No. 9-40789, column 9, lines 8 to 22, it is mainly composed of silicon carbide particles, a solid solution of both SiC and TiC1 produced by thermal decomposition of polytitanocarbosilane, and TiC+-x. This is because it consists of a grain boundary phase.

Regarding the strength of the sintered bodies obtained by the methods described in these publications, for example, in Example 1 of Japanese Patent Publication No. 59-40789, after molding a mixture of silicon carbide powder and polytitanocarbosilane, By sintering the material at 1,200℃, the bending strength (110゛ strength) is 13.0k.
g/mm" sintered body, and in Example 5, after preheating the above mixture at 600'C,
By crushing and hot pressing the crushed product at 1,800℃, the bending strength (flexural strength > 25.1 kg/t
m'' sintered body was obtained.

In recent years, engineering ceramics have come to be required to have higher functionality, and for example, there is a demand for sintered bodies that have high strength and have extremely low strength loss at high temperatures.

Therefore, the present inventors proposed Japanese Patent Application No. 62-279884,
Patent Application No. 62-279885 and Patent Application No. 62-279
No. 886, he provided an invention relating to a high-strength ceramic composite.

The sintered bodies obtained by these inventions all have excellent bending strength and heat resistance, and also have fracture toughness values that are higher than those of ordinary S.
It was superior to the iC sintered body.

However, a sintered body having even better fracture toughness is desired.

Therefore, an object of the present invention is to provide a high-strength, high-toughness sintered body that has excellent heat resistance, high mechanical strength at room temperature, extremely little strength loss even at high temperatures, and excellent toughness. and its manufacturing method.

[Means for Solving the Problems] The present invention provides SiC and M C, -, (M represents Ti or Zr, and X is a number of 0 or more and less than 1.

The above object has been achieved by providing a high-strength, high-toughness sintered body characterized by being composed of a crystal aggregate that maintains a fiber shape and is composed of crystals of (1) and (2).

Furthermore, the present invention provides the following manufacturing method as a preferred method for manufacturing the sintered body of the present invention.

The laminate-free fibers made of any of the vitreous substances listed below (i), (11), or (iii) are laminated, and this laminate is made of
1,700 to 2.200" in a vacuum, in an atmosphere consisting of at least one member selected from the group consisting of an inert gas, a reducing gas, and a hydrocarbon gas. SIC and MC, which are characterized by being heated and sintered in a temperature range of C, -, (M represents Ti or Zr, and X is a number of 0 or more and less than 1.

) A method for producing a high-strength, high-toughness sintered body composed of a crystal aggregate that maintains a fiber shape.

(i) Amorphous material consisting essentially of silicon, M, carbon and oxygen (11) Substantially βSi with a particle size of 500 Å or less each
Solid solution of C, MC1β-SiC and MC and/or crystalline fine particles of MC, -8 and amorphous Si 02
(iii) A mixed system of the amorphous material of (1) above and the aggregate of -) above (however, M in the above formula represents Ti or Zr, and X is 0
The number is greater than or equal to 1 and is less than 1. ) Hereinafter, first, the sintered body of the present invention will be explained.

The crystal aggregates that maintain the fiber shape constituting the ceramic sintered body of the present invention are lump-like, flake-like, and needle-like SiC
It is preferable to include at least one type of crystal and ultrafine particle crystals of SiC and TiC (or ZrC). Here, the lump-like shape preferably means a lump of grains grown in a three-dimensional direction with a side length of 1 to 20 μm, and the flake-like shape preferably means a scale-like shape with a length of 1 to 20 μm. , needle-like means a shape preferably having a length of 1 to 20 um and a length to thickness ratio of 1.5 to 20. Also,
The size of the ultrafine crystals is usually 500 Å or less.

The ceramic sintered body of the present invention preferably contains 40% by weight or more of SiC crystals in the form of lumps, flakes, or needles. If the amount of SiC crystals is too small, the strength of the sintered body will decrease. Further, the upper limit of the amount of the SiC crystal is usually 95% by weight.

Next, a method for manufacturing a ceramic sintered body according to the present invention will be explained.

(i), (11) or (iii) used as a raw material in the method for producing a ceramic sintered body of the present invention.
) has a thick self-sintering property (1,70% without adding a sintering aid).
A good sintered body can be obtained by processing at a temperature of 0 to 2,200°C.

The above-mentioned inorganic fibers may be polygitanocarbosilane or polyzirconocarbosilane produced by the method described in, for example, Japanese Patent Publications No. 60-14 (15), No. 5B-5286, No. 60-2 (1485). It is obtained by melt-spinning, infusible by heat treatment in air, and firing at 800 to 1,500°C in an inert gas.

The above R-free fibers may be used as chopped short fibers obtained by cutting continuous A fibers or continuous F fibers, or may be used as plain woven fabrics, three-dimensional woven fabrics, or nonwoven fabrics woven from continuous fibers. Furthermore, it may be used as a sheet-like product in which continuous fibers are aligned in one direction.

According to the manufacturing method of the present invention, since crystals preferentially develop inside the inorganic fibers, the crystals exhibit a crystal orientation that reflects the usage form of the fibers, and furthermore, the crystals are deformed to a state that can most effectively fill the fiber gaps. A ceramic sintered body, which is an aggregate, is obtained. For example, when the above-mentioned plain woven fabric is used as the a-free fiber, a sintered body in which the crystal aggregates retaining the fiber shape are oriented in the same manner as the plain-woven laminate is obtained; When a sheet-like material is used, a sintered body is obtained in which the crystal aggregates retaining the fiber shape are aligned in one direction, and the sintered body is oriented in the same manner as the sheet-like material laminate. When the original woven fabric is used, a sintered body is obtained in which the crystal aggregates retaining the fiber shape are oriented in the same manner as the three-dimensional woven fabric, and when the above-mentioned chopped short fibers are used as vA loom fibers, a sintered body is obtained. In this method, a sintered body in which crystal aggregates retaining the fiber shape are randomly arranged is obtained. In all of these sintered bodies, the fiber cross section of the crystal aggregates that retain the fiber shape is deformed into a polygonal state, etc., and the crystal aggregates that retain the fiber shape are separated from each other without a matrix intervening. , obtained as well bonded or adhered.

Therefore, in the present invention, the ceramic sintered body of the present invention having excellent performance is produced by creating a laminate of inorganic fibers, then molding it into a desired shape, or heating and sintering it simultaneously with the molding. can be obtained.

As a method for performing sintering, a method in which the laminate is primarily formed and then sintered under pressure, normal pressure, or reduced pressure, or a hot press method in which forming and sintering are performed simultaneously can be used.

In the method of performing the subsequent forming and sintering separately, the subsequent forming is performed for 100 to 100 seconds using a mold press method, a rubber press method, an extrusion method, or a sheet method.

It is possible to obtain a predetermined shape (for example, sheet-like, rod-like, spherical shape, etc.) by applying pressure at a pressure of kg/cIil.

In addition, in the above molding, if necessary, polycarbosilane or polytitanocarbosilane, which is a raw material for inorganic fibers,
Polyzirconocarbosilane or commercially available organic polymers may be used as the binder. Next, the ceramic sintered body of the present invention can be obtained by sintering the molded body.

In addition, when sintering is performed using the Hontopress method, a press mold made of graphite is sprayed with BN as a mold release agent, and while pressing the laminate at a pressure of 2 to 2.000 kg/cIil, It can be heated simultaneously to form a sintered body.

The heating sintering temperature is 1,700-2.200°C, preferably 1.900-2.100'C. By heating to this temperature, SiC can be formed into lumps, flakes or needles.
Crystals are formed, and these SiC crystals are uniformly dispersed in an aggregate of ultrafine particles of SiC and TiC or ZrC.
A highly tough ceramic sintered body is obtained. If the heating sintering temperature is lower than 1,700℃, S will be lumpy, flaky or needle-like.
If iC crystals are not generated and a high-strength sintered body cannot be obtained, and if the heating sintering temperature is higher than 2.200° C., the generated SiC crystals will decompose. The heating and sintering is performed in a vacuum and in an atmosphere consisting of at least one selected from the group consisting of an inert gas, a reducing gas, and a hydrocarbon gas. Examples of inert gases include nitrogen gas and carbon dioxide gas; examples of reducing gases include atomic gases and carbon oxide gas; and examples of hydrocarbon gases include methane gas and ethane gas. , propane gas, butane gas, etc.

The ceramic sintered body of the present invention exhibits extremely high strength at room temperature compared to known ceramic sintered bodies, and further shows almost no decrease in strength even at high temperatures (2 to 10
It has about twice the fracture toughness value. Note that the oxygen and non-stoichiometric amount of carbon contained in the inorganic fibers are 2C+5iO−>SiC+C0,3C+5i during the above sintering.
It is separated by the reaction of Oh→SiC+2CO and does not remain in the sintered body. This lowers the surface energy of the SiC particles and improves sinterability.

Further, in order to completely remove the glassy SiO, a small amount of carbon may be added during the above molding.

Furthermore, if necessary, the laminate before sintering is impregnated with polycarbosilane, polytitanocarbosilane, polyzirconocarbosilane, or a silane coupling agent, which is a raw material for inorganic fibers, and then the laminate is impregnated with a silane coupling agent in a vacuum. 800 to 500°C in an atmosphere consisting of at least one selected from the group consisting of active gas, reducing gas, and hydrocarbon gas.
After preheating at 1,000 to 2,200"C, sintering may be carried out at 1,000 to 2,200"C.

〔Example〕

The present invention will be explained below with reference to Examples.

(Reference example 1) Anhydrous xylene 2.54 in a 5N three-lough flask! and 400 g of sodium were added thereto, heated to the boiling point of xylene under a nitrogen gas stream, and dimethyldichlorosilane 11 was added dropwise over 1 hour. After the dropwise addition was completed, the mixture was heated under reflux for 10 hours to form a precipitate. This precipitate was filtered and washed first with methanol and then with water to obtain a white powder of polydimethylsilane 4.
20g was obtained.

On the other hand, 759 g of diphenyldichlorosilane and 12 g of boric acid
4 g in n-butyl ether under nitrogen gas atmosphere, 10
The resulting white resinous material was heated at a temperature of 0 to 120''C and further heated in vacuum at 400°C for 1 hour to obtain 530g of polyborodiphenylsiloxane.

Next, 8.21 g of the above polyborodiphenylsiloxane was added and mixed to 250 g of the above polydimethylsilane, and the mixture was heated to 350° C. under a nitrogen stream in a 21 quartz tube equipped with a reflux tube to polymerize for 6 hours. After cooling at room temperature, add xylene? Take it out as a liquid, evaporate the xylene,
The mixture was concentrated under a nitrogen stream for 1 hour at °C to obtain polycarbosilane.

10 g of tetrabutoxytitanium was added to 50 g of the above polycarbonate, and 40 ad! of xylene was added to the mixture. After stirring at 130"C for 1 hour under a nitrogen gas atmosphere, the temperature was slowly raised and polymerization was carried out at 320"C for 2 hours to obtain polytitano, which is the raw material for the inorganic continuous fiber used in the present invention. Carbosilane fj) was added.

(Example 1) After melt-spinning the polytitanocarbosilane obtained in Reference Example 1, it was heated to 170°C at a heating rate of 20°C/hr in air to make it infusible, and then spun for 200°C under a nitrogen atmosphere. ℃/hr
The fibers were heated to 1,000° C. at a heating rate of 1,000° C., held for 1 hour, and then cooled to obtain inorganic continuous fibers.

Laminate the flat rock material made of the above inorganic continuous fibers, and dice the laminate using carbon dice (3+n+sX 10mmX 10nv).
Place it in the sheet form of a) and heat it under an argon stream for 600 minutes.
kg/cd at 2,000'C for 0.5 hours to obtain a ceramic sintered body of the present invention.

The obtained ceramic sintered body of the present invention has a bending strength of 80
kg/+will (room temperature), 76 kg/yen” (1,400
"C), the density was 3.0 g/c+1. Also, the fracture toughness value (Kic; 24
)showed that.

In addition, when the fractured surface of the ceramic sintered body was observed using a surface reflection electron microscope, it was found that the fibrous crystal aggregates deformed into a polygonal state were most effectively closest packed, as shown in the photo shown in Part 1. The fiber orientation of the plain woven fabric was maintained.

In addition, when the above fibrous crystal aggregate is further enlarged and examined,
As shown in the photograph shown in FIG. 2, the presence of needle-like or flake-like crystals (SiC) was observed.

〔Effect of the invention〕

The sintered body of the present invention has excellent heat resistance, high mechanical strength at room temperature, extremely little decrease in strength even at high temperatures, and excellent toughness. According to the method, the above sintered body can be manufactured industrially.

[Brief explanation of the drawing]

FIG. 1 is a surface reflection electron micrograph showing the crystal structure of the sintered body of the present invention obtained in Example 1, and FIG.
2 is a surface reflection electron micrograph showing a further enlarged version of FIG. 1. FIG. Figure 2

Claims (15)

[Claims] (1) It is characterized by being composed of a crystal aggregate that maintains a fibrous shape and is made of crystals of SiC and MC_1_-_x (M represents Ti or Zr, and x is a number from 0 to less than 1). High strength and high toughness sintered body. (2) Crystal aggregates that retain the fiber shape are composed of lump-like, flake-like, or needle-like SiC crystals, SiC and TiC (
The high-strength, high-toughness sintered body according to claim 1, characterized in that it consists of ultrafine particle crystals of ZrC or ZrC). (3) High strength and high toughness according to claim (1) or (2), characterized in that the crystal aggregate that maintains the fiber shape is deformed into a form that can most effectively fill the fiber gaps. Sintered body. (4) The high-strength, high-toughness sintered body according to claim (3), wherein at least a portion of the fiber cross section of the crystal aggregate that maintains the fiber shape is deformed into a polygonal state. (5) The crystal aggregates retaining the fiber shape are well bonded or adhered to each other without intervening a matrix. High strength and high toughness sintered body. (6) Claim (5) characterized in that the crystal aggregates retaining the fiber shape are in the same orientation as the plain weave laminate.
High strength and high toughness sintered body as described. (7) The high-strength, high-toughness sintered material according to claim (5), characterized in that the crystal aggregates retaining the fiber shape are oriented in the same manner as the sheet-like material laminate that is aligned in one direction. Concretion. (8) The high-strength, high-toughness sintered body according to claim (5), wherein the crystal aggregates retaining the fiber shape are in an orientation similar to that of a three-dimensional fabric. (9) The high-strength, high-toughness sintered body according to claim (5), wherein the crystal aggregates retaining a fiber shape are arranged randomly. (10) Layering inorganic fibers made of any of the inorganic substances listed in (i), (ii), or (iii) below, molding this laminate into a predetermined shape, and placing it in a vacuum at the same time or after the molding. , SiC and MC_1_-_
A method for manufacturing a high-strength, high-toughness sintered body composed of a crystal aggregate that maintains a fiber shape and is made of crystals of x (M represents Ti or Zr, and x is a number from 0 to less than 1). (i) An amorphous material consisting essentially of silicon, M, carbon and oxygen (ii) Substantially β-S having a particle size of 500 Å or less each
iC, MC, solid solution of β-SiC and MC and/or crystalline fine particles of MC_1_-_x and amorphous Si
Aggregate consisting of O_ and MO_2 (iii) A mixed system of the amorphous material of the above (i) and the aggregate of the above (ii) (However, M in the above formula represents Ti or Zr, and X is 0
The number is greater than or equal to 1 and is less than 1. ) (11) The method for producing a high-strength, high-toughness sintered body according to claim (10), wherein the inorganic fibers are chopped short fibers. (12) The method for producing a high-strength, high-toughness sintered body according to claim (10), wherein the inorganic fibers are knitted into a plain weave. (13) The method for producing a high-strength, high-toughness sintered body according to claim (10), wherein the inorganic fiber is a sheet-like material that is aligned in one direction. (14) The method for producing a high-strength, high-toughness sintered body according to claim (10), wherein the inorganic fibers are woven into a nonwoven fabric or a three-dimensional fabric. (15) Any one of claims (10) to (14), wherein the inorganic fiber is surface-treated with polycarbosilane, polytitanocarbosilane, polyzirconocarbosilane, or a silane coupling agent. A method for producing a high-strength, high-toughness sintered body as described in .