JPH05286765A - Silicon carbide-based composite material and its production - Google Patents

Abstract

(57) [Summary] [Structure] The present invention comprises 70 to 90 vol% of silicon carbide, 1
0-30 vol% titanium carbide, 3-9w in terms of boron
t% boron or boron compound, and 5w in terms of carbon
Silicon carbide composite material containing titanium boride and having a relative density of 80% or more, which is obtained by firing a green compact of a mixture of t% or less of carbon or a carbonizable organic compound in a non-oxidizing atmosphere, and the carbonization. The present invention relates to a method for manufacturing a silicon-based composite material. [Effect] In the silicon carbide composite of the present invention, titanium carbide and boron compounded in the silicon carbide matrix react in the firing process to form and precipitate titanium boride. Compared with the case where the composites of, the oxide layer or hydroxide layer on the surface of titanium boride does not hinder the sintering, is dense, and has good compatibility with the silicon carbide matrix. It has excellent strength.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicon carbide based composite material having excellent strength and fracture toughness at ordinary temperature and high temperature and a method for producing the same.

[0002]

BACKGROUND OF THE INVENTION Silicon carbide is widely used as a structural material or wear resistant material because it has high hardness, high corrosion resistance, and high strength at high temperatures. However, when it is used as a high-temperature structural member for a gas turbine or the like, it has a low fracture toughness value, and is liable to fracture due to impact or stress concentration by foreign matter, and has not been widely put into practical use in terms of reliability. As means for solving this, for example, Japanese Patent Application Laid-Open No. 1-87563 discloses a non-oxide type composite ceramics sintered body, but since titanium boride is used as a starting material, the fracture toughness value is Although high, it is pointed out that the bending strength at high temperature is low. Accordingly, the present invention is to provide a silicon carbide based composite material which has high strength not only at room temperature but also at high temperature and excellent fracture toughness, and a method for producing the same.

[0003]

DISCLOSURE OF THE INVENTION As a result of intensive studies to solve the above-mentioned problems, the present inventors have made a silicon carbide composite material having a high density, high strength at high temperature, and excellent fracture toughness. Further, they have found the manufacturing method thereof and completed the present invention.

That is, the gist of the present invention is (1) 70-90.
The pressure of a mixture of vol% silicon carbide, 10 to 30 vol% titanium carbide, 3 to 9 wt% of boron or boron compound in terms of boron, and 5 wt% or less in terms of carbon of carbon or a carbonizable organic compound. A silicon carbide composite material containing titanium boride and having a relative density of 80% or more, which is obtained by firing a powder in a non-oxidizing atmosphere, and (2) 70-
Pressure of a mixture of 90 vol% silicon carbide, 10 to 30 vol% titanium carbide, 3 to 9 wt% of boron or boron compound in terms of boron, and 5 wt% or less of carbon or carbonizable organic compound in terms of carbon. When firing the powder in a non-oxidizing atmosphere, the temperature range of 1100 to 1600 ° C. is raised at a heating rate of 20 ° C./min or less, and the main firing is performed at 160
The method for producing a silicon carbide based composite material according to claim 1, wherein the method is performed at 0 ° C to 2200 ° C.

The silicon carbide used in the present invention may be in either α or β crystal form and has a purity of 90% or more, preferably 96% or more and a particle size of 5 μm or less, preferably 3 μm or less. If the purity is less than 90%, the strength characteristics of the obtained composite material will not be exhibited, and if the particle size exceeds 5 μm, the sinterability will be poor and it will be difficult to obtain a high-density sintered body.
The amount of silicon carbide used is 70 to 90 vol%.

The titanium carbide used in the present invention has a purity of 90%.
Or more, preferably 96% or more, particle size 0.01 to 10 μ
m, preferably 0.01 to 5 μm. 90% purity
If it is less than the above range, for example, oxygen in titanium carbide hinders sintering, so that it is difficult to obtain a high-density sintered body. If the particle size is less than 0.01 μm, it is substantially difficult to mix and disperse uniformly, the surface area increases, and the reaction of oxygen in the air promotes the production of titanium oxide on the surface of titanium carbide, resulting in sintering. Inhibit. If the particle size exceeds 10 μm, it is difficult to obtain a high-strength sintered body. The amount of titanium carbide added is
It is 10 to 30 vol%. If it is less than 10 vol%, no improvement in mechanical properties due to compounding is observed. Also, 30v
When it exceeds ol%, the continuous phase of the silicon carbide matrix is reduced and the mechanical properties of the composite sintered body are impaired.

The boron used in the present invention is metallic boron,
One or more selected from boron carbide and organic compounds of boron. The purity of the boron source used is 90% or more, preferably 95% or more. If the purity is less than 90%, the reaction between titanium carbide and boron is hindered by a side reaction due to impurities, and a uniform reaction cannot be expected. The amount of boron added is 3 to 9 wt% in terms of boron. If the amount of boron added is less than 3 wt%, the sintering of silicon carbide does not proceed sufficiently and it is difficult to obtain a dense sintered body.
On the other hand, if it exceeds 9 wt%, free boron acts as a fracture starting point, and mechanical properties such as strength are impaired.

The carbon used in the present invention is selected from carbon black and carbonizable organic compounds such as phenol resin, furan resin, polyacrylonitrile resin, pitch, tar, and two or more kinds. When these carbonizable organic compounds are used, it is desirable to carry out preliminary firing in a non-oxidizing atmosphere to carbonize the organic compounds, if necessary. The amount of carbon added is 5 wt% or less, preferably 1 to 5 wt%. When the amount of carbon added exceeds 5 wt%, it is difficult to obtain a dense sintered body due to free carbon.

The silicon carbide based composite material of the present invention comprises 70 to 90 vol% silicon carbide and 10 to 30 vol% as described above.
% Titanium carbide, 3-9 wt% boron or boron compound in terms of boron, and 5 wt% or less carbon or carbonaceous organic compound in terms of carbon of a mixture powder compact fired in a non-oxidizing atmosphere It is obtained by doing. That is, a predetermined amount of silicon carbide, titanium carbide, boron, carbon in the present invention is mixed by a wet mill or a dry mill by a mixing and pulverizing device such as an attritor mill or a ball mill, and after granulation using a spray dryer or the like, A green compact is prepared by die pressing, casting, rubber pressing, etc., and is fired in a non-oxidizing atmosphere. The firing method is not particularly limited, and may be any known firing method such as an atmospheric pressure sintering method, a hot pressing method, and a hot isostatic pressing method.

In the firing process of the present invention, titanium carbide and boron react to form titanium boride as represented by the following formula. TiC + 2B → TiB ₂ + C This titanium boride formation reaction proceeds from 1100 ° C. to 160 ° C.
The rate of temperature rise is 2 because it involves volume expansion in the temperature range of 0 ° C.
It should be performed at 0 ° C./min or less, preferably 10 ° C./min or less. If it exceeds 20 ° C./minute, cracks occur in the obtained sintered body, and a dense sintered body cannot be obtained. Particularly, in the case of pressureless firing, it is desirable that the temperature be 8 ° C./minute or less. The firing temperature is 1600 ° C to 2200 ° C, preferably 2100 ° C to 2200 ° C as the main firing. Firing temperature is 160
If the temperature is lower than 0 ° C, the silicon carbide matrix is not sufficiently sintered, and a dense sintered body cannot be obtained. Also, 2200 ℃
Above, due to sublimation of silicon carbide and growth of abnormal particles,
It is difficult to obtain a sintered body having practically sufficient strength. The firing is performed in a non-oxidizing atmosphere, for example, in an inert atmosphere such as an argon gas stream or in a vacuum.

In the silicon carbide composite material of the present invention thus obtained, the components after firing are composed of silicon carbide, titanium boride and graphite in the stoichiometric ratio of the above reaction formula. In a non-stoichiometric ratio, silicon carbide, titanium boride, graphite, unreacted boron,
It is composed of titanium carbide. That is, the silicon carbide based composite material of the present invention contains titanium boride obtained by reacting titanium carbide and boron in the firing process in a composite state in a silicon carbide matrix. The relative density of the silicon carbide composite material is usually 80% or more, preferably 90% or more.

Further, in the silicon carbide composite of the present invention, the titanium carbide and boron compounded in the silicon carbide matrix as described above react in the firing process to form titanium boride.
As compared with the conventional case where titanium boride is compounded with silicon carbide, the precipitation does not hinder the sintering due to the oxide layer or hydroxide layer on the surface of titanium boride, and it is dense and has a silicon carbide matrix. It has excellent fracture toughness value and high strength at high temperature.

[0013]

EXAMPLES The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples.

Examples 1 to 9 Raw materials α-silicon carbide (Starck, A-10), titanium carbide, boron and carbon were weighed in predetermined amounts, and wet-mixed for 4 hours in isopropanol using an attritor mill. A dry powder was obtained. The amount of silicon carbide added is 70 to 90 vol.
%, Titanium carbide was 10 to 30 vol%, boron was 5 or 9 wt%, and carbon was 1 or 3 wt%, and various raw material compositions shown in Table 1 were prepared. Firing these powders in vacuum at a pressure of 50 MPa at 2100 ° C to 220 ° C.
Hot press sintering was performed at 0 ° C. for 1 hour (Examples 1 to 1).
4). Alternatively, the temperature was raised to 2200 ° C. in an argon gas flow in a thermal expansion meter using a carbon heating element (Examples 5 to 9). The relative density of the obtained sintered body was measured and the crystal phase was identified. This sintered body conforms to JIS R1601,
A test piece was prepared and the bending strength was measured by the 4-point bending method in air at room temperature and 1350 ° C. The fracture toughness was evaluated by the Vickers indenter method (IF method). The texture of the sintered body was observed with a reflection microscope, and the state of crack propagation from the Vickers indenter was observed with a scanning electron microscope.

FIG. 1 shows the measurement results of a sample obtained by adding 90 vol% of silicon carbide, 10 vol% of titanium carbide, 5 wt% of boron and 3 wt% of carbon with a thermal dilatometer (Example 6). Figure 1
More clearly, during heating 1100 to 1600 ℃
A linear expansion of about 5% was measured over time. Since only the titanium boride was observed and the titanium carbide was not observed in the sample immediately after the expansion, it is considered that titanium boride and boron were reacted in this temperature range to generate titanium boride and carbon. The relative density of the obtained sintered body is, for example, 90% by volume of hot-sintered silicon carbide and titanium carbide 1
98% of a sample added with 0 vol%, 5 wt% of boron and 3 wt% of carbon (Example 2), 80 vol% of pressureless sintered silicon carbide, 20 vol% of titanium carbide, 9 wt% of boron, 3 wt% of carbon % Was 98% (Example 7), and it was revealed that a high-density silicon carbide-titanium boride composite body can be produced even by pressureless sintering. However, as shown in Comparative Example 1 to be described later, a high density sample could not be obtained from a sample having a small amount of boron added and a composition in which titanium carbide and titanium boride coexist even after the reaction. The pressureless sintered body had a structure in which titanium boride particles having a size of 1 to 3 μm were dispersed in a silicon carbide matrix, but the hot-pressed sintered body had titanium boride particles having a submicron size of 2 to 2 μm. It was a tissue assembled in the range of 3 μm. The fracture toughness value of the titanium carbide 30 vol% added sample (Example 8) was about twice that of the non-added sample (Comparative Example 6 described later).
Further, the bending strength was almost the same as that at room temperature up to 1350 ° C. Table 1 shows the physical properties of the obtained sintered bodies and their test results.

[0016]

[Table 1]

Comparative Examples 1 to 6 Using the raw material compositions shown in Table 2, pressureless sintering was performed up to 2200 ° C. in an argon gas stream to obtain sintered bodies. The relative density, bending strength and fracture toughness of the obtained sintered body were measured in the same manner as in Examples 1-9. Table 2 shows the physical properties of the obtained sintered bodies and their test results.

[0018]

[Table 2]

[0019]

EFFECTS OF THE INVENTION In the silicon carbide composite of the present invention, titanium carbide and boron compounded in the silicon carbide matrix react with each other during the firing process, and titanium boride is produced and precipitated, so that the conventional silicon carbide can be obtained. Fracture toughness value because it is dense and has good compatibility with the silicon carbide matrix without the oxide layer or hydroxide layer on the surface of titanium boride inhibiting sintering as compared with the case of compounding titanium oxide. It has excellent strength at high temperature.

[Brief description of drawings]

FIG. 1 shows the measurement results of a sample thermal dilatometer in Example 6.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Michael J. Hoffmann Stuttgart 80 Germany, Heisenberg Strasse 5, Max-Planck-Institut Für Metal Forschün Institute Für Bergstoff Bissenshaft

Claims (2)

[Claims] 1. 70 to 90 vol% of silicon carbide, 10
30 vol% titanium carbide, 3-9 wt% in terms of boron
Boron or boron compound, and 5 wt% in terms of carbon
A silicon carbide composite material containing titanium boride and having a relative density of 80% or more, obtained by firing a green compact of a mixture of the following carbon or carbonizable organic compounds in a non-oxidizing atmosphere. 2. 70 to 90 vol% silicon carbide, 10
30 vol% titanium carbide, 3-9 wt% in terms of boron
Boron or boron compound, and 5 wt% in terms of carbon
When firing a green compact of a mixture of the following carbon or carbonizable organic compounds in a non-oxidizing atmosphere,
The method for producing a silicon carbide based composite material according to claim 1, wherein the temperature range of 1600 ° C. is raised at a heating rate of 20 ° C./min or less, and the main firing is performed at 1600 ° C. to 2200 ° C.