JPH10139548A - Molybdenum disilicide-base composite material and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a molybdenum disilicide-base composite material (sintered compact) having improved characteristics at room temp. and high temp. and useful as a superheat resistant structural material. SOLUTION: This composite material is a sintered compact with a composite structure having a matrix made of Mo(Si, Al)2 [the pref. atomic ratio of Si:Al is (1-x):x (0.03<=x<=0.20)] as a molybdenum disilicide-base intermetallic compd. and a grain boundary phase based on α-Al2 O3 crystals and contg. 5-20vol% uniformly dispersed β-SiC particles of nm size as a dispresed phase in the grains and grain boundaries. the sintered compact is produced by adding about 0.1-10wt.% sintering and such as boron oxide to a mixture of Mo(Si, Al)2 powder with 5-20vol% SiC powder of nm size, preferably 50-200nm size, subjecting the resultant starting material to be sintered to pressureless sintering at about 1,500-1,750 deg.C and subjecting a formed grain boundary phase to crystallization heat treatment at about 1,200-1,350 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a molybdenum disilicide-based composite material, and more particularly, to the alloying of molybdenum disilicide forming a matrix with aluminum, the crystallization of a grain boundary phase, and the dispersion of nanometer-sized silicon carbide particles. The present invention relates to a molybdenum disilicide composite material having improved room temperature and high temperature characteristics based on dispersion strengthening of matrix intragranular and intergranular phases and useful as an ultra-high temperature structural member and a method for producing the same.

[0002]

_2. Description of the Related Art Molybdenum disilicide [MoSi ₂ ] is an intermetallic compound having a high melting point (about 2030 ° C.), forming an SiO ₂ film on the surface at a high temperature, and exhibiting excellent oxidation resistance. Further, since it has conductivity and relatively high emissivity, it is widely used as a heating element in an atmosphere of oxygen and air. Further, its density is relatively low at 6.27 g / cm ^3, and it is expected to be applied as an ultra-high temperature structural material used in a high temperature environment around 1500 ° C. However, the fracture toughness, the fracture strength, the reliability, and the like are not sufficient to enable application as a structural material such as an aircraft member, and further improvement in these properties is required. As a measure for improving the characteristics, composites with ceramics and metals have been attempted in many fields. The compounding technique is intended to disperse various second phases having a granular or fibrous shape in a matrix to form a fine mixed phase structure, thereby realizing improved properties as a dispersion strengthening action.

[0003]

However, the conventional attempts to improve the properties of molybdenum disilicide by compounding have mainly been to provide a micron-sized second phase to control the structure and to provide a complementary effect dependent on the dispersion strengthening action. There is a characteristic improvement effect within a range that can be linearly predicted.
In order to further improve the characteristics of molybdenum disilicide, it is necessary to consider a material design different from the conventional composite technology. Further, in the production of molybdenum disilicide practical members, powder metallurgy is considered indispensable.
In this case, the molybdenum disilicide powder used as a sintering raw material inevitably accompanies the surface oxide (mainly SiO ₂ ) of the particles. Although SiO ₂ derived from the surface oxide forms a liquid phase in the sintering process and promotes the sintering reaction, the resulting sintered body has a structure in which a large amount of SiO ₂ glass phase is interposed at the grain boundaries. Become. This grain boundary SiO ₂ glass phase is
High temperature characteristics of the sintered body are greatly reduced. By using a powder having a large particle size (small specific surface area) as a sintering raw material, the grain boundary SiO ₂ glass phase of the sintered body can be reduced, but a sufficient sintering reaction is achieved. Becomes difficult. Therefore, the room temperature strength of the sintered body is about 200M.
It will be at a low level of about Pa, and it will not be possible to provide room temperature and high temperature characteristics at a high level in a well-balanced manner.

Further, as a process for producing a sintered body, the normal pressure sintering method is extremely advantageous in terms of cost as compared with a hot press method or a hot isostatic pressing method, but molybdenum disilicide is difficult to burn. Because it is a binder, when applying the normal pressure sintering method,
It is necessary to increase the content of SiO ₂ in the raw material powder to enhance the sinterability. However, as described above, increasing the amount of SiO ₂ in the sintering raw material powder requires a grain boundary S
This results in an increase in the iO ₂ glass phase and a decrease in the high-temperature strength. That is, it is practically impossible to produce a molybdenum disilicide sintered body excellent in room temperature and high temperature characteristics by applying atmospheric pressure sintering which is economically advantageous as an industrial production method by conventional techniques. In view of the above, the present invention provides a molybdenum disilicide-based dispersion-strengthened composite material having improved room temperature and high temperature properties, and a pressure-sensitive sintering method which is economically advantageous as an industrial production process. It provides a way to:

[0005]

The molybdenum disilicide composite material of the present invention has an aluminum-substituted molybdenum disilicide intermetallic compound [Mo (Si, Al) ₂ ] as a matrix phase and a grain boundary phase of Al ₂ O _3. The main phase of the crystal is 5 to 2 as a disperse phase within and at the grain boundaries of the matrix.
It is characterized by being a sintered body having a composite structure in which nanometer-sized SiC particles occupying 0% by volume are uniformly dispersed. The molybdenum disilicide-based composite material is an aluminum-substituted molybdenum disilicide intermetallic compound [Mo (S
i, Al) ₂ ] powder was added with 5 to 20% by volume of silicon carbide powder having a nanometer size, and 0.1 to 10% by weight of a sintering aid based on the total amount was mixed. After molding the mixed powder into a desired shape, in a non-oxidizing atmosphere,
It is manufactured by a normal pressure sintering at a temperature of 1500 to 1750 ° C., and then a heat treatment at 1200 to 1350 ° C. as a crystallization treatment of a grain boundary phase.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The molybdenum disilicide composite material of the present invention comprises, as a matrix constituent phase, an intermetallic compound [Mo (Si, Al) ₂ ] in which a part of Si of molybdenum disilicide is substituted by Al. The matrix grain boundary is α-Al ₂
It exhibits a grain boundary phase rich in O ₃ crystals. SiO _{2 at the} grain boundaries
The glass phase is substantially absent or, if present, in very small amounts. Then, the matrix [Mo (Si, A
1) In the grain boundaries of ₂ ] and at the grain boundaries having Al ₂ O ₃ as a main phase,
Nanometer-sized SiC particles (5-20
% By weight) having a fine composite structure uniformly dispersed. The matrix has a two-phase structure of tetragonal MoSi ₂ and hexagonal Mo (Si, Al) ₂ having few slip systems.

[0007] The Al ₂ O ₃ crystal in the grain boundary phase includes aluminum oxide accompanying the raw material powder and preferential oxidation of Al in the matrix generated during the sintering process (such as SiO ₂ which is a surface oxide of the raw material powder). Reaction). Even if the raw material powder has a fine particle size (has a large specific surface area and a large amount of surface oxide brought in), most of the SiO _{2 in} the sintered body disappears from the grain boundaries due to the preferential oxidation reaction of Al,
A grain boundary phase rich in ₂ O ₃ crystals is formed. The SiC particles, which are a dispersed phase, have high heat resistance and are thermodynamically Mo
It has high stability to Si ₂ and SiO ₂ . The nanometer-sized fine SiC particles effectively suppress the grain growth of the matrix during the sintering process to give the matrix a fine grain structure (average grain size: about 2 to 5 μm), and are incorporated into the matrix grains and into the grain boundaries. And uniformly dispersed.

[0008] As described above, the composite material of the present invention is composed of a matrix alloy, a SiO ₂ glass phase as a grain boundary phase and an Al ₂ O phase.
Change to ₃ crystal phase, and the SiC particles of nanometer is obtained by realizing the characteristics improvement by the matrix grains, the grain boundary dispersion strengthening of the disperse phase, the oxide phase (1) matrix grain boundaries, The Al ₂ O ₃ crystal phase strengthens the grain boundary phase as compared with the SiO ₂ glass phase, suppresses a decrease in strength at high temperatures, and increases hardness. The fracture mode changes from intergranular fracture seen in a molybdenum disilicide sintered body having low grain boundary strength to intragranular fracture. (2) The creep resistance of the matrix itself is enhanced as a control effect of a phase structure in which the matrix is composed of two phases of tetragonal MoSi ₂ and hexagonal Mo (Si, Al) ₂ having a small slip system. (3) As an effect of alloying aluminum, the peeling resistance of the oxide film on the surface is strengthened, the repeated oxidation resistance in a high-temperature environment is improved, and the powdering phenomenon at around 500 ° C. is suppressed and prevented.

(4) Nanometer-sized Si as a dispersed phase
C particles form the microstructure of the matrix,
In the _{matrix, MoSi 2 -Mo (Si, Al} )
_{In the 2} / SiC composite and the grain boundary phase, an Al ₂ O ₃ / SiC composite is formed to increase the room temperature and high temperature strength. (5) SiC particles directly bond with the matrix to form a strong interface, and as a structural control effect of intragranular and intergranular boundaries, control of grain boundary sliding and slow crack growth at high temperatures, etc. It is possible to maintain strength. (6) The thermal expansion coefficient of SiC is smaller than that of MoSi ₂ which is a constituent phase of the matrix (SiC: 3.3 × 10 ⁻⁶ K
⁻¹ , MoSi ₂ : 6.8 × 10 ⁻⁶ K ⁻¹ ), and as a mechanism for increasing toughness due to residual stress, an effect of enhancing high-temperature characteristics can be obtained.

The aluminum-substituted molybdenum disilicide [Mo (Si, A)
l) ₂ ] has a chemical composition of Si: Al (atomic ratio) = 1−
X: When X, it is preferable that X has a composition in the range of 0.03 to 0.20. If the value of X is less than this, A
It is difficult to sufficiently secure the substitution solid solution effect of 1 (such as control of the two-phase structure of the matrix and control of the grain boundary phase by preferential oxidation reaction of Al). This is because the ratio of the hexagonal crystal of the alloy increases more than necessary, causing the sintered body to be embrittled, and the high-temperature characteristics are impaired due to a decrease in the melting point due to a decrease in the covalent bondability and an increase in the metal bond. . The SiC particles that are the dispersed phase are nanometer-sized ultrafine particles, so that the matrix grain boundaries and the grain boundaries are effectively dispersed and strengthened. The selection of the particle size is arbitrary, but if it is too fine, solid solution disappears in the matrix during the sintering reaction process depending on the sintering treatment conditions, and the function as a dispersed phase may be lost. The thickness is preferably 50 nm or more.
It is preferably 0 nm or less. More preferably about 50
２００200 nm. When the content of the SiC particles is 5 to 20
Limited to the range of volume%, less than 5% by volume,
If the dispersing effect becomes insufficient, and if it exceeds 20% by volume,
This is because the particles are likely to agglomerate and difficult to uniformly disperse, and the sinterability is reduced, making it difficult to produce a dense sintered body by the normal pressure sintering method.

Next, a method for producing the composite material of the present invention will be described. The composite material of the present invention comprises molybdenum disilicide [M
oSi ₂ ], an intermetallic compound [Mo (Si, Al) ₂ ] powder in which silicon is partially substituted with aluminum, and a nanometer-sized SiC powder, and a mixture obtained by adding an appropriate amount of a sintering aid to the mixture. It is manufactured as a sintering raw material through a sintering process and a heat treatment step for controlling (crystallizing) a grain boundary phase. It is a matter of course that pressure sintering methods such as hot pressing and hot isostatic pressing can be applied to the sintering process.
By adjusting the particle size of the raw material powder and selecting an appropriate sintering aid, it is possible to secure improved properties desired as a practical member by using a normal pressure sintering method.

An aluminum-substituted molybdenum disilicide intermetallic compound [Mo (Si, A
l) ₂ ] is Mo: Si: Al (atomic ratio) = 1: 2 (1
-X): A composition adjusted to 2X [X is 0.03 to 0.20] is preferably used. By using a powder having this composition, the control of the grain boundary phase (formation of an Al ₂ O ₃ crystal rich phase) and the matrix crystal structure [tetragonal MoSi ₂ and hexagonal Mo
(The balance between the two-phase constitution of (Si, Al) ₂ and the ratio of the two phases)] can be achieved successfully. The powder particle size is suitably about 0.5 to 2.0 μm (average particle size). When the normal pressure sintering method is applied, the average particle size is 0.5 to 2.0 μm to enhance sinterability. It is preferred to use a 1.0 μm fine powder.

The aluminum-substituted molybdenum disilicide intermetallic compound powder can be obtained, for example, as a product of a combustion synthesis reaction. That is, molybdenum powder, silicon powder and aluminum powder are mixed to form a powder compact as it is or in an appropriately shaped form, and then ignited in a controlled atmosphere (preferably Ar gas or vacuum atmosphere) to cause a combustion reaction. Is carried out to obtain the aluminum-substituted molybdenum disilicide intermetallic compound suitable as a matrix material. As a matrix forming raw material, instead of the aluminum-substituted molybdenum disilicide intermetallic compound [Mo (Si, Al) ₂ ], MoSi ₂
It is conceivable to apply a method of performing reaction sintering using a mixture of powder and aluminum metal powder, but in this case, aluminum metal is mainly used at a relatively low temperature range of about 660 ° C during sintering. A liquid phase is formed as a component, and grain growth is promoted. The resulting sintered body has a coarse structure, and is accompanied by problems such as a decrease in high-temperature characteristics due to residual unreacted aluminum and a change in composition due to evaporation of aluminum. I do. Aluminum-substituted molybdenum disilicide intermetallic compound [Mo
When (Si, Al) ₂ ] powder is used, such problems can be avoided and a fine and uniform structure can be ensured.

The above-mentioned aluminum-substituted molybdenum disilicide gold
Intergeneric compound powder [Mo (Si, Al)_TwoIs a dispersed phase
And a sintering aid component. SiC powder
The powder is nanometer-sized ultrafine particles as described above.
The amount is adjusted to 5 to 20% by volume. Sintering aid
The choice of minutes is important. As a suitable auxiliary, boron oxide
Elementary (B_TwoO _Three), Yttrium oxide (Y_TwoO_Three), Oxidation
Ytterbium (Yb_TwoO_Three) And the like. these
Atmospheric pressure baking is more cost-effective by adding the appropriate amount of
Composites with improved room and high temperature properties using the knotting method
A sintered body can be obtained. The amount of the auxiliary
Aluminum to ensure that the liquid phase in the
Of substituted molybdenum disilicide intermetallic compound powder and SiC powder
0.1 to 10% by weight based on the mixture (when multiple types are used in combination)
Is the total amount). Less than 0.1%
Insufficient sinterability improving effect, large amount exceeding 10% by weight
When blended in a grain boundary phase, the grain boundary phase becomes brittle,
This is because the property is lowered.

The sintering process is performed in a temperature range according to the sintering method applied. The sintering temperature in the hot press method is about 1450 to 1600 ° C. The sintering temperature in the case of applying the normal pressure sintering method is suitably in the range of about 1500 to 1750 ° C. At a temperature lower than 1500 ° C., the sintering reaction becomes insufficient, and it becomes difficult to sufficiently advance the densification of the sintered body. On the other hand, at a temperature higher than 1750 ° C., the structure becomes coarse due to the growth of the matrix grains, and This is because the properties of the body are reduced. The sintering temperature greatly affects the properties of the obtained composite sintered body. The sintering temperature when the compounding ratio of the SiC powder in the sintering raw material is relatively low is preferably set to a lower temperature within the above temperature range, and set to a higher temperature in accordance with the increase in the compounding ratio. By setting the sintering temperature according to the composition of the sintering raw material, the effect of improving the properties of the composite material is maximized. During the sintering process, some of the SiC particles are trapped in the matrix particles, and the remainder is incorporated in the grain boundary phase. During the sintering, a ternary eutectic reaction composed of Al ₂ O ₃ , SiO ₂ and a sintering aid component (when the sintering aid is boron oxide, Al ₂ O ₃ —SiO ₂ —B ₂ O ₃
Ternary eutectic reaction], a liquid phase is formed at the grain boundary. The liquid phase generation temperature can be easily controlled by the amount of the sintering aid. At the temperature at which the SiC particles are incorporated into the matrix particles, the glass phase has already been exhausted to the particle boundaries, there is almost no glass phase at the interface between the matrix and the SiC particles, and the two directly bond to form a strong interface.

After completion of the sintering process, the temperature is about 1200 ° C.
Heat treatment at 1350 ° C. is performed. Processing time is about 4-7Hr
It is about. In this heat treatment, A in the matrix
1 atom diffuses and moves to the grain boundary, and SiO ₂ and B
₂ O ₃ is reduced. The reason why the treatment temperature is set to 1200 ° C. or higher is that at lower temperatures, the diffusion of Al and the reduction reaction of the grain boundary oxide cannot be sufficiently achieved.
The reason why the upper limit is set to 50 ° C. is that if the temperature exceeds 50 ° C., the structure becomes coarse due to the grain growth of the matrix.
By this heat treatment, SiO ₂ almost disappears and the grain boundary phase becomes A
It becomes a l ₂ O ₃ crystal rich phase. Molybdenum boride [MoB, Mo ₂ B] is formed from B ₂ O ₃ , and the particles serve as a dispersion strengthening phase.

The composite material of the present invention thus obtained has a M
oSi_Two-Mo (Si, Al)_Two/ SiC fine
The composite having a large particle size is used as a matrix, and the grain boundary phase is S
iO _TwoAlmost no glass phase, Al_TwoO_ThreeCrystal as main phase
Α-Al_TwoO_Three/ SiC composite, and this
Intra- and intergranular strengthening type with simultaneously controlled grain boundary structure and properties
Improved room temperature and high temperature characteristics as described above as a composite material
To embody.

[0018]

【Example】

[1] Preparation of sample sintered body (1) Preparation of sintering raw material [Chemical composition of matrix forming raw material [Mo-Si-Al intermetallic compound]] Mo: 63.39 (33.15), Si: 31.15 (55.64) , Al: 4.41 (8.2
0), O: 0.82 (2.57), C: 0.09 (0.38), Fe: 0.08 (0.07),
% By weight (atomic%). [Chemical composition of the dispersed phase-forming material [SiC]] _{SiC:> 99wt%, SiO 2} : 0.15wt%, free C: 0.10wt%, Fe: 120
ppm, Al: 48ppm, Ca: 40ppm, Mg: 10ppm. Cr: 30ppm, Ni: 20
ppm. The mixed powder of the intermetallic compound [Mo (Si, Al) _2] and silicon carbide [SiC], boron oxide [B ₂ O _3] were added as sintering aid ingredients, wet 1-butanol as a dispersion medium Perform ball mill mixing. After drying with an evaporator and treatment with a dry ball mill, the mixture is classified and used as a starting material. The average particle size of the Mo-Si-Al intermetallic compound in the starting material powder is
1.3 μm, the average particle size of the silicon carbide particles is 150 nm.

(2) Compacting: A single-shaft compact (6.4 × 4.5 × 5) is obtained by preforming with a mold (pressing force: 24 MPa).
3 mm), sealed in a plastic film bag under reduced pressure, and then subjected to cold isostatic pressing (pressure: 300 MPa) to obtain a green compact. (3) Sintering: The green compact is placed in a sintering furnace and subjected to normal pressure sintering (atmospheric pressure: 0.1 MPa) in an argon atmosphere. (4) Heat treatment: After the sintering treatment, the temperature is gradually lowered to 1200 ° C. in a furnace, and the temperature is maintained at a predetermined temperature to crystallize the grain boundary phase of the sintered body. Through the above steps, sample sintered bodies Nos. 1 to 7 (inventive examples) are obtained.

As a comparative example, the following test sintered bodies were produced according to the same steps as described above. Molybdenum disilicide [Mo
Si ₂ ] powder (average particle size: 1.0 μm) as a sintering material, a single-phase sintered body (sample No. 11), aluminum-substituted molybdenum disilicide [Mo (Si, Al) ₂ ] (chemical composition And a single-phase sintered body (sample material No. 12) using the same sintering raw material as described above. Molybdenum disilicide [MoSi ₂ ] powder (average particle size: 1.
0 μm) and silicon carbide [SiC] powder (average particle size: 150 n
composite sintered body (sample material)
No. 13), aluminum-substituted molybdenum disilicide [Mo
(Si, Al) ₂ ] and a powder mixture of SiC powder [each having the same chemical composition and particle size as the above-mentioned invention,
composite material (sample materials No. 14 and No. 15) using iC powder as a sintering raw material.

Table 1 shows the hardness (Vickers hardness) [load: 98 N, as the raw material composition of each test sintered body, sintering conditions and heat treatment conditions, and various room temperature characteristics of the obtained product sintered body. Holding time: 15s], bending strength [3-point bending test, test piece: JIS R
1601,, Loading speed: 0.5 mm / min, Span distance: 30 mm
] And fracture toughness [calculated by IF method].

[0022]

[Table 1]

In the table, the invention examples (Nos. 1 to 7) and the test material No. 11
Compared to (MoSi ₂ single phase material) and test material No. 12 (Mo (Si, Al) ₂ single phase material), matrix grain growth of both test material No. 11 _and No. 12 While the structure of the invention example has a remarkably fine structure while exhibiting a vigorous and coarse structure, various properties such as hardness, fracture strength, and fracture toughness are greatly enhanced. Further, as can be seen from the mutual comparison of the invention examples (Nos. 1 to 7), the composite material of the present invention has an appropriate sintering temperature depending on the blending amount of the dispersed phase component (nanometer-sized SiC particles). Adjustment maximizes the combined effect. When the amount of the dispersed phase component is relatively small, as in Test Material Nos. 1 and 2, the mixing amount is as shown in Test Material Nos. In the case of medium, the intermediate temperature range of about 1650 ° C
When a high blending amount is used, as in No. 7, a high temperature range around 1700 ° C is appropriate, and the sintering reaction in normal-pressure sintering is performed by controlling the temperature according to the amount of the dispersed phase components. It is possible to obtain a sintered product having a material characteristic which is achieved without any shortcomings and has highly improved material properties as a compounding effect of the dispersed phase component.

Further, the test material No. 13 [MoSi ₂ -SiC composite material] was used as an example of the invention (Nos. 1 to 7) as the effect of compounding the dispersed phase component.
It has a microstructure equivalent to that of, and shows relatively high levels of hardness and toughness, but its strength is low, and it is greatly different from those of the invention examples. Test material No.14 and No.15
[All are Mo (Si, Al) ₂ -SiC composite materials as in the invention examples] have a fine structure and high hardness and toughness, but none of them have a small effect of improving strength. . This is because the sintering reaction was insufficient due to the excessive amount of the dispersed phase component of 30 vol%, and the densification was not sufficiently achieved. This insufficiency of densification cannot be sufficiently solved even by applying high-temperature sintering at 1800 ° C., as in Test Material No. 15. Excessive blending of such dispersed phase components should be avoided, and in order to ensure highly improved material properties as a combined effect under industrial manufacturing conditions by the normal pressure sintering method, the blending amount is It can be seen that it should be up to 20 vol%.

FIG. 1 shows an X-ray diffraction pattern [a, M:
o (Si, Al) ₂ intermetallic compound powder, b: Test material No. 12,
c: Test material No. 3], and FIGS. 2 to 4 are scanning electron microscope images showing the microstructure of the test sintered body [FIG. 2: Test material No. 11,
Fig. 3: Test material No. 12, Fig. 4: Test material No. 3], Fig. 5
FIGS. 6 and 7 show the change in bending strength of each sample sintered body with temperature, and FIGS. 6 and 7 show scanning electron microscope images showing the fracture surface of the sample sintered body [FIG. 6: Sample No. 3, FIG. Specimen No. 12].

As shown in FIG. 1, X-ray diffraction
The main constituent phase of the composite sintered body of the invention example is tetragonal Mo.
Si_Two, Hexagonal Mo (Si, Al)_Two, Al_TwoO_Three,
Mo _<5Si_ThreeC_<1, And SiC. SiO_TwoGala
No substantial abundance of the water phase is detected. Al_TwoO_Threephase
Is used for the preferential oxidation reaction of Al in the matrix during the sintering process.
Generated from Mo_<5Si_ThreeC_<1Phase (Nowotn
y phase) is the C (and sintered
Produced by the reaction with C) mixed during the manufacturing process
is there. In the composite sintered body of the invention example, hexagonal Mo (S
i, Al)_TwoMoSi for_TwoThe ratio of raw materials
What is higher than that of the powder is the sintering process
Change in Al concentration due to preferential oxidation of Al
It is.

2 to 4, the test sintered body N of FIG.
o.11 [Sintering raw material: MoSi ₂ powder] was obtained by dispersing SiO ₂ glass phase having irregular shape,
2 [Sintering raw material: Mo (Si, Al) ₂ powder] has a structure in which Al ₂ O ₃ crystal phase is dispersed. On the other hand, the example of the invention of FIG. 4 has fine SiC particles, Al ₂ O ₃ —SiC.
It has a structure in which particles are uniformly dispersed.

As shown in FIG. 5, the sintered material of the invention material [Mo
(Si, Al) ₂ -SiC composite material) was used at room temperature and high temperature range for test material No. 11 (MoSi ₂ single phase material) and test material No. 12 (Mo (S
i, Al) ₂ single phase material].
In addition, when compared with the test material No. 13 [MoSi ₂ -SiC composite material], the test material No. 13 showed higher strength than the invented material in a temperature range lower than about 1100 ° C. , The strengths of the two are reversed. That is,
The invented material has high strength even in a high temperature region exceeding about 1100 ° C., and the difference from the test material No. 13 is obvious. In addition, as is clear from the comparison of the fractured surfaces (FIG. 6: invention material, FIG. 7: test material No. 12) of the test sintered bodies in FIGS.
Test material No. 12 (Mo (Si, Al) ₂ single phase material) has a relatively flat fracture surface, while the invention material has a complex fracture surface with fine irregularities. Thus, a structure in which nanometer-sized SiC particles strengthen the intragranular and grain boundaries of the matrix as a dispersing effect is observed.

[0029]

According to the present invention, the molybdenum disilicide-based composite material of the present invention can control the composition and crystal structure of matrix grains and grain boundaries,
It has improved room temperature and high temperature characteristics as an effect based on dispersion strengthening of intragranular and grain boundaries by dispersed phase particles of nanometer size, and it is used not only for general high temperature structural materials but also for aircraft components,
It is useful as other ultra-high temperature structural members, and according to the present invention, this hardly sinterable material can be produced cost-effectively by the normal pressure sintering method, and can be applied to various engineering applications. Is what makes it possible.

[Brief description of the drawings]

FIG. 1 is a view showing an X-ray diffraction pattern of a sintered body.

FIG. 2 is a photomicrograph (magnification: 4000) showing a microstructure of a sintered body.

FIG. 3 is a photomicrograph (magnification: 4000) showing a microstructure of a sintered body instead of a drawing.

FIG. 4 is a micrograph (magnification × 4000) showing a microstructure of a sintered body, which is a drawing substitute.

FIG. 5 is a glass showing a change in temperature of bending strength of a sintered body.

FIG. 6 is a photomicrograph (magnification: 4000) showing a fractured surface of a sintered body.

FIG. 7 is a photomicrograph (magnification: 4000) showing a fractured surface of a sintered body.

[Procedure amendment]

[Submission date] November 6, 1996

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Claims (5)

[Claims] 1. An aluminum-substituted molybdenum disilicide intermetallic compound [Mo (Si, Al) ₂ ] is used as a matrix phase, and a grain boundary phase is made mainly of Al ₂ O ₃ crystals, and is composed of intragranular and grain boundaries of the matrix. And 5 to 20 as a disperse phase
A molybdenum disilicide-based composite material, which is a sintered body having a composite structure in which nanometer-sized SiC particles occupying volume% are uniformly dispersed. 2. An aluminum-substituted molybdenum disilicide intermetallic compound [Mo (Si, A
l) ₂ ] is Si: Al (atomic ratio) = 1−X: X [where X = 0.0
3. The molybdenum disilicide-based composite material according to claim 1, wherein the composite material has a composition of 3 to 0.20]. 3. A nanometer-sized silicon carbide powder is added to the aluminum-substituted molybdenum disilicide intermetallic compound powder [Mo (Si, Al) ₂ ] in an amount of 5 to 20% by volume, and 0.1 to 10% by volume based on the total amount. After mixing 10% by weight of a sintering aid and molding the resulting mixed powder into a desired shape,
In a non-oxidizing atmosphere, normal pressure sintering is performed at a temperature of 1500 to 1750 ° C.
2. A heat treatment at 1350 ° C.
3. The method for producing a molybdenum disilicide-based composite material according to item 1. 4. An aluminum-substituted molybdenum disilicide intermetallic compound [Mo (Si, Al) ₂ ] according to claim 3, wherein Mo: Si: Al (atomic ratio) = 1: 2 (1-
X): The method for producing a molybdenum disilicide-based composite material according to claim 2, wherein a powder having 2X (where X = 0.03 to 0.20) is used. 5. The method according to claim 3, wherein one or more oxides selected from boron oxide, yttrium oxide, and ytterbium oxide are used as the sintering aid. 2. The method for producing a molybdenum disilicide-based composite material according to item 1.