JPH0987005A - Martensitic transformation type ceramic solid solution, its production and high toughness composite material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a material excellent in toughness and strength by using a martensitic transformation type ceramic solid soln. represented by a rational formula of (Ln, Ln'0.05-0.5 )2 (Si, Al0.05-0.5 )3 N4 Ox (hereafter formula A) as a ceramic material or a mixture of the solid soln. with other ceramics. SOLUTION: Powders of Ln2 O3 , Ln'2 O3 , Al2 O3 and Si3 N4 are mixed by means of a mixer such as a ball mill and the resultant mixture is fired at 1,400-1,800 deg.C for 1-150min in an atmosphere of a non-oxidizing gas such as gaseous nitrogen with a high-temp. furnace such as a discharge plasma sintering machine to obtain the objective solid soln. represented by the rational formula A. This solid soln. is mixed with one or more kinds of compds. selected from among Al2 O3 , C-ZrO2 , perovskite ABO3 type multiple oxides, multiple bismuth oxide, ferrite, garnet, rare earth element-transition metal multiple oxides, germanates, phosphates, titanates, nitrides, carbides, borides and silicides and the resultant mixture is fired to obtain the objective high toughness composite material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a martensitic transformation type ceramic compound, a method for producing the same, and a high toughness composite material. In the field of inorganic materials, particularly in the field of ceramics, high toughness is obtained by performing martensitic transformation. It is a proposal for the novel ceramic compound (solid solution) and high toughness composite material shown.

[0002] The ceramic compound according to the present invention and the composite material using the same are used for engine parts, gas turbine blades, parts for gas turbines, parts for corrosion-resistant equipment, parts for crucibles, ball mills, and heat for high-temperature furnaces. Heat exchangers, heat-resistant materials for high-altitude flying objects, combustion tubes, parts for die-casting, insulating materials,
Fusion reactor materials, nuclear reactor materials, solar reactor materials, tools, thermal insulation materials, electronic circuit boards, seal materials, fittings and valve parts, pumps, nozzles, rollers, guides, ferrules, It is effectively used in bearings and other wide fields.

[0003]

2. Description of the Related Art In general, ceramics have many advantages, but a major disadvantage is that they have low toughness and are brittle.
To overcome this drawback, tetragonal zirconia utilizing martensitic transformation has been proposed, and is one of the toughest ceramic materials. The mechanism of high靱化high tenacity zirconia, stabilized tetragonal at high temperatures, it is added compound _{CaO, MgO, Y 2 O 3} , Ce
It is considered that this is due to the stress-induced phase transformation in which the tetragonal phase is transformed into a monoclinic phase by a stress by being stabilized to room temperature by the action of O ₂ or the like.

[0004]

As is clear from the above examples of stabilized and partially stabilized zirconia as high toughness ceramics, martensitic transformation is a very effective mechanism for toughening ceramic compounds. It is. However, to date, compounds exhibiting such properties have
Nothing is known other than tetragonal zirconia, and the toughening of ceramics using this zirconia is also known as Al ₂ O ₃
Has been successful, but in fact, sufficient results have not been obtained for silicon nitride, silicon carbide or other ceramics which are important as high-temperature materials. ("NATURE" (London) 258 [557] p703-704 [19
75) RCGarvie, RHJ Hannink and RTPascoe)

[0005] A main object of the present invention is to develop a new ceramic compound (solid solution) that undergoes martensitic transformation to increase or toughen. A specific object of the present invention is to provide ceramics and composite materials having excellent toughness and strength. Another object of the present invention is to propose an effective method for producing the above-mentioned ceramic compound.

[0006]

Means for Solving the Problems As a result of intensive studies to overcome the above-mentioned problems, the present inventors have determined that the mechanism of toughening zirconia has been changed from tetragonal to monoclinic due to stress-induced phase transformation. The increase in volume that occurs during the course of the change in the cracks is not only because the toughness is exhibited by preventing crack propagation, but also because
The mechanism of toughening by two martensitic transformations was clarified. In particular, a phenomenon called superelasticity or pseudoelasticity occurs when a compound that undergoes martensitic transformation forms twins after martensitic transformation, and the twins move on a twin plane due to stress, thereby increasing the mechanism of toughening. It is expressed. Therefore, if such a martensitic transformation compound is present, it should be able to be widely used for the production of high toughness ceramics.

[0007] The following novel compounds that transform into martensite have been developed to meet such demands. That is, the present invention relates to (Ln, Ln ′ _0.05-0.5 ) ₂ (Si, A
l _0.05-0.5) is a martensite transformation ceramic solid solution represented by the rational formula of ₃ N ₄ O _x.

The present invention also relates to the above compound, for example, (Ln,
Ln _1/3 ) ₂ (Si, Al _1/3 ) ₃ N ₄ O _{x and the} like; (a) a mixed powder of Ln ₂ O ₃ , Ln ′ ₂ O ₃ , Al ₂ O ₃ , and Si ₃ N ₄ ; _{(b) 1 / 2Ln 4 Al} 2 O 9, 1 / 3Ln' mixed powder _{2 O 3, Si 3 N 4} ;
And (c) a mixed powder of Ln ₂ Si ₃ O ₃ N ₄ , 1 / 2Al ₂ O ₃ , and 1 / 3Ln ′ ₂ O ₃ ; each of which is 1400 to 1800 in a non-oxidizing gas atmosphere.
This is a method of producing by firing at a temperature of 1 to 150 minutes.

The present invention also relates to (Ln, Ln ′ _0.05-0.5 ) ₂
(Si, Al _0.05-0.5) martensitic transformation ceramic solid solution represented by the rational formula of _{3 N 4 O x, Al 2} O 3, ZrO 2, perovskite ABO ₃ type composite oxide, a composite bismuth oxide, ferrite , Garnet, rare earth transition metal composite oxide, germanate, phosphate, titanate, nitride, carbide, boride, silicide, and the mixture is mixed and fired to form a composite It is a high toughness composite material characterized by the following.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have synthesized various oxide and nitride-based ceramic compounds and searched for their properties in order to find a new compound having a superelastic effect by martensitic transformation. As a result, Ln ₂ O ₃ · Si ₃ N ₄
The compound was found to undergo martensitic transformation. However, the effect of toughening was insufficient, so (Ln, Ln
When a solid solution represented by the _descriptive formula of ' _0.05-0.5 ) ₂ (Si, Al _0.05-0.5 ) ₃ N ₄ O _x was synthesized, a large toughening effect was obtained. Here, when Ln 'and Al are 0.05 or less, there is almost no effect of increasing toughness, and when Ln' and Al are 0.5 or more, impurities are generated, so that the range is 0.05 to 0.5. In addition,
In this descriptive formula, Ln and Ln ′ are Sc, Y, La, Ce, Pr,
It shows each rare earth element of Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu, and is a combination of these two kinds. Note that Ln 'and Al always exist in the solid solution with the same atomic weight. Therefore, Ln 'may be the same element as Ln. x varies with the amount of cations, and x =
The values are as shown in 3.38 to 7.3.

[0011] One of the above ceramic compounds according to the present invention
FIG. 2 shows an X-ray diffraction diagram of Y ₂ AlCe _2/3 O _5.5 N ₄ , which clearly shows that a single Y ₂ O ₃ .Si ₃ N ₄ type solid solution is formed. . FIG. 1 shows the results of measuring the thermal expansion of this compound in a nitrogen gas from room temperature to 1500 ° C. As shown in FIG.
Thermal expansion suddenly becomes larger than ℃.
It expands rapidly again from 1240 ° C and peaks and contracts at 1325 ° C. That is, the two rapid volume changes described above indicate that the compound undergoes martensitic transformation.

(Ln, Ln ′ _0.05-0.5 ) ₂ (Si, Al _0.05-0.5 ) ₃ N
_{In order for the 4} O _x solid solution to be a high toughness ceramic, it is necessary that it forms soft thermoelastic martensite and that twins are formed by the occurrence of martensite transformation. It is desirable that the particle size be 50 μm or less.

The ceramic compound according to the present invention exhibits high toughness by itself, but further includes other compounds such as Al.
₂ O ₃ , C-ZrO ₂ , perovskite ABO ₃ type composite oxide, composite bismuth oxide, ferrite, garnet, rare earth transition metal composite oxide, germanate, phosphate, titanate, nitride, carbide, Either boride or silicide
The toughness of these materials can be improved even in the case of a composite material in which more than one species are mixed and fired to form a composite. In the composite material thus obtained, residual stress is generated in the compound due to the difference in thermal expansion between the two raw materials, and the residual stress also causes (Ln, Ln ′ _0.05-0.5 ) ₂ (Si, Al _0.05-0.5 ) ₃ Twins can be formed in N ₄ O _x . That is, the ceramic compound and the composite material according to the present invention absorb the traveling energy of cracks by the superelastic effect accompanying twinning,
The progress of cracks is prevented, and high toughness is achieved.

Further, the present invention relates to another method for forming twins for _toughening , which comprises (Ln, Ln ′ _0.05-0.5 ) ₂ (Si,
Al _0.05-0.5 ) ₃ N ₄ O _{x A} sintered body or a composite material containing the same is subjected to a mechanical shock or a thermal shock due to quenching to form twins, It has the same superelastic effect as.

Next, the (Ln, Ln ′ _0.05-0.5 ) ₂ (S
A method for producing a ceramic solid solution represented by the _chemical formula of i, Al _0.05-0.5 ) ₃ N ₄ O _x will be described. First, Ln ₂ O ₃ , Ln ′ ₂ O ₃ , Al ₂ O ₃ , Si ₃ N ₄ 1/2 LnAl ₂ O ₉ , 1 / 3Ln ′ ₂ O ₃ , Si ₃ N ₄ Ln ₂ Si ₃ O ₃ N ₄ , 1 / 2Al ₂ O ₃ and 1 / 3Ln ′ ₂ O ₃ are used. The above raw materials are mixed by applying a mixing method such as a ball mill, a rod mill, a double coat blender, and a V-type mixer. However, as a starting material,
When a compound such as Ln ₂ Si ₃ O ₃ N ₄ or Ln ₄ Al ₂ O ₉ is used, impurities are less likely to be mixed into the product, which is advantageous.

Next, the mixed material is fired using a high-temperature furnace. The atmosphere of the furnace is vacuum,
It is necessary to use a non-oxidizing gas such as a nitrogen gas or an inert gas. Among them, a nitrogen gas atmosphere is most suitable. The sintering temperature is optimally in the range of 1350 to 1700 ° C. This is because the formation reaction does not occur at 1350 ° C or lower, and the compound dissolves and partially decomposes at 1700 ° C or higher. Preferably
The range of 1400 to 1650 ° C is good. The holding time during the firing is suitably from 1 minute to 150 minutes. If the time is less than 1 minute, the reaction time is too short and the reaction does not occur uniformly, and if it is more than 150 minutes, the reaction time is too long and the cost is high. Preferably, good results are obtained in the range of 1 to 120 minutes. The high-temperature furnace used here refers to a furnace capable of generating a high temperature of 1000 ° C. or higher.
Specific examples thereof include an atmosphere furnace using tungsten, molybdenum, platinum, or graphite as a heating element, a hot press, a hot isostatic press, and a pressurized sintering machine such as a discharge plasma sintering machine. Especially when using a discharge plasma sintering machine,
The reaction can be completed even if the holding time is several minutes.

[0017]

【Example】

Example 1 Table 1 shows that (Ln, Ln ′ _0.05-0.5 ) ₂ (Si, Al _0.05-0.5 ) ₃ N ₄ O _x
The conditions of the type of raw material, the number of moles mixed, the firing atmosphere, the firing temperature, and the firing time for producing the above are shown. A non-oxidizing gas atmosphere furnace was used for firing, and the pressure was 1 atm. The temperature was raised to the firing temperature over 60 minutes.

[0018]

[Table 1]

FIG. 2 shows the X-ray diffraction diagram of the product No. 4 among the production experiments No. 1 to No. 6 shown in Table 1. The X-ray diffraction diagrams of the other No. 1, No. 2, No. 3, No. 5, and No. 6 are almost the same as in FIG. 2, and the same crystal structure is obtained even if the type of raw material and rare earth oxide are changed. (Ln, Ln´ _0.05-0.5 ) ₂ (Si, Al
_0.05-0.5 ) ₃ N ₄ O _x solid solution is formed.

The above Y ₂ AlCe _2/3 Si ₃ N ₄ O _x compound (No. 4) was pulverized, and was crushed in a nitrogen gas using a discharge plasma sintering machine.
It was kept at 1400 ° C. for 1 minute under the pressure of a to obtain a fired body. The bending strength of this sintered body is 1000 MPa and the fracture toughness value is 10 MPa.
MPam ^1/2 .

The compound according to the present invention is comparable to the highest toughness zirconia among ceramics. Furthermore, the feature of this sintered body is that the strength when the surface is polished with, for example, 110 μm diamond is 10%.
It becomes a little large at 50MPa. This is because twins were formed on the surface by polishing. Generally, the strength of ceramics decreases when the surface is polished with such a large diamond. In particular, zirconia undergoes a transformation from tetragonal to monoclinic from the surface by such polishing,
The strength is significantly reduced.

Example 2 A fired product of a Y ₂ AlCe _2/3 Si ₃ O _5.5 N ₄ compound (N
Table 2 shows the conditions when the raw materials of o.11) and composite materials (Nos. 12 to 19) obtained by adding them to various ceramics and mixing them were produced using a discharge plasma sintering machine. Pressure is 29.4
MPa and uniform for all samples. Table 2 also shows, as comparative examples, the characteristics of hot-pressed SiC, sintered SiC, hot-pressed Si ₃ N ₄ , sintered Al ₂ O ₃ , and hot-pressed ZrO ₂ . The high toughness of the compounds of the present invention is due to martensitic transformation.

The toughness value of commercially available ceramics is the largest in hot-pressed ZrO ₂ , and the hot-pressed Si ₃ N ₄ has Kc = 7.0.
MPa · m ^1/2 and the second size, otherwise Kc =
5.0 MPa · m ^1/2 or less. The composite material to which the compound of the present invention is added has the toughness value of hot pressed ZrO ₂ , which indicates that the effect of improving the toughness is great. The temperature rise to the sintering temperature is a short time in the range of 10 to 20 minutes. The obtained sintered body and composite material were dense without pores.

[0024]

[Table 2]

[0025]

As described above, according to the present invention, a newly developed (Ln, Ln ′ _0.05-0.5 ) ₂ (Si, Al _0.05-0.5 ) ₃ N
_{The 4} O _x solid solution undergoes martensitic transformation, and the toughness and strength of the ceramic material obtained from it alone or the composite material obtained by mixing it with other ceramics are large, and the conventional high toughness zirconia with the highest toughness is obtained. It is comparable. Therefore, the compounds of the present invention are also very useful as raw materials for composite materials.

[Brief description of the drawings]

FIG. 1 is a diagram of a linear expansion curve of a ceramic compound according to the present invention and a differential curve thereof.

FIG. 2 is an X-ray diffraction diagram of the ceramic compound according to the present invention.

Claims (5)

[Claims] (1) (Ln, Ln ' _0.05-0.5 ) ₂ (Si, Al _0.05-0.5 ) ₃ N
A martensitic transformation type ceramic solid solution represented by the formula of ₄ O _x . 2. A method of mixing powders of Ln ₂ O ₃ , Ln ′ ₂ O ₃ , Al ₂ O ₃ , and Si ₃ N ₄ , and mixing the mixed powder at a temperature of 1400 to 1800 ° C. in a non-oxidizing gas atmosphere. And bake for 1-150 minutes, (Ln,
A method for producing a martensitic transformation type ceramic solid solution, characterized by obtaining a solid solution represented by the following formula: Ln ′ _0.05-0.5 ) ₂ (Si, Al _0.05-0.5 ) ₃ N ₄ O _x . 3. A powder mixture of Ln ₄ Al ₂ O ₉ , 1 / 3Ln ′ ₂ O ₃ and Si ₃ N ₄ is mixed, and the mixed powder is mixed in a non-oxidizing gas atmosphere.
Firing at a temperature of 1350-1700 ° C for 1-150 minutes, (Ln, Ln
_{'0.05-0.5) 2 (Si, Al} 0.05-0.5) 3 N 4 O x manufacturing method of the martensitic transformation ceramic solid solution, characterized in that to obtain a solid solution represented by the rational formula of. 4. A powder mixture of Ln ₂ Si ₃ O ₃ N ₄ , 1 / 2Al ₂ O ₃ and 1 / 3Ln ′ ₂ O ₃ is mixed, and the mixed powder is mixed in a non-oxidizing gas atmosphere at 1350 to 1700. Bake for 1 to 150 minutes at a temperature of
_{n, Ln' 0.05-0.5) 2 (Si} , Al 0.05-0.5) 3 N 4 O x manufacturing method of the martensitic transformation ceramic solid solution, characterized in that to obtain a solid solution represented by the rational formula of. (5) (Ln, Ln ' _0.05-0.5 ) ₂ (Si, Al _0.05-0.5 ) ₃ N
A martensitic transformation type ceramic solid solution represented by the formula of ₄ O _x is added to Al ₂ O ₃ , C-ZrO ₂ , perovskite ABO ₃ type composite oxide, composite bismuth oxide, ferrite, garnet, rare earth transition metal composite oxide. High-toughness composite material characterized by mixing at least one of a material, a germanate, a phosphate, a titanate, a nitride, a carbide, a boride, and a silicide, and sintering the mixture. .