JPS59102862A - Composite sintered ceramics - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to composite sintered ceramics, and more particularly to composite sintered ceramics that have high electrical conductivity and are capable of electrical discharge machining.

Ceramics have excellent heat resistance and oxidation resistance, so they are attracting attention as heat-resistant members and structural materials for machinery. Generally, in order to obtain high strength and high density oxide ceramics,
It is said that it is preferable to use a hot processing molding method, a so-called hot press method. However, in this method, the material is processed in a mold with a simple shape, so it is difficult to mold and manufacture parts with complex shapes.
This point is a major technical limitation of the hot press method. Further, although the hot pressing method does not produce a high-strength sintered body, there is a firing method in air or other atmosphere that has been widely used for ceramics.

However, in this case as well, it is difficult to determine the dimensions of the component with high precision in one step of sintering due to phenomena such as shrinkage that accompanies firing.

Therefore, in either method, it is ultimately essential to process the sintered body with high precision, but ceramics generally have the drawback of being extremely brittle. For this reason, the cutting process for ceramics is different from that for metal materials, the processing speed is limited, and it is difficult to obtain highly accurate dimensions, so improvements are desired in terms of both time and cost. In order to make effective use of the various excellent properties of ceramics and widely use them as various structural materials, we need technology and/or technology that can process them into desired shapes with high precision, similar to metal materials. Development of new materials is necessary. For example, manufacturing heat exchanger members, valves, gears, gas turbine blades, etc. requires not only simple cutting but also three-dimensional processing. When manufacturing molds with complex shapes using metal materials, it is possible to process curved surfaces with high precision using electrical discharge machining.
It has been impossible to perform electric discharge machining on many ceramics with low electrical conductivity.

As a result of various studies aimed at solving or alleviating problems in the processing of known ceramic materials, the present inventor discovered that ceramics contain a specific amount of distinctive silicon carbide crystals (usually called whiskers or whiskers). ) and a sintered material in which powder having a specific conductivity is dispersed has been found to satisfy these requirements. That is, the present invention focuses on group ①,
A ceramic having a parent phase of an oxide, nitride or carbide of a Group or IV element and having a specific resistance of 10 Ω-cm or less, the ceramic containing fibrous material in an amount of 5 to 50% based on the total weight of the ceramic. The present invention relates to a composite sintered ceramic characterized by containing silicon carbide crystals and 2 to 20% of conductive carbide, nitride, or boride powder dispersed therein.

Since the composite sintered ceramic of the present invention has high electrical conductivity, it has excellent electrical discharge machinability.

In particular, this composite ceramic has better electrical discharge machining characteristics because the conductive fine powder is uniformly dispersed in the sintered structure, compared to sintered ceramics that are simply a composite of fibrous silicon carbide crystals. will improve. Specifically, the electrical conductivity of the composite ceramic becomes higher, making it possible to improve the machining speed during electrical discharge machining. Furthermore, since electrical conduction within the tissue becomes more uniform, the finishing accuracy of the machined surface is improved. That is, a more uniform surface or line cut side occurs due to the electric discharge, which has the effect of reducing the surface roughness of the machined surface.

Fibrous silicon carbide (Si C
) The length and thickness of the crystals are not particularly limited, but the length is usually 10 to 500 μm, preferably 50 to 500 μm.
The thickness is usually 0.1 to 10μ, preferably 0.
It is preferable to use a material with a diameter of about 5 to 3 μm. length is 10
If it becomes shorter than μm at the #l end, a large amount of addition is required to increase electrical conductivity to the extent that electrical discharge machining is possible, as is the case when granular SiC is added and molded, and the original characteristics of ceramics are lost. There is a tendency to When the thickness of fibrous SiC becomes extremely thinner than 0.1 μm, mN
tends to break, resulting in a similar result as when using granular SiC. On the other hand, if the thickness becomes extremely thicker than 10 μm, the rigidity of the fiber increases, so that densification by sintering tends to become difficult.

The amount of fibrous SiC crystals dispersed in the ceramic is preferably 5 to 50% based on the total weight. When the amount of 3iCm fibers is less than 5%, the electrical conductivity of the sintered body is not sufficiently improved, while when it exceeds 50%, the densification of the sintered body tends to decrease. Fibrous S
The amount of iC crystal added is more preferably 10 to 40% of the total weight.

Carbide, nitride, or boride is used as the conductive powder added to improve electrical discharge machinability. An example of such a carbide is 3i C.

T! C, Zr C5B4 C5WC, Hf C, Ta
Examples of nitrides include TiN, TaN, ZrN, NbN, and VN.
Examples of borides include T!
B2, ZrB2, Hf82, Ta82, etc. can be mentioned. The type and amount of these conductive powders to be used may be appropriately determined in consideration of the amount of fibrous SiC crystals to be added, the electrical conductivity of the powder itself, and the like. However, if the total amount of both the SiC crystal and the conductive powder exceeds 70% of the total weight, a problem arises in that the original characteristics of the matrix ceramic to be composited are impaired.

If the amount of conductive powder added is less than 2%, no improvement in electrical discharge machining properties will be observed, and if it is more than 20%, the mechanical properties of the matrix ceramic will deteriorate (specifically, at high temperatures ( >800°C). In addition, the particle size of the conductive powder is not particularly limited, but
It is usually 2 μm or less, preferably 1 μm or less. If the particle size becomes too large, no improvement in discharge characteristics will be observed, and the strength will also tend to decrease.

In the present invention, oxides, nitrides, or carbides of Group (1), Group (2), or Group IV elements are used as the matrix. A wide variety of known oxides, nitrides, or compounds of group (1), (2), or (2) group elements can be used.

Examples of solid oxides include alumina, zirconia, magnesia, ferrites such as Fe2O3, single oxides such as uranium oxide and thorium oxide, MgAQ204, N! F
eO&,N! Various spinel-type compounds such as Cr0A, M(l Fe2Q, etc., la of perovskite structure)
Composite oxides such as Cr 03, La Sr Cr O3, Sr Zr 03, etc., nitrides such as silicon nitride, aluminum nitride, boron nitride, etc., and carbides such as silicon carbide,
Examples include boron carbide and titanium carbide. In the present invention, when using the same matrix as the conductive powder that is combined to improve electrical discharge machining characteristics, the conductive powder is likely to be absorbed into the matrix during sintering and lose its effectiveness. , it is preferred to use other types of conductive powders.

By doing so, fine particles of the conductive substance remain at the grain boundaries of the matrix crystal, and the discharge characteristics are further improved.

The composite ceramic of the present invention is manufactured as follows.

That is, a predetermined amount of fibrous SiC crystals and a predetermined amount of conductive powder are added to and mixed with ceramic powder to serve as a matrix, and after uniformly dispersing the mixture, a binder of about 0.1 to 2% of the weight of the mixture is added. is added, molded, dried, and sintered to obtain the desired composite ceramic. As the binder, preferably used is a solution of polyvinyl alcohol, acrylic resin, cellulose, sodium alginate, etc. in water, alcohol, or other organic solvent. A paste consisting of matrix ceramic powder, SiC crystal powder, and binder is molded into a predetermined shape by injection molding, extrusion molding, etc., and the resulting composite is pre-dried under heat or reduced pressure, and then heated to 600°C or less. The binder is removed by heating. Next, the dried molded body is sintered at a temperature of about 1200 to 2000° C. with or without pressure.

In addition, if necessary, add a small amount of MgO1 to AQ203 or Mgo, Y203, AQ203 to 513N4.
This does not preclude the combined use of sintering aids such as oxides or nitrides.

The composite sintered ceramics of the present invention not only makes it possible to manufacture mechanical parts with complex shapes, and also makes it possible to efficiently manufacture large quantities of small parts from large sintered bodies. Compared to a composite of only IN-like SiC crystals, the electrical discharge machining speed is improved, and it is possible to obtain a machined surface with high accuracy and excellent smoothness.

Example 1 100 Ifi parts of SI3N & powder (0.5-2 μm), 5 parts by weight of Mg0 as a sintering aid, and well-dispersed Si
C whisker (thickness 0.1 to 5 μm, length 50 to 500
um) 30 parts by weight, conductive powder bound SIC powder (1μ
m or less >10 parts by weight and 2 parts by weight of polyvinyl alcohol as a binder were added and thoroughly mixed to form a paste.

The resulting paste is formed into a thin plate using a vacuum filtration method.
300 ka/cm after drying at 130℃ for 10 hours
A sintered body with a relative density of 100% was obtained by sintering at 1800'C under pressure of 2.

Table 1 shows the specific resistance of the obtained sintered body, the wire machining speed in wire-cut electrical discharge machining, the roughness of the machined surface, and the air temperature strength. However, wire-cut electrical discharge machining requires a discharge pulse width of 6μ5eC, a discharge body dwell time of 20μ5eC, a current peak value of 3.5A, a tap voltage of 100V, and a wire diameter of 20μm.
This was done under the following conditions.

Comparative Example 1 A sintered body was obtained in the same manner as in Example 1 except that the conductive powder was not mixed with SiC powder. The physical properties of the obtained sintered body are also shown in Table 1.

Comparative Example 2 A sintered body was obtained in the same manner as in Example 1 except that fibrous SiC crystals and SiC powder were not added and combined.

The physical properties of the sintered body are shown in Table 1. However, since electrical discharge machining is not possible, machining speed and machining roughness are not shown.

Table 1 Example 2 100 parts by weight of AQ203 powder (0.2 to 1 μn+) was added with M as a sintering aid (102 parts by weight, well divided iB(I)
k S i C whiskers (thickness 0.1 to 5 μm.

Length 50 to 500 μm > 10 parts, conductive powder T
Add 5 parts by weight of iN powder (0.2-1.5 μm) and add enough? The combined materials were sintered at 1700°C under a force of 300 k(]/cm2 to obtain a sintered body with a relative density of 100%.

Table 2 shows the specific resistance of the obtained sintered body, the wire machining speed in wire-cut electric discharge machining, the surface roughness of the machined surface, and the room temperature strength. However, wire cut electrical discharge machining requires a discharge pulse width of 8 μsec, a discharge body stop time of 15 μsec, a current peak value of 8.5 A, a tap voltage of 110 V, and a wire diameter of 20 μsec.
The test was carried out under the conditions of μm.

Example 3 A sintered body was obtained in the same manner as in Example 2 except that 20 parts by weight of TiN powder as a conductive powder was combined. The physical properties of the obtained sintered body are also shown in Table 2.

Comparative Example 3 A sintered body was obtained in the same manner as in Example 2 except that fibrous SiC crystals and TiN powder were not added and combined.

The physical properties of the sintered body are shown in Table 2.

Table 2 (that's all)

Claims (1)

[Claims] ■ Ceramics with a matrix of oxides, nitrides, or carbides of group ■, group ■, or group IV elements and having a specific resistance of 10 Ω-cm or less, with
A composite sintered ceramic comprising 50% of fibrous silicon carbide crystals and 2 to 20% of conductive carbide, nitride or boride powder dispersed therein.