JPH05319911A - Fiber reinforced ceramics - Google Patents

Abstract

(57) [Summary] [Structure] At least one selected from titanium carbide whiskers, titanium nitride whiskers, and titanium carbonitride whiskers, which are heat-treated in an oxidizing atmosphere to form an oxide film in a matrix mainly composed of alumina. By adding seed whiskers in a proportion of 5 to 80% by volume, or by adding a sintering aid or an oxide film forming aid and baking, a part or all of the whiskers has a thickness of 300 nm or less. An oxide film containing Ti is formed. [Effect] Since the wettability between the matrix component and the whisker component can be improved and the occurrence of voids due to defective sintering can be suppressed, the strength, toughness and hardness of the sintered body can be increased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to fiber-reinforced ceramics containing fibrous substances such as whiskers, and more particularly to ceramics having excellent high toughness and suitable for wear resistant materials and tool materials.

[0002]

2. Description of the Related Art Alumina-based sintered bodies have been applied to various industrial machine parts as materials having excellent wear resistance,
Due to the drawback of poor toughness, the field of cutting tools has not expanded much. Therefore, various improvements have been conventionally proposed to improve the toughness. To improve the toughness by adding a fibrous substance typified by silicon carbide (SiC) whiskers to one of the examples, it has been proposed in JP-A-61-286271 and JP-A-62-41776. ing.

Since fiber-reinforced ceramics containing such SiC whiskers has high hardness of SiC itself and good thermal conductivity, it is used as a cutting tool for cutting a part of super heat-resistant alloy (rough cutting of Inconel 718). Although it shows excellent performance, since SiC has a property of easily reacting with iron, particularly iron oxide, when SUS304 or cast iron is cut, for example, wear rapidly progresses and cutting becomes impossible. There is.

Therefore, in recent years, for the purpose of preventing such reactivity with the work material, instead of SiC whiskers, a fibrous substance of titanium carbide (TiC) which has a lower reactivity with iron than SiC. It has been proposed to add (whiskers).

[0005]

However, ceramics containing such TiC whiskers have not yet been sufficiently investigated from the viewpoint of characteristics such as transverse rupture strength, toughness, hardness, etc. The current situation is that the level has not been reached.

Particularly, in terms of sinterability, when Al ₂ O ₃ is used as a main component as a matrix component, voids are generated in the sintered body, or an unsintered portion in which the unsintered portion exists in the sintered body. There was a problem in terms of the uniformity and sinterability of the bound body. Further, there is a problem that chipping tends to occur in the sintered body, and a sintered body having stable characteristics cannot be obtained.

[0007]

Means for Solving the Problems The inventors of the present invention have made extensive studies on the above problems, and in particular, regarding the sinterability, the wettability is lowered near the interface between the matrix and the whiskers. It was found that defective sintering occurred in the portion where the whiskers were aggregated.

Then, the present inventors have studied to improve the wettability between the TiC or TiN-based whisker component and the alumina matrix component. As a result, by forming a metal oxide film on the surface of the whisker, The inventors have found that the wettability to the matrix is significantly improved and a uniformly densified sintered body can be obtained.

That is, the present invention provides a fiber-reinforced ceramics containing at least one kind of whiskers selected from titanium carbide whiskers, titanium nitride whiskers, and titanium carbonitride whiskers in an alumina matrix. 300n thick on the surface
It is characterized by having a coating film made of a metal oxide of m or less.

The present invention will be described in detail below.

The fiber-reinforced ceramics of the present invention comprises a matrix component containing alumina as a main component and a whisker component composed of a cubic compound such as titanium carbide whiskers, titanium nitride whiskers and titanium carbonitride whiskers.

At this time, the whisker component to be blended is itself composed of a single crystal or a polycrystal, and the average diameter thereof is preferably 10 μm or less, particularly 0.5 to 4.0 μm, and the major diameter / minor diameter. An average aspect ratio to be displayed is 3 to 100, particularly 10 to 50. When the average diameter is 4 μm or less, the grain growth of the matrix during firing does not become excessive and high bending strength can be maintained, whereas when the average diameter is larger than 4 μm, it is difficult to control the grain growth of the matrix during firing. Becomes, strength,
Both toughness is likely to decrease. On the other hand, if the average aspect ratio is less than 3, the effect of fiber reinforcement is small and the toughness decreases, and
If it is larger than 0, it is difficult to mix the raw materials and the particles cannot be uniformly dispersed, so that the density of the sintered body is lowered, and thus the toughness tends to be lowered.

These whiskers are composed of acicular particles, have the function of suppressing the grain growth of the matrix component consisting of Al ₂ O ₃ during sintering, and have the effect of increasing the strength of the sintered body itself. This whisker ingredient is 5-8
It is dispersed and contained in an amount of 0% by volume, particularly 25 to 60% by volume. This is because when the amount of whiskers is less than 5% by volume, the amount of whiskers is small, and the effect of suppressing the grain growth of the matrix is small, the strength of the sintered body decreases, and when it exceeds 80% by volume, the sinterability deteriorates. This is because it becomes difficult to obtain a sintered body having a density.

According to the present invention, it is important to form a metal oxide film on a part or all of the surface of the added whiskers. The Ti-containing oxide coating may be, for example, TiO ₂ or a reaction product of TiO ₂ and other components contained in the ceramic. This oxide film may be formed on a part or all of the surface of the ceramic whisker, and the thickness thereof is 300 nm or less,
In particular, the thickness is preferably 5 to 100 nm. The thickness of the coating film according to the present invention is 300 nm or less because it is 300 nm.
If it exceeds, the hardness of the sintered body tends to decrease, and the wear resistance of the material tends to decrease. The optimum film thickness varies depending on the components forming the film, but generally 100 nm or less shows excellent properties.

Several methods can be used as a method for forming such an oxide film. One is a method of oxidizing the whisker surface by heat-treating the whisker raw material at a temperature of 500 ° C. or lower in an oxidizing atmosphere. At this time, the amount of oxygen is 10% or less of the weight of the whiskers, preferably 4% or less. When the heat treatment temperature exceeds 500 ° C., it becomes difficult to control the oxygen amount.

As another method, a metal oxide having a property of reacting with whiskers at a temperature during sintering or heating, for example, iron oxide, nickel oxide, cobalt oxide or the like is used in an amount corresponding to a desired coating thickness. It is also effective to add.

Further, as another method, it is effective to temporarily introduce a small amount of oxygen into the atmosphere during firing to partially oxidize it. For example, in the case of performing hot press firing, even if the raw material is filled in a carbon mold in the atmosphere and oxygen is present in the mold, the same firing temperature is maintained without performing gas replacement. The effect is obtained.

By such a treatment, the treatment may be performed so that the oxygen content in the whiskers finally becomes 0.2 to 7% by weight.

According to the present invention, the above Al ₂ O _{3 is also used.}
-It is desirable to incorporate a sintering aid to improve the formation of whisker surface coatings on TiC whisker-based materials. As the sintering aid to be used, those known as a sintering aid of Al ₂ O ₃ are used, and for example, MgO, Ca
Examples thereof include O, SrO, SiO ₂ , and oxides of Group 3a elements of the periodic table. These sintering aids are preferably used in a proportion of 0.02% to 8% by weight, particularly 0.5% to 5% by weight, based on the total amount. In addition, as the Group 3a element of the periodic table, particularly Yb, Nd, Er, Ce, Sm, Y, G
d, Dy and La are mentioned.

In the production of the fiber-reinforced ceramics of the present invention, alumina powder, a predetermined whisker component raw material, a sintering aid or an aid for forming the above-mentioned oxide coating is mixed in the above-mentioned ratio. The above mixture of each raw material is
It is fired after being formed into a desired shape by a desired forming means such as a die press, a cold isostatic press, an extrusion molding and the like.

For the calcination, a hot pressing method, a hot isostatic calcination method or the like is applied. Baking is 1450 to 1950 ° C
The temperature may be 0.5 to 6.0 hours in a reducing atmosphere in which an inert gas such as Ar or He is present, or in the presence of carbon or the like, and a pressurized or reduced pressure atmosphere thereof. During the firing, oxygen can be partially introduced as described above.

According to the present invention, the pressure application condition at the time of firing is important for increasing the density of the sintered body, and it is better to increase the pressure application rate in a high temperature range of 1000 ° C. or higher. Further, it may be enclosed in a glass capsule or the like, or may be subjected to HIP treatment using glass as a pressure medium.

[0023]

According to the present invention, the metal oxide film containing Ti is formed on the surface of the whiskers, whereby the wettability between the whiskers and the matrix component is improved and the sinterability can be enhanced. As a result, it is possible to suppress the occurrence of voids or the like due to defective sintering in the sintered body, so that the original improvement effect of the addition of whiskers can be exhibited, and the strength, toughness, and hardness of the sintered body can be exhibited. Can be increased.

[0024]

EXAMPLES Al ₂ O ₃ powder having an average particle size of 1 μm or less and a purity of 99.9% or more and various metal oxides shown in Table 1 were weighed in predetermined amounts, and then mixed and pulverized in an attrition mill for 12 hours.
On the other hand, TiC whiskers, TiCN whiskers or TiN whiskers having an average particle size (minor axis) of 2.0 μm and an average aspect ratio of 30 to 50 are subjected to an oxidation treatment at 150 ° C. for 10 minutes to 6 hours to obtain oxygen having different oxygen contents Created a whisker. Then, whiskers of this were added to the matrix components in the amounts shown in Table 1, sealed with nylon balls in a nylon pot, and mixed for 12 hours in a rotary mill. The mixed slurry was dried to be used as a raw material for hot pressing, and fired under the conditions shown in Tables 1 and 2 to prepare a bending test piece based on JIS.

Each of the obtained samples was ground to JIS 1601.
The three-point bending bending strength based on the above, Vickers hardness and K1c were measured by IF method after polishing to a mirror surface state. In addition, the thickness of the oxide film formed on the surface of the whiskers was measured from the fracture surface of the sintered body by an electron micrograph. The results are shown in Tables 1 and 2.

[0026]

[Table 1]

[0027]

[Table 2]

According to Tables 1 and 2, the samples No, 1, 1 prepared without oxidizing the whiskers were used.
Nos. 4 and 20 had low characteristics, and many voids were observed at the aggregated portions of the whiskers in the sintered body. In addition, the samples No. 9, 9 and 19 whose oxide film exceeds 300 nm
In both cases, the hardness decreased, and when used as a cutting tool, the amount of wear was large, and chipping was likely to occur, and the characteristics were greatly deteriorated.

On the other hand, all the samples of the present invention exhibit excellent hardness, strength and toughness, and a transverse strength of 70 kg /
mm ² , toughness of 5.0 MPa · m ^1/2 or more and Vickers hardness of 1800 kg / mm ² or more were achieved.

[0030]

As described in detail above, according to the present invention, the wettability between the matrix component and the whisker component is improved,
Since the generation of voids due to poor sintering can be suppressed, the strength, toughness and hardness of the sintered body can be increased. As a result, the range of application as various industrial machine component materials such as wear resistant materials and tools can be further expanded.

Claims (1)

[Claims] 1. A matrix containing alumina as a main component,
In a fiber reinforced ceramic containing at least one kind of whiskers selected from titanium carbide whiskers, titanium nitride whiskers, and titanium carbonitride whiskers, a metal oxide film having a thickness of 300 nm or less is formed on a part or all of the whiskers surface. Fiber-reinforced ceramics characterized by the following.