JP2720093B2 - Fiber reinforced ceramics - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to ceramics containing a fibrous substance such as whiskers, and more particularly to ceramics excellent in high toughness and particularly suitable for tools.

(Prior Art) Alumina (hereinafter, referred to as Al ₂ O ₃ ) sintered body has been proposed variously because of its abrasion resistance, but its inferior toughness.

One of them is to improve the toughness by blending a fibrous substance typified by silicon carbide (hereinafter referred to as SiC) whiskers in JP-A-61-286271 and JP-A-62-41776.
And so on.

All of these are mainly made of Al ₂ O ₃ , added with SiC whiskers, and fired by hot pressing or the like.

Fiber-reinforced ceramics containing such SiC whiskers have high hardness of SiC itself and good thermal conductivity,
When used as a cutting tool, it shows excellent cutting characteristics when cutting some super heat-resistant alloys (rough cutting of Inconel 718).

It has also been proposed to use titanium carbide (hereinafter referred to as TiC) whiskers in addition to SiC whiskers as a fibrous substance.

(Problems to be Solved by the Invention) However, since SiC easily reacts with iron, particularly iron oxide, Al ₂ O ₃ -SiC whisker-based tools are often mainly composed of other Al ₂ O _3. The amount of wear tends to be larger than that of tools. For example, when SUS304 is cut, conventional Al ₂ O
_{In the case of a 3} series tool, even if the cutting conditions are sufficient, the tool containing SiC whiskers rapidly wears out, making cutting impossible.

Also, it has been confirmed that the amount of wear in cutting of cast iron is larger than that of Al ₂ O ₃ based tools.

Further, Al ₂ O ₃ —TiC-based tools tend to have insufficient toughness, and have a drawback that they tend to be broken when an excessive load occurs during cutting.

(Means for Solving the Problems) The present inventors have repeatedly studied the above problems, and as a result,
The Al ₂ O ₃ instead of using the SiC and TiC whiskers as toughness reinforcing material in a composite material mainly composed, by substituting a part or all of the Al ₂ O ₃ acicular Al ₂ O _3, mixed TiC thereto By doing so, it has been found that a fiber-reinforced ceramic having high toughness and bending strength and sufficiently applicable to cutting of iron-based materials can be obtained.

Further, the present inventors have found that, in the above Al ₂ O ₃ -TiC-based ceramics,
A material having better mechanical properties such as toughness than the Al ₂ O ₃ -SiC whisker-added system was obtained.

That is, the present invention substantially has TiC in a ratio of 20 to 70% by weight, and the balance is composed of Al ₂ O ₃ , a sintering aid and unavoidable impurities, and the sintered body has an aspect ratio of 1.5 or more. Needle-like A
l ₂ O ₃ is present in a proportion of 5% by volume or more,
It is characterized in that a Group IIIa oxide of the periodic table is selected as a sintering aid and is added at a ratio of 0.01 to 8% by weight.

 Hereinafter, the present invention will be described in detail.

The major feature of the fiber reinforced ceramics of the present invention is that it contains Al ₂ O ₃ and TiC as main components, further contains a sintering aid and unavoidable impurities, and a part or all of the Al ₂ O ₃ component is acicular. It consists of particles. The addition of this acicular Al ₂ O ₃ greatly improves the toughness of the sintered body while maintaining the wear resistance and non-reactivity with iron of the Al ₂ O ₃ itself, and the addition of Al ₂ O ₃ by the addition of TiC Can suppress grain growth and increase the strength of the sintered body. According to the ceramic of the present invention, the TiC component is dispersed and contained at a ratio of 20 to 70% by weight, particularly 30 to 50% by weight, and particles having an aspect ratio of 1.5 or more as acicular Al ₂ O ₃ are contained in the sintered body. Volume% or more, especially 20
It is present in a volume% or more.

Here, the reason for limiting the amount of TiC to the above range is that if the amount is less than 20 weight, the effect of suppressing the grain growth of Al ₂ O ₃ is weakened, and the acicular Al ₂ O ₃ becomes spherical, If the content exceeds 70% by weight, the sinterability decreases, and the fracture toughness and the bending strength also decrease. The reason why the amount of the acicular Al ₂ O ₃ is limited to 5% by volume or more is that if the amount is less than 5% by volume, improvement in toughness of the sintered body cannot be expected.

Further, according to the present invention, a sintering aid is blended to improve the sinterability of the Al ₂ O ₃ —TiC-based material. Examples of the sintering aid used include at least one selected from Group IIIa oxides of the periodic table, and specifically, Yb, Nd, E
r, Ce, Sm, Y, Gd, Dy and La. These sintering aids are contained in a total amount of 0.01 to 8% by weight, particularly 1 to 5% by weight. If the amount of the auxiliary agent is less than 0.01% by weight, sinterability is poor and a dense material cannot be obtained, and acicular Al ₂ O ₃
No improvement in toughness in the added system. 8% by weight
Even if it exceeds, voids are generated in the sintered body, which is not desirable.

In producing the fiber-reinforced ceramics of the present invention, a needle-like Al ₂ O ₃ or a component capable of forming needle-like Al ₂ O ₃ by firing and a TiC powder are used as raw materials, and a sintering aid is added thereto and mixed. I do.

The acicular Al ₂ O ₃ used in the present invention itself is composed of a single crystal or polycrystal, and has an average diameter of 2 μm.
m or less, particularly preferably 0.2 to 0.7 μm, and the average of the aspect ratio represented by the major axis / minor axis is 3 to 100, particularly 10
To 30 are used. When the average diameter is 2 μm or less, the grain growth during sintering does not become excessive, and a high transverse rupture strength can be maintained. On the other hand, when the average diameter is larger than 2 μm, the grain growth of the crystal grains during sintering is remarkable, Control becomes difficult, the strength is reduced, and the toughness varies. Also, when used as a cutting tool, the flank boundary wear tends to increase.

On the other hand, if the average aspect ratio is less than 3, the effect of fiber reinforcement is reduced and the toughness is reduced. If the average is more than 100, the handling of the raw materials is difficult and uniform dispersion is not possible, and the toughness tends to be reduced. Even in this case, if a part of the mixture is crushed and mixed, it can be used without any problem.

The above acicular Al ₂ O ₃ can be easily produced based on, for example, a production method described in Japanese Patent Application No. 1-308619, and according to this production method, a needle-like Al ₂ O ₃ is used instead of the acicular Al ₂ O ₃ . Even if aluminum borate is used, needle-like Al ₂ O ₃ is generated by firing, so there is no problem, but in this case, boron oxide is generated by decomposition of aluminum borate, and boron oxide deteriorates the characteristics of the sintered body Therefore, it is necessary to take care that the amount of boron in the sintered body does not exceed 5% by weight.

On the other hand, the size and shape of the TiC component can be arbitrarily selected, but the average particle size is preferably 3 μm or less in order to increase the effect of suppressing grain growth.

According to the present invention, in the mixing of the TiC component and the Al ₂ O ₃ component, the needle-like Al ₂ O ₃ tends to have a smaller aspect ratio by firing, so that it may be present in the sintered body. It is desirable to mix in a slightly larger amount than the amount to be mixed.

The mixture of each of the above-mentioned raw materials is formed and fired by a desired forming means, for example, a die press, a cold isostatic press, an extrusion molding or the like.

As the firing, a normal firing, a hot press method, a hot isostatic firing method, or the like is applied. Calcination is performed at a temperature of 1450 to 1850 ° C, Ar, He
In a reducing atmosphere in which an inert gas such as carbon or the like is present, and in a pressurized or reduced pressure atmosphere,
It may be performed for 6.0 hours, and in order to obtain a high-density sintered body, a normal firing and a hot press method are used to obtain a theoretical density ratio of 96.
% Sintered body and hot isostatic firing
It may be fired at 500 to 2000 atm and 1450 to 1800 ° C.

 Hereinafter, the present invention will be described with reference to the following examples.

(Example 1) Al ₂ O ₃ powder having an average particle diameter of 1 μm or less and a purity of 99.9% or more, TiC powder having an average particle diameter of 1 μm or less, and a sintering aid powder were weighed and then mixed and pulverized for 12 hours by an attrition mill. did.
A predetermined amount of Al ₂ O ₃ having an aspect ratio of 10 to 30 was added to the mixed powder, sealed in a nylon pot together with a nylon ball, and mixed for 12 hours by a rotary mill. The slurry after mixing was dried to obtain a raw material for hot pressing.

This raw material is filled in a carbon mold and heated at 1700 ° C for 1 hour for 30 hours.
Hot press firing was performed at a pressure of 0 kg / cm ² to prepare a bending test piece based on JIS.

Each obtained sample was polished and polished to a three-point bending strength, Vickers hardness and a mirror surface based on JIS1601, and K1c was measured by IM method. The Al ₂ O ₃ particles having an aspect ratio of 1.5 or more in the sintered body were determined by surface analysis from an electron micrograph.

 The results are shown in Table 1.

According to Table 1, samples Nos. 1 to 8 to which an appropriate amount of Group IIIa oxide of the periodic table was added as a sintering aid were all acicular Al ₂ O
_It shows better characteristics than Sample No. 20 which does not contain ₃ .
In Sample No. 9 and Sample No. 14 in which the amount of the sintering aid added was small, voids were generated in the sintered body, and both the bending strength and the hardness decreased.
Sample N with less Al ₂ O ₃ with aspect ratio of 1.5 or more in sintered body
In o.21, the improvement in fracture toughness was slight. Sample No. 25 containing a small amount of titanium carbide had a low hardness, and sample No. 30 having a too large amount reduced the sinterability, so that a dense sintered body could not be obtained.

Furthermore, in samples No. 31, 32, and 33 using MgO, SiO ₂ and CaO conventionally used as an auxiliary in the matrix, sintering was insufficient and voids were confirmed, and the characteristic values could be satisfied. Did not.

For these conventional examples, the products of the present invention has excellent flexural strength and toughness both, specifically bending strength 55 Kg / mm ² or more, toughness 5.5MPam ^1/2 or more void-free dense Ceramics.

(Example 2) In Table 1, an RNGN1204 shape tool was prepared using the compositions of Nos. 1 and 23 and No. 20 for comparison.

Using these tool specimens, cut Inconel 718 (solution-treated product) at 2mm, feed 0.3mm / rev, cutting speed 300m
After cutting for 5 minutes at / min, the tools of samples Nos. 1 and 23 were able to perform stable cutting with less chipping of the boundary wear portion than the comparative sample No. 20. Also, there was little flank wear. As described above, the product of the present invention exhibited excellent wear resistance as compared with the comparative example.

As described in detail above (Effect of the Invention) According to the present invention, Al ₂ O ₃ by containing the acicular Al ₂ O ₃ in -TiC ceramics, Al ₂ O ₃ which has been conventionally used - Excellent wear resistance and strength compared to TiC and Al ₂ O ₃ -SiC systems are obtained, and as a material for tools that can be used for any work material or for other machine parts, fiber reinforced ceramics Applications can be expanded.

Claims (1)

(57) [Claims] 1. Titanium carbide is 20 to 70% by weight, and at least one of Group IIIa oxides of the periodic table is used as a sintering aid in an amount of 0.0
A sintered body containing aluminum oxide and unavoidable impurities in an amount of 1 to 8% by weight, and aluminum oxide having an aspect ratio of 1.5 or more in the sintered body in an amount of 5% by volume.
Fiber reinforced ceramics characterized by being present in the above ratio.