JP2794121B2 - Fiber reinforced ceramics - Google Patents

Description

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

(Prior art and its problems) Various proposals have conventionally been made from alumina (Al ₂ O ₃ ) -based sintered bodies because of their poor abrasion resistance and poor toughness.

One of them is to improve the toughness by blending a fibrous substance typified by SiC whiskers.
No. 6,271, JP-A-62-41776 and the like.

All of these are made mainly of alumina, 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).

(Problems to be Solved by the Invention) However, since SiC easily reacts with iron, particularly iron oxide, Al ₂ O ₃ -SiC whisker tools are often used for other whisker tools.
There is a tendency for the amount of wear to increase as compared with tools mainly composed of Al ₂ O ₃ . For example, when SUS304 is cut, conventional Al ₂ O ₃
If the tool is a system tool, even if the cutting conditions are sufficient, the wear containing the SiC whisker rapidly develops wear, making it impossible to cut.

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.

As described above, the Al ₂ O ₃ —SiC whisker-based tool has a problem that the cutting performance varies greatly depending on the work material.

At present, this is regarded as a so-called unstable tool, whose performance is significantly changed by a change in steel material, from the viewpoint of a tool user, and is currently avoided.

(Means for Solving the Problems) The present inventor has studied the above problems, and as a result,
It has been found that the above problem can be solved by using a titanium carbide (TiC) whisker as a fibrous substance to be added to Al ₂ O ₃ .

TiC is originally superior to SiC in terms of reactivity to iron, so by dispersing it in an appropriate amount in Al ₂ O ₃ ,
Very good abrasion resistance can be provided. However, TiC has a property that Young's modulus is slightly lower than SiC and the theoretical strength is lower than SiC.

Therefore, the present inventors have developed Al ₂ O ₃ containing TiC whiskers.
In porous ceramics, we found the best sintering aid and found the best shape of TiC whiskers to solve the above-mentioned drawbacks in toughness, and obtained a material with better toughness than the SiC whisker-added system.

That is, the present invention provides a matrix comprising at least one of Group IIIa oxides of the periodic table in an amount of 0.3 to 8% by weight, and the balance substantially consisting of alumina, having an average diameter of 2 μm or less and an aspect ratio of 1 to 2. 10-70%, more than 2.0 90-3
It is characterized in that titanium carbide having a ratio of 0% is dispersed and contained at a ratio of 10 to 60% by volume.

 Hereinafter, the present invention will be described in detail.

The TiC whiskers used in the present invention themselves are made of single crystal or polycrystalline, and have an average diameter of 2 μm or less, particularly preferably 0.2 to 1.0 μm, and an aspect ratio of 1 to 2 represented by a long diameter / short diameter. Things 10-70
%, It is important to use whiskers having a shape distribution of more than 2.0, 90 to 30%.

The reason why the average diameter is limited to the above range is that when the average diameter is 2 μm or less,
This is because the stress due to the difference in thermal expansion with Al ₂ O ₃ does not become excessive, and high bending strength can be maintained. If it is larger than 2 μm, it is difficult to disperse uniformly, and the strength and toughness vary. Also, when used as a cutting tool, the flank boundary wear tends to increase.

On the other hand, as for the aspect ratio, as shown in FIG. 1, as the ratio of the aspect ratio exceeding 2 increases, the toughness improves as the ratio increases. However, when the aspect ratio exceeds 90%, the sinterability deteriorates and voids are easily generated. The flexural strength is improved as the ratio of the aspect ratios 1 to 2 is increased, but when it exceeds 70%, the toughness is remarkably reduced, so that the effect of whisker addition cannot be obtained.
If the aspect ratio 2 or more is less than 30% or the aspect ratio 1 or 2 is less than 10%, the transverse rupture strength and toughness are the same as those of the Al ₂ O ₃ —TiC particle dispersion system, and the whisker addition effect is low. I can't get it.

As a matrix component for dispersing the whiskers, Al ₂ O ₃ containing at least one oxide of a rare earth element as a sintering aid in an amount of 0.3 to 8% by weight, particularly 1 to 5% by weight, is used. Used. If the amount of the auxiliary agent is less than 0.3% by weight, sinterability is poor and a dense material cannot be obtained. If it exceeds 8% by weight, the hardness of the sintered body is reduced, and the cutting performance is significantly deteriorated.

Note that rare earth oxides are particularly Yb, Nd, Er, Ce, S
m, Y, Gd, Dy, and La.

According to the invention, the whiskers are dispersed in the matrix at a rate of 10 to 60% by volume, in particular 30 to 50% by volume. If the whisker dispersion is less than 10% by volume, the effect of adding whiskers is insufficient, and if it exceeds 60% by volume, the sinterability is reduced.

In order to manufacture such ceramics, first, the Ti
The C whiskers and the matrix are mixed and pulverized at the above-mentioned ratios, and then molded and fired by a desired molding means, for example, a die press, a cold isostatic press, or extrusion molding.

As the firing, a normal firing, a hot press method, a hot isostatic firing method, or the like is applied. Sintering is performed at a temperature of 1650 to 1850 ° C.
Such a reducing atmosphere in which an inert gas or carbon or the like is present, and a pressurized or reduced pressure atmosphere may be performed for 2.0 to 6.0 hours.In particular, in order to obtain a highly dense body,
A sintered body having a theoretical density ratio of 96% or more may be obtained by ordinary firing and hot pressing, and then hot isostatic firing may be performed.

 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 and a rare earth oxide powder were weighed at the ratio shown in Table 1, and then mixed and pulverized for 12 hours by an attrition mill. Five kinds of TiC whiskers as shown in Table 1 (average diameter of 1 μm) were added to this mixed powder.
Was added in a predetermined amount, sealed in a nylon pot together with nylon balls, 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 1750 ° 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 to obtain a three-point bending strength based on JIS1601, and polished to a mirror surface to obtain K1 by IM method.
c was measured.

 The results are shown in Table 2.

The results in Table 2 are plotted in FIG.

(Example 2) In the same manner as in Example 1, B among the whiskers shown in Table 1 was used as a TiC whisker, and a TiC whisker was used as a matrix.
A sintered body dispersed in alumina containing 3% by weight of Yb ₂ O ₃ was obtained, and the bending strength and toughness were measured in the same manner as in Example 1.

 The results are shown in Table 3.

According to Table 3, the average diameter of the TiC whiskers used is 2
No. 1 larger than μm had variations in the characteristic values of both the bending strength and the toughness, and also had unevenness in the dispersibility. TiC
No. 6 in which the amount of whisker added was less than 10% by volume did not show improvement in the transverse rupture strength and toughness.

No. 13 in which the amount of whiskers exceeds 60% by volume, No. 14 in which the rare earth oxide is not contained in the matrix, and No. 15 in which the amount of the rare earth oxide is less than 0.3% by weight are all sintered. Due to insufficient bonding, voids remained in the sintered body, and voids were also confirmed in No. 20 containing excessive rare earth oxides.

Furthermore, in Nos. 29, 30, and 31 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 were not satisfactory. Was.

For these comparative examples, the present invention product 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 3) In Table 3, the composition of No. 9 was compared with the composition of Example 2 using SiC whiskers having a diameter of 0.7 μm and an aspect ratio of 30 in place of TiC whiskers in Example 2 for comparison.
An NGN1204 shaped tool was created.

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 No. 9 tool showed slightly better wear resistance than the comparative product.

Similarly, when a tool of SNGN120412 shape was created and SUS304 was cut at a depth of cut of 2 mm, feed of 0.3 mm / rev, and a cutting speed of 300 m / min, the wear of the comparative product rapidly developed and was broken, whereas the No. 9 tool Could cut for more than 10 minutes.

(Effects of the Invention) As described in detail above, according to the present invention, the reactivity with iron oxide is reduced by dispersing and containing TiC whiskers having a specific shape distribution in an alumina matrix,
In addition, it is possible to obtain ceramics with excellent bending strength and toughness, thereby obtaining excellent performance as a tool that can cut any work material, and expanding the use of fiber reinforced ceramics as various machine parts. it can.

[Brief description of the drawings]

FIG. 1 is a view showing the relationship between the whisker shape distribution and the bending strength and toughness.

Claims (1)

(57) [Claims] 1. An oxide of at least one of Group IIIa oxides of the Periodic Table having an average diameter of 2 μm or less in a matrix substantially consisting of 0.3 to 8 wt. A fiber-reinforced ceramic comprising 10 to 60% by volume of titanium carbide whiskers having a shape distribution of 70%, more than 2.0 and 90 to 30%.