JP2887242B2 - Fiber reinforced ceramics - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fiber reinforced ceramic suitable for a cutting tool for cutting alloys such as iron, nickel, cobalt and the like or various materials.

[0002]

From BACKGROUND ART Conventionally, as a ceramic tool aluminum oxide (Al ₂ O ₃₎ is the mainstream, Al ₂ O
Although No. ₃ itself is excellent in wear resistance, it is inferior in strength and toughness, and various improvements have been made to eliminate these drawbacks. A typical material is Al ₂ O ₃
Against zirconium oxide (ZrO ₂ ) and silicon carbide (S
iC) or titanium carbide (TiC) is added to form a composite, and the material itself has been toughened. However, cutting conditions and the like as a tool have become more severe.
Tool materials are also required to have higher toughness and wear resistance.

[0003] In recent years, fiber-reinforced ceramics to which a fibrous substance made of various ceramics has been added in place of the above structure have attracted attention. Among them, a whisker-reinforced material obtained by dispersing whiskers of silicon carbide (SiC) in a matrix has attracted attention as a material for cutting difficult-to-cut materials because of its excellent properties.

[0004]

However, even when these whisker reinforced materials are used, the cutting of difficult-to-cut materials has a significantly shorter tool life than the case of cutting other materials, and in some cases, breaks. Wear may occur, and further improvement in wear resistance and fracture resistance as tool performance is required.

In particular, in the matrix-whisker system, the technical point is how to uniformly disperse the whiskers themselves in the matrix, based on the idea that the presence of aggregates of the whiskers themselves becomes a starting point of destruction and lowers the strength. Various uniform dispersion methods have been proposed, but the characteristics have not yet been improved. Further, a third additive capable of improving the sinterability and the properties has been searched for, but is not a definitive measure.

Accordingly, the present invention provides a ceramic excellent in toughness, especially in a fiber reinforced ceramic containing silicon carbide whiskers, and by using this, a fiber excellent in chipping resistance in cutting of difficult-to-cut materials. It is intended to provide reinforced ceramics.

[0007]

[Means for Solving the Problems] The present inventors have investigated the strengthening mechanism of the whisker-reinforced material and have repeatedly studied methods for improving various characteristics. Obtained the viewpoint of affecting the strength and toughness, and based on this, conducted a detailed study, contrary to the conventional idea of uniformly dispersing whiskers in the matrix, the area where whiskers are densely present in the matrix When scattered, the toughness was significantly improved while maintaining high hardness, and when cutting difficult-to-cut materials using this sintered body, we found that destructive wear was prevented and excellent cutting performance could be exhibited. Was. Further, it has been found that by setting the amount of free carbon in the sintered body to a predetermined value or less, characteristics having more excellent fracture resistance can be obtained.

That is, the fiber reinforced ceramics of the present invention comprises:
A matrix containing silicon carbide whiskers dispersed therein, wherein a plurality of regions where the silicon carbide whiskers are densely present are present, and the amount of free carbon in the ceramics is 0.16% by weight or less. It is characterized by the following.

Hereinafter, the present invention will be described in detail. The fiber reinforced ceramics of the present invention is roughly classified into a matrix component and a silicon carbide whisker component in terms of composition. This silicon carbide whisker is desirably 10 to 50% by volume, particularly 20 to 40% by volume.
By dispersing and containing at a ratio of volume%, the strength and toughness can be effectively improved, and when the addition amount of silicon carbide whisker is more than 50 volume%, the sinterability of the whole system is reduced, and desired characteristics are obtained. Can not be obtained, 10% by volume
If the amount is smaller than the above, the strengthening effect due to the addition of the silicon carbide whisker is reduced, and no improvement in the characteristics is observed.

It is believed that the improvement in toughness and strength in such a matrix-ceramic whisker-added system is due to the effect of pulling out the whisker (pull-out effect) on the progress of the crack. In order to exert the above-mentioned effect on the progress, it is important to disperse the whiskers uniformly and randomly in the matrix as shown in FIG.

On the other hand, in the present invention, silicon carbide whiskers are intentionally dispersed in a matrix in a non-uniform manner. Specifically, FIG. 1 is a schematic view of the structure of the fiber-reinforced ceramic of the present invention. Thus, region A where silicon carbide whiskers are densely formed in the matrix is formed, and such regions are scattered in the matrix. Region A where silicon carbide whiskers are densely present preferably has an average diameter of 20 μm to 200 μm, more preferably 40 μm to 200 μm.
Preferably, it is 150 μm. The regions A are uniformly scattered in the matrix, and the thickness between the regions A is 0.5 μm to 50 μm, particularly 3 to 3 μm.
The silicon carbide whiskers having a thickness of 0 μm are arranged so that the layer B is sparsely present. As a result, a fiber-reinforced ceramic having less chipping than the conventional one and having excellent fracture resistance can be obtained.

The matrix component used in the fiber reinforced ceramics of the present invention includes aluminum oxide, zirconium oxide, silicon nitride, silicon carbide and the like. From the viewpoint of wear resistance as a tool material, aluminum oxide is used. In this case, the aluminum oxide is preferably present as particles having an average crystal grain size of 0.2 to 10 μm. On the other hand, silicon carbide whiskers have a diameter of 0.3 to 2.0 μm and a length of 1.5 to 200 μm.
It is preferable that the whiskers are present as relatively short fibers of 3 to 50 μm, especially in a region where silicon carbide whiskers are densely present.

According to the fiber reinforced ceramics of the present invention, Y, Yb, Er, Dy, Sc,
In addition to oxides of Group 3a elements of the periodic table such as Ce, MgO,
By adding an oxide such as CaO, SiO ₂ , TiO ₂ , and Al ₁₈ B ₄ O _{33, the} sinterability of the system can be improved, and the properties such as hardness and toughness can naturally be improved. In addition, these additives are 0.1 to 1 with respect to the total amount.
It is desirable to add at a ratio of 0% by weight.

Among the sintered bodies having these characteristics, the amount of free carbon in the sintered body greatly affects the life of the cutting tool. This free carbon is contained in the silicon carbide whiskers or is formed from the reaction and decomposition of the raw materials and the matrix of the surface of the SiC whiskers during sintering,
It is considered that it mainly exists at the interface between the matrix and the silicon carbide and determines the bond between the matrix and the silicon carbide whisker. The amount of free carbon is preferably 0.16% by weight or less, particularly preferably 0.10% by weight or less. If the content is more than 0.16% by weight, the bond between the matrix and the whisker is reduced, and the particles are greatly shed during cutting, and the tool life is greatly reduced due to increased wear and initial generation of chipping. The amount of free carbon can be controlled by removing and reacting carbon produced by reaction and decomposition of the raw material and the surface of the SiC whisker during sintering in a firing atmosphere or an additive.
More specifically, it can be controlled by firing in a vacuum or nitrogen gas as an atmosphere, or by adding a metal such as metal Si, ZrO ₂ , TiN, SiO ₂ or an oxide and a nitride. Even in a reducing atmosphere, the amount of free carbon can be controlled under the above conditions.

According to a conventional method, such a fiber-reinforced ceramic sintered body is prepared by mixing a matrix material such as Al ₂ O ₃ and a silicon carbide whisker in a liquid, drying the mixture, and sintering by a hot press method or the like. Relative density 9
A method of obtaining a high-density body of 5% or more is adopted. On the other hand, according to the method of the present invention, a matrix material such as Al ₂ O ₃ and a whisker material and other additives are blended at a desired compounding ratio as required, and this is sufficiently mixed with a solvent by a known method. , And dried by spray drying to obtain an average particle diameter of 20 to 200 μm.
Create powder of about m.

According to the present invention, the spray-dried powder has an agglomerated portion where silicon carbide whiskers are densely present in the powder, and the silicon carbide whisker is sparsely present around the agglomerated portion and a large amount of matrix component is present. A powder having a surface portion to be formed is prepared.

Such a powder can be formed by controlling various conditions in spray drying. Specifically, it is necessary to control the slurry viscosity after blending to 6.0 poise or less, particularly 2 poise or less.
If it is higher than 0 poise, it is difficult to form a cohesive portion where whiskers exist densely and a surface layer portion where whiskers exist sparsely.
The temperature of the hot air in the spray-dry is between 80 ° C and 250 ° C.
However, the temperature is desirably 100 ° C to 200 ° C. In this case, if the inlet temperature is higher than the outlet temperature, the above-described desirable structure is likely to be formed. Atomizer rotation speed is 5000r
pm to 15000 rpm, preferably 8000 rpm
rpm to 10,000 rpm and the diameter of the aggregated portion is 20 μm
It tends to be 200 μm. If it is lower than 5000 rpm, the diameter of the aggregated portion tends to be large, and if it is higher than 15000 rpm, the diameter tends to be small. As described above, the diameter of the agglomerated portion and the thickness of the surface portion can be controlled by the conditions of the composition, the amount of whiskers, the slurry concentration and viscosity, and the spray-dry condition.

Next, after removing coarse particles from the powder obtained as described above by a mesh pass, hot press firing is performed. In the hot press firing, a pressure of 350 kg / cm ² or more is applied in a reducing atmosphere containing vacuum, an inert gas such as Ar or N _2, and carbon to 1650.
By sintering at a temperature of from ℃ to 2,000 ℃ for about 0.5 to 20 hours, it is possible to densify to a relative density of 99% or more. Further, as another firing method, after firing at a temperature of 1650 ° C. to 2000 ° C. in a vacuum or an inert gas or a reducing atmosphere, the temperature is further increased to 1650 ° C. in an inert atmosphere.
Hot isostatic firing at ２０００2000 ° C. can further increase the density.

[0019]

According to the conventional matrix-whisker addition system, when cracks develop in the ceramic, the cracks are deflected by running through the matrix and reaching randomly oriented whiskers. It consists of a mechanism in which energy disappears and cracks stop growing.However, according to the ceramics of the present invention, silicon carbide whiskers are dispersed unevenly, and areas where silicon carbide whiskers are densely present in the ceramics are formed in the matrix. By forming a dotted structure, the toughness can be dramatically increased.

Considering the reason, cracks easily propagate in the matrix, but when they reach the region where the silicon carbide whiskers are densely located, the cracks rapidly lose their energy due to the action of the densely located whiskers. It is considered that the crack cannot be further developed in the region A.
Further, since the amount of free carbon in the sintered body is set to 0.16% by weight or less, the bond between the silicon carbide whiskers and the matrix is strengthened, so that the fracture resistance can be further improved.
Therefore, for example, when the ceramic of the present invention is used as a tool material, it is excellent in strength, toughness, and the like, and can effectively prevent chipping accompanying the development of destructive wear and cracks in cutting difficult-to-cut materials.

[0021]

EXAMPLE An Al ₂ O ₃ powder (average particle size 0.2 μm),
SiC whiskers (short axis length 0.5 to 1.0 μm, aspect ratio 50, length 20 to 100 μm) were weighed in the proportions shown in Table 1 and thoroughly mixed with a nylon ball using water as a solvent and slurry. Was prepared. Next, this slurry was adjusted to a concentration of a viscosity of 0.2 to 4.0 poise or less, and the inlet temperature was 200 ° C., the outlet temperature was 120 ° C., and the atomizer rotation speed was 1
Spray-dry at 0000 rpm and average particle size 80
μm granulated powder was prepared.

Thereafter, the compact obtained by press-molding into a tool shape RNGN120416 was hot-pressed at 1650 to 2000 ° C. under a pressure of 350 kg / cm ² to produce a sintered body having a relative density of 99% or more.

[0023] As a comparative example, the mixture press-molded in a similar those uniformly mixing method with a ball mill in the same composition system, a pressure 350kg / cm ² 1650~
It was fired at 2000 ° C. for 1 hour to prepare a comparative sintered body.

For each of the obtained sintered bodies, the size of the whisker aggregation region and the thickness of the whisker-sparse layer were measured at several points by an electron micrograph, and the average value was determined. Further, an amount of free carbon in the sintered body was ground Al ₂ O ₃ and ZrO ₂ mortar sintered body, then, subjected to mesh pass at 200-325 mesh to remove coarse grains. that time,
Calculate the amount mixed from the mortar and use the carbon analyzer EMIA
The free carbon was removed as CO ₂ at 850 ° C. × 10 min with a −511 type to determine the weight difference, and the difference was calculated by subtracting the amount mixed from the mortar. It should be noted that JSS110-8 (Iron for castings, No. 1, No. A) was used as a standard sample, and the calculation was performed while confirming the measurement accuracy.

Further, JISR1601 for the sintered body
The bending strength and the toughness value were measured by the IF method, respectively, and the Vickers hardness was measured based on the above. Furthermore, using Inconel 718 as a work material, a cutting speed of 300 m / mi
A cutting test was performed under the cutting conditions of n, a cut of 1.0 mm / rev, and a feed of 0.1 mm, and the time until chipping occurred in the tool and the amount of flank wear after cutting for 3 minutes were measured. Table 2 shows the results.

[0026]

[Table 1]

[0027]

[Table 2]

As is clear from Tables 1 and 2, the whiskers are partially agglomerated according to the present invention,
Sample N in which the amount of free carbon was suppressed to 0.16% by weight or less
With respect to o, 1 to 9, it can be seen that properties such as toughness are excellent and the tool life is remarkably improved. In order to confirm the reason, the present inventor observed the progress of cracks between the comparative product and the present invention product, and in the comparative product, the crack was extended while being deflected by the whiskers. In the agglomeration region, the cracks stopped reliably, and the length of the cracks was shorter in the product of the present invention than in the comparative product. It was found that all the products exhibited long life.

Samples Nos. 11, 14 to 16 are samples in which no agglomerated regions are generated.

[0030]

As described in detail above, the fiber reinforced ceramics of the present invention has high hardness and high toughness, and can prevent chipping during cutting even in difficult-to-cut materials such as Inconel. Therefore, cutting stability with respect to the tool life can be provided, and the tool life can be extended.

[Brief description of the drawings]

FIG. 1 is a schematic view of the structure of the fiber reinforced ceramics of the present invention.

FIG. 2 is a schematic view of the structure of a conventional fiber-reinforced ceramic.

[Explanation of symbols]

 A Area where whiskers exist densely B Area where whiskers exist sparsely

Claims (1)

(57) [Claims] 1. A fiber-reinforced ceramic comprising silicon carbide whiskers dispersed in a matrix, wherein agglomeration regions in which the silicon carbide whiskers are densely scattered are scattered throughout the matrix and free carbon in the ceramics is provided. A fiber-reinforced ceramic having an amount of 0.16% by weight or less.