JP2581939B2 - High-strength alumina sintered body and method for producing the same - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a sintered body containing alumina and zirconia as a main component and a method for producing the same, and particularly to an improvement of a sintered body useful as a cutting tool or a material for high temperature. About.

(Prior art)

A tool made of ceramic has advantages such as excellent hardness, wear resistance, and heat resistance, but has a problem that chipping and chipping easily occur, and its use has been limited to finishing and the like. However, with the advancement of machine tools, there is an increasing need to increase the cutting speed and lengthen the cycle time for tool change. Corresponding ceramic tools are also required to be stable and have high strength.

Alumina (Al ₂ O ₃ ) has attracted attention as a material useful as a cutting tool because of its low reactivity with metals and excellent wear resistance, but there was a problem of low fracture toughness (K ₁ c). Zirconia (ZrO ₂ ) has high flexural strength and fracture toughness, but shows a sharp decrease in strength at 200 to 300 ° C, is thermally unstable, and reacts violently with iron. There was nothing.

Therefore, by dispersing containing ZrO ₂ in Al ₂ O _3, possible to improve the fracture toughness of the Al ₂ O ₃ it is performed. Conventionally, two types of methods for improving the fracture toughness have been proposed. One is monoclinic ZrO _{2 in} Al ₂ O ₃ sintered body.
And microcracks are generated by the phase transition of ZrO ₂ .

The other is to disperse tetragonal ZrO ₂ in an Al ₂ O ₃ sintered body to absorb the energy at the crack tip by the phase transition of ZrO ₂ .

[Problems to be solved by the invention]

However, in the former, although the fracture toughness is improved, the bending strength is low and it is not practical. The effect of improving the fracture toughness in the latter method is slightly bending strength of inferior is greatly improved by the effects and the like of the compression stress produced by the processing of the energy absorption and the surface at the crack tip than in the former case, Al ₂ O
During ₃ ZrO ₂ in order to present the ZrO ₂ as tetragonal 0.3
It is necessary to disperse as fine particles having a size of 0.5 μm or less.

Since it is technically very difficult to control ZrO ₂ in the sintered body to 0.5 μm or less, even if a small amount of a stabilizer such as MgO, CaO, Y ₂ O ₃ is added and the ZrO ₂ particles are about 1 μm, It was controlled so that metastable tetragonal ZrO ₂ could be produced.

In the above method, there is a problem that some particles are excessively stabilized due to non-uniform dispersion of the additive and do not contribute to energy absorption at the crack tip. Metastabilization of the crystals has not been performed, and it has been almost impossible to metastabilize the cubic crystals without adding any stabilizer.

[Object of the invention]

The present invention is aimed at solving the problems as described above, in particular, without the addition of stabilizing agents such as described above, substantially consists Al ₂ O ₃ and ZrO _2, An object of the present invention is to provide an alumina-based sintered body having excellent bending strength and fracture toughness and a method for producing the same.

[Means for solving the problem]

The present inventor has repeated research on the above-mentioned problem,
Al ₂ O ₃ and distortion occur ZrO ₂ powder in the dry ground powder itself, after molding it, cubic ZrO ₂ or tetragonal and cubic in relatively when fired at a low temperature alumina crystal intermediate ZrO ₂
It has been found that the crystals can be made metastable, which results in better transverse strength and fracture toughness than the conventional tetragonal ZrO ₂ dispersion.

That is, the sintered body of the present invention is an alumina-based sintered body composed of 1 to 30% by weight of ZrO ₂ and the balance being Al ₂ O ₃ and unavoidable impurities, and is a measurement chart of laser Raman spectroscopic analysis of the sintered body. Characterized in that a peak of ZrO ₂ exists at a position of 600 ± 10 cm ⁻¹ .

The manufacturing method of the sintered body, a ZrO ₂ powder 1 to 30
After dry-pulverizing and activating the alumina powder containing the weight%, after molding, it is fired at a low temperature of 1500 ° C. or less.

Usually, in the Al ₂ O ₃ —ZrO ₂ system, the improvement in the transverse rupture strength and the improvement in the toughness were contradictory. To improve the transverse rupture strength, it is effective to atomize ZrO _{2 in} the sintered body (0.5 μm or less). However, some ZrO ₂ becomes too stable.
Metastable ZrO ₂ involved in energy absorption is reduced, and fracture energy is not absorbed and toughness is reduced. On the other hand, ZrO ₂ particles
When the thickness is about 0.5 to 1.0 μm, the transition from tetragonal ZrO ₂ to monoclinic ZrO ₂ becomes easy and the toughness is improved, but the microcracks and ZrO ₂ particles generated by the transition become fracture sources and the bending strength decreases. I do.

On the other hand, in the present invention, the bending strength and the fracture toughness are simultaneously improved. The basic composition of the sintered body in the present invention is such that ZrO ₂ is 1 to 30% by weight, particularly 15 to 20% by weight, and the balance is composed of Al ₂ O ₃ and unavoidable impurities, and the amount of ZrO ₂ is 1% by weight. If the amount is less than 30%, the toughness decreases. If the amount of ZrO ₂ exceeds 30% by weight, the bending strength and the toughness decrease.

It is desirable that the inevitable impurities of SiO ₂ , Fe ₂ O ₃ , and TiO ₂ be reduced as much as possible, but there is no problem if it is 3% by weight or less based on the total amount.

The features of the alumina sintered body according to the present invention will be described with reference to the measurement charts in the laser Raman spectroscopy shown in FIGS. 1 and 2. Comparing the charts of FIG. 1 and FIG. 2, it is understood that a peak exists near 600 cm ⁻¹ in FIG. When the peak at 600 cm ^-1 is examined, it is generally found that monoclinic ZrO ₂ (m-ZrO ₂ )
0 cm ^-1, 180cm ^-1, and 630 cm ^-1, tetragonal ZrO ₂ (t-ZrO ₂₎
Has a main peak near 270 cm ^-1 and 640 cm ^-1 , whereas cubic ZrO ₂ (c-ZrO ₂ ) has a main peak near 610 to 600 cm ^-1 . From this, it is determined that this 600 cm ⁻¹ peak indicates cubic ZrO ₂ .

In particular, the peak height Hc of c-ZrO ₂ around 600 cm ⁻¹ is, as apparent from the examples described later, the ratio (Hc / Hc / H ₂₎ in comparison with the peak height _HA of Al ₂ O ₃ around 415 cm ^−1. The larger the value of H _A ) is, the more excellent the characteristics are. Particularly, (Hc / H _A ) × 100
Above 20 the properties are even better.

Next, the characteristics of the sintered body of the present invention are analyzed based on the X-ray diffraction curve.

FIG. 3 is an X-ray diffraction curve of the sintered body of the present invention, and FIG. 4 is an X-ray diffraction curve of the sintered body of the comparative example.

The X-ray diffraction curve of ZrO ₂ has been studied in the past. For example, monoclinic ZrO ₂ has been studied by Lewis et al. (ANP Dept.
CINCINATTI, 15, OHIO) is, Smith, etc. for the tetragonal _{ZrO 2 (Anaual Report to the Joint} Committee on Powder D
iffraction Standard, 1973), but also for the cubic _{ZrO 2 Katz (J, Am,} Ceram, Soc., 54,531,1971) are presented respectively.

Normally, a tetragonal crystal is used in the X-ray diffraction curve of Cu-K α ray.
The (101) plane of ZrO ₂ (t-ZrO ₂ ) has a peak at 29.8 °, and the crystal plane spacing is 2.995 °, while cubic ZrO 2
The (111) plane of ₂ (C-ZrO ₂ ) has a peak at 30.5 °, and the crystal plane spacing is 2.93 °. On the other hand, the sintered body of the present invention has a ZrO ₂ of more than 29.8 ゜, and its crystal plane spacing is
It is considered to be in the range of 2.93 to 2.995Å. Also, c-Z
The peak of rO ₂ is 2θ = 30.5 °, 35.1 °, 50.6 °, 60.
The peaks of 35.1% and 63.1% overlap with those of α-alumina, and 50.6% are monoclinic Zr
The peak of O ₂ (m-ZrO ₂ ) or tetragonal ZrO ₂ overlaps, 63.3 ° overlaps with the peak of α-Al ₂ O ₃ , and 63.1 ° overlaps with the peak of m-ZrO ₂ .

Therefore, the peak between 59.5 ゜ and 61 ゜ and 62.0 ゜ and 63.5 ゜
Assuming that the peak heights between ゜ are H ₆₀ and H ₆₃ respectively, c−Z
If rO ₂ is not present, the ratio between the main peak height of α-Al ₂ O ₃ (referred to as H ₄₃ ) and H ₆₀ is such that H ₆₀ becomes a peak of α-Al ₂ O ₃ only, It becomes constant at ₆₀ / H ₄₃ = 0.07. Similarly, m-Z
The ratio of the main peak height (H ₂₈ ) of rO ₂ to H ₆₃ is such that H ₆₃ is m-ZrO ₂
H ₆₃ / H ₂₈ = 0.1 constant because the peak is only at the peak.

However, in the sintered body of the present invention, as is apparent from the examples described later, H ₆₃ / H ₂₈ > 0.1 and H ₆₀ / H ₄₃ > 0.07, which are significantly larger than those in the case where C-ZrO ₂ is not present. It has become large.

Therefore, c-ZrO ₂ or t
-ZrO ₂ and c-ZrO ₂ intermediate crystalline considered (C'-ZrO ₂₎ is present.

Thus Al ₂ O c-ZrO ₂ with respect to external stress by the presence of c-ZrO ₂ or C'-ZrO ₂ in ₃ (C'-
ZrO ₂ ) → t-ZrO ₂ → m-ZrO ₂ The fracture toughness for absorbing energy in two stages is improved. Moreover, t-ZrO ₂ →
c-ZrO ₂ (C′-ZrO ₂ ) → t− rather than the phase transition of m-ZrO ₂
Since the volume change is larger in the phase transition of ZrO ₂ → m-ZrO ₂ , the residual compressive stress on the surface after processing is increased, thereby improving the bending strength.

According to the present invention, Al ₂ O ₃ crystal particles in the sintered body
Although present as particles of 0.3 to 1.0 μm, ZrO ₂ crystal particles
It is desirable to exist in a size of ~ 1.5 μm, especially 0.1 to 0.5 μm, and when the size of ZrO ₂ particles exceeds 1.5 μm, cracks accompanying phase transition become a fracture source and cause a decrease in bending strength. .

Further, the crystal phase of ZrO ₂ is c-ZrO ₂ or C′-ZrO ₂
And it is desirable that t-ZrO ₂ is included majority, monoclinic ZrO ₂ is less than 50% of the total ZrO _2, preferably in particular 20% or less, the toughness falls exceeds 50%.

According to the method for producing a sintered body of the present invention, first, ZrO ₂ powder is 1 to 30% by weight, particularly 15 to 20% by weight, and the balance is substantially
A mixed powder composed of Al ₂ O ₃ powder is prepared. It is desirable that any powder used is a fine powder having a BET specific surface area of 10 m ² / g or more.

Next, the mixed powder is pulverized in a dry manner to perform a powder activation treatment. This activation causes distortion of the ZrO ₂ powder and Al ₂ O ₃ powder crystals in the mixed powder. As the activation treatment means, means which is difficult in wet grinding with a ball mill which has been generally used conventionally and which can perform high-speed grinding is adopted. For example, high-speed vibration mill or wear mill (attrit
An ion mill or the like is suitable, and pulverization is performed until the ZrO ₂ crystal of the raw material powder is distorted.

It should be noted that this pulverization may be performed before mixing the Al ₂ O ₃ powder and the ZrO ₂ powder.

The mixed powder thus activated is molded by known molding means, for example, by press molding, cold molding (CIP), injection molding, slurry casting, etc., and then transferred to firing.

The sintering can be performed at a low temperature of 1500 ° C. or less because the sinterability of the powder itself is improved by the above-described activation treatment.

The sintering may be carried out in an atmosphere for about 1 to 6 hours. As the sintering means, known means can be used, and specifically, normal pressure sintering in air or an inert gas, hot pressing, hot isostatic sintering or the like can be adopted, but a high-density sintered body is obtained. For this reason, it is desirable to perform normal pressure firing at a temperature of 1500 ° C. or less, preliminary firing by hot pressing, and then hot isostatic firing at 1500 ° C. or less. As a result, a sintered body substantially free of pores is obtained.

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

〔Example〕

Al ₂ O ₃ powder with a BET specific surface area of 10 m ² / g or more and a purity of 99.99% or more, and ZrO ₂ with a BET specific surface area of 10 m ² / g or more and a purity of 99.9% or more
The powder was dry-ground with an attrition mill to activate the powder. When the obtained powder was analyzed by X-ray diffraction, distortion was found in the crystal of the ZrO ₂ powder.

The obtained powder was weighed at the ratio shown in Table 1 and mixed.
6% of an organic binder is added and spray granulation is performed.
The granulated powder was formed into a desired shape and subjected to CIP treatment (cold isostatic pressing) at 6 t / cm ² .

The obtained molded body is fired at 350 ° C. to remove the binder, and then prefired at 1450 ° C. for 2 hours in the air, and the obtained sintered body is heated at 1400 ° C. for 1 hour in Ar at 2000 atm. The sample was subjected to hydrostatic pressure treatment for a period of time to obtain samples Nos. 1 to 7 substantially containing no pores.

In addition, as a comparative example, what was wet-mixed with a ball mill without performing dry pulverization was molded in the same manner as above, and this was
Pre-fired in the air at 00 ° C for 6 hours, and further hot-hydrostatically fired at 1400 ° C for 1 hour in 2000 atmospheres of argon.
8,9 samples were obtained.

The obtained sample was subjected to laser Raman measurement using a laser of 4880Å200 mW.

The scanning speed was 120 cm ^-1 / min, and the sampling interval was 1.0 cm ^-1 .

The chart of the sample No. 5 is shown in FIG. 1, and the chart of the sample No. 10 is shown in FIG.

The presence or absence of a peak near 600 cm ^-1 and the peak ratio (Hc / H _A ) to the peak height _HA of Al ₂ O ₃ near 415 cm ^-1 (Hc / H _A ) × 100 (%) were determined from the chart of each sample. Was.

For each of the obtained samples, the annealed surface was subjected to X-ray diffraction measurement using Cu-Kα radiation, and the content of monoclinic in ZrO ₂ , Zr
The frequency of the maximum peak of O ₂ , H ₆₃ / H ₂₈ , H ₆₀ / H ₄₃ was examined.

The single crystal content in ZrO ₂ in the X-ray diffraction measurement is represented by the following formula: [t-ZrO ₂ (101) plane peak height] / [m-ZrO
₂ peak height of (111) plane + peak height of m-ZrO ₂ (111) plane + peak height of t-ZrO ₂ (101) plane].

The flexural strength is in accordance with JISR1601, and the sample is 3 × 4 × 40
It was processed into a shape of mm and measured by three-point bending.

Further, the fracture toughness was determined from the indentation and crack size generated by applying a load of 20 kg using a diamond indenter for Vickers hardness using Niihara's formula.

 The results are shown in Table 1.

Further, as a comparative example, a mixed powder of 20% of ZrO ₂ powder containing 80% of Al ₂ O ₃ powder and 3 mol% of Y ₂ O ₃ was wet-pulverized by a hole mill and formed by the same method as in the above-described embodiment. The firing temperature was set to 1,500 ° C for pre-firing and 1,400 ° C for HIP.
Sample was obtained.

FIG. 3 shows an X-ray diffraction chart of Sample No. 5 in Table 1 and FIG. 4 shows an X-ray diffraction chart of Sample No. 9 in Table 1.

According to the results in Table 1, the system containing no ZrO ₂ (No.
In 1), both fracture toughness and bending strength are low. In No. 7 in which the amount of ZrO ₂ exceeds 30% by weight among the samples subjected to high energy grinding, ZrO ₂ is tetragonal (t-ZrO ₂ ) in the sintered body, and the maximum peak frequency is 30.2 °. However, the content of monoclinic is high and the fracture toughness is low.

On the other hand, when dry grinding is not performed (Nos. 8 and 9),
ZrO ₂ was tetragonal and had a high monoclinic content and low flexural strength.

Furthermore, No. 10 and 11 obtained by the conventional method are all tetragonal Zr
Although the content of O ₂ is large and the content of monoclinic ZrO ₂ is small, the effect is insufficient compared with the present invention.

Although the sample of No. 9 has improved fracture toughness, the bending strength is hardly improved.

In contrast to these comparative examples, all of the samples Nos. 2 to 6 of the present invention achieved a fracture toughness of 4.2 MN / m ^3/2 or more and a flexural strength of 90 kg / mm ² or more, and in particular, Hc / _HA was 10%. The above, in other words H
₆₃ / H ₂₈ is 1.7 or more, H ₆₀ / H ₄₃ is 0.3 or more, fracture toughness 4.3MN
/ m ^3/2 or more, and a flexural strength of 95 kg / mm ² or more.

〔The invention's effect〕

As described above in detail, according to the present invention, in a simple system in which ZrO ₂ is blended with Al ₂ O ₃ , the raw material powder is dry-pulverized to activate the powder, and the powder is molded and formed into a low temperature of 1500 ° C. or less. By sintering, a sintered body in which metastable cubic ZrO ₂ is dispersed in Al ₂ O ₃ is obtained, and thereby excellent bending strength and toughness are obtained.

In addition, this manufacturing method is excellent in mass productivity and economical efficiency because a simple system can provide excellent characteristics without requiring complicated control. Although the sintered body of the present invention is particularly useful for cutting tools, it can be used for other wear-resistant parts, high-temperature materials up to 1000 ° C., artificial bones, and the like.

[Brief description of the drawings]

FIG. 1 is a chart in laser Raman spectroscopy of the product of the present invention (Example No. 5), and FIG. 2 is a comparative product (Example No. 1).
0) is a chart in laser Raman spectroscopy, FIG. 3 is an X-ray diffraction chart of the product of the present invention (No. 5),
FIG. 4 is an X-ray diffraction chart of a comparative product (No. 9).

Claims (2)

(57) [Claims] 1 to 30% by weight of ZrO ₂ , the balance being substantially Al
_An alumina-based sintered body comprising ₂ O ₃ and unavoidable impurities, wherein a ZrO ₂ peak is present at a position of 600 ± 10 cm ^{−1 in} a measurement chart of laser Raman spectroscopic analysis of the sintered body. High-strength alumina sintered body. 2. A mixed powder comprising 1 to 30% by weight of ZrO ₂ powder and the balance being Al ₂ O ₃ powder is dry-pulverized, activated, molded, and fired at a temperature of 1500 ° C. or less. For producing a high-strength alumina-based sintered body.