JPS6050746B2 - Method for producing aluminum oxide-based ceramic with high toughness and hardness - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing an aluminum oxide-based ceramic having high toughness and hardness and particularly suitable for use as cutting tools, corrosion-resistant and wear-resistant parts, and the like.

Conventionally, ceramics made of aluminum oxide (hereinafter referred to as A'203) have high hardness and are also excellent in wear resistance and corrosion resistance, so they have been used for corrosion and wear resistance in cutting tools and various nozzles. Used for manufacturing parts, etc.

However, this conventional Ae2O3 ceramic has high hardness as described above.
Although it has stiffness, it has poor toughness, 3-5k9/7T0n
It has a low fracture toughness of about 2, so although it has future potential, it is actually only used in fields where tensile stress or impact force is not applied much. Therefore, in order to improve the toughness and strength of the above-mentioned Af2O3 ceramic and thereby enable its application in a wide range of fields, titanium carbide (hereinafter referred to as Ti) was developed.
An A'203-TjC ceramic has been proposed, in which A'203-TiC ceramic is added, and it is true that this A'203-TiC ceramic has a relatively high fracture toughness of about 5 to 5.5k9・Go÷. This brought about a turning point in the field of application, for example, it became possible to use it in applications where impact force is applied, such as the edge of a milling cutter.

However, when this conventional Ae2O3-TiC ceramic is used, for example, as a cutting tool, its reliability against chipping of the cutting edge is somewhat lacking, and therefore, when used as a cutting tool in automatically operated machine tools. There was a problem with that. In addition, an Ae2O3-ZrO2 ceramic has been proposed in which zirconium oxide (hereinafter referred to as ZrO2) is added as a toughness-improving component. Due to the volume change during the phase transformation from the low-temperature monoclinic phase to the low-temperature monoclinic phase, many extremely fine cracks occur inside the sintered ceramic, and these fine cracks prevent the propagation of large cracks. However, regardless of whether this mechanism is true or not, it results in superior toughness compared to other conventional ceramics, but on the other hand, it maintains high hardness, which is an important characteristic of this type of ceramic. Therefore, when used as a cutting tool to cut highly hard work materials, there are problems such as damage to the cutting edge due to insufficient hardness. It was hot.

Therefore, from the above-mentioned viewpoint, the present inventors focused particularly on the above-mentioned conventional A'203-ZrO2 ceramic, and conducted research in order to provide it with the contradictory characteristics of high hardness and high toughness at the same time. As a result, (a) the above conventional Ae2O3
- In ZrO2 ceramic, according to the above-mentioned conventional strengthening mechanism, ZrO2 added during the cooling process after sintering
It has been thought that it is preferable to cause rO2 to undergo a phase transformation from tetragonal to monoclinic as much as possible to generate many microcracks inside the sintered ceramic, but various experimental results by the present inventors show that the phase of ZrO Toughness is significantly improved by suppressing transformation as much as possible, and by allowing as many tetragonal crystals as possible to exist.

(b) Conventionally, when sintering Ae2O3-ZrO2 ceramics, the atmosphere during the sintering process is a reducing gas atmosphere containing carbon, or a mixed gas atmosphere of a reducing gas containing carbon and nitrogen, and the inside of the green compact is During sintering in the initial stage of sintering, where the sintering atmosphere can freely circulate, that is, from around 1500°C, which is close to the sintering temperature, to during sintering, when sintering has not yet fully progressed, there is a Carbon and nitrogen in the sintering atmosphere that have entered and Zr distributed in the green compact
By reacting with O2, the surface portion is formed into one or more of Zr carbides, carbonitrides, carbonates, and carbonitrides (hereinafter collectively referred to as Zr carbon-nitrogen-oxides). ) to form ZrO2 whose surface is surrounded by carbon, nitrogen, and oxides of Zr (in this case, Af2O3 is chemically stable and does not react with the sintering atmosphere). In the process, the phase transformation of ZrO2 from the high-temperature tetragonal phase to the low-temperature monoclinic phase is substantially suppressed, and the ceramic after sintering contains many tetragonal crystals and has high hardness. and to have high toughness.

c) In producing the A'203-based ceramic of (b) above, additional raw material powders include magnesium oxide (hereinafter referred to as MgO) powder, silicon oxide (hereinafter referred to as SiO2) powder, and yttrium oxide (hereinafter referred to as Y2O3). ) powder, nickel oxide (hereinafter referred to as NiO) powder, and chromium oxide (hereinafter referred to as Cr2O3) powder (hereinafter collectively referred to as sintering accelerator powder). As sintering is generally promoted, sufficient densification can be achieved by ordinary sintering alone.

(d) Furthermore, if aluminum nitride (hereinafter referred to as AeN) powder is also blended as the raw material powder, the resulting A
e2O3-based ceramic has no loss of toughness,
To have even higher hardness.

The findings shown in (a) to (d) above were obtained.

This invention was made based on the above knowledge, and uses ZrO2 and Ae2O3 powders as raw material powders, and further contains sintering accelerator powder and AeN powder as necessary.
Either or both of these powders are used, and these raw powders are mixed with ZrO2 powder: 1 to 20%, and if necessary, sintering accelerator powder: 0.1 to 2% and AeN.
Powder: Contains one or two of 0.5 to 5%,
The balance consists of Al2O3 powder (more than volume %,
All % indications below mean volume %), and then sintered according to the usual powder metallurgy method.
By setting the atmosphere during the sintering process to a reducing gas atmosphere containing carbon or a mixed gas atmosphere of a reducing gas containing carbon and nitrogen, the green compact is The surface part of ZrO2 distributed inside,
Carbon/nitrogen/Zr with a conversion rate of 0.1 to 10% as a whole
After converting to oxide and sintering the high temperature phase tetragonal Ae
The above A'20 is present in large quantities in the 2O3 group ceramic.
It is characterized in that the three-base ceramic has both high hardness and high toughness. Next, A of this invention
In the method for manufacturing f2O3-based ceramics, the reason why the composition of the raw material powder and the converted content of carbon, nitride, and oxide of Zr are limited as described above will be explained.

(a) Amount of ZrO2 powder As mentioned above, ZrO2 powder has the effect of improving the toughness of ceramics, but if the amount is less than 1%, the desired toughness can be secured; If the content exceeds this amount, the hardness will be significantly lowered, so the content was set at 1 to 20%.

(b) Amount of sintering accelerator powder These powders contain A'2
Since it has the effect of promoting the sintering of Al2O3 and suppressing the grain growth of Al2O3, it is blended as necessary when these properties are particularly required, but if the blending amount is 0.1
If the amount is less than 2%, the desired effect cannot be obtained.
If the content exceeds 0.1, the amount of brittle glass phase or spinel phase generated at the grain boundaries of Ae2O3 grains increases, resulting in a decrease in strength.
It was set at ~2%.

(c) Blend amount of A'N powder In addition to suppressing grain growth of Ae2O3, AeN powder has the following properties:
Since it has the effect of increasing the hardness of ceramics, it is added as necessary when particularly high hardness is required, but if the amount added is less than 0.5%, the desired effect cannot be obtained; If the content exceeds 5%, cavities are likely to occur in the ceramic and cause a decrease in strength.
The blending amount was determined to be 0.5 to 5%.

(d) Conversion content of carbon, nitride, and oxides in Zr These components are thought to be formed finely on the surface of ZrO2 particles during the sintering process, and as a result, the decrease in hardness due to the inclusion of ZrO2 is prevented, and the hardness is actually increased. As the
By restraining the ZrO2 particles, the ZrO2 particles are
Since it acts to suppress the phase transformation l of rO2 from the high-temperature phase of tetragonal to the low-temperature phase of monoclinic, the ceramic after cooling has more tetragonal crystals and has even better toughness. However, if the converted content is less than 0.1%, the desired high hardness and toughness cannot be achieved, and on the other hand, it is difficult to increase the converted content to more than 10%. Not only that, but the sinterability also deteriorates, so the converted content was set at 0.1 to 10%.

In carrying out the method of the present invention, particularly regarding sintering, methods such as a hot press method, a normal sintering method, and a method of performing hot isostatic pressure sintering after normal sintering can be applied.

In addition, the converted content of carbon, nitride, and oxides of Zr depends on the partial pressure of carbon and nitrogen in the sintering atmosphere, the particle size and blending amount of ZrO2 powder, and the heating rate to the sintering temperature. Can be adjusted.

Furthermore, the content of carbon, nitride, and oxides of Zr in ceramics is usually measured using an electron beam microanalyzer, but if necessary, the carbon content can be measured using a carbon quantitative analysis method using a carbon combustion method. Based on this measurement result, Z
A method for calculating the content of carbon, nitride, and oxides in r is also used.

Next, the method of the present invention will be explained using examples and comparing with comparative examples.

Example 1 As a raw material powder, a powder having an average particle size of 0.4 μm was used.
-Af2O3 powder and ZrO2 with the same 0.9μm
Prepare powders, blend these raw material powders into the composition shown in Table 1, mix these blended powders in a ball mill for 3 days using methyl alcohol as a dispersion medium, and then dry. This mixed powder was filled into a graphite mold and hot-pressed at a temperature of 1,500°C while applying a pressure of 150k91d in a CO gas atmosphere of 1 atm to produce the ceramic 1 of the present invention. -4 were produced.

Moreover, for the purpose of comparison, Comparative Ceramics 1 to 4 were manufactured under the same conditions except that the atmosphere of the hot breath was set to vacuum. The final component composition, theoretical density ratio, hardness, and fracture toughness of the ceramics 1 to 4 of the present invention and comparative ceramics 1 to 4 obtained as a result were compared with those of commercially available ceramics 1 and 2 as shown in Table 1. It was shown.

From the first displayed results, ceramics 1 to 4 of the present invention are:
It is clear that all of them have high hardness that is almost equivalent to that of commercially available ceramics, and that they have much better toughness than commercially available ceramics and comparative ceramics that do not contain Zr carbonate (ZrCO).

Example 2 As raw material powder, α-
Ae2O3 powder, ZrO2 powder, SiO2 powder, and Or'203 powder, 0.7 μm (7) MgO powder, 0.5 μm Y2O3 powder, 1.0 μm (7) NiO
Prepare powder, blend these raw powders into the composition shown in Table 2, mix these blended powders in a ball mill for 3 days using methyl alcohol as a dispersion medium, dry, and then add to this mixed powder. Paraffin was added as a plasticizer in an amount of 3% by weight based on the entire mixed powder, and press molding was performed.The resulting green compact was then heated in vacuum at a temperature of 800°C.
After holding for 1 hour to volatilize the paraffin,
Sintering was carried out in a mixed gas atmosphere of r(7)CO gas and 1rr(7)N2 gas at a temperature of 1600°C for 1 hour, and part of the ZrO2 was converted into Zr carbonitoxide (ZrCN).
Ceramics 5 to 8 of the present invention were produced by converting into O).

In addition, for the purpose of comparison, Comparative Ceramics 5 to 8 were manufactured under the same conditions except that the sintering atmosphere was set to 1 atm atmosphere. In addition, Table 2 shows the resulting cera of the present invention *8
The content of ZrCNO in Miku 5 to 8 is shown. As shown in Table 2, it is clear that ceramics 5 to 8 of the present invention have higher hardness and particularly superior toughness than comparative ceramics 5 to 8 that do not contain ZrCNO.

Furthermore, when producing the ceramic 6 of the present invention, sintering was carried out under the same conditions except that the partial pressure of CO gas in the sintering atmosphere was variously changed, and the content of ZrCNO in the obtained ceramic was measured using an electron beam. Measured using a microanalyzer, and based on the measurement results, ZrCN of the blended ZrO2
When the conversion rate to O was calculated, the results are shown in Figure 1. From this result, for example, by changing the partial pressure of the gas components that make up the sintering atmosphere, it is possible to convert carbon, nitride, and oxides of metals. It can be seen that the content of can be adjusted.

Example 3 The same Zr used in Example 2 was used as the raw material powder.
O2 powder, α-A'203 powder, MgO powder, and AeN powder having an average particle size of 1.1 μm were prepared, and these raw material powders were blended into the composition shown in Table 3, and the mixture was heated in a sintering atmosphere. , alternately with a vacuum atmosphere every other time,
5t0rr (7) CO gas and 10t. A mixed gas atmosphere with N2 gas of 0rr is created, and a part of ZrO2 becomes Zr.
Ceramics 9 to 14 of the present invention were manufactured under the same conditions as in Example 2 except for converting to carbonitride (ZrCN).

Moreover, for the purpose of comparison, comparative ceramics 9 to 14 were manufactured under the same conditions except that the sintering atmosphere was only a vacuum. Zr in the ceramics 9 to 14 of the present invention obtained as a result
The CN content is also shown in Table 3. Table 3 also shows ceramics 9 to 14 of the present invention and comparative ceramic 9.
Measurement results of theoretical density ratio of ~14, hardness, and fracture toughness are also shown. From the results shown in Table 3, it can be seen that ceramics 9 to 14 of the present invention have higher hardness and toughness than comparative ceramics 9 to 14 in which no ZrCN is formed, as in Examples 1 and 2. is clear.

As described above, according to the method of the present invention, a part of ZrO2 is converted into Zr carbon, nitride, and oxide by simply specifying the sintering atmosphere of Ae2O3-based ceramic, which has contradictory properties such as hardness and toughness. The resulting Ae2O3-based ceramic has extremely high toughness and hardness, so it can be used in cutting tools, nozzles, and other corrosion-resistant and wear-resistant parts that require these properties. When used as such, it provides industrially useful effects such as exhibiting excellent performance over a long period of time.

[Brief explanation of the drawing]

Figure 1 shows the partial pressure of CO gas in the sintering atmosphere and the composition of ZrO2.
It is a figure which shows the relationship with the conversion rate to ZrCNO.

Claims (1)

[Claims] 1. Zirconium oxide powder and aluminum oxide powder are used as raw material powders, and these raw material powders are combined into a blended composition containing 1 to 20% by volume of zirconium oxide powder and the remainder consisting of aluminum oxide powder. When producing an aluminum oxide-based ceramic by mixing and press-forming into a green compact under normal conditions and sintering, the sintering atmosphere is a reducing gas atmosphere containing carbon or a carbon-containing reducing gas atmosphere. By creating a mixed gas atmosphere of nitrogen and a reducing gas containing Oxidation with high toughness and high hardness characterized by converting Zr into one or more of carbides, carbonitrides, carbonates, and carbonitrides at a conversion rate of ~10% by volume A method for producing aluminum-based ceramics. 2 The green compact contains, in volume %, zirconium oxide powder: 1 to 20%, one or two of magnesium oxide powder, silicon oxide powder, yttrium oxide powder, nickel oxide powder, and chromium oxide powder: 0.1 to 2%, and the remainder is aluminum oxide powder. Method. 3. Zirconium oxide powder, aluminum nitride powder, and aluminum oxide powder are used as raw material powders, and these raw material powders contain zirconium oxide powder: 1 to 20% by volume, and aluminum nitride powder: 0.5 to 5% by volume. The remaining aluminum oxide powder is blended into a composition, mixed under normal conditions, press-formed into a green compact, and then sintered to produce an aluminum oxide-based ceramic. By creating a reducing gas atmosphere containing carbon or a mixed gas atmosphere with a reducing gas containing carbon, the surface of the zirconium oxide distributed in the green compact is reduced during the initial sintering process. of,
One of the carbides, carbonitrides, carbonates, and carbonitoxides of Zr with a conversion rate of 0.1 to 10% by volume in total proportion.
A method for producing an aluminum oxide-based ceramic having high toughness and high hardness, the method comprising converting into one or more types. 4 The compacted powder contains, in terms of volume, zirconium oxide powder: 1 to 20%, aluminum nitride powder: 0.5 to 5%, magnesium oxide powder, silicon oxide powder, yttrium oxide powder, nickel oxide powder, and chromium oxide powder 0.1 to 2% of one or two of the above, and the remainder is aluminum oxide powder. A method for producing an aluminum oxide-based ceramic having hardness.