JPS6222949B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a zirconium oxide ceramic having both high hardness and high toughness. In general, ceramics have high hardness but low toughness, so their uses are limited.
Recently, zirconium oxide (hereinafter referred to as ZrO ₂ ) ceramics, which have high toughness, have been attracting attention in place of aluminum oxide (hereinafter referred to as Al ₂ O ₃ ) type ceramics, which have traditionally been the mainstream. This high-toughness ZrO ₂ ceramic has a main component of
It has a composition consisting of ZrO ₂ and a small amount of Al ₂ O ₃ , but the reason why this ceramic has high toughness is
ZrO ₂ , the main component, consists of tetragonal and cubic crystals, or monoclinic, tetragonal, and cubic crystals, and thus two or three types of ZrO ₂ with different crystal structures can be used.
It is said that this is due to the coexistence of the two. but,
On the other hand, this high-toughness ZrO ₂ ceramic has low hardness and is problematic in terms of wear resistance. Therefore, from the above-mentioned viewpoint, the present inventors focused on the above-mentioned conventional high-toughness ZrO ₂ ceramic and conducted research to impart high hardness to it without impairing its high toughness. As a result, zirconium carbide (hereinafter referred to as ZrC) or zirconium carbonitride (hereinafter referred to as ZrCN) was added to the ZrO ₂ during sintering, rather than as a dispersed phase forming component.
They found that if a part of ZrO 2 , that is, the surface part, is contained in a reduced-converted state, the resulting ZrO ₂ ceramic will have high hardness and toughness. Therefore, the present invention has been made based on the above-mentioned knowledge, and uses unstabilized ZrO ₂ powder, which has a monoclinic crystal structure at room temperature and a tetragonal crystal structure at about 1000° C. or higher, as a raw material powder; Unstabilized ZrO ₂ powder with one of oxides such as Ca, Mg, and Y
Stabilized cubic ZrO ₂ powder containing more than one species to have a cubic crystal structure stable at room temperature, and
Prepare Al ₂ O ₃ powder and carbon powder if necessary. These raw material powders are blended into a predetermined composition, mixed under normal conditions, and formed into a green compact. This green compact is then heated in a vacuum. The unstabilized and stabilized cubes are sintered under normal conditions, in a nitrogen atmosphere, in a carbon-containing reducing gas atmosphere, or in a mixed gas atmosphere of a carbon-containing reducing gas and nitrogen gas. ZrC or _ZrCN : 1-20%, _Al2O3 : 0.5-5%, tetragonal or tetragonal, produced by reducing the surface part of _crystalline ZrO2 to ZrC or ZrCN. ZrO ₂ of crystal and monoclinic crystal (however, in this case, the monoclinic/tetragonal capacitance ratio is 6/4 or less):
5-30%, cubic ZrO ₂ and unavoidable impurities: the remainder, and has a composition consisting of tetragonal and cubic
ZrO ₂ , or monoclinic, tetragonal, and cubic ZrO ₂ , the surface of which is composed of ZrC or _ZrCN , and has a structure in which Al ₂ O ₃ is uniformly dispersed, and has high hardness and toughness. It has the following characteristics. Next, the reason for limiting the component composition range as described above in the ZrO ₂ ceramic of the present invention will be explained. (a) ZrC or ZrCN These components have the effect of significantly increasing the hardness of _ceramic and improving its wear _resistance . It has the effect of metastabilizing and further improving toughness, but its content is 1%.
If the content is less than 20%, the desired effect cannot be obtained, and on the other hand, if the content exceeds 20%, sintering will be required for an unnecessarily long time, which is not economical. ~20%. (b) Al ₂ O ₃ This component has the effect of suppressing the grain growth of ZrO ₂ and preventing a decrease in the toughness of ceramics.
If the content is less than 0.5%, the desired grain growth suppressing effect cannot be obtained, while if the content exceeds 5%, the sinterability will deteriorate and cause a decrease in toughness. Therefore, the content should be reduced to 0.5%. It was set at ~5%. (c) The presence of truncated ZrO ₂ in the metastable state of tetragonal ZrO ₂ gives ceramics excellent toughness, but if the content is less than 5%, the desired high toughness cannot be achieved. However, if the content exceeds 30%, the hardness of the ceramic will decrease significantly, so the content was set at 5 to 30%. In this case, even if a part of the tetragonal ZrO ₂ is occupied by monoclinic ZrO ₂ , if the content ratio, that is, the monoclinic/tetragonal capacity ratio is 6/4 or less, the high Toughness can be maintained. Furthermore, in the ZrO ₂ ceramic of the present invention, in many cases, one or more of tungsten carbide, Co, Ni, and Fe may be mixed as unavoidable impurities when mixing the blended powder. As long as the content does not exceed 3% by volume in total, it will not affect the ceramic properties in any way. Next, the ZrO ₂ ceramic of the present invention and its manufacturing method will be specifically explained with reference to Examples. Example 1 As raw material powder, average particle size: 1.2 μm
CaO stabilized cubic ZrO ₂ powder, 0.6 μm Al ₂ O ₃
Powder and non-stabilized ZrO ₂ powder were prepared, these raw material powders were blended into the composition shown in Table 1, and after mixing in a ball mill for 2 days,
The green compact is formed into a green compact at a pressure of 1 ton/cm ² and then heated in a mixed gas atmosphere of carbon-containing reducing gas and nitrogen gas consisting of CO: 1 torr and N ₂ : 0.5 torr at a temperature of: By sintering under the conditions of holding at 1600°C for 1.5 hours, a ceramic 1 of the present invention having the composition shown in Table 1 and having a structure in which the surface portions of both ZrO ₂ are composed of ZrCN can be obtained. -5 were produced, respectively. In addition, for the purpose of comparison, the ceramics 1 to 5 of the present invention were prepared with the exception that the sintering atmosphere was 1 atm atmosphere.
Comparative ceramics 1 to 5 were manufactured under the same manufacturing conditions as in Example 1. Rockwell hardness (A scale) and fracture toughness values were measured for the resulting ceramics 1 to 5 of the present invention and comparative ceramics 1 to 5, and
The measurement results are shown in Table 1. From the results shown in Table 1, ceramics 1 to 5 of the present invention all have high hardness and high toughness, while comparative ceramics 1 to 5 have

[Table] Because the crystal atmosphere is air, there is no formation of ZrCN, so the hardness is relatively low and the tetragonal crystal structure is formed.
It is clear that those with a high ratio of monoclinic ZrO ₂ to ZrO ₂ have poor toughness. Example 2 Raw material powder has an average particle size of 1 μm
_Y2O3 stabilized cubic _{ZrO2 powder} , _{0.6μm Al2O3}
Powder and unstabilized ZrO ₂ powder, as well as 2 μm
Prepare graphite powder, mix these raw powders to the composition shown in Table 2, mix them in a ball mill for 2 days, and then shape them into a green compact at a pressure of 1 ton/cm ² . By sintering the powder in a CO gas atmosphere of 0.1 torr at a temperature of 1600°C for 2 hours, the powder has the same composition shown in Table 2 and the surface portion of both ZrO ₂ . Ceramics 6 to 10 of the present invention each having a structure composed of ZrC were manufactured. For the purpose of comparison, ceramics 6 to 10 of the present invention were also prepared with the same composition as shown in Table 2, and with the exception that the sintering atmosphere was 1 atm atmosphere.

【table】

[Table] Comparative ceramics 6 to 10 were each manufactured under the same manufacturing conditions. The hardness and fracture toughness of the resulting ceramics were also measured in the same manner as in Example 1, and the results are shown in Table 2. As shown in Table 2, the ceramic 6 of the present invention
~10 has high hardness and high toughness, whereas comparative ceramics 6~10 have high hardness and toughness due to the absence of ZrC formation.
It is clear that the toughness is inferior when the hardness is relatively low and the proportion of monoclinic crystals is high. In addition, the component contents of the ceramic compositions in Examples 1 and 2 above were determined by irradiating the mirror-polished surface of the sample with X-rays at a predetermined output, and for each component,
It was determined by measuring the peak height at a reflection angle unique to each component and calculating the ratio of the resulting peak height to the peak height determined for the standard sample. As mentioned above, the ZrO ₂ ceramic produced by the method of the present invention has high hardness and toughness, as well as excellent heat resistance and corrosion resistance, so it can be used in cutting applications that require these properties. When used as tools, wear-resistant parts such as bearings and wire-drawing dies, and seal ring materials, it stably exhibits outstanding performance over a long period of time.

Claims (1)

[Claims] 1. Zirconium carbide or zirconium carbonitride: 1 to 20%, aluminum oxide: 0.5 to 5%, tetragonal zirconium oxide: 5 to 30%, cubic zirconium oxide and inevitable impurities:
The remainder has a composition (volume % or more) consisting of the following, and the surface portion of the tetragonal and cubic zirconium oxides is composed of zirconium carbide or zirconium carbonitride, and has a structure in which aluminum oxide is uniformly dispersed. Zirconium oxide ceramic with high hardness and toughness. 2 Zirconium carbide or zirconium carbonitride: 1 to 20%, aluminum oxide: 0.5 to 5%, monoclinic and tetragonal zirconium oxide (monoclinic/tetragonal capacity ratio: 6/4 or less): 5 to 30
%, cubic zirconium oxide and unavoidable impurities:
The remainder has a composition (volume % or more) consisting of the following, and the surface portion of monoclinic, tetragonal, and cubic zirconium oxide is composed of zirconium carbide or zirconium carbonitride, and has a structure in which aluminum oxide is uniformly dispersed. A zirconium oxide ceramic having high hardness and high toughness.