JPS6257597B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to sialon-based ceramics that exhibit outstanding wear resistance when used as cutting tools, wear-resistant tools, and the like. In recent years, silicon nitride (hereinafter referred to as Si ₃ N ₄ )-based ceramics have attracted attention as materials for cutting tools and wear-resistant tools.
Since Si ₃ N ₄ is a compound with strong covalent bonding properties, it has poor sintering properties, so hot pressing is often used to manufacture it, and in this case it is difficult to manufacture products with complex shapes. , and productivity is low. _Furthermore , _β-
A compound in which part of the Si in the Si ₃ N ₄ lattice is replaced with Al and part of the N is replaced with O, i.e. β- expressed by the composition formula: Si ₆ -zAlzOzN ₈ -z (O<z≦4.3). Attempts have been made to use sialon-based ceramics, which have sialon as a main component, as cutting tools and wear-resistant tools, but although these sialon-based ceramics have high toughness, their hardness is only about 92 on the Rockwell hardness A scale. Currently, it does not exhibit the desired wear resistance because it is not high. Therefore, from the above-mentioned viewpoint, the present inventors focused on the conventional sialon-based ceramics containing β-sialon as a main component, and added high-quality materials to this ceramic without impairing its good sinterability. As a result of research to add hardness and ensure excellent wear resistance, (a) In addition to the above β-SiAlON, a part of the Si in the α-Si ₃ N ₄ lattice was replaced with Al and N Replace part of with O,
Furthermore, one or more of Li, Na, Ca, Mg, Y, and rare earth elements (hereinafter collectively referred to as M) enters into the same lattice, resulting in a solid solution structure. Compound, that is, compositional formula: Mx (Si, Al) ₁₂ (O, N) ₁₆ (where O<x
≦2) When α-sialon expressed by 2) is present, the resulting ceramic has improved hardness and excellent wear resistance. In this case, the ratio of α-sialon and β-sialon (α/β) is 25/75 to 25/75 in terms of capacity ratio.
It is best to set the ratio to 95/5 because if the ratio of α-sialon is less than 25, the desired effect of improving hardness will be small, while if the ratio exceeds 95, the sinterability will decrease. It must be based on something. In addition, β-Sialon is represented by the composition formula: Si ₆ -zAlzOzN ₈ -z as described above, and O<z≦
It is necessary to satisfy the condition of 4.3, which means that z
This is because there is no composition with a value of over 4.3, but even within this range, as z increases, coarse cavities are more likely to occur in the ceramic and the strength also decreases. It is preferable that O<z≦2.0. Furthermore, α-SiAlON, as mentioned above,
Compositional formula: Mx (Si, Al) ₁₂ (O, N) ₁₆ It exists under the condition of O<x≦2, but this
This is based on the reason that if the composition exceeds 2, M cannot be completely dissolved in solid solution while penetrating into the lattice gaps. In addition,
Si, Al, O, and N in α-sialon
It is assumed that the ratio changes depending on the type of M and the value of x, and is determined so that the positive and negative valences are equal. (b) Zirconium oxide (hereinafter referred to as ZrO _{2 ) and hafnium oxide (hereinafter referred to as HfO 2 )} are added to the ceramics described in (a) above in which α-sialon and β-sialon coexist as dispersed phase forming components. When one or two of these are included,
Grain growth of SiAlON during sintering is suppressed and sinterability is improved, so that the hardness of the ceramics is further improved and the wear resistance is further improved. In this case, the content of ZrO ₂ and HfO ₂ is preferably 1 to 40% by volume, because if the content is less than 1% by volume, the desired effect of improving hardness and wear resistance cannot be obtained. This is because if the content exceeds 40% by volume, the sinterability will decrease and the excellent thermal shock resistance of Sialon will be impaired. (c) When the ceramics of (b) above contain a composite acid/nitride of the elements contained in M above, Si, and Al as binder phase forming components, these binder phase forming components have a low melting point. Therefore, during sintering, a liquid phase is formed to promote sintering, and after sintering, it exists as a glassy or crystalline material at the grain boundaries of Sialon, making the ceramic sufficiently dense. to become stronger and have higher strength. In this case, the content of the binder phase forming component is preferably 1 to 20% by volume, which is
This is because if the content is less than 1% by volume, the desired high density cannot be achieved, whereas if the content exceeds 20% by volume, the strength of the ceramic will decrease. The findings shown in (a) to (c) above were obtained. This invention was made based on the above knowledge, and includes (1) Compositional formula: Si ₆ -zAlzOzN ₈ -z (where O<z
≦4.3) and the compositional formula: Mx (Si, Al) ₁₂ (O, N) ₁₆ (however, O<
The main component is α- _SiAlON represented _by Composite acid/nitride as: 1
~20% by volume, and α-Sialon/
It is characterized by excellent wear resistance of sialon-based ceramics having a β-sialon capacity ratio in the range of 25/75 to 95/5. Furthermore, the ceramics of the present invention includes, as a raw material powder, Si ₃ N ₄ powder + Al ₂ O ₃ powder + AlN powder, Si ₃ N ₄ powder + SiO ₂ powder + AlN powder, Si ₂ ON ₂ powder + AlN powder, or any of the above. Combined α and β−
Sialon-forming compound powder (preferably Si ₃ N ₄ with a high α phase content), M oxide and nitride powder that can be dissolved in α-sialon and also form a binder phase, dispersed phase forming component Prepare ZrO ₂ and HfO ₂ powders, as
These raw material powders are blended into a predetermined composition, and in this case, from the composition calculated from the composition formula of β-Sialon.
The powder mixture is blended and mixed so that Al and N are increased, and then the mixed powder is hot pressed at a temperature within the range of 1550 to 1800°C, or a green compact formed from the mixed powder is sintered at the temperature. It can be manufactured by tying. Note that the above sintering may be performed under normal conditions, but in this case, the thickness of the surface-altered layer of the ceramic after sintering becomes thicker, so it is preferable to embed the green compact in the Si ₃ N ₄ powder. Sintering is preferred. In addition, sintering must be performed in an atmosphere containing N ₂ to suppress the decomposition of Si ₃ N ₄ during sintering, and in this case, a mixture of N ₂ and H ₂ or N ₂ and Ar is required. Although gas may be used, it is preferable to use an atmosphere containing only N ₂ . Further, the atmospheric pressure may be about 0.9 atm, but preferably 1 atm, and more preferably 1 atm or more, but in this case a special sintering furnace is required. Also, the sintering temperature is as above
1550-1800℃, preferably 1650-1750℃
A temperature within the range of . Furthermore, if the ceramics after sintering are subjected to hot isostatic sintering as necessary, the densification will proceed even further. Next, the ceramics of the present invention will be specifically explained using examples. Example As a raw material powder, Si ₃ N ₄ with an average particle size of 0.8 μm
(α phase content: 95% by volume) powder and CaO powder,
0.5 μm α-Al ₂ O ₃ powder and MgO powder,
0.9 μm AlN powder, 1.5 μm CeO ₂ powder, 1.1 μm Li ₂ O powder and Na ₂ O powder,
0.6 μm Y ₂ O ₃ powder, 0.4 μm ZrO ₂ powder,
HfO ₂ powder with a diameter of 0.5 μm and various rare earth oxide powders each with a diameter of 1.5 μm were prepared, and these raw material powders were blended into the composition shown in Table 1, and mixed for 24 hours in a wet ball mill. This mixed powder was then dried, and then molded into a green compact at a pressure of 1 ton/cm ² , and this green compact was placed in a Si ₃ N ₄ crucible in a nitrogen atmosphere of 1 atm at a temperature of 1700°C. Ceramics 1 to 15 of the present invention and Comparative Ceramics 1 to 3 were produced by sintering under conditions of holding for 1 hour. Note that Comparative Ceramics 1 to 3 all have compositions in which the content of one of the constituent components (those marked with * in Table 1) is outside the scope of the present invention. The resulting Ceramics 1 to 15 of the present invention and Comparative Ceramics 1 to 3 were examined using a microscope.

【table】

【table】

[Table] In addition to examining the composition by observation and X-ray diffraction, we also measured the hardness (Rockwell hardness A scale), and from this, we cut a cutting chip in accordance with SNG432. Work material: FC30 round bar, A cast iron high-speed cutting test was conducted under the following conditions: cutting speed: 400 m/min, depth of cut: 2.5 mm, feed: 0.25 mm/rev., cutting time: 5 min, and the flank wear width of the cutting edge was measured. These results are shown in Table 1. From the results shown in Table 1, ceramics 1 to 15 of the present invention all exhibit high hardness and excellent wear resistance, whereas comparative ceramics 1 to 3 exhibit high hardness and excellent wear resistance.
As can be seen in the figure, it is clear that if the content of any of the constituent components is outside the range of the present invention, the hardness and wear resistance will be poor. As mentioned above, the ceramic of the present invention has high hardness and exhibits excellent wear resistance in practical use, so when used as a cutting tool or a wear-resistant tool, it will last for an extremely long time. It consistently demonstrates excellent performance.

Claims (1)

[Claims] 1. Compositional formula: Si ₆ -zAlzOzN ₈ -z (where O<z
≦4.3) and the compositional formula: Mx (Si, Al) ₁₂ (O, N) ₁₆ (where O<x
≦2, M: represents one or more of Li, Na, Ca, Mg, Y, and rare earth elements), and in addition, as a dispersed phase forming component. One or two of zirconium oxide and hafnium oxide: 1-
40% by volume, a composite acid/nitride of the elements contained in the above M, Si, and Al as a binder phase forming component: 1 to 20% by volume, and the above α-sialon/β-sialon volume ratio Sialon-based ceramics with excellent wear resistance, characterized in that the ratio is within the range of 25/75 to 95/5.