JPH0470270B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a wear-resistant silicon nitride-based sintered body suitable for use in ceramics for machining, particularly cutting tools, wear-resistant materials, and corrosion-resistant materials. Silicon nitride has excellent heat resistance, thermal shock resistance, mechanical strength at high temperatures, oxidation resistance, corrosion resistance to chemicals, and corrosion resistance to molten metal, and is also highly hard, so it is used as a high-temperature electrical insulating material, an electronic component material, It is widely used in physical and chemical products, metal industrial refractories, nuclear reactor materials, MHD power generation materials, and high-temperature structural parts such as jet engines, rocket nozzles, and turbine blades. Since Si ₃ N ₄ is a substance with strong covalent bonding properties, it is difficult to obtain a high-density sintered body compared to oxides such as Al ₂ O ₃ and ZrO ₂ which have strong ionic bonding properties. For this reason, the reaction sintering method or the hot pressing method is mainly used as the sintering method for Si ₃ N ₄ . In addition, there is _a method to obtain a high _- density sintered body of Si ₃ N ₄ .
A commonly used method is to add a sintering aid such as Al ₂ O ₃ , AlN, MgO, Y ₂ O ₃ and perform pressure sintering. In a sintered body in which MgO is added as a sintering aid to Si ₃ N ₄ , MgO reacts with Si ₃ N ₄ during the sintering process to generate a low melting point liquid phase and promote sinterability. Another drawback is that Mg-containing lower silicates remaining at the grain boundaries deteriorate the high-temperature properties of the sintered body. Also, Si ₃
The sintered body is made by adding _Y2O3 as _a sintering aid to _N4 .
Although it has excellent high-temperature properties as a sintered body, it has a drawback that its strength is low because its sinterability promotion effect during the sintering process is weak and a dense sintered body cannot be obtained. Sialon-based sintered bodies are among the silicon nitride-based sintered bodies that have been proposed mainly for high-temperature structural parts such as jet engines, rocket nozzles, and turbine blades in order to improve these drawbacks. Sialon-based sintered bodies are sintered bodies made by adding Al ₂ O ₃ or AlN as a sintering aid to Si ₃ N ₄ as a solid solution, and Si ₃ N ₄ as a sintering aid.
Added other additives such as Al ₂ O ₃ or AlN and Y ₂ O ₃
It is collectively known as a Si ₃ N ₄ based sintered body with Al solid solution.
These sialon-based sintered bodies have Al ₂ O ₃ or AlN with strong ionic bonding properties dissolved in the Si ₃ N ₄ lattice, which reduces the inherent covalent bonding properties of Si ₃ N ₄ and prevents sintering. during the sintering process as well as deteriorating the properties of the body.
Although lower oxides containing Al element improve sinterability, after sintering, a fragile glass phase containing Al elements remains at the grain boundaries of SiAlON particles, drastically reducing the high-temperature properties of the sintered body. There is a drawback that it does. During cutting, the tip of a cutting tool's cutting tool undergoes a combination of complex forms such as high-temperature compression, thermal shock, oxidation, corrosion, clearance wear, adhesive wear, and drag wear. When a sialon-based sintered body is used as a cutting tool material, under dry cutting conditions, a glass phase remains in the grain boundaries of the sialon-based sintered body.
Compared to Al ₂ O ₃ ceramics, wear resistance at high temperatures tends to be inferior, and under wet cutting conditions using water-soluble cutting oil, AlN components from the elements that make up Sialon are hydrolyzed, decomposed and vaporized significantly. It has the disadvantage of poor wear resistance because it induces tool damage. As research and development other than sialon-based sintered bodies, an attempt was made to apply Si ₃ N ₄ material to cutting tools in JP-A-49-113803. This Japanese Patent Application Publication No. 49-113803 discloses that Si ₃ N ₄ is used as a sintering aid.
This is a sintered body that uses MgO and Y ₂ O ₃ and has a spinel compound of MgO and Y ₂ O ₃ dissolved in Si ₃ N ₄ . However, MgO and Y ₂ O ₃ are simple 2
Tresvyatskii et al. {Izr, _Akad , Nauk _SSSR , Neorg; Mater, 7
[11}2020 (1971)} reported. Even if a spinel compound such as MgO・Y ₂ O ₃ with strong ionic bonding properties were dissolved in Si ₃ N ₄ , the original covalent bonding properties of Si ₃ N ₄ would deteriorate and the process would be severe, such as when cutting cast steel. Under such cutting conditions, it is impossible to obtain performance superior to conventional Al ₂ O ₃ ceramics. fact,
In JP-A-49-113803, Al-Si which belongs to light cutting
When cutting an alloy for 2 minutes under the following cutting conditions: cutting speed 300 m/min, depth of cut 1.5 mm, and feed rate 0.3 mm/rev, side flank wear tends to be extremely large at 0.15 to 0.2 mm. There are practical problems. The present invention solves the above-mentioned drawbacks and problems, and can be used in the cutting speed range used with conventional cutting tool materials, as well as in high-speed cutting ranges that are impractical with conventional cutting tool materials. The purpose is to provide a tool material that is of high quality. The wear-resistant silicon nitride-based sintered body of the present invention has a wear resistance of 0.5 to
10% by weight magnesium oxide and 0.5-10% by weight yttrium oxide and 0.1-4.5% by weight 4a, 5a, 6a
at least one binder phase reinforcing agent selected from single metal compounds and composite metal compounds of group transition metal carbides, nitrides, carbonitrides, carbonates, nitrides, and carbonitrides; and the remainder. It is a sintered body obtained by mixing and sintering silicon nitride and unavoidable impurities. The present invention uses MgO, which has a weak effect of increasing high temperature strength but contributes to promoting sinterability, in the binder phase, which is a sintering aid for Si ₃ N ₄ and Si ₃ N ₄ , and MgO, which has a weak effect of promoting sinterability but contributes to high temperature strength. It was confirmed that a dense sintered body could be obtained by adding Y ₂ O ₃ to increase the Si ₃ N ₄ −
Si ₃ without reducing the density of MgO−Y ₂ O ₃ based sintered body
As a result of various research into ways to improve wear resistance at high temperatures, which is a drawback of N ₄ −MgO−Y ₂ O ₃ -based sintered bodies, 4a, 5a, and
The present invention was completed by discovering that a Group 6a transition metal compound improves the wear resistance of Si ₃ N ₄ -MgO-Y ₂ O ₃ based sintered bodies at high temperatures. That is, the wear-resistant silicon nitride-based sintered body of the present invention is
In order to make Si ₃ N ₄ into a dense sintered body, MgO and Y ₂ O ₃ are added to the binder phase, which is a sintering aid, and serve as a binder phase strengthening agent to improve wear resistance at high temperatures. at least one selected from single metal compounds and composite metal compounds of carbides, nitrides, carbonitrides, carbonates, nitrides, and carbonitrides of group 4a, 5a, and 6a transition metals. It is dispersed. When Si ₃ N ₄ , the binder phase, and the binder phase strengthener are sintered in this way, the binder phases MgO and Y ₂ O ₃ are converted into Si ₃ N ₄
At the same time, MgO and Y ₂ O ₃ , which are binder phases, oxidize a part of the surface of the binder phase strengthener, and Si ₃ N ₄ also Since it reacts with the sintered body, it further promotes the densification of the sintered body. Also, the binder phase strengthener is the binder phase MgO and Y ₂
It is thought that wear resistance at high temperatures is increased by being dispersed in the binder phase while being partially oxidized by O ₃ . The binder phase strengthener used here is 4a containing carbon and/or nitrogen,
Among group 5a and 6a transition metal compounds, transition metal compounds of group 4a, 5a and 6a containing nitrogen are particularly desirable because of their reactivity with Si ₃ N ₄ . For the wear-resistant silicon nitride-based sintered body of the present invention, it is preferable to use as a starting material Si ₃ N ₄ powder that is as fine as possible (preferably an average particle size of 5μ or less) and has a low oxygen content. MgO and Y ₂
Among single metal compounds and composite metal compounds of carbides, nitrides, carbonitrides, carbonates, nitrides, and carbonitrides of O ₃ and group 4a, 5a, and 6a transition metals that are binder phase strengthening agents. At least one of the selected types may be added or mixed individually, but in order to suppress coarsening and rod-like formation of Si ₃ N ₄ particles in the structure of the sintered body, it is necessary to combine the binder phase and the binder phase reinforcing agent. It is preferable to use a method in which a composite compound is added to Si ₃ N ₄ as a starting material and mixed. When the wear-resistant silicon nitride-based sintered body of the present invention contains Al, a glassy phase remains in the grain boundary phase of Si ₃ N ₄ , which reduces the properties of the sintered body required as a cutting tool. As an impurity contained in the raw material powder, it is necessary to reduce the Al content as much as possible, and it is also necessary to avoid mixing Al during the manufacturing process.
For example, it is preferable not to use Al-containing materials for containers, balls, etc. used when mixing and pulverizing raw materials. Si ₃ N ₄ is α−Si ₃ N ₄
However, the wear-resistant silicon nitride _{-based sintered body of the present invention may mainly use α-Si 3 N 4 as a starting} material, or α-Si ₃ N ₄ and β
A mixture of -Si ₃ N ₄ may be used as the starting material, or primarily β-Si ₃ N ₄ may be used as the starting material, or even α-Si ₃ N ₄ and/or β- A mixture of Si ₃ N ₄ and amorphous silicon nitride may be used as the starting material. Sintering methods include normal sintering (pressureless sintering), energized pressure sintering, and hot pressing in a vacuum or non-oxidizing atmosphere. It is also possible to promote densification of the sintered body in combination. The reason for limiting the numerical values will be explained here. When MgO, which is a binder phase, is less than 0.5% by weight, the effect of promoting sinterability is weak, and when it exceeds 10% by weight, Mg-containing lower silicates increase after sintering, and the high temperature strength of the sintered body decreases. For MgO content 0.5~10
It was determined as weight %. Y ₂ O ₃ , which is a binder phase, is less effective in improving the high temperature strength of the sintered body when it is less than 0.5% by weight, and when it exceeds 10% by weight, the total binder phase amount of MgO and Y ₂ O ₃ increases, resulting in high temperature This results in a decrease in wear resistance.
_{The Y2O3} content was determined to be 0.5-10% by weight. Selected from single metal compounds and composite metal compounds of carbides, nitrides, carbonitrides, carbonates, nitrides, and carbonitrides of group 4a, 5a, and 6a transition metals, which are binder phase strengthening agents. At least one or more
If it is less than 0.1% by weight, it will be dispersed in the binder phase and _the effect of increasing wear resistance at high temperatures will be weak, and if it exceeds 4.5% by weight, it will be difficult to obtain a dense sintered _body . The content of the binder phase reinforcing agent was determined to be 0.1 to 4.5% by weight because the high temperature properties, particularly the thermal shock resistance, and the abrasion resistance associated with this decrease. Next, the wear-resistant silicon nitride-based sintered body of the present invention will be specifically described according to Examples. Example 1 Si ₃ N ₄ with an average particle size of 1μ, MgO, Y ₂ O ₃ and 4a, 5a,
Using powders of single metal compounds and composite metal compounds of group 6a transition metals, each sample was blended in the proportions shown in Table 1, and each blended sample was mixed with a WC-based cemented carbide ball in a hexane solvent. The mixture was mixed and ground in a stainless steel container. After removing the solvent from the obtained mixed powder by evaporation, it was filled into a carbon mold coated with BN powder, and after replacing the inside of the furnace with _N2 gas, it was heated for 150~
Molding pressure of 400Kg/ ^cm2 , temperature of 1700~1900℃, 60
Pressure sintered for ~120 minutes. The manufacturing conditions for each sample are shown in Table 1, and the various properties of the obtained sintered bodies are shown in Table 2. The results shown in Table 2 confirm that the wear-resistant silicon nitride-based sintered body of the present invention has achieved high density and high hardness, and has excellent thermal shock resistance. The thermal shock test conducted here involves holding the sample at each temperature for 20 minutes, then immersing it in water at about 20℃ (room temperature) to check whether or not cracks have occurred in the sample. showed the highest temperature that could be withstood without cracking.

【table】

[Table] Example 2 Using powders of MgO and Y ₂ O ₃ as the binder phase and a single metal compound and a composite metal compound of group 4a, 5a, and 6a transition metals as the binder phase strengthener, a predetermined ratio was used. After heating in vacuum at 1400 to 1600°C for 1 hour, the mixture was ground and mixed to produce a composite compound powder consisting of a binder phase and a binder phase reinforcing agent. This composite compound powder and average particle size
Each sample was mixed using 1μ Si ₃ N ₄ powder in the proportions shown in Table 3, mixed and ground in the same manner as in Example 1, and then sintered. The manufacturing conditions for each sample are shown in Table 3, and the various properties of the obtained sintered bodies are shown in Table 4. Various properties of the sintered body were determined in the same manner as in Example 1.

【table】

[Table] Example 3 Inventive product 2 shown in Table 1 of Example 1,
Sintered bodies of 5, 8, 9 and comparative products 1 and 2 and Example 2
Among them, the sintered bodies of the present invention products 11 and 14 and comparative products 3, 4, and 5 shown in Table 3 were respectively CIS standard SNP432.
The wear-resistant silicon nitride-based sintered body of the present invention molded into the same shape and commercially available Al ₂ O ₃ ceramics and Sialon ceramics were molded into the same shape and in addition to the following (A) and (B) for comparison. A cutting test was conducted under these conditions. (A) Turning test conditions Work material FC25 Chip shape SNP432 Honing 0.1×-30° Cutting speed 600m/min Depth of cut 1.5mm Feed rate 0.7mm/rev Cutting time 30min (B) Milling test conditions Work material FCD55 Chip shape SNP432 Honing 0.1×−30° Cutting speed 140 m/min Depth of cut 1.5 mm Feed rate 0.18 mm/tooth Table 5 shows the cutting test results under conditions (A) and (B). As shown in Table 5, the wear-resistant silicon nitride-based sintered body of the present invention has significantly higher wear resistance and chipping resistance than conventional Al ₂ O ₃ ceramics, sialon ceramics, and comparative products 1 to 5. It was confirmed that it was excellent. In addition, the wear-resistant silicon nitride-based sintered body of the present invention can be used satisfactorily even under severe cutting conditions such as high speed and high feed rate, which was generally considered impossible with conventional cutting tool materials, and can be used in new cutting processing areas. We can hope to pave the way.

[Table] From the above Examples 1, 2, and 3, the wear-resistant silicon nitride-based sintered body of the present invention can be used as a cutting tool, a wear-resistant material, and a corrosion-resistant material that applies the inherent corrosion resistance of Si ₃ N ₄ . Furthermore, there is a possibility that it can be used for conventional ceramic applications including structural materials, and it can be judged that the industrial value is extremely high.

Claims (1)

[Claims] 1 0.5-10% by weight of magnesium oxide and 0.5-10%
wt% yttrium oxide and 0.5-4.5 wt%
At least one type of bond selected from single metal compounds and composite metal compounds of carbides, nitrides, carbonitrides, carbonates, nitrides, and carbonitrides of group 4a, 5a, and 6a transition metals. A wear-resistant silicon nitride-based sintered body characterized by having a composition containing a phase strengthener, residual silicon nitride, and unavoidable impurities.