JPH0247425B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a high-toughness silicon nitride sintered body suitable for ceramics for machining, particularly cutting tools, wear-resistant materials, and corrosion-resistant materials. Silicon nitride is a compound with strong covalent bonding,
Compared to ionic crystals and metal crystals, it has a large ratio of grain boundary energy to surface energy, self-diffusion is very slow, and it is a material that is difficult to sinter because it decomposes and evaporates at high temperatures. For this reason, even if silicon nitride is sintered using a pressureless ordinary sintering method, a dense sintered body cannot be obtained, and sintering aids such as MgO, Y ₂ O ₃ , Al ₂ O ₃ , and AlN are generally used. A dense sintered body is obtained by a hot pressing method or a hot isostatic pressing method (HIP) using reactive sintering or liquid phase sintering. In this way, MgO,
Added sintering aids such as Y ₂ O ₃ , Al ₂ O ₃ , AlN, etc.
Si ₃ N ₄ sintered bodies contain a glass phase of magnesium silicate, a glass phase of yttrium silicate, or an Al element close to enstatite (MgSiO ₃ ) composition in the binder phase that binds the hard phase of Si ₃ N ₄ . A glass phase consisting of lower silicates is produced.
These glass phases become liquid phases at low temperatures and form Si ₃ N ₄
Although it promotes sinterability, it remains at the grain boundaries even after sintering, resulting in a decrease in high-temperature strength.
The direction of crystallization of the binder phase has been studied to improve the drawbacks of the binder phase consisting of a glass phase, and proposals have been made mainly for high-temperature structural materials such as jet engines, rocket nozzles, and turbine blades. Sialon-based sintered bodies are examples of silicon nitride-based sintered bodies. 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.
It is collectively known as an Al-containing Si ₃ N ₄ -based sintered body in which other additives such as Al ₂ O ₃ or AlN and Y ₂ O ₃ are dissolved as a sintering aid in Si ₃ N ₄ . However, this sialon-based sintered body has Al ₂ O ₃ or AlN, which has strong ionic bonding properties, dissolved in solid solution in the Si ₃ N ₄ lattice, so the covalent bonding property is reduced and the original characteristics of Si ₃ N ₄ are lost. In addition to deterioration, lower oxynitrides involving the Al element promote sinterability, but remain as a brittle glass phase at the grain boundaries of SiAlON (SiAlON) particles after sintering, unless heat treatment for crystallization is performed. There is a problem in that the high temperature properties of the sintered body are drastically reduced. The present invention solves the above-mentioned drawbacks and problems, and creates a wear-resistant and high-toughness silicon nitride sinter that can be used from conventional cutting areas to high-speed cutting areas by defining the crystallization of the binder phase. Its purpose is to provide unity. The high toughness silicon nitride sintered body of the present invention has a weight ratio of 65
A sintered body consisting of a binder phase of ~99% silicon nitride, a binder phase of 1~35% oxynitrodiene silicate, and unavoidable impurities. )c()d}(NxOy)z, () represents the group metal of the periodic table,
() indicates a group metal of the periodic table; () indicates a group metal of the periodic table; a, b, c, d are Si, (), (), and molar ratio of the metal elements in (), respectively. , x and y are N (nitrogen) and O (oxygen), respectively.
represents the molar ratio of the nonmetallic element, z represents the molar ratio of the nonmetallic element to the metal element, and a, b,
c, d, x, y and z are each positive numbers and 1≦a
≦3, 0<b≦2, 0<c≦2, 0<d≦1, a
+b+c+d=5, 0<x<7, 0<y<7, x
+y=7, 0.9≦x≦1, the group metal represents Li and/or Na, and the group metal represents one or more selected from Be, Mg, Ca, Sr, and Ba. The group metal represents one or more selected from B, Al, Ga, and rare earth elements, and is a silicon nitride sintered body comprising a binder phase that always contains one or more of the rare earth elements. The rare earth elements used here are Sc, Y, La, Ce, Pr, Nd,
Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm,
Collectively refers to the 17 elements Yb and Lu. In the high-toughness silicon nitride sintered body of the present invention, the binder phase that binds the hard phase mainly composed of Si ₃ N ₄ is a gehlenite mineral phase Ca ₂ Al (AiSi) O ₇ or an acamanite mineral phase.
The bonded phase is crystallized by forming a solid solution compound with the same shape as the melilite crystal structure, such as Ca ₂ MgSi ₂ O ₇ . Like this {Sia()b()
The sintered body of silicon nitride and a crystallized binder phase close to the melilite composition represented by c()d}(NxOy)z is a binder phase with a composition containing rare earth elements and nitrogen elements, unlike the actual melilite crystal structure. Because of this, the inherent properties of the hard phase, which is mainly composed of Si ₃ N ₄ with strong covalent bonding, are not degraded, and the internal stress caused by the crystal anisotropy between this bonded phase and the hard phase is small.
It is a high-toughness silicon nitride sintered body that also increases the bonding strength between the binder phase and the hard phase. In the high toughness silicon nitride sintered body of the present invention, the binder phase is a cation in a rare earth element oxide or nitride.
The cations in Si ₃ N ₄ may mutually substitute to form a two-dimensionally connected network of oxynitride silicates, but the cation-deficient structure tends to result in a glass phase. By controlling the addition amounts of Group and Group elements of the periodic table, it is possible to easily form oxynitrodiene silicate close to the melilite phase, and to form a crystalline binder phase and Si ₃ N ₄ that are stable. It is a sintered body with a hard phase. Close to this melilite phase {Sia()b()
The bonding phase represented by c()d}(NxOy)z is an element in which Li and/or Na, which are group elements of the periodic table, form a strong glass phase. After solidification, it is dissolved in trace amounts in the binder phase together with rare earth elements, giving it a chemical affinity with the hard phase of Si ₃ N ₄ through nitrogen. Moreover, the binder phase becomes crystalline and contributes to the increase in strength and densification of the sintered body.
One or more of these promotes sintering together with group group elements during the sintering process, reacts with Si ₃ N ₄ which is a hard phase, and facilitates the formation of oxynitrodiene silicate close to the melilite phase together with group group elements. After solidification, nitrogen is interposed to improve the bonding strength of Si ₃ N ₄ particles and improve thermal conductivity, and B, Al, Ga, and rare earth elements, which are group elements of the periodic table, form the hard phase.
It forms a solid solution and combines with Si ₃ N ₄ to form oxynitrodiene silicate, which is close to the melilite phase, which is a crystalline binder phase with high covalent bonding properties, and the grain boundary phase of the Si ₃ N ₄ sintered body is crystallographically determined. This significantly contributes to improved thermal shock resistance and toughness. This {Sia()
b()c()d}(NxOy)z When B, Al, and Ga, which are easily dissolved in solid solution in Si ₃ N ₄ , are dissolved together with rare earth elements in the bonded phase of oxynitrodiene silicate, it is a hard phase. It contributes to increasing the bonding strength between Si ₃ N ₄ and the bonding phase, especially the bonding strength of oxynitrodiene silicate with solid solution of Al element and Si ₃ N ₄
A sintered body with a hard phase has improved oxidation resistance and welding resistance, and a sintered body with a Si ₃ N ₄ hard phase and a binder phase of oxynitrogiensilicate in which element B is dissolved has a lower coefficient of thermal expansion. , to further increase thermal shock resistance in order to improve electrical insulation. The high toughness silicon nitride sintered body of the present invention has a phase close to the melilite phase {Sia()b()c()d}(NxOy)
Because it is a dense sintered body consisting of a crystalline binder phase represented by z and a hard phase mainly composed of Si ₃ N ₄ , it becomes hot locally from the cutting edge to the cutting edge like a cutting tool.
It is effective enough to withstand even when used as a material that is subjected to a mixture of extremely severe thermal stress and load. The high toughness silicon nitride sintered body of the present invention has {Sia()
b () c () d} (N
A small amount of Group B elements, which are the same group as Si, may be mixed. In particular, if Ge, which is the same group as Si, is mixed in 30 mol% or less based on the Si in the binder phase, the thermal shock resistance of the sintered body will be reduced. It is effective in improving toughness and toughness. The starting materials for the high toughness silicon nitride sintered body of the present invention are:
Li, a group element of the periodic table, Be, a group Na element,
Oxynitrodiene silicate is produced in the sintering process using a multi-component compound consisting of oxides, nitrides, silicides of Ca, Sr, Ba, group elements B, Al, Ga, rare earth elements, and various combinations thereof. It may be a binder phase with a crystalline structure, or it may be close to the acamanite mineral phase containing the above-mentioned group, group, or group elements from the viewpoint of crystalline formation {()()()} ₃
[Si ₂ O ₇ ], close to melilite mineral phase {()()
()} Si [Si ₂ O ₃ N ₄ ], various types such as {() () ()} SiO ₃ close to the enstatite mineral phase and {() () ()} ₂ SiO ₄ close to the forsterite mineral phase It is also good to combine a composite silicate with a single compound of the above-mentioned groups, groups, or group elements. In particular, when the above-mentioned composite silicates or tetragonal composite oxynitride silicates are used as a starting material, sintering The Si ₃ N ₄ particles in the body structure become spheroidal, and the formation of rod-shaped or coarse particles with a large aspect ratio, which are found in general sintered body structures, can be prevented. When a sintered body in which Si ₃ N ₄ particles are spheroidized and refined in this way is used as a cutting tool material, the chipping resistance and wear resistance of the tool are significantly improved. Si ₃ N ₄ as a starting material contains a small amount of SiO ₂ to make the bonding phase an oxynitrodiene silicate structure similar to the Si-containing melilite phase.
A small amount of SiO ₂ may be adsorbed on the surface of Si ₃ N ₄ powder,
Also, the crystal structure of the Si ₃ N ₄ starting material is α-type Si ₃ N ₄ ,
Even when α-type Si ₃ N ₄ and β-type Si ₃ N ₄ , which is stable at high temperatures, coexist, α-type Si ₃ N ₄ and amorphous Si ₃ N ₄ coexist,
Even if a mixture of α-type Si ₃ N ₄ , β-type Si ₃ N ₄ and amorphous Si ₃ N ₄ is used, there is no problem in obtaining the high toughness silicon nitride sintered body of the present invention. Sintering methods include normal sintering (pressureless sintering) in vacuum or a non-oxidizing atmosphere such as N ₂ or Ar, electrification pressure sintering, and hot press sintering. Hydrostatic pressing sintering (HIP) can also be combined to promote densification of the sintered body. The reason for limiting the numerical values will be explained here. Relationship between hard phase amount and binder phase amount When the hard phase amount exceeds 99% by weight, the binder phase amount becomes relatively less than 1% by weight, which makes it less effective as a sintering aid and makes sintering difficult. It is difficult to sinter the material Si ₃ N ₄ densely, and the amount of hard phase is 65
If it is less than 35% by weight, the relative amount of binder phase is 35% by weight.
The hardness of the sintered body is low because the amount exceeds
The inherent properties of Si ₃ N ₄ also deteriorate. For this purpose, the hard phase Si ₃ N ₄ was determined to be 65 to 99% by weight, and the binder phase amount was determined to be 1 to 35% by weight. Regarding the binder phase: If the Si content in the binder phase, which is expressed as {Sia()b()c()d}(NxOy)z, is less than 1 mol, the sinterability will deteriorate and the oxynitrodiene phase will be close to the melilite phase. Manufacturing conditions such as high temperature or long-time sintering are required to form silicates, and when the amount exceeds 3 moles, silicates with a low melting point are likely to be formed. The content of group elements is determined to be 1≦a≦3 in order to remain in the grain boundaries of the sintered body and reduce the high-temperature properties of the sintered body. This is a necessary component for improving properties, but if the amount exceeds 2 moles, the amount of other metal elements becomes relatively small, making it difficult to form an oxynitrodiene silicate close to the melilite phase. The content of group elements is a necessary component to promote sinterability and correct the cations of oxynitrodiene silicate, which is close to the melilite phase, but if it exceeds 2 moles, the content of group elements such as enstatite becomes the main component. Since silicates with a low melting point are likely to be formed and the high-temperature properties of the sintered body are deteriorated, 0<c≦2 is set. It is a component that makes it easier to correct the cations of oxynitrodiene silicate, which is close to the group, and is necessary for densification of the sintered body, but when the amount exceeds 1 mol, a glass phase remains in the grain boundary phase of the sintered body. 0<d≦1 in order to reduce the high-temperature properties. The amount of nonmetallic element N is a necessary component to improve the bonding strength with the hard phase mainly composed of Si ₃ N ₄ , and the amount of O is a necessary component to promote sinterability. In order to crystallize oxynitrodiene silicate, which is close to the melilite phase with the nonmetallic elements N and O, 0<x<7, 0<y<7 are set, and {Sia
The oxynitrodiene silicate of ()b()c()d}(NxOy)z may be a stoichiometric compound or an unstable compound, and in the case of a non-stoichiometric compound, the nonmetallic element is
If the amount is less than 0.9 mol, it becomes difficult to form a melilite phase structure, so it was set as 0.9≦z≦1. Next, the high toughness silicon nitride sintered body of the present invention will be explained in detail according to Examples. Example 1 Si ₃ N ₄ and various sintering aids were blended in the composition shown in Table 1, and mixed and ground for 48 hours using cemented carbide balls in a hexane solvent. After removing the solvent from the obtained mixed powder by evaporation, it was filled into a carbon mold coated with BN powder, and after purging the inside of the furnace with N ₂ gas, it was heated at 1650℃ at a molding pressure of 150 to 400 Kg/mm ²
Pressure sintering was carried out at a temperature range of 1850°C for 30 minutes to 2 hours.
When the hard phase and bonded phase of the obtained sintered body were analyzed by X-ray diffraction, it was found that the hard phase was mainly composed of Si ₃ N ₄ , had a melilite crystal structure, and in some samples was thought to contain a small amount of tungsten silicide. Among these, the binder phase of the melilite crystal structure was calculated from the blended phase composition and shown in Table 2, and the hardness and thermal shock resistance tests of the sintered body were also conducted and shown in Table 2. The thermal shock test conducted here was conducted at approximately 20°C after holding the sample at each temperature for 3 minutes.
When the samples were immersed in water at room temperature, each sample showed the highest temperature it could withstand without cracking.

【table】

【table】

[Table] As is clear from the results in Table 2 () ()
It was confirmed that the sintered body of Si ₃ N ₄ and the binder phase of oxynitrodiene silicate containing rare earth elements consisting of oxynitrides of group () group elements has high hardness and excellent thermal shock resistance. Example 2 Among the samples obtained in Example 1, the sintered body No. 3 in Table 2 was compared with a commercially available Al ₂ O ₃ -TiC ceramic sintered body and a sialon-based sintered body. The sintered body was molded into the CIS standard SNP432 shape and a cutting test was conducted under the following conditions. Cutting test conditions with milling cutter Work material FCD60 (50 mm x 200 mm square material surface) Cutting speed 150 m/min Depth of cut 1.5 mm Feed 0.176 mm/rev Table feed 0.52 mm/min Test results Al ₂ O ₃ −TiC ceramic sintered body The sialon-based sintered body broke when cutting 140mm the first time and 150mm the second time, and the sialon sintered material broke 200mm the first time and 150mm the second time.
Sample No. 3 of the high toughness silicon nitride sintered body of the present invention, whereas chipping occurred when cutting 400 mm for the second time.
Even after cutting 1000 mm for both the first and second cutting, it was still usable due to normal wear. Example 3 Among the samples obtained in Example 1, the sintered body No. 5 in Table 2 was compared with a commercially available Al ₂ O ₃ -TiC ceramic sintered body and a sialon-based sintered body. The sintered body was molded into the CIS standard SNP432 shape and a cutting test was conducted under the following conditions. Cutting test conditions by turning Work material S48C (400φmm x 1500mm) Cutting speed 250m/min Depth of cut 1.5mm Cutting time 0.5min Feed 0.3mm/rev After the test, when comparing the average flank wear amount of each sample, it was found that Al ₂ O ₃ −TiC ceramic sintered body is 0.11mm
Sample No. of the high-toughness silicon nitride sintered body of the present invention has a wear amount of 0.72 mm for the sialon-based sintered body.
No. 5 had a wear amount of 0.09 mm. Example 4 Among the samples obtained in Example 1, the sintered body No. 11 in Table 2 was compared with a commercially available Al ₂ O ₃ -TiC ceramic sintered body and a sialon-based sintered body. Example 2,
Similarly to 3, the following cutting test was conducted using a sample of SNP432. Cutting test conditions by turning Work material FC35 (350φmm x 1500mm) Cutting speed 600m/min Depth of cut 1.5mm Feed 0.7mm/rev Test results The Al ₂ O ₃ -TiC ceramic sintered body broke after cutting for about 1 minute. However, while the sialon-based sintered body exhibited chipping after approximately 7 minutes of cutting, and chip wear exceeded 0.3 mm, the high-toughness silicon nitride sintered body of the present invention showed normal wear even after 60 minutes of cutting. It was still in usable condition. Example 5 Among the samples obtained in Example 1, the sintered body No. 15 in Table 2, a commercially available Al ₂ O ₃ -TiC ceramic sintered body, and a sialon sintered body were each heated to a height of 12.7φmm. Sa8
It was formed into a round chip with a diameter of mm, and a cutting test was conducted under the following conditions. Cutting test conditions by turning Work material Waspaloy (Ni-based super alloy) Cutting speed 170 m/min Depth of cut 2.0 mm Feed 0.4 mm/rev Test results The Al ₂ O ₃ -TiC ceramic sintered body broke after cutting for about 45 seconds. Although the sialon-based sintered body broke after cutting for about 30 seconds, the high-toughness silicon nitride sintered body of the present invention showed normal wear even after cutting for about 2 minutes and 45 seconds and remained usable. Example 6 Among the samples obtained in Example 1, the sintered body No. 17 in Table 2 and the commercially available Al ₂ O ₃ -TiC ceramic sintered body were each molded into SNCN54ZTN of the CIS standard and subjected to the following conditions. A cutting test was conducted. Cutting test conditions with milling cutter Work material Case-hardened steel (HRc55) Black skin cutting Cutting speed 270 m/min Depth of cut 4.5 mm Feed 0.20 mm/rev (per tooth) Table feed 600 mm/min Test results Al ₂ O ₃ −TiC system While the ceramic sintered body reached the end of its life due to chipping after cutting for about 2 minutes and 10 seconds, the high-toughness silicon nitride sintered body of the present invention showed normal wear even after cutting for about 24 minutes and remained usable. It was hot. As is clear from the above examples, when used as a cutting tool, the high toughness silicon nitride sintered body of the present invention has a service life that is 5 to 30 times longer than conventional ceramics, depending on the cutting conditions. , especially for applications that require chipping resistance such as milling cutting conditions and black scale cutting, applications that are used under high-speed, high-feed cutting conditions, and even for cutting difficult-to-cut materials such as super alloys. It is a high toughness silicon nitride sintered body that exhibits a long life. In addition, since the high toughness silicon nitride sintered body of the present invention is a material with high hardness and thermal shock resistance, it can be fully used as an abrasion impact resistant material and a high temperature structural material, and has the inherent corrosion resistance of silicon nitride. It is a material of extremely high industrial value that can be used in various corrosion-resistant materials, and even in applications that combine wear resistance, corrosion resistance, and thermal shock resistance.

Claims (1)

[Scope of Claims] 1. Consists of a binder phase of 65 to 99% silicon nitride and 1 to 35% oxynitrodiene silicate by weight, and unavoidable impurities, and the binder phase is {Sia()b()c( )d}(NxOy)z When expressed as, () represents a group metal of the periodic table, () represents a group metal of the periodic table, () represents a group metal of the periodic table, and a, b , c, d represent the molar ratio of the metal elements Si, (), (), (), respectively, x, y represent the molar ratio of the nonmetallic elements N (nitrogen) and O (oxygen), respectively, and z represents the molar ratio of non-metallic elements to metallic elements, a,
b, c, d, x, y and z are each positive numbers 1
≦a≦3, 0<b≦2, 0<c≦2, 0<d≦
1, a+b+c+d=5, 0<x<7, 0<y<
7. There is a relationship: x+y=7, 0.9≦x≦1,
Group metals represent Li and/or Na; Group metals represent one or more selected from Be, Mg, Ca, Sr, and Ba; Group metals include B, Al, Ga, and rare earth elements. Indicates one or more types selected from among
Moreover, the high toughness silicon nitride sintered body is characterized in that it always contains one or more rare earth elements. 2 30 mol% or less of the Si contained in the binder phase of the oxynitrodiene silicate
The high-toughness silicon nitride sintered body according to claim 1, wherein the silicon nitride sintered body is substituted with Ge.