JP5717466B2 - Silicon nitride sintered body - Google Patents

Description

  The present invention relates to a silicon nitride sintered body having excellent mechanical characteristics.

  Since the silicon nitride sintered body has excellent mechanical properties, it is suitably used for various structural members. By the way, since silicon nitride has a strong covalent bond and it is difficult to sinter with only silicon nitride powder, sintering is performed by adding various sintering aids.

For example, Patent Literature 1 discloses a sialon sintered body composed of sialon particles and a grain boundary phase as a silicon nitride sintered body using Y ₂ O ₃ or Al ₂ O ₃ as a sintering aid. In addition, the total amount of the grain boundary phase is 20 wt% or less, and Si, Al, and Y in terms of oxides of the grain boundary phase are expressed in terms of weight ratio in the SiO ₂ —Al ₂ O ₃ —Y ₂ O ₃ ternary system ( SiO ₂ , Al ₂ O ₃ , Y ₂ O ₃ ) composition is point A (20, 10, 70), point B (20, 25, 65), point C (30, 25).
, 55) and a high toughness sialon sintered body in a region surrounded by four points D (30, 10, 60) has been proposed.

Patent Document 2 discloses a silicon nitride sintered body in which Y ₂ O ₃ and Al ₂ O ₃ are added as sintering aids. While being 15% by weight or more of the total amount of the binder, the ratio between the oxygen content of silicon nitride (expressed in terms of SiO ₂ content) and the amount of Y ₂ O ₃ and Al ₂ O ₃ is SiO ₂ − In the triangular diagram (expressed by weight ratio) showing the Y ₂ O ₃ —Al ₂ O ₃ ternary system, point A (0, 80, 20), point B (9, 73, 18), point C (9, 55) , 36), and a silicon nitride sintered body in a region surrounded by four points D (0, 60, 40) has been proposed.

Japanese Patent No. 2820846 Japanese Patent No. 2863569

As suggested by the tough sialon sintered body described in Patent Document 1 and the silicon nitride sintered body described in Patent Document 2, in order to improve mechanical properties in each manufacturer, a sintering aid component and content are included. In the silicon nitride sintered body using Y ₂ O ₃ or Al ₂ O ₃ as a sintering aid, only Y ₂ SiAlO ₅ N crystals exist in the grain boundary phase, although the amount and the like have been studied earnestly. There was a problem that fracture toughness was lowered.

The present invention has been devised to solve the above-mentioned problems, and without reducing the fracture toughness like a silicon nitride sintered body in which only Y ₂ SiAlO ₅ N crystals exist, An object is to provide an excellent silicon nitride sintered body.

The silicon nitride sintered material of the present invention, _Y 2 _{O 3} 14 wt% 5 wt% or more in terms of less, _Al 2 _{O 3} in terms of 2 mass% to 5 mass% or less and in terms of SiO ₂ 0.5 wt% 2 Contains less than mass%
And the remainder is a silicon nitride sintered body made of silicon nitride , wherein the silicon nitride is a main phase , and a crystal of Y ₂ SiAlO ₅ N and a crystal of Y ₄ SiAlO ₈ N are present in the grain boundary phase , In the X-ray diffraction chart, when the peak intensity of a Y ₂ SiAlO ₅ N crystal near 2θ = 32.6 ° is X and the peak intensity of a Y ₄ SiAlO ₈ N crystal near 2θ = 29.4 ° is Y , the ratio X / Y is characterized der Rukoto 0.85 to 1.2.

According to the silicon nitride sintered body of the present invention , 5% by mass to 14% by mass in terms of Y ₂ O ₃ , 2% by mass to 5% by mass in terms of Al ₂ O ₃ , and 0.5% by mass in terms of SiO ₂ More than 2% by mass
It is a silicon nitride-based sintered body that is fully contained and the balance is made of silicon nitride, in which silicon nitride is the main phase , and Y ₂ SiAlO ₅ N crystals and Y ₄ SiAlO ₈ N crystals exist in the grain boundary phase. In the X-ray diffraction chart, when the peak intensity of Y ₂ SiAlO ₅ N crystals near 2θ = 32.6 ° is X and the peak intensity of Y ₄ SiAlO ₈ N crystals near 2θ = 29.4 ° is Y , the ratio the X / Y is 0.85 to 1.2 der Rukoto, Y ₂ SiAlO 5 _N without lowering the fracture toughness as crystals only the existing set of silicon nitride sintered bodies of silicon nitride sintered body The strength of can be improved.

An example of the X-ray diffraction chart of the silicon nitride sintered body of the present embodiment is shown.

  Hereinafter, the silicon nitride sintered body of this embodiment will be described.

The silicon nitride sintered body of the present embodiment is 5% by mass to 14% by mass in terms of Y ₂ O ₃ , 2% by mass to 5% by mass in terms of Al ₂ O ₃ , and 0.5% by mass or more in terms of SiO _2. Less than 2% by mass
A silicon nitride sintered body containing silicon nitride as a main component , wherein silicon nitride is a main phase , and a crystal of Y ₂ SiAlO ₅ N and a crystal of Y ₄ SiAlO ₈ N are present in the grain boundary phase , In the X-ray diffraction chart, when the peak intensity of a Y ₂ SiAlO ₅ N crystal near 2θ = 32.6 ° is X and the peak intensity of a Y ₄ SiAlO ₈ N crystal near 2θ = 29.4 ° is Y , the ratio X / Y is characterized der Rukoto 0.85 to 1.2. In the present embodiment, the main phase means that the volume ratio in the silicon nitride sintered body is 50% by volume or more, and the volume ratio of the main phase is preferably 84% by volume or more. Moreover, in order to sinter silicon nitride with high covalent bonding, a sintering aid is required, and the grain boundary phase formed by this sintering aid has a volume ratio of 5% by volume or more. Therefore, the volume ratio of the main phase is 84% by volume or more and 95% by volume or less, and the volume ratio of the grain boundary phase is more preferably 5% by volume or more and 16% by volume or less. In the present embodiment, a space between silicon nitride crystals is called a grain boundary phase.

The composition of the silicon nitride sintered body in which the volume ratio of the main phase is 84% to 95% by volume and the volume ratio of the grain boundary phase is 5% to 16% by volume is Y ₂ O. ₃ 14 wt% 5 wt% or more in terms of less, _Al 2 _{O 3} contains less than 0.5 mass% or more 2% by mass 2 mass% to 5 mass% or less and in terms of SiO ₂ in terms of the balance being silicon nitride is there.

Here, an example of how to obtain the volume ratio is described. First, the oxygen content in the silicon nitride sintered body is determined by an infrared absorption method using an oxygen analyzer (EMGA-650FA manufactured by Horiba, Ltd.).
Next, quantitative analysis of Y and Al is performed using an ICP (Inductively Coupled Plasma) emission spectroscopic analyzer (ICPS-8100, manufactured by Shimadzu Corporation). Next, the quantitative values of Y and Al obtained by quantitative analysis are converted into Y ₂ O ₃ and Al ₂ O ₃ , respectively, and the amount of oxygen required in terms of this oxide is determined as oxygen in the silicon nitride sintered body. The amount of oxygen is subtracted and converted to SiO ₂ from the subtracted oxygen amount. Then, the amounts of Y ₂ O ₃ , Al ₂ O ₃ , and SiO ₂ respectively converted are subtracted from 100 to obtain the content of Si ₃ N ₄ .

Next, assuming that the content of Y ₂ O ₃ is a, the content of Al ₂ O ₃ is b, the content of SiO ₂ is c, and the content of silicon nitride is d, each theoretical density (Y ₂ O ₃ : 5.02 g / cm ³ , Al ₂ O ₃ : 3.98 g / cm ³ , SiO ₂ : 2.65 g / cm ³ , Si ₃ N ₄ : 3.18 g / cm ³ ), and using the following formula (d / 3.18) The volume ratio of the main phase can be obtained by /(a/5.02+b/3.98+c/2.65+d/3.18)×100. When a = 9.5, b = 3.5, c = 1.0, and d = 86, the volume ratio of the main phase is 90% by volume.

Whether or not Y ₂ SiAlO ₅ N crystals and Y ₄ SiAlO ₈ N crystals exist in the grain boundary phase is determined using an X-ray diffractometer (D8 ADVANCE manufactured by Bruker AXS). An X-ray diffraction chart is obtained as a result of irradiating the surface of the bonded body with CuKα rays and scanning the angle difference (2θ) and diffraction X-ray intensity between the diffraction direction and incident direction of CuKα rays with a detector. The presence of crystals may be confirmed by identifying using a JCPDS card.

Specifically, an X-ray diffraction chart of the silicon nitride sintered body of this embodiment is shown in FIG. In this X-ray diffraction chart, peaks indicating the presence of silicon nitride crystals appear at 2θ = 23.5 °, 27.2 °, 33.6 °, and 36 °. When a Y ₂ SiAlO ₅ N crystal is present, a peak appears at 2θ = 32 ° to 33 ° (32.6 °), and when a Y ₄ SiAlO ₈ N crystal is present, 2θ = 29. A peak appears between ° and around 31 ° (29.4 °, 30.7 °, 31.1 °). Moreover, the broad peak between the peaks indicating the presence of silicon nitride, Y ₂ SiAlO ₅ N and Y ₄ SiAlO ₈ N indicates that an amorphous phase is present in the silicon nitride sintered body. Show.

As shown in the X-ray diffraction chart of FIG. 1, the silicon nitride sintered body of this embodiment in which the crystals of Y ₂ SiAlO ₅ N and Y ₄ SiAlO ₈ N are present is Y ₂ SiAlO _5. The strength of the silicon nitride based sintered body can be improved without reducing the fracture toughness as in the case of the silicon nitride based sintered body in which only N crystals exist.

The reason why the presence of the Y ₂ SiAlO ₅ N crystal and the Y ₄ SiAlO ₈ N crystal can improve the strength of the silicon nitride-based sintered body without lowering the fracture toughness. However, the existence of Y ₂ SiAlO ₅ N crystals and Y ₄ SiAlO ₈ N crystals in the grain boundary phase makes it possible to grow grains of silicon nitride crystals as the main phase during sintering. In this case, the stress applied between the silicon nitride crystal, the Y ₂ SiAlO ₅ N crystal, and the Y ₄ SiAlO ₈ N crystal remains in the sintered body, thereby suppressing a decrease in fracture toughness and nitriding. It is considered that the strength can be improved because a sintered body having a fine structure can be obtained by suppressing the growth of silicon crystal grains.

Here, the fracture toughness can be evaluated by a fracture toughness value measured in accordance with an indenter press-in method (IF method) defined in JIS R 1607-2010.
It can be evaluated by a 4-point bending strength value obtained by a 4-point bending strength test according to 1601-2008.

In addition, it is contained 5% by mass or more and 14% by mass or less in terms of Y ₂ O ₃ , ₂ % by mass or more and 5% by mass or less in terms of Al ₂ O ₃ , and 0.5% by mass or more and less than 2% by mass in terms of SiO ₂ , and the rest is nitrided As a specific mechanical characteristic of a silicon nitride sintered body made of silicon and containing Y ₂ SiAlO ₅ N crystals and Y ₄ SiAlO ₈ N crystals in the grain boundary phase, fracture toughness (K _IC ) is 6.0. MPa · m ^{1
/ 2} or more, and the 4-point bending strength is 800 MPa or more.

The silicon nitride sintered body of this embodiment has a peak intensity of Y ₂ SiAlO ₅ N crystal near 2θ = 32.6 ° in the X-ray diffraction chart as X, and Y ₄ SiAlO ₈ N near 2θ = 29.4 °. When the peak intensity of the crystal is Y, the ratio X / Y is preferably 1.2 or less (excluding 0). When the ratio X / Y is 1.2 or less (excluding 0), fracture toughness and strength can be improved.

Specifically, it contains 5% by mass or more and 14% by mass or less in terms of Y ₂ O ₃ , 2% by mass or more and 5% by mass or less in terms of Al ₂ O ₃ , and 0.5% by mass or more and less than 2% by mass in terms of SiO ₂ , The balance is made of silicon nitride, Y ₂ SiAlO ₅ N crystal and Y ₄ SiAlO ₈ N crystal exist in the grain boundary phase, and the peak of Y ₂ SiAlO ₅ N crystal near 2θ = 32.6 ° in the X-ray diffraction chart. When the strength is X and the peak intensity of Y ₄ SiAlO ₈ N crystal near 2θ = 29.4 ° is Y, if the ratio X / Y is 1.2 or less (excluding 0), the fracture toughness is 6.5 MPa · m ^1/2 or more The four-point bending strength can be 900 MPa or more.

In the silicon nitride sintered body of this embodiment, it is preferable that WSi ₂ and FeSi ₂ crystals further exist in the grain boundary phase. Since the crystals of WSi ₂ and FeSi ₂ are thermodynamically stable and the grain boundary phase hardly undergoes phase transformation even when mechanical stress or thermal stress is applied, the strength at high temperature can be improved. Incidentally, the content of W and Fe, with respect to _{Si 3 N 4, Y 2 O} 3, Al 2 O 3, the sum of SiO ₂ 100 mass% constituting the silicon nitride sintered body, W is terms _of WO ₃ 3 mass% or less (excluding 0 mass%) and Fe is preferably 2 mass% or less (excluding 0 mass%) in terms of Fe ₂ O ₃ .

And, as a specific _{characteristic,} Y 2 _{O 3} 14 wt% 5 wt% or more in terms of less, _Al 2 _{O 3} in terms of 2 mass% to 5 mass% or less and in terms of SiO ₂ 0.5 wt% or more 2% In a silicon nitride sintered body containing less than 100% by mass of silicon nitride sintered body, W is ₃ % by mass or less (not including 0% by mass) in terms of WO ₃ and Fe is in terms of Fe ₂ O ₃ Silicon nitride containing 2% by mass or less (excluding 0% by mass) and having WSi ₂ and FeSi ₂ crystals in addition to Y ₂ SiAlO ₅ N crystals and Y ₄ SiAlO ₈ N crystals in the grain boundary phase High temperature (800 ℃
) Can be set to 700 MPa or more. In addition, WSi _{2 in the} grain boundary phase
Whether or not FeSi ₂ crystals are present, using a wavelength dispersive X-ray microanalyzer (JXA-8600M type manufactured by JEOL Ltd.), the grain boundary phase, that is, outside the region where Si and N coexist, A region where W and Si are present and a region where Fe and Si are present may be confirmed, and the crystal structure may be confirmed by transmission electron microscope (TEM) analysis. Also high temperature (800 ℃)
The strength at may be measured in accordance with JIS R 1604-2008.

Moreover, the silicon nitride based sintered body of the present embodiment has a YSiO ₂ N (borastite), Y ₅ (Si ₄ ) ₃ N (apatite), Y ₂ Si ₂ O ₇ (disilicate) phase as a grain boundary phase. And at least one crystal of Y ₂ SiO ₅ (monosilicate) may be present. Since these crystals are difficult to soften as compared with the amorphous phase, they are effective in improving the strength at a high temperature (800 ° C.).

  Next, a method for manufacturing the silicon nitride sintered body of this embodiment will be described.

First, as starting materials, Si powder (average particle size D50 = 0.5 to 100 μm) and Si ₃ N ₄ powder (α conversion ratio of 50% or more, average particle size D50 = 0.5 to 10 μm) and a sintering aid A certain Y ₂ O ₃ powder (average particle diameter D50 = 0.5-10 μm), Al ₂ O ₃ powder (average particle diameter D50 = 0.5-10 μm) and SiO ₂ powder (average particle diameter D50 = 0.5-10 μm) are prepared. . Thereafter, each powder is weighed in a predetermined amount, and put together with various binders such as polyvinyl alcohol (PVA) and polyethylene glycol (PEG) into a mill such as a rotary mill, a vibration mill, a bead mill, etc., and wet-mixed and pulverized. Make it.

Then, the mass ratio of the Si powder and _Si 3 _{N 4} powder is 80: 20 to 90: weighed so as to be 10. The composition of the silicon nitride-based sintered body is 5% by mass to 14% by mass in terms of Y ₂ O ₃ , 2% by mass to 5% by mass in terms of Al ₂ O ₃ , and 0.5% by mass or more in terms of SiO _2. In order to contain less than 2% by mass and the balance is made of silicon nitride, when the mass ratio of Si powder to Si ₃ N ₄ powder is 85:15, Y ₂ O ₃ powder and Al ₂ O ₃ powder Are weighed so that they are 7.3 to 20% by mass and 2.9 to 7.3% by mass, respectively. The reason why the mass% differs between when each powder is weighed and the content of the silicon nitride sintered body is that the Si powder is nitrided to form silicon nitride.

Also, the SiO ₂ powder, it is necessary to content in terms of SiO ₂ contained in the silicon nitride sintered body is weighed so that less than 2% by mass to 0.5% by mass, pre-addition of SiO ₂ powder The amount of SiO ₂ powder added may be determined by confirming the amount of SiO ₂ contained in the silicon nitride-based sintered body produced without the above. Therefore, SiO ₂ powder is not intended to be necessarily added, become an be included SiO ₂ in SiO ₂ powder silicon nitride sintered body without addition of the, Si powder and _Si 3 _{N 4} powder This is due to the oxidization of oxygen and Si powder contained inevitably. The content of the silicon nitride sintered body of Y ₂ O ₃ : Al ₂ O ₃ : SiO ₂ is 59 to 75% by mass: 20 to 28% by mass: 5 to 13% by mass. preferable.

In order to make WSi ₂ and FeSi ₂ crystals exist in the grain boundary phase, Fe ₂ O ₃ powder (average particle size D50 = 0.1 to ₃ μm) and WO ₃ powder (average particle size D50 = 0.1 to ₃ μm) are prepared. Then, with respect to 100% by mass of the starting material powder described above, 3% by mass or less of Fe ₂ O ₃ powder (excluding 0% by mass or less) and 2% by mass or less of WO ₃ powder (excluding 0% by mass or less) are weighed. Can be added to the starting material.

  Next, the slurry is spray-granulated using a spray granulation dryer (spray dryer) to obtain spherical granules, and then the spherical granules are used for a powder press molding method or an isostatic press (rubber press) molding method. And then, if necessary, cut to obtain a molded body.

Next, this molded body was fired at a nitrogen partial pressure of 50 kPa to 1.1 MPa at a temperature of 1000 to 1400 ° C. to obtain a nitride having a silicon nitride alpha conversion ratio of 90% or more. Firing is performed at a maximum temperature of 1750 to 1900 ° C. with a nitrogen partial pressure of 300 kPa. In order for the Y ₂ SiAlO ₅ N crystal and the Y ₄ SiAlO ₈ N crystal to be present in the grain boundary phase, it is important to set the cooling rate from the maximum temperature to 1200 ° C. to 10 ° C./min or less. The rate of temperature decrease from the maximum temperature to 1200 ° C. was set to 10 ° C./min or less because at a temperature decrease rate exceeding 10 ° C./min, Y ₂ SiAlO ₅ N crystals and Y ₄ SiAlO ₈ N crystals were used as the grain boundary phase. This is because it cannot exist. In addition, when the rate of temperature decrease from the maximum temperature to 1200 ° C. is less than 5 ° C./min, it is difficult for Y ₄ SiAlO ₈ N crystals to be present in the grain boundary phase, so the rate of temperature decrease from the maximum temperature to 1200 ° C. is 5 ° C. / It is preferable that the temperature is from min to 10 ° C./min.

Further, in the X-ray diffraction chart, the ratio when the peak intensity of the Y ₂ SiAlO ₅ N crystal near 2θ = 32.6 ° is X and the peak intensity of the Y ₄ SiAlO ₈ N crystal near 2θ = 29.4 ° is Y. In order to make X / Y 1.2 or less (excluding 0), it is preferable to set the cooling rate to 7 to 10 ° C./min.

Then, the silicon nitride sintered body of this embodiment can be obtained by cooling to room temperature. The silicon nitride-based sintered body of the present embodiment thus obtained has silicon nitride as a main phase, and Y ₂ SiAlO ₅ N crystals and Y ₄ SiAlO ₈ N crystals exist in the grain boundary phase. Thus, a silicon nitride sintered body with improved strength can be obtained without reducing fracture toughness.

  Thus, since the silicon nitride based sintered body of the present embodiment has excellent mechanical properties, it can be suitably used as a structural member that requires these properties. Moreover, it is applicable also to the member for molten metal etc. which contact | connects various molten metal.

  Examples of the silicon nitride sintered body of the present invention will be described below.

First, the presence / absence of Y ₂ SiAlO ₅ N crystals and Y ₄ SiAlO ₈ N crystals, and fracture toughness and strength were confirmed by varying the rate of temperature decrease from the highest temperature during firing to 1200 ° C. As starting materials, Si powder (average particle size D50 = 10 μm) and Si ₃ N ₄ powder (α conversion ratio of 50% or more, average particle size D50 = 1 μm) and Y ₂ O ₃ powder (average) as a sintering aid Particle diameter D50 = 1 μm) and Al ₂ O ₃ powder (average particle diameter D50 = 1 μm), Si powder 67 mass%, Si ₃ N ₄ powder 14 mass%, Y ₂ O ₃ powder 14 mass% 5% by mass of Al ₂ O ₃ powder was weighed.

Thereafter, the weighed powder, binder, and solvent were put in a rotary mill and mixed and pulverized for a predetermined time to obtain a slurry. Then, the slurry was sprayed and granulated using a spray granulation drying device to obtain spherical granules, and the spherical granules were filled in a predetermined mold and molded by a powder press molding method to obtain a compact. Next, the compact was fired at a nitrogen partial pressure of 120 kPa at a temperature of 1300 ° C.
After obtaining a nitride having a conversion rate of 90% or more, it was further maintained at a maximum temperature of 1750 ° C. for 5 hours at a nitrogen partial pressure of 120 kPa. The conditions up to here are the same, and the temperature-decreasing rate from the maximum temperature to 1200 ° C., one is 15 ° C./min, the other is 10 ° C./min, and then cooled to room temperature. A quality sintered body was obtained.

Then, the oxygen content in the silicon nitride sintered body was determined by an infrared absorption method using an oxygen analyzer (EMGA-650FA manufactured by Horiba, Ltd.). Further, Y and Al were quantitatively analyzed using an ICP emission spectroscopic analyzer (ICPS-8100 manufactured by Shimadzu Corporation), converted into Y ₂ O ₃ and Al ₂ O ₃ , respectively, and the oxygen required for this oxide conversion The amount was subtracted from the oxygen content in the silicon nitride sintered body, and converted to SiO ₂ from the subtracted oxygen amount. Then, by subtracting _Y 2 _O 3 in terms _{respectively,} Al ₂ O 3, a SiO ₂ content from 100 to determine the content of silicon nitride. As a result, the composition of the silicon nitride-based sintered body is 85.7% by mass of silicon nitride, 9.6% by mass in terms of Y ₂ O ₃ , 3.5% by mass in terms of Al ₂ O ₃ , and in terms of SiO ₂ 1.2
It was mass%.

Also, using an X-ray diffractometer (D8 ADVANCE manufactured by Bruker AXS), the surface of the silicon nitride sintered body is irradiated with CuKα rays, and the angle difference (2θ) between the diffraction direction and the incident direction of CuKα rays and diffraction X An X-ray diffraction chart as a result of scanning the line intensity with a detector was obtained. As a result, when the rate of temperature decrease from the maximum temperature to 1200 ° C. was 15 ° C./min, there were no peaks near 2θ = 29.4 ° and 32.6 °. On the other hand, when the rate of temperature decrease from the maximum temperature to 1200 ° C. is 10 ° C./min, a Y ₂ SiAlO ₅ N crystal peak is observed around 2θ = 32.6 ° and 2θ = 29.4 °. A crystal peak of Y ₄ SiAlO ₈ N was confirmed. Each crystal was identified from the value of 2θ using a JCPDS card.

  Next, with respect to fracture toughness and strength, the silicon nitride sintered body was subjected to polishing and grinding so as to be a test piece in accordance with JIS R 1607-2010 and JIS R 1601-2008. And fracture toughness was measured based on the indenter press-in method (IF method) prescribed | regulated by JISR1607-2010. Further, the 4-point bending strength was measured by a 4-point bending strength test based on JIS R 1601-2008.

As a result, although the value of fracture toughness was similar, the silicon nitride sintered body produced at a rate of temperature decrease from the maximum temperature of 1200 ° C to 10 ° C / min had a 4-point bending strength value of 10 to 20 %, And the presence of Y ₂ SiAlO ₅ N crystals and Y ₄ SiAlO ₈ N crystals in the grain boundary phase revealed that the strength could be improved.

  Next, a powder similar to that in Example 1 was prepared, weighed so as to have the composition shown in Table 1, and a silicon nitride sintered body was produced in the same manner as in Example 1. The rate of temperature decrease from the maximum temperature to 1200 ° C. was 8 ° C./min, and the composition was determined by the same method as in Example 1.

  Further, fracture toughness and strength were measured in the same manner as in Example 1. The results are shown in Table 1.

As shown in Table 1, 5% by mass or more and 14% by mass or less in terms of Y ₂ O ₃ , 2% by mass or more and 5% by mass or less in terms of Al ₂ O ₃ , and 0.5% by mass or more and less than 2% by mass in terms of SiO ₂ , The balance of the sample No. 2 consisting of silicon nitride. Nos. 2 to 8 had a fracture toughness value of 6 MPa · m ^1/2 or more and a four-point bending strength value of 800 MPa or more, which was superior in fracture toughness and strength to a sample having a composition outside this range. . Sample No. 5 and Sample No. 6 is compared with Sample No. 5 is superior in fracture toughness and 4-point bending strength, and the mass ratio of the content of silicon nitride sintered body of Y ₂ O ₃ : Al ₂ O ₃ : SiO ₂ is 59 to 75% by mass: 20 to It was found that 28% by mass: 5 to 13% by mass was superior in mechanical properties.

Next, sample no. Each powder was weighed so as to have the same composition as in No. 4, and up to a nitride was produced by the same production method as in Example 1. Next, with a nitrogen partial pressure of 120 kPa, the sample was held at the maximum temperature of 1750 ° C. for 5 hours, and the cooling rate from the maximum temperature to 1200 ° C. was set as shown in Table 1, and then cooled to room temperature. . 14 to 17 silicon nitride sintered bodies were obtained. Then, fracture toughness and strength were measured in the same manner as in Example 1. The results are shown in Table 2.

As a result shown in Table 2, the peak intensity of Y ₂ SiAlO ₅ N crystal near 2θ = 32.6 ° in the X-ray diffraction chart is X, and the peak intensity of Y ₄ SiAlO ₈ N crystal near 2θ = 29.4 ° is Y Sample No. with a ratio X / Y of 1.2 or less Nos. 14 to 16 are sample Nos. With a ratio X / Y of 1.31. It was found that fracture toughness and 4-point bending strength were superior to 17.

Next, sample no. Each powder was weighed so as to have the same composition as 15. Then, _Fe 2 _{O 3} powder (average particle diameter D50 = 0.1~3μm), WO ₃ powder (average particle size D50 = 0.1 to 3 m) were prepared, Si powder, _Si 3 _{N 4 powder,} Y 2 _{O 3} powder, Fe ₂ O ₃ powder is added 2 mass% or less (excluding 0 mass% or less) and WO ₃ powder is added 1 mass% or less (excluding 0 mass% or less) to 100 mass% of the total Al ₂ O ₃ powder. For the subsequent steps, sample No. A silicon nitride sintered body was obtained by the same production method as in No. 15.

Then, for the obtained silicon nitride-based sintered body, using a wavelength dispersive X-ray microanalyzer device (JXA-8600M type manufactured by JEOL Ltd.), the grain boundary phase, that is, outside the region where Si and N coexist, A region where Si and Si exist and a region where Fe and Si exist are confirmed. Next, it was confirmed to be WSi ₂ and FeSi ₂ by transmission electron microscope (TEM) analysis. And sample No. of Example 3 15 and the silicon nitride sintered body obtained this time,
High temperature (800 ° C) after grinding to a test piece size in accordance with R 1604-2008
A 4-point bending strength test was conducted.

As a result, the silicon nitride-based sintered body obtained this time was the sample No. 3 of Example 3. The value of the 4-point bending strength at a higher temperature (800 ° C.) than 15 was larger, and it was found that the strength at high temperature could be improved by the presence of WSi ₂ and FeSi ₂ crystals in the grain boundary phase.

Claims (1)

Y ₂ O ₃ 14 wt% 5 wt% or more in terms of less, _Al 2 _{O 3} contains less than 0.5 mass% or more 2% by mass 2 mass% to 5 mass% or less and in terms of SiO ₂ in terms of the balance nitride A silicon nitride-based sintered body made of silicon , wherein the silicon nitride is a main phase , Y ₂ SiAlO ₅ N crystals and Y ₄ SiAlO ₈ N crystals exist in the grain boundary phase, and in the X-ray diffraction chart When the peak intensity of the Y ₂ SiAlO ₅ N crystal near 2θ = 32.6 ° is X and the peak intensity of the Y ₄ SiAlO ₈ N crystal near 2θ = 29.4 ° is Y , the ratio X / Y is silicon nitride sintered body, characterized in der Rukoto 0.85 to 1.2.

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