KR20180121257A - Pressureless Sintered Dense Silicon Nitride Body Having High Toughness and High Strength without Rare-Earth Compounds and Silicon Nitride Structural Parts and the Manufacturing Method of the Same - Google Patents

Abstract

The present invention relates to a high-toughness high-strength silicon nitride sintered body and a silicon nitride structural member manufactured by an atmospheric pressure sintering process which does not use a rare earth element. The crystal phase of silicon nitride is not less than 88 wt%, and a rare earth element or rare earth compound is not contained as a sintering aid. 1.5-4 wt% of Mg element converted to oxide, 0.5-2.5 wt% of Al element converted to oxide, 1-5 wt% of Ti element converted to oxide, and 1-4.5 wt% of Si element converted to oxide are contained necessarily as sintering aids. The weight ratio of Al element converted to oxide to Mg element converted to oxide is in the range of 1:1 to 1:2.5, the weight ratio of Al element converted to oxide to Si element converted to oxide is in the range of 1:1 to 1:3, and the weight ratio of Al element converted to oxide to Ti element converted to oxide is in the range of 1:1 to 1:4.5.

Description

Technical Field [0001] The present invention relates to a pressureless sintered high-strength sintered silicon nitride sintered body, a silicon nitride structural member, and a method of manufacturing the same. Same}

The present invention relates to a high-toughness and high-strength silicon nitride sintered body and a silicon nitride structural member manufactured by an atmospheric pressure sintering process that does not use rare earths and a manufacturing method thereof. More particularly, the present invention relates to a silicon- Wherein the weight ratio of the Al element to the oxide is 1: 1 to 1: 2.5, the amount of the Al element is converted to the oxide, and the weight ratio of the Si element to the oxide is 1: 1 to 1: 3, In terms of oxides: the weight ratio of Ti element to oxide is in the range of 1: 1 to 1: 4.5, and the content of the crystalline silicon nitride is in the range of 88 to 95% by weight. A high strength and high strength silicon nitride sintered body, a structural member and a manufacturing method thereof.

Ceramics mainly composed of silicon nitride (Si ₃ N ₄ ) is a ceramic material having chemical bonds formed by covalent bonds, and generally has excellent properties such as high strength, abrasion resistance, thermal shock resistance and electrical insulation. Particularly, And is widely used for high temperature structural members such as automobile engine parts, abrasion resistance members for cutting tools and ball bearings, ceramic balls for Al molten metal, and substrates for power devices.

BACKGROUND ART Conventionally, silicon nitride ceramics has a rare earth oxide (mostly Y ₂ O ₃ (For example, Al ₂ O _3, AlN, or the like) is added to an oxide or a nitride such as Al ₂ O ₃ or the like as a sintering aid. However, rare earths contain only a very small amount of earth crust, which has a limited supply and a high price compared to other oxide additives.

In the field of high-temperature structural materials such as cutting tools, steel production rollers, aluminum melt materials, automobile engine parts, and gas turbines, which are applications of silicon nitride ceramics, the necessity of materials having high toughness, high strength, abrasion resistance and heat resistance is increasing In order to produce a high strength and high strength material, sintering method is used for sintering / hot isostatic pressing (SIN) after gas pressure sintering or high pressure sintering / HIP) are mainly used.

Gas pressure sintering is suitable for producing high-toughness silicon nitride material by promoting grain growth of silicon nitride by using nitrogen gas pressure to prevent decomposition of silicon nitride at a high sintering temperature. However, compared to a normal pressure sintering process, Equipment is required, and the sintering temperature is very high, so that the energy consumption is large.

The concept of a high-temperature hydrostatic sintering process after pressureless sintering is to achieve densification of silicon nitride through an atmospheric pressure sintering process and to promote densification and particle growth through a high-temperature hydrostatic sintering process as a two-step process, Process. However, the process time becomes too long due to the two-step sintering process of high-temperature hydrostatic sintering after normal pressure sintering, and a high-temperature hydrostatic sintering furnace, which is an expensive high-temperature sintering apparatus, must be constructed. There is a disadvantage that it is expensive.

Conventionally, atmospheric pressure sintering process of silicon nitride has been studied by a number of researchers, but silicon nitride is thermodynamically unstable at a temperature exceeding 1800 ° C. under atmospheric pressure (1 atm) nitrogen atmosphere, and decomposition reaction of silicon nitride progresses (Si ₃ N ₄ → 3Si + 2N ₂ ↑) The sintering temperature should be kept at 1800 ° C or lower, and Y ₂ O ₃ -Al ₂ O ₃ or Y ₂ O ₃ -AlN or RE ₂ O ₃ -Al ₂ O ₃ ( RE = Yb, Lu, Sm, Gd). In this case, the viscosity of the liquid phase at the sintering temperature is too high. If the sintering process is carried out at a temperature of 1800 ° C. or lower, There is a disadvantage in that it is difficult to produce a high-tough silicon nitride material because of insufficient growth.

All currently commercialized silicon nitride materials use at least one rare earth oxide (mostly Y ₂ O ₃ ) as a sintering aid and rare earths contain only a very small amount in the earth's crust, so their amount is limited, The price of rare earths is continuously rising due to the increase in demand.

Until now, the technology to manufacture high-toughness and high-strength silicon nitride materials by the pressureless sintering process without using rare earth oxides has been an industrially important technology in the silicon nitride material industry which has not been reported.

Korean Registered Patent No. 10-0325325 (Registered Date: Feb. 2002) Korean Registered Patent No. 10-0731392 (Registered on June 15, 2007) Korean Registered Patent No. 10-0889387 (Registered on Mar. 3, 2009) Korean Registered Patent No. 10-1130716 (Registered on March 20, 2012)

(2) a sintering temperature is as low as 1800 占 폚 or lower; and (3) the sintering temperature is lower than 1800 占 폚. 3) the use of rare earth oxides, which are expensive and are likely to be strategically weaponized, and (4) high-toughness and high-strength silicon nitride materials.

In order to achieve the above-mentioned object, the present invention provides a method of manufacturing a semiconductor device, comprising the steps of: a) a ratio of an amount of an Al element converted to an oxide: an amount of a Mg element converted to an oxide in a weight ratio of 1: 1 to 1: 2.5, : A weight ratio of the Si element to the oxide in terms of oxide is in the range of 1: 1 to 1: 3, and the weight ratio of the Al element to the oxide in terms of Ti is 1: 1 to 1: 4.5 , And the content of the crystalline silicon nitride is in the range of 88 wt% to 95 wt%. The high-toughness and high-strength silicon nitride sintered body produced by the pressureless sintering process is also provided.

The Al, Mg, Ti and Si are added as a sintering auxiliary agent, 0.5 to 2.5% by weight of Al element converted to oxide, 1.5 to 4% by weight of Mg element converted to oxide, By weight and 1% by weight to 5% by weight in terms of oxides of Si, respectively.

Preferably, the sintered body has a flexural strength of at least 900 MPa, a fracture toughness of at least 9 MPa.m ^1/2 , a hardness of at least 15 GPa, and a porosity ratio of more than 0% to 2.0%.

The sintered body preferably has a flexural strength of at least 900 MPa, a fracture toughness of at least 9 MPa.m ^1/2 , a hardness of at least 15 GPa, and a thermal conductivity of at least 70 W / mK.

It is preferable that the average grain length of the crystalline silicon nitride is at least 1 占 퐉 and the average longest aspect ratio of the upper 10% in the long grain size distribution of the crystalline silicon nitride grains is at least 5.

It is preferably sintered in the range of 1720 DEG C to 1800 DEG C and 1 hour to 24 hours under the nitrogen pressure of 1 atm (atmospheric pressure).

Wherein the amount of oxide of the Al element is 0.5 wt% to 2 wt%, the amount of Mg element is 1.5 wt% to 3 wt%, the conversion amount of Ti element is 1 wt% to 4 wt% % To 3.5% by weight.

More specifically, the present invention provides a silicon nitride structural member containing a high-toughness and high-strength silicon nitride sintered body produced by an atmospheric pressure sintering process including the above silicon nitride sintered body.

Wherein the structural member is at least one selected from the group consisting of a ceramics member for molten aluminum, a ceramic roller for manufacturing steel, a ceramic ball, a ceramics part for mounting on a vehicle, a brazing jig, an extrusion jig, a soldering tank, a cutting tool, a jig for a semiconductor manufacturing apparatus, And the like.

The present invention also provides a method for producing a semiconductor device, comprising the steps of: mixing an Al element in an amount of 1: 1 to 1: 2.5 in terms of an amount of a Mg element converted into an oxide; Wherein the weight ratio of Al to Ti is in the range of 1: 1 to 1: 3, the amount of Al element in terms of oxide is in the range of 1: 1 to 1: 4.5 in terms of the amount of Ti element in terms of oxide, By weight of the starting material is in the range of from 88% by weight to 95% by weight; Molding the mixed starting material to produce a shaped body; And sintering the formed body at normal pressure. The present invention also provides a method of manufacturing a high-toughness high-strength silicon nitride sintered body manufactured by the pressureless sintering process.

The sintering is performed in a nitrogen atmosphere, and it is preferable that the sintering is performed in a range of 1720 ° C to 1800 ° C and 1 hour to 24 hours under a nitrogen pressure of 1 atm (atmospheric pressure).

According to the present invention, by using a sintering aid which is not a rare earth element, a high-toughness and high-strength silicon nitride sintered body and a silicon nitride structural member which can not be reached by a conventional technique without addition of a rare earth oxide can be manufactured by a pressure sintering process.

The high-toughness and high-strength silicon nitride materials and silicon nitride structural members produced by the pressure-sintering process according to the present invention are excellent in (1) high-priced rare earth oxides or their compounds are not used, (2) (4) atmospheric pressure sintering process; (5) relatively low-cost Al ₂ O ₃ , MgO, SiO ₂ and TiO ₂ are used as essential sintering additives (6) a bending strength of 900 MPa or more, a fracture toughness of 9 MPa.m ^1/2 or more, a hardness of 15 GPa or more, a thermal conductivity of 70 W / mK or more, and a porosity of 2% or less A high-strength and high-strength silicon nitride material and a silicon nitride structure material can be produced.

FIG. 1 is a microstructure photograph of a high-toughness and high-strength silicon nitride material produced by an atmospheric pressure sintering process according to an embodiment of the present invention. The average length of the silicon nitride particles is 1 μm or more, Is an electron microscope image of a silicon nitride material having an average aspect ratio of 5 or more.
FIG. 2 is a microstructure photograph showing the progress of cracking in a high-toughness and high-strength silicon nitride material produced by an atmospheric pressure sintering process according to an embodiment of the present invention, wherein Si ₃ N ₄ particles are crack bridging and crack diffraction and a fracture toughness is enhanced by a crack deflection mechanism.
FIG. 3 is a microstructure photograph of a high-toughness and high-strength silicon nitride material produced by an atmospheric pressure sintering process according to an embodiment of the present invention. The average length of the silicon nitride particles is 1 μm or more, % Of average length ratio of 5 or more.

In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear.

Embodiments in accordance with the concepts of the present invention are capable of various modifications and may take various forms, so that specific embodiments are exemplified and will be described in detail in this specification or application. It should be understood, however, that the embodiments according to the concepts of the present invention are not intended to be limited to any particular mode of disclosure, but rather all variations, equivalents, and alternatives falling within the spirit and scope of the present invention.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The singular expressions include plural expressions unless the context clearly dictates otherwise. In this specification, the terms " comprises ", or " having ", and the like, are intended to specify the presence of stated features, integers, steps, operations, elements, , Steps, operations, components, parts, or combinations thereof, as a matter of principle.

Hereinafter, the present invention will be described in detail.

During the sintering process of silicon nitride, the grain growth of silicon nitride greatly depends on the viscosity of the liquid phase. When the viscosity of the liquid phase is low, the mass transfer through the liquid phase is actively promoted and the particle growth is promoted. However, when the viscosity of the liquid phase is high, the mass transfer through the liquid phase is slowed and the particle growth is not sufficient. If grain growth of silicon nitride is not sufficient, it is impossible to obtain a tough material having a fracture toughness of 9 MPa.m < ^{1/2 >} or more. The most widely used method for lowering the viscosity of the liquid phase is to increase the sintering temperature. However, since the decomposition of silicon nitride occurs at a temperature higher than 1800 ° C in a nitrogen atmosphere at 1 atm, nitrogen gas pressure sintering or high-temperature hydrostatic sintering is widely used in the production of a high-tough silicon nitride material. However, when four kinds of oxides including Mg, Al, Ti and Si elements are simultaneously added as sintering aids, the inventors have found that the melting point drop due to the fourth component is sufficiently higher than the melting point of the liquid phase obtained in the conventional two- Characterized in that the average grain size of the crystalline silicon nitride is at least 1 占 퐉 and the average aspect ratio of the upper 10% in the aspect ratio distribution of the crystalline silicon nitride grains is at least 5 even at a sintering temperature of not higher than 1800 占 폚 The present invention has been accomplished on the basis of these findings.

If any one of the four oxides including Mg, Al, Ti and Si elements is not added as a sintering aid in the present invention, the viscosity of the liquid phase becomes high and the particle growth is insufficient at a temperature of 1800 占 폚 or lower, m < ^{2/2 &} gt ;, and in some cases, the sintering is not sufficient and the residual porosity is increased to more than 2%. Therefore, if all four oxides including Mg, Al, Ti and Si elements are essentially added as sintering aids, the flexural strength proposed in the present invention is 900 MPa or more and the fracture toughness is 9 MPa.m ^1/2 or more , A high-toughness and high-strength silicon nitride material and a silicon nitride structural member having a hardness of 15 GPa or more, a thermal conductivity of 70 W / mK or more, and a porosity of 2% or less.

(1) adding oxides containing elements of Mg, Al, Ti and Si as sintering aids essential for silicon nitride powder and uniformly mixing them, (2) mixing the mixture , And (3) sintering the molded body.

In the step of mixing the silicon nitride and the additive, the content of the crystalline silicon nitride is preferably limited to 88 wt% or more and 95 wt% or less, and the sintering auxiliary essentially added is preferably 0.5 wt% to 2.5 wt% 1 wt% to 5 wt% in terms of oxide of Ti element, 1 wt% to 4.5 wt% in terms of oxide of Si element, 1.5 wt% to 4 wt% of Mg element converted to oxide, Rare earth element or rare earth compound as a sintering auxiliary agent.

Further, it is preferable that the weight ratio of the amount of Al element converted to oxide to the amount of Mg element converted to oxide is in the range of 1: 1 to 1: 2.5, and the amount of Al element converted into oxide: amount of Si element converted into oxide Is in the range of 1: 1 to 1: 3, and the weight ratio of the Al element converted to the oxide to the Ti element converted to the oxide is in the range of 1: 1 to 1: 4.5.

If the content of silicon nitride is less than 88% by weight in the above composition, the fraction of the second phase and residual liquid phase present at junctions such as triple points and quadrature centers in the sintered body becomes too high and the bending strength is lowered to less than 900 MPa And when the content of silicon nitride is more than 95% by weight, the amount of the sintering assistant is too small so that the sintering is not sufficient and the residual porosity exceeds 2% and the bending strength is lowered to less than 900 MPa. Therefore, the content of silicon nitride on the crystal phase has its critical meaning at 88 wt% or more and 95 wt% or less.

The composition ranges and the relative weight ratios of the sintering aids are determined through a number of experiments. When additives having a composition out of the above range are used, the sintered density becomes low and the porosity exceeds 2%. When the bending strength is less than 900 MPa or the fracture toughness is 9 MPa.m < ^{/ RTI} > ^1/2 . Therefore, the composition range of the sintering auxiliary agent is critical to the upper and lower limits of the amounts specified above.

Wherein the amount of oxide of the Al element is 0.5 wt% to 2 wt%, the amount of Mg element is 1.5 wt% to 3 wt%, the amount of Ti element is 1 wt% to 4 wt% It is more preferable that the oxide converted amount of Si element is 1 wt% to 3.5 wt%. In this case, the mechanical properties can be further improved.

The mixing method of the silicon nitride and the additive group is not particularly limited, and any mixing method capable of producing a uniform mixture can be used. For example, a normal ball mill, a planetary mill, a stirrer, an attritor, or the like can be used.

The method for producing the molded body can be used as long as it is a usual method for forming ceramics. For example, it can be applied to a wide variety of materials, such as uniaxial pressing, cold isostatic pressing, hydrostatic pressing after uniaxial pressing, slip casting, tape casting, extrusion, gel casting, Injection molding and the like can be used.

The sintering of the molded body is preferably carried out in a range of 1 hour to 24 hours in a temperature range of 1720 ° C to 1800 ° C in a nitrogen atmosphere of 1 atm without applying pressure using a graphite furnace. If the sintering temperature is lower than 1720 ° C, the sintering does not proceed sufficiently and the residual pores are present in excess of 2%. If the sintering temperature is higher than 1800 ° C, the silicon nitride and silicon nitride are decomposed into silicon and nitrogen, And the sintering temperature is preferably limited to a range of 1720 to 1800 占 폚.

When the sintering time is less than 1 hour at the maximum temperature, the sintering does not proceed sufficiently and the residual porosity exceeds 2%. When the sintering is performed for more than 24 hours, the residual porosity becomes 2% . ≪ / RTI > Therefore, the sintering time is preferably limited to a range of 1 hour to 24 hours.

Hereinafter, the present invention will be described in more detail with reference to examples.

The embodiments presented are only a concrete example of the present invention and are not intended to limit the scope of the present invention.

< Example  1>

3.2 wt% SiO ₂ , 3.0 wt% MgO, 2.0 wt% TiO ₂ , and 1.8 wt% Al ₂ O ₃ were added to 90 wt% of α-Si ₃ N ₄ powder as a sintering auxiliary agent, ethanol was used as a solvent, The balls were wet-mixed using a polypropylene bottle for 24 hours.

Thereafter, the mixed slurry was dried, granulated using a 60 mesh sieve, pressurized at a pressure of 25 MPa, and uniaxially pressed to obtain a primary molded body of 45 x 35 x 10 mm ³ size , Followed by cold isostatic pressing at a pressure of 276 MPa to prepare a final molded article.

The compact was placed in a graphite crucible and sintered at atmospheric pressure in a graphite furnace at 1780 占 폚 for 3 hours using a nitrogen atmosphere.

FIG. 1 is a photograph of a microstructure of silicon nitride sintered at atmospheric pressure according to an embodiment of the present invention. The average diameter of the silicon nitride particles is 1 占 퐉 or more and the average of the upper 10% It was found that the grown silicon nitride particles were well grown, and the porosity of the sintered body was as low as 0.3%.

The sintered body was cut and polished into a bar-shaped sample of 2 mm x 1.5 mm x 25 mm in size conforming to ASTM C 1161-13 standard. The tensile surfaces of the bars were polished with 1 micron diamond paste and rounded corners to avoid large edge defects and stress scaling caused by sectioning. The bending strength test was carried out at a crosshead speed of 0.2 mm / min using a four-point bending strength measurement method with internal and external spans of 10 mm and 20 mm, respectively. The measured 4-point bending strength was 915 MPa .

The fracture toughness of the sintered body was measured using the Korea Industrial Standard (KS L 1600, the fracture toughness test method of high performance ceramics), the measured fracture toughness was excellent as 9.0 MPa.m ^1/2. This is because fracture toughness is effectively enhanced by a fracture toughness improving mechanism such as crack bridging and crack diffraction as shown in Fig.

The hardness of the specimen was 15.5 GPa, and the thermal conductivity measured by laser flash method was 71 W / mK, which was excellent.

< Example  2>

3.4% by weight SiO ₂ , 2.8% by weight MgO, 3.2% by weight TiO ₂ and 1.6% by weight Al ₂ O ₃ were added to 89% by weight of α-Si ₃ N ₄ powder as a sintering auxiliary agent and ethanol was used as a solvent. The balls were wet-mixed using a polypropylene bottle for 24 hours.

The mixed slurry was dried, granulated using a 60 mesh sieve, subjected to a pressure of 25 MPa to prepare a primary compact having a size of 40 × 40 × 10 mm ³ by uniaxial pressing, Followed by cold isostatic pressing at a pressure of 276 MPa to prepare a final molded article.

The compact was placed in a graphite crucible and sintered at atmospheric pressure in a graphite furnace at 1740 DEG C for 15 hours using a nitrogen atmosphere.

FIG. 3 is a photograph of the microstructure of the pressureless sintered silicon nitride observed by a scanning electron microscope, showing that silicon nitride particles having an average diameter of 1 탆 or more and having an average length of 6.3% And the porosity of the sintered body was as low as 0.7%.

The sintered body was cut and polished into a bar-shaped sample of 2 mm x 1.5 mm x 25 mm in size conforming to ASTM C 1161-13 standard. The tensile surface of the rod was polished with a 1 micron diamond paste and rounded corners to avoid large corner defects and stress scaling caused by sectioning. The bending strength test was carried out at a crosshead speed of 0.2 mm / min using a four-point bending strength measurement method with internal and external spans of 10 mm and 20 mm, respectively. The measured four-point bending strength was excellent at 924 MPa .

The fracture toughness of the sintered body was measured using the Korea Industrial Standard (KS L 1600, the fracture toughness test method of high performance ceramics), the measured fracture toughness was excellent as 9.2 MPa.m ^1/2. This is because the fracture toughness improves effectively by the fracture toughness improving mechanism such as crack bridging and crack diffraction.

The hardness of the specimen was 15.3 GPa, and the thermal conductivity measured by the laser flash method was excellent at 76 W / mK.

< Example  3>

the α-Si ₃ N ₄ powder 90.2% by weight of β-Si ₃ N ₄ powder was added 1% by weight seed particles, 3.0% by weight as a sintering aid SiO _2, 2.6 wt% MgO, 1.9% by weight TiO _2, 1.3 wt. % Al ₂ O ₃ was added, and ethanol was used as a solvent, and silicon nitride ball and Teflon jar were wet mixed using a planetary mill for 5 hours.

The mixed slurry was dried, granulated using a 60 mesh sieve, subjected to a pressure of 25 MPa to prepare a primary compact having a size of 40 × 40 × 10 mm ³ by uniaxial pressing, Followed by cold isostatic pressing at a pressure of 276 MPa to prepare a final molded article. The compact was placed in a graphite crucible and sintered at atmospheric pressure in a graphite furnace at 1790 占 폚 for 4 hours using a nitrogen atmosphere.

The average diameter of silicon nitride particles was more than 1 ㎛ and the average of the upper 10% of the silicon nitride particles was 5.8. The silicon nitride particles were well grown and the porosity of the sintered body was very low at 0.3% in the manufactured pressureless sintered silicon nitride material.

The sintered body was cut and polished into a bar-shaped sample of 2 mm x 1.5 mm x 25 mm in size conforming to ASTM C 1161-13 standard. The tensile surface of the rod was polished with a 1 micron diamond paste and rounded corners to avoid large corner defects and stress scaling caused by sectioning. The bending strength test was carried out at a crosshead speed of 0.2 mm / min using a four-point bending strength measurement method with internal and external spans of 10 mm and 20 mm, respectively. The measured four-point bending strength was excellent at 954 MPa .

The fracture toughness of the sintered body was measured using KS L 1600 (Fracture Toughness Test Method for High Performance Ceramic Products) and the measured fracture toughness was excellent at 9.8 MPa.m ^1/2 . This is because the fracture toughness improves effectively by the fracture toughness improving mechanism such as crack bridging and crack diffraction.

The hardness of the specimen was 15.5 GPa, and the thermal conductivity measured by the laser flash method was 81 W / mK, which was excellent.

< Example  4>

2.4 wt% SiO ₂ , 2.0 wt% MgO, 1.3 wt% TiO ₂ and 1.3 wt% Al ₂ O ₃ were added to 93 wt% of α-Si ₃ N ₄ powder as a sintering auxiliary agent, and ethanol was used as a solvent, The balls were wet-blended in a planetary mill for 6 hours using a Teflon jar.

The mixed slurry was dried, granulated using a 60 mesh sieve, subjected to a pressure of 25 MPa to prepare a primary compact having a size of 40 × 40 × 10 mm ³ by uniaxial pressing, Followed by cold isostatic pressing at a pressure of 290 MPa to prepare a final molded article. The compact was placed in a graphite crucible and sintered at atmospheric pressure in a graphite furnace at 1760 ° C for 8 hours using a nitrogen atmosphere.

The average diameter of silicon nitride particles was more than 1 ㎛ and the average length of the upper 10% of the silicon nitride particles was 5.7. The silicon nitride particles were well grown and the porosity of the sintered body was very low at 0.6% in the manufactured pressureless sintered silicon nitride material.

The sintered body was cut and polished into a bar-shaped sample of 2 mm x 1.5 mm x 25 mm in size conforming to ASTM C 1161-13 standard. The tensile surface of the rod was polished with a 1 micron diamond paste and rounded corners to avoid large corner defects and stress scaling caused by sectioning. The bending strength test was carried out at a crosshead speed of 0.2 mm / min using a four-point bending strength measurement method with internal and external spans of 10 mm and 20 mm, respectively. The measured 4-point bending strength was excellent at 937 MPa .

The fracture toughness of the sintered body was measured by using KS L 1600 (Fracture Toughness Test Method of High Performance Ceramic Product). The fracture toughness measured was excellent at 9.0 MPa.m ^1/2 . This is because the fracture toughness improves effectively by the fracture toughness improving mechanism such as crack bridging and crack diffraction.

The hardness of the specimen was 15.8 GPa and the thermal conductivity measured by the laser flash method was excellent at 72 W / mK.

< Example  5>

α-Si ₃ N ₄ powder 94.4% by weight of the β-Si ₃ N to ₄ was added to the powder of 0.5 weight% as a seed particle, and a sintering aid of 1.8 wt% SiO _2, 1.5 wt% MgO, 1.0% by weight TiO _2, 0.8 wt. % Al ₂ O ₃ was added, and ethanol was used as a solvent and wet-mixed in a planetary mill using a silicon nitride ball and a Teflon jar for 6 hours.

The mixed slurry was dried, granulated using a 60 mesh sieve, subjected to a pressure of 25 MPa to prepare a primary compact having a size of 40 × 40 × 10 mm ³ by uniaxial pressing, Followed by cold isostatic pressing at a pressure of 390 MPa to prepare a final shaped article. The compact was placed in a graphite crucible and sintered at atmospheric pressure in a graphite furnace at 1795 DEG C for 3 hours using a nitrogen atmosphere.

The average diameter of silicon nitride particles was more than 1 ㎛ and the average of the upper 10% of the silicon nitride particles was 6.1. The silicon nitride particles were well grown and the porosity of the sintered body was very low at 0.3% in the manufactured pressureless sintered silicon nitride material.

The sintered body was cut and polished into a bar-shaped sample of 2 mm x 1.5 mm x 25 mm in size conforming to ASTM C 1161-13 standard. The tensile surface of the rod was polished with a 1 micron diamond paste and rounded corners to avoid large corner defects and stress scaling caused by sectioning. The bending strength test was carried out at a crosshead speed of 0.2 mm / min using a four-point bending strength measurement method with internal and external spans of 10 mm and 20 mm, respectively. The measured 4-point bending strength was 917 MPa, Respectively.

The fracture toughness of the sintered body was measured using the Korea Industrial Standard (KS L 1600, the fracture toughness test method of high performance ceramics), the measured fracture toughness was excellent as 10.1 MPa.m ^1/2. This is because the fracture toughness improves effectively by the fracture toughness improving mechanism such as crack bridging and crack diffraction.

The hardness of the specimen was 15.3 GPa and the thermal conductivity measured by the laser flash method was 80 W / mK, which was excellent.

In the case of Examples 1 to 5, (1) no expensive rare earth oxides or compounds thereof were added at all, (2) a sintering method of high pressure after pressure sintering or normal pressure sintering, which is generally used for producing a high- (3) As shown in [Fig. 1] and [Fig. 3], the average length of the silicon nitride particles is not less than 1 탆, and the average of the top 10% of the silicon nitride particles is 5 Silicon nitride particles and silicon nitride structural members having a fracture toughness of 9 MPa.m &lt; ^1/2 &gt; or more, a flexural strength of 900 MPa or more, and a thermal conductivity of 70 W / mK or more.

This is a new four-component sintering system composed of SiO ₂ -MgO-TiO ₂ -Al ₂ O ₃ which promotes grain growth of silicon nitride having a long length ratio by forming a liquid phase having a low viscosity at a relatively low temperature of 1800 ° C or less, It is due to the preparation composition.

In general, when sintering silicon nitride, a two-component sintering auxiliary composed of one rare-earth oxide and one oxide is added (for example, Y ₂ O ₃ -Al ₂ O ₃ or Y ₂ O ₃ -AlN) silicon nitride material is produced. In the general two-component ceramic phase diagram, the addition of the second component to the first component results in a lowering of the melting point having a lower melting point between the two components, and the lowering of the melting point causes the lowering of the melting point to occur rapidly by adding the third substance and the fourth substance There is a possibility to happen. _{SiO 2 -MgO-TiO 2 -Al 2} O 3 The four-component sintering aids satisfying the technical idea of the present invention have a higher melting point lower than that of the two-component sintering aids, The viscosity of the liquid phase is lowered due to the low melting point of the liquid phase at a relatively low temperature and the grain growth is promoted thereby to obtain a microstructure including a large number of long silicon nitride particles. From this, it is possible to obtain a high- The material could be manufactured. As described in the present invention, when the four-component sintering aid is added, the decrease of the melting point is observed indirectly by the particle growth of promoted silicon nitride.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. Therefore, the embodiments disclosed in the present invention are intended to illustrate rather than limit the scope of the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. The scope of protection of the present invention should be construed according to the claims, and all technical ideas within the scope of the claims should be construed as being included in the scope of the present invention.

Claims (11)

The weight ratio of the Al element to the oxide: Mg element to oxide amount is in the range of 1: 1 to 1: 2.5,
The weight ratio of the Al element to the oxide: Si element to oxide weight ratio is in the range of 1: 1 to 1: 3,
Wherein the weight ratio of the Al element to the oxide: Ti element to oxide is in the range of 1: 1 to 1: 4.5,
Characterized in that the content of crystalline silicon nitride is in the range of 88 wt% to 95 wt%, and the sintered body of high-toughness and high-strength silicon nitride produced by the pressureless sintering process. The method according to claim 1,
The Al, Mg, Ti, and Si are added as sintering aids,
0.5% to 2.5% by weight of Al element converted to oxide,
1.5% to 4% by weight of Mg element converted to oxide,
The Ti element is converted to oxide in an amount of 1 wt% to 5 wt%
And a silicon element in an amount of 1 wt% to 4.5 wt% in terms of an oxide. The method according to claim 1,
Characterized in that the bending strength is at least 900 MPa, the fracture toughness is at least 9 MPa.m ^1/2 , the hardness is at least 15 GPa, and the porosity is in excess of 0% to 2.0% High strength silicon nitride sintered body. The method according to claim 1,
Characterized in that the bending strength is at least 900 MPa, the fracture toughness is at least 9 MPa.m ^1/2 , the hardness is at least 15 GPa, and the thermal conductivity is at least 70 W / mK. High strength silicon nitride sintered body. The method according to claim 1,
Characterized in that the average grain length of the crystalline silicon nitride is at least 1 占 퐉 and the average aspect ratio of the upper 10% in the aspect ratio distribution of the crystalline silicon nitride grains is at least 5. The sintered body of the high toughness and high strength silicon nitride produced by the pressureless sintering process. The method according to claim 1,
Wherein the sintered body is sintered at a nitrogen pressure of 1 atm (atmospheric pressure) in a range of 1720 ° C to 1800 ° C and 1 hour to 24 hours. The method according to claim 1,
Wherein the amount of oxide of the Al element is 0.5 wt% to 2 wt%, the amount of Mg element is 1.5 wt% to 3 wt%, the conversion amount of Ti element is 1 wt% to 4 wt% % To 3.5% by weight of the sintered body of high-toughness and high-strength silicon nitride produced by the pressureless sintering process. A silicon nitride structural member containing a high-toughness high-strength silicon nitride sintered body manufactured by an atmospheric pressure sintering process comprising the silicon nitride sintered body according to any one of claims 1 to 7. 9. The method of claim 8,
A ceramic member for aluminum, a ceramic roller for manufacturing steel, a ceramic ball, a ceramics part for mounting on a vehicle, a brazing jig, an extrusion jig, a soldering tank, a cutting tool, a jig for a semiconductor manufacturing apparatus, Wherein the sintered body of silicon nitride having high toughness and high strength is produced by a normal pressure sintering process. Wherein the weight ratio of the Al element to the oxide is in the range of 1: 1 to 1: 2.5 in terms of the amount of the Mg element converted to the oxide and the Al element is converted into the oxide: Is in the range of 1: 1 to 1: 3, the weight ratio of the Al element to the oxide: Ti element in terms of oxide is in the range of 1: 1 to 1: 4.5, the crystalline silicon nitride content is 88 weight To 95% by weight of the starting material;
Molding the mixed starting material to produce a shaped body; And
Sintering the formed body at normal pressure;
Wherein the silicon nitride sintered body is manufactured by a normal pressure sintering process. 11. The method of claim 10,
Wherein the sintering is performed in a nitrogen atmosphere and is sintered at a pressure of 1 atm (atmospheric pressure) in a range of 1720 ° C to 1800 ° C and in a range of 1 hour to 24 hours. (Method for manufacturing high strength silicon nitride sintered body).

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