JPH11100277A - Silicon nitride sintered compact and coated silicon nitride sintered compact - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain excellent thermal conductivity by forming from a matrix consisting essentially of silicon nitride and the a grain boundary phase containing a crystalline conjugated oxide containing a rare earth element and a group IVa element as the remainder. SOLUTION: This sintered compact is composed of 90-99.5% matrix consisting essentially of silicon nitride and the grain boundary phase containing the crystalline conjugated oxide, which contains the rare earth element expressed by a formula, R2 M2-x O7-2x and the group IVa element in periodic table, and a vitreous material containing Mg element at need. A coated silicon nitride sintered compact is obtained by forming a coating film of one or more kinds selected from a group IVa, Va and VIa metal, Al, Si and the carbide, nitride, oxide and having 0.5-20 μm film thickness on the whole surface or a part of the surface of the sintered compact. As the crystalline conjugated oxide, Y2 Hf2-x O7-2x , Y2 Zr2-x O7-2x , Sc2 Hf2-x O7-2x , (yDy)2 Hf2-x O7-2x and the like are mentioned. In the formula, M represents a group IVa element in periodic table, R represents a rare earth element such as Y, Sc and (x) satisfies -1<x<1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicon nitride-based sintered body comprising a matrix containing silicon nitride as a main component and a grain boundary phase, and a coated nitride formed by coating a film on the surface of the sintered body. More specifically, silicon-based sintered bodies include cutting tools such as turning tools, milling tools, drills and end mills, wear-resistant tools such as slitters, pushes, guides, nozzles, and balls, engines, The present invention relates to a silicon nitride-based sintered body that is most suitable as a structural material for various machine parts and jigs represented by a rotor and a coated silicon nitride-based sintered body obtained by coating a film on the surface of the sintered body. .

[0002]

2. Description of the Related Art In general, a ceramic sintered body containing silicon nitride or sialon as a main component is excellent in bending strength, fracture toughness and thermal shock resistance, so that it can be put to practical use as a cutting tool, a wear-resistant tool or various mechanical parts. Is underway. Among this type of sintered body, a sialon-based sintered body has a lower thermal conductivity than a silicon nitride-based sintered body, and thus tends to have poor thermal shock resistance. Representative examples of the sialon-based sintered body, which focus on high-temperature characteristics such as thermal shock resistance, are disclosed in JP-A-6-298567 and JP-A-8-98857.
There is 337777 gazette. On the other hand, a silicon nitride-based sintered body is compared with a sialon-based sintered body when used as a cutting tool for cutting a work material of an iron-based material because silicon nitride itself has an excellent affinity for an iron-based material. May have a short life. Numerous improvements have been made to this silicon nitride-based sintered body. Among them, as a representative example of the composition of the grain boundary phase, Japanese Patent Publication No. 52-3650 and Japanese Unexamined Patent Publication No. Sho 62
JP-A-153169, JP-A-9-20563 and JP-A-9-142935.

[0003]

As a prior art, Japanese Patent Application Laid-Open No. 6-298567 discloses a matrix containing β-sialon as a main component and a composite oxide containing Hf and / or Zr as a main component. A sialon-based sintered body composed of a grain boundary phase and Japanese Patent Application Laid-Open No. 8-337777, which is an invention of the present inventors, discloses a matrix containing sialon as a main component, one or more rare earth elements and one or more group 4a elements in the periodic table. It discloses a sialon-based sintered body composed of a composite oxide containing one kind of element from groups 2a, 6a, 7a and 8a of the table and a grain boundary phase as a main component. The sintered bodies disclosed in these two publications tend to have a low thermal conductivity due to having sialon as a main component, especially when they are used as cutting tools in heavy load and high temperature regions. There is a problem that has not been reached.

[0004] Among other prior art, Japanese Patent Publication No. 52-3
No. 650 discloses that silicon nitride has a content of 60 to 90 mol% and the balance is magnesium oxide, zinc oxide and nickel oxide.
And a hypereutectic aluminum-silicon alloy comprising at least one of aluminum oxide, chromium oxide, yttrium oxide and titanium oxide, wherein these oxides constitute a spinel oxide and form a solid solution in silicon nitride. A cutting tool material is disclosed. In the sintered body disclosed in this publication, the lattice vibration of silicon nitride is disturbed by the solid solution of spinel oxide in silicon nitride, and phonons are scattered to lower the thermal conductivity. There is a problem that it is difficult to increase the.

Japanese Patent Application Laid-Open No. Sho 62-153169 discloses an oxide of a rare earth element and at least one oxide selected from the group consisting of oxides, carbides and silicides of Hf, Ta or Nb.
There is disclosed a silicon nitride-based sintered body obtained by firing a ceramic mixture composed of a seed, aluminum nitride, and the remainder silicon nitride. Further, JP-A-9-20563 discloses that Mg, Al, carbon and oxygen, Ti, Hf,
A silicon nitride-based sintered body composed of a grain boundary phase composed of at least one type of W and a balance of silicon nitride is disclosed. Japanese Patent Application Laid-Open No. 9-142935 discloses a rare earth element,
It discloses a silicon nitride-based sintered body composed of an amorphous grain boundary phase containing Al, Mg, Si, oxygen and nitrogen, and β-silicon nitride as a balance. Of these three publications,
The sintered body disclosed in the above two publications does not satisfy the strength and toughness of the sintered body even if the thermal conductivity can be increased, and the cutting tool in a heavy load and a high temperature region. When used as, there is a problem that the cutting life is short due to chipping or chipping. The sintered body disclosed in the remaining one publication has a problem that the abrasion resistance and the impact resistance in a high-temperature region are significantly deteriorated because of the amorphous grain boundary phase.

The present invention has solved the above-mentioned problems. Specifically, the present invention is excellent in thermal conductivity and has improved thermal shock resistance, strength at high temperatures, toughness, fracture resistance and wear resistance. Silicon nitride-based sintered body that has been improved to achieve high durability, especially when used as a cutting tool in high-temperature cutting, high-speed cutting of black-skinned workpieces and wet cutting, and has a long life. The purpose is to provide.

[0007]

SUMMARY OF THE INVENTION The present inventors have developed a long-lasting cutting tool material in view of the relationship between silicon nitride and the grain boundary phase which also serves as a sintering aid and bonding of the silicon nitride. During the study over the period, in order to suppress the boundary damage of the cutting tool that occurs when cutting a black-skinned work material, first, it is necessary to reduce the thermal stress generated at the boundary portion,
In order to reduce the thermal stress, it is preferable to increase the thermal conductivity of the cutting tool. Second, it is important that the cutting tool has high hardness, strength and toughness from room temperature to high temperature. Obtained knowledge. To complete this first finding, high stability at high temperatures and high thermal conductivity,
In order to satisfy these, a substance having excellent crystallinity, a substance having excellent thermal conductivity, and a substance having a high affinity for silicon nitride are preferable, and a substance satisfying these is a rare earth element and a 4a group element of the periodic table. Second, it is a complex oxide containing
Was obtained. The present invention has been completed based on these first and second findings.

That is, the silicon nitride-based sintered body of the present invention
A matrix containing silicon nitride as a main component is 90 to 99.5.
% By weight, and the balance consists of a grain boundary phase containing a crystalline composite oxide containing a rare earth element and a Group 4a element of the periodic table.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The matrix in the sintered body of the present invention is substantially composed of silicon nitride or 90 wt.
% Or more of a composition component in which other oxides, nitrides, and carbides are mixed or dissolved in silicon nitride.
One or more of silicon aluminum oxynitride (specifically, for example, Si ₁₂ Al ₁₈ O ₃₉ N ₈ ), silicon carbide, and sialon are mixed and dissolved in 0 wt% or more of silicon nitride. is there. This matrix is preferably substantially composed of silicon nitride. Depending on the application, α-type and / or β-type silicon nitride may be used properly.
In particular, in applications where importance is placed on strength and toughness, it is preferable to use substantially β-type silicon nitride.

[0010] The grain boundary phase in the sintered body of the present invention is composed of only a crystalline composite oxide or contains a crystalline composite oxide as a main component and other glassy substances as an amorphous substance. Can be cited as a typical example. The crystalline composite oxide contained in this grain boundary phase is _Ra M _b
O _c (where R represents at least one kind of rare earth element including Sc and Y, M represents at least one kind of element of Group 4a of the periodic table, and O represents oxygen. ,
a> 0, b> 0, c> 0) and / or R _a M _b M ′ _d O _c (where M ′
Is an element other than R and M, a positive number of d> 0, and the others are the same as those described above).

The crystalline composite oxide is represented by R ₂ M _2-x O _7-2x
(Where R, M, and O are the same as above, and X satisfies -1 <X <1), a stable oxide is obtained, and a sintered body is formed. This is preferred because it increases the thermal conductivity and improves thermal shock resistance. In particular, it is preferable to use one or more of R = Y, Dy, Yb, and Sm, and to use M = Zr and / or Hf because the above-described effects tend to be enhanced. The crystalline complex oxides, specifically, for example, _{Y 2 Hf 2-x O 7-2x} , Y 2 Zr 2-x O 7-2x, S c2 Hf 2-x O
_7-2x , (YDy) ₂ Hf _2-x O _7-2x , (YDy) ₂ Zr _2-x
O _7-2x , (YDy) ₂ (ZrHf) _2-x O _7-2x , Sc
₂ (HfMgz) _2-x O _7-2x , Y ₂ (HfMgz) _2-x O
_7-2x , Dy ₂ (HfMgz) _2-x O _7-2x , Dy ₂ (HfM
gz) _2-x O _7-2x , (YDy) ₂ (HfMgz) _2-x O
_7-2x and Y ₂ (HfCrz) _2-x O _7-2x .

The grain boundary phase containing the crystalline composite oxide as a main component is preferably mixed with an amorphous glassy substance from the viewpoint of sinterability. Mg in this grain boundary phase
The inclusion of the element is preferable because a Mg-containing glassy substance is easily formed, and the effect of promoting the sinterability is produced. When this glassy substance contains the Mg element, the Si element, the oxygen element, and the nitrogen element, in addition to the effect of promoting the sinterability, it also has the effect of improving the strength and toughness of the sintered body. This is preferable.

The contents of the grain boundary phase and the matrix in the sintered body are in a relative relationship.
When the amount is less than 10% by weight, the amount of the grain boundary phase is relatively 10% by weight.
When the amount of the matrix is more than 99% by weight, the amount of the grain boundary phase is relatively less than 1% by weight. The sinterability, strength, and toughness are significantly reduced.

A metal, Al, Si of the 4a, 5a, 6a group of the periodic table is provided on the entire surface or a part of the surface of the silicon nitride based sintered body.
And their mutual alloys, or 4a, 5 of the periodic table
a, group 6a metals, carbides, nitrides, oxides of Al and Si and their mutual solid solutions, or diamond;
Forming a coating having a thickness of 0.5 to 20 μm comprising at least one single layer selected from diamond-like carbon, cubic boron nitride, and hard boron nitride, or at least two types of multiple layers; It is preferable to use a silicon-based sintered body because the wear resistance is further improved. The applicable range of the coating thickness of the coated silicon nitride-based sintered body varies depending on the application, the shape of the sintered body, the coating material, and the composition of the coating in terms of single layer, multiple layers, particle size of the coating, crystal of the coating, and the like. However, the thickness is preferably 1 to 8 μm for severe applications such as cutting tools.

The sintered body of the present invention can be manufactured by a conventional powder metallurgy method. In particular,
For example, various starting materials can be weighed, inserted into a mixing vessel together with an organic solvent and a pulverizing medium, and can be manufactured through wet mixing, drying, powder molding, preheating, and sintering steps. The sintering step at this time is sintering at 1500 to 2000 ° C. in an atmosphere of nitrogen gas and inert gas, and the pressure during sintering is reduced or increased (hot pressing). It is also preferable to perform hot isostatic pressing (HIP) after sintering because it tends to increase strength and toughness.

In order to form a film on the surface of the thus obtained sintered body, a conventional chemical vapor deposition method (CV
D method), physical vapor deposition method (PVD method) or plasma CVD
It can be performed by the method.

[0017]

In the silicon nitride-based sintered body of the present invention, the matrix mainly functions to improve the thermal shock resistance and wear resistance, and the grain boundary phase which is uniformly dispersed at the grain boundaries of the matrix mainly has strength and toughness. And the crystalline composite oxide in the grain boundary phase acts to increase the thermal conductivity,
In addition, it acts to balance both mechanical strength, thermal shock resistance and abrasion resistance at high temperatures, and promotes sintering during the sintering process when a glassy substance is contained in the grain boundary phase. The synergistic effect between the matrix and the grain boundary phase further enhances wear resistance, thermal shock resistance, chipping resistance and heat resistance at high temperatures.

[0018]

[Experimental test 1] Si ₃ N _{4 having} an average particle size of 0.7 μm, 0.1 μm.
2 μm MgO, 0.5 μm Y ₂ O ₃ , Dy ₂ O ₃ , 0.
Using various commercially available powders of 4 μm HfO ₂ , 0.2 μm Al ₂ O ₃ , and ZrO ₂ having a primary particle diameter of 300 °, the hexane solvent and Si ₃ N ₄ were mixed in the proportions shown in Table 1.
Wet mixing by a ball mill was performed together with the pulverization medium of the base sintered body. After adding 6 wt% of paraffin wax as a molding aid to the mixed powder thus obtained, a powder compact was formed at a pressure of ² ton / cm ² using a mold. After preheating this powder compact and dewaxing it, 5 kg
/ Cm ^{2 in} a pressurized nitrogen gas atmosphere, temperature 1900 ° C, 2
Sintering is performed under the conditions of holding for 1 hour, and HI is further performed for 1 hour at a temperature of 1700 ° C. in a nitrogen gas atmosphere at 1000 atm.
P treatment was performed to obtain inventive products 1 to 5 and comparative products 1 to 8.

The compositions of the matrix and the grain boundary phase of the sintered bodies of the inventive products 1 to 5 and comparative products 1 to 8 thus obtained were investigated by crystal X-ray diffraction, characteristic X-ray diffraction and fluorescent X-ray diffraction. The results are shown in Table 2. The hardness, flexural strength, fracture toughness (K1c method obtained from cracks with a Vickers indenter), and thermal conductivity of each of the sintered products of the present invention products 1 to 5 and comparative products 1 to 8 were measured at room temperature. Further, the high-temperature hardness and high-temperature bending strength at 1200 ° C. were measured, and the results are shown in Table 3.

Next, products 1 to 5 of the present invention and comparative products 1 to 8
Using each of the sintered compacts, a dry milling test under the following condition (A) and a wet intermittent turning test under the condition (B) were performed, and the results are shown in Table 4. (A) The dry milling cutting test conditions are as follows: Work material: FC250 (180 mm ×
60mm black scale), cutting speed: 600m / min, depth of cut: 3.0mm, feed: 0.1mm / tooth, tool shape S
NGN120412, Evaluation: Measured the boundary wear amount (V _N ) after cutting the 180 mm × 60 mm area portion 30 times,
(B) The wet intermittent turning test condition is as follows: Work material: FC350
(180mm outer diameter x 90mm inner diameter end face, with 4 grooves),
Cutting speed: 500-250m / min (constant rotation speed),
Depth of cut: 2.0 mm, feed: 0.3 mm / rev, tool shape: SNGN120412, evaluation: The number of end face cutting (passing) until chipping or chipping was measured.

From the above results, the comparison product 5 for the product 1 of the present invention, the comparison product 6 for the product 2 of the invention, the comparison product 7 for the product 3 of the invention, and the comparison product 8 for the product 4 of the invention are compared with each other. The product of the present invention has higher hardness and flexural strength at room temperature and high temperature, higher fracture toughness at room temperature, and significantly higher thermal conductivity than sialon-based sintered bodies. It is clear that they are significantly superior in impact resistance and thermal shock resistance.

[0022]

[Table 1]

[0023]

[Table 2]

[0024]

[Table 3]

[0025]

[Table 4]

[0026]

Test 2 Using the sintered bodies of the products 1 to 3 of the present invention and the comparative products 3 and 4 obtained in the test 1, the surfaces of the respective sintered bodies were coated by a conventional CVD method. To form the coated silicon nitride-based sintered body of the present invention.
Comparative products 10 and 11, which were coated sintered bodies in comparison with No. 8, were obtained.
The coating at this time is a layer formed adjacent to the surface of the sintered body as a first layer, and sequentially coated with a second layer and a third layer.

Inventive products 6 to 8 thus obtained and Comparative product 1
The thickness and composition of the coatings 0 and 11 were confirmed by X-ray diffraction and SEM, and the results are shown in Table 5. Further, using the products 6 to 8 of the present invention and the comparative products 10 and 11, (B) a continuous turning test by a wet method in the execution test 1 and the following (C)
A cutting test was performed by a wet-type continuous turning test according to the conditions, and the results are shown in Table 6. (C) The wet continuous turning test conditions are as follows: work material: FC350, cutting speed: 800 m /
min, depth of cut: 1.5 mm, feed: 0.7 mm / blade,
Cutting time: 2 min, Tool shape: SNGN12041
2. Evaluation: The flank average wear amount VBmm was used.

[0028]

[Table 5]

[0029]

[Table 6]

[0030]

The silicon nitride-based sintered body of the present invention has a higher hardness than conventional silicon nitride-based sintered bodies, silicon nitride-based sintered bodies deviating from the present invention, and conventional sialon-based sintered bodies. , Strength and fracture toughness, particularly high hardness and strength at high temperature and remarkably high thermal conductivity.
In addition to excellent toughness and fracture resistance, it has an effect of remarkably increasing the thermal shock resistance, and has an excellent effect of significantly prolonging the life when used as a cutting tool in a high load and high temperature region.

Claims (9)

[Claims] 1. A grain boundary phase containing a crystalline composite oxide containing 90 to 99.5% by weight of a matrix containing silicon nitride as a main component and a balance of a rare earth element and a Group 4a element of the periodic table. A silicon nitride-based sintered body, comprising: 2. The silicon nitride-based sintered body according to claim 1, wherein a main component of said matrix is β-silicon nitride. 3. The crystalline composite oxide is R ₂ M _2-xO
7-2x (where R is one of the rare earth elements including Sc and Y)
A compound oxide represented by the following formula: M represents an element of Hf and / or Zr, O represents an oxygen element, and has a relation of -1 <X <1. 3. The silicon nitride-based sintered body according to 1 or 2. 4. The silicon nitride-based sintered body according to claim 1, wherein the crystalline composite oxide contains an element of yttrium and / or dysprosium. 5. The silicon nitride-based sintered body according to claim 1, wherein said grain boundary phase contains a glassy substance in addition to said crystalline composite oxide. . 6. The silicon nitride based sintered body according to claim 1, wherein said grain boundary phase contains a magnesium element. 7. The silicon nitride based sintered body according to claim 6, wherein said magnesium element is contained in a glassy substance. 8. The silicon nitride-based sintered body according to claim 5, wherein the glassy substance is an amorphous substance containing a magnesium element, a silicon element, an oxygen element, and a nitrogen element. 9. The group 4a, 5a, 6a of the periodic table on the entire surface or a part of the surface of the silicon nitride-based sintered body according to claim 1, 2, 3, 4, 5, 6, 7, or 8. Metals, Al, Si
And their mutual alloys, or 4a, 5 of the periodic table
a, 6a group elements, carbides, nitrides, oxides of Al and Si and their mutual solid solutions, or diamond,
A coating having a total thickness of 0.5 to 20 μm, which is composed of a single layer selected from diamond-like carbon, cubic boron nitride, and hard boron nitride, or a laminate of two or more layers. Characterized coated silicon nitride based sintered body.