JPS60145957A - High tenacity sintered body - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to high-toughness engineering ceramics having a wide range of applications.

[Prior art and its problems]

Silicon carbide, like silicon nitride, is chemically stable, has excellent wear resistance and thermal shock resistance, and has many advantages such as high strength and hardness at high temperatures, making it the most promising material for engineering ceramics.

Conventionally, the biggest drawback of such silicon carbide sintered bodies is said to be poor fracture toughness, and the essential problem is that they are easy to break.

Therefore, many researchers have begun research into microstructural structures that can absorb stress, and in the past, cermets with metal interposed at the grain boundaries have been actively researched, but recently cermets with metastable zirconia interposed therein have been actively researched.

Currently, cermet is still considered unsuitable as a structural material because it undergoes plastic deformation and oxidative deterioration at high temperatures, but alumina material, which has increased toughness by adding zirconia, is used as tough ceramics for cutting tools and other applications. The scope of research is being expanded to include engine parts.

However, both toughened alumina and toughened zirconia are oxides and undergo plastic deformation at temperatures above 1000"C, so they cannot function as independent structural materials. For example, when pistons and cylinder heads are made of ceramics, In research, the cold end side is supported by a back amplifier made of metal structural material, and the ceramics are simply replaced with the role of a heat insulating material.If 1.
It is thought that if the toughness of metastable or semi-stable zirconia could be imparted to silicon carbide or silicon nitride, which have strong covalent bonds, an ideal function as a ceramic structural material could be obtained.

However, if zirconia is simply added to silicon carbide and fired, 2 ZrO2+ 35iC-" 2 ZrC+ 3 S
iO↑+C○↑ (1) Due to the reaction of the formula (1), a large amount of gas is generated during firing, making it impossible to obtain a dense sintered body, and the high temperature strength is lowered in addition to the generation of gas, which prevents densification. Also(
ZrC, which is a product of formula 1), has the problem of deteriorating the oxidation resistance of the sintered body.

[Purpose of the invention]

An object of the present invention is to realize a sintered body that has both the high-temperature mechanical properties of silicon carbide and the high toughness that metastable or semi-stable zirconia does not provide.

[Structure of the invention]

The present inventors added an excessive amount of ZrO2 crystal stabilizer to a composition consisting of SiC and ZrO2, and fired it under pressure in an atmosphere to obtain SiC and ZrO2 of formula (1).
It has been found that a dense sintered body can be obtained by forming a non-stoichiometric grain boundary phase that is stable at high temperatures while inhibiting the decomposition reaction of rO2. In addition, the present inventors have discovered that by adding a high-temperature stable metal nitride to the above compound, the grain boundary phase becomes a non-stoichiometric compound containing N, and the mechanical properties of the sintered body are improved. This discovery led to the present invention.

The characteristics of the present invention are, firstly, that in order to partially stabilize zirconia and form a grain boundary phase, Y203. Sm203'.

Er2 03 + Ce2 03 , Yb2 03.
Nd2 03. MgO.

One or more zirconia crystal stabilizers such as CaO are added in an amount of 1 to 40 atomic equivalent percent of the metal element present in the stabilizer relative to Zr. and,
The second feature is that S is used to improve the mechanical properties of the sintered body.
AIN activates iC and forms a non-stoichiometric compound containing nitrogen as a grain boundary phase.

GeN, BeN, Be3N2, Cr2N,
CrN, BN.

GaN, Si3N4, Nb3N4, Ta
It is made by adding 1 to 20 atomic equivalent percent of one or more high temperature stable nitrides such as N and NbN.

Yet another feature of the present invention is that in order to prevent the decomposition reaction shown in equation (1), the partial pressure of product gases such as Sin and C○ is The knowledge that it is not always necessary to act on decomposition reactions, and that the decomposition reaction can be controlled simply by the pressure of an inert gas with a relatively large molecular weight, such as Ar, has made it possible to use a wide variety of compounds. It is.

In producing the sintered body of the present invention, the above compound is heated to a temperature of 1,600 to 21
00°C2 The firing is preferably carried out at 1700°C to 2000°C, but in order to prevent porosity caused by the reaction in equation (1) and obtain a densified sintered body, an inert gas with a relatively large atomic weight is required. effective, e.g. Ne−, than tj e.
The effect of suppressing decomposition is greater with Ar than with Ne, with Kr than with ^r, and with Xe, and it is desirable to carry out pressure sintering in an atmosphere at a pressure of 2 to 100 atmospheres using these inert gases and/or N2 gas. Furthermore, by simultaneously applying the partial pressure of -carbon oxide gas, the oxidative decomposition of SiC can be controlled more effectively. The upper limit of the inert gas pressure may not be 100 atm, but greater effects cannot be expected. This gas pressure sintering is one of the important requirements for obtaining a dense sintered body.

Among the above compounds, ZrO2 is easily reduced by SiC to form ZrC, but by gas pressure sintering, oxidative decomposition of SiC is suppressed and the amount of ZrO2 reduced is controlled to be small.

By adding carbon to the compound, ZrO2 → ZrC increases under pressureless sintering conditions, but 20 to 1 in Ar
The reaction of ZrO2=ZrC is greatly suppressed under the pressure sintering conditions of 000 atmospheres. The requirement for high toughness is to retain a large amount of metastable or semistable zirconia, and controlling the amount of carbon in the compound and gas pressure sintering can satisfy the object of the present invention.

The high toughness of the sintered body of the present invention is due to the fact that the ZrO2 in the sintered body is tetragonal, despite the addition of about 40 atomic equivalents of stabilizer to monoclinic ZrO2 as a starting material. This is obtained by

In another experiment of ours with ZrO2 stabilizer only, ZrO2
The content of rare earth oxides relative to rO2 is 5 mol% for y2 o3, 3 mol% for CeO2, Sc203,
Sm203, Br203, Nd203.

For Tb2O3 and the like, cubic ZrO2 diffraction lines have been confirmed in the sintered body at 3 to 7 mol % respectively.

That is, in the sintered body of the compound according to the present invention, the stabilizer, in addition to functioning as a stabilizer for zirconia, is consumed in the formation of non-stoichiometric compounds at the grain boundaries containing nitrogen, and also in the formation of non-stoichiometric compounds at the grain boundaries containing nitrogen. ZrO2 is also low or difficult to confirm. Although there are many areas that are still unclear in research, the present invention has made it possible to obtain a highly tough and dense silicon carbide sintered body.

Experimental examples regarding each factor that affects the sintered body of the present invention are shown below.

(Experimental Example-1) Table 1 shows the results of experiments regarding ZrO2 blends at various weight ratios to 100 parts by weight of SiC in the soil composition. It can be seen from this that when ZrO2 is less than 5 parts by weight, densification does not proceed, and when it exceeds 80 parts by weight, the fracture toughness value deteriorates.

(Experimental example-2) ZrO245.5 for soil volume composition 5t0100 parts by weight
Tables 2 and 3 show the results of experiments in which the weight part was fixed and the Zr○2 crystal stabilizer and its addition amount were varied.

As a result, it was found that the appropriate amount of the stabilizing agent added was in the range of 1 to 40 atomic equivalent percent of the metal element present as a stabilizer relative to Zr, and the effects of adding all the stabilizers were observed. .

(Experimental Example-3) Table 4 shows the results of experimental examples regarding ZrO2 blends at various weight ratios to 100 parts by weight of SiC in the soil composition. Regarding N004 containing 95 parts by weight of ZrO2, the theoretical density ratio decreased slightly, and the strength and fracture toughness values decreased significantly. With N058 containing 3 parts by weight of ZrO2, sufficient sintered density could not be obtained at temperatures up to 2000° C., and the fracture toughness and strength decreased. Therefore, Zr025~ has the highest fracture toughness value.
It is in the range of 80 parts by weight.

(Experiment Example 4) An experiment was conducted by fixing 100 parts by weight of SiC, 245 parts by weight of ZrO, and 10.2 parts by weight of metal nitride ^IN, and changing the ratio of rare earth element oxides. The results are shown in Table 5.

In the case of Y203, Z is compared between No. 10 and No. -11.
Even if the atomic equivalent % of Y to r exceeds 40%, it will only become expensive and will not lead to improved performance, and when the atomic equivalent % of Y to Zr is less than 1%, the fracture toughness value, Mechanical properties such as strength were significantly reduced. Ce2
Regarding O3, the atomic equivalent % of Ce to Zr is 40
% or more, the effect is small, and if it is 1% or less, the mechanical properties similarly deteriorate significantly. Therefore, for rare earth elements, Z
It can be seen that the appropriate range of atomic equivalent % to r is 1 to 40%.

(Experimental Example-5) Composition in which one or two of various rare earth element oxides were added to a composition fixed with 100 parts by weight of SiC, 45]i parts by ZrO2', and 10.2 parts by weight of metal nitride AIN. Table 6 shows the results of the experimental examples regarding the products. While the fracture toughness value of commercially available silicon carbide sintered bodies is 17 to 21 kgf/+u%, Sm2O3, Sc2o3. Eu2
03.

Er203, Y203, etc. showed higher fracture toughness values.

(Experimental Example-6) Table 7 shows 100 parts by weight of 5iC, 35 parts by weight of ZrO, and 10 parts by weight of Y20 (Y31 atomic equivalent % relative to Zr).
Table 7 shows the experimental results when the metal nitride and the amount added were varied while the metal nitride was fixed. The sintering conditions are the same as in Example 2.

Experiments No. 29 to No. 33 used AI as a metal nitride.
As a result of changing the atomic equivalent % of ^l to St in the soil volume composition from 0.7 to 25% using N, it can be seen that when the atomic equivalent % of Al to Si is 1.0% or less, the densification power j is It can be seen that when it is sufficient and 20% or more, densification progresses but mechanical properties deteriorate.

Experiments No. 34-No. 38 used Ge as a metal nitride.
Using N, the atomic equivalent % of Ge to St is 0.5 to 2.
The results are shown when the change is made up to 2%, and it was found that although the theoretical density ratio and mechanical properties are slightly inferior compared to AIN, it exhibits similar behavior to AIN.

(Experimental Example-7) Table 8 shows the results of an experiment in which 100 parts by weight of SiC, 33 parts by weight of ZrO, and the rare earth element oxide were fixed at 38.5 parts by weight of Y2, and the metal nitride and the amount added were changed. As a result, densification was observed for all metal nitrides, especially B
The effect was remarkable for H.

(Experimental Example-8) The same molded body as in Example 2 was heated to an Ar:CO gas volume ratio of 80.
When pressurized sintering was performed at 30 atmospheres and 1800° C. using a mixed gas of:

(Experimental Example-9) Carbon residual ratio 6 was used instead of the non-carbon residual organic binder of Example 2.
A molded body obtained under the same conditions using a 0iv10 phenolic resin as a binder was subjected to atmospheric pressure sintering at 1800°C under static pressures of 1.5 and 25 atm. 1.5, the theoretical density ratio is 62%, the weight change is -25 匈10. Theoretical density ratio is 95% at Ar pressure of 25 atm.
, the weight change was -4!10.

(Experimental Example-10) Table 9 shows the conditions and results of an experiment using MgO and CaO as ZrO2 stabilizers. From now on MgO and C
It can be seen that when aO is used as a stabilizer, a dense sintered body can be obtained, but the mechanical strength is relatively low. Although the reason for this is not clear, it is thought that the composition of the grain boundary phase has an effect. Although not shown, the hot bending strength at 1400° C. was lower in the case of addition of HgO and CaO than in the case of addition of rare earth oxidation.

〔Example〕

Hereinafter, examples of the sintered body of the present invention will be given along with comparative examples, and the effects thereof will be explained.

Example 1 Commercially available α as SiC with a purity of 99% or more and an average particle size of 0.3μ
Commercially available monoclinic ZrO2 with a purity of 99% or more and an average particle size of 0.2 μm was used as the ZrO2.

SiC200g, ZrO290g, and Y2031
9 g was mixed in a ball mill in ethanol with a non-charcoal organic binder, then dried, and the resulting powder was mixed with 2
Rubber pressing was performed at a pressure of ton/C4. The thus obtained molded body was heated to 1800 m
The material was heated to 100°C and pressure sintered in an atmosphere.

As a result, a sintered body with 95% of the theoretical density was obtained, the weight change before and after sintering was -4w10, and the fracture toughness was 21 kg.
f/Ryu, the three-point bending strength was 72 kg/va 2.

Example 2 Commercially available α with a purity of 99% or more and an average particle size of 0.3μ as SiC
Commercially available monoclinic ZrO2 with a purity of 99% or more and an average particle size of 0.2 μm was used as ZrO2. 5iC20
0g, Zr0z 90g, AlN9.3g and y20
3], 9 g was mixed with a non-charcoal organic binder in a Pall mill in ethanol, dried, and 2 tons/
Rubber pressed with a pressure of cJ. The obtained molded body was
Atmospheric pressure sintering was performed by heating to 1800° C. in an instrument environment at 0 atm.

As a result, a sintered body with a theoretical density ratio of 94% was obtained, the weight change before and after sintering was -4w10, and the fracture toughness was 25 kg.
f/yn%, 3-point bending strength is 80kg/m*”
Met. X-ray analysis revealed that the volume composition was tetragonal ZrO2 and αSiC, and ZrC was not observed. The peak of ZrO2 was shifted to the higher angle side from the normal position.

Comparative Example 1 A molded body similar to Example 2 was heated to 1800°C in an Ar atmosphere of 1.5 atm. The theoretical density ratio of the obtained sintered body was 73%, and the weight change before and after sintering was the same. It was 20w10. X-ray analysis revealed that no ZrO2 peak was observed, but an extremely large ZrC peak was observed.

Comparative Example 2 The same molded body as in Example 2 was heated in Ar at 25 and 100 atm.
When heated to 1800℃ in an atmosphere, the former had a theoretical density ratio of 90%, a fracture toughness value of 22 kgf/tm%,
A sintered body with a 3-point bending strength of 71.3 kg/H2, a theoretical density ratio of 96.5%, a fracture toughness of 28 kgf/1%, and a 3-point bending strength of 84.4 kg/N2 was obtained.

From Example-2, Comparative Example-1, and Comparative Example-2, a dense sintered body cannot be obtained unless atmosphere pressure sintering is performed;
It can be seen that even if the atmosphere is pressurized to a level higher than atmospheric pressure, no significant effect can be obtained.

Comparative Example-3 A molded product similar to that of Example 2 was heated under an instrument atmosphere of 50 atmospheres for 16 hours.
When heated at 00°C and 2100°C, the obtained sintered body had a theoretical density ratio of 65% in the former case, and 78% in the latter case.
%Met. 1600°C and 2100°C from Comparative Example 3
It can be seen that a dense sintered body cannot be obtained even if pressure sintered in an atmosphere.

Example 3 Commercially available β-crystalline SiC with a purity of 99% or more and an average particle size of 0.3μ was used as the SiC, and commercially available monoclinic ZrO2 with a purity of 99% or more and an average grain size of 0.2μ was used as the ZrO2.

200 g of 5iC and 290 g of ZrO were wet mixed together with a binder, dried, and rubber pressed at a pressure of 2 ton/cJM. The obtained compact was heated to 1800° C. in an Ar atmosphere of 50 atm to perform atmospheric pressure sintering.

As a result, a sintered body with a theoretical density ratio of 93% was obtained, a fracture toughness value of 20 kgf/m%, and a three-point bending strength of 70 kg/m%.
It was N2.

Example 4 A mixture obtained by adding 9.3 g of AlN to the formulation of Example 3 was wet mixed with a binder, dried, and otherwise molded and sintered in the same manner as in Example 3. The obtained sintered body has a theoretical density ratio of 95
%, the fracture toughness value was 23 kgf/+n'i, and the 3-point bending strength was 75 kg/m++2.

It can be seen from Examples 3 and 4 that the present invention provides similar effects even when the crystal type of SiC is β crystal.

Claims (1)

[Claims] 1. A high-toughness sintered body, characterized in that it is obtained by atmospheric sintering of a molded body of silicon carbide powder containing zirconia and a zirconia stabilizer. 2. A high-toughness sintered body characterized by being formed by atmospheric sintering of a molded body of silicon carbide powder containing zirconia, a zirconia stabilizer, and a high-temperature stable metal nitride. 3. Zirconia is contained in an amount of 5 to 100 parts by weight of silicon carbide.
The high toughness sintered body according to claim 1 or 2, characterized in that it contains 80 parts by weight. 4. High toughness according to claim 1 or 2, wherein the zirconia stabilizer contains a metal element in an amount of 1 to 40 atomic equivalents relative to zirconium in the zirconia. Sintered body. 5. Zirconia stabilizers include yttrium oxide, cerium oxide, scandium oxide, lanthanum oxide, neodymium oxide, samarium oxide, europium oxide, erbium oxide, thulium oxide, interbium oxide, lutetium oxide, praseodymium oxide, promethium oxide, and Claim 1, characterized in that it is one or a mixture of two or more of the group consisting of gadolinium, terbium oxide, dysprosium oxide, holmium oxide, magnesium oxide, calcium oxide, samarium boride, and hardened lanthanum.
The high toughness sintered body according to item 1 or 2. 6. High toughness according to claim 1 or 2, characterized in that the amount of metal elements present in the metal nitride' is 1 to 20 atomic equivalent % with respect to silicon in the molded article Sintered body. 7. The metal nitride is one or a mixture of two or more of the group consisting of aluminum nitride, boron nitride, germanium nitride, beryllium nitride, chromium nitride, gallium nitride, silicon nitride, niobium nitride, tantalum nitride, and hafnium nitride. A high toughness sintered body according to claim 1 or 2, characterized by: 8. The high-toughness sintered body according to claim 1 or 2, wherein the atmosphere sintering is sintering in a non-oxidizing or inert pressurized atmosphere. 9. The high toughness sintered body according to claim 8, wherein the pressure of the pressurized atmosphere is 2 to 100 atmospheres. 10. The high-toughness sintered body according to claim 1 or 2, wherein the atmosphere sintering is performed in an atmosphere containing carbon monoxide gas. 11. The high toughness sintered body according to claim 1 or 2, wherein the atmosphere sintering is carried out at 1600°C to 2100°C, preferably 1700°C to 2000°C.