JPH013066A - Ceramic composite 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 The present invention relates to ceramic materials and methods of manufacturing the same. This material has exceptionally good properties as a ceramic material for industrial technology or as a tool for cutting metals. In particular, the present invention relates to alumina-based materials whose wear resistance and toughness are enhanced by favorable microstructure and phase structure.

The addition of refractory hard components combined with chromium-containing and zirconia is the basis for the favorable properties.

Several recent advances in materials engineering have made it possible to produce ceramics with significantly improved mechanical properties. This, combined with excellent properties such as thermal resistance, resistance to corrosion and erosion, and light weight, makes ceramics useful in new applications such as motor parts, heat exchangers, metal cutting tools, bearings, etc. I have to. Ceramic's potential as a high-performance material is highly valued. Generally good physical properties of ceramic materials are used in engineering, space, marine,
It offers the possibility of meeting the rapidly increasing demand for materials needed in the electronic and bio-industries. Apart from the possibility of meeting the ever-increasing demands of new sectors, the introduction of high-performance ceramics may be suitable to replace materials in existing structures.

An application field where the special properties of ceramic materials can be used from a long-term perspective is in high-temperature technology fields such as internal combustion engines. In high heat fields of this type, very large amounts of energy can be realized due to the higher working temperatures and the associated high efficiency possibilities. Another important factor for the use of ceramic components is the possibility of further weight reduction. The application of ceramic materials to the wear-resistant field lies in the use of ceramic's wear and corrosion resistance. In particular, mention may be made of the use as a metal cutting tool. In addition, ceramic materials such as alumina already play an important role in bearings and seals for pumps in the highly corrosive environment of the chemical industry.
It fulfills its function. Much effort has been devoted to improving the mechanical properties of ceramic materials, and laboratory and pilot scale tests have yielded very promising results.

Flexural strengths at levels greater than 500 MPa have been reported for many materials. The compressive strength of ceramic materials is generally very high.

Ceramic materials exhibit high theoretical strength determined by the bonding energies of their atoms. However, this is not suitable for today's practice. A drawback to the more general use of ceramic engineering materials is the brittleness of the materials. This brittleness, along with a tendency to dissipate in strength data, results in excessive sensitivity to overload and thermal shock.

Methods to address the brittleness of ceramic materials and the associated low fracture toughness include so-called strengthening mechanisms (stress-induced phase transformation, micro-crank strengthening and biased strengthening) and fiber reinforcement (incorporation of ceramic fibers or whiskers into the ceramic matrix). is of use.

Another approach is to bring the fracture fragility level of the ceramic composite closer to that of ceramic carbides and brittle steels. The most interesting ceramic materials are compositions based on Al 203 , Zr0t , Si3N4 or SiC.

Another problem today is poor reproducibility. This is also related to the brittleness and low fracture resistance of ceramic materials. This results in a maximum allowable defect size (microcranks, pores, large grains or crystals) of 1001 in metals.
Compared to the size of 1 Inn or more, the size must be kept to a small size of 10 to 20 Inn.

This places great demands on the purity of the raw materials and the absence of extraneous particles, as well as on manufacturing processes that do not introduce such defects.

Furthermore, machining of ceramic sintered bodies results in surface damage that can be used as a measure of strength.

Due to their brittleness, ceramic materials are generally non-forgeable in nature, i.e. single defects (weakest link)
causes destruction. The fracture resistance of ceramic cutting materials is extremely important. Conventional monolithic ceramic materials have as a rule a relatively low fracture resistance, with the exception of compositions in which ZrO□ or partially stabilized ZrO is present.

Tetragonal transformation of ZrO□ is in the densely sintered ceramic body,
or a small amount of YzO:t, MgO and/or CaO
is maintained in a metastable form in composites made by adding ZrO to ZrO, before sintering. Monolithic materials such as SiC and Al 20:I, on the other hand, have low fracture toughness of 3-5 MPa" and strengths on the order of 200-500 MPa. Alumina-based ceramic cutting tools for metal cutting are characterized by extremely good chemical stability and can therefore be used to carry out chisopforming operations at high speeds without suffering from wear due to oxidation or chemical dissolution. . A severe limitation to the use of pure alumina materials is the material's sensitivity to mechanical shock, which reduces its usefulness for interrupted cutting operations such as milling.

It is well known that the fracture resistance of ceramic materials can be significantly improved by incorporating fibers or whiskers.

Whiskers generally refer to very fine hair-like single crystals less than 5 feet in diameter, often less than 2 feet in diameter. The fiber material is always polycrystalline and, as a rule, has a diameter of 5 or more. For example, in previous literature, β20. How can thin SiC whiskers in the base metal provide extremely favorable effects such as doubled fracture resistance, much better fracture strength, and more than doubled reliability by adding a sufficient amount of whiskers? Sufficient explanation has been given. However, SiC whisker-reinforced alumina materials are difficult to densify to the high densities required to utilize advanced material properties.

Pressureless, sintering methods are used with the addition of small amounts of SiC whiskers, but this does not provide optimal reinforcement. The larger the amount added, the more expensive a hot press or hot isostatic press must be applied.

Mechanical performance is considered to be the limiting factor for these improvements.
The many advantages of ceramic matrix materials such as alumina open the door to potential applications in many areas where they are not available. An important application of this type is the use of ceramics in cutting operations, such as turning, milling, drilling, etc. The improved performance also opens up new possibilities for high-temperature applications such as internal combustion engines and gas turbines.

The incorporation of particles of hard components into alumina-based ceramic materials exhibits a favorable effect, namely wear resistance. For example, the addition of TiC or TiN to alumina produces a material with very good properties as an indexable cutting insert for certain metal cutting applications.

The limiting factor for manufacturing is that the refractory hard component phase, regardless of the particle or fiber shape, has the desired volumetric fraction for optimum effectiveness without special methods such as pressing. It is impossible to sinter at high density. This hot pressing is an expensive technique, and there are limits to the production of sintered products with complex external shapes.

The present inventor has added metal oxides to alumina, and has studied for a long time how this addition affects sinterability and structure. As a result, it was found that most metal oxides have negative effects. For example, low density and abnormal grain growth on alumina occur. To give one example, the inventors have discovered that only the addition of chromium oxide (CrzO+) to alumina during sintering in an inert gas atmosphere promotes grain abnormal growth. However, the present invention is TVB of the periodic table.

It has been surprisingly discovered that when chromium oxide is added to alumina with a suitable combination of group VB or VIB elements, it does not exhibit the adverse behavior of grain overgrowth described above. Instead, a uniform and dense composite of very fine grains was obtained. The inventors have discovered that this composite exhibits significantly increased toughness behavior with very high hardness and chemical stability. Increased toughness can be obtained when the hard material is in the form of fibers, for example when TiN or TiC whiskers are added to alumina in the presence of ZrO and the amount of chromium added is between 2 w,t,% and 10 w,t,%. ,
It can be stated with particular certainty that this will occur. Testing of this composite as a cutting tool material showed that it behaved very well.

Furthermore, according to another experiment, IVB other than Crz03.

Alumina-based composites can be sintered more easily by adding small amounts of oxides of elements from groups VB or VIB, preferably together with hard refractory compounds such as carbides, nitrides, or borides of elements from that group. done. Oxides appear to aid sintering to a greater or lesser extent by reactions that form oxycarbide-like phases via liquid phases at the grain boundaries. In this way, pressureless sintering of composite materials became possible. However, the good effects obtained with chromium oxide and chromium compounds, which decompose into one oxide during heating, were not found.

By combining hard components with different oxides, one of which is chromia, ceramic composite materials with the required properties can be obtained as desired. For example, from the addition of approximately 7% chromium oxide, 2% zirconia and 30% titanium nitride-titanium carbide mixture to alumina, a remarkable A suitable composite material was obtained. Its Vickers hardness was superior to that of alumina ceramics, and its fracture resistance was significantly increased. This material was dense, with fine grains of about 11 rm or less, and exhibited excellent cutting tool behavior. mostly sintering skin
n) was not found. This type of surface area usually occurs during high temperature processing due to undesirable reactions between the atmosphere and the sintered body. Therefore, the complex contours are finally formed at low temperatures and require no or little polishing or post-forming processing. For comparison, alumina with 7% chromium oxide alone or 7% chromium oxide and 2% Zr0g added to 16
Sintering temperatures lower than 00'C do not result in dense materials, and temperatures higher than this result in abnormal grain growth.

The inventor conducted a series of experiments and determined that TiN and/or T
The effects on the microstructure of alumina materials containing iC hard components were studied by varying the amounts of ZrO2 and CrzO+ added. Electron microprobe analysis is Cr2O.

revealed some surprising positive (beneficial) effects on the microstructure by the addition of . With the addition of ZrO2 alone, a small positive effect on the density of the sintered material can be noted, but still requires a very high sintering temperature of approximately 1800°C. The structure obtained was a coarse grain-like structure with 2 to 4 grains, and the added Zr
O□ is a non-homogeneous titanium-zirconium phase (Ti, Z
r (of type C, N, O)) or is converted into an inactive oxide phase, i.e. does not remain in an active metastable tetragonal modification. Ta.

The measured value of fracture strength was low. As mentioned above, when CrzO:+ was added together with ZrO2, the sintering temperature could be lowered to about 1600°C, and the density was still very high. In this case, 1-
A smaller, very fine grain-like microstructure was obtained. The added ZrO2 did not react further, and the structure maintained a high degree of tetragonal system.

The addition of CrzO3 occurs at grain boundaries, since the Si and other impurities coming from the raw materials accumulate in very small amounts of the crystalline phase and do not remain as a glassy film, which is known to particularly degrade high-temperature properties. It seems to further purify the . Measurements on chromium-containing materials show that this material has a high hardness with HV 1 >1900 and K rc >
It was shown that the material had a significantly high fracture toughness of 5 MPam''.

The invention therefore relates to materials with extraordinary properties based on alumina. This material of the invention combines the benefits obtained by the addition of a refractory hard component with improved fracture resistance. The favorable selection of microstructure and phase composition resulted in a combination of properties superior to those of known alumina-based compositions. Another aspect of the invention is a method for producing this type of superior material by so-called pressureless sintering.

This new composite material can be sintered at low enough temperatures to provide several advantages. - Layer-fine grain-like microstructure provides improved mechanical properties. Zirconia and hafnia, which greatly improve the toughness of ceramic-tsuku composites through a conversion toughening mechanism, can be added without being converted into other inert compounds. Typically, by adding zirconia or hafnia and sintering at higher temperatures under a protective atmosphere of nitrogen,
These compounds are converted to oxynitrides and nitrides which degrade good properties.

It is important that the added ZrO□, uroz or partially stabilized zirconia remains highly in the sintered material as a metastable tetragonal modification at low temperatures.

The relative amount of tetragonal Zr0z is higher than 70% as determined by X-ray diffraction analysis. The total amount of Zr0z is 2 to 16
w, t, %, preferably 2 to 1 O-0z1%.

Refractory materials such as carbides, nitrides or borides are particularly suitable for
It is appropriate that it be contained in the alumina composition in an amount of 50 w, t, %, preferably 10 to 4 o, t, 1%. Such materials can be present alone, in combination, or as mixed crystals, such as titanium carbonitride. Particularly suitable materials include
Mention may be made of the elements of groups IVB, VB or VIB of the periodic table or carbides, nitrides or borides of aluminium, boron, silicon, preferably titanium, zirconium, molybdenum or tungsten.

The refractory material may be present as particles and/or whiskers, fibers or platelets.

In order to obtain a preferred microstructure, it must have an average grain size of less than 10 microns, preferably less than 5 p. The diameter of the whisker or fiber is 51! IIl
It should preferably be less than or equal to 2 txn, and the length/diameter ratio should be greater than 10, preferably greater than 15. The platelets have a diameter of 5-50ρ and a diameter of 0.
It should have a wall thickness of 5-8 μm.

The amount of refractory whiskers, fibers or platelets added is 5 to 5 to give a good reinforcing effect to the alumina matrix.
greater than w,t,%, preferably 10w,t,%
It should be larger, but smaller than 40v,t,%. TiN, Tic and TiBz or mixtures of these phases in the form of whiskers are particularly suitable. The relative density should be greater than 98% of the theoretical density (TD), preferably greater than 98% of TD. The amount of simultaneously added ZrO7 and II f O2 is larger than 9% in February-September, and the amount of chromia added is 1w,
t, should be greater than %.

In order to obtain optimum properties, the inventors have determined that the phase composition of the ceramic composite is ZrO□, I
It has been found that it should contain fo□ and/or partially stabilized ZrO.The amount of ZrO□ etc. to be added is 2 to 1
6w,t,%, preferably 2 to 10iv,t,%, and the amount of tetragonal ZrO□O is greater than 70% of the amount of ZrO□ present as determined by X-ray diffraction analysis, preferably 80%.
Should be greater than %. Chromium is one of the phases mentioned above,
It must be primarily present integrated with the alumina and/or refractory hard phase, but it is also permissible to be present as a chromium entity containing phase in the microstructure. Total 1 of chromium is Cr2O.

1-2C) v,t,%, preferably 2-2C calculated as
It should correspond to 10 w,t,%. The material should be densely sintered with a relative density of greater than 98%, preferably greater than 99%. Chromium may be added in the form of other mixed oxides, hydroxides, etc. These materials are decomposed or converted into chromium containing an oxide phase during the heating or sintering process.

The ceramic material according to the invention can be further improved by coating it with a thin abrasion-resistant layer of a refractory hard material. This ceramic material has a core (core part)
In order to obtain a surface area with a different composition and/or structure, a second or second sintering treatment may be performed. This surface area is typically thicker than the sintered skin and remains even after polishing operations.

In January, the raw materials of alumina and zirconia were carefully crushed into sub-micron size. This pulverized raw material was dried and made into granules, which were then pressed to make a powder compact. This was sintered at 1600°C for 2 hours in air. The resulting densities are shown in the table below. This result is greater than 98% of TD (theoretical density) but not greater than 99% of TD in the case of more ZrO□ addition. X-ray diffraction measurements showed that the relative amount of tetragonal ZrO□ was large when the added amount of ZrO□ was small, but it decreased to 75% tetragonal ZrO when ZrO□ was added at 16 w, t, %. This example uses less than 16w,t,% of ZrO□ with a tetragonal proportion of 70%.
It can be added if it exceeds %.

To achieve density higher than 99% of TD, Bost-
) (IP (hot equilibrium breath) at 1500'c, 10
The test was carried out at 0 MPa for 1 hour. The relative amount of tetragonal ZrO□ was not changed by this hot press sintering.

Below margin 0 99.1
99.82 96 99.0
99.84 93 98.9
99.66 B5
98,9 99.7B 79
98.8 99.816
75 98.7 99.920
67 98.5 99.7
24 62 9B, 2
The raw materials for alumina and titanium nitride were carefully ground to sub-micron size. This ground raw material was dried into granules and then pressed into powder compacts. Sintering was carried out at 1775° C. for 2 hours under a protective nitrogen atmosphere.

The resulting densities are shown in Table H. This density is about 25
TiN additions up to w,t,% are higher than 98% of TD, but TiN additions are not higher than 99% of TD. A post-HIP treatment at 1600° C. and 100 MPa for 2 hours is necessary to improve the density.

In this example, despite the high sintering temperature, the addition of typical hard components such as TiN does not result in acceptable densities at additions greater than 1Qw,t,%.

0 99.1 99.810
9B, 9 99.720 98.3
99.330 97.6
99.440 96.9 99.15
A number of alumina materials doped with ZrO, TiN, Tic and CrzO= were prepared. These materials 1 to 9 were sintered at 1775° C. for 2 hours in a nitrogen atmosphere. Fully sintered blank has a temperature of about 0.1 to 0.2 at 1775℃ *wa
It had a sintered skin. Two materials (m21[L4
) was Bost-HI for 2 hours at 1600℃ and 100MPa.
Heat treated with P. Material NQlo~20 is 1650
It was sintered for 1 hour at 0.degree. C. and no undesirable noticeable sintered skin was observed. The materials related to the present invention are magnetic 10~
15 and corners 17-20. For all these materials of the invention, very good, ie high, densities were obtained despite the low sintering temperatures. Also, in these cases, ZrO2 is present and the amount of tetragonal ZrO2 is large.

130%TiN 97.6-2
30%TiN 99.4 - Post - Old 515%TiN+15%TiC96,4730
%TiN, 2%Zr0z 9B, 8 68
830%TiN, 4%Zr0t 99.5
489 30% TiN, 8% Zr0t 9
9.3 332%ZrO2,2%Crz(h
98.6 >905NGN12041
Cutting inserts of type 2 are made of materials lIh2, 3゜4, 8
, 9.10, 11, 12, 13.14 and 15 blanks. Materials Nos. 10-15 were manufactured in accordance with the present invention.

The following performance tests were conducted.

A, Steel 5S2310 (IIRC64) 60m/
Continuous turning at a speed of minutes. However, the feed rate is 0.23 mm/rotation: and the cutting depth is 0.5 m. The criterion for life is failure and the values given in the table below are the average values of 6 tests.

Below is the margin -l2" Kei - Takuji] L finishing 2 4.87 3 2.99 4 3.61 8 0.54 9 0.54 10 5.65 11 7.29 12 4.49 13 6 .93 14 5.58 15 8.21 B. Interrupted turning of cast iron on special workpieces for testing edge fracture resistance.

However, the speed is 400 m/min, the feed is 0.2 (bm/rotation, and the cutting depth is 2**.

The criterion for lifespan is failure, and the values in the table below are the average values of 15 sample tests.

− Hayashi Ichiryoichi − Kotobuki Ichimei” Kuni [ 21゜48 3 1.31 4 1.67 13 2.49 9　　　　　　　2.59 10 1.28 11 2.20 12 1, 63 13 2.45 14 2.33 15 1.27 Wear resistance in C0 cast iron turning (SSO125).

However, the speed is 600 m/min, the feed is 0.25 m5/rotation, and the cutting depth is 1. O*m.

Margin D below shows the life in turning steel (SS2541-03).

However, the cutting speed was 475 m/min, the feed was 0.30 mm/rotation, and the cutting depth was '1**.

The criterion for longevity is failure and the values in the table below are the average of three sample tests.

The following margins (--1 starvation) 21, 2 31, 2 40, 8 80, 5 91, 0 101, 5 111, 4 121, 0 131, 6 141, 4 151, 5 E, bulk destruction Interrupted turning of cast iron (S50125) in special workpieces for testing toughness.

However, the cutting speed was 500 m/min, the feed rate was 0.50 mm/rotation, and the cutting depth was 0.3 sm.

The criterion for determining lifespan is failure, and the values in the table below are the average values of 21 sample tests.

-Ta1 old (--Touji) and k 3 1.41.

10 1, 66 11 2.62 12 1.82 13 3.91 14 2.56 15 3.09 ML (Continuous turning of hardened steel (IIRC62) ball bearings.

However, cutting speed 70m/min, feed 0.711■/rotation,
Cutting depth 0.5 w, no cutting fluid, and insert type RNGN120800, tool life was the average of three tests.

Materials No. 3 and No. 15 of Example 3 were used. The insert with material TT15 had a lifespan of 5 complete inserts.
The lifespan of the inserts was 58.

■ Rising heat hardness is 100 by Vickers indentation method.
Measured with 0 g load. The materials used were 11h2, 3°8 and 15 of Example 3. Alumina doped with 4 w, t, % ZrO was used as a reference material, and an improvement in thermal hardness was observed in material grade 15 according to the present invention.

Reference 1980 1180 730 23w,t,% TiN and 7w,t as hard components
A series of alumina materials containing ,% TiC were sintered at low temperature with the addition of different metal oxides. The results are summarized in the table below.

Margin below 1600 1 87.3 ---"
2 88.5---~1650
1 88.1 ---〃2 89.7
--- 1700 1 90.4 ---〃2
91.8 --- 3.5%Crz (h 1600
1 96.2 ---〃2 -9
7.3 ---~ 1650 1 97.9 ---〃2
98. G---170019'1.
4 --- ” 2 99.7 -m-4%Z
r0z, 7% Kanazoz 1600 1 9
8.4 86II2 99. I Q3
1650 1 99.5 92〃2
99.5 92 1700 1 99.8 79〃2
99.7 82 29%ZrO, 10.5%Crz (h 1600
1 99.6 >90〃2 +00.0
>90 1650 1 100.0 >90〃210
0.0〉90 1700 1 100.0 >90〃2
100.0 >90 8%7. rth, 3.5? -6Crz(h 1
600 1 99.3 83〃2 9
9.3 87 1650 1 99.7 90〃2
99.3 80 1700 1 99.7 84〃2
99.8 83 12%7rOz, +2%CrzO31600199,
250〃2 99.6 56 1650 1 99.2 39”
2 99.2 531700 1
99.2 30712 99.6 31 4%Zr0z, 10.5%CrzOi 1600
1 99.4 74=-299,576 1650199,570 〃2 99.7 7+ 1700 1 99.8 65〃2
99.8 68 2% Zr0z, 1% gate o0z 1600 2
93.2 41'jj%ll not allowed 1650 1
95.3 = 2%1r02.6%o
0i 1600 2 91.2
”1650 ] 92.0
-22%Zr0z+10%Mo0i
1600] 89.5”lG5
0]92.2noI 2%Zr(h, 6%-0,160029,1,7l/1
650 1 95.3 ”2% Zr
O2, 6%v, o51600 2 92.716
50 1 93.0 2%Zr0z, 6%NbzOs 1600
2 97.8 >901650 1
98.6 >902%Zr0z, 10%Nbz
05 1600 2 98.8 >9
01650 1 99.1 >902%Z
r0z, 6%FezOx 1600 2
92.4 Undetectable 1650 1 92.1
Non-detectable materials according to the present invention typically provide very high densities at relatively low sintering temperatures of 1600°C. IV
B.

It is also clear that the addition of oxides of VB or VIB group elements increases the sintering ability compared to no addition.

Claims (4)

[Claims] 1. Alumina, refractory hard component phase and ZrO_2, HfO
Based on _2 and/or partially stabilized ZrO_2, 9
In a sintered body of ceramic composite material having a relative density greater than 8%, from 1 to 20 w. t. The amount of chromium corresponding to % Cr_2O_3 is between 2 and 16 w. t. % of ZrO_2, HfO_2 and/or partially stabilized ZrO_2 and
More than 0% tetragonal crystal modification and 1
Grain size particles smaller than 0 μm and/or 5p
whiskers or fibers with a diameter less than m and a length/diameter ratio greater than 10 and/or from 5 to 50μ
A sintered body, characterized in that it is integrated with a platelet having a diameter of m and a thickness of 0.5 to 8 μm. 2. Claim 1, characterized in that the refractory hard component phase is one or more carbides, nitrides, or borides of elements VIB, VB, or VIB of the periodic table, or boron, aluminum, or silicon. The described sintered body. 3. Claims 1 and 2, characterized in that the refractory hard component phase is one or more nitrides, carbides, or borides of titanium, zirconium, molybdenum, or tungsten. sintered body. 4. The sintered body according to any one of claims 1 to 3, wherein the refractory hard component phase exists as whiskers of TiN, TiC, and TiB_2 or a mixed compound thereof.