JPH04315508A - Ceramic cutting tool and manufacture thereof - Google Patents

Abstract

PURPOSE:To manufacture a cutting tool made of ceramic which sufficiently copes with cutting of gray cast iron and ductile cast iron by providing a fine ceramic texture through precise control of a sintering condition by using an Si whisker having alpha type crystal structure wherein diameter and length are specified. CONSTITUTION:Raw material powder consisting of 7-40 volume % SiC whisker which has an average diameter of 0.1-0.5mum and an average length of 2-50mum and 50% or more of which has alpha type crystal structure, 1-12 volume % ZrO2, and a rest part being substantially Al2O3 is pressurized and sintered at 1500-1700 deg.C at a pressure of 150-500kg/cm<2> for 30 minutes-five hours.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic cutting tool and a method of manufacturing the same, and more particularly to a silicon carbide whisker-reinforced ceramic cutting tool with excellent fracture resistance and wear resistance and a method of manufacturing the same.

0002

[Prior Art and Problems to be Solved by the Invention] Various cutting tools, including tips attached to the tips of cutting tools used in lathes, etc., are generally made of high-speed tool steel called high-speed steel, WC-Co series, etc. Hard metals are used, but recently Al2O3 and Al
Cutting tools made of ceramics such as 2 O3 -TiC and Si3 N4 have been developed and are in some use. Such ceramic cutting tools have high oxidation resistance, good heat resistance, and high strength at high temperatures, so they are particularly aimed at being used as tools for high-speed cutting.

[0003] However, Al2 O3 and Al2
Alumina-based ceramics such as O3 -TiC have a drawback of poor fracture resistance (low toughness). Also, Si
Since 3N4 ceramics have high reactivity with iron, cutting tools made of this type of ceramics have the disadvantage of reduced wear resistance when iron-based members are used as work materials. As described above, the range of use of conventional ceramic cutting tools is extremely limited, and there is room for improvement.

[0004] Therefore, in order to improve the fracture resistance of cutting tools made of Al2O3 ceramics, ZrO2 and/or SiC whiskers are added to Al2O3 to form composite ceramics, thereby increasing the toughness of cutting tools. Attempts have been made to increase strength, and some have been put into practical use.

For example, US Pat. No. 4,218,253 discloses a ceramic in which ZrO2 is added to Al2O3 to increase toughness and strength. Also, JP-A-61-174165 and U.S. Patent No. 496175
No. 7 discloses a cutting tool made of SiC whisker-reinforced Al2O3. In particular, in the case of composite ceramics incorporating whiskers such as SiC whiskers, the aim is to apply them to work materials that are difficult to cut, such as superalloys.

[0006] In the SiC whisker-reinforced Al2O3 cutting tools disclosed in Japanese Patent Application Laid-open No. 61-174165 and US Pat.
pany)'s Advanced Materials (Advan)
There is a description of using SiC whiskers of the ced Materials) group, that is, SiC whiskers having a single crystal structure with an average diameter of about 0.6 μm and an aspect ratio of 15 to 150.

However, according to the research conducted by the present inventors, the average diameter is about 0.6 μm and the aspect ratio is 15 to 1.
Al2O3-SiC with 50 SiC whiskers
Whisker cutting tools can perform good cutting when the work material is a superalloy such as a Ni-based superalloy.
It is not sufficient for ferrous work materials such as gray cast iron and ductile cast iron. That is, a cutting tool made of Al2O3 having SiC whiskers of such a size has a sufficient level of chipping resistance, but is inferior in wear resistance. Specifically, an Al2O3-SiC whisker cutting tool using SiC whiskers of the above size is as follows:
When gray cast iron is used as a workpiece material, it has about twice the life of a Si3 N4 cutting tool. Furthermore, when ductile cast iron is used as a work material, the tool life is approximately 1.5 to 3 times longer than that of a carbide coated tool, but such a lifespan is by no means sufficient from the viewpoint of cost/performance.

[0008] Also, in Japanese Patent Application Laid-Open No. 2-139102, A
A ceramic cutting tool consisting of l2O3-SiC whiskers-ZrO2 is disclosed. This ceramic cutting tool contains 27-35% by volume of SiC whiskers and Zr.
O2 is 3-12% by volume, the remainder is essentially Al2O3
It is made of ceramics. here,
High toughness and strength are achieved by adding ZrO2 and SiC whiskers to Al2O3 to form a composite. When ZrO2 is added to Al2O3, transformation of ZrO2 (
It absorbs the energy that would cause fracture due to the transformation (from cubic crystal to monoclinic martensite), thereby increasing the toughness of the ceramic. In addition, the introduction of whiskers can be expected to improve the strength due to the bridging effect of the whiskers (the whiskers cross the crack, forming a so-called bridge and strengthening the ceramic) at the crack forming area. Furthermore, as a multi-toughening effect, we can expect an improvement in strength due to the synergistic effect of simultaneous compounding of ZrO2 and whiskers.

[0009] In the above-mentioned Japanese Patent Application Laid-Open No. 2-139102, the SiC whiskers used have an aspect ratio of 3 to 2.
There is a description that it is from 00, but there is no particular explanation about the others. In that example, the average diameter is 0
．． 6 μm and an aspect ratio of 5 to 50 are used.

However, according to research conducted by the present inventors, when SiC whiskers with an average diameter of about 0.6 μm are used, even if the amounts of Al2O3, SiC whiskers, and ZrO2 are appropriately mixed, The dispersion of ZrO2 was not so good, and ZrO2
The effects of increasing the toughness and strength of ceramics cannot be sufficiently obtained by adding .

[0011] Accordingly, an object of the present invention is to provide a ceramic cutting tool with good wear resistance and a method for manufacturing the same, which can be sufficiently applied to iron-based work materials such as gray cast iron and ductile cast iron. It is to be.

0012

[Means for Solving the Problem] Basically, high toughness can be achieved by introducing whiskers into ceramics to form a composite, but P. F. Beocher et al.
Journal of American Ce
ramicSociety, Volume 71 (12) 105
0-1061, 1988, the increase in fracture toughness ΔK of whisker-reinforced ceramics (composites) is generally expressed as ΔK=σf [Vf ・r・Ec ・Gm /6(1−
ν2 ) Ew ·Gi ]1/2. Here, σf is the fracture strength of the whisker, and Vf
is the whisker volume fraction, r is the whisker radius, Ec is the Young's modulus of the composite, Gm is the strain energy release rate of the matrix, ν is the Poisson's ratio of the composite, and Ew is the whisker and Gi is the strain energy release rate of the whisker/matrix interface.

According to this formula, the blended amount of whiskers is (
(volume ratio), the fracture strength of the whisker is high, and the larger the whisker diameter, the better the fracture toughness of the ceramic composite.

However, in reality, defects may exist inside the whisker, so A. Kelly’s “S”
Strong Solids”,Oxford U
As stated in University Press, 1966, it is expected that the smaller the diameter of the whisker, the smaller the probability that it will have internal defects, and therefore the stronger it will be.

[0015] Also, as stated in the above book, high strength whiskers essentially have smooth surfaces. Furthermore, from the viewpoint of the crystal structure, those having sliding planes that are closer to parallel to the whisker axis are more likely to deform and have inferior strength. Comparing the two crystal types of SiC whiskers, α-type (hexagonal) and β-type (cubic), the α-type whisker, which grows in the c-axis direction, has a smoother surface, and the sliding plane is almost aligned with the whisker axis. Because the whiskers are vertical, they have higher strength than whiskers with a β-type crystal structure.

By the way, in order to evaluate the characteristics of a cutting tool, taking as an example the wear of the flank surface in a cutting test using a ferrous material as a workpiece, for example, Katsumura et al. the Japan
n Society of Powder a
nd Metallurgy), Volume 137, No. 7
, pp. 1082-87, 1990, cutting tools made of Al2O3-SiC particles have better wear resistance than cutting tools made of Al2O3-SiC whiskers. This seems to mean that in terms of improving wear resistance, it is better for the ceramic structure in the cutting tool material to be as fine as possible.

As a result of intensive research into cutting tools in consideration of the above points, the present inventors selected a system in which ZrO2 and SiC whiskers are introduced into Al2O3 ceramics. From the point of view, SiC whiskers themselves should have high fracture strength, that is, basically α-type ones, and from the point of view of wear resistance, the structure of the ceramic composite should be made as fine as possible, that is, SiC whiskers with a small diameter, and
In manufacturing the tool, the inventors discovered that if the sintering conditions were precisely controlled to create a fine ceramic structure, it was possible to obtain a ceramic cutting tool with excellent fracture resistance and friction resistance, and this led to the idea of the present invention. .

[0018] That is, the ceramic cutting tool of the present invention comprising Al2O3, SiC whiskers and ZrO2 contains 7 to 40% by volume of SiC whiskers and ZrO2
is 1 to 12% by volume, the remainder substantially consists of Al2O3, the average diameter and average length of the SiC whiskers are 0.1 to 0.5 μm and 2 to 50 μm, respectively, and % or more has an α-type crystal structure.

[0019] Furthermore, the method for manufacturing a ceramic cutting tool of the present invention includes (a) Al2O3 powder, (b) an average diameter and an average length of 0.1 to 0.5 μm, respectively, and 2.
Using a raw material powder containing SiC whiskers having a diameter of ~50 μm and having an α-type crystal structure of 50% or more, and (c) ZrO2 powder, at 1500 to 1700 °C,
It is characterized by performing pressure sintering at a pressure of 150 to 500 kg/cm2 for 30 minutes to 5 hours.

The present invention will be explained in detail below.

[0021] In the present invention, the average diameter is 0.1 to 0.5μ.
m, and SiC whiskers with an average length of 2 to 50 μm are used. If the average diameter of SiC whiskers is less than 0.1 μm, the improvement in toughness and strength will not be sufficient, and if it is larger than 0.5 μm, the fine structure of the composite ceramic will not be as fine, resulting in poor wear resistance. become inferior. Further, if the average length of the SiC whiskers is less than 2 μm, the strength cannot be improved sufficiently by the whiskers. On the other hand, if the average length exceeds 50 μm, the probability of introducing defects into the sintered body increases, resulting in a decrease in the strength of the composite.

[0022] Preferably, the average diameter is 0.2 to 0.4μ.
m, more preferably about 0.3 μm, with an average length of 10
SiC whiskers of ~40 μm, more preferably about 30 μm, are used.

Furthermore, in the present invention, at least 50% or more of the SiC whiskers used shall consist of α-type crystals. If the content of SiC whiskers having an α-type crystal structure is less than 50%, no improvement in the strength and toughness of the cutting tool is observed. Preferably, 80% or more of the SiC whiskers are of the α type.

[0024] As will be described later, ZrO2 is dispersed in the ceramic matrix of the present invention, but since ZrO2 tends to come into contact with SiC whiskers and disperse,
By using whiskers, the dispersion state of ZrO2 is improved, and a composite ceramic having a fine structure can be obtained. This greatly improves the wear resistance of the cutting tool.

[0025] In the present invention, ZrO2 and SiC whiskers are simultaneously composited into the Al2O3 matrix, and high toughness of the ceramic can be achieved by multi-toughening. From the viewpoint of increasing toughness with ZrO2, as mentioned above, the increase in toughness is achieved by absorbing fracture energy (energy when cracks occur) through the transformation of ZrO2 (transformation from cubic to monoclinic martensite). It depends. In addition, the compressive stress on the whiskers increases in the ZrO2 transformation region behind the crack (behind the crack tip in the direction in which the crack runs), which has the additional effect of making the whisker bridging mechanism stronger. . Furthermore, as mentioned above, addition of ZrO2 can suppress grain growth in the matrix and achieve a finer structure.

The composition of each component is as follows. That is, assuming that the total of Al2O3, ZrO2 and SiC whiskers is 100% by volume, the SiC whiskers are
40% by volume, 1 to 12% by volume of ZrO2, and the remainder substantially Al2O3.

[0027] If the amount of SiC whiskers is less than 7% by volume, the strength and toughness of the composite ceramic forming the cutting tool will not be sufficiently improved. On the other hand, when SiC whiskers are added in an amount exceeding 40% by volume, Al2O3
The wear resistance of the cutting tool decreases as the amount of Preferably, the SiC whisker content is 15-35% by volume.

Furthermore, if the ZrO2 content is less than 1% by volume, no increase in the toughness and strength of the finally obtained composite ceramic can be expected. Furthermore, the ceramic structure becomes insufficiently refined, resulting in poor wear resistance. on the other hand,
When ZrO2 is added in an amount exceeding 12% by volume, the hardness of the composite ceramic decreases and it does not have sufficient wear resistance as a cutting tool. Preferably, the amount of ZrO2 is 2 to 10% by volume, more preferably about 5% by volume.

A in ceramics having the above component ratio
It is desirable that the average particle size of l2O3 is 2 μm or less. When the average particle size exceeds 2 μm, wear resistance decreases. Note that the average particle size of Al2O3 in the ceramics is 2 μm.
In order to
3 and sintered by the manufacturing method described below.

Next, a method for manufacturing the Al2O3-SiC whisker-ZrO2 composite ceramic will be explained.

First, the raw materials Al2O3 powder and Zr
A predetermined amount of O2 powder and SiC whiskers of the above-mentioned standard are taken and mixed. It is preferable to use Al2O3 powder having an average particle size of about 0.3 to 1 μm. This mixing is preferably carried out sufficiently (for example, for 48 hours or more) using a ball mill or the like.

[0032] In addition, MgO, Y2 O3
, NiO, and other oxides may be added as sintering aids.

[0033] As the raw material ZrO2, Y2
A material partially stabilized with O3, CaO, HfO2, etc. may also be used.

Next, after drying the obtained mixed powder, it is put into a mold of a desired shape and pressure sintered at 1500 to 1700°C for 30 minutes to 5 hours while applying a pressure of 150 to 500 kg/cm2. I do.

[0035] Sintering at a pressure of less than 150 kg/cm2 does not make the material dense enough to withstand practical use as a cutting tool. Furthermore, since there is no difference in effectiveness even if the pressure exceeds 500 kg/cm2, the upper limit is set at 500 kg/cm2.

On the other hand, if the sintering temperature is less than 1500°C, densification of the ceramic cannot be achieved. Additionally, when sintered at temperatures exceeding 1700°C, Al2O3
grains grow, making it impossible to achieve a fine crystal structure, resulting in decreased wear resistance. Thus, in the method of the present invention, it is important to perform the sintering at a relatively low temperature, thereby reducing Al2O3 in the ceramics.
Preferably, the average particle size is suppressed to 2 μm or less.

Furthermore, if the sintering time is less than 30 minutes, densification of the ceramic cannot be achieved. On the other hand, if the sintering time exceeds 5 hours, grain growth of Al2O3 will occur, resulting in a decrease in wear resistance.

Next, the obtained sintered body is ground by a known method to produce a desired cutting tool.

[0039]

EXAMPLES The present invention will be explained in more detail with reference to the following specific examples.

Example 1 Partially stabilized Zr containing 70% by volume of α-Al2O3 (average particle size of 1 μm or less) and 2% by mole of Y2O3
5% O2 by volume, SiC whiskers (average diameter 0.3μ)
m, average length 30 μm, ratio of α-type crystals (α/(α+
A mixed powder containing 25% by volume of 80% β)) was wet mixed in a ball mill for 96 hours, and then dried.

[0041] The obtained mixed powder was heated at 1600 kg/cm2 in an argon gas stream while applying a pressure of 450 kg/cm2.
Pressure sintering was performed at ℃ for 1 hour to obtain a sintered body of 90φ x 6mm.

From the obtained sintered body, model number SNGN120
A cutting tip having a shape of 408 was cut out and ground.

Using the cutting tips obtained above, a cutting test was conducted under the following cutting conditions (cutting conditions 1).

Cutting conditions 1 Work material: Inconel 718 Cutting speed: 100 m/min Feed: 0.15 mm/rotation Depth of cut:
2mm Holder: FN11R-44A Cutting agent: Not used

Flank wear width (Va) after cutting for 1 minute
When the boundary wear width (Vn) was measured, Va was 0.11 mm and Vn was 0.23 mm.

Further, a cutting test was conducted on this cutting tip under the following conditions (cutting condition 2).

[0047] Cutting conditions 2 Work material: FCD60 Cutting speed: 300 m/min Feed: 0.1 mm/rotation Depth of cut: 1.5 mm Cutter: CSBRN2525 (150φ, test with single blade) Cutting agent: Not used

The flank wear width (Va) when cutting 250 mm in 3 passes was 0.22 mm with this cutting tip.

Comparative Example 1 For comparison, commercially available SiC whiskers (average diameter approximately 0
．． A cutting tool made of composite ceramics was produced in the same manner as in Example 1, except that the diameter was 6 μm and the aspect ratio was 15 to 150).

A cutting test was conducted on this cutting tip under cutting conditions 1 of Example 1, and the flank wear width (Va) and boundary wear width (Vn) after cutting for 1 minute were measured. The result is that Va is 0.15mm and Vn is 0.3
It was 4 mm.

[0051] Also, for this cutting tip, Example 1
A cutting test was conducted under cutting conditions 2. 250mm 3
The flank wear width (Va) during pass cutting was 0.46 mm with this cutting tip.

Si used in Examples 2 to 4 and Comparative Examples 2 to 7
Average diameter of C whiskers, ratio of crystal types, and Al2
Table 1 shows the blending amounts of O3, ZrO2, and SiC whiskers.
Al2 was prepared in the same manner as in Example 1 except as shown in
A cutting tip made of O3-SiC whisker-ZrO2 composite ceramics was produced.

A cutting test was conducted on the obtained cutting tip under cutting condition 1 of Example 1, and the boundary wear width (Vn) was measured. The results are shown in Table 2.

Further, cutting tests were conducted on the obtained cutting chips under cutting conditions 2 of Example 1, and flank wear (Va
) was measured. The results are shown in Table 3.

[0055]
Table 1 Al2 O3
SiC whisker
ZrO2
Mixture Mixture Average diameter α/(α+β) Mixture Example No. (
Capacity%) (Capacity%) (μm) (%
) (Volume %) Example 2 80
5 0.3
80 5 Example 3 60
35 0.3
80 5 Example 4
65 25 0.3
80 10 Comparative example 2
90 5 0.3
80 5 Comparative example 3
50 45 0.3
80 5 Comparative Example 4 70 25 0
．． 8 95 5
Comparative example 5 70 25
0.4 0
5 Comparative Example 6 70 25
1.0 0
5 Comparative Example 7 70 2
5 0.3 30
5

[0056]

[0057]

Examples 5, 6 and Comparative Examples 8 to 13 Cutting chips were prepared in the same manner as in Example 1 (with the same composition as in Example 1), except that pressure sintering was performed under the conditions shown in Table 4. did.

A cutting test was conducted on the obtained cutting tip under the same conditions as cutting condition 2 in Example 1. In this cutting test, the flank wear width was measured after three passes of 250 mm were cut. The results are also shown in Table 4.

[0060]
Table 4 Pressure sintering Pressure sintering Pressure sintering
boundary
temperature pressure
Time Wear width Example No.
．． (℃) (kg/c
m2) (hour) (mm)
Example 5 1620 4
50 1 0.22
Example 6 1550 3
00 1 0.27
Comparative example 8 1400 4
50 1 Lost in 10 seconds Comparative example 9 1800
450 1 0.
37 Comparative Example 10 1600
450 0.25 Comparative example 11 lost in 5 seconds 1600 450
7 Defective in 29 seconds Comparative example 12 1600 10
Comparative example 13 1800 6 lost in 0 1 51 seconds
00 1 0.24

Examples 7 to 11, Comparative Examples 14 to 21 Cutting tips obtained in Examples 1 to 4 (Examples 7 to 11 in that order),
The cutting chips obtained in Comparative Examples 4 to 11 (Comparative Examples 14 to 21 in that order) were further subjected to a cutting test under the following conditions (cutting conditions 3). The results are shown in Table 5. In addition, each cutting tip was analyzed using a scanning electron microscope to detect Al2O3.
The structure of the matrix was observed and the average particle size was measured. The results are also shown in Table 5.

Cutting conditions 3 Work material: FC25 Cutting speed: 300m/min Feed: 0.4mm/rotation Cut: 1.5mm Chip model number: SNGN120408 Holder: FN11R-44A Cutting agent: Not used Cutting time: 10 minutes

[0063]
Table 5
Flank wear width Al2 O3
Example No. (mm
) Average particle size (μm)
Example 7 0.09
0.9
Example 8 0.08
1.1 Example 9 0.19 0
．． 7 Example 10
0.17 0.8
Example 11
0.18 1.1
Comparative example 14 0.31
1.5
Comparative example 15 0.21
1.0
Comparative example 16 0.49
2.6 Comparative Example 17
0.25 1.0
Comparative example 18 0.27
0.6 Comparative example 19
0.25 2.2
Comparative example 20 0.22
0.9 Comparative example 21
0.26 2.1

00
64]

[Effects of the Invention] As explained above, the cutting tool according to the present invention has excellent chipping resistance and wear resistance. The cutting tool according to the present invention can effectively cut not only superalloys but also ferrous materials such as gray cast iron and ductile cast iron.

The cutting tool according to the present invention is suitable for various cutting tips, drills, etc.

Claims (8)

[Claims] Claim 1: A ceramic cutting tool made of Al2O3, SiC whiskers and ZrO2, in which S
iC whisker is 7-40% by volume and ZrO2 is 1-40% by volume.
12% by volume, the remainder substantially consists of Al2O3, and the average diameter and average length of the SiC whiskers are 0.1 to 0.5 μm and 2 to 50 μm, respectively,
A ceramic cutting tool characterized in that 50% or more of the SiC whiskers have an α-type crystal structure. 2. The ceramic cutting tool according to claim 1, wherein the average diameter and average length of the SiC whiskers are 0.2 to 0.4 μm and 10 to 40 μm, respectively.
A ceramic cutting tool characterized by: 3. The ceramic cutting tool according to claim 1, wherein 80% or more of the SiC whiskers have an α-type crystal structure. 4. The ceramic cutting tool according to claim 1, wherein the SiC whisker content is 15 to 35% by volume. 5. The ceramic cutting tool according to claim 1, wherein the average grain size of the Al2O3 is 2.0 μm or less. 6. The ceramic cutting tool according to claim 1, wherein the ZrO2 content is 5% by volume. Claim 7: (a) Al2O3 powder; (b)
) Average diameter and average length are each 0.1 to 0.5μ
(c) ZrO2
1500 to 170 using raw material powder containing powder.
At 0°C, at a pressure of 150 to 500 kg/cm2, 30
A method for manufacturing a ceramic cutting tool, characterized by performing pressure sintering for minutes to 5 hours. 8. The method of claim 7, wherein the ceramic cutting tool contains 7 to 40% by volume of SiC whiskers, 1 to 12% by volume of ZrO2, and the remainder is substantially Al2O3. (a) and (b) above
and (c) a method for producing a ceramic cutting tool, characterized by using a raw material powder blended with the ingredients.