JPH0526746B2 - - Google Patents

Description

[Detailed description of the invention]

B. Field of Industrial Application The present invention relates to an alumina-silicon carbide heat-resistant composite sintered body and a method for manufacturing the same. The present invention relates to the alumina-silicon carbide heat-resistant composite sintered body having high high-temperature hardness and suitable as a material for high-temperature structures, and a method for manufacturing the same. B. Prior Art Alumina is most widely used among ceramics, such as integrated circuit substrates and packages, and chips for cutting tools. However, although alumina is a chemically extremely stable substance, its mechanical strength decreases at temperatures above 800°C, which is relatively low for ceramics, so it is not suitable for cutting tools whose cutting edges are heated to high temperatures during use. Silicon nitride and silicon carbide are not satisfactory as materials for chips, and silicon nitride and silicon carbide are used in that field. Ceramics mainly made of alumina are
It is easier to sinter than silicon nitride and silicon carbide,
If the mechanical properties at high temperatures are improved, the range of applications will be further expanded. An alumina-zirconia composite sintered body is known as an example of improving the mechanical properties of alumina ceramics by combining a second phase. Special Public Service 1984-
Publication No. 25748 describes that metastable tetragonal crystals of zirconia are allowed to remain at room temperature, and due to the residual compressive stress caused by the approximately 4% volume expansion of the tetragonal to monoclinic transformation induced by the stress at the crack tip. , discloses a technique that significantly improves mechanical properties at room temperature.
However, at high temperatures above about 900° C., which is the temperature of the above-mentioned transformation, the above-mentioned effects cannot be expected. In addition, as an example of improving the mechanical strength of alumina ceramics at room temperature, Wahi et al.
Journal of Materials Science 15875-885,
As reported in 1980, there is an example of combining titanium carbide. In addition, as an example of improving the fracture toughness of alumina ceramics, although the mechanical strength is not improved, Mc and Cauley report on Ceramic Engineering
Ceramic Engineering Science Proceedings by Ba-Mica and Rice, as reported in Science Proceedings 2639-660, 1982.
2639-660, 1982, there is an example of a composite of plate-shaped boron nitride, but none of these papers mention mechanical properties at high temperatures. C. Purpose of the Invention The present invention has been made in view of the above-mentioned circumstances. The object of the present invention is to provide a tool tip and a method for manufacturing the same. D. Structure of the Invention The first invention is such that silicon carbide whiskers exhibiting a fibrous shape with a diameter of 0.5 μm or less and a length of 20 μm or less are substantially separated from each other in an alumina matrix and have a volume ratio of 2 to 20 μm.
Relates to a cutting tool tip made of ceramics with a 30% dispersed structure. The second invention is to form a mixed powder consisting of 2 to 30 volume % of silicon carbide whiskers exhibiting a fibrous shape with a diameter of 0.5 μm or less and a length of 20 μm or less, and the remainder being substantially alumina powder, and The present invention relates to a method for manufacturing a cutting tool chip according to the first invention, which is sintered at a temperature within a range of 1800°C. The destruction of alumina ceramics at high temperatures is
Evans et al. Fracture Mechanics of Ceramics,
6423-448, 1983, it is controlled by cavitation (nucleation of cracks) under stress and the growth and coalescence of cracks until they reach a critical crack size (sub-critical), but both Preferential diffusion at grain boundaries and localized stress states are the subject of ideas. As a result of intensive research, the inventor discovered that silicon carbide particles with an average particle size of 3 μm or less, or silicon carbide fibers (whiskers) with a diameter of 0.5 μm or less and a length of 20 μm or less, were incorporated into an alumina matrix independently (separated from each other). mechanical properties at high temperatures by providing localized residual stress at the alumina matrix grain boundaries or by providing conditions that resist atomic diffusion and crack growth at the grain boundaries. It has been found that the properties can be improved. The above mechanism will be explained in detail below. A case in which the silicon carbide particles are smaller than the alumina crystal grains and a case in which the silicon carbide particles are approximately the same size will be considered.
Furthermore, in the former case, we will consider cases in which silicon carbide particles are present at grain boundaries in the alumina matrix and cases in which silicon carbide particles are present within crystal grains. Silicon carbide particles are smaller than alumina crystal grains,
If silicon carbide particles 2 exist at grain boundaries in the alumina matrix, as shown schematically in Fig. This is because silicon carbide has a smaller thermal expansion coefficient than alumina), which is unfavorable for cavitation and crack growth, but moreover, it narrows the diffusion path of atoms in the three grain boundary phases under high temperature stress, resulting in overall The mechanical properties at high temperatures are improved by slowing the diffusion rate of silicon carbide particles and by forming bridges on three grain boundary surfaces and acting as resistance to crack growth. From the viewpoint of forming crosslinks at grain boundaries, fibrous silicon carbide has a greater effect than silicon carbide particles. When silicon carbide particles exist within the crystal grains of the alumina matrix, as schematically shown in Figure 2, a compressive residual stress Sc is applied to the three grain boundaries of the alumina crystal grains 1 in the vicinity of the silicon carbide particles 2, Relieves local stress levels and improves mechanical properties at high temperatures. If the silicon carbide particles are about the same size as the alumina crystal grains, as schematically shown in Figure 3,
Compressive residual stress on the three grain boundary surfaces of alumina crystal grains 1 perpendicular to the external tensile stress So above and below silicon carbide particles 2
Sc and improves mechanical properties at high temperatures. Further, tensile residual stress St is applied to the left and right grain boundary 3a planes of silicon carbide particles 2, which is not preferable for cavitation or crack growth, but moreover,
The silicon carbide particles act to prevent the left and right cracks from coalescing, improving mechanical properties at high temperatures. Note that the maximum compressive residual stress exists at the silicon carbide particle/alumina crystal grain interface, and crack growth along this interface is difficult, and fracture will not occur along this interface. Although the case where silicon carbide is in the form of particles has been described above, the principle is similar to that described above when silicon carbide is in the form of fibers. From the foregoing, it can be understood that silicon carbide dispersed in the alumina matrix improves mechanical properties at high temperatures by substantially separating and dispersing the silicon carbide from each other. Residual stress near the silicon carbide particles or fibers is caused by the difference in thermal expansion coefficients between silicon carbide and alumina. The former has a smaller coefficient of thermal expansion than the latter. Silicon carbide, which has higher high-temperature hardness than alumina, contributes to the hardness at high temperatures. In the case of silicon carbide fibers, the improvement in high temperature hardness is particularly remarkable. The present invention has been made based on the above findings. Next, each phase constituting the sintered body, sintering conditions, etc. will be explained. The α-type alumina constituting the matrix can be conveniently used, but other crystal forms such as the γ-type may also be used. Purity is preferably 98% or higher, and particle size is the average particle size.
Those having an average particle diameter of 5 μm or less are preferable, and those having an average particle size of 1 μm or less are more preferable. The silicon carbide dispersed in the matrix may be in the α-type or β-type crystal form. The purity is preferably 98% or more, and the shape may be equiaxed (particle), but fibrous is particularly preferable. The average particle size of the silicon carbide particles is 3 μm or less. If this exceeds 3 μm, microcracks will occur during cooling to room temperature after sintering, and the mechanical strength at room temperature will decrease. In the case of fibrous silicon carbide, the diameter is 0.5 μm or less and the length is 20 μm.
The following shall apply. If the diameter exceeds 0.5 μm or less, microcracks are likely to occur as in the case of the above particles, and if the length exceeds 20 μm, the silicon carbide fibers become entangled and cannot be separated from each other, especially at room temperature. Mechanical strength begins to decrease. The proportion of silicon carbide in the matrix is 2 to 30% by volume of the entire sintered body (the area ratio under a microscope is also 2 to 30%). If this amount is less than 2% by volume, the effect of improving high temperature strength will not be noticeable, and if this amount exceeds 30% by volume, there will be many areas where silicon carbide comes into contact with each other, and the mechanical strength at room temperature and high temperature will be reduced. It then begins to decline. If silicon carbide is fibrous, the upper limit of the amount of dispersion is 20
Particularly preferred is volume %. Although the sintered body according to the present invention is composed of two components, alumina and silicon carbide, there may be a small amount of other components contained as impurities in the raw material. Furthermore, as in the case of a typical alumina-based sintered body, it is preferable to contain a small amount of magnesia (MgO) in order to suppress the growth of alumina crystal grains during sintering. As the molding method, all customary molding methods such as press molding, slurry casting, injection molding, and extrusion molding can be employed. Of course, hot pressing can also be used. Sintering at 1400~1800 in vacuum or non-oxidizing atmosphere
Perform at a temperature within the range of °C. If the sintering temperature is lower than 1400℃, the density of the obtained sintered body will be low,
At high temperatures exceeding 1800°C, abnormal growth of alumina crystal grains occurs, and in both cases, mechanical strength and hardness at room temperature and high temperature decrease. The optimum sintering temperature varies depending on pressureless sintering, hot pressing and amount of silicon carbide. When the amount of silicon carbide is 2 to 15% by volume in normal pressure sintering, the temperature is preferably 1600 to 1700°C, and when the amount is 15 to 30% by volume, the temperature is preferably 1700 to 1800°C. When the amount of silicon carbide in the hot press is 2 to 15% by volume, the temperature is preferably 1400 to 1600°C, and when the amount is 15 to 30% by volume, the temperature is preferably 1600 to 1700°C. E. Examples Specific examples of the present invention will be described below. Alpha-type alumina powder with a purity of 99% or more and an average particle size of 0.7 μm is blended with silicon carbide powder or fiber length 9 μm as shown in Table 1 below, and mixed with ethyl alcohol in a ball mill using a plastic container and alumina balls. A liquid mixture was wet-mixed for 1 hour and dried to form a mixed powder. After press-molding these mixed powders, it is made into a compact of approximately 20 x 50 x 15 mm by isostatic hydrostatic pressure of 1500 kg/ ^cm2 , and this compact is sintered in an argon gas stream under the conditions shown in Table 1. Sintered.

[Table] A 3 x 4 x 36 mm bending test piece and a 3 x 4 x 4 mm hardness test piece were taken from these sintered bodies using a diamond grindstone and a diamond blade. A mirror finish was applied to the hardness test piece using a 1 μm diamond grindstone. Note that the density of the hardness test piece was measured before the hardness test. The bending test was performed using an outer fulcrum distance of 30 mm and an inner fulcrum distance of 30 mm.
The hardness test was performed using a 4-point bending test method with a crosshead speed of 10 mm and a crosshead speed of 0.5 mm/min using a Vickers hardness tester at a load of 1 kg in an argon flow. The test temperatures for both tests were room temperature, 1000°C, and 1200°C. The test results are also listed in Table 1. From the same table, the alumina-silicon carbide heat-resistant composite sintered body according to the example has the same bending strength and hardness at room temperature as the conventional single-phase alumina sintered body, and has lower bending strength and hardness at high temperatures. It can be seen that both have been significantly improved. In addition, the sintered body in which fibrous silicon carbide is dispersed has higher hardness at both room temperature and high temperature than the sintered body in which granular silicon carbide is dispersed, and its bending strength is further improved, especially at high temperatures of 1200°C. has been done. Next, the results of an experiment on the cutting performance of a cutting tool tip made of an alumina-silicon carbide fiber sintered body will be explained. Silicon carbide fibers (whiskers) with an average particle size of 0.2 μm and an average length of 9 μm were blended with α-type alumina powder with a purity of 99.9% or more and an average particle size of 0.7 μm as shown in Table 2 below, and the same as above was added. After wet mixing with a ball mill to sufficiently uniformly disperse the mixture, the mixture was dried. This mixed powder was mixed in an argon gas stream for 1 hour to obtain a diameter.
It was pressure sintered to a size of 90mm and 6mm thick. In the pressure sintering, the molding pressure was 450 kg/cm ² and the sintering temperature is shown in Table 2. The model number is determined from the sintered body thus obtained.
A cutting chip of SNGN120408 was cut and ground, and a cutting test was conducted under the conditions shown below. Cutting test conditions Work material Spheroidal graphite cast iron FCD60 (round bar) Cutting speed 300 m/min Feed 0.3 mm/rev Depth of cut 1 mm Cutting oil dry Cutting time 105 seconds The test results are shown in Table 2. For comparison, Table 2 shows the results of similar tests using a chip containing 40% by volume of silicon carbide fiber, a commercially available alumina cutting chip, an alumina-titanium carbide cutting chip, and a silicon nitride cutting chip. is also listed.

【table】

[Table] From Table 2, it can be seen that the chips based on the present invention have significantly improved durability compared to the comparative chips. F. Effects of the Invention The cutting tool tip based on the present invention has a diameter of 0.5 μm.
Hereinafter, since the ceramic is made of a structure in which fibrous silicon carbide whiskers with a length of 20 μm or less are dispersed in an alumina base material in an amount of 2 to 30% by volume, they are substantially separated from each other. It has extremely high mechanical strength and hardness, and with very little wear, it can withstand long-term use. Further, as described above, the manufacturing method according to the present invention requires only the use of ordinary ceramic manufacturing equipment and does not require any special equipment, so that the manufacturing cost is low.

[Brief explanation of the drawing]

The drawings are diagrams schematically showing the microscopic structure of the alumina-silicon carbide heat-resistant composite sintered body according to the present invention and the state of residual stress in the vicinity of silicon carbide particles.
The figure is a schematic diagram of silicon carbide particles existing at the grain boundaries of alumina, Figure 2 is a schematic diagram of silicon carbide particles existing within alumina crystal grains, and Figure 3 is a schematic diagram of silicon carbide particles and alumina crystal grains. FIG. In addition, in the symbols shown in the drawings, 1...Alumina crystal grain, 2...Silicon carbide particle, 3...Alumina crystal grain boundary, 3a...Alumina crystal grain boundary in contact with silicon carbide particle, St... Residual tensile stress, Sc...
Residual compressive stress, So...external tensile stress.

Claims (1)

[Claims] 1. Silicon carbide whiskers exhibiting a fibrous shape with a diameter of 0.5 μm or less and a length of 20 μm or less are contained in an alumina base.
A tip for a cutting tool made of ceramics having a structure that is substantially separated from each other and dispersed by 2 to 30% by volume. 2 Form a mixed powder consisting of 2 to 30% by volume of silicon carbide whiskers exhibiting a fibrous shape with a diameter of 0.5 μm or less and a length of 20 μm or less, and the remainder being substantially alumina powder, and heat this compact at a temperature in the range of 1400 to 1800°C. A method for producing chips for cutting tools that is sintered at high temperatures.