JPH0535108B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for manufacturing a high hardness, high density silicon nitride sintered body.

Conventional technology Traditionally, ceramics are sintered by adding a binder.
It required heating and holding for at least 60 minutes at a temperature of 1,600 to 2,000°C and a pressure of normal pressure to 2,000 atmospheres.

These methods have already been disclosed in patent publications (Japanese Patent Publications No. 58-49509 and Japanese Patent Publication No. 59-3955).

Problems to be Solved by the Invention However, the above-mentioned prior art had the following drawbacks.

(1) Due to the addition of a binder, the hardness was lower than that of sintering without the addition of a binder.

(2) The density of the sintered body obtained at normal pressure to about 2000 atm can reach the theoretical density by using a binder, but it cannot reach the theoretical density if no additives are used. The drawback was that only low hardness could be obtained.

(3) In order to obtain a high-density sintered body, it is necessary to maintain the above-mentioned temperature for more than one hour, and the cost is high, which hinders industrial use.

Purpose of the Invention The present invention has been made in view of the above-mentioned circumstances, and its purpose is to enable ultra-high pressure and high temperature heating, and to achieve a high melting point and refractory material that could not be sintered conventionally without the addition of a binder. It is possible to sinter the solid material by using external heating in addition to ultra-high pressure and rapid heating using thermite, or by reducing the oxygen concentration of the raw material powder to 1.6%.
By doing the following, we have developed a method for manufacturing a high-hardness, high-density silicon nitride sintered body that can obtain a dense and highly hard sintered body without coarsening the crystal grains even in non-oxide ceramics with poor thermal conductivity. It is about providing.

Means and Effects for Solving the Problems In order to achieve the above objects, the present invention provides Al
Alternatively, a mixed composition of Si and Fe ₂ O ₃ (hereinafter referred to as a thermite composition) is filled into a high-pressure device together with a molded body made of Si ₃ N ₄ , and the mixture composition is combined with the thermite composition.
Si ₃ N ₄ is pressurized to a pressure of 1 GPa or higher to cause a reaction in the thermite composition as follows: 2Al + Fe ₂ O ₃ → Al ₂ O ₃ + 2Fe + 204Kcal Si + 2/3Fe ₂ O ₃ → SiO ₂ + 4/3Fe + 86Kcal, and this is pre-sintered. Following the preliminary sintering step, the sintered body is heated to a temperature of 1600 to 2000.
℃, pressure of 1 GPa or more for 5 to 30 minutes, and in this embodiment, Si ₃ N ₄ raw material powder with an unavoidable oxygen impurity concentration of 1.6% or less and an average particle size of 6 μm or less is used without the addition of a binder. It is designed to be sintered.

Embodiments Hereinafter, embodiments of the present invention will be described based on the drawings.

Figure 1 shows an ultra-high pressure generator. In the figure, 1 is a cylinder, 2 is a piston, 3 is a pyrofluorite gasket, 4 is a pyrofluorite insulation material,
5, 6 and 7 are steel plates, steel rings, steel plates or Mo plates, 8 is a ceramic insulation material, 9 is a graphite heater, 10 is a pyrofluorite insulation material, 11
1 is a hexagonal boron nitride molded body, 12 is a thermite composition, and 13 is a ceramic powder to be sintered.

The cylinder 1 and piston 2 form an ultra-high pressure generating container, and the pyrofluorite gasket 3 has the role of a pressure seal.

A copper plate 5, a steel ring 6, a steel plate or Mo plate 7, and a ceramic heat insulating material 8 are an assembly that supplies current to a graphite heater _{9 .} The mixture ignites a heat source for sintering ceramics by an exothermic reaction of the following formula: 2Al+Fe ₂ O ₃ →Al ₂ O ₃ +2Fe+204 Kcal, and also constitutes an external heater for sintering the ceramic powder to be sintered.

The hexagonal boron nitride molded body 11 functions to prevent the reaction between the ceramic powder 13 to be sintered and the thermite composition 12 and to provide electrical insulation from the graphite heater 9.

The ultra-high pressure generator described above is operated as follows.

Ceramic powder to be sintered 13, thermite composition 12, and other components are placed in cylinder 1, and a load is applied to piton 2 to generate a pressure of 20,000 atmospheres in the sample section. Electricity is applied to the graphite heater 9 from the opposed piston 2 to heat the sample chamber to 830 to 920°C and ignite the thermite composition 12. After thermite ignites, the sample chamber temperature is set to 1600 using the graphite heater 9.
The temperature is raised to ~2000°C in a short period of time, held for about 5 to 30 minutes, and then the sample section is cooled down, the pressure is removed, and the sintered body is recovered.

The results of the present invention will be explained based on the following examples.

Average particle size 0.6~6μm, oxygen content 0.5~2.1%
1.6 g of Si ₃ N ₄ powder was put into a disk shape with a diameter of 12.8 mm, and 10.5 gr of thermite composition, which is a mixture of Al powder and Fe ₂ O ₃ powder at a molar ratio of 2/1, was put into a disk shape with a diameter of 30 mm.
It was divided into 21.7 mm x 21.7 mm cylindrical pieces and cold-molded, and placed in the ultra-high pressure generator shown in FIG.

These ceramics to be sintered were subjected to the pressure and heat sintering treatment described above. The pressure is 20,000 atmospheres, and the thermite calorific value is 10 Kcal. The temperature of the sample part heated by the graphite heater after thermite ignition was 1800℃. The relative density and hardness of the obtained sintered body are shown in Figure 2.
It is shown in Figure 3.

The Si ₃ N ₄ raw material powder with an oxygen concentration of 1.6% or less was densified to a relative sintering density of 98 to 99% or more without the addition of a binder, and the hardness of the sintered body increased to 1800 to 2100 Kg/mm ² or more. FIG. 4 shows the effect of pressure on the relative density of the sintered body. If the sintering pressure is less than 10,000 atmospheres, decomposition of Si ₃ N ₄ will occur at the same time, and densification will be insufficient. Although increasing pressure tends to promote densification, when comparing the properties of the sintered body obtained and the cost of generating ultra-high pressure,
10,000 to 20,000 atm is preferable.

FIG. 5 shows the relationship between the hardness and oxygen content of Si ₃ N ₄ subjected to normal high-pressure sintering in comparison with FIG. 2.
From the comparison between the two, it is clear that the low oxygen Si ₃ N ₄ sintered body obtained by the sintering method of the present invention has significantly superior hardness.

Effects of the Invention As detailed above, the method for producing a high-hardness, high-density silicon nitride sintered body according to the present invention combines Al or Si and Fe ₂ O ₃
The mixed composition (hereinafter referred to as thermite composition) of
The thermite composition and Si ₃ N ₄ are put into an ultra-high pressure generator together with a molded body made of Si ₃ N ₄ under pressure.
Pressure is applied to 1 GPa or more to cause a reaction in the thermite composition as follows: 2Al + Fe ₂ O ₃ → Al ₂ O ₃ + 2Fe + 204 Kcal Si + 2/3 Fe ₂ O ₃ → SiO ₂ + 4/3 Fe + 86 Kcal, and pre-sintering is performed. Following this pre-sintering step, The temperature of the sintered body is 1600~2000
℃ and a pressure of 1 GPa or higher for 5 to 30 minutes.

Therefore, ultra-high pressure and high temperature heating is possible.
High melting point, which previously could not be sintered without the addition of a binder.
It is possible to sinter difficult-to-sinter materials. By using external heating in addition to rapid heating using ultra-high pressure and thermite, and by keeping the oxygen concentration of the raw material powder to 1.6% or less, non-oxide ceramics with poor thermal conductivity can be made dense and highly hard without coarsening the crystal grains. A sintered body is obtained.

Due to the above effects, industrially extremely useful non-oxide ceramic materials can be produced. For example, the Si ₃ N ₄ sintered body shown in the example has higher hardness than conventional materials without the addition of a binder, and is promising as a cutting tool.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram of the configuration of the ultra-high pressure generator used in the method of the present invention, Figure 2 is a diagram of the relationship between the relative sintered density of Si ₃ N ₄ and the amount of oxygen, and Figure 3 is a diagram showing the hardness of the Si ₃ N ₄ sintered body. Figure 4 contains 1.0wt% oxygen.
FIG. 5 is a graph showing the effect of pressure on the relative sintered density of Si ₃ N ₄ , and is a graph showing the relationship between the hardness of the normally high-pressure sintered Si ₃ N ₄ sintered body and the amount of oxygen.

Claims (1)

[Claims] 1. A mixed composition of Al or Si and Fe ₂ O ₃ (hereinafter referred to as a thermite composition) is filled into an ultra-high pressure generator together with a molded body made of Si ₃ N ₄ , and the said thermite composition is and Si ₃ N ₄ are pressurized to a pressure of 1 GPa or more to cause a reaction in the thermite composition as follows: 2Al + Fe ₂ O ₃ → Al ₂ O ₃ + 2Fe + 204 Kcal Si + 2/3 Fe ₂ O ₃ → SiO ₂ + 4/3 Fe + 86 Kcal, and pre-sintering is performed. Following this preliminary sintering step, the sintered body is heated to a temperature of 1600 to 2000.
A method for producing a high-hardness, high-density silicon nitride sintered body, characterized in that sintering is carried out at a temperature of 5 to 30 minutes at a temperature of 1 GPa or higher. 2. The high-hardness, high-density silicon nitride sintered body according to claim 1, which is sintered without adding a binder using Si ₃ N ₄ raw material powder with an unavoidable oxygen impurity concentration of 1.6% or less and an average particle size of 6 μm or less. Manufacturing method.