JPS63277577A - Production of sintered material having high toughness - Google Patents

Abstract

PURPOSE:To obtain a sintered material having high toughness, in a short time in high production efficiency, using a pressurized self-combustion sintering proc ess, by dispersing a rod like or fibrous component resistant to fusion and decom position by ignition reaction into the formed raw material. CONSTITUTION:Raw materials (e.g. a mixture of metallic titanium powder and carbon black) necessary for the production of a sintered article by pressu rized self-combustion sintering process are mixed with a rod like or fibrous component (e.g. silicon carbide whisker) resistant to fusion and decomposition in the combustion reaction. The mixture is molded to obtain a molded article containing dispersed rod-like or fibrous component. The molded article is ignited under pressure to start the combustion reaction to effect the simultaneous synthe sis and sintering by the heat generated by the combustion process to obtain the objective sintered article having high toughness. The energy of the produc tion process can be remarkably saved and the production time can be shortened.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for producing composite ceramics or cermets such as titanium carbide, titanium carbide-alumina, titanium carbide-titanium, etc., toughened with fibers.

Conventional Technology Ceramics such as titanium carbide generally have a high melting point and high hardness, making them suitable for use under harsh conditions. These ceramics generally have the disadvantage of being brittle, and therefore have not been used as bulk materials, but have mostly been used in the form of powders or coatings. However, if these ceramics can be stably used as bulk materials, material substitution will occur in various fields, and such substitution will lead to dramatic energy savings. Furthermore,
There is no doubt that the development of new industrial fields, such as space exploration, will accelerate. In recent years, improving the brittleness of ceramics has become more important than ever.

An effective method for toughening ceramics is to combine them with fibers or whiskers. Conventionally, in order to produce ceramics such as titanium carbide and titanium boride in which fibers or whiskers are dispersed, the method is to thoroughly mix the raw material powder and fibers or whiskers, then mold and sinter at a high temperature of 1,600 to 2,200 degrees Celsius for a long time. I've been exposed to it. but,
These ceramics are difficult to sinter, and producing a sintered body by this method consumes a large amount of energy. Therefore, efforts are being made to add various additives as sintering aids to lower the temperature required for densification.

Recently, as a new method for sintering ceramics, after thoroughly mixing powders of metal and nonmetallic elements (carbon, boron, etc.),
After molding, a part of the molded body is ignited under high pressure to start a reaction, and the reaction propagates sequentially throughout the body from the ignition point, and as the reaction propagates, carbides and borides are synthesized and a sintered body is produced. Simultaneous pressurized self-combustion sintering method (High pressure self-combustion sintering method)
h Pressure Self-Combustio
n Sintering Method) ;HPC8
Act) has been proposed. According to this method, high-purity ceramics can be obtained in an energy-saving process and in a short time.

Problems to be Solved by the Invention In the conventional manufacturing method of fiber-reinforced ceramics in which a mixture of raw material powder and fibers or whiskers is sintered, a relatively large amount of sintering aid is added in order to produce a dense sintered body. As a result, the bonding strength at the grain boundaries of the sintered body decreases, making it easier for cracks to propagate through the grain boundaries (this causes the problem that the effect of dispersing fibers or whiskers cannot be sufficiently obtained) .

Means to Solve the Problems In a method of manufacturing sintered bodies using the heat generated by compound formation, columnar or fibrous components that do not melt or decompose during combustion reactions are dispersed in the raw material molded body. and ignite the molded body under pressure to start a combustion reaction,
The heat generated as a result of the combustion process performs sintering at the same time as synthesis.

During the reaction process for producing the active compound, the columnar or fibrous components dispersed in the raw material molded body are surrounded by the compound in a high-temperature molten state produced by the surrounding self-heating reaction. Since the columnar or fibrous components dispersed in the raw material molded body do not generate heat, the compound in a high temperature molten state is solidified by absorbing heat from the columnar or fibrous components. At this time, a structure in which the fiber component penetrates through the crystal grains is realized. If the melting point or decomposition point of the columnar or fibrous component is lower than the maximum temperature reached by the combustion reaction, the columnar or fibrous component will completely dissolve or decompose during the combustion reaction and the columnar or fibrous structure will remain intact. The melting point or decomposition point of the columnar or fibrous component must be higher than the highest temperature reached by the combustion reaction, since the combustion reaction may not occur.

Furthermore, according to the pressurized self-combustion sintering method, a dense sintered body can be obtained with an extremely small amount of sintering aid or without the addition of a sintering aid compared to normal sintering methods. The bond strength becomes stronger, and not only toughness but also high strength can be achieved, which is extremely advantageous.

Examples Example 1 An attempt was made to produce titanium carbide reinforced with silicon carbide whiskers.

Metallic titanium powder with a particle size of 10 μ■ and carbon black made from acetylene were mixed in a ratio of 1.0:0.9.
The mixed powder is further mixed at a molar ratio of 100
10 wt of silicon carbide whiskers were wet-mixed for 20 hours. A molded body with a diameter of 25 mm and a height of 10 cm was produced by applying uniaxial pressure at a pressure of 100 MPa. After the molded body was maintained under pressure at 200° C. for 2 hours in an argon atmosphere (1 atm), the molded body was ignited and a combustion reaction was started by applying electricity to the tungsten filament provided at the bottom of the sample.

The density of the obtained sintered body measured by the Archimedes method was 96.8 zero, which is the theoretical density. When the fracture surface was observed with a scanning electron microscope, it was confirmed that the added silicon carbide whiskers had a structure in which they penetrated the crystal grains of titanium carbide that was the matrix. The fracture toughness value determined by the indentation method is 6.9 MPaJa+
Met.

Example 2 An attempt was made to produce a titanium carbide-alumina composite ceramic reinforced with silicon carbide whiskers.

Metal aluminum powder with a particle size of 10 μm, titanium oxide (Ti02) with a particle size of 1° to 2 μm, and carbon black made from acetylene were mixed in a ratio of 4.0:3.0:2.
The mixed powder was blended at a molar ratio of 7 and wet-mixed in ethanol, and then silicon carbide whiskers were wet-mixed to make the mixed powder 100%. A molded body was produced in the same manner as in Example 1, heat treated, and ignited.

The density of the obtained sintered body measured by the Archimedes method was 97.5 zero, which is the theoretical density. When the fracture surface was observed with a scanning electron microscope, it was confirmed that the added silicon carbide whiskers had a structure in which they penetrated the matrix of titanium carbide and alumina crystal grains. Fracture toughness value determined by indentation method is 9.3
It was MPaJm.

Example 3 An attempt was made to produce a cermet made of titanium carbide and titanium reinforced with silicon carbide whiskers.

A metallic titanium powder with a particle size of 10 μ is mixed with carbon black made from acetylene at a molar ratio of 1.0 F and 0.90, and then the mixed powder is set as 100 zero, and a metallic titanium powder with a particle size of 10 μ is 3Q wt, L carbonized. 10 wt of silicon whiskers *wet mixed.

A molded body was produced in the same manner as in Example 1, heat treated, and ignited.

The density of the obtained sintered body measured by the Archimedes method was 99 zero or more of the theoretical density. When the fracture surface was observed with a scanning electron microscope, it was confirmed that the added silicon carbide whiskers had a structure in which they penetrated the crystal grains of titanium carbide that was the matrix. In addition, metallic titanium well wetted titanium carbide and silicon carbide whiskers.

Fracture toughness value determined by indentation method is 7.8
It was MPaJm.

Effects of the Invention According to the present invention, since a sintered body reinforced with fibers or whiskers is manufactured using the heat generated by compound generation, the manufacturing process is very energy-saving and can be completed in a very short time, resulting in high production efficiency. will be extremely high. Moreover, the sintered body manufactured by the present invention has a structure in which the columnar or fibrous components penetrate through the crystal grains of other components constituting the sintered body, and furthermore, a large amount of sinter is present at the grain boundaries. Since there is no auxiliary agent present, the grain boundary portions are not particularly weak in terms of strength and exhibit extremely high toughness.

Claims (2)

[Claims] (1) In a method for manufacturing a sintered body using heat generated by compound formation, a columnar or fibrous component that does not melt or decompose during a combustion reaction is dispersed in a raw material molded body, and the molded body is A method for producing tough sintered bodies in which a combustion reaction is initiated by igniting the substance under pressure, and the heat generated as a result of the combustion process is used to synthesize and sinter at the same time. (2) The method for producing a tough sintered body according to claim 1, wherein the columnar or fibrous component is a silicon carbide whisker.