JPS61178472A - Heat treatment of silicon nitride 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 (Field of Industrial Application) The present invention relates to a heat treatment method for ceramic sintered bodies with high mechanical strength and complex shapes, particularly for ceramic sintered bodies used in high-temperature atmospheres. It is used for.

(Prior art) As a prior art related to the present invention, Japanese Patent Application Laid-Open No. 59-1469
There is a publication entitled No. 81 "Silicon nitride sintered body and its manufacturing method", which uses a pressureless sintering method to add Sr and Mg as sintering aids to silicon nitride raw material powder.

Manufacture of silicon nitride sintered bodies by adding rare earth elements and Zr oxides or oxynitrides, molding them as prepared raw materials, and then firing in a nitrogen atmosphere or inert gas atmosphere to increase strength, fracture and fracture toughness. It's a method.

(Problems to be Solved by the Invention) However, the fracture toughness of the sintered bodies manufactured by the above method for producing silicon nitride sintered bodies is 7.0 MN/mT or less on average at room temperature, and the strength is even lower at high temperatures. In particular, the silicon nitride sintered body manufactured by the above-mentioned method cannot be used as is, especially in products that have a complex shape and require high strength at high temperatures, such as turbo rotors for automobiles.

For this reason, improvement methods are being developed to increase strength and fracture toughness, such as adding more types of sintering aids, improving firing conditions, and conducting complex test processes such as evaluating each raw material. However, they all have the problem of being complicated and time-consuming, which further increases costs.

The present invention provides a relatively simple heat treatment method for increasing the fracture toughness of a silicon nitride sintered body to at least 7.0 or more.

[Structure of the invention]

(Means to solve the problem) The technical measures taken to solve the above technical problem are:
It is as follows. That is, as a silicon nitride sintered body, si,
N, , containing MgO as a sintering aid, or containing MgO, ZrO as a sintering aid, as well as Y-03, Al,, OB.

For products to which MgO etc. are added as a sintering aid, after mixing the raw materials and molding into a product shape by injection molding, approximately 180
After producing a ceramic sintered body by firing in an inert gas at a temperature of 0°C, fracture toughness is improved by holding it at normal pressure for 2 hours in an oxidizing atmosphere of 800°C to 1100°C, and then performing a heat treatment of natural cooling. It is something that increases

(Operation) The technical means is as follows. That is, S ii
0.1-15% by weight of MgO in N$&, Zr
% to 0.1 to 11% by weight of sintering aid and the balance is 70% by weight
The above S i 3 Nt was mixed, molded in a mold, fired to make a ceramic sintered body, and further heat treated at 80°C.
By keeping the ceramic sintered body in a furnace at 0 to 1100°C for 2 hours and allowing it to cool naturally, the surface of the ceramic sintered body changes from Si to N to a glassy SiO material, which significantly reduces the surface hardness. This improves fracture toughness.

A test piece with a thickness of 3 days, a medium size of 4 m, and a length of 40 cranes was made using the above method and fired in the above inert gas.
, A2. A3. ...and further 800-1100
B1, B2. B3. ...
and their fracture toughness was measured. As a measurement method, both ends of the test piece are supported, and the critical stress intensity factor Kc is determined by a microindentation method, and a comparative study is performed. For fracture toughness measurement of ceramic samples, see Ceramics Association Journal, 91.
(7) 339-43 (1983) P, 41.

Table 1 and Table 2 below show the relationship between the heat treatment temperature and fracture toughness of ceramic sintered bodies as a heat treatment method.

Table 2 The fracture toughness in Tables 1 and 2, K C represents the fracture toughness of the ceramic, and the unit is MN/m''.

From the above, the fracture toughness of the heat treatment after holding in the range of 800 to 1100℃ for 2 hours was 8.0 to 9.0, which is 10 to 15% higher than that of conventional products. Fracture toughness is also expected to be significantly improved.

(Example) Examples of the present invention will be described below.

Adding MgO and ZrO to St and N as sintering aids,
After mixing the raw materials, they are adjusted for about 300 hours to make a uniform fine powder, and after adding water, cross-wiring, and degreasing, a complex-shaped turbo rotor with blades is molded in a mold by injection molding, and the shape is tested. Pieces were also made at the same time.

Next, it was fired in an inert gas at about 1800° C. to obtain a sintered body of a turbo rotor and a test piece.

Next, it was placed in a furnace (electric furnace) under 1 atm in an oxidizing atmosphere, and the temperature was gradually increased at a rate of 10 to 15 degrees per minute, and after reaching 1000 degrees, it was kept in the furnace for 2 hours, and then naturally cooled. A sintered body and a test piece of a turbo rotor were obtained.

The result of measuring the fracture toughness of the test piece is Kc
were all 8.0 or higher.

〔Effect of the invention〕 The present invention has the following unique effects.

It is also possible to mix yttrium (Y) in addition to MgO and zro- as a sintering aid in 5t7Ntf to improve the fracture toughness at high temperatures without a heat treatment process, but yttrium is extremely expensive and its use is difficult. In contrast, the method of the present invention increases the fracture toughness by 10 to 15% by simply using a general-purpose electric furnace, which significantly reduces the cost of automobile parts. ' is preferred for what is required.

Claims (1)

[Claims] Silicon nitride powder containing MgO as a sintering aid,
Or MgO, ZrO_2, further Y_2O_3, Al
In a method for producing a silicon nitride sintered body by a pressureless sintering method using a silicon nitride raw material containing _2O_3 and MgO,
The silicon nitride sintered body was heated to a temperature of 800 to 1100 in a heating furnace.
A heat treatment method for a silicon nitride sintered body, in which the heat treatment is performed by holding the temperature constant at a temperature of ℃ for 2 hours and then cooling it.