JPH0741803A - Production of metal powder sintered body - Google Patents

Abstract

PURPOSE:To improve the corrosion resistance of a sintered body by forming a ceramic film on the surface of the green compact of metal powder while it is sintered. CONSTITUTION:The green compact 11 of stainless steel constituted of SUS304 with 120 mum average particle size is set on a bed, and the inside of a vacuum sintering furnace 1 is evacuated to regulate its atmospheric pressure into 1.0X10<-4> Torr. At this time, an auxiliary port 6 is also opened, and the inside of an auxiliary chamber 9 set with Al 10 is evacuated. After that, the inside of the sintering furnace 1 is heated at 120 deg.C/hr by a heater 4. In the case the auxiliary port 6 is opened at the point of time at which the temp. of the inside of the sintering furnace 1 reaches 1200 deg.C, the auxiliary chamber 9 is heated by radiation heat by the heater 4, and the Al 10 is evaporated and diffused into the sintering furnace 1. This Al is laminated on the surface of the green compact 11 and is brought into reaction with oxygen in the green compact 11 to form an aluminum oxide film on the surface of the green compact 11. In this state, heating is continued, the temp. of the inside of the sintering furnace 1 is raised to 1300 deg.C, and holding is executed for 2hr. Next, the auxiliary port 6 is closed, the heating is completed, and the sintering furnace 1 is air-cooled to obtain the sintered body.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a metal powder sintered body.

[0002]

2. Description of the Related Art In the manufacture of powder metallurgy, when molding metal powder into a predetermined shape, mold molding, hydrostatic molding, hot pressing, tape forming, extrusion molding, casting molding, metal powder injection molding, etc. Various methods are known. For example, in Japanese Unexamined Patent Publication No. 59-123302, metal powder and an organic binder are kneaded and compressed by a molding die to obtain a preform, and then the preform is sintered.

[0003]

However, whichever method is used, the metal powder sintered body after sintering is not porous but its mechanical strength is weaker than that of the ingot material. The surface is not smooth and the skin is rough. That is, the surface area for a given volume is extremely larger than that of the ingot material. In such a state, as is well known, an increase in surface area causes deterioration of corrosion resistance. Therefore, there is a problem that the corrosion resistance of the metal powder sintered body is extremely poor compared with that of the ingot having the same shape. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method capable of producing a metal powder sintered body with improved corrosion resistance.

[0004]

The manufacturing method of the present invention is characterized by depositing a metal oxide film or a ceramics film on the surface of a compact while sintering the compact of the metal powder. In the above method, the metal oxide film or the ceramic film is adhered to the surface of the metal powder sintered body to cover the surface of the sintered body, so that the corrosion resistance of the sintered body is improved.

[0005]

Example 1 FIG. 1 shows a vacuum sintering furnace 1 used in Example 1 of the present invention. In this vacuum sintering furnace 1, an exhaust port 2 is provided on a side surface portion, an auxiliary port 6 is provided on a bottom surface portion, an installation table 12 is provided inside, and a powder compact 11 formed by molding metal powder on the installation table 12 is provided. Is placed. A heating heater 4 is arranged around the installation table 12 inside the vacuum sintering furnace 1, and electric power is supplied to the heating heater 4 from a heater terminal 3 penetrating the ceiling portion of the sintering furnace 1. To be done. An exhaust bubble 7 and a leak valve 8 are attached to the exhaust port 2, and a vacuum pump (not shown) is connected to an extension of the exhaust bubble 7. On the other hand, an auxiliary chamber 9 is connected to the auxiliary port 6 via a valve 6a, and aluminum 10 is set in the auxiliary chamber 9.

In the above structure, a stainless steel powder compact 11 made of SUS304 having an average grain size of 120 μm is installed on the installation table 12 in the vacuum sintering furnace 1. Then, the exhaust valve 7 is opened, the inside of the vacuum sintering furnace 1 is evacuated by a vacuum pump, and the atmospheric pressure is set to 1.33 × 10 ⁻² Pa (1.0 × 10
^-4 Torr). At this time, the auxiliary port 6 is also opened to exhaust the inside of the auxiliary chamber 9. After that, the auxiliary port 6 is closed, the heater 4 is energized, and the temperature inside the vacuum sintering furnace 1 is increased by 120 ° C.
/ H. When the temperature inside the vacuum sintering furnace 1 reaches 1200 ° C., the auxiliary port 6 is opened again. Heating is continued in this state, the temperature in the vacuum sintering furnace 1 is raised to 1300 ° C., and the temperature is maintained for 2 hours. After that, the auxiliary port 6 is closed, the energization of the heater 4 is terminated, and the vacuum sintering furnace 1 is allowed to cool to obtain a metal powder sintered body.

In the above method, by opening the auxiliary port 6 at 1200 ° C., the inside of the auxiliary chamber 9 is heated by the radiant heat of the heater 4. This heating and atmospheric pressure is 1.33 × 1
By being 0 Pa (1.0 × 10 ⁻⁴ Torr),
Aluminum 10 evaporates and diffuses into the vacuum sintering furnace 1. And this gasified aluminum is the green compact 11
Is laminated on the surface of the powder, reacts with oxygen in the green compact 11,
An aluminum oxide film such as 10 or AlO ₂ or Al ₂ O _{3 is} deposited on the surface of the green compact 11.

In this embodiment, since the aluminum oxide film is deposited on the surface of the final metal powder sintered body, the corrosion resistance is extremely improved. Moreover, since the aluminum oxide film can be formed simultaneously with the sintering, the number of steps is not increased.

[0009]

[Embodiment 2] FIG. 2 shows a vacuum sintering furnace 1 used in Embodiment 2 of the present invention. The same elements as those in the vacuum sintering furnace of the above embodiment are designated by the same reference numerals. A gas inlet 21 having a gas inlet valve 22 is provided in the upper side surface portion of the vacuum sintering furnace 1 of this embodiment, and N ₂ gas is supplied from the gas inlet 21. Silicon 23 is set in the auxiliary chamber 9.

In the above structure, F is used as the green compact 11.
A compact made of 96% e powder and 4% Ni powder is used.
First, the exhaust valve 7 is opened, and the vacuum pump 1 is used for the vacuum sintering furnace 1.
The inside is evacuated and the atmospheric pressure is 1.33 × 10 ^-2 Pa (1.
0 × 10 ⁻⁴ Torr). At this time, the auxiliary port 6 is also opened to exhaust the inside of the auxiliary chamber 9. After that, the auxiliary port 6 is closed, the heater 4 is energized, and the inside of the vacuum sintering furnace 1 is heated at a temperature rising rate of 145 ° C./H. When the inside of the vacuum sintering furnace reaches 1000 ° C., the auxiliary port 6 is opened again, and at the same time, the gas introduction valve 22 is opened to introduce N ₂ gas into the vacuum sintering furnace 1 from the gas introduction port 21. . Heating is continued in this state, the temperature inside the vacuum sintering furnace 1 is raised to 1200 ° C., and the temperature is maintained for 3 hours.

In such a method, by opening the auxiliary port 6 at 1000 ° C., the inside of the auxiliary chamber 9 is heated by the radiant heat of the heater 4. This heating and atmospheric pressure are 1.
Since it is 33 × 10 ⁻² Pa (1.0 × 10 ⁻⁴ Torr), the silicon 23 evaporates. Then, this gasified silicon reacts with N ₂ gas filling the vacuum sintering furnace 1 to become Si ₃ N ₄ , and this Si ₃ N ₄ film adheres to the surface of the green compact 11.

Also in the second embodiment as described above, since the Si ₃ N ₄ film is deposited on the surface of the final sintered metal powder,
Corrosion resistance is extremely improved. Moreover, since the Si ₃ N ₄ film is formed simultaneously with the sintering, the number of steps is not increased.

[0013]

As described above, according to the present invention, the metal oxide film or the ceramic film is adhered to the surface of the metal powder compact while sintering, so that the corrosion resistance of the metal powder sintered body is remarkably improved. .

[Brief description of drawings]

FIG. 1 is a sectional view of a vacuum sintering furnace used in Example 1 of the present invention.

FIG. 2 is a sectional view of a vacuum sintering furnace used in Example 2 of the present invention.

[Explanation of symbols]

 1 Vacuum sintering furnace 4 Heater 6 Auxiliary port 9 Auxiliary chamber

Claims (1)

[Claims] 1. A method for producing a metal powder sintered body, which comprises depositing a metal oxide film or a ceramics film on the surface of the molded body while sintering the molded body of metal powder.