JPH0762406A - Production of powder hot compact material - Google Patents

Abstract

PURPOSE:To provide a production method of the powder hot compact material by which the material is subjected to very easy HIP treatment without sealing a compact body or sintered compact into a capsule and improved fatigue strength is attained. CONSTITUTION:The powder coating body coated with a scaly powder on the surface of a powder compact body or the sintered compact formed by sintering the powder compact body is formed. In this way, the open bores existing on the surface of the compact body or the sintered compact are clogged surely by the high density layer of the scaly powder. This powder coaing body is exposed to high temp.high pressure as it is to be subjected to HIP treatment and a powder hot compact material is formed. The obtained material has compacted surface and attains improved fatigue strength effectively.

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 powder hot forming material from raw material powder such as metal powder or ceramic powder.

[0002]

2. Description of the Related Art Heretofore, a method utilizing HIP treatment has been known as a method for sintering a compact formed from raw material powder such as metal powder or ceramic powder to high strength and true density. For example, Japanese Unexamined Patent Publication No. 3-55739 discloses a sintering method using HIP treatment as described below. First, a molded body having a predetermined shape is formed from the raw material powder by dry press molding, the molded body is housed in a capsule, and then the boron nitride (BN) powder is filled in the capsule,
Furthermore, the inside of the capsule is vacuum sealed. Then, this capsule is housed in a HIP processing furnace, and under an argon gas atmosphere,
Raise the temperature to 1000 ° C and 1500 atm, pressurize for 90 minutes,
HIP treatment is performed to obtain a sintered body.

Further, it is possible to increase the strength by sintering a compact formed from the raw material powder by press molding or the like, and further encapsulating the sintered compact in the same manner as above and HIPing it. Has been done.

[0004]

However, in the above-mentioned conventional method, when the molded body formed from the raw material powder or the sintered body obtained by sintering the molded body is subjected to the HIP treatment, the molded body or the sintered body is obtained. Must be enclosed in a capsule,
It was troublesome, and this capsule had to be removed later by machining or the like. It should be noted that encapsulating the molded body or the sintered body in the capsule in this way is because there are a large number of open pores (holes communicating with the outside world) on the surface of the molded body or the sintered body, so that the HIP treatment is performed. This is because the pressure transmitting gas of No. 2 passes through the open pores, the external pressure becomes equal to the internal pressure of the pores, and the HIP process cannot be performed.

The present invention has been made in view of the above circumstances, and makes it possible to carry out HIP processing very easily without encapsulating a molded body or a sintered body in a capsule, and at the same time, treat the surface of the member. It is a technical problem to be solved to provide a method for producing a powder hot-formed material capable of effectively increasing the fatigue strength by increasing the density from the inside to the inside.

[0006]

A method for producing a powder hot-formed material according to the present invention, which solves the above-mentioned problems, comprises a powder compact or a flaky powder on the surface of a sintered compact obtained by sintering the powder compact. And a step of forming a powder coated body by exposing the powder coated body as it is to high temperature and high pressure to perform a HIP treatment. To do.

The kind of raw material powder is not particularly limited, and various metal powders, ceramic powders, or a mixture thereof can be used. The type of the scaly powder is also not particularly limited, but it is preferably one that does not generate impurities, melt, or sublime during heat treatment or by reacting with the pressure transmitting gas. If impurities are generated or the flaky powder is melted during HIP processing, these can get into the open pores of the compact or sintered body and become impurities when it becomes the final product. If the scaly powder is sublimated, the effect of applying the scaly powder to the surface of the molded body or the sintered body is lost. As a preferable kind of the flaky powder,
Examples thereof include graphite, boron nitride (BN), molybdenum disulfide (MoS ₂ ), metal powder and the like.

Regarding the size and the amount (thickness) of the scale-like powder, when the surface of the compact or the sintered body is coated, the open pores existing on the surface are surely closed. There is no particular limitation as long as it is possible. The preferred size of the flaky powder can be 1 μm to 500 μm, and the thickness to be applied is 0.05 to 0.5.
It is preferably mm.

Further, the method of applying the flaky powder to the surface of the molded body or the sintered body is not particularly limited, and a spray coating method, a brush or a roll coating method can be employed.

[0010]

In the powder coated body obtained by coating the surface of the powder compact or the sintered body with the flaky powder, the open pores existing on the surface of the compact or the sintered body have a high density layer of the flaky powder. Is securely blocked by. Therefore, when the powder coating body is subjected to high temperature and high pressure, the pressure medium does not communicate with the pores existing inside the powder coating body so that the internal pressure and the pressure medium are not the same. Therefore, the powder medium can be surely compacted by the pressure medium. Therefore, according to the present invention, it is not necessary to enclose the powder coated body in a capsule or the like as in the conventional case, and it is possible to perform the HIP treatment extremely easily.

Further, when the powder coating body whose open pores on the surface are blocked by the flaky powder is subjected to the HIP treatment, the surface of the treated member can be smoothed and compacted. Therefore, the powder hot forming material obtained by the present invention can effectively improve the fatigue strength.

[0012]

EXAMPLES Examples embodying the present invention will be described below. (Example 1) A columnar shape (size: 14 x 17 x 100 mm) was formed from pure iron powder (average particle size: 75 µm) by press molding (pressure: 500 MPa), and a compact density: 6.8 g.
A powder compact of / cm ³ was obtained.

On the surface of this powder compact, a paste of scaly graphite powder (size: 10 μm) is applied in an amount of about 0.1 to 0.3.
After coating with a thickness of mm, under nitrogen atmosphere, 600 ℃ × 3
It was dried under the condition of 0 minutes. Then, the powder compact coated with the scaly powder is housed in a HIP processing furnace,
HI under the nitrogen gas atmosphere of a under the condition of 1150 ° C. for 1 minute
P treatment was performed to obtain a powder hot compact as a sintered body.

The density of the obtained powder hot forming material was 7.83 g / cm ³ , which was close to the true density. (Example 2) Al-17Si-4Cu-0.5Mg (J
Aluminum powder equivalent to IS A390 (average particle size:
D ₅₀ = 35 μm) was adopted as a method of die lubrication (as the oil lubricant, zinc stearate was dissolved in alcohol), and 600
Mold press molding was performed at a pressure of MPa to obtain a powder compact having a plate bending test piece shape. The density of the molded body at this time is 2.
It was 21 g / cm ³ .

Next, the powder compact was sintered in a nitrogen gas atmosphere at 480 ° C. for 1 hour to obtain a sintered compact. The zinc stearate adhering to the surface at this time was dewaxed. On the surface of this sintered body, a paste of scaly aluminum powder (size: 10 μm) was added in an amount of about 0.
After being applied in a thickness of 2 mm, it was gradually heated under a nitrogen atmosphere and dried at 200 ° C. for 60 minutes.

Next, the sintered body coated with the above-mentioned scaly powder was placed in a HIP processing furnace, subjected to HIP processing under a nitrogen gas atmosphere of 180 MPa at 500 ° C. for 1 minute, and sintered forged. A powder hot forming material as a material was obtained. The density of the powder hot forming material at this time was 2.80 g / cm ³ . (Evaluation of Fatigue Strength) With respect to the test piece of the powder hot forming material obtained by the same method as in Example 2 above, as the T6 treatment, the test piece was heated under the condition of 480 ° C. × 1 hour, cooled with water, and then cooled with 175.
Aging treatment was carried out at 10 ° C for 10 hours. And the plate bending fatigue test of this test piece was implemented. The results are shown in Table 1.

Comparative Example 1 A sintered body was obtained by the same method as in Example 2 above. And using a forging die, temperature: 5
The mold was hot forged under the conditions of 00 ° C. and pressure: 400 MPa. The same T6 as above was applied to the obtained test piece.
After the treatment, a plate bending fatigue test was carried out. The results are also shown in Table 1.

[0018]

[Table 1] As a result, it was confirmed that the sintered forged material obtained in Example 2 can improve the bending fatigue strength as compared with the one obtained by hot forging using the forging die of Comparative Example 1. This is because in the method of Comparative Example 1 using a forging die, the surface layer portion of the sintered body comes into contact with the forging die during forging, so that the deformation resistance increases due to cooling from the forging die and the sliding resistance with the forging die causes. It is considered that, while the surface layer portion could not be sufficiently consolidated, the method of Example 2 did not adversely affect the forging die, and the surface layer portion was sufficiently consolidated.

[0019]

As described above in detail, according to the method for producing a powder hot compact of the present invention, the powder compact or the sintered compact is coated with the flaky powder on the surface of the powder compact, and the HIP is applied as it is.
Since it is processed, it is not necessary to enclose the powder coated body in a capsule at the time of HIP processing as in the prior art, and it is extremely easy to obtain a powder hot forming material having a high density and high strength by the HIP processing. it can.

Further, since the surface of the hot molded powder material obtained by the method of the present invention is densified, the fatigue strength can be effectively improved. Furthermore, according to the present invention, graphite, boron nitride, molybdenum disulfide, etc., which are solid lubricants, are used as the scaly powder, and this compact is slidable after HIP without removing them from the surface of the powder hot compact. When used as a moving member, the sliding characteristics are improved.

Claims (1)

[Claims] 1. A step of applying a flaky powder to the surface of a powder compact or a sintered body obtained by sintering the powder compact to form a powder coated body, and the powder coated body as it is. high temperature,
And a step of forming a powder hot forming material by subjecting it to HIP treatment by exposing it to a high pressure.