JPH0551609A - Production of sintered injection-molded powder compact excellent in surface property - Google Patents

Abstract

PURPOSE:To improve the adhesion, surface roughness, etc., by providing a layer excellent in surface properties such as heat resistance on the surface layer of the sintered injection-molded powder compact by the well-known method. CONSTITUTION:A component of basic shape with the rate of shrinkage specified is injection-molded, the surface-reformed component is injection molded to 0.3-2.0mm thickness with the rate of shrinkage adjusted so that both components are firmly held to each other, and both components are then combined, degreased and sintered.

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 sintered body by injection molding which has a modified surface excellent in surface properties such as heat resistance.

[0002]

2. Description of the Related Art In recent years, the operating temperature of engines has tended to increase in order to improve their efficiency. As a material for these high-temperature parts, heat-resistant alloys centering on Ni base are widely used, but recently, in order to further increase heat resistance, parts having surface modification such as ceramics have been manufactured.

As these surface modification methods, thermal spraying, overlaying, etc. are mainly used. For example, in the combustion chamber of a jet engine, the surface in contact with the material is about 100 μm.
Thick Nichrome alloy is sprayed on the base, and about 300 μm
It is provided with a thermal insulation coating formed by spraying a thick ceramic coating (MgO + ZrO ₂ ) (Japan Iron and Steel Institute 14th Shiraishi Memorial Lecture, November 17, 1987).

On the other hand, Japanese Laid-Open Patent Publication No. 2-44056 discloses a method of manufacturing a sintered part in which parts molded by injection molding are assembled into a complicated shape and then degreased and sintered.
This technique is essentially different from the method for producing a powder sintered body by injection molding of the present invention for the purpose of surface modification.

[0005]

By the way, in the thermal spraying method or the overlay method, it is difficult to accurately control the thickness. In particular, when the shape of the parts becomes complicated, there are some areas where the surface modification layer has a non-uniform thickness and where surface modification is difficult.
Such non-uniformity of the thickness of the modified layer may lead to peeling of the layer due to thermal strain during heating and cooling.

Further, in the conventional thermal spraying method, the surface roughness after modification tends to become rough. Therefore, in rotating parts such as a jet engine, resistance to combustion gas flow increases, which causes a decrease in energy efficiency. Therefore, the present invention, in order to solve problems such as insufficient peeling resistance, increase in combustion gas flow resistance due to the large roughness of the modified surface,
It is an object of the present invention to propose a method for producing a powder sintered body by injection molding, which has a surface-modified layer having at least excellent adhesion strength and low surface roughness.

[0007]

According to the present invention, in a powder injection molding method, a basic shape part adjusted to a predetermined shrinkage ratio is injection-molded, while a surface modification corresponding to a surface modification portion of the basic shape part is performed. The shrinkage rate of the quality parts is adjusted to be larger or smaller than the shrinkage rate of the basic shape parts so that they are in close contact with each other. A method for producing a powder sintered body by injection molding, which is excellent in surface properties, characterized by performing degreasing / sintering treatment. Desirably, both are mixed between a basic shape part and a surface modified part. This is a method for producing a powder sintered body which has a composition and which is subjected to degreasing / sintering treatment with an intermediate layer interposed between the two, which is adjusted.

[0008]

[Operation] The present invention will be described in detail below. In the present invention, both the basic shape part and the surface modified part are formed by injection molding using metal powder, ceramic powder, or the like. For basic shape parts, focus on fatigue strength and toughness.
A heat resistant alloy such as a base is desirable, and these powders are kneaded with a binder composed of a thermoplastic resin, wax and other additives,
Mold into the desired shape. On the other hand, surface-modified parts were made of ceramics, heat-resistant intermetallic compounds, and other powders when heat resistance was important, and stellite and other powders when erosion resistance was important. Kneading is performed using a binder, preferably the same kind of binder, and injection molding is performed. At this time, the amount of the binder is adjusted so that the shrinkage ratio during sintering becomes larger or smaller than that of the basic shaped part depending on the usage site of the surface-modified part so that the two are in close contact.

Since the surface-modified part is thin, when it is subjected to a degreasing treatment alone, it may deform in shape.
Therefore, after assembling and integrating the parts with the molded body, degreasing,
It is necessary to perform a sintering process. Next, the thickness of the surface modification layer will be described. If the thickness of the modified layer (after sintering) is 0.3 mm or less, it does not show sufficient heat insulation. On the other hand, if the thickness exceeds 2.0 mm, the difference in the thermal expansion coefficient between the basic shape part and the modified part makes it easier to peel due to the thermal strain that occurs when the temperature rises and falls. Therefore, the thickness of the modified layer should be 0.3 mm or more and 2.0 mm or less.

As described above, according to the present invention, it is possible to accurately manufacture a complex shaped part in which different kinds of modified layers are uniformly present on the surface of the basic shaped part. Furthermore, in the present invention, by interposing an intermediate layer having a mixed composition of the basic shape part and the surface modified part, and having a shrinkage ratio adjusted between the two, The binding force of can be further improved.

Next, the present invention will be described in more detail with reference to Examples.

[0012]

[Example] By the water atomizing method, Cr 15.5 wt%, Fe
8.0 wt%, C 0.15 wt%, Mn 1.0 wt%, Si 0.5 wt%, Cu
A Ni-base heat-resistant alloy powder having an average particle size of 10 μm and containing 0.5 wt% and the balance Ni was manufactured. Also, prepare Zr ₂ O ₃ powder with an average particle size of 8.0 μm, add binders consisting of thermoplastic resin, wax, etc. to the powders mixed individually and 50 wt%, knead with a pressure kneader, and injection molding The compound was manufactured. The linear shrinkage from the compact to the sintered body was 17.4% for Ni-based powder compound and Zr ₂ O ₃ powder compound.
The compound of 17.6% and 2 kinds of powder mixture was 17.5%.

Using these parts, first, an injection-molded article was obtained which constitutes a basic-shape part made of the Ni-base heat-resistant alloy powder (A) having the shape shown in FIG. Next, surface-modified parts having the shapes shown in FIG. 2 were obtained for the Zr ₂ O ₃ powder (B) and the mixed powder (D). The surface-modified part of the shape shown in FIG. 3 Zr ₂
Using O ₃ powder (C), a surface-modified component with the same shape as shown in Fig. 4
Injection molding was performed using Zr ₂ O ₃ powder (E).

These molded bodies were combined in the combinations shown in Table 1 as shown in FIGS. 5 and 6, and then integrated, and degreased at 500 ° C. for 15 hours in a nitrogen atmosphere, and then in vacuum. Sintering treatment was performed at 1300 ° C. for 4 hours. As a comparative example, a Zr ₂ O ₃ coating was sprayed on a basic shape part by a plasma jet. The temperature of the heating point was 2200 to 2300 ° C, and the film thickness was 500 μm on average.

A 200 g steel ball was dropped from a height of 50 cm on the surface of the product after sintering (position P in FIG. 5 (center of the disk)), and the degree of peeling of the surface layer was visually determined. It can be seen that the surface modified layer according to the method of the present invention is superior in adhesiveness and surface roughness as compared with the Zr ₂ O ₃ sprayed coating of the comparative material. Further, in No. 4 in which the thickness of the surface-modified part after sintering exceeded 2.0 mm, cracking occurred during sintering.

[0016]

[Table 1]

In this example, the surface-modified component covers the outside of the basic-shaped component, but the basic-shaped component may be cylindrical and the surface-modified component may be combined with the inner surface thereof. In this case, the size of the contraction rate is opposite to that in the above-mentioned embodiment.

[0018]

EFFECTS OF THE INVENTION The present invention enables surface modification with high dimensional accuracy, and enables cost reduction in the production of complex shaped parts having excellent surface properties.

[Brief description of drawings]

FIG. 1 is a view showing a shape of a molded body.

FIG. 2 is a diagram showing a shape of a molded body.

FIG. 3 is a view showing a shape of a molded body.

FIG. 4 is a diagram showing a shape of a molded body.

FIG. 5 is a view showing combination and integration of molded bodies.

FIG. 6 is a view showing combination and integration of molded bodies.

Claims (2)

[Claims] 1. In a powder injection molding method, a basic shape part adjusted to a predetermined shrinkage rate is injection-molded, and on the other hand, the shrinkage rate of a surface-modified part corresponding to a surface modification required portion of the basic shape part is Injection molding of a material adjusted to have a shrinkage ratio larger or smaller than that of the basic shape parts so that they adhere well to each other, and then performing degreasing / sintering treatment by combining them in a thickness range of 0.3 to 2.0 mm. A method for producing a powder sintered body by injection molding, which is excellent in surface properties. 2. A degreasing / sintering process is performed between a basic shape part and a surface modified part by interposing an intermediate layer having a mixed composition of the two and having a shrinkage ratio adjusted therebetween. The method for producing a powder sintered body by injection molding, which has excellent surface properties, according to claim 1.