JP3188754B2 - Method for producing defect-free liquid phase sintered alloy - Google Patents

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 liquid phase sintered alloy such as a tungsten (W) alloy at a high yield by preventing shrinkage cavities.

[0002]

2. Description of the Related Art W-Ni-F which is one of liquid phase sintered alloys
Since e-based alloys have the characteristics of high specific gravity and high rigidity,
It has been used as a core material and quill. In the production of this W alloy sintered body, it has been required to secure and improve ductility and improve the yield.

As a method of securing and improving ductility, there is a temperature gradient imparting quenching method already disclosed by the present inventor in Japanese Patent Application Laid-Open No. 4-36428. According to the method, the cooling rate after the liquid phase sintering is set to 8 ° C./min or more, and at least one end of the sintered body is cooled from the liquid phase sintering temperature to the liquid phase forming temperature. , And a defect generation position of a shrinkage cavity is controlled by applying a temperature gradient to the shrinkage cavity.

On the other hand, as a method of improving the yield,
There is a method for preventing shrinkage cavities by replenishing latent heat of coagulation disclosed by the inventor of the present invention in JP-A-4-36407. In this method, a metal or the like having a melting point similar to that of a sintered alloy is disposed at an end of a sintered body which is rapidly cooled after liquid phase sintering. To prevent the occurrence of deep sinkholes in the area.

[0005] The basic concept of the above two methods is that during liquid phase solidification during cooling of the sintered body, a one-way temperature gradient (heat flow rate) is always applied to the sintered body from one end to the other end. That is, the liquid phase in the sintered body is unidirectionally solidified, thereby producing a sound sintered body free of defects with a high yield. In particular,
In the latter method, the surface layer at one end of the sintered body is placed in the same position as the final solidification position in order to eliminate the part that is surrounded by the solidification shell and decompressed due to solidification shrinkage and eventually becomes a shrinkage cavity. The point is to supply heat well.

However, it has been found that the coagulation latent heat replenishment method proposed in Japanese Patent Application Laid-Open No. 4-36407 has the following problems. That is, due to the shrinkage of the sintered body caused by densification at the time of sintering, a gap occurs between the latent heat supply means and the sintered body. There are cases.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and to provide a method for preventing shrinkage cavities of a liquid phase sintered body by a simple method.

[0008]

Means for Solving the Problems When the present inventors have manufactured a W alloy sintered body using a continuous sintering furnace, the sintered body manufactured under certain conditions has shrinkage cavities. Discovered that it is hardly seen. The conditions relate to the material and shape of the portion of the push rod that pushes the sintered body in the continuous furnace in contact with the sintered body, and the degree of close contact between the part and the rear end surface of the sintered body. Was. The inventor has since repeated experiments,
The present invention has been completed.

In the method for producing a defect-free liquid phase sintered alloy according to the present invention, in a cooling process after liquid phase sintering, a heat supply body is brought into contact with a part of a sintered body to supply heat to the same. By doing
The final solidification position of the liquid phase is controlled.

[0010] The liquid phase sintered alloy to which the present invention is applied is not limited to a specific material. In addition, ceramics are also included in the alloy. As an example, the sintered alloy is a tungsten alloy containing 90 to 98% by weight of tungsten, nickel and iron. Other examples include WC-Co cemented carbide, Fe
-It is applicable to Cu-based alloys and the like.

The cooling process after the liquid phase sintering in the present invention means the cooling process from the liquid phase sintering temperature to the time when the liquid phase is solidified at the final solidification position of the sintered body. After the entire sintered body is in the solid phase, the mechanism of the present invention does not work.

In the present invention, the term "heat supply body" refers to any object that discharges heat to the outside in the cooling process. Examples of the form of heat include latent heat of solidification, sensible heat released during cooling expressed by specific heat × temperature change, and the like.

In the present invention, the point is that the heat supply body is brought into contact with a part of the sintered body. By bringing them into contact, both heat conduction and heat radiation from the heat supply body to the sintered body can be increased.

The present invention makes it possible to set the final solidification position of the liquid phase to the surface layer of the sintered body. Thus, the liquid phase metal in the surface layer can be supplied to the negative pressure portion accompanying the solidification shrinkage inside the sintered body. As a result, a sintered body having no shrinkage cavity inside can be obtained.

The W alloy used in one embodiment of the present invention will be described. This W alloy has a W content of 90 to 98% by weight. If the W content is less than 90% by weight (hereinafter simply referred to as "%"), the liquid phase during sintering becomes too large and the shape of the sintered body is broken. Also, the specific gravity becomes low. If the W content exceeds 98%, the liquid phase during sintering becomes too small, and the sintering density decreases.

Nickel and iron become liquid phases during sintering and serve as sintering aids. The content is preferably 2 to 10% in total. The relative ratio between the nickel and iron contents is Ni: Fe
= 5: 5 to 8: 2 is preferred. The liquidus in this composition range,
Since the temperature of the solidus becomes the lowest and the region of the solid-liquid coexisting phase is narrowed, the sintering can be performed efficiently. Also, instead of Ni and Fe, Co is added in an amount of 0.1 to improve ductility.
You may make it contain 5% or less.

In one embodiment of the present invention, the heat supply body is a push rod for pressing a rear end surface of a sintered body in a continuous sintering furnace,
A defect-free liquid in which the contact portion of the push rod with the sintered body is made of a refractory material that does not react with the tungsten alloy, and the contact portion covers 50% or more of the same surface area including the center of the rear end surface of the sintered body. This is a method for producing a phase sintered alloy.

This embodiment will be described with reference to FIG. Inside the heating furnace 1, means for placing a sintered body such as a furnace tube 2 is provided. The sintering target 3 (formed before the sintering furnace is inserted) moves from right to left in FIG. 1 while being pushed by the push rod 4 in the furnace tube 2. The inside of the heating furnace 1 is set to the temperature distribution shown in FIG. 3, and the sintered body 3 is subjected to liquid phase sintering.

In this embodiment, the push rod serves as a heat supply. The contact portion of the push rod with the material to be sintered (hereinafter referred to as the push rod tip) is made of a material that does not react with the W alloy and does not deform or melt even at a temperature equal to or higher than the sintering temperature of the W alloy. For example, it is an alumina-based / zirconia-based refractory.

The material forming the tip of the push rod preferably has a low thermal conductivity and a large heat capacity. For example, alumina (thermal conductivity 10 to 30 W / m · k, heat capacity 0.80 to
1.00 cal / cm ³ · ° C), zirconia (thermal conductivity 0.5
~ 4.0W / mk, heat capacity 0.63-0.78cal / cm
³ ° C) is preferred.

Increasing the porosity of the refractory lowers the thermal conductivity and reduces the heat capacity. Since these changes in physical properties do not change the overall function as a heat supplier, there is no limitation in this regard. However, since the push rod is in direct contact with the sintered body, if the porosity is too large, the liquid phase of the sintered body may be inserted into the hole of the push rod and joined. For this reason, the porosity of the refractory is preferably 10% or less. The end face of the push rod that comes into contact with the sintered body
In order to prevent the liquid phase from being inserted and to supply heat efficiently, it is preferable to make the surface as smooth as possible.
The surface roughness Rmax is preferably not more than 500 μm.

It is preferable that the contact portion between the tip of the push rod and the sintered body covers 50% or more of the same area including the center of the rear end surface of the sintered body. The central portion of the rear end face of the sintered body is the portion where shrinkage cavities are most likely to occur, and it is necessary to sufficiently supply heat to the surface layer of the portion to reach the final solidification position.

In another embodiment of the present invention, a sintered body made of a tungsten alloy powder compact containing 90 to 98% by weight of tungsten, nickel and iron is subjected to liquid phase sintering using a continuous sintering furnace. At this time, a plurality of the sintering bodies are arranged in a row by inserting a spacer between each, wherein a contact portion between the spacer and the sintering body is made of a refractory material that does not react with the tungsten alloy, The contact portion covers 50% or more of the same area including the center of the end surface of the sintered body, and the rows are sequentially fed through a continuous sintering furnace, and the tungsten-based defect-free liquid phase firing is characterized in that This is a method for manufacturing a bonding gold.

This embodiment will be described with reference to FIG. The configurations of the heating furnace 1 and the furnace tube 2 are the same as those of the above-described embodiment of the push rod. The difference is that a plurality of sintered bodies 3 are arranged in tandem, and spacers 5 are inserted between the sintered bodies 3. This row is sent from right to left in FIG. 2 while sliding in the furnace tube from one end to the other end of the heating furnace in order by means such as pushing the rear end with a push rod, and is fired over the entire length of the sintered body. Is tied.

The properties required of the material forming the spacer are the same as those of the material forming the tip of the push rod described above. Further, the matters concerning the contact between the spacer and the sintered body are the same as those of the tip of the push rod.

[0026]

EXAMPLES A hydrogen-reduced tungsten powder, a carbonyl nickel powder, a carbonyl iron powder and a hydrogen-reduced cobalt powder were used as raw material powders and mixed using a V-type mixer. Molding is performed using a cold isostatic press at a pressure of ² ton / cm ² and a diameter of 3
A molded article having a length of 0 mm and a length of 400 mm was obtained. Ingredient composition is 93wt
% W-4.9 wt% Ni-2.0 wt% Fe-0.1 wt% Co. This compact was sintered by two methods, a method using a push rod shown in FIG. 1 and a method using a spacer shown in FIG.

In sintering using a push rod, a compact (sintered body) 3 was inserted into a furnace core tube 2 installed in a heating furnace 1, and the compact was moved using a push rod 4 to perform sintering. In this example, the refractory shown in Table 1 was used as the push rod. In the sintering using the spacer, the compact (sintered body) 3 and the spacer 5 were alternately inserted into the furnace tube 2 installed in the heating furnace 1 and sintered. In this embodiment, the refractory shown in Table 1 was used as the spacer. Further, the area in contact with the molded body was changed using spacers of various shapes, and the results were compared in Table 1.

[0028]

[Table 1]

In any of the sintering methods, as shown in FIG. 3, the heating furnace is set at a maximum temperature of 1530 ° C., and the molded body moves at a rate of 10 mm / min through a furnace tube sealed in a hydrogen atmosphere. Phase sintered. The sintered body taken out of the sintering furnace was subjected to a vacuum heat treatment at 1150 ° C. for 2 hours under a degree of vacuum of 10 ⁻⁴ Torr to obtain a test object. The specimen was cut to measure the shrinkage cavity depth, and the rear end of the specimen was polished to # 800, and then the presence or absence of a shrinkage cavity was examined by a dye penetration test. As shown in Table 1, in the example according to the present invention, a sintered body having no shrinkage cavity defect was obtained. On the other hand, in the case of the comparative example, there were problems such as insufficient shrinkage cavity prevention effect and reaction and fusion between the sintered body and the push rod.

The cross-sectional area ratio with the molded body in Table 1 is a value obtained by dividing the contact area between the end surface and the heat supply body by the area of the end face after sintering shrinkage of the object to be sintered, and is shown as a percentage. Things.

[0031]

As apparent from the above description, the present invention has the following effects. (1) By controlling the final solidification position of the liquid phase in the liquid phase sintered alloy sintered body by a simple method, a sintered body without shrinkage cavities can be provided. (2) It is not necessary to cut off the shrinkage cavity, and the product yield is improved. (3) In the embodiment of the W alloy, a high yield can be achieved without impairing the toughness of the alloy.

[Brief description of the drawings]

FIG. 1 is a view showing a continuous sintering method using a push rod according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating a continuous sintering method using a spacer according to an embodiment of the present invention.

FIG. 3 is a diagram showing an example of a temperature distribution in a continuous sintering furnace used in the embodiment shown in FIGS.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Heating furnace 2 Furnace tube 3 Sintered body 4 Push rod 5 Spacer

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B22F 3/10 101 B22F 3/10 C22C 1/04

Claims (2)

(57) [Claims] 1. A method for producing a liquid phase sintered alloy for controlling a final solidification position of a liquid phase by bringing a heat supply body into contact with a part of a body to be sintered and supplying heat to the part. The heat supply body is a push rod that presses the rear end face of the sintered body in the continuous sintering furnace, and a contact portion of the push rod with the sintered body is made of a refractory material that does not react with the tungsten alloy. Covers 50% or more of the surface area including the center of the rear end face of the sintered body. 2. A liquid-phase sintering process comprising a tungsten alloy powder compact containing 90 to 98% by weight of tungsten, nickel and iron in a liquid phase using a continuous sintering furnace.
A plurality of the sintering bodies are arranged in a row by inserting a spacer between them, and a contact portion between the spacer and the sintering body is made of a refractory material that does not react with the tungsten alloy, The contact portion covers 50% or more of the same surface area including the central portion of the end face of the sintered body, and the rows are sequentially fed through a continuous sintering furnace, and the tungsten-based defect-free liquid phase sintered alloy is characterized in that Production method.