KR100568970B1 - Method of sintering body having high hardness - Google Patents

Abstract

The present invention relates to a method of manufacturing a high hardness sintered body in which a polycrystalline diamond (PolyCrystaline Diamond (hereinafter referred to as PCD)) high hardness layer is formed on a cemented carbide substrate.

Preparing a sintered raw material powder containing diamond powder; Placing the sintered raw material powder on a WC / Co based cemented carbide substrate; The cemented carbide substrate and the sintered raw material powder are at least one selected from the group consisting of catalyst transition metals belonging to 4 to 6 cycles of Groups 4 to 6 and their carbide, nitride, carbonitride and intersolvent compounds of the catalyst transition metal. Charged into a sintered crucible comprising a high melting point material and a low melting point material which is one or more binders selected from Fe, Co, and Ni, and sintered under high temperature and high pressure where diamond is stable, thereby forming a PC (PolyCrystaline Diamond) on the cemented carbide substrate. Forming a high hardness layer.

According to the present invention, it is possible to prevent abnormal diamond grain growth of the PCD layer of the high hardness sintered body without adding a binder powder containing an additional grain growth inhibitory material, so that not only the excellent machinability but also the high hardness sintered body have excellent workability. Can be prepared.

WC / Co cemented carbide substrate, metal base composite, polycrystalline diamond, grain growth inhibitor

Description

Manufacturing method of high hardness sintered body {METHOD OF SINTERING BODY HAVING HIGH HARDNESS}             

1 is a schematic view showing a conventional method for producing a high hardness sintered body,

2 is a schematic view showing a method for producing a high hardness sintered body of the present invention,

3A is an electron micrograph of a high hardness sintered body manufactured by a conventional manufacturing method,

3B is an electron micrograph of the high hardness sintered body produced by the production method of the present invention.

The present invention relates to a method of manufacturing a high hardness sintered body in which a polycrystalline diamond (PolyCrystaline Diamond (hereinafter referred to as PCD)) high hardness layer is formed on a cemented carbide substrate, and in particular, abnormal growth of diamond particles during sintering can be suppressed. It is related with the manufacturing method of a high hardness sintered compact.

High hardness sintered bodies in which a PCD high hardness layer is formed on a WC / Co based cemented carbide substrate are widely used as tool materials. 1 is a schematic view showing a method for producing such a conventional high hardness sintered body.

As shown in the drawing, the conventional high hardness sintered compact is placed on a WC / Co-based cemented carbide substrate with a raw material powder mixed with a diamond powder and a binder powder containing cobalt as a main component, and has a high melting point material of 2000 ° C. or higher (eg, Ta, Mo, It is charged into a refractory metal crucible consisting of Nb and the like, and diamond is sintered under stable high temperature and high pressure to be manufactured.

The main binder of the polycrystalline diamond sintered layer is cobalt diffused from the cemented carbide substrate or contained in the binder powder of the raw material powder. Cobalt is melted under the sintering temperature and pressure to form a liquid phase. The liquid cobalt serves as a catalyst for the PCD formation reaction. That is, since the activity of diamond in the liquid cobalt is very high, the growth and bonding reaction of the diamond particles diffused into the liquid cobalt is active to form a polycrystalline.

On the other hand, the crucible is made of a high melting point material of 2000 ℃ or more, it is maintained stable without melting during the PCD sintering process.

However, according to the conventional manufacturing method, there was a problem that the particles near the surface of the diamond adjacent to the crucible grow abnormally during the sintering process.

When diamond causes grain growth, a sintered compact having microcrystals of a target particle size cannot be produced. In addition, when the workpiece is cut with a tool made of a sintered body in which abnormal grain growth has occurred, there is a problem that the roughness of the workpiece cut surface is deteriorated.

In particular, when the diamond particles grow abnormally to 100 µm or more, there is a problem in that electrical discharge machine (EDM) wire discharge processing for producing a sintered compact is not possible.

In order to prevent abnormal grain growth of the diamond, carbides, nitrides, borides or mixed powders of Group 4 to 6 metals located at the grain boundaries of the diamond particles and hinder the diamond grain growth are mixed with the diamond powder and sintered. This has been proposed.

However, according to the above method, the grain growth inhibitory materials may be segregated in the PCD layer, thereby lowering the homogeneity of the mechanical properties of the sintered body. In order to prevent this, the grain growth inhibitor is finely ground and mixed evenly below the diamond powder, but even in this case, the problem of segregation is not completely solved.

In addition, in the case of the above method, there is a problem in that other materials other than cobalt as a binder fill the diamond, thereby decreasing the sintered density.

The present invention has been made to solve the above problems, and provides a method for producing a high hardness sintered body that can suppress the growth of particles by producing a high hardness sintered body using a crucible that suppresses the generation of the liquid cobalt pool causing particle growth. It aims to do it.

High hardness sintered body manufacturing method of the present invention for achieving the above object,

Preparing a sintered raw material powder containing diamond powder;

Placing the sintered raw material powder on a WC / Co based cemented carbide substrate;

The cemented carbide substrate and the sintered raw material powder are at least one selected from the group consisting of catalyst transition metals belonging to 4 to 6 cycles of Groups 4 to 6 and their carbide, nitride, carbonitride and intersolvent compounds of the catalyst transition metal. Charged into a sintered crucible composed of a high melting point material and a low melting point material which is one or more binders selected from Fe, Co, and Ni, and sintered under high temperature and high pressure where diamond is stable, thereby forming a PC (PolyCrystaline Diamond) on a cemented carbide substrate. Forming a coating layer.

The binder of the crucible is preferably 5 ~ 30wt%.

Moreover, it is preferable that the average particle size of the said diamond powder is 3 micrometers or less.

On the other hand, the sintered raw material powder is one selected from the group consisting of catalyst transition metals belonging to 4 to 6 cycles of Groups 3 to 10 and their carbide, nitrides, borides, carbonitrides and intersolvent compounds of the catalyst transition metals It is preferable to include the binder material powder which consists of the above.

Hereinafter, the present invention will be described in detail.

As a result of careful study, the inventors found that the grain growth occurs near the diamond surface because the liquid pool of cobalt melted from the cemented carbide or binder is formed along the walls of the refractory metal crucible. That is, the diamond particles in the cobalt liquid pool is very active, it was determined that the diamond particles in the area adjacent to the liquid pool is abnormally grown.

It is assumed that the liquid pool of cobalt is formed by a so-called squeeze out phenomenon. Squeeze out refers to the cobalt component between diamonds being pushed to the outside as the sintering process is gradually approaching, and the conventional crucible is stable and dense pure metal (Mo, Ta, Nb, etc.) at the sintering temperature. And cobalt, which is pushed out to form a liquid pool along the crucible wall.

The present inventors have focused on the above-described grain growth mechanism, and have studied the direction in which the liquid pool of cobalt is not formed or reduced along the crucible wall. As a result, the sintered crucible of the sintered crucible can be absorbed to absorb the squeezed out liquid cobalt. It has been found that by constructing a crucible capable of absorbing liquid pools, particle growth can be prevented.

According to the research of the present inventors, such a crucible is selected from the group consisting of catalyst transition metals belonging to groups 4 to 6 of Groups 4 to 6 and their carbide, nitride, carbonitride and intersolvent compounds of the catalyst transition metal. It was found that a sintered crucible composed of at least one high melting point material and a low melting point material which is at least one binder selected from Fe, Co, and Ni is suitable.

Among the sintered crucibles, the high-melting point materials composed of the catalyst transition metals belonging to the 4-6 cycles of Groups 4 to 6, their carbides, nitrides, carbonitrides, and inter-solid compounds of the catalyst transition metals are 1000 to 1700, which are PCD sintering conditions. It is a material that does not melt under 3 ℃ ~ 10GPa and remains in a solid state. It also plays a role in suppressing particle growth.

Also, Fe, Co, and Ni in the sintered crucibles are materials which form a high rate of employment with cobalt, which is a binder of diamond powder, and are melted under the sintering conditions.

Prior to sintering, the crucible has a structure in which the high melting point material is gradually embedded in the low melting point binder, and the binding material is interposed between the high melting point materials to bond the high melting point materials to each other.

Specific grain growth inhibition mechanism of the present invention is as follows.

When the cemented carbide substrate on which the diamond powder or the mixed powder of the diamond powder and the binder powder is placed is placed in the crucible of the above structure and the diamond is sintered under stable high temperature and high pressure, the liquid substance having almost 100% cobalt by the squeeze out is crucible. Elution along the wall.

In addition, since the binder component of the crucible is composed of at least one of Fe, Co, and Ni of low melting point, the binder component is also melted during the sintering process, and the high melting point material particles in the crucible are in a solid state and floating on the binder liquid phase. Becomes

In terms of concentration equilibrium, since the crucible wall has almost 100% cobalt, the high melting point material particles in the binder enter the liquid material on the crucible wall, and the liquid cobalt on the crucible wall flows toward the binder liquid in the crucible.

This process takes place at about the same time, making it very difficult to form a large cobalt liquid pool on the crucible wall that can cause abnormal grain growth.

On the other hand, if the amount of binder in the crucible is less than 5%, the high melting point material in the crucible tends to be brittle due to the so-called eta phase, and the fluidity of the high melting point material is lowered, so that the movement to the liquid pool is suppressed. It is difficult to prevent liquid pool formation effectively. In addition, when the amount of the binder in the crucible exceeds 30wt%, the shape of the crucible may collapse during the sintering process. Therefore, the amount of the binder is preferably 5 ~ 30wt%.

The characteristic feature of the present invention is not to prevent particle growth by interposing a particle growth inhibitor material between diamonds as in the prior art, but near the surface of the PCD layer where the problem particle growth occurs (where the liquid cobalt pool is formed). Particle growth inhibitory material or liquid cobalt pool formation interfering material is interposed in the vicinity, and the liquid cobalt pool flows to the crucible, thereby suppressing particle growth.

Therefore, the present invention has the advantage that there is no problem of segregation of the grain growth inhibitory material or a decrease in sintered densities as in the prior art.

On the other hand, abnormal growth of diamond grains occurs as the size of the diamond powder becomes smaller. This is because the smaller the size of the diamond powder, the larger the interface with the liquid cobalt in contact with it, the greater the interfacial energy that becomes the driving force for grain growth.

In general, when the average particle size of the raw material diamond powder exceeds 3 μm, the frequency of occurrence of abnormal particle growth due to lack of interfacial energy is greatly reduced. Therefore, the present invention is particularly meaningful in the case of fine diamond powder sintering of 3 mu m or less.

Theoretically, since the diamond powder can be sintered only by the cobalt component diffused from the cemented carbide substrate, the raw material powder can be composed of pure diamond powder without adding a separate binder powder to the sintered raw material powder.

However, it is common to mix the binder powder in advance with the diamond powder for the uniformity of the structure of the sintered compact.

The binder mainly added to the sintered raw material powder is a catalyst metal such as Fe, Co, and Ni, but other catalyst metals may be added to add other properties. The binder powder may use at least one of a catalyst transition metal belonging to 4 to 6 cycles of Group 3 to Group 10, and carbides, nitrides, borides, carbonitrides, and inter-solid-solvent compounds of the catalyst transition metals.

Hereinafter, with reference to the accompanying drawings will be described a preferred embodiment of the present invention.

EXAMPLE

Psalter A B C D Diamond Powder Average Particle Size 2 2 2 4 Co wt% in binder powder 5 5 5 5 WC wt% in binder powder                                          0 20 35 0

WC-8wt was mixed with a diamond powder with an average particle size of 2 µm and 4 µm, and a binder powder composed of cobalt powder with an average particle size of 1.5 µm and a WC powder with an average particle size of 0.8 µm was prepared as a sintered raw material powder. After placing on a cemented carbide substrate of% Co, the mixed raw material powder and the substrate were charged in a WC-6wt% Co crucible and a Ta crucible, respectively, and sintered at 1600 ° C. and 6 Gpa for 1 hour using a belt-type high pressure equipment. .

The sintered sintered body was polished, polished and EDM wire-discharge cut to observe the cut surface. As a result, the grain growth did not occur in all the specimens in the Example specimen of the present invention charged in the WC-6wt% Co crucible. Figure 3b is a photograph of the cut surface of the sintered body sintered using the sintered raw material powder of the specimen A composition. As shown, it can be seen that grain growth hardly occurred.

However, in the case of Comparative Samples A and B charged into a Ta crucible and sintered, grain growth of about 100 μm or more occurred seriously. Figure 3a is a photograph of the cut surface of the sintered body using the sintered raw material of the specimen B composition, it can be seen that severe grain growth occurred.

On the other hand, in the case of Comparative Example C to which WC was added 35wt% grain growth did not occur, it is understood that the grain growth did not occur because the WC interferes with the bonding of the diamond particles.

In addition, in Comparative Example B, it was found that the average particle size of the diamond particles exceeded 3 µm, so that the driving force necessary for grain growth was insufficient, so that severe grain growth hardly occurred.

As such, in the case of the present invention, regardless of the composition of the binder contained in the raw material powder, the growth of the particles hardly occurred, but in the case of the comparative example, it was necessary to add a considerable amount of WC to prevent grain growth.

As described above, according to the present invention, since it is possible to prevent abnormal diamond grain growth of the PCD layer of the high hardness sintered body without adding the binder powder containing the additional grain growth inhibitory material, The high hardness sintered compact excellent in workability can be manufactured.

Claims (4)

Preparing a sintered raw material powder containing diamond powder; Placing the sintered raw material powder on a WC / Co based cemented carbide substrate; The cemented carbide substrate and the sintered raw material powder are at least one selected from the group consisting of catalyst transition metals belonging to 4 to 6 cycles of Groups 4 to 6 and their carbide, nitride, carbonitride and intersolvent compounds of the catalyst transition metal. Charged into a sintered crucible comprising a high melting point material and a low melting point material which is one or more binders selected from Fe, Co, and Ni, and sintered under high temperature and high pressure where diamond is stable, thereby forming a PC (PolyCrystaline Diamond) on the cemented carbide substrate. Forming a high hardness layer; Method for producing a high hardness sintered body comprising a. The method of claim 1, The binder of the crucible is a method for producing a high hardness sintered body, characterized in that 5 ~ 30wt%. The method according to claim 1 or 2, The average particle size of the diamond powder is a manufacturing method of a high hardness sintered compact, characterized in that 3㎛ or less The method of claim 1, The sintered raw material powder is at least one selected from the group consisting of catalyst transition metals belonging to groups 4 to 6 of Groups 3 to 10, their carbides, nitrides, borides, carbonitrides, and inter-solid compounds of the catalyst transition metals. Method for producing a high hardness sintered body comprising a binder powder made of.

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