JPH0238365A - Complex sliding member of high-temperature-reisistant and high-strength graphite base - Google Patents

Abstract

PURPOSE:To provide the title member with excellent friction and wear characteristics, mechanical strength and heat resistance by forming a sintered material containing specific metal boride and boron carbide dispersed in graphite. CONSTITUTION:A complex sliding member of high-temperature-resistaut and high strength graphite base which comprises a sintered material of a mixture of (A) carbon powder (e.g., coke powder, carbon black powder or graphite powder), (B) at least one powder selected from borides (e.g., TiB, VB2 or CrB) of groups IVa, Va and VIa metals and carbides (e.g., TiC, VC or WC) and (C) boron carbide powder wherein the sintered material consists of graphite and the metal boride and boron carbide dispersed into the graphite. In the member, the blending ratio of the component B and the component C is 3-20wt.% component B and 2-25wt.% component C based on total amounts of the components A, B and C.

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to a high-temperature-resistant, high-strength graphite-based composite sliding member useful as a component that generates friction due to sliding, such as a retainer for a sliding bearing or a rolling bearing, or a sliding valve. be. More specifically, the present invention exhibits good properties against friction and wear, especially at high temperatures, and is suitable for use under so-called dry friction conditions, where it is difficult to use fluid lubricants such as lubricating oil and grease. The present invention relates to a suitable high temperature resistant, high strength graphite composite sliding member.

BACKGROUND OF THE INVENTION In recent years, with the development of mechatronics, there has been an increasing demand for sliding members with good friction and wear characteristics, especially in high-temperature regions.

For sliding parts used in the high temperature range of 300 to 500°C, it is not possible to use fluid lubricants such as lubricating oil or grease between the contact surfaces. Solid lubricants are used. This solid lubricant generally does not have the fluidity and wettability of fluid lubricants, so when using it, it is necessary to apply, impregnate,
It is not possible to use means such as applying pressure.

Therefore, in the case of a solid lubricant, it is applied by coating the friction surface with the solid lubricant, making the sliding member itself with the solid lubricant, or mixing it with other materials. There must be. In all of these methods, the lubrication effect is achieved only when a portion of the solid lubricant is transferred to the surface of the mating material between the sliding contact surfaces and a solid lubricant film of the desired thickness is formed. Therefore, the quality of film formation of the solid lubricant film on the surface of the mating material is determined by friction,
This will affect the wear characteristics.

However, conventionally, graphite, which has self-lubricating properties, good thermal conductivity, is non-fusible, has a small coefficient of thermal expansion, and has excellent heat resistance, has been most commonly used as a solid lubricant. ing.

The graphite used in these sliding parts is generally classified into natural graphite and artificial graphite, but in applications where the solid lubricant itself is used as a sliding part, it is slightly inferior in terms of friction and wear characteristics. However, artificial graphite is commonly used because it can produce high-strength molded bodies.

Conventionally, the method for obtaining this high-strength graphite compact is as follows.
For example, aggregate such as coke powder is molded using a binder such as coal tar pitch, which itself becomes carbonized and graphitized by heating and baking, and is then molded to a 700 to 110
After firing at a temperature of 0°C, impregnating agents such as pitch are infiltrated and firing is performed again, followed by heat treatment at a temperature of 2,500 to 3,000°C to graphitize. In order to obtain a graphite molded body, a method of impregnating a graphite molded body with resin or metal has also been used.

However, although the high-strength graphite compact obtained by this method can be used as a sliding member as it is, the friction and wear characteristics, especially the formation of a solid lubricant (graphite) film on the surface of the mating material in high-temperature regions, are important. There are problems with film properties, etc., which results in disadvantages in friction and wear characteristics such as a high coefficient of friction and a large amount of wear.In addition, the above method requires an extremely long manufacturing time such as graphitization of coke powder. It also has the disadvantage of requiring a long time (generally said to be 2 to 3 months).

Therefore, the present inventors first developed a mixture containing amorphous carbon powder, a specific metal boride powder, and natural graphite powder or Quiche graphite powder in a predetermined ratio in order to create a sliding member that improves these drawbacks. proposed a graphite-metal boride sliding member made of a sintered body (Japanese Patent Publication No. 13954/1983).

However, with this graphite-metal boride sliding member, it is possible to obtain a graphite molded body in a short time, and it is possible to obtain a graphite compact in a high temperature region, which is a drawback of graphite sliding members obtained using conventional pitch binders. Although improvements have been made in the ability to form a graphite film on the surface of the mating material and the friction and wear characteristics, mechanical It has the disadvantage that it has insufficient strength and heat resistance, and cannot be used in applications that require particularly high strength and heat resistance.

Problems to be Solved by the Invention The present invention solves the disadvantages of graphite sliding members obtained using conventional pitch binders, such as the transferability of a solid lubricant (graphite) film to the surface of a mating material in a high-temperature region and the structure. The purpose of this invention is to provide a sliding member that has improved mechanical strength and heat resistance, as well as solving the problems of insufficient film properties and friction and wear characteristics.

Means for Solving the Problems As a result of intensive research to develop a sliding member that exhibits high strength even at high temperatures, the inventors found that boron carbide graphitizes carbon in the same way as metal borides. Focusing on its ability to accelerate and accelerate sintering as well as its excellent heat resistance, this boron carbide powder was blended with carbon powder in a predetermined ratio along with certain metal boride powders and metal carbide powders. obtained by sintering a mixture consisting of
It was discovered that a sintered body in which metal borides and boron carbide are dispersed in black ship exhibits excellent friction and wear characteristics, as well as excellent mechanical strength and heat resistance, and based on this knowledge, the present invention was completed. I ended up doing it.

That is, the present invention provides at least one powder selected from (A) carbon powder and (B) borides and carbides of metals belonging to Group IVa, Group Va, and Group Via of the Periodic Table. 3 to 20% by weight, and (C) boron carbide powder 2 to 2
5% by weight, and the sintered body is composed of graphite and a metal boride and boron carbide dispersed in the graphite. A sliding member is provided.

In the present invention, examples of the carbon powder used as component (A) include coke powder, anthracite powder, carbon black powder, charcoal powder, and artificial graphite. These may be used alone or in combination of two or more.

In the present invention, as the component (B),
At least one powder selected from borides and carbides of metals belonging to Group A, Group Va, and Group VIa is used. Examples of the metal borides include titanium boride (TiB), titanium diboride (TiBz), zirconium diboride (ZrB2), and hafnium diboride (H
fB2), vanadium diboride (VB2), niobium diboride (NbB), tantalum diboride (TaBz), chromium boride (CrB), chromium diboride (crBz), molybdenum boride (MoB), molybdenum diboride (Mo
Examples include tungsten boride (WB), tungsten diboride (WB), and these may be used alone or in combination of two or more.

Further, as the metal carbide, for example, titanium carbide (Ti
C), zirconium carbide (ZrC), hafnium carbide (
HfC), bar6dium carbide (VC), niobium carbide (Nb
C), tantalum carbide (TaC), chromium carbide (Cr3C)
2), molybdenum carbide (MoC), tungsten carbide (
vic), and these may be used alone or in combination of two or more. Furthermore, in the present invention, the metal boride powder and metal carbide powder may be used in combination.

The metal carbide powder reacts with the boron carbide powder blended as component (C) during the pressure/heat sintering process, changes into metal boride, and is dispersed and contained in the sintered body.

In the present invention, boron carbide powder is used as component (C). This boron carbide powder has a graphitization promoting effect and a sintering promoting effect during sintering of the carbon powder, and
When a metal carbide powder is used as the component (b), it also has the effect of reacting with the powder and converting the metal carbide into a metal boride.

The blending ratio of the metal boride powder or metal carbide powder of the component (B) and the boron carbide powder of the component (C) to the carbon powder of the component (A) is determined by the graphitization of the carbon during the pressure/heat sintering process. It is determined based on the balance between high density, mechanical strength, friction and wear characteristics, and heat resistance of the sintered body. Further, the graphitization promoting effect of the metal boride and boron carbide is exerted by the boron in the metal boride and boron carbide being diffused and dissolved into the carbon powder during the pressure/heat sintering process.

For these reasons, in the present invention, the blending amounts of component (B) and component (C) are as follows: (A), (B) and (C)
Based on the total weight of the components, it is necessary to choose between 3 and 20% by weight and between 2 and 25% by weight, respectively. (B)
If the amount of the component and component (C) is less than the above range, the effect of promoting graphitization will not be sufficiently exhibited, and if it is more than the above range, the friction and wear characteristics will tend to deteriorate.

The effect of metal borides and boron carbide on the friction and wear characteristics is that although they themselves do not exhibit the same lubricity as graphite or molybdenum disulfide, by being dispersed and contained in a sintered body (graphite body), they are able to interact with the mating material. It promotes the formation of a solid lubricant (graphite) film on the surface of the mating material during friction, and increases the durability of the film during dry friction.

Therefore, when a large amount of these borides are dispersed and contained in a sintered body, friction with metal borides and boron carbide, which themselves do not exhibit lubricity, occurs in friction with the mating material, reducing the friction and wear characteristics. I will let you do it.

In addition, when using metal carbide powder as component (B),
During the sintering process, this metal carbide powder needs to react with the boron carbide of component (C) to completely change into metal boride and be dispersed and contained in the sintered body. The amount of boron carbide powder as component (C) is within the above range and is stoichiometrically larger than the amount of the metal carbide powder, so that at least 2% by weight of boron carbide is dispersed in the sintered body. It is important that it be included.

The sliding member of the present invention is produced by uniformly mixing the component (A), the component (B), and the component (C) at predetermined ratios, and filling a graphite mold with this mixture. / cm”
above, preferably under a pressure of 150 to 300 to 9/cm", and above 1500 °C, preferably 1800 to 250 °C
By sintering at a temperature of 0° C., a graphite-based composite sliding member in which metal boride and boron carbide are dispersed and contained in the sintered body is obtained.

Table 1 shows the physical property values of different examples of the graphite-based composite sliding member of the present invention thus obtained.

In Table 1, graphite-based composite sliding members ■ and ■ are a mixture of carbon powder, 3 to 20% by weight of metal boride powder, and 2 to 20% by weight of boron carbide powder, and a mixture of carbon powder and metal carbide powder of 3 to 20% by weight, respectively. This is a sintered body obtained by pressurizing and heating a mixture of 5% to 25% by weight of boron carbide powder.

The friction and wear characteristics in the table are as follows: Dimensions of sliding member: length 20mm, width 20mtn, thickness 7
mm block-shaped sliding member mating material: outer diameter 18 mm, inner diameter 14 mm, length 20 mr
A cylindrical body made of stainless steel Weight: 20 kgf/cm" Speed: 5 m/min Testing machine: Suzumoto thrust tester The values were measured under the test conditions of a test atmosphere temperature of 2500°C.

In addition, the results of testing the heat resistance of the graphite-based composite sliding members (1) and (2) are shown graphically in the figure.

This graph shows the relationship between the standing time and the hardness of the sliding members (1) and (2) after test pieces of the sliding members (2) and (2) were left in a furnace maintained at a temperature of 560°C. .

In addition, in the figure, symbol A is a graphite-based composite sliding member (■), B is a graphite-based composite sliding member (■), and C and D are graphite sliding members using a pitch binder and Japanese Patent Publication No. 63-13954, respectively.
This is a graphite-based sliding member disclosed in the publication.

From this figure, it can be seen that the graphite-based composite sliding member of the present invention exhibits no change in hardness and has excellent heat resistance.

Effects of the Invention The graphite-based composite sliding member of the present invention not only has excellent friction and wear characteristics, but also has significantly improved mechanical strength and heat resistance because metal borides and boron carbide are dispersed in the graphite. 50 which could not be used with the conventional one.
It can be used in a high temperature range of about 0'O.

Examples Next, the present invention will be explained in more detail with reference to examples.
The present invention is not limited in any way by these examples.

Example 1 Chromium diboride powder 3 with an average particle size of 7 μm was added to the calcined pitch coke powder with a particle size of 150 μm or less based on the total mixed powder.
1i amount% and boron carbide powder 2% by weight,
A uniform mixed powder of coke powder, chromium diboride powder and boron carbide powder was obtained.

This mixed powder was filled into a graphite mold and weighed 200 kg/cm”
The temperature was raised to 2100° C. under pressure of 100° C. and sintered by holding at this temperature for 1 hour.

Then, after cooling to room temperature (20°C), take out the
A graphite-based composite sliding member was obtained.

The physical property values and friction and wear characteristics of this material were determined as Sample No. 2 in Table 2.
, l.

The friction and wear characteristics in the table were conducted under the same test conditions as described above, and the amount of wear was measured 5 hours after the start of the test.

Example 2 The same calcined pitch coke powder as in Example 1 was mixed at a ratio of 10% by weight of chromium diboride powder and 10% by weight of boron carbide powder with respect to the total mixed powder, and the coke powder, chromium diboride powder, and carbonized A uniform mixed powder of boron powder was obtained. Thereafter, sintering was performed in the same manner as in Example 1 to obtain a graphite-based composite sliding member.

The physical property values and friction and wear characteristics of this material are shown in Table 2 for sample No.
, 2.

Example 3 The same calcined pitch coke powder as in Example 1 was mixed with 20% by weight of chromium diboride powder and 20% by weight of boron carbide powder based on the total mixed powder, and the coke powder, chromium diboride powder, and carbonized A uniform mixed powder of boron powder was obtained.

Thereafter, sintering was performed in the same manner as in Example 1 to obtain a graphite-based composite sliding member.

The physical property values and friction and wear characteristics of this material were determined as Sample No. 2 in Table 2.
, 3.

Example 4 To the same calcined pitch coke powder as in Example 1, zirconium diboride powder 1 with an average particle size of 7 pm was added to the total mixed powder.
A uniform mixed powder of coke powder, zirconium diboride powder, and boron carbide powder was obtained by mixing 0% by weight and 10% by weight of boron carbide powder.

Thereafter, sintering was performed in the same manner as in Example 1 to obtain a graphite-based composite sliding member.

The physical property values and friction and wear characteristics of this material were determined as Sample No. 2 in Table 2.
, 4.

Example 5 The same calcined pitch coke powder as in Example 1 was mixed with 10% by weight of niobium diboride powder and 10% by weight of boron carbide powder with an average particle size of 7 μm based on the total mixed powder. A uniform mixed powder of niobium oxide powder and boron carbide was obtained.

Thereafter, sintering was performed in the same manner as in Example 1 to obtain a graphite-based composite sliding member.

The physical property values and friction and wear characteristics of this material were determined as Sample No. 2 in Table 2.
, 5.

Example 6 In the same calcined pitch coke powder as in Example 1, 5% by weight of chromium diboride powder with an average particle size of 7 μm was added to the total mixed powder.
, 5% by weight of molybdenum diboride powder and 10% by weight of boron carbide powder to obtain a uniform mixed powder of coke powder, chromium diboride powder, molybdenum diboride powder, and boron carbide powder.

Thereafter, sintering was performed in the same manner as in Example 1 to obtain a graphite-based composite sliding member.

The physical property values and friction and wear characteristics of this material were determined as Sample No. 2 in Table 2.
, 6.

Example 7 To the same calcined pitch coke powder as in Example 1, 3% by weight of chromium carbide powder and 5% by weight of boron carbide powder were added to the total mixed powder.
A uniform mixture of coke powder, chromium carbide powder, and boron carbide powder was obtained by mixing them in a proportion of % by weight.

Thereafter, sintering was performed in the same manner as in Example 1 to obtain a graphite-based composite sliding member.

X
Confirmed by line diffraction. The physical property values and friction and wear characteristics of this material are shown in Sample No. 007 in Table 2.

Example 8 The same calcined pitch coke powder used in Example 1 was
5% by weight of titanium carbide powder and 10% by weight of boron carbide powder were mixed with respect to the total mixed powder to obtain a uniform mixture of coke powder, titanium carbide powder, and boron carbide powder.

Thereafter, sintering was performed in the same manner as in Example 1 to obtain a graphite-based composite sliding member.

It was confirmed by X-ray diffraction that all titanium carbide in this graphite-based composite sliding member reacted with boron carbide and changed to titanium diboride. The physical properties and friction and wear characteristics of this material are shown in Table 2 as Sample No.

8.

Example 9 The same calcined pitch coke powder used in Example 1 was mixed with 5% by weight of niobium carbide powder and 10% by weight of boron carbide powder based on the total mixed powder. A homogeneous mixture of powder and boron carbide powder was obtained.

Thereafter, sintering was performed in the same manner as in Example 1 to obtain a graphite-based composite sliding member.

It was confirmed by X-ray diffraction that all niobium carbide in this graphite-based composite sliding member reacted with boron carbide and changed to niobium diboride. The physical properties and friction and wear characteristics of this material are shown in Table 2 as Sample No.

9.

Comparative Example 1 The same calcined pitch coke powder used in Example 1 was
The total mixed powder was mixed with 10% by weight of chromium diboride powder and 10% by weight of natural graphite powder, and then sintered in the same manner as in Example 1 to obtain a graphite-based composite sliding member ( (Japanese Patent Application No. 59-233276).

The physical property values and friction and wear characteristics of this material were determined as Sample No. 2 in Table 2.
, IO.

Comparative Example 2 A graphite sliding member made of a graphite molded body obtained using pitch-based binder 1. The physical properties and friction and wear characteristics of this member are shown in Samples No. and 11 in Table 2.

From Table 2, it can be seen that the graphite-based sliding members of the present invention (Examples 1 to 9) have significantly improved mechanical strength, particularly bending strength. Furthermore, it exhibited stable performance even in friction under a high-temperature atmosphere of 500°C, and it was confirmed that a thin graphite film was formed on the surface of the mating material after the test.

[Brief explanation of the drawing]

The figure is a graph showing the results of a test on the heat resistance of the graphite-based composite sliding member of the present invention and a conventional graphite sliding member. Patent applicant: Director of the Agency of Industrial Science and Technology Kozo Iizuka (and one other person) Sub-agent Akira Agata

Claims (1)

[Claims] 1 (A) Carbon powder and (B) 3 to 20% by weight of at least one powder selected from borides and carbides of metals belonging to Group IVa, Group Va, and Group VIa of the Periodic Table.
and (C) 2 to 25% by weight of boron carbide powder, and the sintered body is composed of graphite and metal boride and boron carbide dispersed in the graphite. A high-temperature resistant, high-strength graphite-based composite sliding member.